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 synthesiz ed by a modified Pechini process, The evolution of the crystalline CaA l2O4 phase during calcination was studied using multiple analytical te chniques, including DRTFTS, C-13 and Al-27 MAS FT-NMR, and XRD, for bo th pure CaAl2O4 and CaAl2O4-coated Al2O3 precursor powders, In both po wders, decomposition proceeded via hydrocarbon chain scission and remo val of ester groups at low temperatures (T less than or equal to 450 d egrees C), followed by the formation of inorganic carbonates at higher temperatures (T greater than or equal to 450 degrees C), These decomp osition processes mere accelerated by the underlying Al2O3 cores. Tran smission electron microscopy (TEM) of the fully calcined powders showe d that the inert alpha-Al2O3 particles were surrounded by relatively u niform CaAl2O3 coatings ranging in thickness from approximately 10 to 100 nm.