Abstract
The acoustic emission (AE) technique was used for the real-time monitoring of microcracking in a green quartz porcelain mixture (50 wt% kaolin, 25 wt% quartz and 25 wt% feldspar) subjected to heating up to 1150 degrees C with a heating rate of 5 degrees C/min. Two sources of microcracking were identified.
The first one, which begins at a temperature of 50 degrees C, is connected to the liberation of physically bound water. The second source is caused by differences between the thermal expansion of crystals (kaolinite/metakaolinite, feldspar and alpha-quartz/beta-quartz).
The alpha -> beta transformation of quartz is not detected with AE. The vanishing of cracking at 600 degrees C correlates with the increase of the Young's modulus and is ascribed to solid-state sintering, which fortifies crystal interfaces between metakaolinite, feldspar and beta-quartz. (C) 2012 Elsevier Ltd and Techna Group S.r.l.
All rights reserved.