The high temperature vaporization and thermodynamics of the titanium oxides. XI. Stoichiometric titanium monoxide

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Abstract
Vaporization measurements by the Knudsen technique and by mass spectrometry have been performed on the incongruently vaporizing titanium monoxide at the stoichiometric composition. Over this sample at 1806 K Ti(g) has a higher pressure than TiO(g) by a factor of about 3.5. The free energy difference between TiO(g) and TiO(s) is the first primary result, and its value at 1806 K of 63.3±2.0 kcal/mole is independent of auxiliary data. The second primary result is the activity of Ti, 0.13±0.04, in nearly stoichiometric TiO at the same temperature. Over the temperature range 1694–1919 K, the pressures of the various species are given by the equation lnP=−A/RT+B/R, and the values of the parameters A in kcal/mole and B in e.u. are for Ti 116.3±3.2 and 31.8±1.8; TiO, 130.2±3.0 and 37.0±2.0; O, 175.6±4.9 and 34.0±2.7; O2, 229.4±9.8 and 36.2±5.4, respectively. The second‐law enthalpy and entropy of vaporization at 298 K of TiO to form TiO(g) are 138.2±3.0 kcal/mole and 45.0±2.0 e.u., respectively. The third‐law value is 141.2±0.1 kcal/mole. The results corroborate the values given in the 1975 Supplement to the JANAF Tables, but show that previously reported values of the O2 potential are too high by a factor of about 43.

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