Aluminothermic method

Aluminothermal Method. Calcium metal is produced by high temperature vacuum reduction of calcium oxide in the aluminothermal process. This process, in which aluminum [7429-90-5] metal serves as the reducing agent, was commercialized in the 1940s. The reactions, which are thermodynamically unfavorable at temperatures below 2000°C, have been summarized as ... 

If CaaPg is to be used only as a raw material for the preparation of PH3, it can be prepared by the aluminothermic method. The drawback of this procedure is that the product phosphide cannot be separated from the AI3O3. 

In 1906 Werner von Bolton at Siemens Halske in Germany manufactured niobium by the aluminothermic method and purified it by repeated re-melting in a vacuum furnace. 

Ferroniobium is manufactured using the aluminothermic method described for ferrovanadium. The alloy is used as a furnace addition to give steel a specified niobium content. Brazil is the world s biggest producer of ferroniobium. An aluminothermic charge can be composed of 18 tonnes pyrochlore, 4 tonnes hematite, 6 tonnes aluminum powder and 0.5-0.75 tonnes each of lime and fluorspar. From the reaction an 11-tonnes ingot with 65-70% Nb is obtained. 

Fig. 1. Flow diagram for aluminothermic process showiag alternative methods of aluminum removal from alloy regulus.

Electrolysis. Although in Western countries the aluminothermic process has now completely replaced the electrolytic method, electrolysis is beheved to be the method used for calcium production in the People s RepubHc of China and the Commonwealth of Independent States (CIS). This process likely involves the production of a calcium—copper alloy, which is then redistilled to give calcium metal. 

Vanadium metal can be prepared either by the reduction of vanadium chloride with hydrogen or magnesium or by the reduction of vanadium oxide with calcium, aluminum, or carbon. The oldest and most commonly used method for producing vanadium metal on a commercial scale is the reduction of V2Os with calcium. Recently, a two-step process involving the aluminothermic reduction of vanadium oxide combined with electron-beam melting has been developed. This method makes possible the production of a purer grade of vanadium metal, ie, of the quality required for nuclear reactors (qv). 

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. 

Uranous Arsenide, UgASj, may be obtained by methods similar to those employed for the phosphide (see p. 827). When obtained bypassing h drogen over a fused mixture of sodium uranous chloride and sodium arsenide it is a greyish powder wliich readily burns in the air. It is sometimes obtained in a pj-rophoric condition. An aluminium-containing product results when the aluminothermic jiroeess, using an oxide of uranium and arsenious oxide, is employed. The purest arsenide is obtained in the crj stalline form when a mixture of hj drogen and arsenic vapour is passed over sodium uranium chloride. It is rapidly decomposed bj nitric acid. 

The starting alloy is usually prepared by fusion of the components this fusion should yield as homogeneous a structure as possible [39]. In another method, a fine powder of the pure catalytic metal is mixed with A1 powder the mixture is pressed into tablets and sintered for some time at moderate (of the order of 700°C) temperatures [46]. The Raney alloys can also be obtained by aluminothermic synthesis [11]. 

The second method involves the addition of high heat producing extraneous oxidizers. Frequently mentioned are barium peroxide and other strong oxidizers such as lead dioxide, sodium persulfate (NagSOg) and even chlorate. Kuhne claims such additions for the aluminothermic production of numerous metals, and Cueilleron and Pascand for aluminum/titanium alloys. ... 

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 %. 

This is the case, for instance, for K2Sip6 which in an aluminothermic reaction provides in situ the Al-Si clad (molten fiUer metal) normally used for controlled atmosphere brazing (CAB) of aluminium. In the case of zinc, the primary objective is not only to form a clad but to obtain a homogeneous diffusion layer into the aluminium, which is needed for some applications and which would have to be otherwise applied by costly intensive methods like electrochemical galvanization, plasma coating or thermal spray coating. 

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