Titanium with low oxygen content has been expected to be obtainable by direct reduction of titanium dioxide with saturated calcium vapor, because it can remove the oxygen to the extent to which it is able to overcome the affinity of the oxygen for the metal in the solid solution range.
A knowledge of the thermodynamic stability of oxygen in the Ti-O solid soluton is indispensable in any discussion of the refining of titanium from its oxide. Oxygen in titanium has, however, so high stability that ordinary gas equilibration or EMF method using solid electrolyte is not applicable to activity measurement. In this investigation, titanium metal was, therefore, equilibrated under coexistence of saturated calcium vapor and calcium oxide in closed bombs of steel at temperatures between 1173 and 1573 K, quenched and analysed for oxygen. The equilibrium gas concentrations were 300 and 900 mass ppm at 1173 and 1573 K, respectively. The data were then used to derive the relationship among oxygen potential, temperature and composition in the β-Ti phase field:
(This article is not displayable. Please see full text pdf.)
Attempts were made to produce titanium by reducting TiO₂ powders with saturated calcium vapors at 1273 K according to
(This article is not displayable. Please see full text pdf.)
\ oindentElectron micrographs of the reduction products showed that the reduced titanium particles were completely surrounded with the solid reaction product, CaO. The reduction rate become very low at the reduction stage at which the decomposition of oxide almost ceased and the deoxidation of the Ti-O solid solution began to take place.