Vapor Pressures of TiO(g) in Equilibrium with Ti2O3(s) and Ti3O5(s, β); Dissociation Energy of TiO(g)

The vapor in equilibrium with Ti2O3(s) and Ti3O5(s, β) at 1720°C was examined with a mass spectrometer equipped with a Knudsen cell high temperature inlet system. With 50-eV ionizing electrons, the ions TiO+, Ti+, and TiO2+ were observed. Ionization efficiency curves indicated that Ti+ resulted from dissociative ionization of TiO(g). The ions TiO+ and TiO2+ resulted from the parents TiO(g) and TiO2(g), respectively. The intensities of TiO+ and TiO2+ over the temperature range from 1675 to 1770°C indicated that PTiO/PTiO2=4.066. The principal vaporization reaction was 2 Ti2O3(s) ⇄ Ti3O5(s, β) + TiO(g).The vapor pressures of TiO(g) were determined as a function of T by using the Knudsen effusion method. A value of D0o[TiO(g)] of 160.82±4.56 kcal/mole was determined through a ``third-law'' analysis of the data. This value is compared with values determined recently through studies of isomolecular reactions. A value for D0o[TiO2(g)] of 310.37±2.96 kcal/mole was derived.