IDENTIFICATION OF SOLID-SOLUTIONS AND OTHER PHASES IN STRONTIUM AND BARIUM CATALYSTS CONTAINING OXIDES OF MAGNESIUM, ALUMINUM OR SILICON ASADDITIVE .2. CATALYST CHARACTERIZATION

This paper presents the results of thermoanalytical studies (TG/DTA) t o examine the influence of additives (MgO, Al2O3 or SiO2) on the therm al stability of SrCO3 and BaCO3. Since any destabilization is expected to be maximised when the carbonates and the additives are in intimate contact, viz., solid solution, the possibility of the formation of so lid solution and other stoichiometric compounds has been explored and the phases identified by X-ray diffraction (XRD). Thermogravimetry dat a show that the incorporation of MgO in SrCO3 and BaCO3 lowers the car bonate decomposition temperatures by as much as about 150-degrees-C. D estabilization is also observed using alumina or silica, although the extent to which this occurs is moderate compared with MgO as an additi ve. Moreover, SiO2 interacts strongly and irreversibly forming Ba2SiO4 , BaSiO3 or Sr2SiO4 and SrSiO3. Al2O3 also interacts, albeit mildly, f orming BaAl2O4 or SrAl2O4. A solid solution of the type (MgBa)(CO3)2 i s the only phase detected by XRD in the coprecipitated carbonates cont aining magnesium. Carbonate stability depends on the environment. Whil st a carbon dioxide environment suppresses decomposition, hydrogen enh ances decomposition through provision of another reaction channel.