Preparation of Alumina-Chromium Composites by Reactive Hot-Pressing A1 + Cr2o3 Based Powders D
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
Historical Development of the Periodic Classification of the Chemical Elements
THE HISTORICAL DEVELOPMENT OF THE PERIODIC CLASSIFICATION OF THE CHEMICAL ELEMENTS by RONALD LEE FFISTER B. S., Kansas State University, 1962 A MASTER'S REPORT submitted in partial fulfillment of the requirements for the degree FASTER OF SCIENCE Department of Physical Science KANSAS STATE UNIVERSITY Manhattan, Kansas 196A Approved by: Major PrafeLoor ii |c/ TABLE OF CONTENTS t<y THE PROBLEM AND DEFINITION 0? TEH-IS USED 1 The Problem 1 Statement of the Problem 1 Importance of the Study 1 Definition of Terms Used 2 Atomic Number 2 Atomic Weight 2 Element 2 Periodic Classification 2 Periodic Lav • • 3 BRIEF RtiVJiM OF THE LITERATURE 3 Books .3 Other References. .A BACKGROUND HISTORY A Purpose A Early Attempts at Classification A Early "Elements" A Attempts by Aristotle 6 Other Attempts 7 DOBEREBIER'S TRIADS AND SUBSEQUENT INVESTIGATIONS. 8 The Triad Theory of Dobereiner 10 Investigations by Others. ... .10 Dumas 10 Pettehkofer 10 Odling 11 iii TEE TELLURIC EELIX OF DE CHANCOURTOIS H Development of the Telluric Helix 11 Acceptance of the Helix 12 NEWLANDS' LAW OF THE OCTAVES 12 Newlands' Chemical Background 12 The Law of the Octaves. .........' 13 Acceptance and Significance of Newlands' Work 15 THE CONTRIBUTIONS OF LOTHAR MEYER ' 16 Chemical Background of Meyer 16 Lothar Meyer's Arrangement of the Elements. 17 THE WORK OF MENDELEEV AND ITS CONSEQUENCES 19 Mendeleev's Scientific Background .19 Development of the Periodic Law . .19 Significance of Mendeleev's Table 21 Atomic Weight Corrections. 21 Prediction of Hew Elements . .22 Influence -
Chromium Compounds Hazard Summary
Chromium Compounds Hazard Summary Chromium occurs in the environment primarily in two valence states, trivalent chromium (Cr III) and hexavalent chromium (Cr VI). Exposure may occur from natural or industrial sources of chromium. Chromium III is much less toxic than chromium (VI). The respiratory tract is also the major target organ for chromium (III) toxicity, similar to chromium (VI). Chromium (III) is an essential element in humans. The body can detoxify some amount of chromium (VI) to chromium (III). The respiratory tract is the major target organ for chromium (VI) toxicity, for acute (short-term) and chronic (long-term) inhalation exposures. Shortness of breath, coughing, and wheezing were reported from a case of acute exposure to chromium (VI), while perforations and ulcerations of the septum, bronchitis, decreased pulmonary function, pneumonia, and other respiratory effects have been noted from chronic exposure. Human studies have clearly established that inhaled chromium (VI) is a human carcinogen, resulting in an increased risk of lung cancer. Animal studies have shown chromium (VI) to cause lung tumors via inhalation exposure. Please Note: The main sources of information for this fact sheet are EPA's Integrated Risk Information System (IRIS) (7), which contains information on inhalation chronic toxicity and the RfC and oral chronic toxicity and the RfD, and the carcinogenic effects of chromium including the unit cancer risk for inhalation exposure, EPA's Toxicological Review of Trivalent Chromium and Toxicological Review of Hexavalent Chromium (3), and the Agency for Toxic Substances and Disease Registry's (ATSDR's) Toxicological Profile for Chromium. (1) Uses The metal chromium is used mainly for making steel and other alloys. -
The Influence of Heavy Metals and Organic Matter on Hexavalent
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Archivio della ricerca- Università di Roma La Sapienza 289 A publication of CHEMICAL ENGINEERING TRANSACTIONS VOL. 47, 2016 The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Angelo Chianese, Luca Di Palma, Elisabetta Petrucci, Marco Stoller Copyright © 2016, AIDIC Servizi S.r.l., ISBN 978-88-95608-38-9; ISSN 2283-9216 DOI: 10.3303/CET1647049 The Influence of Heavy Metals and Organic Matter on Hexavalent Chromium Reduction by Nano Zero Valent Iron in Soil Mouhamadou Thierno Gueyea, Luca Di Palmab, Gunel Allahverdeyevac, Irene b b b b Bavasso , Elisabetta Petrucci , Marco Stoller , Giorgio Vilardi a Université Cheikh Anta Diop de Dakar (UCAD), Dakar Fann, Senegal b Sapienza Università di Roma, Dipartimento di Ingegneria Chimica Materiali Ambiente, via Eudossiana 18, 00184 Roma c Baku State University, 23 Khalilov St., Baku, Azerbaijan During the last decades great attention has been payed at evaluating the feasibility of Cr(VI) reduction in soil 0 by nano zero valent iron (nZVI). An inhibitory effect on the Cr(VI) reduction by Fe nanoparticles is generally shown in the presence of high level of heavy metals and natural organic matter in soil. Heavy metals in the environment can react with nZVI by redox reactions, precipitation/dissolution reactions, and adsorption/desorption phenomena. As a result of the presence of metals as Ni, Pb, a decrease in the rate of Cr(VI) reduction was observed. Hence, in the present study, experimental tests of Cr(VI) reduction by nZVI in the presence of selected heavy metals, such as nickel and lead, and in the presence of high level of organic matter, are presented and discussed. -
Periodic Table 1 Periodic Table
Periodic table 1 Periodic table This article is about the table used in chemistry. For other uses, see Periodic table (disambiguation). The periodic table is a tabular arrangement of the chemical elements, organized on the basis of their atomic numbers (numbers of protons in the nucleus), electron configurations , and recurring chemical properties. Elements are presented in order of increasing atomic number, which is typically listed with the chemical symbol in each box. The standard form of the table consists of a grid of elements laid out in 18 columns and 7 Standard 18-column form of the periodic table. For the color legend, see section Layout, rows, with a double row of elements under the larger table. below that. The table can also be deconstructed into four rectangular blocks: the s-block to the left, the p-block to the right, the d-block in the middle, and the f-block below that. The rows of the table are called periods; the columns are called groups, with some of these having names such as halogens or noble gases. Since, by definition, a periodic table incorporates recurring trends, any such table can be used to derive relationships between the properties of the elements and predict the properties of new, yet to be discovered or synthesized, elements. As a result, a periodic table—whether in the standard form or some other variant—provides a useful framework for analyzing chemical behavior, and such tables are widely used in chemistry and other sciences. Although precursors exist, Dmitri Mendeleev is generally credited with the publication, in 1869, of the first widely recognized periodic table. -
Massachusetts Chemical Fact Sheet
Massachusetts Chemical Fact Sheet Hexavalent Chromium Table 1: HEXAVALENT CHROMIUM COMPOUNDS: Compounds SELECTED EXAMPLES* Compound Chemical Formula CAS # This fact sheet is part of a series of chemical fact sheets Ammonium chromate (NH ) Cr0 7788-98-9 developed by TURI to help Massachusetts companies, 4 2 4 community organizations and residents understand the Ammonium dichromate (NH4)2Cr2O7 7789-09-5 chemical’s use and health and environmental effects, as Barium chromate BaCrO4 10294-40-3 well as the availability of safer alternatives. tert-Butyl Chromate [(CH3)3CO]2CrO2 1189-85-1 Hexavalent chromium compounds are a toxic form of Calcium chromate CaCrO4 13765-19-0 chromium and are used in a variety of industrial processes Chromic acid H2CrO4 7738-94-5 and products. Chromium VI chloride CrCl6 14986-48-2 Hexavalent chromium compounds are human carcinogens, Chromic trioxide CrO3 1333-82-0 mutagens and developmental toxicants and are acutely Hexavalent chromium ion Cr6+ 18540-29-9 toxic. Non-hexavalent chromium compounds do not pose Lead chromate PbCrO4 7758-97-6 the same level of concern with regard to either chronic or Lead chromate oxide PbCrO4-PbO 8454-12-1 acute toxicity. Potassium chlorochromate KCrO3Cl 16037-50-6 Until 2011, all chromium compounds were treated as Potassium chromate K2CrO4 7789-00-6 a single category under TURA. Beginning with Potassium dichromate K Cr O 7778-50-9 reporting year 2012, hexavalent chromium 2 2 7 compounds are reportable under TURA as a Silver chromate Ag2CrO4 7784-01-2 separate category and are designated as a Higher Sodium chromate Na2CrO4 7775-11-3 Hazard Substance, which lowers the reporting Sodium dichromate 7789-12-0 threshold to 1,000 lb/year. -
Chromium 28.07.2020.Pdf
Chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard and brittle transition metal. Chromium is the main additive in stainless steel, to which it adds anti-corrosive properties. Chromium is also highly valued as a metal that is able to be highly polished while resisting tarnishing. Polished chromium reflects almost 70% of the visible spectrum, with almost 90% of infrared light being reflected. Ferrochromium alloy is commercially produced from chromite by silicothermic or aluminothermic reactions and chromium metal by roasting and leaching processes followed by reduction with carbon and then aluminium. Chromium metal is of high value for its high corrosion resistance and hardness. A major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Stainless steel and chrome plating (electroplating with chromium) together comprise 85% of the commercial use. Ores:- Although chromium occurs in many minerals, the only ore exploited commercially is chromite. This spinel mineral is ideally composed of ferrous oxide and chromic oxide with the chemical composition FeO · Cr2O3, but it is often found in nature with magnesia (MgO) substituting for FeO and alumina (A12O3) or ferric oxide (Fe2O3) substituting for Cr2O3. Other minerals such as silica (SiO2) are also present. Extraction:- Chromite, FeCr2O4, is the most commercially useful ore, and is extensively used for extraction of chromium. Chromium is produced in two forms: (a) Ferrochrome by the reduction of chromite with coke in an electric arc furnace. -
Development of Copper-Chromium Electrical Contact Materials by Powder Forging
Development of Copper-Chromium electrical contact materials by Powder Forging 1 2 3 N. N. Gotkhindikar , S.V.Vanjari , D. B. Nigade 1Department of Mechanical Engineering, SSPMCOE ,Kankavli, Maharashtra,(India) 2,3 Department of Mechanical Engineering, SSPMCOE, Kankavli, Maharashtra, (India) ABSTRACT The electrical contacts form an integral part of circuit interrupters for which the desirable properties of contact materials are high mechanical strength, high electrical and thermal conductivity, high wear and weld resistance. Despite of different manufacturing techniques like electro-slag crucible melting, vacuum arc smelting, vacuum continuous smelting etc.; the Powder Forging being a solid state process and having high densification factor is an efficient method for the production of electrical contact materials. In the present study Cu-Cr30 wt. % alloys are prepared from elemental powders by sinter-forging. Nb is also added in varying quantities to improve the electrical and mechanical properties and the forging temperature is also varied .The variation in contact material properties due to these changes are tabulated and compared. Keywords: Powder forging, SEM, XRD, EDS, Elemental mapping, Sinter-forging etc. I.INTRODUCTION Over past 50 years, contact materials based on Cu-Cr have become established for the use in vacuum interrupters for medium voltage switches. They are used as contactors and circuit breakers within a voltage range of 1 kV to 75 kV. The vacuum circuit breaker is such a kind of circuit breaking instrument where the arc quenching occurs in vacuum. For higher voltages vacuum technology has been developed but not commercially viable [1]. For current carrying contacts which material used plays vital role in performance of vacuum circuit breaker. -
Testing Serum Cobalt and Chromium in People with Metal-On-Metal Hip Replacements
Testing serum cobalt and chromium in people with metal-on-metal hip replacements Metal-on-metal hip replacements and resurfacings are associated with higher than acceptable failure rates, and particularly high-risk devices have been recalled. While the number of patients who have high-risk prostheses in New Zealand is low, the media coverage of the issue is likely to have caused anxiety in the large number of people who have received hip replacements. Identifying patients who have received a metal-on-metal hip prosthesis and regularly reviewing any symptoms and monitoring serum cobalt and chromium levels will help to detect those with potentially failing devices, and provide reassurance to others. Hip replacements and metal toxicity Modern prostheses rarely fail, regardless of construction material. Metal-on-metal hip prostheses have a failure A metal-on-metal hip prosthesis refers to a device in which rate that is higher than is generally acceptable for medical the head on top of the femoral stem and the bearing surface devices, however, the majority of people with a metal-on- of the acetabular cup are made of a cobalt-chromium alloy metal hip replacement will have few or no problems with rather than ceramic or polyethylene. In New Zealand the the prosthesis. number of people with metal-on-metal hip prostheses is low relative to other countries. Of the approximately 7000 Failure of a metal-on-metal prosthesis is a complex end- hip replacements performed in New Zealand each year,1 point, which primarily occurs due to one of two reasons. metal-on-metal implant prostheses account for only 8% Firstly, the level of natural lubrication that occurs in shallow of the total.2 A small percentage of these metal-on-metal artificial acetabular components, i.e. -
The Preparation of Chromium Metal by a Sealed, Cold-Hearth, Plasma-Assisted Aluminothermic Method
The preparation of chromium metal by a sealed, cold-hearth, plasma-assisted aluminothermic method by L.R. Nelson * applications of aluminothermic-reduction technology to the production of metals. Synopsis Future expansion of aluminothermic metal production depends, in part, on the capability The efficiency and cost-effectiveness of the aluminothennic to prove that metal oxides from new sources reduction process in the production of ferro-alloys and 'pure' are amenable to processing. For evaluation of metals depends strongly on appropriate balancing of the process the suitability to aluminothermic reduction of energy required. Insufficient energy results in a poor metal yield, chromic oxide from a unique source, a sealed, while over-supply can result in excessive fuming and possibly even cold-hearth, plasma-assisted test unit was ejection of the reactor contents in a potentially dangerous 'thennite developed. This provided a means of evaluating bomb' reaction. This situation becomes even more critical when the suitability of limited quantities of oxide from new sources must be the aluminothermic preparation of 'pure' evaluated, dictating smaller-scale testwork. The resulting higher chromium metal from a chromic oxide source. relative heat losses from the system complicates control of the This paper gives details of the technique and energy balance, and usually requires the addition of thermal describes the experimental results. boosters or reactant preheating in order to sustain an autothermic process. This often detracts from the quality of the metal product, Process energy required and adds to the hazards of batch aluminothennic-reduction testing. The development of a small-scale method (producing less than General aluminothermic processes 2,5 kg of metal) for the plasma-assisted aluminothennic reduction of chromium oxide that overcomes such difficulties is described. -
Synthesis and Alkali Metal Ion-Binding Properties of a Chromium(III) Triacetylide Complex Louise A
Published on Web 09/04/2002 Synthesis and Alkali Metal Ion-Binding Properties of a Chromium(III) Triacetylide Complex Louise A. Berben and Jeffrey R. Long* Department of Chemistry, UniVersity of California, Berkeley, California 94720-1460 Received June 16, 2002 The prospect of discovering new single-molecule magnets1 with higher blocking temperatures has prompted much recent interest in the synthesis of high-spin clusters. Metal-cyanide coordination clusters are particularly attractive in this arena, because the linear bridging geometry favored by cyanide permits some predictability as to product geometry and magnetic ground state. Here, much of our own effort has focused on the incorporation of corner units such as [(Me3tacn)Cr(CN)3] (Me3tacn ) N,N′,N′′-trimethyl-1,4,7- triazacyclononane) into high-nuclearity clusters.2 To increase the strength of the magnetic exchange coupling in these species, we now propose to replace cyanide with the isoelectronic acetylenediide Figure 1. Structure of the triacetylide complex [(Me3tacn)Cr(CCH)3](2); ligand, CtC2-, for which the symmetric nature and higher charge for clarity, only the acetylide H atoms are shown. The complex resides on a three-fold rotation axis of the crystal. Selected interatomic distances (Å) are expected to enhance the overlap between ligand and metal and angles (deg): Cr-C(1) 2.057(3), Cr-N 2.166(2), C(1)-C(2) 1.201- orbitals. Toward that end, we herein report the synthesis of the (4), C(1)-Cr-C(1′) 94.14(9), C(1)-Cr-N 90.1(1), N-Cr-N 81.10(9), - - triacetylide precursor complex [(Me3tacn)Cr(CCH)3], along with Cr C(1) C(2) 175.5(2). -
Phase-Diagram Study of Alloys in the Iron-Chromium-Molybdenum-Nickel
Journal of Research of the Nalional Bureau of Standards Vol. 58, No.1, January 1957 Research Paper 2728 Phase-Diagram Study of Alloys in the Iron-Chromium Molybdenum-Nickel System c. 1. Bechtoldt and H. C. Vacher Alloys in the iron-chromium-molybdenum-nickcl system were examined after quenching from 2,200°, 2,000°, 1,800°, 1,650°, and 1,500° F. Composit ional limits of stability of seven phases were summarized in diagrams. Fe,Mo was foun d. to be a stable phase; and a ternary phase, not previously reported, was identified to have the approximate composition of 4 p ercen t of chromium, 53 p ercent of iron, and 43 p ercent of molybdenum. 1. Introduction metals. Seventy-percent-iron alloys, made from chromium, iron, molybdenum, and nickel powders, A study was made recently at the Bureau [1 ,2)1 whose source and purity are shown in table 1, were of the microstructures in austenitic stainless steels sintered at 2,500° F , cooled slowly to room tempera containing approximately 3.5 perce nt of molybde ture, reheated to 2,200°, 2,000°, 1,800°, 1,650°, and mun. This study showed that the m icrocon stituents 1,5 00 ° F , and then quenched to room temperature. sigma (a-), chi (x), and carbides could be separated A large range of compositions was covered (fig. 1) from t llC alpha iron (ex Fe ) and gamma iI'on ('Y F e) T An1-!,; 1. N{anufacturer and chemical analyses of metal powders phases by dissolution and then identifi ed by X -r ay diffraction . -
The Nutritional Relationships of Chromium David L
The Nutritional Relationships of Chromium David L. Watts, Ph.D., F.A.C.E.P.1 In 1959 a physiological role for chromium was determined. It is known that chromium is a 1. Trace Elements, Inc., P.O. Box 514, Addison. Texas 75001. constituent of the glucose tolerance factor urine.10 Doisy and co-workers reported that both the (GTF) and is synergistic with insulin in liver and hair levels of chromium in diabetics were promoting cellular glucose uptake. Chromium decreased proportionately.11 The chromium content deficiency produces an increase in the found in the hair is apparently related to and requirement for insulin. Chromium facilitates reflective of chromium nutritional status.12 An insulin at intracellular sites including the increase in TMA chromium levels have been ribosomes, and is known to stimulate some reported in patients receiving chromium enzymes in vitro. Chromium is important for supplementation.13 Thus TMA is a useful tool for the structure and metabolism of nucleic acids.1 evaluating chromium nutrition and tissue storage, 2 3 particularly since biological GTF is significantly active in hair follicles.14 Body Content and Requirements The total body content of chromium in the Conditions Associated with Chromium adult is estimated at 5 to 6 milligrams. Animal Deficiency studies have shown that chromium A number of physiological and disease concentrations are high in the spleen, testes, conditions are related to chromium status and have epididymis, and bone marrow. Tissue shown a correlate with TMA chromium levels. chromium levels are highest at birth and decline with age. The daily requirement for Diabetes chromium based upon urinary excretion studies Hambidge, et al, reported that children with has been estimated at 1 microgram per day.