Synthesis of cerium aluminate by the mechanical activation of aluminum and ceria precursors and firing in controlled atmospheres

Single-phase cerium aluminate was synthesized from mixtures of ceria and metallic aluminum by milling and firing under controlled conditions in reducing (10%H-2 + 90%N-2) or inert atmospheres (N-2 or CO2). Firing in an inert atmosphere (CO2) did not yield conversion to cerium aluminate, and conversion was also low after firing in reducing conditions (10%H-2 + 90%N-2) and only improved slightly on changing from powder mixtures with coarse Al powder (15 mu m) to mixtures with submicron Al (0.77 mu m). High-energy milling promoted reactivity by the combined effects of improved homogeneity, decreasing grain size of the Al precursor, increase in lattice strain and decrease in crystallite size down to 40-50 nm. Extensive oxidation of the metallic Al precursor after long-term milling prevented complete conversion to cerium aluminate even after firing under reducing conditions at temperatures up to 1400 degrees C. Thermodynamic modeling of the Al-Ce-O system provided interpretation for differences between firing in reducing and inert atmospheres. Controlled milling time hinders oxidation of Al to the poorly reactive alpha-Al2O3 polymorph. This was supported by thermogravimetry after controlled milling and yielded phase pure CeAlO3 at T >= 1200 degrees C. The high conversion was achieved even by firing at 1100 degrees C under an inert atmosphere.