Synthesis of CaAl4O7 via citric acid precursor

CaAl4O7 was synthesized by citric acid precursor method. The effects of the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration on the formation of CaAl4O7 were investigated. Increasing the molar ratio of citric acid to total metal cations concentration promoted the formation of CaAl4O7. When the molar ratio of citric acid to total metal cations concentration was 2, well-crystallized, single-phase CaAl4O7 was synthesized at 1000 °C for 2 h for the precursor with unadjusted pH, but it could not be obtained for the precursor with pH 7. Increasing the molar ratio of citric acid to total metal cations concentration up to 4, single-phase CaAl4O7 was synthesized at 800 °C for 2 h for the precursors with pH 7, but it was obtained at 850 °C for 2 h for the precursors with unadjusted pH. DSC, TG and XRD were used to characterize the precursors and the derived oxide powders.