Temperature programmed decomposition of thorium nitrate pentahydrate

Abstract

Temperature programmed decomposition (TPD) of thorium nitrate pentahydrate has been studied using evolved gas analysis-mass spectrometry (EGA-MS) in the temperature range 300-1200 K. A thermogravimetric (TGA) investigation was also carried out in the same temperature range. Complexity of the TGA decomposition profile was resolved through use of EGA-MS data. The activation energies and pre-exponential factors were determined for various gas release stages from the fractional extent of decomposition plots. Residues left over after each decomposition stage were analysed using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XRD investigations revealed formation of a nanocrystalline thoria intermediate product, ultimately agglomerating to a microcrystalline phase. The XPS investigations indicated systematic alteration in the chemical environment around the thorium atom while the Th⁴⁺ oxidation state remained unchanged. This was further corroborated from the analysis of shake-up satellites of Th (4f_5/2) spectra. The O/Th ratios for various intermediate products were also determined.