Thermal Conductivity: VII, Analysis of Variation of Conductivity with Temperature for Al 2 O 3 , BeO, and MgO

The results of previously published investigations into the thermal conductivities of alumina, magnesia, and beryllia by five different methods in different temperature ranges are summarized in the empirical equation k = A/(T − 125) + 8.5 × 10 −36 T 10 , where A = 16.2 for alumina, 18.8 for magnesia, and 55.4 for beryllia; the equation is valid (within about 10%) from room temperature to 1800°C. for alumina and magnesia and from 1000° to 1800°C. for beryllia. The departure from the reciprocal temperature law at the higher temperatures (represented by the second term in the equation) is believed to be due to an increase in the apparent conductivity by the passage of radiant energy through the translucent specimens.