Conversion of (NH4)2[ReF6] into ReO2 mixed phases: A thermal analysis study

Abstract

The thermal behavior of (NH4)2[ReF6] was evaluated in an alumina crucible using simultaneous thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) in an argon atmosphere. The TGA of (NH4)2[ReF6] is characterized by a single step decomposition while the DSC exhibits two exothermic peaks. Powder X-ray diffraction (PXRD) analyses of the decomposition products show the presence of a mixed ReO2 phase. The formation of ReO2 is driven by the reaction of (NH4)2[ReF6] with Al2O3 at the grain boundary of the alumina crucible. XRD peak broadenings due to the combined effect of crystallite size and lattice strain were evaluated using both Scherrer and Williamson-Hall methods.