Abstract :
Sm(NO3)3·6H2O and Sm2(C2O4)3·10H2O were used as precursors for the formation of Sm2O3. Thermal processes involved in the decomposition course of both salts up to 800 °C in air were monitored by nonisothermal gravimetry and differential thermal analysis. Intermediates and final solid products were characterized by IR-spectroscopy, X-ray diffraction and scanning electron microscopy. The results showed that Sm(NO3)3·6H2O decomposes completely through nine endothermic mass loss processes. The dehydration occurs through the first four steps at 90, 125, 195, and 240 °C, culminating in a crystalline nitrate monohydrate, which subsequently decomposes to Sm(OH)(NO3)2 at 355 °C. The latter decomposes rapidly to form a stable and crystalline SmO(NO3) at 460 °C, through nonstoichoimetric unstable intermediates. Finally Sm2O3 forms at 520 °C. For the oxalate, the dehydration occurs in five steps: the anhydrous oxalate is thermally unstable and immediately decomposes to Sm2O3 at 645 °C through two unstable intermediates. The crystalline oxide obtained from the nitrate contains larger pores than the oxide obtained from the oxalate, as indicated from scanning electron microscopy (SEM) results.
