Thermophysical properties of the system Al2O3 - MgO

Abstract

Dense samples of two different magnesia spinels and alumina spinel and magnesia spinel composites were prepared by powder metallurgy techniques and characterised by quantitative metallography, x-ray, and electron microprobe analysis. For four kinds of pure spinels, the thermal conductivity, λ, was determined from thermal diffusivity data measured together with heat capacity and thermal expansion. Up to about 1000 K, thermal resistivity, 1/λ, of the spinels follows the relationship A + BT, and then becomes more or less temperature dependent. Three stoichiometric spinels show the same value of B, (14.4 ′ 0.2) × 10 - 5 m W - 1 , while the nonstoichiometric compound (Mg 0 . 8 5 Al 0 . 1 5 )Al 2 O 4 has B of 10.6 × 10 - 5 m W - 1 . The composites of the alumina-rich compositions at low temperatures obey the mixing rule. This is not the case for the magnesia-rich side of the phase composition. The high-temperature thermal conductivity function of the composites shows very complex behaviour.