Methods of titanium sponge production

Titanium metal is available in the earth's crust predominantly in the form of oxide minerals. It is one of the 'difficult to extract' metals mainly due to its high melting point (1663 deg C), high chemical reactivity (reacts/alloys readily with a large number of metallic /non-metallic elements.) and high thermodynamic stability of its oxide, TiO2. Early attempts to reduce titanium dioxide by conventional means of carbothermic, metallo-thermic (by Mg, Al, Si etc) and hydrogen etc have not been successful as the product had always been contaminated with brittle impurities impairing the mechanical properties of the metal. Electrolysis of titanium dioxide in molten fluorides was also tried in vain. Researchers were successful in obtaining pure and ductile metal only when a non-oxygen bearing titanium compound was used as the starting material. Berzellus reduced K2TiF6 with sodium (1825), Claire Deville reduced TiCl4 with sodium (1855) which was later improved by Nilson & Patterson (1887) and further modified by Hunter (1910), van Arkel and de Boer tried dissociation of TiI4 on hot filament and Kroll developed magnesium reduction of TiCl4 (1937) for producing titanium metal of high purity. Electrowinning of titanium by fused salt electrolysis of TiCl4 in molten alkali chloride mixture also yielded titanium with desired purity. Historical developments in titanium extraction metallurgy are discussed in detail in the literature1-3.