Abstract
A technique is proposed whereby recrystallization can be investigated quantitatively in a ceramic material composed of grains widely ranging in size (due to localization of sintering) and containing grain-boundary barriers (such as impurities and micropores) that vary in spatial distribution and quantity. It is shown that only primary recrystallization takes place in alumina sintered at 1550–1700°C and that the grain size distribution is about the same as in a barrier-free material thus implying that the recrystallization proceeds in an effectively homogeneous medium. An addition of 2% Nb2O5 to activate sintering leaves the general pattern of recrystallization unchanged and only quantitative differences are noted. These are an increase in the average particle size (because a liquid phase appears and causes a change in the properties of the boundaries and because structure defects are formed when Nb2O5 dissolves in Al2O3, which accelerates bulk diffusion) and an increase in the number of grain sizes (related to the increased inhomogeneity of contacts between alumina particles).
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