High-Temperature Elastic Properties of Polycrystalline MgO and Al2O3

Adiabatic bulk modulus, Bs, of polycrystalline MgO and Al2O3 was measured from 298° to 1473°K using the resonance technique. The Grüneisen constant, calculated from the measured bulk modulus, was constant over the whole temperature range (1.53 for MgO and 1.34 for Al2O3). Another important parameter, , is constant at high temperature and is 3.1 for MgO and 3.6 for Al2O3. The Poisson's ratio increases linearly with temperature for MgO and Al2O3. To describe the change of bulk modulus with temperature a theoretical equation was verified by using the foregoing constants. A practical form of this theoretical equation is where Bs0 is the adiabatic bulk modulus at 0°K, δ is the quantity , γ is the Grüneisen constant, H is the enthalpy. The experimental data are described very well by this equation, which is equivalent to the empirical equation suggested by Wachtman et al., BsT= Bs0 - CT exp (-Tc/T), where C and Tc are empirical constants.