Mechanochemically Stimulated Synthesis and Low Temperature Sintering of MgAl2O4

A sequence of changes in X-ray patterns on heating of MgAl2O4 precursors synthesized by different methods is considered. It is shown that the presence of only spinel phase peaks can cause the erroneous conclusion of a single-phase nature of the product and thus explain its low sinterability. Mechanochemical treatment of the stoichiometric mixture of aluminum and magnesium hydroxides yields precursors, which form the powders of single-phase spinel with a crystallite size of 15-30 nm (depending on the composition of the gas medium) when heated at 1000 degrees C for an hour. Additional disaggregation of spinel powders through low-intensity mechanical treatment (10g, 5 min) in ethanol gives rise to increased sinterability and allows attaining 95 % density at no more than 1350 degrees C, which is sufficient for successive densification by means of hot isostatic pressing. However, vacuum sintering is less efficient, leading to low density due to residual alkoxy groups enclosed in gas-tight aggregates which are formed in the course of the treatment with ethanol.