Niobium aluminothermic reduction

In the aluminothermic reduction of niobium oxides, the products must reach a temperature of at least about 2470 °C, and hence the heat required to raise niobium metal and alumina from room temperature to this temperature must be estimated. Using the values of the heat capacities and the heats of fusion for niobium and alumina, the following figures can be obtained ... 

The reactor used for the aluminothermic reduction of niobium pentoxide is shown schematically in Figure 4.17 (A). It is a steel pipe, lined on the inside with alumina and provided with a pipe cap. The charge, consisting of stoichiometric amounts of niobium pentoxide and aluminum powder, is blended and loaded in the lined pipe, and covered with alumina. The cap is closed and the reaction initiated by placing the loaded bomb in a gas-fired furnace, preheated to 800 °C, and by raising the temperature of the furnace to 1100 °C. 

Figure 4.17 B Schematic of the reactor for open aluminothermic reduction of niobium pentoxide.

Vanadium forms numerous oxides, the most important of which are vanadium monoxide, vanadium sesquioxide, vanadium dioxide and vanadium pentoxide. In the earlier examples (e.g., oxides of chromium and of niobium) the enthalpy values for the aluminothermic reduction of each of the oxides was given for the purpose of illustration. Normally, the consideration can be restricted to only those oxides which are readily obtained and which can be handled freely without any special or cumbersome precautions. In the case of vanadium for example, it is sufficient to consider the reduction of the sesquioxide (V203) and the pentoxide (V2Os). The pertinent reactions are ... 

Ferrovanadium stands as a major industrially used form of vanadium. Similarly, it is in the form of ferroniobium that the bulk of niobium is used industrially. Aluminothermic reduction is an elegant metallurgical process for the production of these ferroalloys in their practically carbon-free forms. 

Columbium (also known as niobium) and tantalum metals are produced from purified salts, which are prepared from ore concentrates and slags resulting from foreign tin production. The concentrates and slags are leached with hydrofluoric acid to dissolve the metal salts. Solvent extraction or ion exchange is used to purify the columbium and tantalum. The salts of these metals are then reduced by means of one of several techniques, including aluminothermic reduction, sodium reduction, carbon reduction, and electrolysis.19-21 Owing to the reactivity of these metals, special techniques are used to purify and work the metal produced. 

Metallic niobium is generally produced by aluminothermic reduction ofNb205. Generally an excess of A1 is used, producing a Nb-Al alloy to give Nb which may be melted in vacuum or by electron beam or arc furnace. 

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