Influences of cation disorder in commercial spinel powders studied by 27Al MAS NMR on the sintering of transparent MgAl2O4 ceramics

At the Stockholm Conference of the European Ceramic Society 2011 it was shown that together with the particle size of raw powders and the homogeneity of particle coordination in the green bodies the real structure of the lattices is a third major influence on sintering which may differ significantly even at fixed stoichiometry. Antisite defects govern the whole defect chemistry of MgAl2O4 and should, therefore, affect diffusion and sintering. This feature is investigated here by solid state 27Al MAS nuclear magnetic resonance measurements of the occupancy of octahedral and tetrahedral sites. Based on previous results with model powders synthesized in order to identify lattice effects at constant particle size distribution, homogeneity and composition, the study was extended now to commerci al spinel powders of Asian, European, and American manufacturers. The results confirm a correlation of increasing cation disorder with improved sintering densification.