Physicochemical characterization of the formation course of dysprosium oxide from hydrated dysprosium nitrate; Thermoanalytical and microscopic studies

Dy(NO3)(3).6H(2)O was used as a parent compound for the formation of Dy2O3 at up to 900 degrees C in an atmosphere of air. Thermal processes occurring during the decomposition course were monitored by means of thermogravimetry, differential thermal analysis and gas-mass spectroscopy. The intermediates and final solid Products were characterized by X-ray diffractometry and scanning electron microscopy. The results showed that Dy(NO3)(3).6H(2)O decomposes completely through 10 endothermic weight loss processes. The dehydration occurs through the first five steps at 56, 150, 200, 221 and 269 degrees C, forming a crystalline monohydrate nitrate, which decomposes to DSI(OK)(NO3)(2) at 298 degrees C. The latter, decomposes to Dy2O3 at 603 degrees C, through different intermediates; nonstoichiometric unstable, Dy(O)(0.75)(NO3)(1.5) at 352 degrees C; then stable and crystalline DyO(NO3) at 369 degrees C; and nonstoichiometric unstable Dy(O)(0.75)(NO3)(1.5) at 486 degrees C. The decomposition course and surface morphology were supported and followed by SEM. The final product, Dy2O3 at 700 degrees C, has a large crystalline structure with irregular sheet shaped particles containing large pores, voids and cracks. The gaseous decomposition products as identified by gas-mass are water vapor, nitric acid and nitrogen oxides (NO, NO2 and N(2)O5). (C) 1997 Elsevier Science B.V.