Effects of Grain Boundary Phases on the Corrosion of β-SIALON in Molten Copper Oxide

Abstract

The present investigation reveals that grain boundaries of β-SIALON are corroded selectively by molten copper oxide. β-SIALON ceramics become more vulnerable as the amount of grain boundary phase, mainly glass, increases. High density β-SIALON ceramics (fraction to the theoretical density from 0.9 to 1) were heated with CuO powder at 1200°C for 1h in air. The HIPped sample which had the highest density was corroded most severely, in contradiction to the general relationship between density and corrosion of refractories. Cryogenic specific heat measurements showed that the HIPped sample contained the largest amount of grain boundary phases. Among the normally sintered samples, one with larger amount of grain boundary phases was corroded most severely. The difference of the amount of grain boundary phases may have been attributed to the thermal treatment conditions, especially to the cooling rate and the highest temperature attained. The corrosion behavior of β-SIALON ceramics in molten copper oxide coincided well with the results of SEM observations and the data of phase diagrams. Also, the cryogenic specific heat is a sensitive property, with which slight differences of the amount of grain boundary phases can be detected. These small differences can not be distinguished by means of SEM observations or XRD analysis.