Kinetic analysis of the thermal decomposition of Cerium(IV) phosphates

Abstract

Cerium(IV) phosphates (CePs) have been first studied in the late sixties by König et al. Subsequently, Alberti and Clearfield synthesised a large number of these phosphates with different crystal structures and P/Ce ratios ranging from 1:1.1 to 3.0:1. Although the most of their crystal structures remain unknown, the properties observed for these solids made them interesting for applications in the area of catalysis, ion-exchange, trapping of radioactive elements and proton conduction. Two cerium(IV) phosphates, (NH4)2Ce(PO4)2·H2O and Ce2(PO4)2HPO4·H2O have been hydrothermally obtained, in a stainless steel Teflon-lined vessel under autogenous pressure, by using cerium oxide as the source of metal. Microcrystals of the first phosphate were synthesised from the CeO2-CO(NH2)2-H3PO4-H2O system (180 ºC, 5 days) and the second was obtained from CeO2-H3PO4-H2O system (180 ºC, 40 hours). As can be seen on the SEM images, the morphology of these compounds is very different. Kinetic parameters of the thermal degradation of the materials were obtained from thermogravimetric data. The samples were heated from 25 to 1000 °C under a nitrogen atmosphere with different constant heating rates. Isoconversional methods are used to carry out the kinetic analysis.