SYNTHESIS OF STRONTIUM AND BARIUM CERATE AND THEIR REACTION WITH CARBON-DIOXIDE

The log p(CO2) versus 1/T relationships of the equilibria (1) ACO3 + CeO2e reversible ACeO3 + CO2 and (2) ACO3 reversible AO + CO2, in which A = Sr or Ba, were investigated. The methods which have been used are: thermodynamic equilibrium calculations, simultaneous thermogravimetry-differential thermal analysis and high-temperature X-ray diffraction. In pure N2 atmosphere, the synthesis of the cerates proceeds via (1) ACO3 --> AO + CO2 and (2) AO + CeO2 --> ACeO3, which is not calculated thermodynamically, but is apparently kinetically more favourable at low temperatures. SrCeO3 and BaCeO3 react with 1 atm CO2 below 1190-degrees-C and 1185-degrees-C, respectively. For mixtures of CO2 with other gases, the decomposition temperatures can be estimated from the figures presented.