Vanadium Alloys

Aluminium appears to alloy with vanadium in all proportions. The alloys can be prepared by melting aluminium in a crucible and igniting a mixture of vanadium pentoxide on the top, or by reducing a mixture of aluminium, alumina, and vanadium pentoxide, with addition of cryolite and fluorspar, in the electric furnace. They can also be produced by reducing vanadium pentoxide with carbon in the electric furnace in the presence of aluminium, but the product then contains appreciable quantities of carbide. Vanadium-aluminium alloys containing from 30 to 80 per cent, of vanadium have been obtained by the first-mentioned processes; fusion of these with aluminium gives products of lower vanadium content. By the regulated action of acids on these alloys crystals having the composition Al₃V and AlV have been isolated, and the existence of a third compound, AlV₂, has been suggested. The mechanical properties of vanadium- aluminium alloys have not been fully studied, but it has been shown that 2 per cent, of vanadium in aluminium results in substantial increase in the strength and hardness of the rolled and annealed metal. The elongation of the annealed alloy falls, but even with 4 per cent, vanadium it is sufficiently high for most purposes.

Vanadium possesses the property in common with a large number of other metals of forming complex alloys with aluminium and silicon. Several of these vanadium-aluminium-silicides, each possessing different crystalline form, have been obtained by fusing together potassium silicofluoride, aluminium, and ammonium metavanadate in varying proportions. One of the products formed in the presence of a large excess of silicon has the composition V₈Al₂Si₁₃. It yields hexagonal, prismatic needles of density 4.3 and hardness 5. It is a remarkably stable compound, being unattacked by boiling concentrated hydrochloric acid, sulphuric acid, nitric acid, aqua-regia, or fused potassium chlorate. It reacts, however, with fused alkalis and with hydrofluoric acid to give, in the absence of air, a solution of hypovanadous fluoride, VF₂, which rapidly oxidises to vanadous fluoride, VF₃.

Alloys of copper and vanadium are prepared by firing a mixture of vanadium pentoxide, copper oxide, aluminium shot, lime, soda-ash, and fluorspar with the aid of sodium peroxide in a magnesia- lined crucible. Electrolytic methods have also been employed, and are applicable for the preparation of other vanadium alloys. An alloy containing 3.38 per cent, of vanadium and 96.52 per cent, of copper was found to be harder than copper and could be drawn into wire. An aluminium-copper-vanadium alloy has been prepared.

A laboratory method of preparation consists in passing a mixture of hydrogen and vanadium tetrachloride vapour over iron at 900° C. Alloys of iron and vanadium which contained varying quantities of carbon were prepared by Moissan. The freezing-point curve for alloys of iron and vanadium falls from the melting-point of iron (1530° C.) to a minimum at 32 per cent, of vanadium, and then rises to the melting-point of vanadium (1750° C.). As the alloys are homogeneous the metals form a complete series of mixed crystals. A commercially useful alloy containing about 30 per cent, of vanadium is hard but not brittle, and is difficult to pulverise; its specific gravity is about 7.3 and its melting-point lies between 1340° and 1400° C. The presence of silicon in the alloy increases its hardness and brittleness. The temper-colours of iron-vanadium alloys have been studied by Tammann and Siebel.

The solubility of vanadium in mercury is too small for measurement.

Vanadium and nickel are miscible in all proportions in the liquid state up to 36 per cent, vanadium. The solid alloys, which contain up to 20 per cent, vanadium, appear to be homogeneous, but those richer in vanadium consist of two kinds of crystals. These alloys are made by reducing a mixture of vanadium pentoxide and nickel oxide.

Vanadium does not alloy with silver.