Thermal decomposition of liebigite - A high resolution thermogravimetric and hot-stage Raman spectroscopic study

A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of liebigite. Water is lost in two steps at 44 and 302 degrees C. Two mass loss steps are observed for carbon dioxide evolution at 456 and 686 degrees C. The product of the thermal decomposition was found to be a mixture of CaUO4 and Ca3UO6. The thermal decomposition of liebigite was followed by hot-stage Raman spectroscopy. Two Raman bands are observed in the 50 degrees C spectrum at 3504 and 3318 cm(-1) and shift to higher wavenumbers upon thermal treatment; no intensity remains in the bands above 300 degrees C. Three bands assigned to the nu(1) symmetric stretching modes of the (CO3)(2-) units are observed at 1094, 1087 and 1075 cm(-1) in agreement with three structurally distinct (CO3)(2-) units. At 100 degrees C, two bands are found at 1089 and 1078 cm(-1). Thermogravimetric analysis is undertaken as dynamic experiment with a constant heating rate whereas the hot-stage Raman spectroscopic experiment occurs as a staged experiment. Hot stage Raman spectroscopy supports the changes in molecular structure of liebigite during the proposed stages of thermal decomposition as observed in the TG-MS experiment.