Physicochemical characterization of the decomposition course of hydrated holmium nitrate. Thermoanalytical studies

Abstract

Ho(NO 3) 3·5H 2O (HoNit) was used as a parent compound for the formation of Ho 2O 3 at up to 800°C in atmosphere of air. Thermal processes occurring during the decomposition course were monitored by means of differential thermal analysis (DTA), thermogravimetry (TG) and gas-mass spectroscopy. The intermediates and final solid products were characterized by infrared (IR) spectroscopy, X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that, HoNit decomposes completely through eight endothermic weight losses processes. The dehydration occurs through the first four steps at 120°, 140°, 205° and 240°, forming crystalline nitrate monohydrate, which decomposes to Ho(OH)(NO 3) 2 at 265°C. The latter, decomposes immediately to form a stable and crystalline HoO(NO 3) at 368°C, then to nonstoichiometric unstable intermediates; Ho(O) 1.25(NO 3) 0.5 at 500°C. Finally, Ho 2O 3 was formed at 560°C. The decomposition course and surface morphology were supported and followed by SEM. The final product Ho 2O 3 at 600°C has large crystalline with irregular sheet-shaped particles containing large pores, voids and cracks. The gaseous decomposition products as identified by gas-mass spectroscopy are water vapor, nitric acid and nitrogen oxides (NO, NO 2 and N 2O 5).