Thermal conductivity of fused quartz and quartz ceramic at high temperatures and high pressures

The thermal conductivity of fused quartz and quartz ceramic has been measured over the temperature range of 273-423 K and at pressures up to 400 MPa using a steady-state parallel-plate apparatus. It is an absolute, steady-state measurement device with an operational temperature a range of 273-1273 K and pressure range up to 1500 MPa. High-pressure measurements are made in an atmosphere of argon. The estimated accuracy of the method is about +/-2%. Measurements were performed at four temperatures, namely: 273, 323, 373, and 423 K for pressures up to 400 MPa. Thermal conductivity shows linear dependence on temperature for all the studied isobars. The effect of pressure on the thermal conductivity behavior has been under study. The thermal conductivity of fused quartz was found to increase linearly at a rate of 4 x 10(-4) W/(m K MPa). Temperature coefficient of thermal conductivity is 0.0018 W/(m K-2). The sharp thermal conductivity changes for quartz ceramic at pressures between 0.1 and 100 MPa has been found for all isotherms while for fused quartz pressure the dependence of thermal conductivity is linearly in the whole pressure range studied. The measured values of thermal conductivity for fused quartz at atmospheric pressure are compared with the recommended values from the literature. (C) 2000 Elsevier Science Ltd. All rights reserved.