High-temperature thermal expansion of lime, periclase, corundum and spinel

The high-temperature cell parameters of lime (CaO), periclase (MgO), corund um (Al2O3), and spinel (MgAl2O4) have been determined from 300 up to 3000 K through X-ray diffraction experiments with synchrotron radiation. The good agreement found with dilatometric results suggests that vacancy-type defec ts do not make a large contribution to thermal expansion for these oxides, even near the melting point, justifying the use of X-ray diffraction for de termining volume properties up to very high temperatures. Thermal expansion coefficients were determined from the measured cell volumes with equations of the form alpha = alpha(0) + alpha(1)T + alpha(2)/T-2. Along with availa ble isobaric heat capacity and compressibility data, these derived coeffici ents clearly show that anharmonic effects contribute little to the isochori c heat capacities (C-v) of CaO, MgO, and A12O3, which do not depart appreci ably from the 3nR Dulong and Petit limit.