Chromium metal powder

Preparation. In one method a mixture of 9 g. of chromium metal powder (Fisher) and 100 ml. of 6Af hydrochloric acid was stirred with water cooling to room temperature until the reacllon was complete. A deoxygenated solution of... 

The catalyst system for the modem methyl acetate carbonylation process involves rhodium chloride trihydrate [13569-65-8]y methyl iodide [74-88-4], chromium metal powder, and an alumina support or a nickel carbonyl complex with triphenylphosphine, methyl iodide, and chromium hexacarbonyl (34). The use of nitrogen-heterocyclic complexes and rhodium chloride is disclosed in one European patent (35). In another, the alumina catalyst support is treated with an organosilicon compound having either a terminal organophosphine or similar ligands and rhodium or a similar noble metal (36). Such a catalyst enabled methyl acetate carbonylation at 200°C under about 20 MPa (2900 psi) carbon monoxide, with a space-time yield of 140 g anhydride per g rhodium per hour. Conversion was 42.8% with 97.5% selectivity. A homogeneous catalyst system for methyl acetate carbonylation has also been disclosed (37). A description of another synthesis is given where anhydride conversion is about 30%, with 95% selectivity. The reaction occurs at 445 K under 11 MPa partial pressure of carbon monoxide (37). A process based on a montmorillonite support with nickel chloride coordinated with imidazole has been developed (38). Other related processes for carbonylation to yield anhydride are also available (39,40). 

Miscellaneous Methods. Powdered metals such as aluminum, chromium, nickel, and copper, along with various aHoys, can be appHed to parts by electrostatic deposition. The metal strip containing the attached powdered metal must be further processed by cold rolling and sintering to compact and bond the metal powder. 

Chromium oxide is mixed with aluminum powder, placed in a refractory-lined vessel, and ignited with barium peroxide and magnesium powder. The reaction is exothermic and self-sustaining. Chromium metal of 97—99% purity is obtained, the chief impurities being aluminum, iron, and silicon (Table 4). Commercial chromium metal may also be produced from the oxide by reduction with silicon in an electric-arc furnace. 

Consolidation and Fabrication. Chromium metal may be consoHdated by powder metallurgy techniques or by arc melting in an inert atmosphere (8,13,24,25) (see Metallurgy Metallurgy, powder). 

Water-Soluble Trivalent Chromium Compounds. Most water-soluble Cr(III) compounds are produced from the reduction of sodium dichromate or chromic acid solutions. This route is less expensive than dissolving pure chromium metal, it uses high quaHty raw materials that are readily available, and there is more processing fiexibiHty. Finished products from this manufacturing method are marketed as crystals, powders, and Hquid concentrates. 

In a thermite process to produce chromium metal, the mechanically-mixed ingredients were ignited in a large crucible and the reaction proceeded smoothly. When the mixer broke down, manual mixing was used but gave poorer dispersion of the constituents. An explosion after ignition is attributed to a high local concentration of sodium chlorate and aluminium powder in the mixture. 

A( ueous solutions of chromium(ll) sulfate have Ijeen prepared from chromium(lll) sulfate by reduction with zinc powder and from potassium dichromate by reduction with amalgamated zinc and sulfuric acid. Solid chromitim(II) sulfate penlahyrlrate can be obtained from the reaction of highly purified chromium metal... 

Chromium metal is produced hy thermal reduction of chromium(III) oxide, Cr203 by aluminum, silicon or carbon. The starting material in all these thermal reduction processes are Cr203 which is obtained from the natural ore chromite after the removal of iron oxide and other impurities. In the aluminum reduction process, the oxide is mixed with A1 powder and ignited in a refractory-lined vessel. The heat of reaction is sufficient to sustain the reaction at the required high temperature. Chromium obtained is about 98% pure, containing traces of carbon, sulfur and nitrogen. 

Cobalt-chromium alloy (see Chromium and chromium compounds) Cobalt-chromium-molybdenum alloys (see Cobalt and cobalt compounds) Cobalt metal powder (see Cobalt and eobalt compounds)... 

Metallurgy aluminothermic production of chromium metal by reaction of aluminum powder and Cr203... 

Information regarding genotoxic effects in animals after inhalation exposure to chromium or its compounds is limited. Sprague-Dawley rats that inhaled chromium fumes generated from powders of chromium metal by a plasma flame thrower at 1.84 or 0.55 mg chromium(0)/m3 (5 hours/day,... 

The preparation of TiC, VC, NbC, TaC, M02C, WC, and the chromium carbides are important technical processes for the production of carbide powders for hardmetals. Generally, the carbides are prepared by the reduction of oxides with carbon only M02C and WC are manufactured by reaction of the metal powders with graphite or carbon black. 

Available forms (1) Chromium metal as lumps, granules, or powder (2) high- or low-carbon ferro-chromium (3) single crystals, high-purity crystals, or powder run 99.97% pure. 

Chromium Doping. Additions of chromium compounds can be used to produce very fine metal powder grades (<0.5 pm). Chromium oxide is formed during reduction and acts as a grain refiner. Such powders are subsequently carburized to ultrafine WC. Special precautions have to be taken because of the high pyrophoricity of the metal powder. 

Pure chromium(III) iodide can be prepared by the direct reaction of powdered chromium metal with iodine.1 The procedure given here can be used conveniently to prepare quantities up to 25 g. 

Mold design. PTFE resins are molded in molds similar to those utilized for thermosetting resins or metal powders. A complete mold consists of a cylindrical or rectangular die and upper and lower end plates and a mandrel for annular parts. These parts are normally made of tool steel to allow machining, and plated with chromium or nickel to protect them from corrosion. Occasionally, the end plates are made of brass or plastics such as nylon. A small diametrical clearance is designed in the end plates to allow easy assembly and air escape. 

CHROMIUM (7440-47-3) Cr Chromium metal (especially in finely divided or powder form) and insoluble salts react violently with strong oxidants such as hydrogen peroxide. 

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