Mass-spectrometric Study of the Vaporization of Magnesium Oxide from Magnesium Aluminate Spinel

The partial vapor pressures of Mg(g) over the spinel solid solution system, MgO·nAl2O3(n=1.0, 2.0, and 2.8), have been measured by the mass-spectrometric Knudsen-cell method. In the temperature range from 1850 to 2300 K, the pressures are described by these equations: log[P(Mg,g)over 1.0-spinel/atm]=7.72±0.24−(26900±490)⁄T, log[P(Mg,g)over 2.0-spinel/atm]=7.72±0.32−(27400±670)⁄T, log[P(Mg,g)over 2.8-spinel/atm]=7.78±0.42−(27900±1220)⁄T. These observed values were discussed in comparison with the calculated ones obtained by an approximate thermodynamic treatment of an ionic solid solution with composition-dependent vacancies.