Physicochemical characterization of the decomposition course of hydrated ytterbium nitrate: thermoanalytical studies

Yb(NO3)3·6H2O was used as a parent compound for the formation of Yb2O3 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 the gaseous decomposition products were identified by mass spectrometry (GC–MS). The intermediates and final solid products were characterized by IR-spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that, Yb(NO3)3·6H2O decomposes completely through 11 endothermic mass loss processes. The dehydration occurs through the first six steps at 95, 145, 165, 175 and 200 °C, forming crystalline nitrate Yb(NO3)3, which decomposes to YbO0.5(NO3)2 at 250 °C. The latter, decomposes to non-stoichiometric unstable intermediate YbO0.75(NO3)1.5 at 335 °C, which decompose immediately to a stable and crystalline YbONO3 at 365 °C, then to a non-stoichiometric unstable intermediate Yb(O)1.25(NO3)0.5 at 470 °C. Finally, Yb2O3 was formed at 510 °C. The decomposition course and surface morphology were supported and followed by SEM and textural studies (SBET).The final product Yb2O3 at 600 °C has a large irregular sheet shaped particles containing a large pores, voids and cracks and has SBET=45 m2/g. The gaseous decomposition products are water vapor, nitric acid and nitrogen oxides (NO, NO2 and N2O5). The activation energy (ΔE in kJ/mol) was calculated non-isothermally for each thermal processes.