ANALYSIS OF ALTERNATIVES
Legal name of applicants: ZF Luftfahrttechnik GmbH
Submitted by: ZF Luftfahrttechnik GmbH
Substance: Sodium dichromate, EC No: 234-190-3, CAS No: 7789-12-0 (dihydrate), 10588-01-9 (anhydrous)
Use title: Use of Sodium dichromate for surface treatment of metals such as aluminium, steel, zinc, magnesium, titanium, alloys, composites, sealings of anodic films.
Use number: 2
USE NUMBER: 2 ANALYSIS OF ALTERNATIVES
Disclaimer
This document shall not be construed as expressly or implicitly granting a license or any rights to use related to any content or information contained therein. In no event shall applicant be liable in this respect for any damage arising out or in connection with access, use of any content or information contained therein despite the lack of approval to do so.
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CONTENTS
1. SUMMARY 1 2. INTRODUCTION ...... 7 2.1. Substance ...... 7 2.2. Uses of Cr(VI) containing substances ...... 7 2.3. Purpose and benefits of Cr(VI) compounds ...... 7 3. ANALYSIS OF SUBSTANCE FUNCTION...... 9 3.1. Usage ...... 9 3.2. Surface treatment process descriptions ...... 14 3.2.1. Pre-treatment processes ...... 17 3.2.2. Main surface treatment processes ...... 19 3.2.3. Post-treatment processes ...... 20 3.3. Substance specific characteristics of chromates ...... 22 3.3.1. Characteristics and properties of sodium dichromate ...... 22 3.4. Key functionalities of chromate based surface treatments...... 24 3.4.1. Key functionalities of sodium dichromate-based surface pre-treatments ...... 24 3.4.2. Key sodium dichromate functionalities for the main- and post-treatment process ...... 26 3.4.3. Summary of selected quantified key functionalities ...... 28 4. ANNUAL TONNAGE...... 32 4.1. Annual tonnage band of sodium dichromate ...... 32 5. OVERVIEW OF THE PROCESS FOR ALTERNATIVE DEVELOPMENT AND APPROVAL IN THE AEROSPAC SECTOR ...... 33 5.1. Development and qualification ...... 36 5.1.1. Requirements development ...... 36 5.1.2. Technology development ...... 37 5.1.3. Qualification ...... 39 5.1.4. Certification ...... 40 5.1.5. Implementation / industrialisation ...... 42 5.2. Examples ...... 43 6. IDENTIFICATION OF POSSIBLE ALTERNATIVES ...... 45 6.1 Description of efforts made to identify possible alternatives ...... 45 6.1.1. Research and development in the aerospace sector ...... 45 6.1.2. Data searches ...... 46 6.1.3. Consultations ...... 46 6.2 List of possible alternatives ...... 47 7. SUITABILITY AND AVAILABILITY OF POSSIBLE ALTERNATIVES ...... 49 7.1. Main processes & post treatments ...... 49 CATEGORY 1 ALTERNATIVES ...... 49 7.1.1. ALTERNATIVE 1: Acidic surface treatments ...... 49 7.1.2. ALTERNATIVE 2: Silane/siloxane and sol-gel coatings ...... 52 7.1.3. ALTERNATIVE 3: Cr(III)-based surface treatments ...... 58 7.1.4. ALTERNATIVE 4: Water-based post-treatments ...... 64 CATEGORY 2 ALTERNATIVES ...... 69 7.1.5. ALTERNATIVE 5: Molybdates and molybdenum-based processes ...... 69 7.1.6. ALTERNATIVE 6: Organometallics (zirconium and titanium-based products, such as fluorotitanic and fluorozirconic acids) ...... 72 7.1.7. ALTERNATIVE 7: Benzotriazole-based processes, e.g. 5-methyl-1H-benzotriazol...... 75 7.1.8. ALTERNATIVE 8: Chromate-free etch primers ...... 76 7.1.9. ALTERNATIVE 9: Manganese-based processes ...... 78 7.1.10. ALTERNATIVE 10: Cold nickel sealing ...... 82 7.1.11. ALTERNATIVE 11: Magnesium-rich primers ...... 85 7.1.12. ALTERNATIVE 12: Electrolytic paint technology ...... 88 7.1.13. ALTERNATIVE 13: Zinc-nickel electroplating ...... 92 7.2. Pre treatments ...... 94
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7.2.1. Inorganic acids...... 94 7.2.2. Hydrogen peroxide activated benzyl alcohol (with acid) ...... 100 8. OVERALL CONCLUSIONS ON SUITABILITYAND AVAILABILITY OF POSSIBLE ALTERNATIVES ...... 103 9. REFERENCE LIST ...... 107 APPENDIX 1 – JUSTIFICATIONS FOR CONFIDENTIALITY CLAIMS ...... 111 APPENDIX 2 – MASTERLIST OF ALTERNATIVES WITH CLASSIFICATION INTO CATEGORIES 1-3 AND SHORT SUMMARY OF THE REASON FOR CLASSIFICATION OF ALTERNATIVES INTO CATEGORY 3 ...... 112 APPENDIX 3 – INFORMATION ON RELEVANT SUBSTANCES FOR IDENTIFIED ALTERNATIVES ...... 116
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List of Tables: Table 1 : Overview of key potential alternatives for main surface treatments...... 5 Table 2 : Substance of this analysis of alternatives...... 7 Table 3 : Corrosion prone areas on different types of aircraft...... 10 Table 4: Overview of surface treatment processes indicating most important application methods, purpose, as well as example products. This is not intended to be an exhaustive list...... 16 Table 5: Sodium dichromate typical chemical and physical properties...... 24 Table 6: Key functionalities of Cr(VI)-based main processes and post-treatments...... 28 Table 7: Technology Readiness Levels – Overview (US Department of Defence, 2011, adapted 2014)...... 34 Table 8. List of main treatment alternatives categorized...... 47 Table 9. List of pre-treatment alternatives categorized...... 48 Table 10: Sodium dichromate-based surface treatments where acidic based surface treatments may be an alternative...... 50 Table 11: Some commonly used alkoxysilane precursors for sol-gel coatings...... 53 Table 12: Sodium dichromate-based surface treatment processes where sol-gel coatings may be an alternative. .. 54 Table 13: Sodium dichromate-based surface treatment processes where Cr(III)-based processes may be an alternative...... 59 Table 14 : Sodium dichromate-based surface treatment processes where water-based post-treatments may be an alternative...... 66 Table 15: Sodium dichromate-based surface treatment processes where molybdate-based processes may be an alternative...... 69 Table 16: Sodium dichromate-based surface treatment processes of where fluorotitanic and fluorozirconic acid may be an alternative...... 72 Table 17: Sodium dichromate-based surface treatment processes where benzotriazoles may be an alternative. .... 75 Table 18: Sodium dichromate-based surface treatment processes where etch primers may be an alternative...... 77 Table 19: Sodium dichromate-based surface treatment processes where manganese-based products may be an alternative ...... 79 Table 20: Sodium dichromate-based surface treatment processes where cold nickel sealings may be an alternative...... 82 Table 21: Sodium dichromate-based surface treatment processes where Mg rich primers may be an alternative .. 86 Table 22 Sodium dichromate-based surface treatments where electrolytic paint may be an alternative...... 89 Table 23: Sodium dichromate-based surface treatment processes where Zinc-Nickel electroplating may be an alternative...... 92 Table 24 : Overview on the replacement substances used in the different pre-treatment processes...... 94 Table 25: Sodium dichromate-based pre-treatment where hydrogen peroxide activated benzyl alcohol with acids may be an alternative...... 100 Table 26 : Overview of key potential alternatives for main surface treatments...... 104
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List of Figures Figure 1: Surface Treatment Processes steps where sodium dichromate might be involved...... 2 Figure 2: Illustration of the development, qualification, certification and industrialisation process required in the aerospace sector...... 4 Figure 3: Development status of alternatives. Pass. Steel: Passivation of stainless steel; Pass. MC: Passivation of metallic coatings; CCC: Chemical Conversion Coating. Category 1 alternatives in turquoise, Category 2 alternatives in red...... 6 Figure 4: ATR 600 aircraft & Gulfstream V aircraft (UTC Aerospace Systems – Propeller Systems, 2014)...... 10 Figure 5. Schematic illustration of typical corrosion findings in an aircraft fuselage (Airbus)...... 11 Figure 6: Propellers mounted on an aircraft (UTC Aerospace Systems – Propeller Systems, 2014)...... 11 Figure 7: Undercarriage - landing gear, examples (Rowan Technology Group, 2005)...... 12 Figure 8: Gas Turbine Engine sketch example PW4000 92 inch fan engine (www.pw.utc.com/Content/PW400094_Engine/img/B-1-4-1_pw400094_cutaway_high.jpg, 2014)...... 12 Figure 9: Emergency door damper for a civil aircraft. (UTC Aerospace Systems – Propeller Systems, 2014)...... 12 Figure 10: Main & tail rotor shaft elements of a helicopter (Data source; UTC Aerospace Systems – Propeller Systems, 2014)...... 13 Figure 11: Partially assembled main helicopter rotor (UTC Aerospace Systems – Propeller Systems, 2014)...... 13 Figure 12: Surface treatment processes steps where sodium dichromate might be involved...... 15 Figure 13: Surface treatment bath (Airbus Fast Report, 2009)...... 16 Figure 14: Illustration of the qualification, certification and industrialisation processes (EASA, 2014)...... 34 Figure 15: Illustration of the technology development and qualification process (EASA, 2014, amended)...... 39 Figure 16: Development and approval process in the aerospace sector. Examples from previous implementations are included. Loops indicate potentially iterative steps due to unsuccessful evaluation at the formulator or unsuccessful development...... 44 Figure 17: Formation of boehmite during hot water sealing of anodized aluminium surface (Hao & Cheng, 2000)...... 65 Figure 18 : Aluminium test panels after 144 cycles accelerated cyclic, acidified salt spray test according to ASTM G85, Method A2, 1A: Al with dichromate sealing, 1B: Cross-scribed Al with dichromate sealing, 2A: Al with hot water sealing, 2B: Cross-scribed Al with hot water sealing (GE Aviation)...... 66 Figure 19 Variations of amounts of Mn-deposited with immersion time in conversion coatings obtained from various treatment bath (left) ; values of total corrosion resistance of the various conversion coatings obtained in function of immersion time in 5% NaCl ; (right) (Lee et al, 2013)...... 78 Figure 20: Cathodic protection by the Sacrificial Anode method (Pathak et al, 2012) ...... 85 Figure 21: Surface morphology of the scratched coating samples after immersion in 3%NaCl solution for 150 days: A) 50Mg; B) 40Mg 10Al; C) 30Mg 20Al; D) 20Mg 30Al; E)10Mg 40Al; F)50Al (Wang et al, 2013) ...... 86 Figure 22: Electrodeposition process, cathodic and anodic deposition (Pawlik, 2009)...... 88 Figure 23: Components of an electrocoat conveyor process (Pawlik, 2009)...... 89 Figure 24: Development status of alternatives. Pass. Steel: Passivation of stainless steel; Pass. MC: Passivation of metallic coatings. Category 1 alternatives in turquoise, Category 2 alternatives in red...... 105
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Abbreviations AA2024 Aluminium alloy, most commonly used in the aerospace sector ACF Airbus Chromate-Free Al Aluminium Acute Tox. Acute Toxicity AMMTIAC Advanced Materials, Manufacturing, and Testing Information Analysis Center Asp. Tox. Aspiration hazard ASTM American Society for Testing Materials AoA Analysis of Alternatives ASTM American Society for Testing Materials Aquatic Acute Hazardous to the aquatic environment Aquatic chronic Hazardous to the aquatic environment BSA Boric-Sulphuric Acid Anodizing BZT Benzotriazoles CAA Chromic Acid Anodizing Carc. Carcinogenicity CAS unique numerical identifier assigned by Chemical Abstracts Service (CAS number) CCC Chemical Conversion Coatings CCST Miscellaneous Chromium VI Compounds for Surface Treatment REACH Authorization Consortium Cd Cadmium CMR Carcinogenic, Mutagenic and Toxic to Reproduction CPVC Critical Pigment Volume Concentration Cr Chromium Cr(0) Elementary Chromium Cr(III) Trivalent Chromium, Chromium (III) Cr(VI) Hexavalent Chromium, Chromium (VI) CRES Corrosion resistant stainless steel CFRP Carbon-fibre-reinforced-polymer or plastic CSR Chemical Safety Report DT&E Development, Test and Evaluation
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EASA European Aviation Safety Agency EC unique numerical identifier of the European Community (EC number) EHS Environmental Health and Safety EMI Electromagnetic Interference EN European Norm EPA Environmental Protection Agency ESA European Space Agency EU European Union Eye Dam. Serious eye damage Eye Irrit. Eye irritation Flam. Liq. Flammable liquid HITEA Highly Innovative Technology Enablers for Aerospace HV Vickers Hardness HVOF High Velocity Oxy Fuel ISO International Organization for Standardization IVD Ion Vapour Deposition Me Metal Met. Corr. Substance or mixture corrosive to metals Mg Magnesium Mil-DTL United States Military Standard MoCC Molybdate based conversion coatings MRL Manufacturing Readiness Level MRO Maintenance, Repair and Operations MSDS Material Safety Data Sheet Muta. Germ cell mutagenicity NASA National Aeronautics and Space Administration NDSU North Dakota State University Ni Nickel NSST Neutral Salt Spray Test OEM Original Equipment Manufacturer OT&E Operational Test and Evaluation
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Ox. Liq. Oxidising liquid Ox. Sol. Oxidising solid PSA Phosphoric Sulphuric Acid Anodizing PVC Pigment Volume Concentration PVD Physical Vapour Deposition QPL Qualified Products List REACH Registration, Evaluation, Authorisation and Restriction of Chemicals R&D Research and Development Repr. Reproductive toxicity Resp. Sens. Respiratory RoHS Directive on Restriction of Hazardous Substances SAA Sulphuric Acid Anodizing SEA Socio Economic Analysis Skin. corr. Skin corrosion Skin. Sens. Skin sensitisation Skin irrit. Skin irritation Sn Tin SST Salt Spray Test STC Supplemental Type Certificate STOT RE Specific target organ toxicity, repeated exposure STOT SE Specific target organ toxicity, single exposure SVHC Substance of Very High Concern Ti Titanium TRL Technology Readiness Level TSA Tartaric-Sulphuric-Acid-Anodizing US United States VOC Volatile Organic Compounds VTMS Vinyl trimethoxysilane Zr Zirconium
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Glossary
Term Definition The ability of a material to spontaneously repair small amounts of chemical or mechanical damage that exposes areas of metal without any Active corrosion inhibition surface protection (“self-healing properties”). This functionality is advantageous and enhances service life duration of parts, maintenance intervals and on-flight security of air travellers. Parameter describes the tendency of dissimilar particles or surfaces to Adhesion promotion cling to one another (for example adhesion of coating to substrate, adhesion of paint to coating and/or substrate). This terms comprises civil and military applications of aviation and Aerospace space industry. This term comprises the study of the science of navigation through air Aeronautics and space. It defines the methodology of how to design an aircraft, spacecraft or other flying machine. Candidate alternative that has been tested, qualified, fully industrialised Alternative and certified by the Aviation OEM. The definition is only used for the final classification of evaluated alternatives. Electrolytic oxidation process in which the surface of a metal, when anodic, is converted to an insulating coating having desirable protective Anodizing or functional properties. The anodic film formation is mainly driven by the applied voltage. Chromic acid anodizing is one example of anodizing. Typical method for surface treatment of parts. May also be referred to Bath as dipping or immersion. None-bath methods include wiping, spraying, and pen application. The process where two parts are joint together by means of a bonding Bonding material; an adhesive sometimes in combination with a bonding primer and a conversion or anodizing treatment. Potential alternative provided to the Aerospace OEM for their Candidate alternative evaluation. These have already been evaluated in the labs of formulators. Verification that an aircraft and every part of it complies with all Certification applicable airworthiness regulations and associated Certification Specifications (specs). Parameter is defined as the ability of solid materials to resist damage by Chemical resistance chemical exposure. Chromate rinsing after phosphating is a passivation process after phosphate conversion coating (phosphating). It fulfils two requirements Chromate rinsing after by using only one process step (removal of drag-out comprising liquids phosphating) and residuals of former processes adhering to the substrate and passivation of the surface by enhancing corrosion resistance. The flight profile in civil aviation is limited to ferrying passengers and cargo, while in military applications several missions have to be taken into account that require constant technical trade-offs. The flight Civil and military applications frequency of military planes is very low compared to civil planes running on a daily basis. Based on these daily demands to ensure the airworthiness of civil aircraft, the requirements are much more comprehensive. As both applications follow closely the same
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Term Definition development and approval process as indicated in chapter 5, they are covered within this dossier. Surface preparation for subsequent processing including removal of dirt Cleaning and oil. The term has some overlap with the definitions of pickling, descaling and deoxidising. A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. The purpose of applying the coating Coating may be decorative, functional, or both. A coating may be a paint, a lacquer or a metal (e.g. hard chrome, cadmium coating, zinc-nickel coating) or an inorganic substance. Chemical process applied to a substrate producing a superficial layer containing a compound of the substrate metal and an anion of an Conversion Coating environment. Note that within the surface finishing industry a conversion coating is sometimes referred to as a passive coating or passivation. Means applied to the metal surface to prevent or interrupt oxidation of the metal part leading to loss of material. This can be a metal Corrosion protection conversion coating or anodizing, a pre-treatment, paint, water repellent coating, sealant, liquid, adhesive or bonding material. The corrosion protection provides corrosion resistance to the surface. Structural zone (like assembly, component) to which a given Counterpart assembly/part is fitted. Deoxidising is a pre-treatment step required to activate the surface prior to further processing i.e. to remove surface oxides. The term Deoxidising deoxidising is often used interchangeably with pickling. Very little metal is removed during deoxidising. Surface preparation for subsequent processing including removal of Descaling scale and oxides. The term has some overlap with the definitions of pickling, cleaning and deoxidising. Removal of residue that is often left over from etching processes. Desmutting Desmutting is often grouped with cleaning, deoxidizing or pickling. Electroplating is forming a metal coating on the part by an electrochemical method in an electrolyte containing metal ions and the Electroplating part is the cathode, an appropriate anode is used and an electrical current is applied. Process that changes surface as well as removes material. This term has Etching significant overlap with the term pickling. After having passed qualification and certification, the third step is to implement or industrialise the qualified material or process in all Implementation relevant activities and operations of production, maintenance and the supply chain. In-service evaluations are common practice to validate accelerated corrosion results obtained in the laboratory to determine correlation In-service evaluation between accelerated corrosion testing and when used on operating aircraft. A legacy part shall mean any part of an end product for aerospace Legacy part which is manufactured in accordance with a type certification applied for before the earliest sunset date (including any further supplemental or
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Term Definition amended type certificates or a derivative) or for defence and space which is designed in accordance with a military or space development contract signed before the earliest sunset date, and including all production, follow-on development, derivative and modification program contracts, based on that military or space development program. The purpose of the surface treatment is primarily for, but not limited to, corrosion protection. The main treatment occurs after the pre-treatment and before the post treatment. Examples include conversion coating, Main treatment anodizing and passivation of stainless steel. Sometimes conversion coating and anodizing are followed by painting; in which case these can be regarded as the pre-treatment and the painting as the main treatment. Portion of a specification that controls which materials may be used in Materials control the process. Products that have met all requirements may be added to this list by the OEM. Process providing corrosion protection to a substrate or a coating. Note that within the surface finishing industry a passive or passivation Passivation coating is often referred to as a conversion coating. Both terms are used in this document. Is designed to both remove embedded iron/steel particles from stainless Passivation of stainless steel steel and oxidise the surface chromium in the alloy to augment its natural corrosion resistant passive oxide layer. Metallic coatings applied on steel (such as cadmium, zinc, zinc-nickel, or aluminium) need to be passivated for corrosion protection. Passivation of metallic coatings Technically, this kind of passivation is a conversion coating and the process is a post-treatment applied after the application of the non- chromium metal coating. A non-chromated conversion process containing metal phosphates used mainly for some ferrous substrates and is generally used a key for Phosphating subsequent painting, oiling or lubrication films. It sometimes requires a chromated post-treatment (rinsing after phosphating). Pickling is the removal of oxides or other compounds from a metal surface by chemical or electrochemical action. The term pickling is not used consistently with the surface finishing industry and is often Pickling referred to as the following processes: cleaning, scale removal, scale conditioning, deoxidizing, etching, and passivation of stainless steel. This term has overlap with the term Etching. Post-treatment processes are performed after the main surface treatment Post-treatment process to enhance corrosion protection. Pre-treatment processes are used to remove contaminates (e.g. oil, grease, dust), oxides, scale, and previously applied coatings (e.g. Pre-treatment electroplated coatings, anodize coatings, conversion coatings, paint). The pre-treatment process must also provide chemically active surfaces for the subsequent treatment. A series of surface treatment process steps. The individual steps are not stand-alone processes. The processes work together as a system, and Process chain care should be taken not to assess without consideration of the other steps of the process. In assessing candidate alternatives for chromates, the whole process chain has to be taken into account.
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Term Definition OEM validation and verification that all material, components, equipment or processes have to meet or exceed the specific Qualification performance requirements which are defined in the Certification Specifications documented in technical standards or specifications. Numerous aerospace applications require an electrical conductive Resistivity coating for the respective use. Business partnership in which costs and benefits are shared amongst all participating partners. The intention is to rely on the commercial success, while reducing the risk of loss. For the aerospace industry, Risk sharing partners risk-sharing arrangements were made with suppliers to reduce investments and the dependence on loans. The suppliers are responsible for design activities, development and manufacture of major components or systems. Classification and labelling information of substances and products Risk reduction reported during the consultation being used for alternatives / alternative processes are compared to the hazard profile of the used chromate. Material to fill gaps or joints or to exclude the environment in order to prevent electrochemical corrosion between two parts with dissimilar Sealant material composition (metal-metal and metal-carbon composite) or crevice corrosion. This can be applied by means of spatula, extrusion, brush or spray. For a high corrosion resistance micropores of the anodized surface have Sealing to be closed by a post-treatment step (sealing after anodizing). Removal of coatings prior to rework. Differentiation based on the kind Stripping of coating removed (stripping or inorganic finishes, stripping or organic coatings).
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DECLARATION
We, [Applicant’s name], request that the information blanked out in the “public version” of the Analysis of Alternatives is not disclosed. We hereby declare that, to the best of our knowledge as of today ([DATE]) the information is not publicly available, and in accordance with the due measures of protection that we have implemented, a member of the public should not be able to obtain access to this information without our consent or that of the third party whose commercial interests are at stake.
Signature: Date, Place:
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1. SUMMARY This application for Authorisation (AfA) is the culmination of extraordinary effort across industry over several years to share data and prepare a comprehensive and reliable assessment of alternatives that is representative for the industry. The aerospace industry recognises that the use of such sector-specific approach in an upstream application will facilitate assessment by the SEAC. Without this approach, multiple applications for authorisation utilising different approaches, assumptions and terminology are unavoidable; such differences could present challenges for enforcement across the industry. The Analysis of Alternatives (AoA) is based on extensive input and data held by the aerospace sector, associated industries and third parties. The same companies and facilities have reviewed and validated the findings in detail and agree that the AoA is representative of the situation across the industry. This AoA forms part of the AfA for the use of sodium dichromate in the surface treatment of metals. The use, as defined, covers a number of surface treatment processes and steps 1 that may be applied to a number of different metal substrates (e.g. aluminium, steel, zinc, magnesium, titanium, alloys and composites with metallic areas). Surface treatment aims to modify the surface of a substrate so that it performs better under conditions of use. Surface treatment processes using sodium dichromate typically involve immersion of the metal component in each of a series of treatment baths containing chemical solutions or rinses under specific operating conditions 2. Different chemicals and operating conditions are specified for individual surface treatment processes (see Figure 1) in order to effectively treat different substrates and/or confer specific performance characteristics to the treated article. The relevant surface treatment processes which the AfA covers, the characteristics of sodium dichromate and its critical functionality in each of the treatment processes are introduced at chapter 3. The aerospace sector specify surface treatment with sodium dichromate in order to meet strict performance criteria necessary for regulatory compliance and for public safety, as described further below and in chapter 5. This summary aims to shortly explain why the use of sodium dichromate in surface treatment is essential to the aerospace sector. It describes the steps and effort involved in finding and approving a replacement for sodium dichromate in these applications and evaluates potential alternatives in detail (chapter 6 and 7).
Sodium dichromate-based surface treatment systems Chromium has been used for more than 50 years to provide surface protection to critical components and products within the aerospace sector, where the products to which they are applied must operate to the highest safety standards in highly demanding environments for extended time periods. Surface treatments based on chromates, including sodium dichromate have unique technical functions that confer substantial advantage over potential alternatives. These include:
1 See Chapter 3 for detail.
2 Occasional localised ‘touch-up’ of a surface may be made by brush or a pen-stick, as explained in the CSR
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- Outstanding corrosion protection and prevention for nearly all metals under a wide range of conditions - Active corrosion inhibition (self-sealing, e.g. repairing a local scratch to the surface) - Excellent adhesion properties to support application of subsequent coatings or paints - Excellent chemical and electrical resistivity
The chemistry behind chromate surface treatment systems and processes is complex. Surface treatment processes typically involve numerous steps, often including several important pre- treatment and post-treatment steps as well as the main treatment process itself. Figure 1 provides an overview of the applications included in the application for authorisation according to the process steps. These steps are almost always inter-related such that they cannot be separated or individually modified without impairing the overall process or performance of the treated product.
Use Description
Surface Treatment of Metal Parts
Pre Treatment Treatment Post Treatment • Cleaning • Conversion Coating • Sealing after Anodizing • Pickling/Etching • Passivation of Stainless • Rinsing • • Deoxidising Steel Passivation of metallic • Stripping coatings on steel •
Figure 1: Surface Treatment Processes steps where sodium dichromate might be involved.
This means that while the use of sodium dichromate (or a similar chromate) may be specified at different points in the process, it cannot be entirely replaced in the process without impacting the technical performance of the final article. The implications of this are important as chromate-free alternatives for some individual steps are available and used by industry. However, where this is the case, chromates are always specified in one of the other steps within the overall surface treatment system. As of today, no complete chromate-free treatment system, providing all the required properties to the surfaces of all articles in the scope of this application, is industrially available. This means it is imperative to consider the surface treatment system as a whole, rather than the step involving sodium dichromate on its own, when considering alternatives for such surface treatment systems. Furthermore, components that have been surface treated with sodium dichromate typically represent just one of many critical, inter-dependent elements of a component, assembly or system. In general, sodium dichromate-based surface treatment is specified as one element of a complex system with integrated, often critical performance criteria. Compatibility with and technical performance of the overall system are primary considerations of fundamental importance during material specification.
Use of sodium dichromate in surface treatment for the aerospace sector Chromate-based surface treatments are specified in the aerospace sector because they provide superior corrosion resistance and inhibition, improved paint adhesion, low electrical contact resistance and/or enhanced wear-resistance (see chapter 3.4). These characteristics are essential to the safe operation and reliability (airworthiness) of aircraft and spacecraft which operate under extreme environmental conditions. These structures are extremely complex in design, containing millions of highly specified parts, many of which cannot be easily inspected, repaired or removed.
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Structural components (e.g. landing gear, fasteners) and engine parts (e.g. internal components for gas turbines) on aircraft are particularly vulnerable to corrosion. Chromate surface treatment processes and performance have been successively refined and improved as a result of many decades of research and experience in the sector, and reliable data is available to support their performance. While corrosion cannot be totally prevented, despite the highly advanced nature of chromate-based coating systems in place today, there is also extensive experience, amassed over decades, on the appearance and impact of corrosion to support its effective management in these systems. On the other hand, while several potential alternatives to sodium dichromate , predominantly trivalent chromium and mineral acid based systems, are being investigated for different processes, substrates and treatment steps, results so far do not support reliable conclusions regarding their performance as part of such complex systems, in demanding environments and test conditions representative of in-service situations. These potential alternatives do not support all the properties of chromate-based surface treatment systems, and their long-term performance can currently only be estimated. Decreased corrosion protection performance would necessitate shorter inspection intervals, with a substantial impact on associated maintenance costs.
Identification and evaluation of potential alternatives for the aerospace sector An extensive literature survey and consultation with aerospace industry experts was carried out to identify and evaluate potential alternatives to sodium dichromate. A total of 46 potential alternatives for all parts of the process chain were identified. 32 of these substances could be excluded from further consideration based on inadequate performance and 15 potential or candidate alternatives (including processes and substances for all parts of the process chain) are a focus for ongoing research and development (R&D) programs and are examined in further detail in this report. Here, a candidate alternative is defined as a potential alternative provided to the aerospace manufacturer for evaluation following initial evaluation by the formulator. Table 1 at the end of this section summarises the main findings of the AoA for the aerospace sector. In Figure 3, the development status of the alternatives is illustrated. The various main treatment and post-treatments processes and identified potential or candidate alternatives are discussed in chapter 7.1, while the pre- treatments processes are discussed in chapter 7.2. In summary, the analysis shows there are no technically feasible alternatives to chromate-based surface treatment systems for broad application to key applications in the aerospace sector. Several potential alternatives are subject to ongoing R&D, but do not currently support the necessary combination of key functionalities to be considered technically feasible alternatives.
Ongoing development of potential alternatives for the aerospace sector Assuming a technically feasible potential alternative is identified as a result of ongoing R&D, extensive effort is needed beyond that point before it can be considered an alternative to sodium dichromate within the aerospace industry. Aircraft are one of the safest and securest means of transportation, despite having to perform in extreme environments for extended timeframes. This is the result of high regulatory standards and safety requirements. The implications for substance substitution in the aerospace industry is described in detail in a report prepared by ECHA and EASA in 2014, which sets out a strong case for long review periods for the aerospace sector based on the airworthiness requirements deriving from EU Regulation No 216/2008. Performance specifications defined under this regulation drives the choice of substances to be used either directly in the aircraft or during the manufacturing and maintenance activities. It requires that all components, equipment, materials and processes incorporated in an aircraft must be certified, qualified and industrialised before production can commence. The process is illustrated in Figure 2.
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This system robustly ensures new technology and manufacturing processes can be considered ‘mission ready’ through a series of well-defined steps only completed with the actual application of the technology in its final form (and under mission conditions). When a substance used in a material, process, component, or equipment needs to be changed, this extensive system must be followed in order to comply with airworthiness requirements. The system for alternative development through qualification, certification, industrialization and implementation within the aviation sector is mirrored in the defence and space sectors. The detailed process involved in qualification, certification, and industrialisation, and the associated timeframes, are elaborated in chapter 5. Of course, these steps can only proceed once a candidate alternative is identified. Referring to experience, it can take 20 to 25 years to identify and develop a new alternative, even assuming no drawbacks during the various stages of development of these alternatives. Experience over the last 30 years already shows this massively under-estimates the replacement time for chromate surface treatments. Taken together, available evidence clearly shows that no viable alternative for sodium dichromate in surface treatments is expected for at least the next 12 or even 15 years.
Figure 2: Illustration of the development, qualification, certification and industrialisation process required in the aerospace sector.
As a further consideration, while the implications of the development process in the aeronautic and aerospace sectors are clearly extremely demanding, specification of an alternative, once available, can be built into the detailed specification for new aircraft types (and new spacecraft). This is not the situation for existing aircraft types, for which production and/or operation may still be ongoing. Production, maintenance and repair of these models must use the processes and substances already specified following the extensive approval process. Substitution of sodium dichromate-based surface treatment for these ‘legacy’ craft introduces yet another substantial challenge; re- certification of all relevant processes and materials. Unless chromate-free solution are considered as 1:1 replacements, it will be impractical and uneconomical to introduce such changes for many such aircraft types. In this context, the scale and intensity of industry- and company- wide investment in R&D activity to identify alternatives to chromate surface treatment systems is very relevant to the findings of the AoA. Serious efforts to find replacements for chromates have been ongoing within the aerospace industry for over 30 years and there have been several major programs to investigate alternatives to chromates in the aerospace sector over the last 20 years. The level of industry investment to date in such activity is estimated to be at least €100million.
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Table 1: Overview of key potential alternatives for main surface treatments.
Potential Alternative Technical failure • Corrosion resistance not proved for the range of substrates Acidic surface treatments • Does not cover the broad range of different substrates in general • No reproducible results of corrosion resistance on all kind of Organometallics (zirconium and titanium- substrates based products, e.g. • No active corrosion inhibition fluorotitanic/fluorozirconic acids) • Adhesion of coating to substrate not sufficient • Corrosion requirements not met Molybdates and molybdenum-based • No active corrosion inhibition processes • No conductive coating (no resistivity) • Difficult process control • No stand-alone corrosion protection Silane/Siloxane and sol-gel coating • No conductive coating (resistivity not sufficient) • Limitations to geometry of parts (no complex parts) • Inconsistent corrosion results • Limited active corrosion inhibition Cr(III)-based surface treatments • Inconsistent adhesion (coating to substrate) results with poor quality reproducibility at current stage Manganese-based processes • Corrosion resistance insufficient
Concluding remarks A large amount of research over the last 30 years has been deployed to identify and develop viable alternatives to chromate-based surface treatment. Due to its unique functionalities and performance, it is challenging and complex to replace surface treatments based on sodium dichromate (or other chromates) in applications that demand superior performance for corrosion and/or adhesion to deliver safety over extended periods and extreme environmental conditions. Several potential alternatives to sodium dichromate, such as trivalent chromium and mineral acid based systems, are under investigation for the aerospace industry. However, based on experience and with reference to the status of R&D programs, alternatives are not foreseen to be commercially available for key applications in this sector for at least 12 or 15 years. As a result, a review period of 12 years was selected because it coincides with best case (optimistic) estimates by the aerospace industry of the schedule required to industrialise alternatives to sodium dichromate. Since the sunset date for sodium dichromate is in 2017, the covered period of time runs from 2018 to 2030 (taking 2017 as a base year for calculations).
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Figure 3: Development status of alternatives. Pass. Steel: Passivation of stainless steel; Pass. MC: Passivation of metallic coatings; CCC: Chemical Conversion Coating. Category 1 alternatives in turquoise, Category 2 alternatives in red. Figure 3 gives an overview of the TR Level of potential surface treatment alternatives. It is important to note that those readiness levels are best case scenarios for single OEMs/applications only and do not reflect the general development status of the aerospace sector.
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2. INTRODUCTION This AfA is the culmination of extraordinary effort across industry over several years to share data and prepare a comprehensive and reliable assessment of alternatives that is representative for the industry.
The aerospace industry recognises that the use of such sector-specific approach in an upstream application will facilitate assessment by the SEAC. Without this approach, multiple applications for authorisation utilising different approaches, assumptions and terminology are unavoidable; such differences could present challenges for enforcement across the industry.
The AoA is based on extensive input and data held by the aerospace sector, associated industries and third parties. The same companies and facilities have reviewed and validated the findings in detail and agree that the AoA is representative of the situation across the industry.
2.1. Substance The following substance is subject to this analysis of alternatives:
Table 2: Substance of this analysis of alternatives.
Intrinsic Substance Latest application date² Sunset date ³ property(ies) 1 Carcinogenic Sodium dichromate (category 1B) EC No: 234-190-3 Mutagenic CAS No: 7789-12-0 (category 1B) 21 March 2016 21 September 2017 (dihydrate), Toxic for 10588-01-9 (anhydrous) reproduction (category 1B) 1 Referred to in Article 57 of Regulation (EC) No. 1907/2006 ² Date referred to in Article 58(1)(c)(ii) of Regulation (EC) No. 1907/2006 3 Date referred to in Article 58(1)(c)(i) of Regulation (EC) No. 1907/2006
Sodium dichromate is categorized as substance of very high concern (SVHC) and is listed on Annex XIV of Regulation (EC) No 1907/2006. It is an inorganic chromate salt based on hexavalent chromium (Cr(VI)). Adverse effects are discussed in the CSR.
2.2. Uses of Cr(VI) containing substances Cr(VI) containing substances have been widely used since the middle of the 20 th century. The major uses are: - Surface treatment of metals such as aluminium, magnesium, steel, zinc, titanium, and their alloys and coatings (including pre- and post-treatments), - Usage in metal primers, sealants, and various specialty coatings including but not limited to sealants, wash primers, and adhesive bonding primers, - Formulation of mixtures for the above mentioned uses.
2.3. Purpose and benefits of Cr(VI) compounds Hexavalent chromium based substances offer a broad range of functions which have been widely used for over 50 years in the industry in various applications. The multifunctionality of Cr(VI)
Use number: 2 7 ANALYSIS OF ALTERNATIVES provides major properties to the surfaces treated with the respective process. The following key functionalities for the aerospace sector are discussed in more detail in chapter 3.4. - Corrosion resistance: excellent corrosion protection and prevention to nearly all metals in a wide range of environments, - Active corrosion inhibition: when a coating is damaged, e.g. by a scratch exposing the base material to the environment, the solubility properties of the chromates allow them to migrate to the exposed area and inhibit corrosion, - Adhesion promotion (adhesion to subsequent coatings or paint), - Providing low electrical contact resistance (resistivity); - Enhancing wear resistance, - Delivering optimal layer thickness (for the respective treatment and purpose), - Enhancing chemical resistance, - Providing biostatic properties, and - Inhibiting the growth and proliferation of biological organisms.
Several alternatives are being tested to replace sodium dichromate. It is a challenge to find a substitute which meets all requirements for a product, for each use, and specific applications while also being technically and economically feasible. Many alternatives are already qualified for some applications and substrates, but none of them provide all the key properties of sodium dichromate as defined in the following sections.
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3. ANALYSIS OF SUBSTANCE FUNCTION Sodium dichromate is used for surface treatment within the aerospace sector as illustrated in the following sections.
3.1. Usage Surface treatment is aimed to modify the surface to adapt it to specific use conditions. The main uses of sodium dichromate-based surface treatments in the aerospace sector are providing better corrosion resistance, improved paint adhesion, low electrical contact resistance or enhanced wear resistance to surfaces. This is achieved by a process chain which combines initial pre-treatment process steps preparing the surfaces for a subsequent coating, the main process providing the protective coating itself and post-treatment process steps. The complexity of an aircraft, spacecraft and the airworthiness requirements make corrosion resistance, improved paint adhesion, low electrical contact resistance or enhanced wear resistance a very challenging task. Inspection and quality control is very difficult and heavy maintenance is required almost every 10 years and some parts (e.g. structural components) cannot be removed. Metal surfaces and metal parts can be influenced from corrosion by a broad variety of factors, such as: - Temperature, - Humidity, - Salinity of the environment, - Industrial environment, - Surface conditions, - Erosion, - Radiation, - Impurities, - Stress, - Pressure, - Geometry of parts, - Biological growth, - Accumulated liquid, - Operational fluids, and - Galvanic coupling (e.g. at fasteners adjacent to dissimilar metals). All the factors listed above can occur alone or in combinations under certain environments at different parts of an aircraft or spacecraft. Not all components of an aircraft are equally susceptible to corrosion, especially vulnerable components are known to include structural components such as the skin originating at lap joints as well as fasteners and fastener holes, landing gear, other structural components, and engine components. Other major areas susceptible to corrosion include where moisture and liquids are entrapped, such as under fairings. For spacecraft, external parts exposed to harsh environments (e.g. at launch pad Guiana Space Centre, Kourou, French Guiana) interstage skirts and pyrotechnic equipment are susceptible to corrosion. However, corrosion prone areas also vary with the type of aircraft as shown in Table 3.
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Table 3: Corrosion prone areas on different types of aircraft.
Civil Aircraft/Spacecraft Fighter Aircraft Helicopters
Main landing gear Main landing gear Main rotor head assembly
Nose landing gear Nose landing gear Tail rotor assembly
Rudder and elevator shroud areas Missile and gun blast areas Transmission housing of dynamics
Aileron and flap track area, flap Leading edges, hinge lines and air Main rotor blades and leading edges tracks and trailing edges ducts
Access and freight doors Cockpit frames Fuselage
Control cables Wing fold areas EMI/ Lightening Strike Shielding
EMI/ Lightening Strike Shielding Engine intake areas
Galley and Lavatory EMI/ Lightening Strike Shielding
Cargo Areas LO Coatings
Pyrotechnic equipment
Interstage skirts
Anywhere liquid can accumulate
Fuselage in general and in particular inside aircraft, seat
tracks, cargo systems, wingskin, etc.
Importantly, in this demanding environment corrosion may still occur with the highly developed Cr(VI)-containing coating systems. For currently used coatings, decades of extensive experience exists relating to the appearance and impacts of corrosion. Without a well-developed Cr(VI)-free alternative, corrosion will certainly increase, as these alternative coatings do not offer all the crucial properties of Cr(VI) coating systems and their long-term performance can currently only be estimated. Likely, the corrosion problems would not appear suddenly but only after several years, when hundreds of aircraft are delivered. Re-equipping, if possible, would cost hundreds of million €. As a consequence, decreased corrosion protection performance may lead to shorter inspection intervals, which has a significant impact on the maintenance costs for aircraft. Furthermore, for secure adaptation of the inspection intervals a detailed knowledge of the alternatives is a prerequisite Some of the corrosion prone areas, as well as further examples on parts requiring corrosion protection are illustrated in Figure 4 to Figure 11 below:
Figure 4: ATR 600 aircraft & Gulfstream V aircraft (UTC Aerospace Systems – Propeller Systems, 2014).
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Figure 5. Schematic illustration of typical corrosion findings in an aircraft fuselage (Airbus).
Figure 6: Propellers mounted on an aircraft (UTC Aerospace Systems – Propeller Systems, 2014).
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Figure 7: Undercarriage - landing gear, examples (Rowan Technology Group, 2005).
Figure 8: Gas Turbine Engine sketch example PW4000 92 inch fan engine (www.pw.utc.com/Content/PW400094_Engine/img/B-1-4-1_pw400094_cutaway_high.jpg , 2014).
Figure 9: Emergency door damper for a civil aircraft. (UTC Aerospace Systems – Propeller Systems, 2014).
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Figure 10: Main & tail rotor shaft elements of a helicopter (Data source; UTC Aerospace Systems – Propeller Systems, 2014).
Figure 11: Partially assembled main helicopter rotor (UTC Aerospace Systems – Propeller Systems, 2014).
Different kinds of corrosion occur at these prone areas with some of the most common being illustrated in the following paragraphs. Fastener and fastener holes are well known to be susceptible areas for different kinds of corrosion. Galvanic, filiform and crevice corrosion can occur at fasteners in contact with the aircraft skin (dissimilar metal). Stress corrosion cracking is also applicable as fasteners have to withstand stresses or loads. Corrosion fatigue and stress corrosion cracking may develop around fastener holes due to stress concentration at a single point in the hole, and also on structural components which have to withstand stress and are exposed to corrosive environments. Exfoliation corrosion may occur in materials that are susceptible to this form of corrosion (such as crevices of thick extruded or rolled aluminium plate). The potential for exfoliation corrosion to
Use number: 2 13 ANALYSIS OF ALTERNATIVES occur is increased at unprotected panel edges where end-grain is exposed. This is also true for other exposed metal areas such as countersinks. Fretting corrosion occurs when overlapping metallic joints are subject to repeated or cyclic relative movement and where a corrosive environment is present. Treating surfaces susceptible to corrosion with Cr(VI) containing products provides, in combination with the correct choice of material, the required corrosion prevention properties and functionality. Any structural detail where there is an unsealed gap between adjacent components where moisture can become entrapped (like a joint) is highly susceptible to corrosion. Protection can be provided by priming these surfaces adequately. Again the use of hexavalent chromates has proved to be most effective for this purpose. Electrical systems are often subject to corrosion at wires, connectors and contacts, especially where moisture or humid environments are present. Highly corrosive environments are also present in aircraft engines during operations caused by high temperatures and the presence of corrosive gases, high temperature oxidation/corrosion and liquids. Accelerated forms of corrosion can be found at the engine air inlet where airborne solids or rain erosion can damage the metal and coating surfaces. Similar highly corrosive environments are present in helicopter components such as rotor heads, and main and tail rotor blades. There are many more areas which are prone to corrosion in an aircraft. The following list provides a rough overview but is far from being complete: - Bilge areas where wastes of all kinds are collected(e.g. hydraulic fluids, water, dirt); - Control surface actuating rods and fittings may corrode as a consequence of coupling with dissimilar metals, being damaged, or deteriorated protective coatings; - Undercarriage bays (i.e. area of the wheel wells) are affected by debris from the runway; - Battery compartments and vent openings due to battery spillage; - Fuel tanks due to the ingress of moisture and resulting microorganisms that can reside in fuel; - Engine exhaust trail areas affected by exhaust gases; - Galley and lavatory areas are affected by spilled foods and human waste; and - Cargo areas collect all kinds of miscellaneous corrosive materials brought in by the cargo containers (e.g. mud, salt, oils, water, livestock waste, chemical spills, food products, etc.). In this introduction, only examples of corrosion were presented. However, there is often a combination of certain properties required for these parts.
3.2. Surface treatment process descriptions There are various surface treatment processes. These are classified into pre-treatment processes, the main process, and post-treatment processes. These categories are defined in further detail in this subsection. Some examples are listed in Table 4. It is important to recognize that only the combination of processes applied in sequence (pre- treatment, main process step and post-treatment) is able to provide the coating as required. Although the single process steps can be assessed individually, they are not stand-alone processes but part of a process chain or process flow (Figure 12 ).
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In assessing alternatives for sodium dichromate, the whole process chain has to be taken into account. It is possible, that for single process steps (either pre-treatments, main processes or post- treatments) Cr(VI)-free alternatives are already on the market and industrially used. However, the requirements of the sectors (based upon assessment, qualification, industrialisation and certification) can only be met by applying the whole process chain; and as of today, no complete sodium dichromate-free process chain is industrially available providing all the required properties to the surfaces.
Use Description
Surface Treatment of Metal Parts
Pre Treatment Treatment Post Treatment • Cleaning • Conversion Coating • Sealing after Anodizing • Pickling/Etching • Passivation of Stainless • Rinsing • Deoxidising Steel • Passivation of metallic • Stripping • coatings on steel
•
Figure 12: Surface treatment processes steps where sodium dichromate might be involved. Only the combination of adequate pre-treatments, main process step and post-treatment leads to a well-prepared surface providing all necessary key requirements for the respective applications (as described in detail in chapter 3.4). To be clear, the use of Cr(VI) in at least one process step is crucial to ensure the quality of the product and to meet the requirements of the industry. Although single process steps can be assessed individually, they cannot be seen as stand-alone processes but as part of a whole process chain. Consequently, when assessing alternatives for Cr(VI)-based surface treatments, the whole process chain and the performance of the end product has to be taken into account. While R&D on replacement technologies in surface treatments has been ongoing for decades, industry has developed and has already partly qualified alternate treatments for special applications. Therefore, it is possible that for individual process steps, either pre-treatments, main process steps and post-treatments steps, Cr(VI)-free alternatives are already on the market and industrially used. However, it is crucial to consider the following points: - In each case, the performance of the alternative materials/techniques must - importantly - be evaluated as part of a whole system ( Figure 12 ), - Any change of single steps in the process chain of surface treatments, will require component and/or system level testing and evaluation, (re)qualification and implementation into the supply chain; and - Current approvals for coating systems still incorporate at least one process step involving Cr(VI), but mostly several layers of Cr(VI).
We therefore clearly state that for a thorough assessment of replacement technologies it is mandatory to include the whole process chain (including pre- and post-treatments), taking into consideration that for all steps involved, Cr(VI)-free solutions have to be developed, which in combination are technically equivalent to the current Cr(VI) containing treatments. For few applications from the aerospace sector, where corrosion risk is low, first complete Cr(VI)-free solutions exist. Currently, no complete sodium dichromate free process chain is industrially available though for key applications providing all the required properties to the surfaces for all applications.
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Figure 13 shows an industrial surface treatment line.
Figure 13: Surface treatment bath (Airbus Fast Report, 2009).
Table 4: Overview of surface treatment processes indicating most important application methods, purpose, as well as example products. This is not intended to be an exhaustive list.
Process Application Purpose Product/Substrate examples
- Cleaning of copper and Bath, Wipe, Surface preparation for subsequent Cleaning copper alloys, aluminium and Spray processing. magnesium alloys
Removal of mechanically deformed layers, oxides or other compounds - Pickling of stainless steel Pickling/ from a metal surface by chemical - Pre-treatment of Al alloys, Bath Etching or electrochemical action. Removal - Pre-treatment of Carbon- of material selectively to reveal a reinforced Composite parts surface or the surface properties.
Deoxidising is a pre-treatment step required to activate the surface - Pre-treatment of Al alloys Deoxidising Bath prior to further processing (for prior to anodizing example CCC) - Pre-treatment of metallic Removal of metal sulphide and Desmutting Bath substrates after pickling, other complexes after etching etching and deoxidising - Stripping of organic and Bath Stripping is the removal of a inorganic material, such as Stripping Wipe coating from the component paint from steel or hard anodic -treatment processes substrate or an undercoat. Brush coating from Al alloy Pre
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Process Application Purpose Product/Substrate examples
Chemical process that introduces a Chemical Bath - Aluminium chemical coating or changes the Conversion Spray - Magnesium surface of the substrate to improve Coating Wipe the substrate properties (e.g. - Steel (Including Touch up corrosion resistance, or promote - Conversion coating of Phosphating) Brush adhesion of subsequent coatings). metallic coatings Remove embedded iron/steel Passivation of particles from stainless steel to - Stainless Steel Bath Stainless Steel restore its natural corrosion - Any other product examples resistant passive oxide layer.
- Main treatment process Sealing after Sealing of the porous anodic Bath - Anodised aluminium surfaces (Cr(VI)-free) coating providing protective for corrosion resistance anodizing Touch up properties Chromate Cleaning up of a phosphated - Substrates treated with Rinsing (after Bath surface for corrosion protection Phosphate Conversion Coating Phosphating) Process providing corrosion - Metallic coatings on steel Passivation of protection to a metallic coating. such as Cd coatings, Zinc- metallic coatings This is often performed using a Bath based coatings, Aluminium- (Post-treatment chemical conversion coating (CCC) based coatings, Zinc-Nickel CCC) after metal coating by coatings) Post-treatment processes electroplating
3.2.1. Pre-treatment processes A number of pre-treatments are necessary to prepare the surface of the substrates for the subsequent process steps. Adequate preparation of the base metal is a prerequisite: adhesion between a coating and the substrate depends on the force of attraction at molecular levels. Therefore, the surface of the metal must be absolutely free of contaminants, corrosion and other foreign matter until the main treatment process is finished. Additionally, homogeneous formation of anodic films or passivation is influenced by the pre-treatment. Inhomogeneous surfaces will result in unpredictable corrosion performance. A number of different pre-treatments are in place depending on the respective subsequent process and its functionality. The pre-treatments discussed below are based on the use of a Cr(VI) containing solution, while chromate-free pre-treatments are discussed in chapter 7 (evaluation of alternatives).
3.2.1.1 Cleaning All surfaces have to be prepared for subsequent processing by removing dirt, soil and scale, for example from grinding and polishing. Sodium dichromate functional cleaning solutions are used for achieving best results. Cleaning is not a stand-alone process but part of a process chain. Presence of those contaminants influences the appearance of the subsequent layer and increases the susceptibility for fatigue and pit corrosion.
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3.2.1.2 Pickling and etching There is considerable overlap between these terms in the industry. Pickling/Etching is the removal of mechanically deformed layers, oxides or other compounds from a metal surface by chemical or electrochemical action. Typically it removes 0.5 to 3 µm of the substrate, and it is required because the initially unprotected metal surfaces exposed to atmospheric conditions are continuously oxidised. These oxides interfere with subsequent processes (e.g. in passivation the required optimal corrosion protection could not be reached). With regard to aluminium alloys, pickling/etching is additionally used to enhance the surface for adhesive bonding for subsequent processing. Etching is also used to remove smeared in order to ensure the detection by dye penetrant inspection of cracks or other defects formed during metal shaping such as machining or forming. Pickling/etching is not a stand-alone process but part of a process chain. The sodium dichromate is used as it is a strong oxidising agent offering the strongest reduction behaviour and therefore also the best result for tailoring of surfaces. In addition, the use of sodium dichromate-based pickling/etching solutions have a very low impact on the fatigue properties of the treated substrate. A specialized application is when processing stainless steel before bonding. This Cr(VI)-based surface treatment is used for the removal of contamination from the steel surface prior to bonding to create a clean surface and to ensure adequate adhesion of the subsequent bonded layer. The process consists of several steps, the main one being an electrolytic process and a subsequent desmutting step which uses sodium dichromate loaded products. The process removes material/contaminations from the surface and creates a surface topography beneficial for subsequent bonding. The process enables stainless steel to be bonded to other materials independent of type.
3.2.1.3 Deoxidising Deoxidising is a pre-treatment step required to activate the surface prior to further processing. Deoxidising is not a stand-alone process but part of a process chain. Deoxidising is an intermediate process step after degreasing and cleaning prior to subsequent process steps, such as anodizing or conversion coatings. Cr(VI)-based deoxidising is able to fulfil a number of different purposes, depending on the initial pre-treatment and the required subsequent process. As an example, both the pre-treatment processes degreasing and etching are performed under alkaline conditions while a subsequent anodizing is performed under acidic conditions. Therefore, the surface has to be neutralized after the pre-treatments prior to the anodizing process. As a further purpose, deoxidising also removes potentially remaining oxides from the metal surface and activates the surface for the subsequent processes.
The Cr(VI)-based deoxidiser solutions often comprise additives such as nitric acid (HNO 3) and hydrofluoric acid (HF), depending on the specific purpose. According to Harvey et al. (2008), these deoxidisers remove around 1 µm of the surface during the treatment, including the surface oxide and the majority of the intermetallic particles leaving the surface with a chromium containing oxide. Mode of action for aluminium pre-treatment by cleaning, pickling/ etching/ deoxidising: The general mode of action for cleaning, pickling, etching and deoxidising is basically the same. The purpose of all these steps is the removal of oxides and of certain amounts of the base metal from the surface. There are numerous chemical reactions involved with the different constituents of the deoxidising solution, the aluminium oxide layer on the part surface, and the alloying elements (e.g.
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Cu, Si, Mg, Zn) of the substrate. While many of the reactions are intended there are also many unintended reactions. The role of sodium dichromate in the deoxidiser solution is primarily to provide uniform removal of aluminium and alloy metals and activate the surface for subsequent processing.
3.2.1.4 Stripping Stripping is the removal of a coating from the component substrate or an undercoat. Cr(VI)-based stripping solutions can be used for a wide range of substrates and coatings, while it turned out when considering alternatives, the stripping process always has to be adapted taking into account the substrate (metal, specific alloy type) and the kind of coating to be removed. Therefore, stripping can be divided into two main processes as there are stripping of inorganic finishes (such as hard anodic coating from Al alloys) and stripping of organic finishes such as primer and/or paint (from steel, aluminium, nickel/cobalt alloys, titanium, magnesium, corrosion resistant stainless steel (CRES)). Stripping is used to remove the coating (for example an anodic coating applied by chromic acid anodizing (CAA)) without attacking the aluminium substrate itself. This process is used for rework, maintenance and repair operations, when the coating has to be removed and repaired, for example as partial repair. Stripping of coatings, which have been applied more than 10 years ago requires higher temperatures while “younger” coatings are more easily removed. Stripping is not a stand- alone process but part of a metal pre-treatment process chain.
3.2.2. Main surface treatment processes
3.2.2.1 Chemical conversion coating (including phosphate conversion coating: phosphating) Chemical Conversion Coating (CCC) is a chemical process applied to a substrate producing a superficial layer containing a compound of the substrate metal and the process chemistry. In general CCC form an adherent, fixed, insoluble, inorganic crystalline or amorphous surface film of complexes from oxides and chromates or phosphates as an integral part of the metal surface by means of a non-electrolytic chemical reaction between the metal surface and the immersion solution. CCC is usually carried out by immersion of the product in an acidic bath with an aqueous solution containing dissolved sodium dichromate or phosphate salts together with an acid such as sulphuric acid or nitric acid. CCC can also be applied by spray or wipe techniques, more common in repair and non-stationary operations. The thickness of the coating typically is between 0.05 – 2 µm. Cr(VI) coatings possess a unique characteristic of self-healing when damaged. There are two main classes of products which are subject to a CCC treatment, the first are products made of aluminium and its alloys (Al CCC) and magnesium and its alloys (Mg CCC). The second are metallic coatings such as aluminium-based coatings, zinc-based coatings, zinc-nickel-coatings and cadmium coatings applied on metallic substrates (such as steel, stainless steels, aluminium, copper etc.) and on composites substrates where CCC is to provide corrosion protection. This process is further referred to and discussed as passivation of metallic coatings. CCC are used throughout the aerospace sector on a wide variety of components and equipment such as steel landing gear components, fasteners, electrical connectors and enclosures. Mode of action: Various research efforts have been made leading to considerable understanding of the mechanism of metal corrosion and the inhibition provided by sodium dichromate as chromate
Use number: 2 19 ANALYSIS OF ALTERNATIVES conversion coatings over the last decades. The formation of a chromate conversion coating includes several steps, typically starting with a deoxidising and degreasing pre-treatment to prepare the substrate’s surface, followed by the main process step of dipping the substrate in the chromate solution (Vasques et al, 2002). The chemical reactions provided below are specific to aluminium substrate, however, the general mode of action for magnesium substrate or metal coatings are basically the same. According to Vasques et al (2002) and Zhao et al (2001), aluminium exposed to a chromate conversion coating solution results in the simultaneous oxidation of Al to Al 3+ and the reduction of Cr(VI) to Cr(III) as follows: (1) 2 Al 2 Al 3+ + 6e –
3+ + (2) 2 Al + 3 H 2O Al 2O3 + 6 H
2- + - (3) 2(CrO 4) + 10 H +6e Cr(OH) 3 + H 2O The result is a protective hydrated trivalent chromium compound layer, absorbed in the pores of the aluminium oxide layer As residual chromate is retained in the CCC, the chromate provides active corrosion inhibition to the surface by dissolving into the local defect and altering the local environment. Any comparison of an alternative for sodium dichromate in CCC must take this unique property into consideration (Zhao et al., 2001). According to Zhao et al. (2001), the mechanisms for the inhibition of metal 2- alloy dissolution are that the chromate is a very soluble, higher-valent, oxidising ion (CrO 4 or 2- Cr 2O7 ) with a lower valent form that is insoluble and creates an extremely protective film (Cr 2O3 or Cr(OH) 3). The degree of corrosion resistance of conversion coatings is generally proportional to the coating thickness (Deresh, L., 1991).
3.2.2.2 Passivation of stainless steel A material is considered passivated when it shows a high resistance to corrosion in an environment in that one would normally expect corrosion to occur. Stainless steel is considered a material that naturally passivates because it contains chromium as an alloying element that forms a very thin chromium oxide layer on the surface of the stainless steel. This thin chromium oxide layer is responsible for passivating stainless steel. A properly passivated stainless steel can resist corrosion in humid air and salt water. However, if the passive oxide is damaged or destroyed, then passivation is the process used to restore or reform the passive oxide layer on stainless steel alloys, and this passive oxide layer is critical to make stainless steel corrosion resistant. One method that damages the passive oxide layer is by machining or forming stainless steel with steel tools. These steel tools leave small particles of iron embedded in the stainless steel part. A stainless steel part with embedded iron particles would quickly form rust spots if subjected to high humidity or salt spray conditions. Passivation of stainless steel removes embedded iron/steel particles from stainless steel to restore its natural corrosion resistant passive oxide layer.
3.2.3. Post-treatment processes A number of different, sodium dichromate-based post-treatment processes can be applied to the surfaces as described below. Colourings and primers are not part of this AfA.
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3.2.3.1 Sealing after (Cr(VI)-free) anodizing The surfaces of substrates after anodizing are naturally porous, the coating cannot provide the required corrosion resistance without further treatment (Hao, L. & Cheng, B.R., 2000), therefore a sealing post-treatment is necessary for a broad variety of sectors and applications. The process of anodizing is briefly described below to fully cover the process and to understand the need for a post-treatment anodize sealing. However, the AfA does not cover the use of chromates in the anodizing process. Anodizing is an electrolytic oxidation process in which the surface of a metal, when anodic, is converted to a coating having desirable protective or functional properties. The oxide layer partly grows into the substrate and partly grows onto the surface. Anodizing is used to increase corrosion and wear resistance as well as adhesion for subsequent processes. The main commercial application is the treatment of aluminium to create Al2O3 on the surface (RPA Report 2005). Given the natural porous anodized surface, the micropores of the anodized surface have to be closed by a sealing post-treatment step for the requisite long-term corrosion resistance. The sealing step needs to be controlled not to cause poor adhesion of the subsequent paint coatings that are applied to most anodized and sealed aircraft parts. The degree of hydration of the anodize seal needs to be monitored to insure good paint adhesion. Sealing is often performed in a hot aqueous chromate solution (typically > 95°C but below the solution’s boiling point) using mainly sodium dichromate, sodium dichromate or a mixture. For some applications, hot water or salts of other metals are used for sealing. Chromated conversion coatings solutions can also be used for the purpose of sealing after anodizing. Mode of action: The sealing after anodizing step is performed with a dichromate solution comprising chromium trioxide, sodium dichromate, sodium dichromate, or a mixture thereof. During the sealing, chromates and hydroxides precipitate in the pores in the pores of the previously anodized oxide layer and are hydrated. By this process, the pores are closed and an adequate wear resistance and corrosion resistance is provided to the surface. The hydration process (in the course of sealing after anodizing) is pH dependent, but in all cases, the chromate is absorbed to the anodized aluminium surface. Depending on the pH, chromate sealing forms either aluminium oxychromate (equation 1) (at pH lower than 6) or aluminium dioxychromate (equation 2) in the coating micropores (Steele, L.S, & Brandewie, B., 2007).
- - (1) AlO(OH) + HCrO 4 AlO(HCrO 4) + OH
- - (2) (AlO(OH))2 + HCrO 4 (AlO) 2(CrO 4) +OH +H 2O The final step closes the pores by contact with hot water and locks in the chromate in the pores according to equation (3):
(3) Al 2O3 + H 2O 2 AlO(OH) The hydrated aluminium oxide (boehmite) has a larger volume than aluminium oxide, therefore the pores are closed.
3.2.3.2 Passivation of metallic coatings Metallic coatings, such as cadmium, zinc, zinc-nickel, aluminium or Al IVD (by Ion Vapour Deposition coated aluminium), applied on metallic substrate (such as steels, stainless steels,
Use number: 2 21 ANALYSIS OF ALTERNATIVES aluminium, copper etc.) and on composites substrates need to be passivated for corrosion protection. Technically, this kind of passivation is a conversion coating (refer to chapter 3.2.2.1). Passivation is a post-treatment after the application of the non-chromium metal coating. Different kinds of metal coatings are used depending on the respective functionality of the coated part. Cadmium plated parts, for instance, are used due to the unique properties of cadmium required in many high performance aerospace applications; for example the most commonly used aerospace fastener plating material is cadmium. Cadmium is galvanic compatible with aluminium parts and other metallic or composite substrates and protects ferrous components in aluminium assemblies from corrosion (sacrificial corrosion protection). Cadmium plated steel needs to be heat-treated to prevent hydrogen embrittlement. The corrosion resistance of Cd platings is up to 2,000 h in salt spray tests, which can be further enhanced (doubled) by sodium dichromate-based passivation.
3.2.3.3 Chromate rinsing (after phosphating) Chromate rinsing after phosphating is a passivation process after phosphate conversion coating (phosphating). A sodium dichromate rinsing step fulfils two requirements by using only one process step. First, the rinsing removes the drag-out comprising liquids and residuals of former processes adhering to the substrate to ensure that there is no deterioration of the substrate by residuals (RPA Report, 2005). Additionally, by processing at a temperature between 70 and 80°C, the surface is passivated and the corrosion resistance of the surface is enhanced. This enhancement is necessary for phosphate conversion coatings because these coatings have a naturally occurring porosity which would negatively affect the corrosion resistance of the coated surface without any post-treatment (Narayanan, 2005). The rinsing is performed by immersing the product in the rinsing solution. Mode of action: The rinsing step is necessary for the adhesion of subsequent paint coatings to the phosphated surface. The rinsing leads to the deposition of water-insoluble chromate salts which reduce the porosity of the treated surface by about 50%. Additionally, the sodium dichromate solution etches protruding crystals of the phosphate coating to provide a plain surface for subsequent painting. The rinsing is performed with sodium dichromate because the removal is most effective by using a chromate solution (Narayanan, 2005)
3.3. Substance specific characteristics of chromates Corrosion resistance is one of the major functionalities of chromates in surface treatment processes. Sodium dichromate is used as anticorrosive compound in surface treatment processes for a variety of substrates including aluminium, ferrous and magnesium alloys and steel to offer long term environmental protection especially in applications where extreme exterior weathering and environmental conditions require high-end corrosion protection.
3.3.1. Characteristics and properties of sodium dichromate Sodium dichromate is an odourless solid and appears as bright red-orange crystal needles. Sodium dichromate is hygroscopic and very soluble in water. Therefore, it often appears as sodium dichromate dihydrate Na 2Cr 2O7·2H 2O. The solution of sodium dichromate is acidic and a strong oxidising agent. Physical and chemical characteristics of Sodium dichromate are summarized in
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Table 5:
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Table 5: Sodium dichromate typical chemical and physical properties.
Parameter Value
Water solubility ca. 2,355 g/l at 20°C
Specific gravity 2.52 g/cm³
Molecular weight 261.97 g/mol
pH value 3.5 at 25 °C and for a solution of 100 g/l
Melting Point 356.7 °C
Boiling point (decomposition) > 400 °C
3.4. Key functionalities of chromate based surface treatments An overview on the key functionalities and the performance requirements of sodium dichromate in the respective surface treatment is provided in the paragraphs below, subdivided into pre-treatment processes, main processes and post-treatment processes. During the consultation phase, the key functionalities for the here defined use were identified taking the whole surface treatment processes into account. Nevertheless, the most important key functionality for all the main processes and post- treatment processes is corrosion resistance. It should be noted that whereas the numerical values reported for key requirements have been supplied by the industry, these are not necessarily the same for all companies. Furthermore, requirements for individual applications may also vary.
3.4.1. Key functionalities of sodium dichromate-based surface pre-treatments As stated in chapter 3.2.1. , a clear demarcation between the processes of pickling, etching, cleaning, and deoxidizing does not exist. When comparing specifications from different sources, the terminology is not always consistent from one document to another. It can be stated that, with all these processes, adequate surface preparation for subsequent processes can be achieved by removal of surface residues. The main difference is that for cleaning, a less aggressive chemistry is used for light scale removal or removal of other contaminants like shot peen residue. As the aim of the pre-treatment processes is to prepare the surfaces for subsequent process steps, the key functionalities are not always the same as for the main process or the post-treatments discussed in chapter 3.4.2.
3.4.1.1 Cleaning, pickling, etching The key functionality of cleaning, pickling and etching is the adequate removal of oxide and debris from a metal surface. For pickling and etching, selective removal of certain amounts of base material or removal of surface defects is required for surface activation. This process is controlled by the etch rate. The careful control of this step influences the quality of the subsequent coating layer. After these pre-treatments, the processed parts shall be free of pits, corrosion products, discoloration, uneven etching, increased surface roughness or other defects that would prohibit further chemical processing. This can be checked by visual inspection or penetrant inspection
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(ASTM E 1417). The etching rate has to be adequately chosen depending on the metal substrate. Under-etching or over-etching has to be avoided so that the key functionalities of the subsequent layer are not affected (for example: poor adhesion resulting in cracks and blistering). The etch rate is typically controlled by measuring the weight before and after on a witness coupon at a regular interval. In addition, treated surfaces shall be free of intergranular attack in a defined excess or end grain pitting in distinct limits. Further it is important that the baths can be used for a long timeframe with manageable maintenance. Additionally, the racks carrying the parts are usually used in the overall process chain and therefore have to be compatible with the chemicals used in the subsequent process steps.
3.4.1.2 Deoxidising With a Cr(VI)-based deoxidising process step, the key quality criteria is to provide surface activation. The deoxidising causes a metal removal of the substrate, which shall not exceed certain limits (physical measurement using a micrometre). By applying a deoxidising solution, the metal is attacked and end grain pitting and intergranular attack may be caused. Deoxidising shall neither cause end grain pitting nor intergranular attack in certain excess and depth. Furthermore, the appearance of the deoxidised surface (after rinsing) is visually inspected. It has to be a water break free surface without streaks or discolorations and no pitting or selective attack to the substrate, no non-rinseable residuals or contamination from the deoxidising solutions shall be observed on the surface.
3.4.1.3 Stripping of inorganic finishes Specifications require no hydrogen embrittlement during 200 h of sustained load according to ASTM F 519, although the effect of the hydrogen can be removed to a certain extent by subsequent de-embrittlement heat treatment. End grain pitting and intergranular attack negatively influencing the substrate quality, shall not exceed a ratio of (surface) pit size to pit depth of 6:1, which is tested according to ASTM F 2111. Stripping of the inorganic coating may have an impact to a shot peen compressive layer, which can affect the fatigue properties. However, no more than 10% of the thickness of the shot peen layer shall be removed, which is tested by a micrometre. As a certain amount of the base material may be removed by stripping, it must be guaranteed that the parts still conform to the drawing after stripping. This is tested by post processing inspection measurements. Stripping of an inorganic finish from Ti alloys may leave a notable hydrogen content on the substrate, which is tested according to ASTM E 1447. The hydrogen content can cause hydrides to precipitate, which then can lead to embrittlement and cracking under stress. Other parameters which may affect the substrate are residual stress, surface roughness and fatigue. However, as the reason for performing the stripping process is the need to repair a coating, these parameters cannot be worse than for the original (defect) coating. Stress corrosion cracking of the substrate is tested by exposing test specimens for 4.0 ±0.5 h in a molten salt bath. The specimens are rejected if the material shows pitting, cracking or rough etching. Cr(VI)-based stripping solutions can be used for a wide range of substrates and coatings, while it turned out when considering alternatives, the stripping process always has to be adapted taking into account the substrate (metal, specific alloy type) and the kind of coating to be removed.
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3.4.1.4 Stripping of organic coatings (e.g. primers, topcoats and specialty coatings) Sodium dichromate is used as active ingredient for stripping, although the most common active ingredients in solvent brush on paint strippers include methylene chloride (dichloromethane), benzyl alcohol, formic acid or hydrogen peroxide. Different active ingredients are useful for different paint systems. Sodium dichromate used in lower concentrations would still possibly contribute to paint removal, but other active ingredients would provide most of the paint removal action. The important role of sodium dichromate is to mitigate pitting and galvanic corrosion during the stripping process. For the corrosion resistance of substrates where paint became stripped, various tests are carried out described as follows. Sandwich corrosion is tested according to ASTM F 1110. Immersion corrosion is tested according to ASTM F 483. The fluid should neither cause corrosion nor a weight change of any test panel, specific for the respective kind of substrate. Dissimilar metals corrosion is tested by immersing coupled dissimilar metal components together. The test is failed if the panels exhibit pitting, etching or corrosion products. Adhesion is tested according to ISO 2409, mesh peel test, long beam test and other tests depending on the process specific requirements. When stripping off paint from metal substrates, hydrogen embrittlement may occur. No hydrogen embrittlement should be observed during 200 h of sustained load according to ASTM F 519.
No cracks are allowed to occur on the surface after stripping of paint. The fatigue properties are tested according to ASTM E 466 (5 stripping cycles) and no degradation should occur. For composite materials, no evidence of wet media penetration shall be detected after thermographic inspection. The surface roughness of the stripped surface is tested with a profilometer.
3.4.2. Key sodium dichromate functionalities for the main- and post-treatment process As already stated before Cr(VI)-based main processes and post-treatments rely on the use of sodium dichromate due to a number of key functionalities, which are described in detail below.
3.4.2.1 Corrosion resistance Corrosion describes the process of oxidation of a metallic material due to chemical reactions with its surroundings, such as humidity but also corrosive electrolytes. In this context, the parameter corrosion resistance means the ability of a metal aircraft part to withstand gradual destruction by chemical reaction with its environment. For the aerospace sector, this parameter is one of the most important since meeting its minimum requirements plays a key role in assuring the longest possible life cycle of aircraft and all the implicit parts, the feasibility of repairing and maintenance activities and most importantly, the safety of all air travellers. Especially AA2024 contains app. 5% of Cu as alloying element to provide the material strength. But Cu as noble element acts as bulid in corrosion driver. Inhibition of the Cu is mandatory for long-term corrosion stability. The corrosion resistance requirements vary within the aerospace sector and are dependent on the metal substrate (aluminium alloy, steel type), the coating thickness and the respective surface treatment process. Corrosion inhibiting components can be categorized according to basic quality criteria which are inhibitive efficiency and versatility and toxicity. Ideally, the component is applicable in all surface treatment processes, compatible with subsequent layers, and performs effectively on all major metal substrates. Furthermore it has to guarantee product stability (chemically and thermally) and has to reinforce the useful coating properties.
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The ability of a material to spontaneously repair small amounts of chemical or mechanical damage is known as an active corrosion inhibition or self-healing property. If this characteristic is given for a certain material, it is tremendously advantageous and will enhance service life duration of parts, maintenance intervals and on-flight security of air travellers. The requirements for active corrosion inhibition are varying within the aerospace sector and are depending on the metal substrate and the respective surface treatment process. The active corrosion inhibition of Cr(VI)-based surface treatment are generally tested in line with the corrosion resistance based on the same test methods and requirements, as the active corrosion inhibition of a coating are a characteristic feature.
3.4.2.2 Adhesion promotion (adhesion to subsequent coatings or paint) Depending on the final functions of the parts, they may be coated with decorative or protective layers (such as paint). In this analysis, the parameter adhesion describes the tendency of dissimilar particles or surfaces to cling to one another. Regarding the aerospace industry, many parts are exposed to harsh environmental conditions, in contact with other metallic parts or have to withstand strong mechanical forces. The requirements for adhesion vary within the aerospace sector and depend on the specific coating thickness and the function and location of the part.
3.4.2.3 Layer thickness The thickness of the layers or coatings on the substrate are also crucial for the performance of the parts. Not meeting the specified requirements of this parameter could lead to deficiencies for other related characteristics like corrosion and chemical resistance, improper adhesion of coatings to the substrate or increased fatigue properties. With regard to maximum thickness, dimensional constrains by design have to be respected.
3.4.2.4 Chemical resistance This parameter is defined as the ability of solid materials to resist damage by chemical exposure. Especially for aerospace applications, it is highly important that all parts withstand contact with different chemicals like hydraulic fluids, de-icing fluids, greases, oils and lubricants. The chemical modification of protective coatings or the metal parts themselves could escalate maintenance costs and sacrifice to some extent travel safety. The requirements for chemical resistance are varying within the aerospace sector and are depending on the metal substrate, the coating thickness and the respective surface treatment process. A general high-end chemical resistance provided by the sodium dichromate-based surface treatment is typically tested in line with the corrosion resistance based on the same test methods and requirements. More specific tests on chemicals are performed in addition.
3.4.2.5 Resistivity (electrical contact resistance) Electrical resistivity is a property that quantifies how a given material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. Many aerospace applications require electrically conducting materials for static discharge, electromagnetic interference shielding, and electrical bonding (e.g. lightning strike protection). A material that provides good electrical bonding between all joints is required to assist in controlling and shielding against electrical effects. In addition, electrical bonding combined with corrosion
Use number: 2 27 ANALYSIS OF ALTERNATIVES resistance is also a common requirement for metal based aerospace assemblies. Eddy current test is used to detect surface & subsurface defects, corrosion in aircraft structures, fastener holes and bolt holes. Surface defects and Resistivity testing are performed by high frequency. For detection of sub- surface defects low frequency method is carried out.
3.4.3. Summary of selected quantified key functionalities In Table 6 selected quantifiable requirements of the key sodium dichromate functionalities for the main process steps and the post-treatments for the aerospace sector are listed to provide an understanding of the widespread range of requirements. The most relevant key functionalities for the respective processes were selected. A more detailed description also taking different substrates into account is given in the subsequent paragraphs.
Table 6: Key functionalities of Cr(VI)-based main processes and post-treatments.
Quantifiable key Sector Process Requirements (not exhaustive) functionality Al alloy type and part type depending between - 72 h (forged alloy series 2000), - 96 h (wrought alloy series 2000 and 7000) and Corrosion resistance - 168 h for wrought alloy series 5000, 6000 and others) up to - 1000 h in SST (ASTM B117 and ISO 9227) Chemical / Chromate length from scratch <0.5 mm after 960 h Conversion Coating (Filiform corrosion test, EN3665) CCC – GT0 dry, GT1 wet after 168 h (Cross-Cut Test Aluminium CCC Adhesion to subsequent layer ISO 2409), partly immersion for 14 days Adhesive tape test with 7 N/cm
Chemical resistance 168 h to 750 h in SST (ISO 2812, ISO 2409)
Active corrosion inhibition Equivalent to Cr(VI) performance
< 5 m /in² (0.775 m /cm²) and Resistivity < 10 m / in² (1.55 m /cm²) after salt spray exposure (MIL-DTL- 5541 F, Class 3)
Aerospace sector Comparison with chromate protection system with and without varnish (ISO 9227: Without varnish: 30 h with no pits in SST (ISO 9227), 15 cycles with no pits for internal Corrosion resistance ageing cycles. With varnish: 336 h with no pits in SST (ISO 9227) Chromate Conversion - internal ageing cycles: No pits after 15 Coating CCC – cycles Magnesium CCC 336 h salt spray exposure with varnish after Active corrosion inhibition scribing
Layer thickness < 3 µm (microscopic evaluation)
GT0-1 (with primer 12-20 µm, with varnish 60-100 µm and/or another varnish 12-25 µm ) Adhesion to subsequent layer at initial and after 14 days in demineralised water (ISO 2409)
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Quantifiable key Sector Process Requirements (not exhaustive) functionality no impact after immersion 24h in products Chemical resistance oils, fluids, greases, no impact after degreasing with different products Comparison with Cr(VI)-based system Resistivity (internal protocol) Steel type depending: 2 – 24 h ferritic and CRES ((ISO 9227, ASTM B117) Corrosion resistance 96 h to 750 h austenitic CRES (ISO 9227, ASTM B117) 2 - 500 h martensitic steel GT0 dry, GT1 wet after 168 h (Cross-Cut Test Adhesion to subsequent layer Passivation of ISO 2409), partly immersion for 14 days stainless steel No induction of hydrogen embrittlement shall be observed after heat treatment (tested via tensile test (EN2832) or slow bending test EN2831 or other testing procedures. Embrittlement / heat treatment For steels with 1100 MPa ≤ UTS < 1450 MPa, a heat treatment temperature of 190°C for 8 h can be used. Steels with UTS > 1450 MPa require 23 h heat soak at 190°C. No crack or failure shall be observed during the test
Al alloy type depending and if painted or unpainted sealing, between - 72 h (forged alloy series 2000), - 96 h (wrought alloy series 2000 and 7000) and - 168 h for wrought alloy series 5000, 6000 Corrosion resistance and others) up to - 500 -2000 h (ISO 9227, ASTM B117) for Sealing after (Cr(VI)- unpainted parts free) anodizing (with For painted parts : 3000 h (ISO 9227, ASTM subsequent paint or B117) unpainted) length from scratch <0.5 mm after 960 h (Filiform corrosion test, EN3665)
Layer thickness 2-7 µm (determined by the anodic layer)
GT0 dry, GT1 wet after 168 h immersion in Adhesion to subsequent layer water (Cross-Cut Test ISO 2409) After immersion in various fluids, oils or Chemical resistance grease: corrosion resistance in Salt Spray equivalent to Cr(VI)-based system
Chromate Rinsing Corrosion resistance 2 h (ISO 9227)
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Quantifiable key Sector Process Requirements (not exhaustive) functionality after phosphating GT0 dry after 168 h (Cross-Cut Test, ISO Adhesion to subsequent layer 2409) Depending on thickness and type of plating: Corrosion resistance 96-1000 h (ISO 9227, ASTM B117) Depending on the type of coating: Layer thickness < 1 µm, 2 to 7 µm, 7 to 12 µm, 10 to 20 µm Paint adhesion of the coating on the substrate GT 0 or 1 (at initial and after 14 days in Adhesion to subsequent layer water), GT1 wet after 168 cross-cut test (ISO Passivation of 2409) metallic coatings no alteration of the coating after immersion in Chemical resistance chemicals and no corrosion after 750h SST No loss of coating or passivation system after immersion in liquid nitrogen at -196C Temperature resistance 100 Thermal Cycling -180- +200 °C (ECSS Q-ST-70-04) Coating has to be conductive to ensure current Resistivity running
3.4.3.1 Chemical conversion coatings - aluminium Regarding conversion coatings on aluminium and its alloys, the corrosion requirements are depending on the type of Al alloy. The aerospace industry provided a minimum requirement between 72 h for forged alloys of the 2000 series, 96 h for wrought alloys of the 2000 and 7000 series and 168 h for wrought alloys for the 2000, 5000, 6000 and 7000 series up to 1000 h without the appearance of corrosion according to ISO 9227 and ASTM B117. When filiform corrosion is tested according to EN3665, length from scratch <0.5 mm after 960 h is required. The layer thickness must not exceed 1 µm. The most relevant test method for adhesion is cross-cut test according to DIN EN ISO 2409. Resistivity of conversion coated substrates should be below 5 m /in² before salt spray exposure, respectively 10 m /in after salt spray exposure according to MIL-DTL- 5541 F.
3.4.3.2 Chemical conversion coatings - magnesium The corrosion performance is assessed by comparison with the Cr(VI)-containing system according to ISO 9227 and internal protocols for the ageing cycle test. As stated during the consultation, the corrosion requirement of conversion coatings on magnesium substrate is often lower than for conversion coatings on aluminium. The corrosion resistance is usually process controlled and not outcome based. The layer thickness must not exceed 3 µm by microscopic evaluation. Adhesion promotion is tested according to ISO 2409. GT0-1 (with primer 12-20 µm, with varnish 60-100 µmand/or another varnish 12-25 µm) at the initial stage and after 14 days in demineralised water are required. For the measurement of chemical resistance, no impact after 24 h-immersion in various oils, fluids, greases, and no impact after degreasing with different products shall be observed. Resistivity is compared according to internal protocol with Cr(VI)-loaded systems.
3.4.3.3 Passivation of stainless steel
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For passivation of stainless steel, the minimum requirements are highly depending on the kind of passivated stainless steel. The aerospace industry indicated minimum requirements regarding corrosion resistance of 2 – 24 h for ferritic and precipitation hardened CRES and 96 h to 750 h for austenitic CRES as well as 2 h to 500 h for martensitic steel. The tested items shall not show evidence of red rust, nor significant white rust (coating corrosion products). No induction of hydrogen embrittlement shall be observed after heat treatment (tested via tensile test (EN2832) or slow bending test EN2831 or other testing procedures. For steels with 1100 MPa ≤ UTS < 1450 MPa, a heat treatment temperature of 190°C for 8 h can be used. Steels with UTS > 1450 MPa require 23 h heat soak at 190°C. No crack or failure shall be observed during the test.
3.4.3.4 Sealing after (Cr(VI)-free) anodizing For sealed anodized surfaces the aerospace industry has specified different values dependent on the parts, substrates and if the sealing is painted or unpainted. The corrosion requirements are up to 2000 h Salt Spray exposure for unpainted and up to 3000 h for painted parts according to ISO 9227 and ASTM B117. Additionally, the parts should not present blisters or scratchers longer than 0.5 mm after 960 h according to EN 3665. Specifications for anodized surfaces require a layer thickness between 2 – 7 µm. If paint is applied on the layer, the adhesion properties are assessed by the cross cut test according to ISO 2409. Here, specifications ask for GT0 in dry conditions and GT1 in wet conditions after 168 h immersion.
3.4.3.5 Passivation of metallic coatings For passivation of metallic coatings on steel, the aerospace industry indicated minimum requirements regarding corrosion resistance ranging between 96 h and 1000 h SST according to ISO 9227 (with no show of red rust) for zinc, cadmium and aluminium substrates. The tested items shall neither show evidence of red rust, nor significant white rust (coating corrosion products) before 96 h SST. The layer thickness depends on the type of coating (< 1 µm up to 20 µm). Adhesion of the coating to the substrate is assessed by the cross cut test according to ISO 2409. If paint is applied on passivated surfaces, it has to fulfil GT0 under dry conditions, respectively GT1 under wet conditions. Temperature resistance is analysed according to internal standards. The surface has to withstand shrink fitting using liquid nitrogen. No loss of coating or passivation system should be observed after immersion in liquid nitrogen at -196°C.
3.4.3.6 Rinsing after phosphating Steel surfaces where rinsing after phosphating was applied have to withstand 2 h in SST (ISO 9227) and must demonstrate sufficient paint adhesion according to ISO 2409 (GT0). More demanding test programmes are currently under development, ensuring that the quality criteria from the aerospace sector can be met with the alternative treatments.
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4. ANNUAL TONNAGE
4.1. Annual tonnage band of sodium dichromate The confidential average tonnage for the use of sodium dichromate in surface treatments of metals such as aluminium, steel, zinc, magnesium, titanium, alloys and composites is xxx tonnes per year. The annual tonnage band for the use of sodium dichromate in surface treatments of metals such as aluminium, steel, zinc, magnesium, titanium, alloys and composites is 100 - 1000 tonnes per year.
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5. OVERVIEW OF THE PROCESS FOR ALTERNATIVE DEVELOPMENT AND APPROVAL IN THE AEROSPAC SECTOR Much has already been written about the airworthiness and approvals process in the aerospace industry in the document “An elaboration of key aspects of the authorisation process in the context of aviation industry“ published in April 2014 by ECHA and EASA. The document makes a strong case for justification of long review periods for the aerospace sector. In this section we identify key points from the ECHA EASA “elaboration” document and add additional detail and justification for long review periods with specific regard to chromates. Some of the key points identified in the “elaboration” document are: - “The aerospace industry must comply with the airworthiness requirements derived from EU Regulation No 216/2008 in Europe, and with similar airworthiness requirements in all countries where aeronautical products are sold.” - “All components, from seats and galleys to bolts, equipment, materials and processes incorporated in an aircraft fulfil specific functions and must be certified, qualified and industrialised.” In addition the new materials must be developed and evaluated prior to these three steps. - “If a substance used in a material, process, component, or equipment, needs to be changed, this extensive process [of development, qualification, certification and industrialization] has to be followed in order to be compliant with the airworthiness requirements.” - “Although the airworthiness regulations (and associated Certification Specifications) do not specify materials or substances to be used, they set performance specifications to be met (e.g. fire testing protocols, loads to be sustained, damage tolerance, corrosion control, etc.). These performance specifications will drive the choice of substances to be used either directly in the aircraft or during the manufacturing and maintenance activities.” - The development (TRL (Technology Readiness Level) 1-6) process “is an extensive internal approval process with many different steps from basic technology research up to technology demonstration in a lab environment.” - “Depending upon the difficulty of the technical requirements [qualification] can easily take 3-5 years. After initial laboratory testing, each specific application must be reviewed, which means additional testing for specific applications / parts. Airworthiness Certification begins at this same time, this certification can take from 6 months to years. Additional time is needed for production scale-up and development of a supply chain.”
Each one of these points is of significant importance for the aerospace sector with regards to chromates. Further elaboration will be made within this section. The last bullet point highlights that it can take a significant period of time to develop and implement new alternatives. It should be noted that in the case of chromates, the stated time needed for taking an alternative from the development phase through qualification, certification and implementation has been significantly underestimated. Efforts to find replacements for chromates have been ongoing within the aerospace industry for over 30 years. In this time some successful substitutions have been made, but large challenges remain. Efforts thus far to identify equivalents for substances with critical, unique properties like corrosion inhibition have proven that there are no ‘drop-in’ replacement substances for hexavalent chromium. Depending on the specific application and performance requirements, many more years may be required before alternatives are identified and implemented.
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In this section the general process for alternative development through qualification, certification, industrialization and implementation within the aerospace sector is described. This process is also followed closely by the military and space sectors. The long-term operations of aviation applications are similar to the space industry. In the case of the space industry, the lifecycle depends on the type of spacecraft (military or civil launchers, satellites etc.), but it can be at least as complex and challenging as aircraft regarding: lifecycle duration, environment exposure and high requirements. The space sector is a highly valuable sector and a major political concern, as the EU wants to have its own capacity to access to space (e.g. major programs such as Ariane 5, Vega, and all satellite programs for earth observation and telecommunications). Apart from the complexity of the supply, the aerospace sector faces particular unique challenges related to the operating environment, compliance with the airworthiness requirements and spacecraft requirements and the longevity of an aircraft and spacecraft that constrain its ability to adopt changes in materials and processes in the short, medium or even longer terms. Because of the stringent requirements for qualification and certification, a formal process for technology readiness and manufacturing readiness is followed. The process for qualification, certification and industrialization as described in the ECHA EASA “elaboration” document is shown in Figure 14 .
Figure 14: Illustration of the qualification, certification and industrialisation processes (EASA, 2014).
This diagram is perhaps overly simplified and doesn’t indicate the significant level of research and development work required prior to achieving qualification as described in chapter 5.1.. As stated in the “elaboration” document “This process is an extensive internal approval process with many different steps from basic technology research up to technology demonstration in a lab environment.” The actual process followed by OEMs in the aerospace sector more closely follows the framework for TRLs and Manufacturing Readiness Levels (MRLs) originally developed by NASA. OEMs usually adapt this TRL/MRL approach resulting in individual versions which are considered proprietary and cannot be presented here. The NASA version is shown in Table 7.
Table 7: Technology Readiness Levels – Overview (US Department of Defence, 2011, adapted 2014).
TRL# Level Title Description
Lowest level of technology readiness. Scientific research begins to be translated into applied research and development (R&D). 1 Basic principles observed and reported Examples might include paper studies of a technology’s basic properties. Invention begins. Once basic principles are observed, practical Technology concept and/or application applications can be invented. Applications are speculative, and 2 formulated there may be no proof or detailed analysis to support the assumptions. Examples are limited to analytic studies. Active R&D is initiated. This includes analytical studies and Analytical and experimental critical 3 laboratory studies to physically validate the analytical function and/or characteristic proof-of- predictions of separate elements of the technology. Examples
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TRL# Level Title Description concept include components that are not yet integrated or representative.
Basic technological components are integrated to establish that Component and/or breadboard they will work together. This is relatively “low fidelity” 4 validation in laboratory environment compared with the eventual system. Examples include integration of “ad hoc” hardware in the laboratory. Fidelity of breadboard technology increases significantly. The basic technological components are integrated with reasonably Component and/or breadboard 5 realistic supporting elements so they can be tested in a validation in relevant environment simulated environment. Examples include “high-fidelity” laboratory integration of components. Representative model or prototype system, which is well beyond that of TRL 5, is tested in a relevant environment. System / subsystem model or prototype Represents a major step up in a technology’s demonstrated 6 demonstration in a relevant environment readiness. Examples include testing a prototype in a high- fidelity laboratory environment or in a simulated operational environment. Prototype near or at planned operational system. Represents a System prototype demonstration in an major step up from TRL 6 by requiring demonstration of an 7 operational environment actual system prototype in an operational environment (e.g., in an aircraft, in a vehicle, or in space). Technology has been proven to work in its final form and under expected conditions. In almost all cases, this TRL represents the Actual system completed and qualified end of true system development. Examples include 8 through test and demonstration developmental test and evaluation (DT&E) of the system in its intended weapon system to determine if it meets design specifications. Actual application of the technology in its final form and under Actual system through successful mission conditions, such as those encountered in operational 9 mission operations test and evaluation (OT&E). Examples include using the system under operational mission conditions.
In general the TRL assessments guide engineers and management in deciding when a candidate alternative (be it a material or process) is ready to advance to the next level. Early in the process, technical experts establish basic criteria and deliverables required to proceed from one level to the next. As the technology matures, additional stakeholders become involved and the criteria are refined. As specific applications are targeted as initial implementation opportunities, design and certification requirements are added to the criteria. Many more factors have to be taken into account prior to making a decision about transition of technology or replacing a material. A formal gate review process has been established by some companies to control passage between certain levels in the process. A similar set of guidelines for MRLs exist for the management of manufacturing risk and technology transition process. MRLs were designed with a numbering system similar and complementary to TRLs and are also intended to provide a measurement scale and vocabulary to discuss maturity and risk. It is common for manufacturing readiness to be paced by technology or process readiness. Manufacturing processes require stable product technology and design. Many companies combine the aspects of TRLs and MRLs in their maturity assessment criteria, as issues in either the technology or manufacturing development will determine production readiness and implementation of any new technology.
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Referring back, now, to Figure 14 , the general process steps can be loosely correlated to the steps in the TRL and MRL frameworks. Qualification begins after TRL 6 when technology readiness has been demonstrated. Certification begins around TRL 9 at the latest and may be performed in parallel with qualification. Industrialization/Implementation are not tracked on the NASA TRL scale, but some OEMs refer to this phase as TRL 10. As previously stated, what is missing from the diagram is the necessary and significant work that is performed before reaching technology readiness at TRL 6. The following sections describe the highlights of the entire process from definition of needs before technology development begins through to implementation. The emphasis here is to provide a description of the general process while highlighting the inherent complexities. One additional point to keep in mind when reviewing the process description that follows is that there is no guarantee that the initial process to identify an alternative for a substance is successful. Failure is possible at every stage of the TRL process. The impact of failure can be significant in terms of time.
5.1. Development and qualification
5.1.1. Requirements development A need for a design change may be triggered due to many reasons. The one of interest here is when a substance currently used for production of aerospace parts is targeted for sunset (e.g. chromates). Completely removing one substance may impact various parts and systems on an aircraft and may involve many different processes with different performance requirements. Once a substance is identified to be targeted by a regulation, a first step is to identify the materials and processes containing the specific substance. Most companies rely upon the information provided by the chemical manufacturer in the SDS. This information source has many limitations when used for substance identification including: lack of reporting due to protection of proprietary data; reporting large concentration bands to protect specific formulary data; different disclosure requirements based upon country (articles exemption, thresholds, de minimis, specific substance classifications, etc.) to name a few. After identifying the materials and processes and associating them with specifications and other design references parts get identified along with, applications and products potentially impacted. This is the first step in order to assess the impact for the company. This work requires contributions from numerous personnel from various departments of an aerospace company like Materials & Processes, Research & Development, Engineering, Customers Service, Procurement, Manufacturing, Certification, including affiliates in other countries and Risk Sharing Partners. Current production aircraft may have been designed 20 to 30 years ago (or more) using design methods and tools that are not easily revisited, nor were they necessarily standardized between OEMs. Checking and changing the drawings implies updating, e.g. creating the drawings under the new formats and tools, which can involve a tremendous amount of design work. Note: When a new design is needed e.g. to remove a substance, it may not be compatible with the existing one, this means that spare parts designs of the original materials/configurations may need to be preserved in order to be able to produce spare parts for the aircraft using the original (baseline) configuration. This is an additional impact to be taken into account.
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Once a substitution project is launched, technical specialists, from engineering and manufacturing departments, must define the requirements that the alternatives have to fulfil. Alternatives must satisfy numerous requirements. In many cases requirements are identified that introduce competing technical constraints and lead to complex test programmes. This can limit the evaluation of alternatives. For instance, for some materials, dozens of individual engineering requirements with similar quantities of industrial requirements may be defined. Categories of technical requirements may include: - Materials and processes requirements (e.g. corrosion resistance, adhesion strength); - Design requirements (e.g. compatibility of the component’s geometry complexity and with the coating application technique); - Industrial requirements (e.g. robustness and repeatability); and - Environment, Health & Safety (EHS) requirements.
Definition of needs itself can be complex and requires significant timeframe. The complexity can be due to: - Different behaviour of the substitute compared to original product: new requirements may be defined. In this case, sufficient operational feedback to technically understand the phenomenon and to reproduce it at laboratory scale is a must in order to be able to define acceptance criteria; - Requirements may come from suppliers and have an impact on the design; or - Constraints from EHS regulations evolution.
Once initial technical requirements are defined, potential solutions can then be identified and tested. The timeframe for initial requirements development can last up to 6 months. Note that requirements may be added and continue to be refined during the different levels of maturity.
5.1.2. Technology development The development process (typically TRL 4-6) is complex, and several years are often necessary before reaching development phase end (TRL 6). The following points explain why it may be long and complex: - Developing solutions usually necessitates several testing phases before meeting the numerous requirements, which often induce several loops to adjust the formulation / design. - Some tests are long lasting (e.g. some corrosion tests last 3000 h or longer). - In some cases, potential alternatives are patented, preventing multiple sources of supply, which is an obstacle to a large supply-chain deployment due to increases in legal costs and in some cases a reduction in profitability for the business. - When no 1 to 1 replacement solution is available, each alternative process must individually be considered to determine for which specific quantitative application it is suitable. This work represents a significant resources mobilization, especially in term of drawings update and implementation of alternatives which due to the multiple work streams takes longer with higher costs. Moreover, spare parts and maintenance processes redesign may result in complex management both at the OEM and the Airlines. Additionally, substances regulations are evolving throughout the long research and development phase and life cycle of aircraft, which is another challenge for OEMs. There is a risk that significant investments could be made to develop and qualify alternative solutions involving substances with low
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EHS impacts identified at that point in time. Solutions may be developed and finally qualified, however, in the meantime, EHS constraints on those substances increased to a point where they now meet the SVHC criteria. - When the suppliers have no “off the shelf” solutions, they have to develop new ones considering the list of requirements that are often highly complex to combine (see the description of requirements in the above paragraph). - Drawings impact: The replacement of a material / process may impact the complete design of a part. Additionally, the mating part/counterpart functionality must be analysed too (materials compatibility, dimensional compatibility, stress compatibility). This may lead to redesign of the complete part plus mating parts. - Process instructions shall be elaborated.
The description of the development process is included in the qualification section of the ECHA EASA “elaboration” document. The text is reproduced here for continuity. “Qualification precedes certification and is the process under which an organisation determines that a material, process, component or equipment have met or exceeded specific performance requirements as documented in a technical standard or specification. These specifications, often abbreviated as spec(s), contain explicit performance requirements, test methods, acceptance testing, and other characteristics that are based upon the results of research, development and prior product experience. The industry relies upon standards issued by government-accredited bodies, industry or military organisations, or upon company-developed proprietary specs. Most materials and process specifications include either a “Qualified Products List” (QPL) or “Materials Control” section that identifies products that have met the requirements. Application and use of these qualified products must be assessed and certification implications addressed before being used on aircraft hardware. OEMs rely upon the expertise of the chemical formulators to provide viable candidates to test against specific material and process specs.”
It is important to note that many iterations of these formulas are rejected in the formulator’s laboratory and do not proceed to OEM evaluation. Formulators estimate 2 to 5 years before candidates are submitted to OEMs. “Once candidate(s) are developed, the OEM evaluates candidates by performing screening testing. If the candidate passes screening, testing is expanded to increase the likelihood that the preparation will pass qualification. If the candidate fails, which is often the case, material suppliers may choose to reformulate. It is not uncommon to iterate multiple times before a candidate passes screening. In some technically challenging areas, over 100 formulations have been tested with no success. This phase of development can take multiple years depending upon the material requirements. For those materials that pass screening, production scale-up, development of process control documents, manufacturing site qualifications, and extensive qualification testing is required to demonstrate equivalent or better performance to that which is being replaced. This phase of the process can also result in formulation or manufacturing iterations and may take several additional years. Depending on the complexity of the change and the criticality of the application (for example, fire protection or corrosion prevention have high safety implications and require development and testing against multiple, rigorous performance standards), re-certification may be required. The industry is ultimately limited by the material formulators’ willingness to expend their resources to develop alternative materials and technologies to be tested.”
The small volumes of materials sold, demanding performance requirements, and tightly controlled manufacturing processes for aviation customers provides insufficient incentive for reformulation in
38 Use number: 2 ANALYSIS OF ALTERNATIVES some cases. When material formulators are not willing to reformulate their materials, new sources need to be sought.
Figure 15: Illustration of the technology development and qualification process (EASA, 2014, amended).
“This process [TRL 1-6 development] is an extensive internal approval process with many different steps from basic technology research up to technology demonstration in a lab environment. Depending upon the difficulty of the technical requirements, these initial steps can easily take 3-5 years. After initial laboratory testing, each specific application must be reviewed, which means additional testing for specific applications / parts. Airworthiness Certification begins at this same time, this certification can take from 6 months to years. Additional time is needed for production scale-up and development of a supply chain.”
It should be noted that the timeframes for development and qualification stated in the “elaboration” document have been combined and may be understated in the case of chromates. Depending on the application and the complexity of material and process requirements, this process can easily take multiple years. As noted in the “elaboration” document the timeframe for development alone is typically a minimum of 3 to 5 years. Our experience with replacement of the substance addressed in this dossier is that the development takes much longer. For typically successful projects the duration is 3 to 5 years. For unsuccessful projects the development goes through repeated iterations and has taken over 30 years and still continues with limited success.
5.1.3. Qualification Only after a technology has demonstrated technology readiness level 6, do the OEMs begin the qualification. All material, components, equipment or processes have to meet or exceed the specific performance requirements which are defined in the Certification Specifications documented in technical standards or specifications as described in section 5.1.4. . These are issued by military organisations, government-accredited bodies, industries or upon company-developed proprietary specifications. Products which have met all requirements are included in the documents as “Qualified Products List” (QPL) or in the “Materials Control” section. The main reasons for qualification are: - To fulfil requirements by the Airworthiness Authorities European Aviation Safety Agency (EASA) this is the first level of the Aircraft Certification Pyramid,
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- To ensure that only Approved, reliably performing Materials, Parts and Processes are used to produce Aircraft Components and Systems, - To ensure that the product, the process or method is compliant with the Industry Regulations and Aircraft Manufacturer requirements to fulfil a specified function, - To provide a level of confidence and safety, - To ensure consistent quality of products and processes, and - To ensure Supplier control, and to guarantee production and management system robustness, throughout the Supply Chain.
The qualification process is mandatory to demonstrate compliance with airworthiness and certification requirements: the qualification process ensures that the technical and manufacturing requirements documented in the relevant material and/or process specifications are met. The qualification process comprises several steps before materials/processes are qualified. Even if most showstoppers are identified during the development phase, process confirmation/production verification are performed during the qualification phase. In case of failure, product qualification will be cancelled and the development phase must start again from the beginning. Based upon OEM experience, the time period needed to pass the qualification process is estimated to be on the order of 8 years and can be even longer when major test failures occur. This is one of the main challenges for chromates replacement. Depending upon the materials, processes and criticality of the applications being evaluated, in-service evaluation and monitoring will be required and can extend to 15 years or more depending upon application.
5.1.4. Certification This next step is to certify that an aircraft and every part of it complies with all applicable airworthiness regulations and associated Certification Specifications (specs). This step is also well described in the “elaboration” document and is reproduced here for continuity. “Certification is the process under which it is determined that an aircraft, engine, propeller or any other aircraft part or equipment comply with the safety, performance environmental (noise & emissions) and any other requirements contained in the applicable airworthiness regulations, like flammability, corrosion resistance etc. Although the airworthiness regulations (and associated Certification Specifications) do not specify materials or substances to be used, they set performance specifications to be met (e.g. fire testing protocols, loads to be sustained, damage tolerance, corrosion control, etc.). These performance specifications will drive the choice of substances to be used either directly in the aircraft or during the manufacturing and maintenance activities. Some examples of performance requirements are the following: - Resistance to deterioration (e.g. corrosion) Environmental damage (corrosion for metal, delamination for composites) and accidental damage during operation or maintenance. - Corrosive fluids - Hydraulic fluids; Blue water systems (toilet systems and areas); leakage of corrosive fluids/substances from cargo. - Microbiological growth in aircraft fuel tanks due to moisture/contamination in fuel cause severe corrosion. Such corrosion debris has the potential to dislodge from the fuel tanks, migrate through the fuel system, and lead to an in-flight engine shutdown. - Resistance to fire – Flammability Requirements Fire-proof and fire-resistance. Aircraft elements are expected to withstand fire for a specified time without producing toxic fumes; this leads to using products like flame retardants, insulation blankets, heat protection elements in hot areas (e.g. around engines).
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The primary certification of the aircraft (or engine and propeller) is granted to the manufacturer by the Competent Aviation Authority of the “State of Design” which is typically the authority of the state where the manufacturer of the aircraft (or engine or propeller) is officially located (EASA in the case of aircraft designed and manufactured in the EU and European Free Trade Association countries). Aircraft that are exported to other countries will have to be certified (validated) also by the authority of the “State of Registry”. Manufacturers work with the certification authorities to develop a comprehensive plan to demonstrate that the aircraft meets the airworthiness requirements. This activity begins during the initial design phase and addresses the aircraft structure and all systems in normal and specific failure conditions (e.g. tire failure, failure of structural components, hydraulics, electrical or engines). The tests needed to demonstrate compliance, range from thousands of coupon tests of materials, parts and components of the airplane, up to tests that include the complete aircraft or represents the complete aircraft (system). The performance and durability of the various materials have to be confirmed while the behaviour of the parts, components and the complete airplane will have to be tested in the applicable environmental and flight conditions including various potential damage or failure conditions. For a new Type Certificate this overall compliance demonstration covers several thousands of individual test plans of which some will require several years to complete. Often, after the initial issuance of the Type Certificate, the tests that have the objective to demonstrate durability of the aircraft during its service life, will continue. All the different aspects covered by the Type Certificate together define the “approved type design” which includes, among other aspects, all the materials and processes used during manufacturing and maintenance activities. Each individual aircraft has to be produced and maintained in conformity with this approved type design. Changes to the approved type design may be driven by product improvements, improved manufacturing processes, new regulations (including those such as new authorisation requirements under REACH), customer options or the need to perform certain repairs. When new materials or design changes are introduced, the original compliance demonstration will have to be reviewed for applicability and validity, in addition to a review of potential new aspects of the new material or design change that could affect the airworthiness of the aircraft. Depending on the change, this review could be restricted to coupon or component tests, but for other changes this could involve rather extensive testing. E.g. changes in protective coatings could affect not only the corrosion resistance but could also affect the friction characteristics of moving components in actuators in the different environmental conditions, changing the dynamic behaviour of the system, which in the end affects the dynamic response of the airplane. Before the new material or design change can be introduced on the aircraft, all test and compliance demonstrations have to be successfully completed and approved by the Competent Authority. This approval results in the issuance of a Supplemental Type Certificate (STC), change approval or repair approval. It is important to note that, according to the EU Regulation No 216/2008, EASA is the design competent authority for civil aircraft only. Any other aircraft (e.g. military, fire-fighting, state and police aircraft) will have to follow similar rules of the corresponding State of Registry. To be able to maintain and operate an aircraft the responsible organisations must be approved by the competent authority and compliance is verified on a regular basis. Maintenance of an aircraft requires that the organization complies with specific procedures and materials described in the maintenance manuals which are issued by and the responsibility of the OEMs.” As noted in the “elaboration” document, in optimal cases certification can take as little as 6 months but typically will take several years. The duration really depends on the specific material and application.
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5.1.5. Implementation / industrialisation An aircraft consists of several million parts which are provided by thousands of suppliers or manufactured internally by OEMs. Significant investment, worker training and manufacturing documentation may be required to adapt the manufacturing processes which sometimes require changes in existing facilities or the construction of new facilities. The industrial implementation is usually scheduled to follow a step wise approach to minimize the technical risks and benefit from lessons learned. This implies that the replacement is not implemented in one shot in all plants and at all suppliers but stepwise. Each OEM may own several plants, e.g. up to 20 manufacturing sites / final assembly lines worldwide for some of them. Furthermore, the implementation of an alternative process may induce new development and modification in the complete process flow. The following text is reproduced from the “elaboration” document and describes the process for implementation of an alternative: “Industrialisation is an extensive step-by-step methodology followed in order to implement a qualified material or process throughout the manufacturing, supply chain and maintenance operations, leading to the final certification of the aerospace product. This includes re-negotiation with suppliers, investment in process implementation and final audit in order to qualify the processor to the qualified process. Taking into account that an aircraft is assembled from several million parts provided by several thousand suppliers, this provides an indication of the complexity for the industrialisation stage of replacement materials/processes, and the supply chain which provides these parts. Special challenges are: - Low volumes limit influence on changes to suppliers’ materials / processes - Procurement & insertion of new equipment - Scale-up & certification of new process - Incompatibility of coatings could be a risk. - Re-negotiation of long term agreements with suppliers*. - Increased complexity of repairs – Multiple different solutions for different applications as a substitute for a single, robust process. For example, currently all aluminum parts can be repaired with one chromated conversion coating. In some specific cases, the future state could require different conversion coatings for each aluminum alloy and application environment. Since different alloys are not easily distinguishable on the shop floor, ensuring that the proper repair procedures are used will be much more difficult. If alternate means of compliance approvals are requested for repair facilities or airlines, regulatory agencies are unlikely to have adequate knowledge or technical data to make informed assessments. The operating environment, longevity of the aircraft, supply chain complexity, performance and above all airworthiness requirements are some of the considerations which can constrain the ability of the industry to make changes and adopt substitutes in the short, medium or long term.” *Changes to the design or manufacturing may require re-negotiations with suppliers which can be time-consuming, especially when long-term contracts are concerned. The supply chain is complex in the aviation industry; it includes but is not limited to chemical manufacturers, importers, distributors, formulators, component manufacturers, OEMs, Airline operators, and aftermarket repair and overhaul activities. The timeframe for implementation and industrialisation is unknown. Simple changes may take 18 months to 5 years. Our experience with replacement of the substance addressed in this dossier is
42 Use number: 2 ANALYSIS OF ALTERNATIVES that full implementation and industrialization has yet to be accomplished. Implementation by airlines and MROs further requires that an alternative is approved by the OEM and made available in the maintenance documents. When the alternative process is included in the maintenance documents, challenges described above have to be faced by airlines and MRO to implement the alternative. Here, for operating supplies and testing time frames, another 3 years might be necessary, depending on complexity of the alternative. When more alternative processes have to be established simultaneously, as it is currently the case for Tartaric Sulphuric Acid Anodizing (TSA) and Boric-Sulphuric Acid anodizing (BSA), more than 5 years might be necessary to fully implement the alternatives. It is important to note that the implementation/industrialization step ('TRL10') refers to the whole supply chain. This includes external as well as internal industrialization. In case a suitable chrome free alternative is developed in the future, it needs to be implemented across a vast and complicated supply chain, which in turn is time and cost intensive requiring significant additional investment in new machinery and plant on the part of existing suppliers. Additionally, any substitution is linked to major resourcing exercises at new suppliers with the capabilities of industrialising the application of the new products or processes. The switch-off of one production process and the belonging supply chain without validating and qualifying the new alternative process and corresponding supply chain is not feasible. The whole development and approval process is illustrated in Figure 16 .
5.2. Examples In 2003, RoHS (Directive on Restriction of Hazardous Substances, 2002/95/EC) was adopted by the EU and took effect on July 2006. This Directive triggered companies to substitute lead-based solder in electronic assemblies and all subsequent changes in the product designs and manufacturing processes: Basic research was started in the example company in 2003 with the selection and tests of alternative lead-free solder. The Research Program is still running in 2014 and the qualification and industrialization phase is ongoing: Components (IC’s, connectors, printed circuit boards etc.) had to be changed due to the higher soldering temperature that all materials have to withstand with lead-free solder, and most of the manufacturing equipment had to be replaced by new ones. This fundamental replacement of lead (Pb) for aerospace and military applications with harsh environmental conditions will take more than 15 years in total to be deployed up to TRL 9. Work on a replacement for CAA began in 1982. The initial driver for this R&D effort was to reduce emissions of Cr(VI) and comply with federal and local clean air regulations in the US. Initial requirements were identified and four candidate solutions were evaluated. One candidate solution was down selected in 1984. Qualification testing began in 1985. A process specification for BSA was released in 1990. In 1991 and 1992 industrialization began as several Boeing facilities began producing parts using the BSA process. One outside supplier also began processing parts to the Boeing specification in 1992. Evaluation of additional applications continued into the mid-1990s. In 2015, industrialization of the BSA alternative for CAA is still not complete. Many Boeing suppliers are shared with other OEMs and industries impeding the conversion to BSA from CAA because they must continue to support multiple customer requirements. Note that for unprimed parts a dilute chromate seal is still required to provide required corrosion resistance. Work is ongoing to develop alternatives for this application. It is also worth noting that boric acid is now being proposed for Annex XIV requiring authorization. Should this happen alternatives may need to be developed for BSA. Other OEM solutions will need to be evaluated, qualified and certified. Both examples are illustrated in Figure 16 compared to the overall development process as outlined above.
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Figure 16: Development and approval process in the aerospace sector. Examples from previous implementations are included. Loops indicate potentially iterative steps due to unsuccessful evaluation at the formulator or unsuccessful development.
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6. IDENTIFICATION OF POSSIBLE ALTERNATIVES
6.1 Description of efforts made to identify possible alternatives To prepare for the authorisation of 8 Chromium VI Compounds, the industry consortium CCST (Miscellaneous Chromium VI Compounds for Surface Treatment REACH Authorisation Consortium) comprising 28 members, was launched in 2012. The aim of CCST was to efficiently gather and analyse all necessary information for the three pillars of the authorisation dossier (CSR, AoA, SEA).
6.1.1. Research and development in the aerospace sector As mentioned earlier in this document, a large amount of research over the last few decades has been commissioned to identify and develop viable alternatives to Cr(VI). The unique functionalities of Cr(VI) (explained in detail in chapter 3.4) make it challenging and complex to replace the substance in surface treatment applications where superior corrosion or adhesion properties are required to ensure safe performance in a demanding environment. Numerous research programmes were conducted funded by Europe clean sky (MASSPS, ROPCAS, LISA, DOCT, MUST, MULTIPROJECT) as well as programmes funded by USAF or other national funded programmes (e.g. LATEST in UK). Some key research programmes are listed below. Amongst a number of initiatives in that respect, the Airbus Chromate-Free (ACF) project was launched more than 10 years ago with the aim to progressively develop new environmental friendly Cr(VI)-free alternatives to qualified products and processes used in aircraft production and maintenance. Even prior to the launch of ACF, R&D efforts included the objective to remove chromates use. The ACF project is organised into several topics for the different fields of technologies concerned by the replacement. ACF specially addressed applications where chromates are used in production or applied to the aircraft; such as CAA, basic primer, and external paints. In addition, bonding primer, jointing compounds, pickling, sealants, chromate conversion coatings, passivation of stainless steels, passivation of metallic coatings or alternatives to hard chromium are included in the remit of this project. In synergy with ACF, an Airbus Group chromates replacement project is also in place. A similar initiative was set up for spacecraft, the Launcher chromate-free (LCF) project. In 2006, Boeing in cooperation with the Department of Defence started a three-year program called “Environmentally Benign Coating System for Department of Defence Substrates” for the development of new chromate free coating systems, based on rare-earth conversion coatings. Industry is not only working on one-to-one replacements for Cr(VI) applications but also reconsidering whole current coating systems. The large investment in innovative coating technologies may lead successively to a paradigm shift within the next few decades. As an example, the HITEA (Highly Innovative Technology Enablers for Aerospace) project was initiated in 2012; a 17-member consortium consisting of aerospace OEMs, suppliers, paint application companies and academics with the goal to identify and evaluate suitable alternative systems. In 2014, the tested alternatives are planned to reach TRL2. After the initial phase, the project will focus on a handful of promising alternatives, where further testing will be undertaken within the next years and completion of the research project is planned for 2015. Qualification (TRL6) will take up to 5-8 years from now.
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In 2008, the multi-company project SOL-GREEN was initiated for the development of protective coatings of Al/Mg alloys (Cerda et al, 2011). Since these coatings solutions are not based on electrochemical conversion, and so require a complete change in technical approach, the industrial production qualification is expected not before 2025. Phase 1 was finished last year, showing that SOL-GREEN 1 faces some technical issues. Therefore, the main objective of SOL-GREEN 2 is to assess and develop an electrophoresis process to apply the anti-corrosion coatings using a SOL- GEL technique for complex geometry parts. These challenges are currently ongoing and the research is mainly conducted at laboratory scale (TRL 2) at universities and in some partner’s plants. However, as mentioned above, this is a long term solution (10-15 years).
6.1.2. Data searches For the AoA, extensive literature and test reports were provided by the technical experts of the CCST consortium members. Furthermore, searches for publically available documents were conducted to ensure that all potential alternate processes to Cr(VI)-containing applications were considered in the data analysis. In addition to databases for scientific literature, the following programmes were intensively consulted: Toxics Use Reduction Institute, Massachusetts, US (www.turi.org/); The Advanced Materials, Manufacturing, and Testing Information Analysis Center (AMMTIAC: http://ammtiac.alionscience.com/). Searches for SDS for Cr(VI)-containing and chromium-free applications were also conducted. Based on these data, primary scoping led to the development of a generic questionnaire containing potential alternatives to Cr(VI)-based surface treatment processes. As a result of this, additional alternate processes, mentioned by companies from the aerospace sector were included in the initial list of alternatives, which can be found in Appendix 2.
6.1.3. Consultations A questionnaire was provided to all CCST consortium members to get an overview of and experience with the alternatives, completeness and prioritisation of critical parameters for their specific processes and the minimum technical requirements. During this survey, additional alternatives have been identified which were included into the aforementioned initial list. At this stage of the data analysis, several alternatives had been screened out after bilateral discussions with the companies, based on confirmation that they might be general alternatives to Cr(VI)-based processes (e.g. for functional chrome plating), but are not applicable for the use defined here. To verify data and obtain more detailed quantitative information, further focused technical questionnaires were sent out and discussed with the CCST consortium members. In addition, site visits to selected companies were carried out. These were carefully chosen to adequately represent the different uses, industry sectors, countries and the size of companies. Discussions with technical experts followed by a final data analysis led to the formation of a list of alternatives divided into 3 categories, according to their potential to be suitable for the specific use. The most promising alternatives within the here defined use (category 1 and 2) are assessed in detail in the following chapter, the category 3 alternatives are listed in Appendix 2.
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6.2 List of possible alternatives The most promising alternatives are discussed in the following section. To allow a better overview of the different parts of the process chain, the assessment is made for main treatments plus post- treatments (Table 8) and pre-treatments ( Table 9) separately. The main and post-treatment alternatives are classified according to their relevance; as Category 1 (focus of CCST members, relevant R&D on these substances ongoing) or Category 2 (discussed mainly in literature, clear technical limitations, may only be suitable for other industry sectors or for niche applications but not as general alternative). Category 3 alternatives, which are not applicable for the use defined here, are summarised in Appendix 2. Table 8. List of main treatment alternatives categorized.
Category Alternative Surface treatment
Chromate Conversion Coating Acidic surface treatments Passivation of stainless steel
Chromate Conversion Coating
Silane/siloxane and sol-gel coatings Sealing after (Cr(VI)-free) anodizing
Passivation of metallic coatings Category 1 alternatives Chromate Conversion Coating
Cr(III)-based surface treatments Passivation of metallic coatings
Sealing after (Cr(VI)-free) anodizing
Sealing after (Cr(VI)-free) anodizing Water-based post-treatments Rinsing after phosphating
Chromate Conversion Coating Molybdates and molybdenum-based processes Sealing after (Cr(VI)-free) anodizing
Organometallics (zirconium and titanium- Chromate Conversion Coating based products, such as fluorotitanic and fluorozirconic acids) Passivation of metallic coatings
Benzotriazole-based processes, e.g. 5- Chromate Conversion Coating Category 2 methyl-1H-benzotriazol alternatives Chromate-free etch primers Chromate Conversion Coating
Chromate Conversion Coating Manganese-based processes Sealing after (chromate-free) anodizing
Cold nickel sealing Sealing after (Cr(VI)-free) anodizing
Magnesium-rich primers Chromate Conversion Coating (local application)
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Category Alternative Surface treatment
Electrolytic paint technology Chromate Conversion Coating + primer
Zinc-nickel electroplating Passivation of metallic coatings
Table 9. List of pre-treatment alternatives categorized. Surface pre- Alternative Substrate treatment within use i Aluminium and aluminium alloys, Pickling/Etching steel, copper, brass
Inorganic acids Deoxidizing Aluminium and aluminium alloys Stripping of inorganic Aluminium and aluminium alloys finishes Aluminium and aluminium alloys, Hydrogen peroxide activated benzyl alcohol (with Stripping of organic steel (CRES), nickel/cobalt alloys, acids) and inorganic finishes titanium and magnesium
48 Use number: 2 ANALYSIS OF ALTERNATIVES
7. SUITABILITY AND AVAILABILITY OF POSSIBLE ALTERNATIVES For the assessment of the feasibility of the alternatives overview tables with a colour coding have been included in the dossier. With regard to the alternatives classified into category 1 , the tables summarize the technical feasibility of the alternative related to the respective surface treatment discussed. For the alternatives classified into category 2 an overall assessment of the technical and economic feasibility, availability and reduction of overall risk is summarized in a table in the chapter “conclusions”. In case of ongoing R&D efforts for an alternative, the technical feasibility and the availability are classified as “not sufficient”, as at the current stage, the alternative is not technically feasible and not qualified/implemented for the sector. - The colours are as follows: - Red: not sufficient - the parameters/assessment criteria do not fulfil the requirements of the respective sector, - Green: sufficient - the parameters/assessment criteria do fulfil the requirements of the respective sector, and - Yellow – the parameters/assessment criteria fulfil some requirements for some but not all applications (only used for the assessment of the technical feasibility).
Performance parameter / Performance parameter / Fulfilling some requirements Technical feasibility Economic feasibility
Not sufficient Sufficient Not for all applications / sectors
7.1. Main processes & post treatments
CATEGORY 1 ALTERNATIVES The alternatives assessed in this section are considered the most promising ones, where considerable R&D efforts are carried out within the aerospace sector. Category 1 alternatives were often discussed during the consultation phase. In most cases, they are in early research stages and still showed technical limitations when it comes to the demanding requirements from the aerospace sector, such as corrosion performance. However, some of these possible alternatives may already be qualified and used in other industry sectors or for niche applications, respectively for single process steps of the process chain within aerospace but not as general alternatives to Cr(VI) containing surface treatment process chains.
7.1.1. ALTERNATIVE 1: Acidic surface treatments
7.1.1.1 Substance ID and properties A variety of inorganic acids are currently under evaluation as alternatives to Cr(VI) in surface treatment processes within the applied use. Research is currently focused on boric acid, sulphuric acid, phosphoric acid, tartaric acid, nitric acid and citric acid. An overview of which acids are used in the respective surface treatment processes is provided in Table 10 .
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The most important processes, where inorganic acids are used are, anodize coating processes of aluminium and magnesium, conversion coating processes of aluminium, zinc, zinc-nickel, cadmium, magnesium and silver and passivation processes of stainless steel for creating stable oxide coatings or converted oxide layers or passive films. Ferrous metals like iron (or certain steels) may cause interferences with subsequent coatings or platings and are therefore treated with alternative methods. An overview of general information on the substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.1.
7.1.1.2 Technical feasibility The following acids in order of importance are assessed to be a potential alternatives for the following surfaces treatment processes according to Table 10 : Table 10: Sodium dichromate-based surface treatments where acidic based surface treatments may be an alternative.
Surface treatment Substrate / coating Alternative
Chromate Conversion Coating Aluminium and aluminium alloys Acidic anodizing + topcoat or sealant
Nitric acid passivation Passivation of stainless steel Stainless Steel Citric acid passivation
Chromate conversion coating General assessment: The aerospace sector stated that Cr(VI)-free acidic anodizing can be used instead of chromate conversion coating plus paint but only for specific aluminium parts on special aerospace alloys (such as AA2024 or AA7075), as a final corrosion protection layer, and only in cases where no resistive coating is required. In addition, treating a substrate with an anodizing process affects the fatigue properties of the substrate, which does not happen in case of a conversion coating. Furthermore, the process is not feasible technically as a local application and is therefore not usable for MRO or deoxidizer applications or as an electroless process (e.g. for pipes). Corrosion resistance: It is important to note, that acidic anodizing is not a stand-alone chromate conversion coating alternative, because a Cr(VI) primer has to be applied on top to achieve adequate corrosion performance. Layer thickness : Compared to a CCC layer, the surface of the alternative (combining an acidic anodized surface with topcoat) is higher resulting in issues with the mechanical dimensions of the treated parts. Resistivity: Anodized surfaces do not have conductive properties and anodizing processes are only an alternative for conversion coatings prior to paint applications, where conductivity is not a requirement. In general, conversion coatings are applied to substrates due to the conductive properties of the resulting coating. Conclusion : Cr(VI)-free anodized surfaces cannot be sealed, which means that the parts have to be painted with a Cr(VI) primer. Anodizing cannot be used on assemblies. Anodizing plus topcoat or sealant as conversion coating would only be suitable for coatings without required conductivity. As conductivity is a broad requirement of the aerospace sector on conversion coated substrates, the alternative does not fulfil these requirements technically.
50 Use number: 2 ANALYSIS OF ALTERNATIVES
Corrosion Layer thickness Resistivity Stand-alone process MRO application resistance
Passivation of stainless steel General assessment: Nitric or citric acid can be used for the passivation of steels and has been implemented for many years, although they may not be applicable to all kinds of stainless steels but research is ongoing. A post treatment process is necessary for some stainless steels (e.g. high carbon stainless steels such as 440 °C) and is usually performed with sodium dichromate. However, a significant amount of stainless steels which have been applied since the beginning of aircraft production still need to be investigated due to their unavailability for testing (not available in quantity required for the testing; only high volume can be provided): abnormal etching (impact on e.g. end grain pitting/intergranular corrosion) cannot be excluded for some steels. Consequently, general rules of qualification for each production relevant material against specifications shall be established as mitigation and this approach will be implemented in stages. Corrosion resistance: Generally, corrosion resistance test requirements (ISO 9227) for austenitic stainless steel are from 96 h to 750 h and for martensitic stainless steels 2 h to 500 h. It was stated during consultation that nitric acid passivation is qualified for certain austenitic and martensitic stainless steels for particular applications and, for example, a corrosion resistance of 48 h could be reached for martensitic stainless steel after nitric acid passivation. However, this neither covers all kinds of stainless steels, nor the full suite of corrosion requirements of the aerospace sector. Regarding the passivation of stainless steel with citric acid, variation in solution concentration, exposure time and temperature enables the passivation process for austenitic stainless steels and certain non-austenitic steels. The overall performance may be lower compared to Cr(VI) and for some critical steels (e.g. some martensitic or precipitation hardening CRSs), and post-treatments may be necessary to reach the required specifications (IFAM, 2007). Conclusion: R&D is ongoing within the aerospace sector regarding the passivation of stainless steels with citric and nitric acid to improve the quality of the protective surface. However, uncertainties remain about the performance of acidic based passivation alternatives on certain kinds of stainless steels, as crucial requirements and functionalities have not yet been proven or met.
Corrosion resistance Compatibility with substrates Complex geometry
Not for all types of steel Not for all types of steel
7.1.1.3 Economic feasibility The passivation of stainless steel with nitric acid is a mature process and already in use at various aerospace companies, for example qualified for certain austenitic and martensitic stainless steels for particular applications. However, for the use as a replacement of Cr(VI)-based passivation, the final process controls are not yet developed and the economic impact of e.g. complex process control, potential process changes for different kinds of stainless steels passivated by different kinds of acids cannot be assessed at the current stage. When applying nitric acid passivation, higher process temperatures are necessary, resulting in slightly higher process costs. As the anodizing plus topcoat or sealant is technically not feasible, the economic feasibility was not assessed, however, the two- step approach instead of only one conversion coating step is considered to be an economic drawback.
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7.1.1.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 3.1.1), boric acid would be the worst case with a classification as Repr. 1B. Boric acid is a SVHC and included on the Candidate List according to REACH Annex XV due to its toxicity for reproduction. Recently, boric acid was included into the 6 th draft recommendation of priority substances. Apart from boric acid, tartaric acid constitutes the next worse toxicological scenario and is classified as Acute Tox. 4, Skin Irrit. 2, Skin Sens. 1, Eye Irrit. 2, STOT SE 3, Eye Dam. A transition to a nitric acid employing alternative would contradict the tendency to reduce the use of this substance in order to avoid NO x emissions Transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances. However, as some of the alternate substances used are also under observation, the replacement must be carefully evaluated on a case by case basis.
7.1.1.5 Availability (R&D status, timeline until implementation) Anodizing plus topcoat/sealant as conversion coating would only be suitable for coatings without required conductivity. As conductivity is a broad requirement on conversion coated substrates within the aerospace sector, the alternative is unlikely to be pursued under R&D efforts for this purpose. For passivation of stainless steel, nitric acid is qualified for the passivation for certain austenitic and martensitic stainless steels for particular applications in the aerospace sector, but not applicable to all types of steel. Citric acid is already in use for some specific applications, although further R&D efforts have to be undertaken as this alternative process is currently not ready for industrial implementation as general alternative. Taken together, the described replacement substances are promising alternatives, but cannot be applied to all kinds of stainless steel so far. Until all different applications can be performed without Cr(VI), it is expected that at least 12 to 15 years are necessary until full implementation of alternative products in the supply chain.
7.1.1.6 Conclusion on suitability and availability for acidic surface treatments In summary, Cr(VI)-free acidic surface treatments are no alternative to the current conversion coating systems in the civil aerospace sector, but passivation of stainless steels with sodium dichromate free acids is a promising alternative, and nitric acid is already qualified for certain austenitic and martensitic steels for particular applications. At the current stage, not all kind of stainless steels can be treated with these alternative acids and the key functionalities are not sufficiently fulfilled. Further R&D and at least 12 to 15 years are necessary until full implementation of alternative products in the supply chain, if no major drawbacks occur.
7.1.2. ALTERNATIVE 2: Silane/siloxane and sol-gel coatings
7.1.2.1 Substance ID and properties Sol–gel protective coatings have shown excellent chemical stability, oxidation control and enhanced corrosion resistance for metal substrates (Wang & Bierwagen, 2009). Sol-gel describes a wide variety of processes. In general, the evaporation of the solvent and the subsequent destabilization of
52 Use number: 2 ANALYSIS OF ALTERNATIVES the sols lead to a gelation process and the formation of a transparent film due to the small particle size in the sols. Currently, sol gel technology is expanding rapidly, extensive R&D effort is being made and many new products are appearing on the market, especially since the advent of hybrid and nanocomposite materials. The following description of the sol-gel process is derived from Wang & Bierwagen (2009). By using sol-gel coating processes, a network of oxides is formed on the substrate created by the progressive condensation reactions of molecular precursors in a liquid medium. In general, two main processes -an inorganic and an organic process - can be distinguished. When using the inorganic sol-gel process, a network is formed by a colloidal suspension (usually oxides) and the gelation of the sol (colloidal suspension of very small particles, 1 to 100 nm). The organic approach is the most widely used sol-gel process and generally starts with a solution of monomeric metal or metalloid alkoxide precursors in an alcohol or other low-molecular weight organic solvent (M(OR)n). M is a network-forming metal of transition metal such as Si, Ti, Zr, Al, Fe, B, etc. and R is typically an alkyl group (C nH2n+1 ). Typical precursors are silanes and siloxanes (=silicones). Some commonly used alkoxysilane precursors for sol-gel coatings are provided in Table 11 :
Table 11: Some commonly used alkoxysilane precursors for sol-gel coatings.
Abbreviation Chemical name
MTES Methyltriethoxysilane
MTMS Methyltrimethoxysilane
VTMS Vinyltrimethoxysilane
PTMS Phenyltrimethoxysilane
APS 3-Aminopropyltrimethoxysilane
BTSTS Bis-[3-(triethoxysilyl)-propyl]tetrasulfide
TMOS Tetramethylorthosilicate
TEOS Tetraethylorthosilicate
An overview on general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.2. Depending on the geometry (size and shape) of the part to be coated, different technologies such as spraying, immersion, electrodeposion or dip-spin coating can be used for applying a sol-gel coating. The most common and commercially used application technique for sol-gel coatings is dip-spin technology, while spraying technology is the most commoly used technique within the aerospace sector. The dip spin application is performed in a spray chamber using a mesh basket. The parts to be coated with a sol-gel coating via dip spin technology are placed on a conveyor and then metered by weight into a wire mesh basket with a diameter generally between 0.5 to 1.0 m. The basket (full of parts) is then submerged into a coating vat. The basket is then raised out of the coating solution, yet still remains in the vat, and spun up to 600 rpm (revolutions per minute).
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A drying period, resulting in the formation of the respective sol-gel coating, is necessary after the coating application. The exact drying technique varies dependent on different microstructures, quality requirements, and practical applications.
7.1.2.2 Technical feasibility Table 12 summarizes the sodium dichromate-based surface treatment processes where sol-gel coatings (based either on silane or siloxane precursors) may be an alternative. Table 12: Sodium dichromate-based surface treatment processes where sol-gel coatings may be an alternative.
Surface treatment Substrate / coating
Aluminium and aluminium alloys, magnesium Chromate Conversion Coating and magnesium alloys Aluminium and aluminium alloys, magnesium Sealing after (Cr(VI)-free) anodizing and magnesium alloys
Passivation of metallic coatings Cd plated surfaces
General assessment: From academic research, it was stated that thin films without the need for machining or melting can be applied. Literature also highlights that complex shapes can be coated with the sol-gel coating process as (Wang & Bierwagen, 2009). Current challenges with this process include: - Interface properties of sol-gel coatings (adhesion, delamination) determine the quality of the sol-gel coating. General approaches or methods to evaluate these properties have not yet been established, - Processing times are very long and the curing process is performed at high temperatures, - Due to a substantial volume contraction and internal stress accumulation caused by the large amount of evaporation of solvents and water, the coating can easily establish cracks and therefore, the formation conditions of the sol-gel coatings have to be carefully controlled during the drying process (Wang & Bierwagen, 2009).
These scientific statements and expectations from Wang and Bierwagen (2009) are in contrast to numerous industry experience with sol-gel coatings. The performance of the sol-gel coating is strongly dependent on the properties of the pickling solution and/ or the surface pre-treatment and conditions used prior to the sol-gel coating. As a consequence, adhesion and corrosion protection properties are not only a property of the sol-gel system itself, but are strongly linked to the whole process chain including pre-treatments.
Chromate conversion coating General assessment: Sol-Gel applications are used as an alternative to chromate conversion coating for painting and bonding applications, or on the aluminium parts of the exterior fuselage with low corrosion risk due to a clad layer. OEM approvals for wings and some detail parts were granted. As corrosion performance of Sol-Gel coatings is very poor (see below), a Cr(VI)-containing corrosion inhibiting primer has to be applied subsequently for adequate performance. Corrosion resistance: Sol-gel chemistries by themselves do not provide stand-alone corrosion resistance, therefore rely on additives or subsequent coatings to provide the corrosion resistance to meet part requirements. Currently there are no known additives to the silane matrix that have shown
54 Use number: 2 ANALYSIS OF ALTERNATIVES stand-alone corrosion resistance that meets aerospace requirements. In a salt spray test according to ISO 9227, only 72 h without significant corrosion on Al alloys were observed, which is not meeting the specifications of the aerospace sector, especially not for structural parts. For some applications, sufficient corrosion performance can be achieved at the laboratory scale, while other test series have failed. The issue is the poor reproducibility of the current technology. With regard to magnesium substrates, R&D efforts on this alternative have been stopped, as no corrosion protection could be achieved. In general, the active corrosion inhibition of sol-gel coatings shall be improved, as well as the application technique for local purposes, before these coatings can be an alternative to chromate conversion coatings. Fatigue: Since silanes/Sol-gel are a very broad chemistry of coatings, the potential impact on fatigue would have to be assessed on a material by material base. Several companies from the aerospace sector have found silane coatings that could meet similar fatigue performance as conversion coatings for specific applications. Adhesion: Several companies from the aerospace sector have found applications on aluminium substrates where specific organo silanes provide adequate and in some cases improved adhesion properties over chromate conversion coatings for specific paint systems and applications. Since these silanes do not provide adequate stand-alone corrosion performance they are limited to parts that are primed with specific primers though. Layer thickness: In general, sol-gel coatings are very thin and the layer thickness has no impact on the fatigue properties. However, for layers with thicknesses higher than 1-3 µm, elctrical resistance was stated not to be in line with the requirements. For electrical bonding applications, the thickness is too high, leading to electrical insulation. Resistivity: It was confirmed by several aerospace sector companies that the conductive properties of the tested sol-gel coatings are not meeting the requirements for the sector. Sol-gel coatings are non-conductive in general, while the conversion coatings are required to show conductivity. Application technique: Sol-gel coatings typically have a relatively short pot/tank life, in the realm of hours, compared to chrome conversion coatings, which depending on the material can be years or decades. Because of this sol-gel coatings are usually spray applied to parts. This means a change of manufacturing process is required for their implementation. However; they don’t require rinsing, which provides an alternative to immersion processing for large complex parts. However, current technologies showed limitations in applying the coating to complex parts and more sophisticated strategies must be developed to overcome this issue. This is the main objective of project phase 2 of SOL-GREEN. In this project, an electrophoresis process will be assessed and developed to apply anti-corrosion coatings through SOL-GEL technique for complex geometry parts. These challenges are currently ongoing and the research mainly conducted at a laboratory scale. Process temperature: Several products have already been tested by the aerospace sector and found to be insufficient since the curing temperatures are above 100°C, which is clearly not sustainable for the preparation of the entire aircraft or spacecraft and the incompatibilities with e.g. the curing temperature of elastomers and/or composite parts. However, R&D is ongoing on silane-based coatings applied via alternative application procedures and not via sol-gel technique. Conclusion: Sol-gel coatings have already reached the market for some applications including where standalone corrosion is not required and where corrosion resistance is provided by other layers of the coating system (e.g. chromated primer). They are especially important for their adhesion promotion properties. They are technically not suitable as an alternative to chromate conversion coatings where standalone corrosion resistance or conductivity are requirements. Forms of sol-gel coatings that require high curing temperatures are also not suitable for many applications.
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In many cases problems with the application method can also limit the use of sol-gel for certain complex geometries.
Corrosion Application Process Adhesion Layer thickness Resistivity resistance technique temperature
Sealing after (Cr(VI)-free) anodizing General assessment : Sol-Gel technology is intended to be used as alternative for sealing after anodizing. Research is also ongoing on sol-gel coatings to replace the whole anodizing plus sealing process. In general, the same issues can be observed as described above for the conversion coating. The major technical limitation is that currently no solution exists to apply the coating to complex parts with reproducible performance. Sol-gel as an alternative for sealing after anodizing has the major drawback that sol-gel coatings for aerospace applications are predominantly applied via spray process and therefore are not applicable on complex shaped parts. Treatment of complex shaped parts have to be done by immersion. Corrosion resistance: First generation silane based sol-gel coatings were tested in SST to ASTM B117. The results were neither sufficient nor repeatable, because no consistent performance was able to be provided by the sol-gel coating, as the 336 h corrosion resistance was met but also failed for test series at several companies. In summary, it was stated during the consultation, that the corrosion resistance of sol-gel coatings intended to replace the anodizing plus sealing is not sufficient at the current stage. In addition, further testing such as the performance of sol-gel coatings in cyclic corrosion testing is necessary. Chemical resistance: The stability of sol-gel coatings against hydraulic fluids and fuel still has to be tested. Conclusion: Currently, sol-gel coatings are not technically feasible alternatives, neither as sealing alternative nor replacing the whole anodizing plus sealing process. The same disadvantages apply as for conversion coating and further R&D is necessary to improve the performacne. A TRL is not defined yet.
Corrosion Application Process Layer thickness Reproducibility resistance technique temperature
Passivation of metal coatings Corrosion resistance : With regard to sol-gel as a passivation process on Cd plated surfaces , it was stated during the consultation phase within the aerospace sector, that the corrosion resistance is not sufficient at the current stage of R&D. Conclusion : Sol-gel coatings as alternative for Cr(VI) passivation on Cd plated surfaces do not provide sufficeint corrosion resistance at the current stage of R&D. As other alternatives are more promising, no further data is available.
Corrosion resistance
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7.1.2.3 Economic feasibility It was stated during the consultation phase, that the R&D stage of the alternative is too early to assess the economic feasibility in all details, but it should be acceptable compared to the existing technologies. Applying sol-gel coatings by using dip-spin technology limits the throughput of parts to be treated due to the limited volume of the baskets. Additionally, the treatment of larger parts is expected not to be economically feasible given the nature of the application technique. In the case of switching the current application by immersion to sprayed sol-gel coatings, the impact on existing facilities is not known. Equipment such as tank liners, bath heaters and stirrers, bath regeneration systems and waste treatment may need to be modified / added. In the case of spray application the use of automation would be preferred to ensure thickness homogenicity and avoid worker exposure to unknown effects of the spray. Investment and implementation time would therefore need to be considered. Also in some facilities the switch from treatment by bath to a treatment by spray could be problematic (room available, etc).
7.1.2.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. The exact substance identity and composition of products used in the sol-gel process is very often not known as this is confidential business information of suppliers. Therefore, only the hazard classifications for the sol-gel matrix could be taken into account. Based on the available information on the substances used within this alternative (see Appendix 3), they are classified as Flam. Liq. 3, Acute Tox. 4, Eye Dam. 1, Skin Irrit. 2, Eye Irrit. 2, STOT SE 3, Asp. Tox 1, Muta. 1B, Carc. 1B. The substance Vinyl trimethoxysilane (VTMS) constitutes worst case scenario and is included in the CoRAP (Community rolling action plan), indicating substances for evaluation by the EU Member States in the next three years. The evaluation aims to clarify concerns that the manufacture and/or use of these substances could pose a risk to human health or the environment. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non- threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances. However, as some of the alternate substances used are also under observation, the replacement must be carefully evaluated on a case by case basis.
7.1.2.5 Availability (R&D status, timeline until implementation) Products based on aqueous solutions of zirconium salts, which are activated by an organo-silicon compound, are already approved by several companies within the aerospace sector for special parts (e.g. fuselage, wing). These are only for parts and assemblies where the corrosion performance is provided by the subsequent primer and topcoat. They provide good adhesion properties but are insufficient in terms of stand-alone corrosion protection. Nevertheless, these systems are subject to comprehensive R&D efforts worldwide: - The HITEA project covers many aspects of Cr(VI) replacement in the aerospace sector, also including a thorough analysis of sol gel pre-treatment. In 2014, the tested alternatives are at TRL2. After the initial phase, the project will focus on a handful of promising alternatives, where further testing is conducted within the next years. Qualification (TRL 6) will take up to 10 years from now. Sol-gel has also been looked at previously as a pre-treatment and was considered not to be adequate as it gave good adhesion properties, but no anti-corrosion protection. It is currently being looked at again in the HITEA project.
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- The aim of the SOLCOAT project is to develop and improve a sol gel coating for magnesium alloys for industrial manufacture and use. This project is still ongoing. - In 2008, the multi-company project SOL-GREEN was initiated for the development of protective coatings of Al/Mg alloys (Cerda et al, 2011). Since these coatings solutions are not based on electrochemical conversion, but determine a complete technological innovation, the industrial production qualification is not expected before 2025. Phase 1 was finished last year, showing that SOL-GREEN 1 faced some technical issues. Besides the main problem of, by far, insufficient corrosion performance, the layer thickness cannot be controlled adequately with the current dip coating processes. Satisfying results were only achieved on specimens, but not on parts due to their complex geometries. Therefore, the main objective of SOL-GREEN 2 is to assess and develop an electrophoresis process to apply anti-corrosion coatings through SOL-GEL technique for complex geometry parts. These challenges are currently ongoing, the research was mainly conducted at laboratory scale (TRL 2) at universities and in some partner plants. However, as mentioned above, this is a long term solution since for qualification and implementation, 10-15 years will be needed.
7.1.2.6 Conclusion on suitability and availability for silane/siloxane based sol-gel processes Chromate-free sol gel systems are an innovative technology which have arisen over a number of decades and are now part of extensive R&D efforts in the aerospace sector and beyond. The overall performance is sufficient for some applications where sol-gel coatings can be used in combination with a coating system that uses a chromated primer, to improve paint adhesion and for structural adhesive bonding applications. However, various key performance criteria such as standalone corrosion protection, resistivity, coating parts with complex geometries, and temperature limitations pose significant hurdles to implementation of sol-gel coatings for all applications. In summary, chromate-free sol gel systems are not equivalent to sodium dichromate-based surface treatments and are currently not a general alternative. While some applications have been implemented or partially implemented, the maturity of the systems for some applications (e.g. standalone corrosion protection) is still in the early research stages (TRL 2). Another 15 years are necessary to develop and implement these systems into the supply chain if no major drawbacks occur.
7.1.3. ALTERNATIVE 3: Cr(III)-based surface treatments
7.1.3.1 Substance ID and properties Cr(III) processes are generally based on the same principle as the Cr(VI) processes. However, there are major differences in the distinct chemical composition of the solutions and required additives as well as the operating paramters and ancillary equipment, such as ion exchangers or others, depending on the kind of surface treatment. In general, predominantely two types of Cr(III) solutions are used: sulphate- and chloride-based. An overview on general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.3.
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7.1.3.2 Technical feasibility Table 13 summarizes the sodium dichromate-based surface treatment processes where trivalent based surface treatments may be an alternative. Table 13: Sodium dichromate-based surface treatment processes where Cr(III)-based processes may be an alternative.
Surface treatment Substrate / coating
Aluminium and aluminium alloys, Chromate Conversion Coating magnesium and magnesium alloys Aluminium-based deposits and aluminium Passivation of metallic coatings alloys, Cd, Zn-based, ZnNi deposits
Sealing after (Cr(VI)-free) anodizing Aluminium and aluminium alloys
Chromate conversion coating General assessment: The Cr(III) conversion coating currently is the best alternative for chromate conversion coating and is being implemented at different aerospace companies on selective aluminium alloys and applications. This technology is already qualified by some contractors but currently only for 5000 and 6000 aluminium alloys, not for the 2000 and 7000 AA series. Furthermore, Cr(III)-based solutions are qualified according to MIL-DTL-81706. Generally, companies provided results for several commercially available products with significantly varying performance, depending on the substrate used. So far, the process is not robust enough to meet the requirements for all kind of alloys. Therefore, these coatings currently remain at low maturity within the aerospace sector. Corrosion resistance: The aerospace sector stated Cr(III) conversion coating is currently a promising alternative, however the conversion film is not active inhibited with a lower corrosion protection compared to Cr(VI)-based conversion coatings. The main challenge of the process is to identify and consequently specify the optimum process window. For aluminium alloys from 5000 and 6000 series, the degree of corrosion is considerably higher compared to a chromate conversion coating, but the company specific requirement of 168h SST (ASTM B117, ISO 9227) can be met with this process. However, it was stated by several companies from this sector that for alloys from the 2000 series (which is the type of alloy most often used in aerospace industry) and 7000 series, corrosion performance is insufficient for most applications when tested at an industrial scale. Depending on the Cr(III)-based product used, first signs of corrosion appear between 48 to 100 h in salt spray test compared to the company requirements of 168 h (ISO 9227). In addition, Cr(III)- based solutions do not exhibit the same active corrosion inhibiting properties as Cr(VI)-based solutions. Few companies from the aerospace sector stated, that their Cr(III)-based solutions are in line with current specifications for various alloys from aluminium (also on the 2000 and 7000 series), as well as for magnesium and titanium. However, the Cr(III)-based solutions were only applicable under very narrow and controlled process conditions and included Cr(VI)-based pre-treatment. In general, results on the corrosion resistance of Cr(III) conversion coatings are inconsistent within the aerospace sector and further R&D is necessary to obtain reproducible results and high qualitative coatings. Adhesion: Where the applied parts are used for bonding applications, adhesion tests are ongoing and first results with paint indicate promising results. However, existing results from the industry demonstrate that the adhesion performance is currently inconsistent. Depending on the Cr(III)-based
Use number: 2 59 ANALYSIS OF ALTERNATIVES product used, adhesion promotion to subsequent corrosion resistant paints was not in line with the cross-cut requirement of GT1 after water immersion. Reproducibility: Several aerospace companies confirmed that the reproducibility of the process is poor. This is linked to the layer formation within the process, which is influenced by the whole pre- treatment chain. Finding the right process window for good reproducibility remains very challenging especially for Al alloys from the 2000 and 7000 series. Other important parameters such as fatigue properties (which mainly depends on the surface preparation), and conductivity (IFAM, 2008) are equivalent to Cr(VI)-based conversion coatings, thus meeting the requirements of the aerospace sector. Cr(III) conversion coatings for local (conversion coating) repair applications are available on the market. As stated during the consultation, tests performed within the aerospace industry for touch up applications on Al alloys showed that these solutions were not in line with the requirements, especially not meeting the corrosion requirements. Conclusion: To date, Cr(III) based products are not an equivalent replacement for chromate conversion coatings. Several products exist based on Cr(III) technology and the requirements for the aerospace sector can be fulfilled for some special applications. Importantly, none of the various products can currently be seen as a general alternative, as the coating performance is very much dependent on the optimal combination of pre-treatment (often not Cr(VI)-free), product and alloy used. Especially for structural parts, for which highest requirements have to be fulfilled, the maturity of these products is currently low. As a conclusion, Cr(III) conversion coatings as alternative to Cr(VI) conversion coatings are promising alternatives but not yet technically feasible as mostly the corrosion resistance requirements are not met.
Corrosion Paint Repair Layer Fatigue Resistivity Reproducibility resistance Adhesion applications thickness With impact Depending Depending on With impact on on corrosion on solution solution and corrosion and and paint and substrate substrate paint adhesion adhesion
Passivation of metallic coatings General assessment: Passivation is mainly performed on metal coatings such as aluminium and its alloys and cadmium as well as on zinc and zinc-nickel coatings. It was stated during the consultation phase that R&D is underway on passivation on Zn alloys, Cd and Al coatings. Cr(III) conversion coatings are used on zinc and zinc-nickel alloys in the automotive industry and there are plans to transfer this technology to the aerospace industry. As stated during the consultation, one aerospace company commented, that all new qualifications on Zn-Ni and Al IVD are with Cr(III)- based processes instead of Cr(VI) passivation. To date, only a few suppliers are qualified for Zn-Ni and only one supplier is qualified for Al IVD, but the solutions are not applicable to the whole supply-chain yet, as legacy legacy suppliers still have to use Cr(VI)-based processes. As Zn-Ni is not necessarily an environmental improvement over cadmium (Zn-Ni coatings with Cr(III) passivation instead to Cd coating with Cr(VI) passivation), new qualifications will not be prioritised. As a remark, many proprietary products contain cobalt salts which are SVHCs. These cobalt salts are necessary for the corrosion resistance performance. Corrosion resistance: Although successful chromate-free passivation of Al coatings was demonstrated for Al IVD in some tests, outdoor exposure testing has shown Cr(III) passivation not
60 Use number: 2 ANALYSIS OF ALTERNATIVES to be as effective in providing corrosion protection to the coating or exposed steel as Cr(VI)-based passivation and more development work is thus required. For Cr(III) passivated Zn-Ni coatings, greater amounts of corrosion have been observed during salt spray tests compared to Cr(VI) passivated Zn-Ni. Especially for uses where a high level of corrosion resistance is required, a Cr(III) passivation on Zn plated substrates is not suitable and for these purposes, R&D is ongoing and the current TRL level is low (TRL 2-3). Trivalent chromium based passivation of Cd coatings was tested but not fully sufficient, as the requirements regarding corrosion resistance were not met. Some Cr(III) passivated Cd coatings met company specific corrosion requirement of 750 h salt spray exposure, but only when the passivation solution contained cobalt salts. Without cobalt salts, the corrosion resistance was reduced to 336 h after salt spray exposure which is far below the company’s requirements. Depending on Cr(III)- based process performed, white and red corrosion are visible after 48 hours, when tested in salt spray exposure. Active corrosion inhibition: Active corrosion inhibition is poorer compared to Cr(VI)-based passivation. Adhesion of subsequent paint : During outdoor exposure testing, results have shown aluminium on steel exhibiting red corrosion within a scribe after 42 months industrial exposure, whereas there was no red rust in scribe of Cr(VI) passivated cadmium. Reproducibility: The performance is not consistently meeting the requirements since the process reproducibility has to be improved. Corrosion and adhesion properties are currently an issue. Layer thickness: Resulting layer thickness ranges between 250-600 nm, which is sufficient for aerospace applications. Conclusion: In summary, passivation of metallic coatings with trivalent chromium based products are under investigation for various coatings, but have a low maturity so far.
Corrosion Active corrosion Paint Adhesion Reproducibility Layer thickness resistance inhibition For Al IVD coatings In some situations
Sealing after (Cr(VI)-free) anodizing - general assessment General assessment: Given the nature of an anodic coating, a porous surface with insufficient corrosion resistance depending on the application is created. This anodic coating necessarily has to be sealed by post-treatment processes (sealing after anodizing) to provide adequate protection to the substrate. It was stated during the consultation that extensive R&D is ongoing on Cr(III)-based sealing after anodizing alternatives within the aerospace sector.
Sealing after (Cr(VI)-free) anodizing – one process step Corrosion resistance: Tests performed within the aerospace sector on anodized surfaces sealed with Cr(III) showed varying corrosion protection results depending on the underlying anodizing process used. The test results for sealing with Cr(III) products showed that company specific corrosion resistance of 336 in SST can be achieved, but only under controlled laboratory conditions. When tested under industrial conditions, this performance is not reached. This is in line with statements from other companies on Al alloys from 2000 and 7000 series, where corrosion can be observed already after 100 h. The observed differences may be induced due to Cr(VI) impurities which can be found in most commercial Cr(III) products or might come in by contamination of other
Use number: 2 61 ANALYSIS OF ALTERNATIVES processes. Even small amounts of Cr(VI) may drastically increase the performance. Suitability needs to be validated in additional testing more representative for in-service relevant conditions. For local (sealing) repair applications corrosion requirements were clearly not met. Adhesion to subsequent layer: During the consultation period it was reported that although sealing after anodizing closes the pores of the anodic coating, a certain porosity remains, which may possibly negatively affect the corrosion resistance, especially with regard to the highest requirements, but enhances paint adhesion. Resistivity: The sealing aims to clog the pores of anodizing layer which makes it perfectly insulating. Conclusion: Cr(III) sealing after anodizing is a promising alternative. However, as stated by technical experts from industry, although the Cr(III) sealing impregnates the pores of the anodic coating, a certain porosity will remain with current alternative techniques. This limits the corrosion resistance in general. As a consequence, further R&D and improvement is necessary and anticipated on Cr(III) sealing. The implementation (TRL 9) at one company for specific applications is foreseen, but not before 2020.
Corrosion Compatibility with Adhesion to paint One-step process Surface properties resistance substrates
Sealing after (Cr(VI)-free) anodizing – two-step process General assessment: As previously stated, after applying Cr(III)-based sealings, a certain porosity of the sealed surface remains compared to the conventional chromate-based sealing processes. This remaining porosity negatively influences the corrosion resistance of the coating, especially in regard to high corrosion requirements, for example of structural parts. Several companies within the aerospace sector have performed R&D on this issue showing that the remaining pores can be closed by an additional post-treatment process. Consequently, the whole sealing process has to be expanded by an additional process step. For this process, two post-treatments after CCC are under evaluation: Cr(III) plus rare earth elements, which is discussed below, and Cr(III) plus subsequent hot water sealing discussed in section 7.1.4. . One example for a post-treatment comprising two process steps is a Cr(III)-based sealing post- treatment plus a rare earth elements-based additional post-treatment. The process is patent protected by one company in the aerospace sector. As stated during the consultation phase, work is currently ongoing to further improve the corrosion resistance of the layer by closing the remaining pores. The process is stated to be technically feasible, development is in TRL 4. To date, the process has been tested in two treatment shops, where corrosion and fatigue tests are performed. After qualification (TRL6) would be reached, the alternative would need to be tested in further treatment shops to ensure quality and robustness. As stated in chapter 5, generally, from TRL 6 to industrial implementation (TRL 9), at least five years are necessary if no major drawbacks occur. As stated during consultation, it is unlikely that a two-step sealing process will be implemented as a general alternative for the whole aerospace sector. The major technical issue is the implementation of a two- step sealing alternative instead of a one-step Cr(VI)-based process.
Corrosion One-step Compatibility Surface Adhesion resistance process with substrates properties Adhesion on anodizing with a double step process is similar to adhesion on CAA sealed
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7.1.3.3 Economic feasibility Against the background of significant technical failure of these alternate systems, no detailed analysis of economic feasibility was conducted. First indications were made, stating that the process is in general economically feasible. Cd-replacement processes are feasible from an economic point of view.
7.1.3.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 3.1.3), chromium (III) chloride would be the main chemical with a classification as Skin Irrit. 2, Eye Irrit. 2, Acute Tox. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.1.3.5 Availability (R&D status, timeline until implementation) For conversion coating, several products based on Cr(III) are already available on the market and are part of extensive research within the aerospace sector. Furthermore, this technology is already qualified at some contractors but currently only for 5000 and 6000 aluminium series alloys, not for the 2000 and 7000 AA series. First Cr(III)-based solutions are qualified according to MIL-DTL- 81706. Currently, information is inconsistent with regard to their performance in highly demanding environments. For some applications on specific alloys, first implementations may be expected in 2017, other companies reported that TRL 6 can be reached within the next years if test requirements are fulfilled without major drawbacks. However, most applications on high copper containing Al alloys are still far away from industrialization. Most importantly, for structural parts, for which highest requirements have to be fulfilled, the maturity of these products is currently low. Deployment into the supply chain would not be expected before 2030. Clearly, none of the available products can be used as a general alternative for all applications on all substrates. For the passivation of metallic coatings, Cr(III)-based alternatives have a low maturity so far and 12 to 15 are needed for further R&D and before potential implementation of the alternative into the supply chain, if no major drawback occurs. Cr(III) solutions as sealing alternatives were stated to be a promising alternative for equipment and structural parts and plans are underway within the aerospace sector to implement Cr(III) sealing of anodized parts. Further research at the laboratory scale is ongoing to improve the final quality of the coating and to validate suitability with further testing. TRL 6 is not yet reached and the implementation (TRL9) at one company is foreseen, but not before 2020. However, the TRL 9 level capability across the whole aerospace sector is highly dependent on a number of factors, such as the commercial availability of the technique, the demonstration of capability for all kinds of aluminium substrates and all kinds of parts, and the maturity of the supply chain. In addition, there are still substantial efforts needed to develop alternatives for the most challenging applications including aircraft components that are especially vulnerable for corrosion and other areas where moisture and liquids are entrapped. For the use in legacy programs and especially vulnerable parts, additional R&D efforts are needed. For these applications, the developmental process will certainly include multiple iterations and testing until successful implementation. Here, at least 12 to 15 years are necessary until full implementation of alternatives for all applications into the supply chain.
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Additionally, the development of a two-step sealing process comprising Cr(III) sealing after anodizing process is at TRL 4. To date, the process has been tested in two treatment shops, where corrosion and fatigue tests are performed. After qualification (TRL6) would be reached, the alternative would need to be tested in further treatment shops to ensure quality and robustness. As stated in section 5, generally, from TRL6 to industrial implementation (TRL9), at least five years are necessary if no major drawbacks occur. As stated during consultation, it is unlikely that a two- step sealing process will be implemented as a general alternative for the whole aerospace sector. The major technical issue is the implementation of a two-step sealing alternative instead of a one- step process.
7.1.3.6 Conclusion on suitability and availability for Cr(III)-based processes Taking all these extensive R&D efforts for the different processes and the first products on the market into account, it can be stated that Cr(III)-based surface treatments are technically not yet feasible as general alternative to the described Cr(VI)-based surface treatments within the aerospace sector. With regard to conversion coatings first qualifications on specific alloys were carried out for some applications, while the tested products do not show a sufficient performance on all Al alloys. The major technical limitation is the corrosion performance of the coated substrates, especially on the widely used Al alloys from the 2000 and 7000 series. For the passivation of metallic coatings, Cr(III)-based alternatives have a low maturity so far and 12 to 15 years are needed for further R&D and before potential implementation of the alternative into the supply chain, if no major drawback occurs. With regard to Cr(III)-based sealing, the two-step alternative is not considered to become implemented into the supply chain, while a single-step sealing is under intensive development. For this process, at least 12 to 15 years are necessary until full implementation for all applications into the supply chain. In summary, to date Cr(III) is not an alternative to the current systems in the aerospace sector, but represents a promising alternative. First implementations are foreseen for sealing after anodizing or CCC, but not before 2020, if no major drawbacks occur. For the use as structural applications, no completely Cr(VI)-free process chain is currently available, nor is an implementation foreseen within the next decade.
7.1.4. ALTERNATIVE 4: Water-based post-treatments
7.1.4.1 Substance ID and properties Water-based post-treatments, such as hot water sealing, can be used as a sealing post-treatment after anodizing of aluminium and as post-treatment (rinsing) after phosphate conversion coating. With regard to the sealing application, the anodizing process leaves a porous oxide layer, which has to be closed to provide adequate corrosion resistance to the substrate. Without high quality sealing, the anodic surface is highly absorbent to all kinds of dirt, grease, oil and stains and is susceptible to corrosion. The anodized part is immersed into boiling, deionized water, with a temperature ranging between 96°C to 100°C. During the sealing process, hydrated aluminium oxide (boehmite AlOOH) is formed in the pores by three intermediate steps ( Figure 17 ). First, hydrated aluminium oxide precipitates as a gel of pseudoboehmite (boehmite with higher content of water), a reaction that can be controlled by diffusion, pH and chemical composition of the sealing solution. In a second step, an increasing pH leads to condensation of the gel forming crystalline pseudoboehmite, which starts to fill up the pores. Finally, the boehmite recrystallizes from the pseudoboehmite. Boehmite has a
64 Use number: 2 ANALYSIS OF ALTERNATIVES higher volume than pseudoboehmite, consequently the pores of the anodized surface are sealed. The optimal pH for hot water sealing ranges between 5.5 and 6.5. To enhance the performance of the process, various inhibitors such as silicate and phosphate as well as lithium acetate, potassium fluoride or hydrogen fluoride can be added (Hao & Cheng, 2000). Given the nature of the sealing, this alternative is solely applicable on anodized aluminium and aluminium alloys.
Figure 17: Formation of boehmite during hot water sealing of anodized aluminium surface (Hao & Cheng, 2000).
For anodizing processes without stringent surface protection requirements, hot water sealing is an economic and suitable method. Within the aerospace sector, where a highly demanding environment requires long-term corrosion protection, a corrosion resistance of at least 336 h is needed. Replacement solutions for rinsing after phosphate conversion coating on steel have to fulfil two requirements in one process step. As per the classical rinsing step, complete removal of residue from the previous processes must be ensured. Additionally, by using a tempered rinsing (temperature between 70 and 80°C), the surface has to be passivated, which leads to an increased corrosion resistance of the surface. This is especially of importance for phosphated surfaces because these coatings naturally generate a certain porosity which would negatively affect the corrosion performance of the coated surface without any post-treatment (Narayanan, 2005). A non-exhaustive overview on general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.4.
7.1.4.2 Technical feasibility Table 14 summarizes the sodium dichromate-based surface treatment processes where water-based post-treatments may be an alternative:
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Table 14 : Sodium dichromate-based surface treatment processes where water-based post-treatments may be an alternative.
Surface treatment Substrate / coating
Sealing after (Cr(VI)-free) anodizing Aluminium and aluminium alloys
Rinsing after phosphating Steel with phosphate conversion coating
Sealing after (Cr(VI)-free) anodizing – one step Water-based post-treatments, such as hot water sealing, were tested by several companies from the aerospace sector as alternative to sealing after anodizing on aluminium substrates. Corrosion resistance: The results on corrosion resistance vary and depend on the origin and quality of the anodic coating (for example CAA or Sulphuric acid anodizing (SAA)). A 336 h SST requirement according to ISO 9227, specified as minimum corrosion requirement by several companies within the aerospace sector for specific applications and parts can be met under perfect controlled lab conditions for CAA and as stated during the consultation, also for sealed surfaces on SAA. However, maintaining the same water qualities and anodic film quality (which are key to guarantee requirement is met) under manufacturing conditions is not realistic. Further tests on aluminium (2024, 2818 and 7175 alloys) after chromate-free anodizing processes, such as SAA, Tartaric Sulphuric Acid Anodizing (TSA) or Thin Film SAA (TFSAA). Anodizing clearly did not meet corrosion requirements according to salt spray test ASTM G85 as shown in Figure 18 .
Figure 18 : Aluminium test panels after 144 cycles accelerated cyclic, acidified salt spray test according to ASTM G85, Method A2, 1A: Al with dichromate sealing, 1B: Cross-scribed Al with dichromate sealing, 2A: Al with hot water sealing, 2B: Cross-scribed Al with hot water sealing (GE Aviation).
Rapid pH variation and water containing inhibitors (e.g. by phosphate, silicate, and chloride) of boiling water make it challenging to maintain water quality, leading to a short bath life. Additionally, hot water sealing considerably reduces the abrasion resistance and hardness of anodic
66 Use number: 2 ANALYSIS OF ALTERNATIVES coatings (Hao & Cheng, 2000) and subsequent paint adhesion of hot water sealed anodized coatings was reported to be unacceptable. In general, hot water sealing without additives was found to be insufficient as the corrosion requirements of the companies are either not reached at all, or only under perfectly controlled lab conditions (not at an industrial scale). Buffers, such as ammonium acetate and other proprietary additives, may be added to the deionized water to improve the sealing quality, and further R&D was performed for hot water sealing processes plus additives. A number of additive solutions are commercially available. Commonly used additives are lithium acetate, potassium fluoride or hydrogen fluoride. It was expected that the corrosion performance would increase, but in the tests it remained below the corrosion resistance requirement of 336 h SST according to ISO 9227, which is essential for numerous aerospace companies, especially for structural parts. Paint adhesion: The results on paint adhesion are inconsistent and further development on the alternative treatment deems to be necessary. Conclusion: Neither hot water sealing as a stand-alone nor hot water sealing plus additives are able to fulfil the high corrosion requirements, which are essential for numerous aerospace companies, especially for structural parts.
Corrosion Compatibility with Stand-alone process Paint adhesion Surface porosity resistance substrates Process control issues, not for all inconsistent requirements
Sealing after (Cr(VI)-free) anodizing – two step R&D is currently ongoing with regard to trivalent chromium conversion coatings plus an additional hot water sealing step. The disadvantage is that this is a two-step process. Corrosion resistance: The SST performance on Al alloys is inferior compared to a Cr(VI)-based sealing. For some Al alloys, the performance can almost reach 500 h, while for others the corrosion resistance is far from being sufficient. Chemical resistance: Other performance parameters, such as chemical resistance of the surfaces treated by this two-step process, are not yet tested.
Corrosion resistance Single process step Chemical resistance
Rinsing after phosphating on steel General assessment : As stated during the consultation, R&D is currently performed to develop rinsing solutions based on hot water and/or proprietary dips not containing any chromates. Further critical performance factors are in discussion.
Corrosion resistance: To date, surface after rinsing has to withstand 2 h in SST. At the moment, this performance cannot be met with the proposed alternative solutions.
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Adhesion to paint: To date, surfaces after rinsing with sodium dichromate-based solutions demonstrate sufficient paint adhesion according to ISO 2409 (GT0), which at the moment cannot be met with the proposed alternative solutions.
More demanding test programmes are currently under development, with the aim to ensure that all quality criteria from the aerospace sector can be met with the alternative treatments.
Conclusion: At the current stage, chromate-free rinsing after phosphating solutions based on hot water and/or proprietary dips are under development, but are not meeting the requirements regarding corrosion resistance and paint adhesion.
Corrosion resistance Adhesion to paint Surface porosity
7.1.4.3 Economic feasibility Against the background of significant technical failure of this alternative, no detailed analysis of economic feasibility was conducted. However, based on the literature research and consultations, there is no indication that the discussed alternative is not economically feasible in general. Nevertheless, there are some concerns regarding, for example, a short life time of the hot water bath leading to increased costs for maintenance of the bath, change of bath, and bath chemicals. As the hot water sealing requires a relatively long sealing time, a high energy consumption is caused leading again to increased costs (Hao & Cheng, 2000).
7.1.4.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 3.1.4), potassium fluoride as common additive to water-based post-treatments would be the worst case with a classification as Acute Tox. 1, and Skin Corr. 1A. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.1.4.5 Availability (R&D status, timeline until qualification / certification) Hot water sealing without additives is an industrially available and qualified process for applications where the corrosion requirements are not as stringent as for most of the aerospace sector. In general, hot water sealing without additives was found to be insufficient as the corrosion requirements of the companies are either not reached at all, or only under perfect controlled lab conditions (not at an industrial scale). Regarding hot water sealing with additives and water-based rinsing solutions after phosphating of steels, the corrosion requirements of the aerospace sector are not fulfilled. For use as sealing, replacement techniques are subject to further R&D work. Development is also ongoing for the application as an alternate rinsing solution. A TRL is not defined yet. At the current stage of development, water-based sealing is technically not equivalent to Cr(VI)- based sealing and is therefore not a general alternative. According to the current very early stage of research, at least 12 to 15 years are necessary until full implementation of the alternative products into the supply chain.
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7.1.4.6 Conclusion on suitability and availability for water-based post-treatments Water-based post-treatments, nominal hot water sealing with and without additives, and water- based rinsing solutions after phosphating of steel are technically no alternative to sodium dichromate-based post-treatments because the corrosion requirements of the aerospace sector are definitely not fulfilled. At the current stage of development, water-based sealing is technically not equivalent to Cr(VI)-based sealing and is therefore not a general alternative. According to the current very early stage of research, at least 12 to 15 years are necessary until full implementation of the alternative products into the supply chain.
CATEGORY 2 ALTERNATIVES The alternatives assessed in this section are mainly discussed in literature and were rarely mentioned during the consultation phase. In most cases, they are in very early research stages and showed clear technical limitations when it comes to the demanding aerospace sector specific requirements. They may be suitable for other industry sectors or for single process steps of the process chain, but not as general alternative to sodium dichromate containing surface treatment process chains.
7.1.5. ALTERNATIVE 5: Molybdates and molybdenum-based processes
7.1.5.1 Substance ID and properties The coating industry uses molybdate for various processes. It has been used as corrosion inhibitor (e.g. zinc molybdate, calcium zinc molybdate) since the early 1970s and is also used as a molybdenum-based metal coating. Here, a molybdenum coating can be applied by immersion, creating a Molybdate Conversion Coating (MoCC) to form a protective oxide layer on the surface of the metal to be treated, which provides corrosion resistance. Two main types of MoCC are possible: a coating based on sodium molybdate (Na 2MoO 4•2H 2O), and a coating based on a mixture of molybdate and phosphate (e.g. as phosphoric acid). Stabilizer additives such as cerium fluoride are used for the MoCC. A non-exhaustive overview on general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.5.
7.1.5.2 Technical feasibility Table 15 summarizes, the sodium dichromate-based surface treatment processes where molybdate- based processes were assessed to be an applicable alternative.
Table 15: Sodium dichromate-based surface treatment processes where molybdate-based processes may be an alternative.
Surface treatment Substrate / coating
Chromate Conversion Coating Aluminium and aluminium alloys
Sealing after (Cr(VI)-free) anodizing Aluminium and aluminium alloys
Chromate conversion coating General assessment: The MoCC process has to be carefully controlled, as the final corrosion resistance from the treated surface is highly dependent on the substrate, its pre-treatment, and the
Use number: 2 69 ANALYSIS OF ALTERNATIVES process conditions. When applied on aluminium, pH values >9 lead to dissolution of aluminium ions from the substrate, dramatically increasing corrosion rates. The performance at neutral pH is only better if an oxide thickening step is performed beforehand. In this case, molybdate can be incorporated into the pores of the Al oxide, forming a protective layer. The performance can be further improved by surface pickling, which helps to uniformly distribute molybdate in the pores. This leads to a reduction of the amount of chloride ions that are the main reason for pit corrosion (Hamdy et al, 2005). As a conclusion, the quality and long-time corrosion resistance of MoCC is highly dependent on the chemical conditions of the treatment and the reported data suggest that the influence of molybdates is still unclear and various handicaps that limit their application on an industrial scale exist. The corrosion resistance of conversion coatings based on sodium molybdate or a mixture of molybdate and phosphate show less corrosion resistance in salt spray tests as the conventional sodium dichromate-based treatment. For example, corrosion resistance of the sodium molybdate coating withstands maximum 72 h in salt spray test (ECHA Annex XV, 2011), while specifications from the aerospace sector require at least 72 h and significantly more, depending on the specific substrate. The corrosion resistance can be improved by additives such as organic layers or stabilizers. For instance, a US patent is held by Trumble et al (1999) regarding a molybdate- phosphate mixture for conversion coating added with stabilizers such as cerium fluoride. With this stabilizer, the corrosion resistance to standard salt spray tests can be improved, with results up to 300 h. The US Environmental Protection Agency (EPA) developed a new type of heteropolymolybdate-based conversion coating for certain aluminium alloys (2024-T3, 6061-T6, and 7075-T6 aluminium alloys) with a corrosion resistance of 336 h in a salt spray test according ASTM B117 (Minevski, 2002). Corrosion resistance: Recent information provided by the aerospace sector during the consultation phase confirmed that conversion coatings based on molybdate compounds do not meet the aerospace corrosion requirements on Al alloys, especially the not high corrosion resistance for structural parts. Additionally, these kind of alternative coatings do not provide similar active corrosion inhibition properties as sodium dichromate. Resistivity : Molybdate conversion coatings are non-conductive coatings, which clearly do not fulfil the requirements of the aerospace applications. Conclusion: To date, molybdenum-based conversion coatings are technically not feasible as an alternative for chromate conversion coatings.
Corrosion resistance Active corrosion inhibition Resistivity
Sealing after (Cr(VI)-free) anodizing Corrosion resistance : With regard to the use of molybdate salts for sealing after anodizing of aluminium alloys, the corrosion requirements of aluminium alloys treated with a TSAA followed by a molybdate-based sealing have not been reached. The final coating inspected after a 500 h salt spray test according to ISO 9227 showed from 4 pits to more than 15 pits depending on aluminium alloy and therefore the corrosion requirement of no pits after exposure was not met. Conclusion : As a conclusion, molybdate salts for sealing after anodizing are technically not feasible as an alternative to sodium dichromate-based sealings.
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Corrosion resistance Active corrosion inhibition Compatibility with substrates
7.1.5.3 Economic feasibility Against the background of significant technical failure of these alternate systems, no detailed analysis of economic feasibility was conducted. Information was provided that chemical costs can be higher by a factor of 2. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible.
7.1.5.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Sodium molybdate is classified as Skin Irrit. 2, Eye Irrit., Acute Tox. 4, Aquatic Chronic 3 and STOT SE 3. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234- 190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.1.5.5 Availability (R&D status, timeline until qualification / certification) Although intensive R&D has been performed in the past on molybdenum conversion coatings, no industrial implemented molybdenum-based coatings have been developed that sufficiently fulfil the corrosion requirements of the aerospace sector. The final success of molybdenum-based alternatives cannot be determined at the moment. Following the technical assessment, the relevance of these systems is questionable and it was stated that the corrosion performance cannot be reached on aluminium alloys. During the consultation, companies reported that these systems were already screened out at an early stage, as more promising alternatives were chosen for further development.
7.1.5.6 Conclusion on suitability and availability for molybdates and molybdenum-based processes Few developmental products have been reported as replacement systems to chromate conversion coating so far. All of them failed to meet the requirements of the aerospace industry at laboratory scale. During the consultation, companies reported that these systems were screened out at early stage, as more promising alternatives were chosen for further development. It can be concluded that conversion coatings based on molybdate compounds are technically not equivalent to Cr(VI)-based products and are therefore not a general alternative for aerospace applications on aluminium substrates. Following the technical assessment, the relevance of these systems is questionable.
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7.1.6. ALTERNATIVE 6: Organometallics (zirconium and titanium-based products, such as fluorotitanic and fluorozirconic acids)
7.1.6.1 Substance ID and properties Since the late 1970s, organometallic coatings based upon organo-titanates, organo-zirconates or organo-zircoaluminates have been reported and found some applications in adhesive technology. It is generally considered that they form interfacial primary bonds to the substrate via reaction with surface protons. So far, titanates have not found wide use in adhesive technology but are used in the manufacture of some film laminates. In the last few years, a new generation of environment- friendly conversion coatings based on titanium or zirconium oxides has attracted extensive attention owing to good corrosion and wear resistance. Moreover, the new conversion coatings can operate at lower process temperatures. These Ti/Zr-based conversion coatings have been mostly used on aluminium and magnesium alloys. However, reports applying to zinc have been scarce until now (Guan et al, 2011). Products based on fluorotitanic and fluorozirconic acid were stated as alternatives for conversion coatings, respectively passivation in the aerospace sector and a patent protected chrome-free passivation treatment was developed specifically for aluminium alloys. This commercially available solution is based on hexafluorozirconate and is qualified under MIL-DTL-81706 Class 3 for military purposes. The coating can be used as a final finish and can also serve as a base for paints, high performance topcoats, powder paints, lacquers, or as a base for rubber bonding. A non-exhaustive overview on general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.6.
7.1.6.2 Technical feasibility Organometallic products, such as fluorotitanic and fluorozirconic acid are assessed as alternative for the following sodium dichromate-based surface treatments ( Table 16 ):
Table 16: Sodium dichromate-based surface treatment processes of where fluorotitanic and fluorozirconic acid may be an alternative.
Surface treatment Substrate / coating
Aluminium and aluminium alloys, magnesium and its alloys, Chromate Conversion Coating Ti and its alloys
Passivation of metallic coatings IVD Al / Zn / Al / Cd coatings
Chromate conversion coating Corrosion resistance: Several R&D programs in the military and space sector investigated organometallics as alternative to CCC. Products based on Zr are qualified according to MIL-DTL- 81706 Class 3, meaning a corrosion resistance of 168 h on AA2024 and AA7075 has been demonstrated. In contrast, literature reports that the corrosion performance on low copper aluminium alloys might be sufficient, whilst on alloys from the 2000 and 7000 series, the requirements from the aerospace sector are not met (Berry, 2007). Here, surface corrosion and pits were observed within 24 h on AA7075 and AA2219 (ASTM B117), accompanied by poor adhesion results (ESA STM 276, 2008).
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A commercially available Zr-based conversion coating claims to provide corrosion resistance and adhesion for subsequent painting. According to publically available company specific test results, the product withstands over 1000 h in the Neutral Salt spray test (NSST) on various aluminium alloys (5052, 6022, 3003, 1100, 6111, 6061), partly outperforming Cr(VI)-based chromate coatings. Compared to the highest copper containing alloy tested in this trial (Al A356), the product failed the NSST according to ASTM B117. According to a further test report from a supplier on AA2024, the most common alloy used in the aerospace sector and of a high copper content, corrosion appeared after less than 24 h in NSST (ASTM B117) (the criterion for failing was four or more pits on 2 of 3 0.155 m² sized panels). This result is clearly insufficient for the demanding environment of the aerospace sector, where corrosion resistance requirements (alloy type depending) start with a minimum of 72 h on Al alloys of the 2000 series. In general, for copper contents > 2% in the aluminium alloy, the product is not passing the specifications. During the consultation phase information provided by several companies from the aerospace sector confirmed that conversion coatings based on Zr- or Ti-compounds clearly do not meet the corrosion requirements on AA2024 in bare and in painted conditions (> 168 h, ISO 9227, ASTM B117) and corrosion resistance was even lower compared to Cr(III) alternatives. When tested as proprietary Zr-based touch-up formulation, results were not found to be reproducible or repeatable. Conclusion: Testing performed by the aerospace sector confirmed the abovementioned publically available results, namely that on copper containing aluminium alloys the corrosion resistance is not reaching the specific requirements. Therefore, conversion coatings based on Zr and Ti are technically not suitable as alternative for chromate conversion coatings for aerospace applications.
Corrosion resistance Adhesion Reproducibility Active corrosion inhibition
Passivation of metallic coatings General assessment : As stated during the consultation, a Zr-based organometallic alternative has been tested for the passivation of Al coatings (IVD Al) on steel and there are no known problems to treat complex geometric parts with a Zr-based organometallic alternative. Passivation with this alternative is believed not to affect the fatigue properties of the tested IVD Al material. Testing of further coatings (such as zinc, aluminium and cadmium) to be treated with this alternative are under further R&D. Corrosion resistance: No evidence of base metal corrosion (steel, red rust) was determined in the tests and the product met the type II corrosion requirements of 504 h SST (ISO 9227) of the tested company when using the Zr-based alternative coating for passivation on IVD Al. Potentially occurring white rust due to the IVD coating shall not be a cause for rejection (Acorn, 2011). Adhesion to paint: When applied on IVD Al, the adhesion properties to paint on a coating from a commercially available product coatings were found not to be sufficient: they did not meet the Gt0 rating (dry) and Gt1 rating wet (results vary from 1-2 and 2-4 respectively). Layer thickness: The thickness of the passivation layer applied using a commercially available product is commonly 0.1 µm. Chemical resistance: The chemical resistance of IVD Al passivated with a Zr-based organometallic alternative to fuel, hydraulic fluid and runway de-icer is meeting the requirements.
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Conclusion: Zr and Ti formulations are not technically feasible as alternatives to a sodium dichromate-based passivation of metallic coatings and further R&D would be necessary. Although the corrosion requirements might be sufficient, the paint adhesion properties are not in line with the current specifications. The passivation of other coatings/substrates (such as Zinc, Aluminium, and Cadmium) is under further R&D. To date, passivation based on Zr and Ti formulation are technically not suitable for applications within the aviation sector.
Compatibility with Corrosion Adhesion to paint Layer thickness Chemical resistance substrates resistance
7.1.6.3 Economic feasibility Against the background of significant technical failure of this alternative, no detailed analysis of economic feasibility was conducted. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible. However, fluoro acids are very aggressive products in general and investment for modification of the surface treatment line may be needed. Additionally, bath maintainability would require evaluation.
7.1.6.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. In addition, publically available information on specific alternatives products was evaluated. However, the exact substance identity and composition of products used is very often not known as this is confidential business information of suppliers. Based on the available information on the substances used within this alternative (see Appendix 3.1.6), fluorotitanic acid would be the worst case with a classification as Met. Corr. 1, Acute Tox. 2, Acute Tox. 3, Skin Corr. 1B and Eye Dam. 1. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.1.6.5 Availability (R&D status, timeline until qualification / certification) Several products based on these substances are already commercially available and R&D was found to be ongoing on these substances. NASA has implemented an organometallic zirconate coating beneath a primer and topcoat on several aluminium alloys used in solid rocket boosters. Furthermore, there has been some utilisation of Ti/Zr-base coating processes in the architectural, coil coating, and automobile industries. However, in unpainted conditions, inferior corrosion performance on copper-containing aluminium alloys has to be accepted for these applications. For alternate passivation processes on Al, zinc, aluminium and cadmium, R&D efforts are at the early laboratory scale. At the current stage of R&D it is unknown if the technical issues can be solved. Currently, these replacement products clearly do not meet the specifications of the aerospace sector. R&D programs are ongoing within this field but to date, no TRL for aerospace applications has been defined. According to the current early stage of research, another 15 years are necessary to develop and implement these systems into the supply chain.
7.1.6.6 Conclusion on suitability and availability for fluorotitanic- and fluorozirconic-based products
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Some fluorotitanic and fluorozirconic-based replacement systems (developmental and commercial products) to chromate conversion coatings and sodium dichromate-based passivation of metallic coatings have been tested so far by the aerospace sector. Failure in meeting some key requirements has been observed at laboratory scale (e.g. corrosion, adhesion). Thus, it can be concluded that conversion coatings based on Zr and Ti compounds are technically not equivalent to chromate conversion coatings and are not a general alternative for aerospace applications. According to the current early stage of research, another 15 years are necessary to develop and implement these systems into the supply chain. Following the technical assessment, the relevance of these systems is questionable.
7.1.7. ALTERNATIVE 7: Benzotriazole-based processes, e.g. 5-methyl-1H-benzotriazol
7.1.7.1 Substance ID and properties Benzotriazoles (BZT), e.g. 5-methyl-1H-benzotriazol are corrosion inhibiting substances commonly used in primers providing copper blocking properties, especially to aluminium and aluminium alloys. 5-methyl-1H-benzotriazol forms a complex with copper metal at its surface, leading to stabilization of copper and inhibiting oxidation as long as the layer stays intact. An overview on general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.7.
7.1.7.2 Technical feasibility BZT are assessed to be a potential alternative for surface treatments according to Table 17 . Table 17: Sodium dichromate-based surface treatment processes where benzotriazoles may be an alternative.
Surface treatment Substrate / coating
Aluminium and aluminium alloys, Chromate Conversion Coating copper
Chromate conversion coating Regarding BZT as an alternative for chromate conversion coating, it was stated during the consultation phase by the aerospace sector that 1H-benzotriazole was tested in the laboratory as corrosion inhibitor, but is not suitable as stand-alone system. During the R&D process, a low corrosion resistance was shown in in inhibition studies with BZT on AA2024. When mixed with other stabilizers, such as phosphates (Sr-Mg polyphosphates or Na 2HPO 4), the results obtained in laboratory tests were better (IFAM, 2006).
To date, BZT-mixtures are no technically feasible alternatives to replace sodium dichromate-based conversion coating processes as only laboratory testing has been completed, meaning that the alternative is at a very early TRL stage.
Corrosion resistance
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7.1.7.3 Economic feasibility Against the background of significant technical failure of this alternative, no detailed analysis of economic feasibility was conducted. However, it was stated that investments are needed for collecting waste containing the 5-methyl-1H-benzotriazol, as it cannot be discharged to the on-site sewage treatment plant due to its complexing properties. Importantly, the former one-step process has to be adapted to a two-step process.
7.1.7.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 3.1.7), 5-methyl-1H-benzotriazol would be the worst case with a classification as Acute Tox. 4, Skin Irrit. 2, Skin Irrit. 2 and STOT SE 3. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.1.7.5 Availability (R&D status, timeline until qualification / certification) Benzotriazoles are not a stand-alone corrosion protection system and other inhibitors with Al-oxide stabilisation function are necessary. This has to be further investigated and it was stated during the consultation phase to be under R&D. Furthermore, in case suitable combinations of benzotriazoles with other inhibitors can be found in laboratory tests for subsequent primer/paint applications, functionalities and performance have to be further investigated by end-users in the aerospace sector in additional extended tests on top of the known standard tests to simulate real-life conditions. Consequently, the exact timeline until qualification/certification of this alternative with benzotriazoles cannot be estimated at the moment but would certainly be considered to take at least 12 to 15 years, if technically possible.
7.1.7.6 Conclusion on suitability and availability for benzotriazole-based processes As a conclusion, benzotriazoles are not a stand-alone replacement for chromate conversion coating as the corrosion resistance is not sufficient. Further R&D is necessary and if the alternative becomes technically feasible, at least 12 to 15 years are necessary until full implementation of the alternative into the supply chain
7.1.8. ALTERNATIVE 8: Chromate-free etch primers
7.1.8.1 Substance ID and properties Etch primers (nominal wash primer) are designed to physically bond themselves to the substrate to which they are applied to. This is achieved by combining the primer with an acid which microscopically etches the surface of the substrate, thus forming a physical and chemical bond between etch primer and surface. Etch primers are especially used on base metals to enhance corrosion resistance and adhesion of subsequent paint.
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Etch primers for pre-treatment purposes are especially necessary for aluminium, brass and galvanized steel surfaces to optimize the surface performance. According to publicly available data, etch primers are designed to provide high resistance to filiform corrosion and can be used as an alternative pre-treatment to the chromate conversion coating. Additionally, they promote good adhesion to subsequent primers and are applicable to a variety of light alloys and steel. Etch primers for corrosion prevention must be applied to the correct film thickness. A dry film thickness between 8-12 µm is required. If the primer is applied too thick, embrittlement to the subsequent coating occurs. An overview on general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.8.
7.1.8.2 Technical feasibility In Table 18 , the sodium dichromate-based surface treatment processes where etch primers may be an alternative are summarized: Table 18: Sodium dichromate-based surface treatment processes where etch primers may be an alternative.
Surface treatment Substrate / coating
Chromate Conversion Coating Aluminium and aluminium alloys
Chromate conversion coating As alternative to chromate conversion coating, chromate-free etch primers are only qualified for external applications and are therefore not suitable for all over protection as required. As stated during the consultation phase, R&D has been performed on this alternative but surfaces treated with etch primers do not meet the corrosion requirements of the aerospace sector. Moreover, they show insufficient active corrosion inhibition and poor chemical resistance. Nevertheless, chromate free etch primers (wash primers) are used when repainting aircrafts under specific limitations. Chromate free etch primers could only be considered for specific cases such as local repair applications in some cases (for example as paint touch up surface preparation) to provide satisfactory corrosion performance with adequate technologies. In conclusion, etch primers are not a technically feasible alternative for chromate conversion coating in general , they are also not widely applicably for repair conversion coating applications.
7.1.8.3 Economic feasibility Against the background of the significant technical failure of this alternative, no detailed analysis of economic feasibility was conducted. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible.
7.1.8.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 3.1.8), phosphoric acid would be the worst case with a classification as Skin Corr. 1B and Met. Corr.1. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) –
Use number: 2 77 ANALYSIS OF ALTERNATIVES which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.1.8.5 Availability (R&D status, timeline until qualification / certification) Chromate free etch primers are available on the market but are only suitable for limited type of applications. As the use of etch primers for surface treatments within this dossier is not a general technical feasible alternative, therefore the availability was not further assessed.
7.1.8.6 Conclusion on suitability and availability for etch primers Chromate free etch primers are technically not feasible as an alternative to chromate conversion coating, as the corrosion requirements are not fulfilled. They are used as adhesion promoters and can be used in cases, where “normal” conversion coatings may not be applicable, but then sufficiently only in combination with additives and not as stand-alone alternative.
7.1.9. ALTERNATIVE 9: Manganese-based processes
7.1.9.1 Substance ID and properties This alternative comprises all manganese containing processes such as permanganate conversion coatings, permanganate / phosphate conversion coatings and manganese-based sealing processes. In all processes, the permanganate is applied by immersing the substrate in the respective solution.
- The permanganate anion MnO 4 is a strong oxidising agent which is reduced to manganese (IV) oxide while elementary metal is oxidised and dissolved from the substrate as cation (Lee et al, 2013). Adding other substances such as phosphate to the conversion solution can enhance the corrosion resistance of the conversion coating (Lee et al, 2002) (refer to Figure 19 ).
Figure 19 Variations of amounts of Mn-deposited with immersion time in conversion coatings obtained from various treatment bath (left) ; values of total corrosion resistance of the various conversion coatings obtained in function of immersion time in 5% NaCl ; (right) (Lee et al, 2013).
For the use in sealing application, a manganese salt solution was tested. Here, the pores of the anodic coating are filled with manganese oxide (MnO2). The manganese oxide deposit grows from the pore base and deposition is continued until it reaches the outer surface of the coating (Alwitt & Liu, 2001).
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For replacement of conversion coatings on Magnesium and its alloys, conversion coating alternatives based on potassium permanganate are under development within the aerospace sector and two solutions are under investigation: - Solution A with potassium permanganate and potassium dihydrogenophosphate - Solution B with potassium permanganate and dihydrogen hexafluorozirconate.
A non-exhaustive overview of general information on the substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.9.
7.1.9.2 Technical feasibility Manganese-based processes are assessed as alternative for the following sodium dichromate-based surface treatments according to Table 19 . Table 19: Sodium dichromate-based surface treatment processes where manganese-based products may be an alternative
Surface treatment Substrate / coating
Aluminium and aluminium alloys, magnesium and Chromate Conversion Coating magnesium alloys
Sealing after (Cr(VI)-free) anodizing Aluminium and aluminium alloys
Chromate conversion coating Corrosion performance: Various developments and test results have been reported in literature for manganese-based coating solutions. When tested on zinc, the addition of aluminium (as aluminium sulphate Al 2(SO 4)3) and phosphate (as sodium dihydrogenophosphate NaH2PO 4) to the permanganate conversion coatings leads to promising corrosion performance compared to chromate conversion coating (Lee et al, 2002). Further investigations regarding the role of permanganate in permanganate/phosphate coatings on certain kinds of magnesium alloys were performed by Lee et al (2013). According to the authors, adding more permanganate to the phosphate solution resulted in a thinner coating with a compact magnesium oxide layer on the tested substrate. The thinner coatings showed less cracks and a higher corrosion resistance than the thicker coating with less permanganate. When tested on AA2024 by continuous salt spray exposure (ASTM B117) for coated specimens with and without cross-hatch mark for about 750 h, coating discoloration along with the presence of corrosion products were noticed (Yoganandan et al, 2012). According to information from the aerospace sector, permanganate conversion coatings on aluminium and its alloys were tested but found not to be sufficient, as the corrosion requirements were not met. For example, commercially available permanganate-based solutions for conversion coatings were tested but the corrosion resistance in salt spray tests is not sufficient and in addition, not comparable to Cr(III) processes which are the main focus of chromate-free alternatives. With regard to the aerospace sector, manganese-based processes are not usable on high copper containing aluminium alloys (like aluminium alloy 2024) or on titanium and titanium alloys. The process times for manganese-based alternatives are very long compared to sodium dichromate-based processes. With regard to magnesium and its alloys, potassium permanganate conversion coatings are at a very early R&D stage and not all key functionalities have been evaluated yet. It was stated during the consultation that corrosion resistance can currently only be met for one kind of magnesium substrate without varnish. From the initial results tested on solution A (with potassium permanganate and potassium dihydrogenophosphate), the corrosion resistance of the alternative
Use number: 2 79 ANALYSIS OF ALTERNATIVES conversion coating was found to be equivalent to the existing chromate conversion coating. The corrosion resistance of solution B (with potassium permanganate and dihydrogen hexafluorozirconate) was lower compared to the chromate conversion coatings. Layer adhesion on substrate: Adhesion properties are stated to be sufficient for the tested alternatives: GT0-1 at initial and after 14 days in demineralised water (ISO 2409). Layer thickness: The resulting layer thickness of potassium permanganate conversion coatings on magnesium substrate was found to be equivalent to the layer thickness resulting from chromate conversion coatings. Conclusion: In summary, permanganate conversion coatings are technically no alternative to chromate conversion coatings on aluminium alloys for the aerospace sector, but R&D programs cannot currently totally exclude this option. Potassium permanganate conversion coatings as an alternative to chromate conversion coatings on magnesium substrate are in a very early R&D stage, not all key functionalities have been evaluated yet and it was stated during the consultation that corrosion resistance can currently only be met for one kind of magnesium substrate without varnish.
Corrosion resistance Layer adhesion Layer thickness
Sealing after (chromate-free) anodizing Corrosion resistance : Literature data indicate that manganese-based sealing provides corrosion resistance in ambient earth atmosphere as well as other features for special applications such as enhanced conductivity, decreased resistivity and stability to withstand high negative bias voltage in a vacuum plasma without arcing (Alwitt, R.S & Liu, Y., 2001). However, the aerospace sector stated during the consultation that the performance of manganese-based sealings are deemed inferior compared to sodium dichromate-based sealings. Manganese-based alternatives were stated not to show proper performance regarding sealing after sodium dichromate free anodizing, but in combination with other compounds promising results may be obtained (CEST, 2011). The alternative process is still under R&D. Conclusion : In summary, manganese-based sealing solutions are technically not feasible as an alternative to sodium dichromate-based sealing solutions, but R&D is ongoing to enhance the properties.
Corrosion resistance
7.1.9.3 Economic feasibility Against the background of significant technical failure of these alternative systems, no detailed analysis of economic feasibility was conducted. However, based on the literature research and consultations, there is no indication that the discussed alternative is not economically feasible. With regard to potassium permanganate conversion coatings on magnesium substrate it was stated during consultation that implementation of these solutions seems to be of equivalent cost compared to current chromate conversion processes. Solution A is a company specific bath based on easily available products and solution B is a commercial bath.
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7.1.9.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 3.1.9), potassium permanganate would be the worst case with a classification as Ox. Sol. 2, Acute Tox. 4, Aquatic Acute 1, Aquatic Chronic 1, Skin Corr. 1C. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.1.9.5 Availability (R&D status, timeline until qualification / certification) According to literature research, R&D has been performed over a number of years on permanganate conversion coating. None of the systems currently fulfils the corrosion requirements of the aerospace sector. During the consultation, it was reported that these coatings are not applicable on high Cu containing Al alloys, which are the most important substrates used within the aerospace sector. Due to clear technical limitations, this alternative is not part of R&D efforts within the aerospace sector. A TRL is not yet defined. The final success of permanganate-based alternatives cannot be determined at the moment. Following the technical assessment, the relevance of these systems for aluminium substrate is questionable. With regard to potassium permanganate conversion coatings on magnesium substrate, the above mentioned solution A is a company specific bath based on easy available products and solution B is a commercial bath. At the current stage, none of these solutions are implemented in the supply chain, as none are qualified. It has to be noted that magnesium parts are no standard aerospace substrates, and conversion coating on magnesium is a niche application, which explains that R&D efforts on substitution are more difficult than on other subjects (for example chromate conversion coating on aluminium). In general, R&D efforts on potassium permanganate conversion coatings as alternative to chromate conversion coatings on magnesium substrates is in a very early R&D stage and at least 12 to 15 years are necessary until full implementation of the alternative magnesium conversion coating into the supply chain.
It was stated during the consultation, that R&D is ongoing regarding manganese-based alternatives for sealing after sodium dichromate-free anodizing. However, according to the aerospace industry R&D is still in an early stage.
7.1.9.6 Conclusion on suitability and availability for manganese-based processes In literature, few manganese-based products as replacement systems to chromate conversion coating have been reported so far. With regard to aluminium alloys, these are not in line with the minimum corrosion requirements of the civil aerospace. During the consultation, companies did not report in depth experience with these alternatives (laboratory scale) and a TRL is not yet defined. Potassium permanganate conversion coatings as an alternative to chromate conversion coatings on magnesium substrate are in a very early R&D stage, not all key functionalities have been evaluated yet and it was stated during the consultation that corrosion resistance can currently only be met for one kind of magnesium substrate without varnish. Despite the fact that the initial testing results of the alternative conversion coatings are promising, they have been obtained only on one substrate and without varnish. More complete evaluation is needed on these solutions in order to know if they are serious alternative solutions for chromate conversion coating on magnesium. None of the
Use number: 2 81 ANALYSIS OF ALTERNATIVES alternative solutions are already qualified for aerospace applications, and the conversion coating on magnesium substrate is a niche application within the aerospace sector. Thus, it can be concluded that conversion coatings techniques or sealing after anodizing based on permanganate compounds are technically not yet equivalent to sodium dichromate-based processes and are therefore not a general alternative for aerospace applications. According to the current very early stage of research, another 12 to 15 years are necessary to fully develop and implement these systems into real life and the supply chain.
7.1.10. ALTERNATIVE 10: Cold nickel sealing
7.1.10.1 Substance ID and properties Cold nickel sealing involves precipitation of nickel hydroxide during immersion in a bath of nickel salts and fluoride salts. The nickel enters the pores of the anodized surface followed by an ion exchange causing a shift in the local pH value. This shift is sufficient to cause the precipitation of Ni as nickel hydroxide. The Ni hydroxide blocks the pores and seals the surface. Cold nickel sealing is performed with solutions at ambient temperature (Kalantary et al, 1992). A number of cold nickel sealings are commercially available on the market and information on the technical functionality of these substances / sealings is publicly available. According to this information, the cold nickel sealing process is typically performed at a temperature between 26 to 40°C. An overview on general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.10.
7.1.10.2 Technical feasibility Cold nickel sealings may only be an alternative for the sodium dichromate-based sealing after anodizing (Table 20 ):
Table 20: Sodium dichromate-based surface treatment processes where cold nickel sealings may be an alternative.
Surface treatment Substrate / coating
Sealing after (Cr(VI)-free) anodizing Aluminium and aluminium alloys, ferrous alloys
Sealing after (Cr(VI)-free) anodizing General assessment : In general, cold nickel sealings have the advantage, that the process is performed under ambient temperature conditions and with shorter treatment times compared to sodium dichromate-based processes. It was stated, that one disadvantage of cold nickel sealings is, that the surface colour is different from the conventional sodium dichromate sealing. Colour : The cold nickel sealings have a grey to greenish colour instead of a yellowish colour of the chromate-based sealings, which is the typically required colour. As stated during the consultation, cold nickel fluoride seals are approved as an alternative to sodium dichromate-free sealing after anodizing but only by one company in the aerospace sector for some specific parts. These specific applications include, for example, a small cuff with cold nickel sealing integrated to an aircraft fuel system, which fits into a canister fitted to the wing fuel tank. The purpose of this canister is to allow the fuel pump to be removed without the need to drain the fuel system. As a consequence, the cold
82 Use number: 2 ANALYSIS OF ALTERNATIVES nickel sealed part is not visible and the greyish colour is not an issue. On the other hand it is only operated a few times during the life of the aircraft and therefore, not installed in an area with the highest requirements regarding airworthiness. Corrosion resistance : The cold nickel sealing processes were stated during the consultation to be beneficial regarding the prevention of intergranular corrosion, which is a phenomenon potentially following sulphuric anodizing and sealing of 2000 and 7000 series alloys. The alloys where intergranular corrosion appeared were copper rich. On one hand, a high copper percentage in the alloy provides a high strength but on the other hand it is the reason for the intergranular corrosion. During the sealing process, which is normally performed under hot conditions (solution temperature between 96 and 100°C), the copper rich intermetallic compounds are precipitated at the grain boundaries generating a composition difference between the precipitate and the grain mass. This is the method of hardening and provides the strength which the designers require. The composition gradient leads to a potential difference which drives the corrosion. The precipitates are attacked and, due to their small size relative to the grain, pitting occurs. By using a cold water sealing process such as cold nickel, this kind of corrosion effects are stated to be avoidable. It was reported, that cold nickel sealings applied on aluminium and aluminium alloys are able to pass all tests required by DEF STAN 03-24 2008 (chromic anodizing) and DEF STAN 03-25 2008 (SAA), which are British Standards for the military aerospace sector providing requirements and specific properties for the respective anodizing processes on aluminium and aluminium alloys. Additionally, cold sealings were stated during the consultation to meet the corrosion requirements (tested via salt spray test) and paint adhesion requirements where hot sealings are used. It has to be emphasized at this point, that the qualified sealing method under these UK standards is either a chromate-based sealing (STAN 03-25) or hot water sealing (DEF STAN 03-24 2008). Following the UK Defence Standards, the cold nickel sealings are neither foreseen nor allowed as sealing of anodized aluminium. Anodizing with subsequent sealing performed according to the US military specification MIL-A- 8625 specifies sealing (although nickel-based hot sealings) and the option to use “other suitable chemical solutions” without further specifying details. In summary, cold nickel sealings are neither mentioned nor qualified according to the UK military aerospace standard or US military aerospace standard. Although cold nickel sealings may be technically suitable in general for the military sector, they have to fulfil specific military standards such as MIL-A-8625 which are not always comparable to the requirements of the civil aerospace industry. Therefore, sealing processes potentially suitable for military purposes are not directly applicable for the general structure for civil aircraft, as the use/flight frequency of military planes is very low compared to civil planes running 365 days/year, as well as considerations related to the systems and performance envelope of military aircraft. Based on these daily demands to ensure the airworthiness of civil aircraft, these requirements are much more comprehensive. Conclusion : Cold nickel sealing processes may be technically suitable to fulfil the corrosion and adhesion requirements for the military aerospace sector, but the alternative is not qualified to military aerospace standards. As stated during the consultation, the cold nickel sealing alternative is also not qualified following civil aerospace standards and although it is used as sodium dichromate- free anodizing alternative for specific parts, these are parts without structural performance requirements.
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Corrosion resistance Colour
Not qualified for civial aerospace
7.1.10.3 Economic feasibility Against the background of significant technical failure of this alternative, no detailed analysis of economic feasibility was conducted. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible.
Cold nickel sealings have the advantage, that due to the ambient process temperatures, no costs for heating are caused and as the process has a shorter treatment time, costs related to this purpose are expected to be lower.
7.1.10.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Mixtures that include nickel compounds and nickel metal as stated in Appendix 3.1.10 are listed by IARC as a Group 1 chemical with sufficient evidence for mixtures that include nickel compounds and nickel metal of carcinogenicity in humans (IARC Monographs 100C). Based on the available information on the substances used within this alternative (Appendix 3.1.10), nickel fluoride (as exemplary nickel substance) would be the worst case with a classification as Carc. 1A, Muta. 2, Repr. 1B, STOT RE 1, Resp. Sens. 1, Skin Sens. 1, Aquatic Acute 1 and Aquatic Chronic 1. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non- threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances. However, as the alternate substance used is classified as mutagenic, the replacement must be carefully evaluated on a case by case basis.
7.1.10.5 Availability (R&D status, timeline until qualification / certification) Cold nickel sealings are not qualified as an alternative to conventional sealings under the UK and US military aerospace standards. Following the information provided on the technical properties, cold nickel sealings may be applicable as an alternative for the military aerospace sector (when each customer individually is convinced by suitable performance), but as stated during the consultation, they are not approved by the civil aerospace sector. As the risk reduction by using cold nickel sealings as alternative to sodium dichromate sealing is non-significant, it is unlikely that the approval process will be realised for the civil aerospace sector and no timeline can be provided at this stage.
7.1.10.6 Conclusion on suitability and availability for cold nickel sealings In conclusion, cold nickel sealings may be technically suitable to fulfil the corrosion and adhesion requirements for the military aerospace sector, but the alternative is neither qualified for the military aerospace sector nor for the civil aerospace sector. Although the corrosion and adhesion requirements of the military sector are stated to be met, the requirements of the civil aerospace sector are much more demanding and comprehensive to ensure the airworthiness of civil aircraft. In addition, using cold nickel sealings as alternative to sodium dichromate sealing will not significantly reduce the risk and it is unlikely that the approval process will be realised for the civil aerospace sector.
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7.1.11. ALTERNATIVE 11: Magnesium-rich primers
7.1.11.1 Substance ID and properties The concept of Mg-rich primers was developed in the early 2000s by North Dakota State University (NDSU) refining the approach for cathodic corrosion protection of Al alloys without the use of chromate pigments. Magnesium is electrochemically the most active metal in common iron and aluminium alloys and is therefore widely used for corrosion protection to the underlying substrates. Mg-rich primers were stated to be applicable in underground and undersea structures such as ships, submarines and aircraft (Pathak et al, 2012). Their mode of corrosion protection on aluminium alloys is completely different from Cr(VI)-based treatments (Johnson et al, 2007). Magnesium-rich primers were reported by a number of studies for the protection of Al alloys. According to Wang et al (2013), Mg-rich primers are able to provide corrosion protection to the Al substrate by a two-stage mechanism. In the first stage, the Mg particles provide cathodic protection and prevent the aluminium substrate from corrosion. This is caused because magnesium is more electronegative than aluminium and as a result, the Al substrate in this galvanic couple is cathodically polarized while the less noble Mg particles in the coating are anodically dissolved. The sacrificial Mg particles serve as a source of electrical energy (Pathak et al, 2012). In the second stage, precipitation of a porous barrier layer of magnesium oxides is observed and corrosion is further inhibited by a barrier mechanism (Wang et al, 2013). The primary Mg- compounds of interest are magnesium oxide (MgO) and magnesium hydroxide (Mg(OH) 2) since they are the species that would be present on the pigment surface or as the by-product of cathodic protection of the substrate. Based on their properties, the use of a Mg-rich primer leads to a local coating environment with an acid neutralising capability. Since either compound has such poor solubility in water, the local pH under a neutral wet environment would not be raised to any significant amount. These compounds would buffer the local environment to near neutrality (Johnson et al, 2007). Mg-rich coatings, termed as such because they are formulated to ensure that the Mg loading exceeds the CPVC contain Mg particles in physical and electrical contact with each other as well as with the substrate. The protective nature of Mg-rich primers is due to their behaviour as sacrificial anode providing cathodic protection to the underlying iron and/or aluminium alloys ( Figure 20 ) (Pathak et al, 2012).
Figure 20: Cathodic protection by the Sacrificial Anode method (Pathak et al, 2012)
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An overview on general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.1.11.
7.1.11.2 Technical feasibility Mg rich primers are under investigation as an alternative for local chromate conversion coating applications (Table 21 ):
Table 21: Sodium dichromate-based surface treatment processes where Mg rich primers may be an alternative
Surface treatment Substrate / coating
Chromate Conversion Coating (local application) Aluminium and aluminium alloys
Chromate conversion coating (local application) General assessment: Several R&D projects for Mg-rich primers have been described in previously published literature and are still ongoing at academic and industrial scale, specifically for mixtures of Mg particles and epoxies to optimize their performance. In current R&D programs, the Mg rich primers were found to perform well on aluminium alloys and on outdoor exposure at various sites across the US. Nevertheless, factors such as reactivity of the Mg particles in the coating, increases in pH, hydrogen gas liberation at coating metal interfaces and primer adhesion have to be taken into account for further R&D (Pathak et al, 2012). It has also been observed that these same Mg-rich primers fail rapidly and exhibit heavy blistering very early in salt spray tests (Wang & Bierwagen, 2009). A study of Wang et al (2013) partly replaces Mg particles by Al particles and studied the performance of Mg-Al-rich primers (with varying content) an AA2024 aluminium. For the study, aluminium alloy panels were used as substrate and coated with Mg-rich primers with a thickness of the dried primer of about 85 ± 5 µm. Mg-rich primers containing different contents of pure magnesium particles and aluminium particles in the epoxy paint were used for the tests. Cross scratch testes with immersion of the panels for 150 days in 3 wt% NaCl solution were carried out to examine the corrosion resistance. The results, provided in Figure 21 , show that the addition of Al particles decreased the distribution of Mg particles in the primer surface followed by less corrosion products of magnesium in the coating. Here, the Mg-Al rich primer with 20% Mg and 30% Al (D) showed better corrosion protection of Aluminium 2A12 alloy than Mg-rich primer with 50% Mg.
Figure 21: Surface morphology of the scratched coating samples after immersion in 3%NaCl solution for 150 days: A) 50Mg; B) 40Mg 10Al; C) 30Mg 20Al; D) 20Mg 30Al; E)10Mg 40Al; F)50Al (Wang et al, 2013)
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Further research studies have been performed on the behaviour of Mg rich primers for corrosion protection on AA2024-T3. According to Nanna & Bierwagen (2004), salt fog exposure of aluminium coated with Mg rich primers (without topcoat) to atmospheric CO 2 solution showed that magnesium forms (unspecified) magnesium carbonate compound Mg 5(OH) 5•CO 3 on the surface within the first 24 h exposure of the surface. After 500 h SO 2 salt fog exposure, the magnesium carbonates are replaced by a more dense magnesium hydroxide Mg(OH) 2 (brucite). However, during this time the aluminium remains cathodically corrosion protected. For exposure times > 1,300 h, the primer fails and hexahydrite MgSO 4 6H 20 is formed on the surface. Corrosion protection: Mg-rich primers are a potential alternative for local chromate conversion coating applications and R&D for the use of Mg-rich primers is ongoing for potential replacement of some conversion coating applications on aluminium alloys. Standard filiform corrosion tests and salt spray tests are satisfatory but more studies, especially on the long-term stability (for example by Crevice corrosion and cyclic testing) need to be performed. Apart from many studies conducted academically, Mg-rich primers are also currently a subject of research in the aerospace industry as potential alternatives to primer/paint systems (not part of this dossier). Compatibility with substrate: With regard to the substrate, Mg-rich primers might also be used for other substrates such as titanium alloys, steel, CRES and CFRP or on chromate-free anodized surfaces, but the process mechanism has to be further investigated. From the first initial results, Mg rich primers are an promising alternative in relation to the topcoat, but the performance may decrease with the generation of oxides Mg(OH) 2. Therefore, further R&D is necessary to investigate long term stabilities and degradation modes of the primer.
Corrosion resistance Compatibility with substrate
7.1.11.3 Economic feasibility Against the background of significant technical failure of this alternative, no detailed analysis of economic feasibility was conducted. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible.
7.1.11.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 3.1.11), in a worst case they are classified as Flam. Liq. 3, Skin Irrit. 2, Eye Irrit. 2, Skin Sens. 1, Aquatic Chronic 2, Acute Tox. 4, Asp. Tox. 1. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.1.11.5 Availability (R&D status, timeline until qualification / certification) Mg rich primers are commercially available as paint/primer systems. A first Mg rich primer formulation was marketed recently. It is an Mg-rich corrosion inhibiting chromium-free epoxy primer. It has to be stated that, while the detailed composition of this formulation constitutes confidential business information and is not known, the primer contains “VOC exempt solvents”
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(Volatile Organic Carbons = halogenated hydrocarbons) which might not comply with national law (e.g. BImSchV) or EU regulation. Furthermore, the North Dakota State University Research Foundation (NDSU/RF) announced in January 2014 that it has concluded a license agreement with the paint manufacturer. The licensing agreement gives the paint manufacturer exclusive rights in marine and automotive markets to further develop and commercialise the patented coatings technology developed at NDSU. The magnesium-rich technology will be used in primers marketed to both the military and civilian automotive and shipbuilding industries. The products are designed to be applied over chromium-free pre-treatments or bare metal, eliminating Cr(VI) entirely from the coating system. Hence, currently no alternative is on the market, which meets the requirements from the aerospace industry. R&D for primer applications is at low maturity but already reached TRL stage for some applications.
7.1.11.6 Conclusion on suitability and availability for magnesium-rich primers Taking all R&D efforts and the first products on the market into account, it can be stated that Mg rich primers are already qualified for some military purposes (without resistivity as requirement) and might be also used in other sectors (automotive or marine). For the civil aerospace sector, the development is at very early laboratory scale. Test results on Mg rich primers provide promising corrosion protection but the long-term stability has not been assessed yet. In summary, to date Mg-rich primers are not an alternative to the current systems in the civil aerospace sector, but represent an alternative which is currently under investigation at the laboratory scale and at an early stage of R&D. For the majority of applications, a TRL was yet not defined. Therefore, at least 12-15 years are necessary until these alternatives may be fully implemented into the supply chain.
7.1.12. ALTERNATIVE 12: Electrolytic paint technology
7.1.12.1 Substance ID and properties In the electrocoating, or electrodeposition process metal parts are dipped after pre-treatment into an electrically charged tank of coating formulation. Electrical current is used to apply the coating to a conductive substrate via anodic or cathodic deposition (see Figure 22 ).
Figure 22: Electrodeposition process, cathodic and anodic deposition (Pawlik, 2009).
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Within the military sector, the cathodic electrocoat deposition process is applicable for the deposition of positively or negatively charged paint particles (depending on the substrate and application). After coating, the metal part is moved to the rinse stages. In the final step the coated metal parts are thermally cured (30 minutes at 93 °C) to achieve the final coating properties. Curing parameters (time and temperature) can vary according to the substrate, the coated surface, the part thickness and other parameters. According to the supplier, “the electrocoat process can be fully automated and offers increased material utilisation”. A schematic overview of the components of an electrocoat conveyor process can be found in Figure 23 .
Figure 23: Components of an electrocoat conveyor process (Pawlik, 2009). The substance identity and composition of the electrocoating formulation used in the process is not known as this is proprietary to the supplier. Therefore, only limited information on the risk to human health and environment from this alternative is provided in Appendix 3.1.12.
7.1.12.2 Technical feasibility Electrolytic paint is under investigation as an alternative for chromate conversion coatings on the substrates according to Table 22 :
Table 22 Sodium dichromate-based surface treatments where electrolytic paint may be an alternative.
Surface treatment Substrate / coating
Chromate Conversion Coating + primer Aluminium and alloys, Mg, Ti
Chromate Conversion Coating + primer General assessment: This alternative treatment is investigated to replace the combination "chromate conversion + primer" (when it is applied with a thickness of 12 to 20 µm). The performance results which are reported in the following paragraphs are determined within the framework of testing for the military sector. In this sector, some chromate-free coatings must fulfil specific military standards such as MIL-PRF-85582 class N, which are not comparable to the requirements of the civil aerospace industry. Therefore, coatings developed for military purposes are not directly applicable for the general structure for civil aircrafts, as the frequency of military planes is very low compared to civil planes running on a daily basis, as well as considerations related to the systems and performance envelope of military aircrafts. Based on these daily demands to ensure the airworthiness of civil aircrafts, the requirements are much more comprehensive.
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Data from literature assumed that key performance criteria were met for military applications (corrosion, adhesion, flexibility, chemical resistance against different fluids) on Al alloys 2024 and 7075 (Pawlik, 2009). Results of beach exposure testing on corrosion performance are still ongoing (Lingenfelter, 2012). Data on corrosion performance is currently inconsistent. Corrosion resistance: Tests according to ASTM B117 and EN3665 revealed an insufficient corrosion performance on Al alloys with length from scratch exceeding 3 mm after 3000 h and 720 h, respectively. In contrast, another research program reported average length of blisters at the scratch is 1 mm on clad 2024-T3 and 0.25 mm on bare 2024-T3 (Collinet et al, 2012) after 3000 h exposure in the filiform corrosion test (EN 3665) and the neutral salt spray test (ISO 9227). After 6000 h in the neutral salt spray test, results still meet the standard civil aviation requirements. The system does not provide active corrosion inhibition and is as such no replacement for parts that need corrosion protection including active corrosion inhibition. However, when the aerospace industry shared their experience on this new application, their view is not consistent with the current research programs. First results from the aerospace/helicopters sector (civil and military) for corrosion resistance after beach exposure (atmospheric corrosion) and accelerated aging have shown lower performances than reference (chromate conversion coating + Cr(VI) primer). Further extended tests will be applied to assess the long-term performance of the electrocoat systems. Adhesion properties: While in general few issues on adhesion were reported, it has also been noted that electrocoats showed insufficient adherence with various sealants used. Here, adhesion enhancer would be needed. Further tests are needed to improve the performance on this requirement. Other parameter: It was also indicated that higher performances of the electrocoat systems in terms of bending, scratch resistance and corrosion resistance after salt spray exposure compared to reference systems were achieved. It is reported that the electrocoat primer is also applicable for complex-shaped parts and can be coated uniformly. In contrast to the information above, this process is not suitable for assembled aircraft. A major drawback of this treatment is that as it is a dip coating process, it can only be applied to OEM and MRO parts that can be removed from the aircraft during overhaul. Difficulties were also observed with electrocoat stripping, as it has to be carefully evaluated which products are suitable for this process. Indeed, this technology requires development of a new repair and touch-up process. Therefore, another limitation of this process is that electrocoated parts can currently only be repaired by using conventional Cr(VI)-containing anti-corrosive primers. Conclusion : In conclusion, it was confirmed that with this alternative, the current aerospace standards cannot be completely met (especially for conductive requirement, and touch-up & repair process). The produced layers are not conductive and as stated above repairing processes have to be redefined.
Corrosion Active Chemical MRO Complex resistance corrosion Adhesion resistance applications geometries (long term) inhibition
7.1.12.3 Economic feasibility
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Against the background of significant technical failure of these alternate systems, no detailed analysis of economic feasibility was conducted. Life cycle costs have not been established. There is an initial capital requirement for the baths. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible.
7.1.12.4 Reduction of overall risk due to transition to the alternative The substance identity and composition of the electrocoating formulation used in the process is not known as this is proprietary to the supplier. The classification of a commercial product was reported by the supplier during the consultation as Eye Irrit. 2, and Aquatic Chronic 3 as well as Skin Irrit. 2, respectively. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.1.12.5 Availability (R&D status, timeline until qualification / certification) The electrolytic technology has originally been developed for the automotive industry and is currently being adapted to fulfil the requirements of other sectors. A first product was commercially launched in 2012 and is qualified to SAE International’s Aerospace Material Specification (AMS) 3144 for anodic electrodeposition primer for aircraft applications (publically available information as of January 2014). SAE International is a global association of technical experts in the aerospace and automotive industries. Their documents serve as recommendations for the transportation sector mainly within the US and Canada but do not carry any legal force. Within the aerospace industry in the EU, R&D efforts have been ongoing for many years, however so far these systems have not passed the early development phase.
7.1.12.6 Conclusion on suitability and availability for electrolytic paint technology A chromium trioxide-free electrocoat system is available on the market and currently qualified according to AMS 3144. While the overall performance might be sufficient for the military sector, this coating system is not yet generally qualified for civil aerospace. Here, the daily demands, especially with regard to extended corrosion performance are much more comprehensive to ensure the airworthiness of civil aircraft. Further technical limitations were highlighted during the consultation phase. Most importantly, this process is not suitable on non- or partly painted parts, which in some cases represent a significant amount of parts in an aircraft. Furthermore, this process is not applicable for complex geometry parts and assembled aircraft and requires additional works to develop a repair & touch-up process. In summary, electrocoating systems show some important technical limitations which clearly do not qualify them to be a general alternative to chromate conversion coating + primer so far. Since these systems are in early research stages at the aerospace industry (no TRL defined yet), for substitution of the sodium dichromate and to necessarily overcome the existing hurdles, at least 15 years are anticipated until implementation of the alternative products into the supply chain.
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7.1.13. ALTERNATIVE 13: Zinc-nickel electroplating
7.1.13.1 Substance ID and properties Electroplating with a zinc-nickel electrolyte forms metallic coatings from zinc and nickel on the plated substrate (steel) by using the substrate as cathode and an anode and inducing an electrical current. A number of different zinc electroplating types are commercially available and used, these are - acid zinc type electroplating using aqueous soluble zinc salts, such as zinc sulphate, zinc chloride or zinc acetate with sodium hydroxide or potassium hydroxide as conducting salts, - alkaline zinc electroplating, and - cyanide zinc electroplating.
With regard to the below described application, a commercially available alkaline zinc-nickel electroplating solution is evaluated. As the distinct composition is confidential business information, only general information on a typically used zinc compound, a typically used nickel compound and the risk to human health and environment can be provided in Appendix 3.1.13.
7.1.13.2 Technical feasibility Zinc-nickel electroplated coatings are evaluated as alternative for the sodium dichromate-based passivation of cadmium plated coatings (metallic coatings) on steel. In this regard, the alternative would not only replace the passivation step, but also the cadmium plating (Table 23 ).
Table 23: Sodium dichromate-based surface treatment processes where Zinc-Nickel electroplating may be an alternative.
Surface treatment Substrate / coating
Passivation of metallic coatings Steel with cadmium coating
Passivation of metallic coatings Corrosion resistance : It was stated during the consultation that the corrosion resistance of the alternative coating is not sufficient. Chemical resistance: As stated during the consultation, the chemical resistance of the alternative was found to be at least equivalent to Cd coating plus Cr(VI) passivation. Resistivity : The coating does not provide adequate conductive properties at the current stage of R&D and the alternative is not industrially implemented in the supply chain. Fastener applications with lubricant properties as functionality need to be foreseen with an additional lubricant coating on top of the Zinc-Nickel plating. This lubricant coating is not conductive. Therefore, in comparison to a Cr(VI) passivated Cd coating, the alternative coating will be problematic for metallisation applications. Adhesion to subsequent layer : The adhesive properties of the alternative was found to be equivalent compared to a Cr(VI) passivated Cd coating. Layer thickness : As stated during the consolation, the layer thickness of the Zn-Ni-alternative is equivalent to Cr(VI) passivated Cd coating.
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Repair/Touch-up capability: The current treatment of Cd coatings with a Cr(VI) passivation provides a direct touch-up possibility in cases where the cadmium plating thickness does not conform (less than minimum) just after plating by adding cadmium and re-immersing the parts. This touch-up possibility is currently not possible with zinc-nickel bath and R&D studies are in progress to deal with this problem. Conclusion : Zinc-nickel electroplating as alternative to replace Cd coatings and the subsequent Cr(VI) passivation is in the process of evaluation, but at the current stage is not technical feasible. More evaluation tests are needed for these solutions in order to be able to substitute cadmium plating by zinc-nickel plating, notably on metallisation problems and on immersion touch-up. Clearly, for most applications within the aerospace sector, this alternative will not become a realistic substitution as sufficient corrosion resistance will rather be achieved without an additional passivation step.
Corrosion Chemical Repair Adhesion Layer thickness Resistivity resistance resistance capabilities
7.1.13.3 Economic feasibility Against the background of significant technical failure of these alternate systems, no detailed analysis of economic feasibility was conducted. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible. This solution need a more often and stricter chemical following (more maintenance), the bath is more expensive and has a shorter lifetime compared to the Cd plating plus Cr(VI) passivation bath. At the moment, zinc-nickel-electroplating is a specific treatment but it is not deployed in the aerospace supply chain, and so would generally induce increased costs (e.g. for standard parts like fasteners).
7.1.13.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Mixtures that include nickel compounds and nickel metal as stated in Appendix 3.1.13 are listed by IARC as a Group 1 chemical with sufficient evidence for mixtures that include nickel compounds and nickel metal of carcinogenicity in humans (IARC Monographs 100C). Based on the available information on the substances used within this alternative (see Appendix 3.1.13), nickel fluoride (as exemplary nickel substance) would be the worst case with a classification as Carc. 1A, Muta. 2, Repr. 1B, STOT RE 1, Resp. Sens. 1, Skin Sens. 1, Aquatic Acute 1 and Aquatic Chronic 1. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances. However, as the alternate substance used is classified as mutagenic, the replacement must be carefully evaluated on a case by case basis
7.1.13.5 Availability (R&D status, timeline until qualification / certification) R&D efforts on this alternative are well progressed in comparison with other alternatives. But some issues remain; for example, a solution for metallisation, and immersion touch-up possibility. Some initial applications are beginning to be applied for specific parts on new programs. However, the alternative is not yet implemented in the aerospace supply chain.
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7.1.13.6 Conclusion on suitability and availability for zinc-nickel electroplating Zinc-nickel electroplating as alternative to Cd coatings plus Cr(VI) passivation is under evaluation, and might be suitable for some applications in new programs. Technical issues such as insufficient corrosion performance or conductivity need to be addressed. Furthermore, nickel components in the plating solution are classified as CMR substances. In summary, Zinc-nickel electroplating shows some major technical limitations which clearly does not qualify the application to be a general alternative to Cr(VI)-based coating systems so far. Following the technical assessment, the relevance of this applications as general alternative is questionable, as sufficient performance for most applications will not be achieved without a subsequent passivation step. Since these systems are in early research stages (no TRL defined yet), for substitution of Cr(VI)-based treatments at least 15 years are necessary to pass the approval process of the aerospace sector until implementation into the supply chain.
7.2. Pre treatments After several alternatives for the main surface treatment have been assessed in the former chapters, the following chapters concentrate on alternatives for the pre-treatments like, etching, pickling, deoxidizing, and stripping. As already stated in chapter 3.2, only the combination of processes applied in sequence (pre- treatment, main process step and post-treatment) is able to provide the coating as required. Although the single process steps can be assessed individually, they are not stand-alone processes but part of a process chain or process flow and for the assessment of sodium dichromate alternatives, the whole process chain has to be taken into account. At the current stage, only the combination of processes applied in sequence (pre-treatment, main process step and post-treatment) is able to provide the coating as required. Although the single process steps can be assessed individually, they are not stand-alone processes but part of a process chain or process flow.
7.2.1. Inorganic acids
7.2.1.1 Substance ID and properties A variety of inorganic acids is currently under evaluation as alternatives to Cr(VI) in surface pre- treatment processes. Research currently focuses on sulphuric acid, phosphoric acid, nitric acid and a mixture of sulphuric acid, nitric acid, and ferric ions from iron sulphate (named “sulfonitroferric acid”).
An overview of general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.2.1.
7.2.1.2 Technical feasibility Table 24 summarizes the sodium dichromate-based surface pre-treatment processes where inorganic acids may be an alternative: Table 24 : Overview on the replacement substances used in the different pre-treatment processes.
Surface treatment Substrate / coating Alternative
Aluminium and aluminium Mixture of sulphuric acid, nitric acid, and ferric ions Pickling/Etching alloys, steel, copper, brass (“sulfonitroferric acid”)
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Surface treatment Substrate / coating Alternative
Steel Mineral acids, electrolytic pickling
Aluminium and aluminium Mixture of sulphuric acid, nitric acid, and ferric ions Deoxidising alloys, (“sulfonitroferric acid”) Stripping of organic and Aluminium and aluminium Mixture of sulphuric acid, nitric acid, and ferric ions inorganic finishes alloys (“sulfonitroferric acid”)
Pickling/etching – pickling/etching of metal surfaces (e.g. aluminium alloys, copper, brass) General assessment: For metallic substrates such as aluminium alloys, alternatives based on either nitric acid, sulphuric acid, phosphoric acid or combinations together with ferrous ions from iron sulphate (sulfoferric, sulfonitroferric) are in the developmental stage. With this treatment, moderate oxide removal can be performed. This pickling/etching solutions are significantly more aggressive than the Cr(VI)-based one, causing higher degrees of end grain pitting and intergranular attacks. For moderate cleaning purposes, a less aggressive solution is needed. Compared to pre-treatments on steel, where surface characteristics for subsequent bonding are the most critical requirement, the surface preparation of Al and its alloys includes other issues. The treatments applied for preparation of aluminium surfaces currently involve multiple steps containing sodium dichromate, as described in the introduction. Generally, the performance of the subsequent treatments after pickling/etching is strongly linked to the, robust and validated, combination of pre-treatment processes, and to the type / chemical composition of the Al alloy being processed. A mixture of “sulfonitroferric acid” is already qualified and implemented for surface preparation prior CAA, TSA, SAA, PSA and chromate conversion coating on aluminium alloys for some specific applications in some parts of the aerospace sector. It is approved prior to fusion welding, prior to brazing, and for removal of foreign metal contamination. Alkaline etching with sodium hydroxide containing additives, and acid etching with solutions of nitric acid containing fluoride from hydrofluoric acid or ammonium bifluoride are acceptable alternatives to Cr(VI)-based etching solutions used for aluminium, and alkaline etching is preferred for etching aluminium alloys. These substances cannot currently be seen as general alternatives but are only suitable on some metal alloys or for some applications. It was stated during the consultation, that these solutions are not suitable for removal of welding and brazing flux. They are clearly not suitable for localized repairs and to steel substrates. For other substrates, such as copper or brass, phosphoric and fluoride acid solution can be added for the heavy oxides removal, and this solutions may become technical feasible after further development. For Al alloys, this treatment is not adequate, due to the comparatively more aggressive character, as explained in the first paragraph. Process development and Compatibility: Some of the newly developed and partly implemented alternatives are already in use for some applications within the aerospace industry. Importantly, these alternatives do not prepare the surface equivalent to sodium dichromate-based processes. As a consequence, extensive analysis and adjustments of the whole process chain had to be performed until these products were approved. The main issue is that measurable parameters rarely exist for the performance of the pre-treatment alone, so that standard tests mainly have to be performed on the final coating. At this stage, it is very challenging to evaluate which part of the process chain is influencing the surface characteristics of the final coating. Taking all the different applications and alloys used in the aerospace industry into account, it must be stated that substantial efforts are still
Use number: 2 95 ANALYSIS OF ALTERNATIVES needed to implement and adjust the existing pre-treatment chain to the chrome-free alternatives, in order to meet the specifications of the aerospace industry. In summary, implementation of alternative pre-treatments is highly complex and depends on multiple factors. As the pre-treatment steps are all linked to each other and to the performance of the final coating, new processes have to be analysed with regard to potential reaction by-products or impurities influencing subsequent steps or different surface characteristics derived from alternative pre-treatments.
Pickling/etching – pickling of steel General assessment: During the consultation phase it was stated that R&D is ongoing for the use of mineral acids as alternative to pickling of steels with Cr(VI). The pickling of stainless steel with a mixture of nitric acid and hydrofluoric acid is used as a standard process within the aerospace industry, the same applies for pickling of low alloy steels with different mineral acid-based solutions. Currently these alternatives cannot be used for low alloy steels, as the main criteria for these pre-treatments, a sufficiently prepared surface for optimal adhesion of the subsequent layers, is not fulfilled. Additional R&D is necessary to develop appropriate replacement solutions. For pickling before bonding of stainless steels, besides sulphuric acid, also electrolytic pickling can be applied. Here, the metal substrate is the cathode (or the anode, depending on the steel type and exact process) in an electrolytic cell containing a strong acidic solution, such as sulphuric acid. During the consultation phase the aerospace sector stated that lab-scale testing demonstrated the technical feasibility of the process step for pickling of stainless steel prior to bonding with sodium dichromate free solutions, but the need for further chromate-based pre-treatments is still present. Industrial up-scale to demonstrate the suitability of the chromate-free process chain still has to be conducted. In conclusion, neither sulphuric acid pickling of steel before bonding, nor electrolytic pickling are currently alternatives to sodium dichromate-based pickling pre-treatment processes but the alternatives have shown their technical feasibility in lab-scale testing and further R&D has to be performed.
Deoxidising General assessment: Current R&D studies revealed mineral acid-based deoxidiser solutions as potential alternative for special applications within the aerospace sector. As previously stated, a mixture of “sulfonitroferric acid” is already qualified and implemented for surface preparation prior to CAA, TSA, SAA, PSA and chromate conversion coating on aluminium alloys for some specific applications in some parts of the aerospace sector. The deoxidising causes a dissolution of aluminium oxides, which is in line with specifications from the aerospace sector. Furthermore, visual inspection of the appearance of the deoxidised surface (after rinsing) revealed a water break free surface without streaks or discolorations. End grain pitting and intergranular attack: This parameter is within the required ranges for some sectors, but experience in other sectors indicates that failures periodically occur with aged solutions. This can require premature disposal of deoxidising solutions and result in unplanned downtime and possible rework in the processing facility is also within the required ranges. Corrosion resistance: It was stated during the consultation, that these alternatives are within the required ranges for some applications but do not meet the requirements for corrosion protection, when used prior to sealed anodize or conversion coating. Corrosion resistance failures occur intermittently with aged solutions in these applications. This can require premature disposal of deoxidising solutions and result in unplanned downtime and possible rework in the processing facility. When corrosion protection is not a requirement (e.g. as pre-penetrant etching/desmutting
96 Use number: 2 ANALYSIS OF ALTERNATIVES and deoxidizing prior to unsealed anodizing), this solution might be used as alternative to sodium dichromate-based deoxidisers and as stated during consultation, is already implemented for parts of the aerospace sector. Process development and Compatibility: As for alternatives to pickling/etching, the same limitations and concerns apply for the implementation of alternative deoxidizing solutions. As mentioned, some of the newly developed and partly implemented alternatives are already in use for some applications within the aerospace industry. Importantly, these alternatives do not prepare the surface equivalent to sodium dichromate-based processes. As a consequence, extensive analysis and adjustments of the whole process chain had to be performed until these products were approved. The main issue is that measurable parameters rarely exist for the performance of the pre-treatment alone, so standard tests have to be performed mainly on the final coating. At this stage, it is very challenging to evaluate which part of the process chain influences the surface characteristics of the final coating. Taking all the different applications and alloys used in the aerospace industry into account, it must be stated that substantial efforts are still needed to implement and adjust the existing pre-treatment chain to the chrome-free alternatives, in order to meet the specifications of the aerospace industry. As reported during the consultation, for localized repair applications on Aluminium alloys, currently no alternatives to Cr(VI)-based-deoxidizing solutions are available. In summary, the proposed solutions are not suitable as general alternative but can only be used for specific applications (e.g. heavy duty deoxidising) where no corrosion resistance is required. They are not approved for many other applications such as deoxidising of cast and welded parts or light duty deoxidising. Most importantly, these solutions are not generally suitable for adequate surface preparation prior conversion coating on Al alloys where corrosion resistance is a requirement.
Stripping of organic and inorganic finishes It was stated during the consultation phase that for each kind of inorganic finish, such as hard anodic coatings and conventional anodic coatings, spray coatings and conversion coatings, individual stripping alternatives have to be developed, while the current Cr(VI)-based stripping can be used for all substrates and inorganic finishes without differentiation. For some applications on external metallic and customized surfaces on Al alloys, stripping alternatives based on benzyl alcohol (with or without acid, and / or peroxide), or solutions with formic acid are qualified and used. However, for other applications (like landing gear made from e.g. high strength steels, titanium alloys), these products are currently not suitable. General assessment: Current R&D studies revealed a mineral acid-based solution of sulphuric acid and nitric acid with iron sulphate as a potential alternative for the stripping of conversion coatings and anodic coatings from aluminium alloys (but clearly not for the above mentioned hard anodic and thermal spray coatings). These solutions are stated to meet the requirements in general, but with severe limitations. Key parameters: With regard to residual stress, the alternative solutions potentially etch the surface of the parts which can then cause residual stress. A short immersion time of the material to be stripped has to be guaranteed, this is required to avoid impacting residual stress, surface roughness or causing intergranular attack, which can affect the fatigue properties. The short immersion time is also necessary to avoid excessive removal of base material. The corrosion requirements are clearly not met for assemblies with dissimilar metal components. In helicopters, a lot of different metals (mainly Al alloys and steel types) are assembled and the stripping of paint process with sodium dichromate-free alternatives must be adapted to each individual metal. On an assembled helicopter or airplane, it is not possible to clearly differentiate between the individual metals and therefore,
Use number: 2 97 ANALYSIS OF ALTERNATIVES alternative stripping methods would get in contact with materials they are not suitable for. This would increase the risk for galvanic corrosion between the different metals. Besides high strength steel components, (for which the alternative is not applicable in general), other sensitive parts such as windows, pilot tubes, doors, access ports, tires, landing gears, and wheel areas have to be protected prior to the application of the stripping alternative. From a safety point of view, it may be considered that for solutions containing peroxydes severe chemical reaction can take place when the process is not properly controlled. For steel substrates, iron can be dissolved from the metal which may lead to explosive decomposition of Hydrogen peroxide.
In conclusion, these solutions may be technically feasible for some applications but are limited to stripping of conversion coatings and anodic coatings from aluminium alloys, when the respective process control and short immersion time is guaranteed. Nevertheless, it is not a general stripping alternative for the large variety of inorganic coatings and substrates and therefore not technically feasible as general alternative for stripping of inorganic finish within this use. As reported during the consultation, for localized repair applications, currently no alternatives to sodium dichromate- based-stripping solutions are available.
7.2.1.3 Economic feasibility The pickling/etching of stainless steel with a mixture of nitric acid and hydrofluoric acid is used as a standard process within the aerospace industry, but cannot be used for all kind of stainless steel. The final process controls are not yet developed, the economic impact of e.g. complex process control, process changes for different kind of stainless steels to be treated cannot be assessed at the current stage. It was stated during the consultation phase that electrolytic pickling is expected to be more expensive than sodium dichromate-based pickling processes when considering investments needed. The economic feasibility of pickling/etching with sulfonitroferric acid was not assessed in detail, as the alternative is not qualified throughout the whole aerospace sector. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible. Nevertheless, as pickling/etching is at the current stage generally performed in line with the main process step in a way that the pre-treatment and main process are not separated from each other, additional investment costs are expected when separated process steps have to be installed. Against the background of significant technical failure of this alternative, no detailed analysis of economic feasibility was conducted for mineral acid-based deoxidizing and stripping of inorganic finishes alternatives. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible. Nevertheless, with regard to the stripping application, a variety of individual chromate-free stripping processes need to be qualified and implemented instead of one sodium dichromate-based process.
7.2.1.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 3.2.1), nitric acid would be the worst case with a classification as Ox. Liq. 3, Skin Corr. 1A, Met. Corr. 1, Skin Irrit. 2, Eye Dam. 1, STOT SE 3. As such, transition from sodium
98 Use number: 2 ANALYSIS OF ALTERNATIVES dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.2.1.5 Availability Several alternatives based on mineral acids (e.g. nitric acid in combination with hydrofluoric acid) are available for pickling/etching of several types of steel. Some of the newly developed and partly implemented alternatives are already in use for some applications within the aerospace industry. As stated, these alternatives do not prepare the surface equivalent to the sodium dichromate-based processes. As a consequence, extensive analysis and adjustments of the whole process chain had to be performed until these products were approved. The main issue is that measurable parameters rarely exist for the performance of the pre-treatment alone, so standard tests have to be performed mainly on the final coating. At this stage, it is very challenging to evaluate which part of the process chain influences the surface characteristics of the final coating. Taking all the different applications and alloys used in the aerospace industry into account, it must be stated that substantial R&D efforts are still needed to implement and adjust the existing pre-treatment chain to the chrome-free alternatives, in order to meet the specifications of the aerospace industry. For pickling/etching/deoxidizing development of further alternatives is in TRL 3-5. Etching alternatives are estimated to reach TRL 6 in 2018, with subsequent qualification and implementation into the supply chain as pre-treatment for all kind of applications. It was stated during the consultation, that R&D on the deoxidizing alternatives is ongoing and currently at TRL 3-5. It is not expected that the pre-treatment will become technically feasible as an overall replacement for sodium dichromate-based deoxidizing applications. Therefore, no timeline for qualification can be provided. It may become an alternative for special applications where no corrosion resistance is necessary. Further evaluation is necessary to complete evaluation and to incorporation the alternative in the specifications. A lot of R&D has been performed on alternatives for stripping of inorganic finish. It is noted that for each individual inorganic coating to be stripped, individual stripping alternatives have to be evaluated and additionally, different substrates have to be taken into account. As stated during the consultation, there is no generally accepted non-chrome alternative for the stripping of hard anodic coating from aluminium alloys and for the stripping of thermal spray coatings (aluminium oxide) from aluminium alloys at the current stage. Even though a R&D program was started in the 1990s, no alternative was found which meets the requirements such as hydrogen embrittlement, residual stress, surface roughness, fatigue, intergranular attack and end grain pitting, substrate temperature and impact to shot peen compressive layer. Latest R&D studies revealed that mineral acid-based solutions as a potential alternative for the stripping of conversion coatings and anodic coatings from aluminium alloys (but not for the above mentioned hard anodic and thermal spray coatings). It was stated that these solutions can meet the requirements in general, but with severe limitations affecting the processing. Therefore, they are not a general alternative for the wide variety of different inorganic finishes where stripping is required and necessary. With regard to the aerospace sector and taking the different assemblies combining a large variety of metal substrates, types of alloys and coating possibility on an aircraft into account, mineral acid- based solutions are at the current stage not viable as a general alternative to sodium dichromate- based stripping of inorganic finish.
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7.2.1.6 Conclusion on suitability and availability for inorganic acids In summary, for pickling/etching of steel as pre-treatment processes, alternatives for some applications are technically feasible, while currently no general acceptable replacement exists. For some steels and other substrates, development is currently of low maturity. For sodium dichromate- free pickling/etching pre-treatment on aluminium and its alloys, a mixture of sulphuric acid, nitric acid, and ferric ions are commercially available, qualified and in use for some anodizing applications on Al alloys. Since the alternative is technically not yet equivalent to the current process, further R&D is necessary. For localized repairs on anodized layers, the etching step needs to be adapted to each Al-alloy. As a consequence, further development on sodium dichromate-free etching/pickling pre-treatment is necessary before the alternative become broadly deployed throughout the whole aerospace sector, especially as any change of pre-treatment carefully has to be adapted to the subsequent process. Although certain pre-treatments may already be used within the aerospace sector, these are part of a process chain and at the current stage, a Cr(VI) containing subsequent treatment has to be applied to fulfil the respective demands of the aerospace sector. Currently, no complete chromate free process chain is industrially available providing all the required properties to the surfaces for all applications.
Technical feasibility Economic feasibility Risk reduction Availability
Qualified for specific Qualified for specific applications in some applications in some parts of parts of the aerospace the aerospace sector sector
7.2.2. Hydrogen peroxide activated benzyl alcohol (with acid)
7.2.2.1 Substance ID and properties
Hydrogen peroxide (H 2O2) is activating the benzyl alcohol, which can be mixed with acids for enhanced properties. This mixture can then be used for the stripping of organic coatings from different kind of substrates. An overview on general information on substances used within this alternative and the risk to human health and the environment is provided in Appendix 3.2.2.
7.2.2.2 Technical feasibility The alternative solution is under investigation for stripping of paint according to Table 25 :
Table 25: Sodium dichromate-based pre-treatment where hydrogen peroxide activated benzyl alcohol with acids may be an alternative.
Surface treatment Substrate / coating Alternative
Aluminium and aluminium Stripping of inorganic alloys, steel (CRES), Hydrogen peroxide activated benzyl alcohol with acid coatings (paint) nickel/cobalt alloys, Ti, Mg
General assessment: The general problem in replacing Cr(VI) in stripping of paint is, that the chromate-based stripping can be used for all substrates and all kind of paints, while experience from current research shows that it is not realistic that an alternative is able to cover all applications
100 Use number: 2 ANALYSIS OF ALTERNATIVES within the aerospace sector. Certainly, the sodium dichromate-free alternatives need to be adapted individually on the substrate and specific paint. As a consequence, extensive analysis and adjustments have to be performed until alternative products for all the different applications and alloys used in the aerospace industry will be tested and approved. Therefore the benzyl alcohol containing alternatives (with and without acid) are only qualified and used for specific parts within the aerospace sector. If the whole external metallic surface of an aircraft has to be considered including landing gear made from high strength steels – and not only customized surfaces like the fuselage which are mainly from aluminium alloys - the alternative is not suitable as technical issues are faced (galvanic corrosion).. This alternative was tested for various substrates, such as aluminium, steel, CRES, Ni/Co alloys, titanium and magnesium. For some key parameters such as adhesion, residual stress, surface roughness and substrate temperature, the requirements are stated to be met within the aerospace sector. For the limitation of cracks and clad penetration, the alternative can also meet the requirements, but only with restrictions on the dwell time. In general, this makes the process control very difficult and complex and affects the reproducibility. The alternative stripping solution shows technical issues depending on the substrate and is therefore not applicable on all kinds of parts where stripping is required. Hydrogen embrittlement: Most importantly, the alternative has to meet the specifications regarding hydrogen embrittlement when applied on high strength steels. This substrate is often used especially for helicopters in the aerospace industry and commercial aircraft landing gear. Different statements were made on this parameter during the consultation and it is considered a highly critical parameter whose performance is dependent on the respective, company specific recommendations and applications. Corrosion resistance: The corrosion requirements are clearly not met for assemblies with dissimilar metal components. In helicopters, many different metals (mainly Al alloys and steel types) are assembled. In this case, the process of paint stripping with sodium dichromate-free alternatives must be adapted to each individual metal. On an assembled helicopter or airplane, it is not possible to clearly differentiate between the individual metals and therefore, alternative stripping methods would contact with materials that they are not suitable for. This would increase the risk for galvanic corrosion between the different metals. Additional to high strength steel components, for which the alternative is not applicable in general, other sensitive parts such as doors, access ports, tires, landing gears would have to be protected prior to the application of the stripping alternative.
7.2.2.3 Economic feasibility Against the background of technical failure of this alternative, no detailed analysis of economic feasibility was conducted. However, based on the literature research and consultations there is no indication that the discussed alternative is not economically feasible. As it is not foreseen that an equivalent 1:1 replacement for Cr(VI) will be available, a variety of individual chromate-free paint stripping processes would be needed instead of one sodium dichromate-based process, which will significantly increase the costs for these processes.
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7.2.2.4 Reduction of overall risk due to transition to the alternative As the alternative is not technically feasible, only classification and labelling information of substances and products reported during the consultation were reviewed for comparison of the hazard profile. Based on the available information on the substances used within this alternative (see Appendix 3.2.2), hydrogen peroxide would be the worst case with a classification as Ox. Liqu.1, Acute Tox. 4, Skin Corr. 1A, Eye Dam.1, STOT SE 3, Met. Corr. 1. As such, transition from sodium dichromate (CAS 7789-12-0, EC 234-190-3) – which is a non-threshold carcinogen – to one of these substances would constitute a shift to less hazardous substances.
7.2.2.5 Availability (R&D status, timeline until qualification / certification) Hydrogen peroxide activated paint strippers are commercially available and are specified for distinct purposes. It was stated during the consultation, that R&D on the hydrogen peroxide activated benzyl alcohol with acid alternative is ongoing and currently at TRL 3-5 (for some companies), as this is expected to be the most promising alternative to replace the specific applications at the current stage. It is not expected that an alternative will become technically feasible as an overall replacement for sodium dichromate-based paint stripping applications as it is not suitable for assemblies with dissimilar metals. In regard to aircraft that are assembled with a large variety of different metal substrates, the stripping of paint for repair and maintenance applications would be extremely difficult.
7.2.2.6 Conclusion on suitability and availability for hydrogen peroxide activated benzyl alcohol with acid The evaluated sodium dichromate-free stripping of paint alternative is not technically feasible for all applications but it is already used for the paint stripping of fuselage. Therefore, using an alternative method for paint stripping would only replace special applications and purposes and is not a general alternative. In regard to aircraft that are assembled with a large variety of different metal substrates, the stripping of paint for repair and maintenance applications would be extremely difficult.
Technical feasibility Economic feasibility Risk reduction Availability
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8. OVERALL CONCLUSIONS ON SUITABILITYAND AVAILABILITY OF POSSIBLE ALTERNATIVES For this Application for Authorisation, an extensive literature survey and consultation with aerospace industry experts was carried out to identify and evaluate potential alternatives to surface treatments of metals with sodium dichromate such as aluminium, steel, zinc, magnesium, titanium, alloys, composites, sealings of anodic films. Sodium dichromate-based surface treatments are specified in the aerospace sector because they provide superior corrosion resistance and inhibition, improved paint adhesion, low electrical contact resistance and/or enhanced wear-resistance. These characteristics are essential to the safe operation and reliability (airworthiness) of aircraft and spacecraft which operate under extreme environmental conditions. These structures are extremely complex in design, containing millions of highly specified parts, many of which cannot be easily inspected, repaired or removed. Structural components (e.g. landing gear, fasteners) and engine parts on aircraft are particularly vulnerable to corrosion. Surface treatment processes typically involve numerous steps, often including several important pre-treatment and post-treatment steps as well as the main treatment process itself. These steps are almost always inter-related such that they cannot be separated or individually modified without impairing the overall process or performance of the treated product. This means that while the use of sodium dichromate (or a similar chromate) may be specified at different points in the process, it cannot be entirely replaced in the process without impacting the technical performance of the final article. The implications of this are important as chromate-free alternatives for some individual steps are available and used by industry. However, where this is the case, chromates are always specified in one of the other steps within the overall surface treatment system. This means it is imperative to consider the surface treatment system as a whole, rather than the step involving sodium dichromate on its own, when considering alternatives for such surface treatment systems. Furthermore, components that have been surface treated with sodium dichromate typically represent just one of many critical, inter-dependent elements of a component, assembly or system. In general, sodium dichromate-based surface treatment is specified as one element of a complex system with integrated, often critical performance criteria. Compatibility with and technical performance of the overall system are primary considerations of fundamental importance during material specification. A total of 46 potential alternatives for all parts of the process chain were identified and evaluated during the consultation. 32 of these substances could be excluded from further consideration based on inadequate performance and 15 potential or candidate alternatives (including processes and substances for all parts of the process chain) are a focus for ongoing research and development (R&D) programs and are examined in further detail in this report. Here, a candidate alternative is defined as a potential alternative provided to the aerospace manufacturer for evaluation following initial evaluation by the formulator.
While several potential alternatives to surface treatments with sodium dichromate , predominantly trivalent chromium and mineral acid-based systems, are being investigated, substrates and treatment steps, results so far do not support reliable conclusions regarding their performance as part of such complex systems, in demanding environments and real-world situations. These potential alternatives do not support all the properties of chromate-based surface treatment systems, and their long-term performance can currently only be estimated. Decreased corrosion protection performance would necessitate shorter inspection intervals, with a substantial impact on associated maintenance costs. In summary, the analysis shows there are no technically feasible alternatives to sodium dichromate-based surface treatment systems for key applications in the aerospace sector.
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Several potential alternatives are subject to ongoing R&D, but do not currently support the necessary combination of key functionalities to be considered technically feasible alternatives (refer to Table 26 below). Assuming a technically feasible potential alternative is identified as a result of ongoing R&D, extensive effort is needed beyond that point before it can be considered an alternative to sodium dichromate within the aerospace industry. Aircraft are one of the safest and securest means of transportation, despite having to perform in extreme environments for extended timeframes. This is the result of high regulatory standards and safety requirements. Performance specifications defined under EU Regulation No 216/2008 drives the choice of substances to be used either directly in the aircraft or during manufacturing and maintenance activities. It requires that all components, equipment, materials and processes incorporated in an aircraft must be qualified, certified, and industrialised before production can commence. This approval system robustly ensures new technology and manufacturing processes can be considered ‘mission ready’ through a series of well-defined steps only completed with the actual application of the technology in its final form (and under mission conditions). When a substance used in a material, process, component, or equipment needs to be changed, this extensive system must again be followed in order to comply with airworthiness requirements. The system for alternative development through qualification, certification, industrialization and implementation within the aviation sector is mirrored in the defence and space sectors. These approval steps can only proceed once a candidate alternative is identified. Referring to experience, it can take 20 to 25 years to identify and develop a new alternative, even assuming no drawbacks during the various stages of development of these alternatives. Experience over the last 30 years already shows this massively under-estimates the replacement time for chromate surface treatments.
Table 26 : Overview of key potential alternatives for main surface treatments.
Potential Alternative Technical failure
• Corrosion resistance not proved for the range of substrates Acidic surface treatments • Does not cover the broad range of different substrates in general • No reproducible results of corrosion resistance on all kind of Organometallics (zirconium and titanium- substrates based products, e.g. • No active corrosion inhibition fluorotitanic/fluorozirconic acids) • Adhesion of coating to substrate not sufficient • Corrosion requirements not met Molybdates and molybdenum-based • No active corrosion inhibition processes • No conductive coating (no resistivity) • Difficult process control • No stand-alone corrosion protection Silane/Siloxane and sol-gel coating • No conductive coating (resistivity not sufficient) • Limitations to geometry of parts (no complex parts) • Inconsistent corrosion results • Limited active corrosion inhibition Cr(III)-based surface treatments • Inconsistent adhesion (coating to substrate) results with poor quality reproducibility at current stage
Manganese-based processes • Corrosion resistance insufficient
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As a further consideration, while the implications of the development process in the aeronautic and aerospace sectors are clearly extremely demanding, specification of an alternative, once available, can be built into the detailed specification for new aircraft types (and new spacecraft). This is not the situation for existing aircraft types for which production and/or operation will still be ongoing. Production, maintenance and repair of these models must use the processes and substances already specified following the extensive approval process. Substitution of sodium dichromate-based surface treatment for these ‘legacy’ craft introduces yet another substantial challenge; re- certification of all relevant processes and materials. In practice, it will be impractical and uneconomical to introduce such changes for many such aircraft types. In this context, the scale and intensity of industry- and company- wide investment in R&D activity to identify alternatives to chromate surface treatment systems is very relevant to the findings of the AoA. Serious efforts to find replacements for chromates have been ongoing within the aerospace industry for over 30 years and there have been several major programs to investigate alternatives to chromates in the aerospace sector over the last 20 years. The current development status for alternatives for sodium dichromate is depicted in Figure 24 below.
Figure 24: Development status of alternatives. Pass. Steel: Passivation of stainless steel; Pass. MC: Passivation of metallic coatings. Category 1 alternatives in turquoise, Category 2 alternatives in red. It is important to note that the readiness levels are best case scenarios for single OEMs/applications only and do not reflect the general development status of the aerospace sector. A large amount of research over the last 30 years has been deployed to identify and develop viable alternatives to chromate-based surface treatment. Due to its unique functionalities and performance, it is challenging and complex to replace surface treatments based on sodium dichromate (or other chromates) in applications that demand superior performance for corrosion and/or adhesion to deliver safety over extended periods and extreme environmental conditions. Several potential alternatives to sodium dichromate, such as trivalent chromium and mineral acid based systems, are under investigation for the aerospace industry. However, based on experience and with reference to the status of R&D programs, alternatives are not foreseen to be commercially
Use number: 2 105 ANALYSIS OF ALTERNATIVES available for key applications in this sector for at least 10 or 15 years. As a result, a review period of 12 years was selected because it coincides with best case (optimistic) estimates by the aerospace industry of the schedule required to industrialise alternatives to sodium dichromate . Since the sunset date for sodium dichromate, is in 2017, the covered period of time runs from 2018 to 2030 (taking 2017 as a base year for calculations).
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Zhao, J., Xia, L., Sehgal, A., Lu, D., McCreery, R.L. and Frankel, G.S. (2001): Effects of chromate and chromate conversion coatings on corrosion of aluminium alloy 2024-T3. Surface and Coatings Technology 140: 51-57.
Use number: 2 109 ANALYSIS OF ALTERNATIVES
APPENDICES
110 Use number: 2 ANALYSIS OF ALTERNATIVES
APPENDIX 1 – JUSTIFICATIONS FOR CONFIDENTIALITY CLAIMS
Blanked out item Page Justification for blanking reference number 1 46 The precise figure of the average annual tonnage used in the sector is considered as confidential business information. … … … … … …
Use number: 2 111 ANALYSIS OF ALTERNATIVES
APPENDIX 2 – MASTERLIST OF ALTERNATIVES WITH CLASSIFICATION INTO CATEGORIES 1-3 AND SHORT SUMMARY OF THE REASON FOR CLASSIFICATION OF ALTERNATIVES INTO CATEGORY 3
Alternative Substance/ Alternative Nr. Category Screened out because Process This is no alternative for any surface LTAVD (Low Temperature Arc Vapor 1 3 treatment of this application Process is Deposition) (Materials used: Zr, Ti) related to hard chrome applications. Benzotriazole-based processes, e.g. 5- 2 2 methyl-1H-benzotriazol This is no alternative for any surface 90AR3 Monopassirex Chamois or primer 3 3 treatment of this application reactif429-5-302 brun rouge 01AR14 Alternative is a wash primer.
4 Acidic surface treatments 1
- only applicable on steel and materials with high melting temperatures, because the respective process temperature is between 500-1000°C - due to process temperature not applicable on aluminium and aluminium alloys or on magnesium and magnesium Case hardening: Carburising, alloys 5 CarboNitriding, Cyaniding, Nitriding, 3 - corrosion resistance of steel is not Boronising enhanced by case hardening: corrosion resistance was reported to be even lower than the original corrosion resistance of the un-hardened steel - for electrolytic chromium coated steel (ECCS), corrosion resistance was tested not to meet 24 h in SST Chromium-free electroplating (zinc-nickel 6 2 electroplating) - Only applicable for flat and small parts (limited size of vacuum chamber) and not for complex geometries 7 CVD (Chemical Vapour Deposition) 3 - corrosion and wear resistance below the typical requirements - alternative is more hard chrome related This is no alternative for any surface Detonation Gun thermal spray process (D- 8 3 treatment of this application Process is Gun) related to hard chrome applications. This is no alternative for any surface 9 Epoxy coatings (e.g., MIL-DTL 53022) 3 treatment of this application. Etch primers (metal primers with low 10 2 amount of phosphoric acid) This is no alternative for any surface Faraday Technologies (Faradaic process) 11 3 treatment of this application Process is (CrIII) related to hard chrome applications. This is no alternative for any surface 12 HVOF (High Velocity Oxy-fuel) 3 treatment of this application.
13 Organometallics (Zirconium and Titanium 1 based products, such as fluorotitanic and
112 Use number: 2 ANALYSIS OF ALTERNATIVES
Alternative Substance/ Alternative Nr. Category Screened out because Process fluorozirconic acids)
Keronite (plasma electrolytic oxidation This is no alternative for any surface 14 3 PEO) treatment of this application. This is no alternative for any surface 15 Laser alloying and laser cladding 3 treatment of this application. This is no alternative for any surface 16 Mineral Tie-Coat (cathodic mineralisation) 3 treatment of this application Process is related to hard chrome applications. Molybdates and Molybdenum based 17 2 processes - This alternative is more hard chrome 18 Nickel/Tungsten/Boron electroplating 3 related - Applicable only on steel / stainless steel - Organic corrosion inhibitors, such as amines, are good at preventing flash rusting of steel, but can be detrimental if steel is subsequently painted. 19 Organic corrosion inhibitors 3 - R&D has been performed within the aerospace sector on organic corrosion inhibitors resulting that they were found unlikely to provide sufficient corrosion protection.
20 Manganese based processes 2
This is no alternative for any surface 21 Plasma diffusion 3 treatment of this application Process is related to hard chrome applications.
22 Plasma spraying 3 - More hard chrome related.
This is no alternative for any surface 23 Polysulfides 3 treatment of this application. This is no alternative for any surface 24 Polyurethane, (Desothane HS) 3 treatment of this application. This is no alternative for any surface 25 primer E' MAP COATING SA 3 treatment of this application. Sherardising (non-electrolytic zinc-iron - Alternative has technical limitations due 26 3 alloy coating) to process itself (thermal treatment).
27 Silane/Siloxane and Sol-gel coating 1
- Problems when assembled with other materials for almost all high load- sliding wear environments, stainless and 28 Stainless steel 3 corrosion resisting steels with sufficient strength and hardness suffer from galling which destroys their surface in short order. This is no alternative for any surface 29 Tagnite (inorganic silica or vanadate) 3 treatment of this application Potential alternative for CAA on magnesium Trivalent chromium based surface 30 1 treatments
Use number: 2 113 ANALYSIS OF ALTERNATIVES
Alternative Substance/ Alternative Nr. Category Screened out because Process This is no alternative for any surface PVD (Physical vapour deposition), treatment of this application 31 3 Sputtering (Materials used: TiN, ZrN) Alternative is more related to Cadmium plating and hard chrome field Weld facing, Micro-arc welding: Electro This is no alternative for any surface Spark Deposition (ESD), Electro Spark 32 3 treatment of this application Alloying (ESA) (Materials used: Alternative is more hard chrome related Tungsten carbids, Co-based alloys) This is no alternative for any surface 33 Zinc-based materials 3 treatment of this application.
34 Water-based post-treatments 1
35 Cold Nickel Sealing 2
Chromate free passivation after zinc This is no alternative for any surface 36 3 plating treatment of this application. Type II cadmium with other non- chromate passivation nor TCP has not been researched as the results of the most Type II Cadmium passivation (with other 37 3 promising Cr(III) passivation (Type I non-chromate passivation, nor CrIII) Cadmium passivation) has a low maturity and no improves are expected using completely chromium free passivation
38 Magnesium rich primer 2
Potassium permanganate conversion 39 2 coating This is no alternative for any surface 40 Ionic liquids 3 treatment of this application. - danger to abrase too much of the base metal substrate - not for complex geometries and not for inner diameters - problem overheating the substrate by too much mechanical disturbance - media blasting: not suitable for assemblies with faying surfaces and complex geometries. - surface roughness of the base substrate Mechanical methods: Mechanical Sanding difficult to control under mechanical / shotblasting / media blasting / grinding & treatment therefore difficult to meet the 41 3 machining for stripping paint or inorganic substrate specific surface roughness finished limitations. - thin substrates: difficult to keep the residual stress to the substrate as small as possible when using mechanical treatments. - grinding & machining: problems in limitations to base material removement - overheating of the substrate - affecting the substrate causing hydrogen embrittlement, residual stress (distortion), surface roughening and reducing the
114 Use number: 2 ANALYSIS OF ALTERNATIVES
Alternative Substance/ Alternative Nr. Category Screened out because Process fatigue properties of the substrate.
Non-chrome deoxidiser solution (mineral acid based) for stripping of inorganic 42 2 finishes (hard anodize coatings) from aluminium - Not suitable for assemblies with Methylene chloride and phenol for paint dissimilar metals 43 3 stripping - methylene chloride targeted for reduction by other regulations -- Not suitable for assemblies with dissimilar metals 44 Formic acid for paint stripping 3 Not allowed for the use with high strength steels -- Not suitable for composite substrates Heat treatments: Heat gun for paint 45 3 stripping - possible over-heating and damaging of the substrate Hydrogen peroxide activated benzyl 46 2 alcohol (with acid) for paint stripping
Use number: 2 115 ANALYSIS OF ALTERNATIVES
APPENDIX 3 – INFORMATION ON RELEVANT SUBSTANCES FOR IDENTIFIED ALTERNATIVES APPENDIX 3.1: Main processes and post-treatments CATEGORY 1 ALTERNATIVES
APPENDIX 3.1.1: ALTERNATIVE 1: Acidic surface treatments Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Chemical name and Boric acid (mono Physical state at 20°C and Solid (crystalline, composition constituent substance) 101.3 kPa odourless) No melting point detected EC number 233-139-2 Melting point below 1000°C
CAS number 10043-35-3 Density 1.49 g/cm 3
IUPAC name Boric acid Vapour pressure 9.90 10 -8 kPa (25 °C)
Molecular formula H3BO 3 Water solubility 48.40 g/l (20°C, pH 3.6)
Molecular weight 61.83 g/mol Flammability Non flammable
Physicochemical Parameter Value Value properties Chemical name and Sulphuric acid (mono Physical state at 20°C and Liquid (odourless) composition constituent substance) 101.3 kPa 3°C (for 98% sulphuric acid) EC number 231-639-5 Melting point 10.4-10.5°C (for 100% sulphuric acid) 1.81 g/cm 3 (20°C, for 90%) CAS number 7664-93-9 Density 1.83 g/cm 3 (20°C, for 100%)
IUPAC name Sulphuric acid Vapour pressure 0.49 hPa (20°C)
Molecular formula H2SO 4 Water solubility Miscible with water
Flammability Non flammable Molecular weight 98.08 g/mol Flash-point: - Physicochemical Parameter Value Value properties Orthophosphoric acid Chemical name and Physical state at 20°C and Solid (crystalline, if no (mono constituent composition 101.3 kPa water attached) substance)
EC number 231-633-2 Melting point 41.1 °C (101 kPa)
CAS number 7664-38-2 Density 1.84 g/cm 3 (38°C)
116 Use number: 2 ANALYSIS OF ALTERNATIVES
Physicochemical Parameter Value Value properties
IUPAC name Phosphoric acid Vapour pressure 80 Pa (25°C, extrapolated)
Molecular formula H3PO 4 Water solubility 5480g/l (cold water pH0.5)
Molecular weight 98.00 g/mol Flammability/Flash Point -non flammable
Chemical name and Tartaric acid (mono Physical state at 20°C and Solid (odourless) composition constituent substance) 101.3 kPa
EC number 201-766-0 Melting point 171°C (101 kPa)
CAS number 87-69-4 Density 1.76 g/cm 3 (20°C)
IUPAC name Tartaric acid Vapour pressure < 0.005 kPa (20°C)
Molecular formula C4H6O6 Water solubility 1,390 g/l (20°C; pH n.a.)
Molecular weight 150.09 g/mol Flammability Non flammable
Physicochemical Parameter Value Value properties Chemical name and Nitric acid (mono Physical state at 20°C and Liquid (fumes in moist air) composition constituent substance) 101.3 kPa
EC number 231-714-2 Melting point - 41.60 °C
CAS number 7697-37-2 Density 1.51 g/cm 3 (20°C)
IUPAC name Nitric acid Vapour pressure 9.00 kPa (25°C)
Molecular formula HNO 3 Water solubility >1,000g/l (20°C, pH 1)
Non flammable, but can Molecular weight 63.01 g/mol Flammability enhance combustion of other materials Physicochemical Parameter Value Value properties Chemical name and Citric acid (mono Physical state at 20°C and Solid (crystalline) composition constituent substance) 101.3 kPa
EC number 201-269-1 Melting point ca.153°C
CAS number 77-92-9 Density 1.67 g/cm 3 (20°C)
2-hydroxypropane-1,2,3- 2.21 .10 -9 kPa IUPAC name Vapour pressure tricarboxylic acid (25°C, extrapolated)
Molecular formula C6H8O7 Water solubility 592.00 g/l (20°C)
Flammability non flammable Molecular weight 192.13 g/mol Flash Point -
Use number: 2 117 ANALYSIS OF ALTERNATIVES
Table 2: Hazard classification and labelling. Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments REACH registered; Included in CLP Regulation, Annex VI H360FD (May Boric acid (index number 005- damage fertility. (CAS 10043-35-3) Repr. 1B n/a - 007-00-2); May damage the (EC 233-139-2) unborn child) Included according to Annex XVI on the candidate list (SVHC substance) Specific H314 (Causes Concentration severe skin burns limits: REACH registered; Skin Corr. Sulphuric acid and eye damage) Skin Corr. 1A: C ≥ 1A Included in CLP (CAS 7664-93-9) H290 (may be n/a 15%, H314 Regulation, Annex VI Met. Corr. corrosive to Skin Irrit. 2: 5% ≤ (index number 016- (EC 231-639-5) 1 metals) C < 15%, H315 020-00-8); Eye Irrit. 2: 5% ≤ C < 15%; H319 H314 (Causes Skin Corr. severe skin burns n/a Legal classification. Phosphoric acid 1B and eye damage) REACH registered; (orthophosphoric Included in CLP acid) Additional self- Regulation, Annex VI H290 (May be classification (CAS 7664-38-2) Met. Corr. (index number 015- corrosive to n/a according to 1 011-00-6); (EC 231-633-2) metals) REACH registration; Acute Tox. H302 (Harmful if 4 swallowed) 1,005 notifiers Skin Irrit. H315 (Causes classified the 2 skin irritations) substance as listed H317 (May cause in the cells on the Skin Sens. an allergic skin left. Additional 1 reaction) 1,005 1,056 notifiers REACH registered; confirmed the Tartaric acid H319 (Causes Not included in CLP Eye Irrit. 2 serious eye classifications: Regulation, Annex VI; (CAS 87-69-4) Skin. Irrit. 2, Eye irritation) Included in C&L (EC 201-766-0) Irrit. 2 and STOT H335 (May cause inventory STOT SE SE 3. respiratory 3 irritation) H318 (Causes Eye Dam. Further serious eye 1 classifications damage) n/a according to Skin Corr. H315 (Causes REACH 1A skin irritation) registration; H272 (May REACH registered; Nitric acid Ox. Liq. 3 intensify fire; (CAS 7697-37-2) oxidiser) n/a Included in CLP Regulation, Annex VI (EC 231-714-2) Skin Corr. H314 (Causes (index number 007-
118 Use number: 2 ANALYSIS OF ALTERNATIVES
Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments 1A severe skin burns 004-00-1) and eye damage) Additional H290 (May be classification Met. Corr. corrosive to according to 1 metals) REACH registration. Self-classification according to REACH H319 (Causes registration. Eye Irrit. 2 serious eye 2362 irritation) This classification was also notified by >2000 parties to the REACH registered; Citric acid C&L inventory, Not included in CLP (CAS 77-92-9) Skin Irrit. H315 (Causes Regulation, Annex VI; (EC 201-069-1) 2 skin irritation) Classification Included in C&L notified to the C&L inventory H318 (Causes Eye Dam. inventory. serious eye 1 271 damage) Further 163 notifiers classified H335 (May cause STOT SE the substance as respiratory 3 Eye Dam. 1 only. irritation)
APPENDIX 3.1.2: ALTERNATIVE 2: Silane/siloxane and sol-gel coatings Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Chemical name and Methyl trimethoxysilane Physical state at 20°C and liquid composition (MTMS) 101.3 kPa
EC number 214-685-0 Melting point < -77 °C
CAS number 1185-55-3 Density 0.96 g/cm³ (20°C)
IUPAC name trimethoxy(methyl)-silane Vapour pressure 7.84 hPa (20°C)
Molecular formula C4H12 O3Si Water solubility 29 g/l (20°C)
Flammability flammable Molecular weight 136.05 g/mol Flash point 11.5 °C (1013 hPa) Physicochemical Parameter Value Value properties Chemical name and Vinyl trimethoxysilane Physical state at 20°C and liquid composition (VTMS) 101.3 kPa
EC number 220-449-8 Melting point -97 °C
Use number: 2 119 ANALYSIS OF ALTERNATIVES
Physicochemical Parameter Value Value properties
CAS number 2768-02-7 Density 0.97 g/cm³ (20 °C)
IUPAC name Ethenyl(trimethoxy) silane Vapour pressure 920 Pa (20 °C)
Molecular formula C5H12 O3Si Water solubility 9.4 g/l (20 °C, pH = 7)
Flammability flammable Molecular weight 148.05 g/mol Flash point 24 °C
Table2: Hazard classification and labelling. Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments H225 (Highly Classification of Flam. Liq. flammable liquid REACH 2 and vapour) registration ; notified to the C&L inventory by 96 96 H317 (May cause parties. Skin Sens. an allergic skin Further 93 parties 1 reaction) classified the substance as Flam. Liq. 2 only H225 (Highly Instead of Flam. Flam. Liq. flammable liquid Liquid 2 and Skin 2 and vapour) Sens. 1, 296 Skin Irrit. H315 (Causes notifiers submitted 2 skin irritation) the classification as specified on the left H319 (Causes to the C&L REACH registered; Methyl Eye Irrit. 2 serious eye inventory. Not included in the trimethoxysilane irritation) (MTMS) 296 CLP Regulation, Annex VI; (CAS 1185-55-3) 64 additional notifiers submitted Information from C&L (EC 214-685-0) the same H335 (May cause inventory STOT SE classification but respiratory 3 abstained from the irritation) classification as STOT SE 3.
H225 (Highly Flam. Liq. flammable liquid 2 and vapour) One or several Flam. Liq. H226 (Flammable classification as 3 liquid and vapour) specified on the left 62 were notified to the Skin Irrit. H315 (Causes C&L inventory by 2 skin irritation) another 62 parties H319 (Causes in total. Eye Irrit. 2 serious eye irritation)
120 Use number: 2 ANALYSIS OF ALTERNATIVES
Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments Acute Tox. H302 (Harmful if 4 swallowed) Acute Tox. H332 (Harmful if 4 inhaled) Flam. Liq. H226 (Flammable 3 liquid and vapour) Classification 176 included in REACH Acute Tox. H332 (Harmful if registration. REACH registered; 4 inhaled) Not included in the 352 notifiers CLP Regulation, H318 (Causes Eye Dam. submitted the Annex VI; serious eye 352 1 classification as damage) Information from C&L Eye Dam. 1 only. inventory; Skin Irrit. H315 (Causes 2 skin irritation) Included in the CoRAP Vinyl list of substances: trimethoxysilane H319 (Causes - Initial grounds of (VTMS) Eye Irrit. 2 serious eye Additional irritation) classifications concern: Human (CAS 2768-02-7) health/Suspected H335 (May cause Total included in the (EC 220-449-8) STOT SE sensitiser; respiratory number C&L inventory by 3 Exposure/Wide irritation) of notifiers in different additiona combinations. dispersive use; H304 (May be l 32 notifiers Worker exposure; fatal if swallowed Exposure of Asp. Tox 1 notifiers: sumitted the and enters 240 classification as sensitive population; airways) Muta. 1B and Carc. High RCR; H340 (May cause 1B. Aggregated tonnage Muta. 1B genetic effects) - Status: ongoing H350 (May cause Carc. 1B cancer)
APPENDIX 3.1.3: ALTERNATIVE 3: Cr(III)-based surface treatments Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and Chromium(III) sulphate Solid composition 101.3 kPa
EC number 233-253-2 Melting point 90 °C
CAS number 10101-53-8 Density 3.10 g/cm³ (anhydrous)
IUPAC name Chromium(III) sulphate Vapour pressure -
insoluble in water and Molecular formula Cr 2(SO 4)3 Water solubility acids (anhydrous) Soluble as hydrate
Use number: 2 121 ANALYSIS OF ALTERNATIVES
Physicochemical Parameter Value Value properties Flammability Non-flammable Molecular weight 392.18 g/mol Flash Point - Chemical name and Physical state at 20°C and Chromium(III) chloride solid composition 101.3 kPa
EC number 233-038-3 Melting point ca. 1150 °C
CAS number 10025-73-7 Density 2.87 g/cm³ (25 °C)
IUPAC name Chromium(III) chloride Vapour pressure -
Molecular formula CrCl 3 Water solubility 0.585 g/cm³
Flammability Non-flammable Molecular weight 158.36 g/mol Flash Point -
Table2: Hazard classification and labelling . Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments Currently not REACH registered; Not included in the Chromium sulphate 1,103 notifiers did Not CLP Regulation, (CAS 10101-53-8) - 1,103 not classify the classified Annex VI; substance. (EC 233-253-2) Included in C&L inventory
Acute Tox. H302 (Harmful if Additional 6 parties 4 swallowed) notified the Currently not REACH registered; Skin Irrit. H315 (Causes substance as Acute Chromium chloride 2 skin irritation) Tox 4 (H302) only. Not included in the 41 CLP Regulation, (CAS 10025-73-7) Further 6 notifiers H319 (Causes submitted the Annex VI; (EC 233-038-3) Eye Irrit. 2 serious eye classification as as Included in C&L irritation) Acute Tox 4 inventory Acute Tox. H330 (Fatal if (H302) and Aquatic 1 inhaled) Chronic 3 (H412).
122 Use number: 2 ANALYSIS OF ALTERNATIVES
APPENDIX 3.1.4: ALTERNATIVE 4: Water-based post-treatments Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and Potassium fluoride Solid (odourless) composition 101.3 kPa
EC number 232-151-5 Melting point 860°C
CAS number 7789-23-3 Density 2.48 g/cm³
IUPAC name Potassium fluoride Vapour pressure 0.13 hPa (752°C)-
Molecular formula KFl Water solubility 923 g/l (20°C)
Flammability Non flammable Molecular weight 58.1 g/mol Flash point - Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and Lithium acetate Solid (colourless) composition 101.3 kPa
EC number 208-914-3 Melting point 283-285°C
CAS number 546-89-4 Density 1.25 g/cm³
IUPAC name Lithium acetate Vapour pressure -
Molecular formula C2H3O2Li Water solubility 408 g/l (20°C)
Flammability Non flammable Molecular weight 65.9 g/mol Flash point - Chemical name and Physical state at 20°C and Hydrogen fluoride Colourless gas composition 101.3 kPa
EC number 231-634-8 Melting point - 83.36°C
CAS number 7664-39-3 Density 0.97 g/l (20°C)
IUPAC name Hydrogen fluoride Vapour pressure -
Molecular formula HF Water solubility -
Flammability Non flammable Molecular weight 20.01 g/mol Flash point -
Use number: 2 123 ANALYSIS OF ALTERNATIVES
Table 2: Hazard classification and labelling. Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments Acute Tox. H331 (Toxic if 3* inhaled.) REACH registered; Potassium fluoride Acute Tox. H311 (Toxic in Included in the CLP (CAS 7789-23-3) n/a Legal classification 3* contact with skin.) Regulation, Annex VI (EC 232-151-5) (index number: 009- Acute Tox. H301 (Toxic if 005-00-2) 3* swallowed.) 47 notifiers did not classify the substance. Currently not REACH Additional 34 registered; Lithium acetate parties notified the Not included in the (CAS 546-89-4) - - 47 substance as Repr. CLP Regulation, (EC 208-914-3) 2 (H361) only. Annex VI; Additional 21 Information from C&L parties notified the inventory; substance as Acute Tox. 4 (H302). Acute Tox. H330 (Fatal if Specific 2 * inhaled) Concentration Acute Tox. H310 (Fatal in limits: REACH registered; Hydrogen fluoride 1 contact with skin.) Skin Corr. 1A: C ≥ Included in the CLP (CAS 7664-39-3) Acute Tox. H300 (Fatal if n/a 7%, H314 Regulation, Annex VI (EC 231-634-8) 2 * swallowed.) Skin Corr. 1B: 1% (index number: 009- ≤ C < 7%, H314 003-00-1); H314 (Causes Skin Corr. ≤ severe skin burns Eye Irrit. 2: 0,1% 1A and eye damage.) C < 1%; H319
APPENDIX 3.1.5: ALTERNATIVE 5: Molybdates and molybdenum-based processes
Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Disodium molybdate Chemical name and Physical state at 20°C and (monoconstituent Solid (crytaline, odourless) composition 101.3 kPa substance) 687.0°C (anhydrous EC number 7631-95-0 Melting point Substance) CAS number 231-551-7 Density 2.59 g/cm 3 disodium IUPAC name tetraoxomolybdate Vapour pressure - dihydrate
Molecular formula Na 2MoO 4 Water solubility 654.2 g/l
Molecular weight 241. 95 Flammability / Flash point -
124 Use number: 2 ANALYSIS OF ALTERNATIVES
Physicochemical Parameter Value Value properties Orthophosphoric acid Chemical name and Physical state at 20°C and Solid (crystalline, if no (mono constituent composition 101.3 kPa water attached) substance)
EC number 231-633-2 Melting point 41.1 °C (101 kPa)
CAS number 7664-38-2 Density 1.84 g/cm 3 (38°C)
IUPAC name Phosphoric acid Vapour pressure 80 Pa (25°C, extrapolated)
5480 g/ L (cold water, Molecular formula H O P Water solubility 3 4 pH= 0.5) Flammability Non flammable Molecular weight 98.00 g/mol Flash point - Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and Cerium trifluoride Pale pink powder composition 101.3 kPa
EC number 231-841-3 Melting point 1430°C
CAS number 7758-88-5 Density 6.157 g/cm³
IUPAC name cerium(III) trifluoride Vapour pressure -
≤ 1.1 mg/L (20°C, pH= 4) ≤ 0.27 mg/L (20°C, pH Molecular formula CeF 3 Water solubility =7) ≤ 0.077 mg/L (20°C, pH= 9) Flammability Non flammable Molecular weight 197.11 g/mol Flash point -
Table2: Hazard classification and labelling. Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments Skin Irrit. H315 (Causes 2 skin irritation) 118 notifiers H319 (Causes classified the Eye Irrit. 2 serious eye substance with irritation) hazards (see on the 118 left). Sodium molybdate Acute Tox. H332 (Harmful if 4 inhaled) (CAS 7631-95-0) H335 (May cause (EC 231-551-7) STOT SE respiratory 93 notifiers 3 irritation) mentioned the single H412 (Harmful to classification: Aquatic aquatic life with 93 Aquatic Chronic 3. Chronic 3 long lasting effects)
Use number: 2 125 ANALYSIS OF ALTERNATIVES
Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments H314 (Causes Skin Corr. severe skin burns n/a Legal classification. 1B and eye damage) REACH registered; Phosphoric acid Included in CLP (CAS 7664-38-2) Additional self- Regulation, Annex VI H290 (May be classification (EC 231-633-2) Met. Corr. (index number 015- corrosive to n/a according to 1 011-00-6); metals) REACH registration; Not - 7 According to the classified REACH Acute Tox. H312 (Harmful in Registration 4 contact with skin) substance is not classified. Seven Skin Irrit. H315 (Causes notifiers submitted REACH registered; 2 skin irritation) Cerium fluoride this information to Not included in CLP (CAS 7758-88-5) H319 (Causes the C&L inventory. Regulation, Annex VI; Eye Irrit. 2 serious eye 25 Included in C&L (EC 231-841-3) irritation) However, 25 parties inventory Acute Tox. H332 (Harmful if notified the 4 inhaled) substance for H335 (May cause various hazards (see STOT SE respiratory classifications on 3 irritation) the left).
APPENDIX 3.1.6: ALTERNATIVE 6: Organometallics (zirconium and titanium based products, such as fluorotitanic and fluorozirconic acids) Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Hexafluorotitanic acid Chemical name and Physical state at 20°C and Liquid composition named also Dihydrogen- 101.3 kPa hexafluorotitanat (2-)
EC number 241-460-4 Melting point < 0°C
CAS number 17439-11-1 Density 1.675 g/cm³ (25°C)
IUPAC name Hexafluorotitanate(2 -) Vapour pressure 23 hPa (20 °C)
Molecular formula H2F6Ti Water solubility Fully miscible
Molecular weight 163.87 g/mol Flammability -
Chemical name and Physical state at 20°C and Hexafluorozirconic acid liquid composition 101.3 kPa
EC number 234-666-0 Melting point -
126 Use number: 2 ANALYSIS OF ALTERNATIVES
Physicochemical Parameter Value Value properties
CAS number 12021-95-3 Density 1.512 g/cm³ (25 °C)
IUPAC name Hexafluorozirconate(2-) Vapour pressure -
Molecular formula H2F6Zr Water solubility Fully miscible
Molecular weight 207.23 g/mol Flammability -
Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and Zirconium dioxide solid composition 101.3 kPa
EC number 215-227-2 Melting point 2680 °C
CAS number 1314-23-4 Density 5.77 g/cm³ (20 °C)
IUPAC name Zirconium dioxide Vapour pressure -
Molecular formula ZrO 2 Water solubility < 55 µg/l (20 °C, pH 6.5)
Molecular weight 123.22 g/mol Flammability -
Table 2: Hazard classification and labelling. Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments H290 (May be Met. Corr. corrosive to 1 metals) Acute Tox. H301 (Toxic if 3 swallowed) Classification as Acute Tox. H311 (Toxic in included in REACH 33 3 contact with skin) registration. Fluoro- Acute Tox. H331 (Toxic if titanic acid 3 inhaled) REACH registered; (CAS 17439-11-1) H314 (Causes Not included in the Skin Corr. (EC 241-460-4) severe skin burns CLP Regulation, 1B and eye damage) Annex VI; named also Acute Tox. H300 (Fatal if Included in C&L Dihydrogen- 2 swallowed) inventory hexafluorotitanat (2-) Acute Tox. H310 (Fatal in 2 contact with skin) Additional 24 H314 (Causes Skin Corr. 24 notifiers listed other severe skin burns 1B classification. and eye damage) H318 (Causes Eye Dam. serious eye 1 damage)
Use number: 2 127 ANALYSIS OF ALTERNATIVES
Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments Acute Tox. H330 (Fatal if 2 inhaled) Acute Tox. H301 (Toxic if 3 swallowed) Acute Tox. H311 (Toxic in 3 contact with skin) H314 (Causes 76 REACH registered; Skin Corr. Fluoro- severe skin burns 1B Not included in the zirconic acid and eye damage) CLP Regulation, (CAS 12021-95-3) Acute Tox. H330 (Fatal if Annex VI; (EC 234-666-0) 2 inhaled) Included in C&L H290 (May be inventory Met. Corr. Further corrosive to 1 classification metals) - according to Acute Tox. H331 (Toxic if REACH 3 inhaled) registration; Not - 750 classified 750 notifiers did Skin Irrit. H315 (Causes not classify the 2 skin irritation) Zirconium dioxide substance. REACH registered; (CAS 1314-23-4) H319 (Causes Additional 73 Eye Irrit. 2 serious eye notifiers did (EC 215-227-2) 73 irritation) mention human health hazards, see H335 (May cause STOT SE cells on the left). respiratory 3 irritation)
128 Use number: 2 ANALYSIS OF ALTERNATIVES
CATEGORY 2 ALTERNATIVES APPENDIX 3.1.7: ALTERNATIVE 7: Benzotriazole-based processes, e.g. 5-methyl-1H- benzotriazol Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and 5-methyl-1H-benzotriazol solid composition 101.3 kPa
EC number 205-265-8 Melting point 80-82 °C
CAS number 136-85-6 Density ca. 1.3 g/cm³ (predicted)
IUPAC name 5-Methylbenzotriazole Vapour pressure -
Molecular formula C7H7N3 Water solubility 6.0 g/l (25 °C)
Molecular weight 133.15 g/mol Flammability 210-212 °C
Table 2: Hazard classification and labelling. Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments Currently not REACH 36 notifiers notified registered; the substance with H302 (Harmful if the single hazard Not Included in CLP Acute Tox. swallowed) Acute Tox. 4. Regulation, Annex VI; 36 Included in the C&L 4 Inventory
5-methyl-1H-
benzotriazol (6-methylbenzo- Acute Tox. H302 (Harmful if triazole) 4 swallowed) (CAS 136-85-6) Skin Irrit. H315 (Causes Additional 23 (EC 205-265-8) 2 skin irritation) notifiers classified the substance both Included in the C&L H319 (Causes 23 with Acute Tox. 4 Inventory Eye Irrit. 2 serious eye and with three irritation) additional hazards H335 (May cause (see left). STOT SE respiratory 3 irritation)
Use number: 2 129 ANALYSIS OF ALTERNATIVES
APPENDIX 3.1.8: ALTERNATIVE 8: Chromate-free etch primers No distinct composition of commercially available etch primers was available, but etch primers are often based on phosphoric acid wash primer with additives. Therefore, the physicochemical properties and hazard classification provided below bare based on orthophosphoric acid. Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and Orthophosphoric acid liquid composition 101.3 kPa
EC number 231-633-2 Melting point 41.1 °C
1.87 g/cm³ (100% aqueous CAS number 7664-38-2 Density solution)
IUPAC name Phosphoric acid Vapour pressure 4 Pa (20 °C)
548 g/100 ml (20 °C, pH Molecular formula H PO Water solubility 3 4 ca. 0.5) Flammability non flammable Molecular weight 97.97 g/mol Flash point -
Table 2: Hazard classification and labelling. Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments H314 (Causes Skin Corr. REACH registered; severe skin burns n/a Legal classification. Phosphoric acid 1B and eye damage) Included in CLP (orthophosphoric Regulation, Annex VI acid) Additional self- (index number 015- H290 (May be classification (CAS 7664-38-2) Met. Corr. 011-00-6); corrosive to n/a according to (EC 231-633-2) 1 metals) REACH registration CLP inventory
APPENDIX 3.1.9: ALTERNATIVE 9: Manganese based processes Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Potassium permanganate Chemical name and Physical state at 20°C and Solid (dark-purple or (mono constituent composition 101.3 kPa bronze-like) substance)
EC number 231-760-3 Melting point Decomposes <240°C
CAS number 7722-64-7 Density 2.7 g/cm 3 (20°C)
130 Use number: 2 ANALYSIS OF ALTERNATIVES
Physicochemical Parameter Value Value properties potassium oxido(trioxo) IUPAC name Vapour pressure - manganese
Molecular formula KMnO 4 Water solubility ≥64 g/L (20°C)
Non-flammable but will Molecular weight 158.03 g/mol Flammability accelerate the burning of combustible material. Aluminium sulphate Chemical name and Physical state at 20°C and (mono constituent Solid (granules) composition 101.3 kPa substance) No Melting of substance EC number 233-135-0 Melting point (unspecified hydrate) was observed (25°C-550°C). 1.79 g/ cm 3 (at 20°C, CAS number 10043-01-3 Density unspecified hydrate)
IUPAC name Aluminium sulphate Vapour pressure -
> 1000 g/l (20°C, Molecular formula Al (SO ) Water solubility 2 4 3 pH = 2.4) Flammability Non flammable Molecular weight 342.15 g/mol Flash point - Physicochemical Parameter Value Value properties Sodium dihydrogen- Chemical name and Physical state at 20°C and orthophosphate (mono Solid (granules) composition 101.3 kPa constituent substance)
EC number 231-449-2 Melting point > 449°C
CAS number 7558-80-7 Density 2.36 g/ cm 3 (20.5°C)
sodium dihydrogen IUPAC name Vapour pressure - phosphate 50.2-52 .0 %w/w Molecular formula NaH PO Water solubility 2 4 (20°C, pH 3.6-4.0)
Molecular weight 119.98 g/mol Flammability -
Physicochemical Parameter Value Value properties Potassium dihydrogen- Chemical name and Physical state at 20°C and orthophosphate (mono White crystalline solid composition 101.3 kPa constituent substance)
EC number 231-913-4 Melting point 252.6 °C
CAS number 7778-77-0 Density 2.33 g/cm 3 (21.5 °C)
Potassium dihydrogen IUPAC name Vapour pressure 4.5 fPa (25 °C) phosphate
Molecular formula KH 2PO 4 Water solubility 208 g/l (20 °C)
Molecular weight 137.03 g/mol Flammability -
Use number: 2 131 ANALYSIS OF ALTERNATIVES
Physicochemical Parameter Value Value properties Dihydrogen Chemical name and Physical state at 20°C and hexafluorozirconate composition 101.3 kPa (2-)
EC number 234-666-0 Melting point
CAS number 12021-95-3 Density
Hexafluorozirconate IUPAC name Vapour pressure (2-)
Molecular formula H2ZrF 6 Water solubility
Molecular weight Flammability -
Table 2: Hazard classification and labelling . Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments H272 (May Ox. Sol. 2 intensify fire; oxidiser) Acute Tox. H302 (Harmful if 4 * swallowed) Classification according CLP Potassium Aquatic H400 (Very toxic Regulation Annex REACH registered; Acute 1 to aquatic life) permanganate VI; Included in CLP KMnO 4 H410 (Very toxic n/a Regulation, Annex VI (CAS 7722-64-7) Aquatic to aquatic life (index number 025- (EC 231-760-3) Chronic 1 with long lasting 002-00-9); effects) Further H314 (Causes classification Skin Corr. severe skin burns according to 1C and eye damage) REACH registration; H290 (May be Classification Met. Corr. corrosive to included in REACH 1 metals) joint registration and submitted by 131 131 notifiers to the H318 (Causes REACH registered; Aluminium Eye Dam. C&L inventory. serious eye Not included in CLP Sulphate Al 2(SO 4)3 1 361 parties notified damage) Regulation, Annex VI; (CAS 10043-01-3) the substance as Eye Dam. 1 only. Information from C&L (EC 233-135-0) inventory Acute Tox. H302 (Harmful if Additional ~ 180 4 swallowed) notifiers submitted H318 (Causes ~180 one or several of Eye Dam. serious eye the additional 1 damage) classifications on
132 Use number: 2 ANALYSIS OF ALTERNATIVES
Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments H319 (Causes the left to the C&L Eye Irrit. 2 serious eye irritation) Skin Irrit. H315 (Causes 2 skin irritation) H335 (May cause STOT SE respiratory 3 irritation) Aquatic H400 (Very toxic Acute 1 to aquatic life) H410 (Very toxic Aquatic to aquatic life Chronic 1 with long-lasting effects) H411 (Toxic to Aquatic aquatic life with Chronic 2 long-lasting effects) Information from REACH registration; Not notified to the C&L - 502 classified inventory by 502 Sodium parties (of which 51 REACH registered; dihydrogen- did not classify due orthophosphate to lacking data). Not included in CLP Regulation, Annex VI; NaH 2PO 4 Skin Irrit. H315 (Causes Information from C&L (CAS 7558-80-7) 2 skin irritation) One or several inventory (CAS 231-449-2) H319 (Causes classification as Eye Irrit. 2 serious eye specified on the left 77 irritation) were notified to the H335 (May cause C&L inventory by STOT SE respiratory 77 parties in total. 3 irritation) H314 (Causes Skin Corr. severe skin burns 1A, 1B and eye damage) H318 (causes Eye Dam.1 serious eye Potassium damage) dihydrogeno Skin Irrit. H315 (causes skin phosphate 2 irritation) n/a n/a KH 2PO 4 H319 (causes (CAS 7778-77-0) Eye Irrit. 2 serious eye (EC 231-913-4) irritation) H335 (may cause STOT SE respiratory 3 irritation) Acute Tox. H302 (harmful if 4 swallowed)
Use number: 2 133 ANALYSIS OF ALTERNATIVES
Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments H314 (Causes Skin Corr. severe skin burns 1A, 1B and eye damage) H318 (causes Eye Dam.1 serious eye damage) Dihydrogen Skin Irrit. H315 (causes skin hexafluorozirconate 2 irritation) (2-) n/a n/a (CAS 12021-95-3) H319 (causes Eye Irrit. 2 serious eye (EC 234-666-0) irritation) H335 (may cause STOT SE respiratory 3 irritation) Acute Tox. H302 (harmful if 4 swallowed)
APPENDIX 3.1.10: ALTERNATIVE 10: Cold nickel sealing Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Chemical name and Nickel fluoride (mono Physical state at 20°C and Solid (yellowish, green, composition constituent substance) 101.3 kPa odourless)
EC number 233-071-3 Melting point Sublimes at T >1000°C
CAS number 10028-18-9 Density 4.72 g/cm 3
IUPAC name Nickel difluoride Vapour pressure -
Molecular formula NiF 2 Water solubility 40 g/l (at 25°C)
Molecular weight 96.69 g/mol Flammability Not flammable
Physicochemical Parameter Value Value properties Chemical name and Nickel sulphate (mono Physical state at 20°C and Solid (greenish-yellow) composition constituent substance) 101.3 kPa Decompose at T ≥ 840°C EC number 232-104-9 Melting point (anhydrous form) 3.68 g/cm 3 (20°C, CAS number 7786-81-4 Density anhydrous)
IUPAC name Nickel(II)sulfate Vapour pressure -
Molecular formula NiSO 4 Water solubility 293 g/l (20°C, anhydrous)
134 Use number: 2 ANALYSIS OF ALTERNATIVES
Physicochemical Parameter Value Value properties
Molecular weight 154.76 g/mol Flammability Not highly flammable
Physicochemical Parameter Value Value properties Nickel bis(sulphamidate) Chemical name and (mono constituent Physical state at 20°C and Solid (blue, crystalline) composition substance) 101.3 kPa
Decompose between EC number 237-396-1 Melting point 141.63-144.89°C
CAS number 13770-89-3 Density 2.25 g/cm 3 (20°C)
IUPAC name Nickel(II)disulfamate Vapour pressure -
49.9- 60 %w/w
Molecular formula Ni(SO 3)2(NH 2)2 Water solubility (20°C , pH 1.1-1.6) Very soluble
Molecular weight 250.86 g/mol Flammability Non flammable
Table 2: Hazard classification and labelling. Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments H350i (May cause Carc. 1A cancer by inhalation) H341 (Suspected Muta. 2 of causing genetic defects) H360D*** (May Repr. 1B damage the unborn child) H372** (Causes damage to organs REACH registered; Nickel fluoride STOT RE through prolonged Included in CLP NiF 2 1 or repeated - - (CAS 10028-18-9) Regulation, Annex VI exposure) (index number 028- (EC 233-071-3) H334 (May cause 029-00-4); allergy or asthma Resp. symptoms of Sens. 1 breathing difficulties if inhaled) H317 (May cause Skin Sens. an allergic skin 1 reaction) Aquatic H400 (Very toxic Acute 1 to aquatic life)
Use number: 2 135 ANALYSIS OF ALTERNATIVES
Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments H410 (Very toxic Aquatic to aquatic life Chronic 1 with long lasting effects) H350i (May cause Carc. 1A cancer by inhalation) H341 (Suspected Muta. 2 of causing genetic defects) H360D*** (May Repr. 1B damage the unborn child) H372** (Causes damage to organs STOT RE through prolonged 1 or repeated exposure) Acute Tox. H332 (Harmful if 4 * inhaled) REACH registered; Included in CLP Nickel sulphate Acute Tox. H302 (Harmful if Regulation, Annex VI (CAS 7786-81-4) 4 * swallowed) (index number 028- (EC 232-104-9) Skin Irrit. H315 (Causes 009-00-5); 2 skin irritation) H334 (May cause allergy or asthma Resp. symptoms of Sens. 1 breathing difficulties if inhaled) H317 (May cause Skin Sens. an allergic skin 1 reaction) Aquatic H400 (Very toxic Acute 1 to aquatic life) H410 (Very toxic Aquatic to aquatic life Chronic 1 with long lasting effects) H350i (May cause Carc. 1A cancer by inhalation) H341 (Suspected REACH registered; Nickel Sulphamate Muta. 2 of causing genetic Included in CLP (CAS 13770-89-3) defects) - - Regulation, Annex VI (EC 237-396-1) H360D*** (May (index number 028- Repr. 1B damage the 018-00-4); unborn child) STOT RE H372** (Causes 1 damage to organs
136 Use number: 2 ANALYSIS OF ALTERNATIVES
Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments through prolonged or repeated exposure) H334 (May cause allergy or asthma Resp. symptoms of Sens. 1 breathing difficulties if inhaled) H317 (May cause Skin Sens. an allergic skin 1 reaction) Aquatic H400 (Very toxic Acute 1 to aquatic life) H410 (Very toxic Aquatic to aquatic life Chronic 1 with long lasting effects)
APPENDIX 3.1.11: ALTERNATIVE 11: Magnesium rich primers Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Physical state at 20°C liquid and 101.3 kPa EC number / CAS number / IUPAC name / molecular Multiple components Flash point 35°C formula / structure / weight Density 1.318 g/cm³
Table 2: Hazard classification and labelling. Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments Flam. Liq. H226 (Flammable 3 liquid and vapour) Supplier hazard Skin Irrit. H315 (Causes n/a (product is a information from Mg-rich primer 2 skin irritation) n/a mixture of several related SDS for this substances) H319 (Causes product. Eye Irrit. 2 serious eye irritation)
Use number: 2 137 ANALYSIS OF ALTERNATIVES
Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments H317 (May cause Skin Sens. an allergic skin 1 reaction) H411 (Toxic to Aquatic aquatic life with Chronic 2 long lasting effects) H302 (Health hazardous when swallowed) Acute Tox. H312 (Health 4 hazardous by skin contact) H332 (Health hazardous when inhaled) H304 (Can be Asp. Tox. deadly if swallowed or if it 1 penetrates into the respiratory apparatus)
APPENDIX 3.1.12: ALTERNATIVE 12: Electrolytic paint technology Substance IDs and properties for relevant substances: The substance identity and composition of the electrocoating formulation used in the process is not known as this is proprietary of the supplier. Hazard classification and labelling: The substance identity and composition of the electrocoating formulation used in the process is not known as this is proprietary of the supplier. The classification of a commercial product was reported by the supplier during the consultation as Eye Irrit. 2, and Aquatic Chronic 3 as well as Skin Irrit. 2, respectively.
138 Use number: 2 ANALYSIS OF ALTERNATIVES
APPENDIX 3.1.13: ALTERNATIVE 13: Zinc-nickel electroplating Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and Zinc sulphate Solid (white, powder) composition 101.3 kPa
EC number 231-793-3 Melting point Decomposes at 625°C
CAS number 7733-02-0 Density 3.35 g/cm³ (monohydrate)
IUPAC name Zinc sulphate Vapour pressure -
Molecular formula ZnSO 4 Water solubility 210 g/l (monohydrate)
Flammability - Molecular weight 161.47 g/mol Flash point - Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and Nickel sulphate Solid (greenish-yellow) composition 101.3 kPa
EC number 232-104-9 Melting point Decomposes at 840°C
CAS number 7786-81-4 Density 3.68 g/cm 3 at 20°C
IUPAC name nickel(II) sulphate Vapour pressure -
Molecular formula Ni(SO 4)2 Water solubility 293 g/l (at 20°C)
Flammability Non flammable Molecular weight 154.8 g/mol Flash point -
Table 2: Hazard classification and labelling . No. of Hazard Hazard Additional Notifiers Class and Statement classification and Regulatory and CLP Substance Name (CLP Category Code(s) labelling status inventor Code(s) comments (labelling) y) H302 (harmful if swallowed) Acute Tox. 4 H318 (causes serious eye REACH registered; Eye Dam. Zinc sulphate damage) 1 Included in CLP (CAS 7733-02-0) H400 (very toxic Regulation, Annex VI Aquatic to aquatic life) (index number 030- (EC 231-793-3) Acute 1 H410 (very toxic 006-00-9); Aquatic to aquatic life Chronic 1 with long lasting effects) Nickel sulphate Acute Tox. H302 (harmful if REACH registered; Specific (CAS 7786-81-4) 4 swallowed) Concentration Included in CLP
Use number: 2 139 ANALYSIS OF ALTERNATIVES
No. of Hazard Hazard Additional Notifiers Class and Statement classification and Regulatory and CLP Substance Name (CLP Category Code(s) labelling status inventor Code(s) comments (labelling) y) (EC 232-104-9) Skin Irrit. H315 (causes skin limits, M-Factors Regulation, Annex VI 2 irriation) Skin Sens. 1; H317: (index number 028- Skin Sens. H317 (may cause C ≥ 0,01% 009-00-5); 1 an allergic skin STOT RE 1; H372: Acute Tox. reaction) C ≥ 1% 4 H332 (harmful if Skin Irrit. 2; H315: Resp. inhaled) C ≥ 20% Sens. 1 H334 (may cause M=1 allergy or asthma Muta. 2 STOT RE 1; H373: symptoms or Carc. 1A C ≥ 1% breathing Repr. 1B difficulties if STOT RE 2; H373: STOT RE inhaled) 0,1% ≤ C < 1% 1 H341 (suspected Aquatic of causing genetic Acute 1 defects) Aquatic H350i (may cause Chronic 1 cancer by inhalation) H360D (may damage the unborn child) H372 (cause damage to organs) H400 (very toxic to aquatic life) H410 (very toxic to aquatic life with long lasting effects)
140 Use number: 2 ANALYSIS OF ALTERNATIVES
APPENDIX 3.2: Pre-treatments 3.2.1: Inorganic acids Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Chemical name and Sulphuric acid (mono Physical state at 20°C and Liquid (odourless) composition constituent substance) 101.3 kPa 3°C (for 98% sulfuric acid) EC number 231-639-5 Melting point 10.4-10.5°C (for 100% sulfuric acid) 1.81 g/cm 3 (20°C, for 90%) CAS number 7664-93-9 Density 1.83 g/cm 3 (20°C, for 100%)
IUPAC name Sulfuric acid Vapour pressure 0.49 hPa (20°C)
Molecular formula H2SO 4 Water solubility Miscible with water
Flammability Non flammable Molecular weight 98.08 g/mol Flash point - Physicochemical Parameter Value Value properties Orthophosphoric acid Chemical name and Physical state at 20°C and Solid (crystalline, if no (mono constituent composition 101.3 kPa water attached) substance)
EC number 231-633-2 Melting point 41.1 °C (101 kPa)
CAS number 7664-38-2 Density 1.84 g/cm 3 (38°C)
IUPAC name Phosphoric acid Vapour pressure 80 Pa (25°C, extrapolated)
5480g/l (cold water, Molecular formula H PO Water solubility 3 4 pH= 0.5) Flammability Non flammable Molecular weight 98.00 g/mol Flash point - Physicochemical Parameter Value Value properties Chemical name and Nitric acid (mono Physical state at 20°C and Liquid (fumes in moist air) composition constituent substance) 101.3 kPa
EC number 231-714-2 Melting point - 41.60 °C
CAS number 7697-37-2 Density 1.51 g/cm 3 (20°C)
IUPAC name Nitric acid Vapour pressure 9.00 kPa (25°C)
Molecular formula HNO 3 Water solubility > 1000g/l (20°C, pH= -1)
Flammability Non flammable but can enhance combustion of Molecular weight 63.01 g/mol other materials Flash Point -
Use number: 2 141 ANALYSIS OF ALTERNATIVES
Table 2: Hazard classification and labelling. Hazard Hazard Additional Number Class and Statement classification and Regulatory and CLP Substance Name of Category Code(s) labelling status Notifiers Code(s) (labelling) comments Specific H314 (Causes Concentration severe skin burns limits: REACH registered; Skin Corr. Sulphuric acid and eye damage) Skin Corr. 1A: C ≥ 1A Included in CLP (CAS 7664-93-9) H290 (may be n/a 15%, H314 Regulation, Annex VI Met. Corr. corrosive to Skin Irrit. 2: 5% ≤ (index number 016- (EC 231-639-5) 1 metals) C < 15%, H315 020-00-8); Eye Irrit. 2: 5% ≤ C < 15%; H319 H314 (Causes Skin Corr. severe skin burns n/a Legal classification. 1B and eye damage) REACH registered; Phosphoric acid Included in CLP (CAS 7664-38-2) Additional self- Regulation, Annex VI H290 (May be classification (EC 231-633-2) Met. Corr. (index number 015- corrosive to n/a according to 1 011-00-6); metals) REACH registration; H272 (May Ox. Liq. 3 intensify fire; oxidizer)
H314 (Causes Skin Corr. severe skin burns 1A and eye damage) n/a Additional H290 (May be classification Met. Corr. corrosive to according to 1 metals) REACH REACH registered; Nitric acid registration. Included in CLP (CAS 7697-37-2) Classification Regulation, Annex VI Not (EC 231-714-2) - 257 notified to the C&L (index number 007- classified inventory. 004-00-1) Skin Irrit. H315 (Causes 2 skin irritation) Classification notified to the C&L H318 (Causes Eye Dam. inventory. serious eye 1 271 damage) Further 163 notifiers classified H335 (May cause STOT SE the substance as respiratory 3 Eye Dam. 1 only. irrtation)
142 Use number: 2 ANALYSIS OF ALTERNATIVES
3.2.2: Hydrogen peroxide activated benzyl alcohol (with acid) Table 1: Substance IDs and properties for relevant substances.
Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and Liquid (odourless, Hydrogenperoxide composition 101.3 kPa colourless) 0.43°C (1,013 hPa, for EC number 231-765-0 Melting point pure hydrogen peroxide) 1.44 g/cm 3 (calculated for CAS number 7722-84-1 Density pure hydrogen peroxide at 25°C) 2.99 hPa (calculated for IUPAC name Hydrogen peroxide Vapour pressure pure hydrogen peroxide at 25°C) miscible in water in all Molecular formula H O Water solubility 2 2 proportions
Molecular weight 34.01 g/mol Flammability -
Physicochemical Parameter Value Value properties Chemical name and Benzyl alcohol Physical state at 20°C and liquid composition 101.3 kPa
EC number 202-859-9 Melting point - 15.4°C
CAS number 100-51-6 Density 1.04 g/cm 3 (22°C)
IUPAC name Phenylmethanol Vapour pressure 7 Pa (20°C)
Molecular formula C7H8O Water solubility 44.0 g/l (50°C)
Not considered to be Molecular weight 108.14 g/mol Flammability highly flammable Physicochemical Parameter Value Value properties Chemical name and Physical state at 20°C and Sulphuric acid Liquid (odourless) composition 101.3 kPa 3°C (for 98% sulphuric acid) EC number 231-639-5 Melting point 10.4-10.5°C (for 100% sulphuric acid) 1.81 g/cm 3 (20°C, for 90%) CAS number 7664-93-9 Density 1.83 g/cm 3 (20°C, for 100%)
IUPAC name Sulphuric acid Vapour pressure 0.49 hPa (20°C)
Molecular formula H2SO 4 Water solubility Miscible with water
Flammability Non flammable Molecular weight 98.08 g/mol Flash-point: -
Use number: 2 143 ANALYSIS OF ALTERNATIVES
Table 2: Hazard classification and labelling. No. of Hazard Hazard Additional Notifiers Class and Statement classification and Regulatory and CLP Substance Name (CLP Category Code(s) labelling status inventor Code(s) comments (labelling) y) H271 (May cause Ox. Liqu.1 fire or explosion; strong oxidiser) Acute Tox. H302 (Harmfull if 4 swallowed) 550 Liquid H314 (causes Skin Corr. severe skin burns 1A and eye damage) Acute Tox H332 (Harmfull if 4. inhaled) H271 (May cause Ox. Liqu.1 fire or explosion; REACH registered; Hydrogen peroxide strong oxidiser) Included in CLP (CAS 7722-84-1) Regulation, Annex VI Acute Tox. H302 (Harmfull if (EC 231-765-0) (index number 008- 4 swallowed) 003-00-9) H314 (causes Skin Corr. severe skin burns 1A and eye damage) 352 H318 (causes Eye Dam.1 serious eye damage) Acute Tox H332 (Harmfull if 4. inhaled) H335 (may cause STOT SE respiratory 3 irritation) Acute Tox. H302 (Harmful if 4 swallowed) 2502 Acute Tox. H332 (Harmful if 4 inhaled) Acute Tox. H302 (Harmful if 4 swallowed) REACH registered; Benzyl alcohol Included in CLP H312 (Harmful (CAS 100-51-6) Acute Tox Regulation, Annex VI in contact with (EC 202-859-9) 4 (index number 603- skin.) 352 057-00-5 ) H318 (Causes Eye Dam.1 serious eye damage) Acute Tox. H332 (Harmful if 4 inhaled) REACH registered; Sulphuric acid H314 (Causes Skin Corr. Included in CLP (CAS 7664-93-9) severe skin burns n/a 1A Regulation, Annex VI (EC 231-639-5) and eye damage) (index number 016- 020-00-8);
144 Use number: 2 ANALYSIS OF ALTERNATIVES
APPENDIX 3.3: Sources of information Information on substance identities, physicochemical properties, hazard classification and labelling are based on online data searches. All online sources were accessed between June and September 2014. The main sources are: 1. European Chemicals Agency Website: http://echa.europa.eu/de/ 2. ChemSpider Website: http://www.chemspider.com/ 3. Chemical Book Website: http://www.chemicalbook.com/ 4. ChemBlink Website: http://www.chemblink.com/ 5. Sigma Aldrich Website: http://www.sigmaaldrich.com/ 6. PubChem Website: http://pubchem.ncbi.nlm.nih.gov/ 7. Santa Cruz Biotechnology Website: http://www.scbt.com/ 8. Guidechem Website: http://www.guidechem.com / 9. Gestis Stoffdatenbank: http://gestis.itrust.de/
Use number: 2 145