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

Abstract

Single‐phase cerium aluminate was synthesized from mixtures of ceria and metallic aluminum by milling and firing under controlled conditions in reducing (10%H2 + 90%N2) or inert atmospheres (N2 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%H2 + 90%N2) and only improved slightly on changing from powder mixtures with coarse Al powder (15 µm) to mixtures with submicron Al (0.77 µm). 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°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 α‐Al2O3 polymorph. This was supported by thermogravimetry after controlled milling and yielded phase pure CeAlO3 at T ≥ 1200°C. The high conversion was achieved even by firing at 1100°C under an inert atmosphere.

Thermodynamic Guidelines for the Mechanosynthesis or Solid-State Synthesis of MnFe2O4 at Relatively Low Temperatures

“…Quasi-planar chemical potential diagrams for mixed metal-oxide systems were derived analogously to the method that was proposed by Yokokawa and co-authors [29,30], previously applied to assess the phase stability in a variety of systems in solid-state electrochemical applications [31], and to assess their contamination [30,32] or degradation by interaction with reactive gases [33]. Other recent references address relevant issues of materials proposed for catalytic applications in different systems such as Ni − Al − O [34], Fe − Ti − O [35], CaO − SiO − CO 2 [36], etc., or the synthesis of catalytic materials in the systems Fe − Si − O [37], Ca − Fe − O [38], or Ce − Al − O [39], and guidelines for the processing of SrTiO 3 by mechanosynthesis [40].…”