Grain shape in sintered submicrometre alumina

The study compares different approaches to describe quantitatively crystallite shapes in alumina microstructures with grain sizes 0.2 - 2 micrometres. A method is reinvestigated that characterizes the 3-dimesional shape of equiaxed grains and distinguishes equiaxed and non-equiaxed characters by analysing plain sections without additionally required assumptions. Other parameters which describe the shape after anisotropic grain growth are evaluated regarding their ability to identify non-equiaxed shapes with small aspect ratios. The analysis is applied to a wide spectrum of dense microstructures produced by powder and by sol/gel approaches. Whereas each of the procedures can give microstructures that come close to the parameter range associated with equiaxed shapes it is, in fact, impossible to produce alumina microstructures with predominantly equiaxed crystallites.