Calorimetric studies on the strontium-uranium-oxygen system

Enthalpy increment measurements on Sr3U11O36(s) and Sr3U2O9(s) were carried out using a Calvet micro-calorimeter. The enthalpy increment values were least squares analyzed with the constraints that H-0(T) - H-0(298.15 K) at 298.15 K equals zero and C-p.m(0)(298.15 K) equals 1064.2 and 301.8 J K(-1)mol(-1) for Sr3U11O36(s) and Sr3U2O9(s), respectively. The dependence of enthalpy increments with temperature can be given as H-0(T) - H-0(298.15 K) (J mol(-1)) = -304152 + 962.72T (K) + 177.63 x 10(-3)T(2) (K) + 3.954 x 10(-5)/T (K), (Sr3U11O36(s) 299.0 less than or equal to T (K) less than or equal to 1000), H-0(T) - H-0(298.15 K) (J mol(-1)) = -1 15 817 + 319.18T (K) + 58.01 x 10(-3)T(2) (K) + 46.201 x 10(5)/T (K), (Sr3U2O9(s),299.0 less than or equal to T (K) less than or equal to 1000). Thermodynamic functions for Sr3U11O36(s) and Sr3U2O9(s), have been generated using the Delta(r)H(m)(0)(298.15 K), Delta(r)G(m)(0)(T) and S-m(0)(298.15 K) values, either calculated in this study or from the literature. (C) 2000 Elsevier Science B.V. All rights reserved.