Titanium Tetrafluoride, TiF₄

Impure Titanium Tetrafluoride, TiF₄, is formed when magnesium titanifluoride, Mg₂TiF₆, or the corresponding barium salt, BaTiF₆, is decomposed by strong ignition; but it is best prepared by one of the three following methods: (i) the action of fluorine on titanium, (ii) the action of anhydrous hydrogen fluoride on titanium, (iii) the action of anhydrous hydrogen fluoride on titanium tetrachloride at 100°-120° C.; for, owing to the high volatility of hydrogen chloride compared with hydrogen fluoride, the reaction

4HF + TiCl ⇔ 4TiF₄ + 4HCl

proceeds in one direction only.

Titanium tetrafluoride is a colourless mass having a density 2.798 at 20.5° C. It boils at 284° C. and at 444° C. has a vapour density of 64.5 (theory = 62.05). It is noteworthy that the boiling-point of the fluoride is above that of the tetrachloride, TiCl₄ (136° C.); this probably indicates that the former is polymerised near its boiling-point. This difference between the tetrafluoride and tetrachloride is in marked contrast with that between the silicon halides, SiF₄ and SiCl₄, and the corresponding halides of other non-metals and metalloids, and relates titanium to the metals rather than the metalloids. The saline nature of the fluoride is further shown by the fact that it is hygroscopic, and forms a clear solution in water, which deposits the hydrate TiF₄.2H₂O on evaporation. With alcohol the compound TiF₄.C₂H₅OH is formed, and with ammonia the compound TiF₄.2NH₃; but, singularly, it does not combine directly with hydrogen fluoride, although the salts M₂TiF₆ are so well known. Roasting with sulphuric acid converts titanium tetrafluoride into titanic oxide.