Non-isothermal kinetic and thermodynamic study of the decomposition of lead acetate trihydrate

Abstract

The non-isothermal decomposition of lead acetate trihydrate was studied up to 450°C by means of TG, DTG, DTA and DSC measurements in a dynamic atmosphere of N2 (or dry air).The parent salt was found to undergo melting concurrently with the dehydration process, which takes place in two steps between 30 and 110°C. The anhydrous salt melts at 204°C and later forms two intermediate basic lead acetate salts, namely Pb(CH3COO)2 · PbO (between 230 and 270°C) and Pb(CH3COO)2 · 2PbO (between 275 and 325°C) respectively. The latter basic salt decomposes, between 325 and 380°C in N2 atmosphere, to produce a mixture of PbO and a small amount of metallic Pb. In air, however, the decomposition produces solid PbO only.X-ray powder diffraction and IR transmission spectroscopy were used to identify the solid intermediates and products of the reaction. Gas chromatography was used to identify the volatile products of the decomposition in N2 and in O2. Scanning electron microscopy was also used to investigate the structure changes and possible occurrence of melting during the decomposition.Values of the kinetic (ΔE and ln A) and thermodynamic (ΔH, Cp and ΔS) parameters were calculated for the dehydration and decomposition processes.