Hydration of Sm2O3 under mild conditions

The influence of pressure and temperature on Sm2O3 hydration, under mild conditions, are examined. The data and conclusions are referred to previous ones for Yb2O3. At the activation temperatures usually applied, as reported in the literature, to rare earth sesquioxides handled in air, 800-850 K, a non-pure-oxide phase is attained in the case of Sm2O3. Its complete dehydration is achieved at 823 K, but temperature programmed decomposition and Fourier transform-IR data lend support to the formation at this temperature of a dioxymonocarbonate phase which is transformed into the sesquioxide phase above 1100 K. Contrary to the finding for Yb2O3, hydration in bulk Sm2O3 has been observed over the whole pressure range 133-2666 Pa. In the absence of CO2, the temperature of evolution of H2O from bulk-hydrated Sm2O3, about 600 K, is considerably higher than that previously reported for Yb2O3, 440 K, following the cation polarizing pattern for the decomposition of metal hydroxides and oxosalts. (Auth.)