CRYSTALLINE-STRUCTURE AND THERMAL-STABILITY OF DOUBLE STRONTIUM AND BARIUM CARBONATES

The crystalline structures of double salts of composition SrxBa1-xCO3 have been analysed. It has been shown that this series of compounds crystallizes in the orthorhombic system over the entire composition range. Moreover, they conform to Veghard's law. The thermal decomposition of a series of samples of composition SrxBa1-xCO3 (x = 0.2, 0.4, 0.5, 0.6 and 0.8) has been studied by means of the constant rate thermal analysis (CRTA) technique. This method permits monitoring of the vacuum and the sample temperature in such a way that both the pressure in the close vicinity of the sample and the total decomposition rate remain constant over the whole reaction range. The results obtained at a CO2 residual pressure of 4 ×10-5 Torr show that the thermal decomposition of BaSr double salts takes place in a single step, instead of the two step process previously claimed in the literature. The comparative kinetic analysis of both CRTA and TG curves at high vacuum has allowed the reaction mechanism and the activation energy for the process to be established. © 1990.