Phase and microstructural evolution of heat treated nanocrystalline powders in Al2O3-MgO binary system

This paper reports the results of phase and microstructural evolutions duri ng the heat-treatments of nanocrystalline powders in the Al2O3-MgO binary s ystem. The powders were previously synthesized using an exothermic "Auto Ig nition" process and contained non-equilibrium phases. The compositions sele cted spanned the entire binary system acid were divided into four broad cat egories. These are alumina-rich, alumina-rich spinel, stoichiometric spinel and magnesia-rich spinel. The heat treatments were carried out between 110 0 degrees C and 1300 degrees C. The as-heat treated powders were characteri zed by X-ray diffraction (XRD) as well as transmission electron microscopy (TEM). Exaggerated grain growth occurred at both high Al2O3 and high MgO co mpositions when subjected to heat treatments at 1200 degrees C for 2 hours. Nanocrystallinity was maintained for most of the compositions up to 1100 d egrees C. (C)1999 Acta Metallurgica Inc.