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

Abstract

Yb(NO 3) 3·6H 2O was used as a parent compound for the formation of Yb 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 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(NO 3) 3·6H 2O 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(NO 3) 3, which decomposes to YbO 0.5(NO 3) 2 at 250 °C. The latter, decomposes to non-stoichiometric unstable intermediate YbO 0.75(NO 3) 1.5 at 335 °C, which decompose immediately to a stable and crystalline YbONO 3 at 365 °C, then to a non-stoichiometric unstable intermediate Yb(O) 1.25(NO 3) 0.5 at 470 °C. Finally, Yb 2O 3 was formed at 510 °C. The decomposition course and surface morphology were supported and followed by SEM and textural studies ( S BET).The final product Yb 2O 3 at 600 °C has a large irregular sheet shaped particles containing a large pores, voids and cracks and has S BET=45 m 2/g. The gaseous decomposition products are water vapor, nitric acid and nitrogen oxides (NO, NO 2 and N 2O 5). The activation energy (Δ E in kJ/mol) was calculated non-isothermally for each thermal processes.