|Titanium has been prepared in a more or less pure form in many different ways. The methods employed have included (i) the reduction of halogen compounds by metals or hydrogen, (ii) the reduction of titanium dioxide by carbon, silicon, or metals, (iii) the electrolysis of the oxide or other compound. |
Berzelius and Wohler reduced potassium titani-fluoride, K2TiF6, by heating it with sodium or potassium after the manner of the preparation of silicon:
K2TiF6 + 4K = 6KF + Ti;
whilst Wohler and Deville passed the vapour of sodium in a stream of hydrogen over the heated titani-fluoride.
Ebelmen reduced titanium tetrachloride, TiCl4, with hydrogen, whilst Deville was the first to reduce this compound with sodium, a reaction which Nilson and Pettersson subsequently carried out in a wrought-iron bomb, and so obtained a product containing 94 per cent, titanium.
Titanium was obtained by Stahler and Bachran by the ignition of the dichloride in a current of hydrogen at 1100° C.:
2TiCl2 ⇔ TiCl4 + Ti.
When titanium dioxide is reduced with sodium only the lower oxide results, if magnesium is employed the lower oxide is mixed with hydride, whilst aluminium, employed as in the Goldschmidt reaction, yields only an alloy.
When titanium dioxide is reduced with silicon the product always contains this element; and reduction with carbon always yields a product containing, besides carbon, nitrogen absorbed from the air. Moissan has employed this reaction in the electric furnace, however, and has obtained a nearly pure form of titanium by the following method: Artificial titanic oxide is intimately mixed with carbon, then dried and compressed in a cylindrical carbon crucible, which is heated in the electric furnace above the decomposition temperature of the nitride. Fused titanium is thus obtained, above a yellow layer of nitride, below which is the crystalline oxide. The titanium still contains a variable proportion of carbon, which is removed by heating it again as before with more oxide. Thus the metal is obtained free from silicon and nitrogen, but containing about 2 per cent, of carbon. Finally, the metal may be distilled in the electric furnace at a temperature of about 3500° C. under atmospheric pressure and condensed in minute crystals. Wedekind has obtained titanium in a high state of purity by heating titanic oxide with calcium shavings in an evacuated iron vessel.
Borchers and Huppertz have prepared titanium by the reduction of its oxide by electrolytic calcium, the oxide being melted in a bath of fused calcium chloride undergoing electrolysis; and it is claimed that the product is quite free from nitrogen and carbon. Konigsberger and Schilling have prepared titanium containing only a trace of iron and silicon by the electrolysis of rutile with carbon electrodes.