Abstract
The acoustic emission (AE) technique was used for real time monitoring of microcracking in the green quartz porcelain mixture (50 wt. % kaolin, 25 wt. % quartz and 25 wt. % feldspar) submitted to heating up to 1100 oC. Two sources of microcracking were identified.
The first one, which begins at the temperature 50 oC, is connected to liberation of the physically bounded water. The second source is connected to differences between thermal expansions of crystals (kaolinite/metakaolinite, feldspar and -quartz/-quartz).
The transformation of -quartz -quartz, which takes place at 570 oC, is not registered with AE. The vanishing of cracking at 600 oC correlates with the increase in Young's modulus and it is ascribed to solid-state sintering, which fortifies boundaries between crystals (metakaolinite, feldspar and -quartz).