Composition of the Gas Phase over Al2O3 and the Enthalpies of Atomization of AlO, Al2O, and Al2O2

The A1, O, AlO, A1(2)O, A1(2)O(2), WO2 and WO3 partial pressures in the vapor over Al2O3 in a tungsten Knudsen effusion cell between 2300 and 2600 K were derived from A1(+), O+, AlO+, A1(2)O(+), A1(2)O(2)(+) , WO2+, and WO3+ ion intensities. The mass spectrometer was calibrated against the equilibrium constant of the WO3(g) = WO2(g) + O(g) reaction. Refined values of the ionization cross sections of AlO and A1(2)O(2) were used in the partial pressure calculations. The enthalpies of atomization of aluminum suboxides were determined to be Delta H-at(o)(AlO, g, 0) = 510.7 +/- 3.3 kJ mol(-1), Delta H-at(o)(Al2O, g, 0) = 1067.2 +/- 6.9 kJ mol(-1), and Delta H-at(o)(Al2O2, g, 0) = 1556.7 +/- 9.9 kJ mol(-1).