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 D y2O3 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 spectrosc opy. The intermediates and final solid Products were characterized by X-ray diffractometry and scanning electron microscopy. The results sho wed that Dy(NO3)(3).6H(2)O decomposes completely through 10 endothermi c weight loss processes. The dehydration occurs through the first five steps at 56, 150, 200, 221 and 269 degrees C, forming a crystalline m onohydrate nitrate, which decomposes to DSI(OK)(NO3)(2) at 298 degrees C. The latter, decomposes to Dy2O3 at 603 degrees C, through differen t 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 fo llowed 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 oxide s (NO, NO2 and N(2)O5). (C) 1997 Elsevier Science B.V.