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

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