Chromium aluminothermic process

The total heat requirement is thus around 599.98 kj, which is about 548.81 kj more than the heat available from the reaction. This calculation, however, does not take into account the inevitable heat losses due to the nonadiabatic conditions in the reactor. An estimate of these heat losses can be made by considering the industrial practice for aluminothermic chromium metal production. The charge is preheated to about 500 °C before loading into the aluminothermic crucible. This operation adds about 96.65 kj (i.e., 48.9 cal deg-1 475) of heat to the system. It, therefore, appears that around 41.84 kj (96.65 kj - 54.81 kj) of heat is lost due to radiation and convection for every mole of chromium sesquioxide reduced to the metal by the aluminothermic process. 

The production of metals which form very stable oxides by the aluminothermic process, such as manganese, chromium and vanadium is carried out with reactants at room temperature which react to provide enough heat to raise the temperature of the products to high temperatures at which the whole system is liquid. The metal phase which is produced can therefore separate from the liquid slag which is formed. The production of chromium serves as a useful... 

The general method of producing a metai by reduction of its oxide by aluminum is called the Goldschmidt process or aluminothermic process Fig. 251.) Metallic chromium is also made by electrolytic reduction of compounds, usually chromic acid in aqueous solution. 

Oxidation states of chromium - -2, - -3, and -f-6. Oi es of chromium chronate, FeCr204, and crocoite, PbCr04. Chromium metal and its alloys ferrochrome, alloy steels, stainless steel. The aluminothermic process (Goldschrtiidt process). Electrolytic chromium. Chromium trioxide, chromic acid, dichromic acid, potassium chromate, potassium didiromate, sodium chromate, lead chromate. Equilibrium between chromate ion and dichromate ion. Chrome-tanned leather. Chromic oxide (chrome green) chromic ion, chrome alum, chromic chloride, chromic hydroxide, chromite ion. Chromous compounds. Peroxy-chromic acid. 

NICKEL-CHROMIUM-BORON ALLOYS PRODUCTION BY ALUMINOTHERMIC PROCESSES... 

Nickel-Chromium-Boron Alloys Production by Aluminothermic Processes. ..335... 

Pure chromium metal is obtained commercially from the aluminothermic or silicother-mic reduction of chromium sesquioxide, or chromia (Cr Oj), and to a lesser extent by electrowinning. In the aluminothermic process, first the chromia is prepared by the soda-ash roasting of chromite ore. After mixing the raw chromite ore with sodium carbonate or soda... 

The aluminothermic process yields pure chromium metal (97 to 99 wt.% Cr), the major impurities being Al, Fe, C, and Si. Chromium metal can also be produced by the silicother-mic process performed in a submerged-arc furnace to yield pure chromium metal with no aluminum but with 0.8 wt.% Si according to the following reactions ... 

The heat liberated by this reaction is so great as to produce molten chromium. The aluminothermic process is a convenient way of obtaining a small amount of liquid metal, such as iron for welding. 

Ferrochrome (UK, France), or ferrochromium (USA), is a master alloy of iron and chromium containing between 40 and 75 wt.% Cr and varying amounts of carbon and silicon. It is prepared industrially by three different electrothermal processes—the carbothermic, the silicothermic, or the aluminothermic reduction of chromite ore, which is used as the main source of chromium. In the carbothermic process, a charge of chromite ore mixed with lime as fluxing agent is reduced by metallurgical coke or coal as reductant in a three-phase submerged-arc furnace. The overall chemical reaction involved is as follows ... 

Metallic chromium is also produced by an electrolytic method. Ferrochromium is crushed and dissolved at a temperature near the boiling point in a mixture of sulfuric acid and used anolyte. In a crystallizer the iron is separated as iron ammonium sulfate at a temperature of 5°C. The temperature in the electrolytic cells is 53°C. In the process sulfuric add and hexavalent chromium are formed in the anolyte. Because of that it must be prevented from mixing with the catholyte. Otherwise the divalent chromium there wiU be oxidized and the chromium predpitation disturbed. The cathode material is 316-type molybdenum-alloyed stainless steel, the anode material silver-alloyed lead or titanium covered with iridium. For environmental reasons dichromate plants are dosed and the aluminothermic part of the chromium metal production increases. About 1990 it was 60 % and in the begiiming of the 2000s 90 %. 

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