SYNTHESIS AND PROPERTIES OF CAAL2O4-COATED AL2O3 MICROCOMPOSITE POWDERS

Novel microcomposite powders, consisting of inert cores (alpha-Al2O3) surrounded by reactive cement-based coatings (CaAl2O4), were synthesized by a modified Pechini process, The evolution of the crystalline CaAl2O4 phase during calcination was studied using multiple analytical techniques, including DRTFTS, C-13 and Al-27 MAS FT-NMR, and XRD, for both pure CaAl2O4 and CaAl2O4-coated Al2O3 precursor powders, In both powders, decomposition proceeded via hydrocarbon chain scission and removal of ester groups at low temperatures (T less than or equal to 450 degrees C), followed by the formation of inorganic carbonates at higher temperatures (T greater than or equal to 450 degrees C), These decomposition processes mere accelerated by the underlying Al2O3 cores. Transmission electron microscopy (TEM) of the fully calcined powders showed that the inert alpha-Al2O3 particles were surrounded by relatively uniform CaAl2O3 coatings ranging in thickness from approximately 10 to 100 nm.