Thermal Conductivities of MgO, Al2O3, and ZrO2 Powders to 850°C. I. Experimental

Abstract

Thermal conductivities were measured for extensively characterized magnesia, alumina, and zirconia powders. Thermal conductivities of the powders in dry air at atmospheric pressure were determined at volume fractions solid varying from 0.49 to 0.70 as a function of temperature from about 100° to about 850°C. Particle-size distribution, chemical composition, x-ray diffraction pattern, weight loss on heating, pore-free density, and surface area of each powder were measured. Thermal conductivities were determined by a steady-state method employing radial heat flow in a hollow cylinder and by an unsteady-state method based on the model of heating a cylinder of a perfect conductor surrounded by an infinite amount of the material whose thermal conductivity is being measured. The thermal conductivities of the powders increased with increasing volume fraction solid. The influence of gas conductivity was greater than that of the solid on the thermal conductivity of the powers. The thermal conductivity for each powder measured increased at a decreasing rate with increasing temperature, following an approximately quadratic temperature dependence. Thermal conductivity was increased by the presence of a sorbed water film as well as by mechanical pressure on the particles.