EFFECT OF THERMAL HISTORY ON THE THERMAL-DIFFUSIVITY AND THERMAL-EXPANSION OF AN ALUMINA ALUMINUM TITANATE COMPOSITE

A study was conducted of the temperature dependence of the thermal dif fusivity and thermal expansion of an alumina-aluminum titanate composi te heated to a range of maximum temperatures followed by cooling to ro om temperature. Heating to temperatures above about 600-degrees-C resu lted in a hysteresis behavior in which the data on cooling differed fr om the data obtained during heating. For both the thermal diffusivity and thermal expansion, the degree of hysteresis increased with increas ing maximum temperature. On return to room temperature, following heat ing to a temperature of about 1200-degrees-C, the thermal diffusivity exhibited a significant decrease, with a corresponding increase in spe cimen size. This effect was attributed to an increase in microcrack de nsity over the corresponding value prior to heating. On subsequent cyc les of heating and cooling for a maximum temperature of 1200-degrees-C this decrease in thermal diffusivity was partially recovered, indicat ive of the structural integrity of the alumina-aluminum titanate compo site of this study in practical applications involving temperatures of at least 1200-degrees-C.