any one of the compounds of titanium and the halogens of the general formula TiXn, where X is a halogen and n = 2–4. The higher halides, TiX4, are more stable and have been studied more thoroughly than the lower halides. The tetra-halides, TiX4, are formed from the reaction of titanium with dry halogens: with fluorine at 150°C, chlorine at 300°C, bromine at 360°C, and iodine at 55°C. From the standpoint of use, the most important tetrahalides are the chlorides and iodides.
Titanium tetrachloride, TiCl4, is a heavy, colorless liquid with a pungent odor, a density of 1.727 g/cm3 at 20°C, and a boiling point of 136°C; the compound fumes upon exposure to air. It is obtained from the action of chlorine on a mixture of TiO2 and carbon at a temperature of 700°–800°C. Titanium tetrachloride serves as starting material in the commercial production of metallic titanium; its military use derives from its ability to create smoke screens, described by the reaction TiCl4 + 2H2O = TiO2+ 4HC1. Titanium tetraiodide, Til4, occurs as reddish brown crystals with a metallic luster, a density of 4.27–4.40 g/cm3, a melting point of 150°–156°C, and a boiling point of 377°C. It is used in producing titanium metal of high purity.