Thermal decomposition of lead citrate

Abstract

Anydrous lead citrate may be prepared by dehydration of the tetrahydrate or the dihydrate. These preparations show different kinetic behaviour and this has been attributed to differences in structural order. This initial order determines the course of the first stage of the thermal decomposition. After this stage both samples are virtually identical and decompose in a similar manner. Electron micrographs reveal that nucleation occurs randomly on the surfaces of the more ordered particles and nuclei grow rapidly to form spheres of lead metal product. Growth ceases owing to exhaustion of neighbouring reactant but this process acts as the nucleation step for a subsequent higher temperature decomposition stage. The residual carbon, after removal of the CO₂ and H₂O decomposition products, forms a matrix isolating lead spheres from coalescence (in inert atomospheres) even at temperatures above the melting-point of lead. This finely divided lead metal and carbon product is pyrophoric.