SUPERPRIMER: CHROMATE FREE COATING SYSTEM for Dod
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“SUPERPRIMER”: Chromate-Free Coating System For DoD Applications A dissertation submitted to the Division of Research and Advanced Studies of the University of Cincinnati In partial fulfillment of the requirements for the degree of MASTER OF SCIENCE In the Department of Chemical and Materials Engineering of the College of Engineering By TRILOK RANJAN MUGADA B.Tech, Chemical Engineering Jawaharlal Nehru Technological University, India, August 2001 Committee Chair: Dr. William J. van Ooij 2 ABSTRACT The idea of this research topic was to develop a novel, environmentally benign coating system for metal alloy structural components in DoD systems. The coating was chromate-free and contained little or no volatile organic compounds (VOC’s). The integrated organosilane system replaced the chromate system entirely including all chromate pretreatment and all corrosion-inhibiting chromate pigments. The complete system and also most or all of its components were water- borne. The term used to denote this particular primer is “superprimer.” This primer was based on organofunctional silanes that possess an extraordinary ability to protect metals against corrosion. The proposed work integrated organosilanes into a full water-borne coating system. The objective was to replace the current system (metal pretreatment, primer and topcoat) with no sacrifice of corrosion performance. Chapter 1 gives a brief overview on important concepts including corrosion and its control, significance of chromium in corrosion control and its use, silane technology, idea of the superprimer and the objective of this thesis. Chapter 2 gives information about the materials used for preparation of the superprimer. Procedures used for the testing and preparation of the superprimer are discussed. 3 Chapter 3 gives detailed information about the superprimer. In the beginning it gives information about the choice of selecting the components that constitute the primer followed by initial formulation and their results. The developments that led to the final formulation are discussed in detail. Test results including EIS and salt spray results are provided whenever necessary. The silane plus resin combinations can lead to coating formulations but in order to make it perform on par with chromate primers further additions need to be made. Detailed explanation of the idea, purpose and expectations of these additives in the primer are already given in Chapter 1. In Chapter 4, details about the mixing procedure of the additions, different kind of additives tried and their test results are given. There are primarily two important kinds of additives, nano- particles and corrosion inhibitors. Many commercially available particles and inhibitors were tried and tested for corrosion performance. Test results by EIS and salt spray are provided. Zinc-rich primers are as the name suggests primers with heavy loads of zinc metal dust in it. The zinc dust/powder is used as filler and is held in the coating by using a binder. Paints with zinc pigments contain about 80% by weight pigment of which 20% is oxide. Zinc-rich coatings contain 85-95% metallic zinc, by weight, in the dry coating with little or no oxide. Depending the type of binder used the primer can be organic or inorganic. Organic binders can be epoxy, polyurethane, acrylate etc. In inorganic zinc-rich primers the binders are usually silicates. Chapter 5 starts with a 4 brief explanation on the uses, application, and mechanism of action and the idea of zinc-rich primers. It also includes the idea of the zinc-rich superprimer, the formulations, test results etc. Chapter 6 discusses the characterization work that was done in the final stages of this thesis work. The NMR characterization technique was used in the trials to investigate the chemical structural characteristics and changes in the superprimer formulations. For this NMR instruments at Oklahoma State University in Stillwater, OK were used. Both carbon and silicon NMR analysis were applied. Chapter 7 summarizes the conclusions of this thesis. Chapter 8 discusses the recommendations for future work. 5 6 ACKNOWLEDGMENTS I would like to express my sincere thanks and appreciation to my advisor Dr. William J. van Ooij for giving me an opportunity to work with him in his group and guiding me through this thesis. What I learned from him in the past three years has shaped my career and thus my future. Each and everything of his; his zeal toward work, his lectures in class and group meetings, his suggestions, and his emails containing constructive criticism of my work will all be permanent guidelines for whatever I do in my future work. I appreciate the SERDP-DoD of the U.S government for the funding of this project. I am grateful for the funding of this project through the DoD's SERDP, the Strategic Environmental Research and Development Program. I sincerely thank my committee members Dr. R. C. Buchanan and Dr. Jude Iroh for spending time to review my thesis. I thank my senior group members Dr. Danqing Zhu, Matthew Stacy, Vignesh Palanivel, and Anuj Seth, who are still an encouragement. Their works, including their published literature on silanes, have been my guides for the preparation towards this project. I appreciate the efforts of my friend Mr. Chetan Shivane, without which this thesis might still be unfinished. 7 I also thank Dr. Tammy Metroke of Oklahoma State University for the help and guidance with the characterization work in this thesis. Working and learning in our silane lab could not have been more fun without my lab partners and friends Akshay, Shekar, Naveen, Jasspreet, Karthik, Senthil, Kris, Ramki, Madhu Ranjan, Anna, Lin, Hrishi, G.K, Karuna, Seetharam, Pan and Yimin. I specially thank Shashi and Prasan who assisted Dr. Van Ooij during my tenure and with whom I shared an office. I wish to thank my then employers Mr. Kenneth Mazzochi, Mr. William Hand and all others at Park Nameplate, Dover, NH, for their support and for understanding my priority towards this thesis. Finally, I am forever indebted to my family and friends who have been the cornerstones of my life. 8 TABLE OF CONTENTS List of Tables………………………………………………………………………………………………14 List of Figures……………………………………………………………………………………………..15 CHAPTER 1: INTRODUCTION ……………………………………………………….………………..20 1.1 Corrosion……………………………………………………………………………………………..20 1.1.1 Definition……………………………………………………………………………………….20 1.1.2 Theory………………………………………………………………………………………….20 1.1.3 Corrosion Control and its Significance………………………………………………...……25 1.2 Corrosion in the Department of Defense………………………………………………………….27 1.2.1 Coating Technology in DoD………………………………………………………………….31 1.2.2 Chromium: Use, Mechanism, Advantages and Disadvantages…………………………34 1.2.2.1 Use and Methods……………………………………………………………………….34 1.2.2.2 Mechanism………………………………………………………………………………46 1.2.2.3 Advantages of chromate conversion coatings………………………………………48 1.2.2.4 Disadvantages of chromate coatings………………………………………………...49 1.3 Superprimer………………………………………………………………………………………….50 1.3.1 Definition………………………………………………………………………………..50 9 1.3.2 Background and Origin…………………………………………………………………….50 CHAPTER 2: MATERIALS AND TESTING PROCEDURES………………………………………...61 A. Materials………………………………………………………………………………………………..61 A.2.1 Silanes……………………………………………………………………………………..61 A.2.2 Resins……………………………………………………………………………………..62 A.2.3 Particles……………………………………………………………………………………63 A.2.4 Inhibitors…………………………………………………………………………………..63 A.2.5 Metals/ Alloys……………………………………………………………………………..64 B. Testing Procedures……………………………………………………………………………………65 B.2.1 Electrochemical Impedance Spectroscopy……………………………………………65 B.2.2 Salt Spray Test (ASTM B 117)………………………………………………………….65 B.2.3 NMR Spectroscopy………………………………………………………………………66 B.2.4 Infrared Spectroscopy……………………………………………………………………71 B.2.5 Scanning Electron Microscopy (SEM/EDX)…………………………………………...76 B.2.6 Film Hardness Test………………………………………………………………………77 B.2.7 Tape Adhesion Test……………………………………………………………………...78 B.2.8 Solvent Resistance Test ………………………………………………………………79 CHAPTER 3: SUPERPRIMER: FORMULATION, PREPARATION AND TEST RESULTS……...80 10 3.1 Choice of the components…………………………………………………………………80 3.1.1 Chemistry ………………………………………………………………………..81 3.2 Initial Formulations and Results…………………………………………………………...82 3.2.1 Formulations……………………………………………………………………..82 3.2.2 Results……………………………………………………………………………84 3.3 Superprimer Formulation…………………………………………………………………..85 3.4 Test Results…………………………………………………………………………………88 3.5 Improved Formulations…………………………………………………………………….90 3.6 Test Results of Formulation F-6………..…………………………………………………91 3.7 Conclusion…………………………………………………………………………………..92 CHAPTER4: ADDITIVES TO PRIMER……………………………………………….……………..…93 4.1 Pigments/Particles………………………………………………………………………….93 4.1.1 Silica, Alumina and Carbon Black……………………………………………..94 4.2 Results and Discussion…………………………………………………………………….95 4.3 Corrosion Inhibitors……………………………………………………………………..…102 4.3.1 Results and Discussion…………………………………………………...…..103 4.4 Conclusion………………………………………………………………………………….106 11 CHAPTER 5: ZINC RICH SUPERPRIMER……………………………………………………...…..108 5.1 Uses and Applications…………………………………………………………………….108 5.2 Mechanism…………………………………………………………………………………117 5.3 Zinc – Rich Superprimer………………………………………………………………….120 5.3.1 Formulation, Mixing and Coating…………………………………………….120 5.3.2 Results and Discussion……………………………………………………….121 5.4 Conclusion………………………………………………………………………………….126 CHAPTER 6: CHARACTERIZATION ……………………………………………………………..….128 6.1 NMR Characterization…………………………………………………………………….130 6.1.1 Objective and Sample Preparation………………………………………….130