Thermal decomposition of titanyl oxalates of bivalent metals

Abstract

The present study reveals some interesting facts both on the thermoanalytical techniques in general and thermal decomposition of titanyl oxalates in particular. The results of thermal analyses and explanations based on them are definitely limited in scope. This point is very well illustrated by the previous schemes proposed for the decomposition of barium titanyl oxalate, based mainly on DTA and TGA results. Intermediates like BaTiO?(CO)?, BaTiO?(CO) and BaTiO? have been assumed to be formed on the basis of weight loss. It is to be noted that thermoanalytical methods like TGA, which are dynamic in nature, are inadequate to determine the composition of intermediates. The composition of residues isolated from isothermal experiments need not and often do not tally with the apparent compositions assigned by weight?loss measurements in thermal analyses. The dynamic nature of the thermal methods of analysis is also responsible for incomplete reactions and overlap of two reactions resulting in variable weight losses for these steps. If proper attention is not given to such effects, wrong conclusions will be drawn as has happened regarding the last step of decomposition of barium titanyl oxalate. Referring to titanyl oxalates, it may be concluded that the alkaline?earth titanates can be obtained from their respective titanyl oxalates at as low a temperature as 500 to 600°C. The minimum particle size obtained by this method is around 20?µ because the decomposition is accompanied by simultaneous growth in particle size of the products. Lead titanate can be obtained from LTO even at 400 to 500°C. However, it is essential to maintain oxidising conditions to prevent possible reduction of Pb(II). The present study reveals an important fact that gaseous products formed during the thermal decomposition of solids may be held in the solid matrix. Retention of carbon dioxide at various stages of decomposition of alkaline?earth titanyl oxalates has been observed. It is felt that this is a more general phenomenon than hitherto thought of. Finally, it is noted that the decomposition of complex oxalates is more complicated than that of simple oxalates. It is strongly felt that more work is to be done for a better understanding of the general principles involved in the thermal decomposition of complex oxalates in particular and complex substances in general.