SURFACE SEGREGATION AND MORPHOLOGY OF MG-DOPED ALPHA-ALUMINA POWDERS

This work considers the effect of a thermal treatment, at a temperatur e equal to or higher than 1200 degrees C, on the physical and chemical characteristics of submicron alpha-alumina powders, doped with 550 an d 1650 ppm in weight of MgO. The powders have been characterized by TE M, SEM, BET, XPS and chemical analysis. TEM observations show that the grains have elongated and rounded forms and exhibit considerable aggl omeration. The BET surface area of the powder decreases with increasin g annealing time and temperature and increases with the amount of MgO. XPS analysis shows a strong segregation of Mg and this effect is more pronounced when the size of the grains increase. In some cases XPS al so detected the presence of Na, Ca and Si in the surface region of the grains.