The thermal shock of ß-alumina

Abstract

The thermal shock of sodiumβ-alumina with relative densities from 60 to 98% theoretical has been investigated over the temperature range 150 to 700° C by quenching into water. The samples were ring segments cut from electrolyte tubes and were subsequently tested in both compression and tension. For relative densities of 75% and below the thermal shock damage was typical of stable crack growth and a steady decline in strength with sintering temperature was observed. For relative densities of 95% and above, thermal shock causes unstable crack growth and a critical value of ΔT was observed in the range 170 to 250° C depending on initial strength. From the linear relationship between observed ΔTc and the thermal shock resistance parameter,R, it was concluded that the rapid heat transfer during quenching was nucleate water boiling and that cooling from ∼110° C to 0° C was not responsible for damage. The fracture stress after thermal shock above ΔTc was consistent and showed little dependence on initial strength for relative densities ⩾95%. However, the fractional reduction in strength was related to the damage resistance parameterR‴. An estimate of the energy expended in fracture has been made, based on microscopic observation and compared with estimates of the stored strain energy due to thermal stresses.