Temperature programmed decomposition of thorium oxalate hexahydrate

Abstract

Temperature programmed decomposition (TPD) of thorium oxalate hexahydrate (TOH) was studied by evolved gas analysis-mass spectrometry (EGA-MS), thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD). The microcrystalline solid exhibited sequential dehydration. The anhydrous compound yielded amorphous phase Th(CO₃)₂ upon CO release arising out of the bond cleavage. The Th(CO₃)₂ phase transformed to nano-crystalline thoria upon decomposition through an oxycarbonate intermediate. The mechanism underlying various conversion stages exhibited control by random nucleation, diffusion and phase boundary interface motion. From the fractional extent of decomposition data, Arrhenius factors like activation energy and pre-exponential factors were evaluated. Based on these studies, a chemical pathway is proposed for the entire decomposition process.