Synthesis and Properties of CaAl 2 O 4 ‐Coated AI 2 O 3 Microcomposite Powders

Novel microcomposite powders, consisting of inert cores (αAL‐Al 2 O 3 ) surrounded by reactive cement‐based coatings (CaAl 2 O 4 ), were synthesized by a modified Pechini process. The evolution of the crystalline CaAl 2 O 4 phase during calcination was studied using multiple analytical techniques, including DRIFTS, 13 C and 27 AlMAS FT‐NMR, and XRD, for both pure CaAl 2 O 4 and CaAl 2 O 4 ‐coated Al 2 O 3 precursor powders. In both powders, decomposition proceeded via hydrocarbon chain scission and removal of ester groups at low temperatures ( T < 450°C), followed by the formation of inorganic carbonates at higher temperatures ( T > 450°C). These decomposition processes were accelerated by the underlying Al 2 O 3 cores. Transmission electron microscopy (TEM) of the fully calcined powders showed that the inert αAL‐Al 2 O 3 particles were surrounded by relatively uniform CaAl 2 O 4 coatings ranging in thickness from approximately 10 to 100 nm.