Temperature-dependent evolution of grain growth in mullite fibres

Mullite grain size characteristics of four different alumino silicate fibres heat-treated between 1400 and 1700 degrees C in a time frame of 0.5-100h have been determined. Mullite grain sizes show little change up to 1500 degrees C though the grain microstructure develops from mosaic-type to facetted. Above 1500 degrees C grain growth kinetics follow the empirical law D-1/n-D-0(1/n)=kt(D-0)= initial grain size, D= grain size after annealing, 1/n= grain growth exponent, k= reaction constant, and t=firing time). Between 1500 and 1600 degrees C the grain growth exponent is remarkably low (1/n=1/12) but above 1600 degrees C grain growth exponents reach normal values of approximate to 1/3. The vacancy drag model has been used to explain the complex grain growth behaviour of mullite. (c) 2004 Elsevier Ltd. All rights reserved.