Thermal decomposition of lead titanyl oxalate tetrahydrate

Abstract

The thermal behaviour of PbTiO(C20&-4H20(PTO) has been investigated, employing TG, quantitative DTA, infrared spectroscopy and (high temperature) X-ray powder diffraction.The decomposition involves four main steps. The first is the dehydration of the tetrahydrate (30-lSO'C), followed by a small endothermic (27&31O@C) and a large exothermic decomposition of the oxalate. The main (exothermic) oxalate decomposition (310-390°C) rest&s in a stable oxide-carbonate PbTiOz_s(C03)o_s. In the last step a phase transition, release of CO2 and orderin g of the crystalline cubic PbTiO, lattice can be detected (46%53O"C).It can be argued that for thermodynamic reasons the presence of Iead-oxocarbonates in the oxide-carbonate intermediate is not possible.No differences could be found in thermal behaviour of two crystaliographically different synthetic forms of PTO, of which one has an ortharhombic lattice_ IXl-RODUCnONAs is the case with many fine-grained pure ceramic powders, lead titanate is often synthesized via decomposition of an oxalate complex precursor. The present investigation was undertaken as a part of a larger study of influences of synthesis and thermolysis circumstances on decomposition of i-a. ammonium and lead titanyl oxalate complexes.When the study of the behaviour of lead titanyl oxalste tetrahydrate. PbTiO(C20J2~4H,0, (P-TO), was started, the proposals of earlier investigators for the mechanism of the thermal decomposition of the analogous barium titanyl oxalate (BTO) were highly contradictory '*'. It was interesting to see whether the decomposition scheme for the Icad compound had a resemblance to any of the proposed schcw w should have a different explanation. There was a possibility that decomposition cc 9roceed via an oxide-carbonate intermediate, as was found for ammonium titany1 uxalate'. During the experiments for this investigation such an intermediate was indeed considered necessary to explain the data. Recently, Gopalakrishnamurthy et ah4 published a new report on BTO decomposition which

Thermal decomposition of barium titanate precursor prepared by a wet chemical method

“…Barium titanate product is formed by calcination and firing of the precursor obtained from the wet chemical methods. While there have been many studies of the decomposition behavior of precursors reported (Swilam et al, 1973;Gallagher and Thomson, 1965;van de Velde and Oranje, 1976;Chaput and Boilot, 1990), there have not been any quantitative and kinetic investigations carried out because of the complicated reaction routes and numerous intermediates in-volved in the formation of barium titanate in the calcination step.…”