Texture in Na–β-Al2O3 due to microwave processing

Na–β-Al2O3 powder after compaction and subsequent microwave irradiation yielded dense sintered products indicating preferred orientation along either the basal plane (0 0 2) or prismatic plane (2 2 0). The orientation depends on whether the starting material is a commercial powder or a precursor synthesized through wet-chemical route. The product from the latter powder exhibits uniform microstructure as well as a grain size smaller than 5 μm while that from the former shows abnormal grain growth with sizes varying from 1.5 μm up to 25 μm. Vickers hardness measurements yield an average hardness of 7.4 GPa at 0.1 kg load for the samples derived from the wet-chemically derived precursor and 13 GPa at 0.1 kg load for the sintered samples from the commercial powder. The first value is characteristic of crystallites oriented along the (2 2 0) plane while the second value speaks for crystallites oriented along the (0 0 2) plane.