Temperature programmed decomposition of thorium oxalate hexahydrate

Temperature programmed decomposition (TPD) of thorium oxalate hexahydrate ( TOH) was studied by evolved gas analysis-mass spectrometry (EGA-MS), thermo gravimetric analysis (TGA) and powder X-ray diffraction (XRD). The microcry stalline solid exhibited sequential dehydration. The anhydrous compound yie lded amorphous phase Th(CO3)(2) upon CO release arising out of the bond cle avage. The Th(CO3)(2) phase transformed to nano-crystalline thoria upon dec omposition through an oxycarbonate intermediate. The mechanism underlying V arious conversion stages exhibited control by random nucleation, diffusion and phase boundary interface motion. From the fractional extent of decompos ition data, Arrhenius factors like activation energy and pre-exponential fa ctors were evaluated. Based on these studies, a chemical pathway is propose d for the entire decomposition process. (C) 2001 Elsevier Science B.V. All rights reserved.