Molar enthalpies of formation of BaCmO3 and BaCfO3

Abstract

The enthalpies of solution of BaCmO3 and BaCfO3 in 1.00 mol dm -3 HCIO4 were measured at 298.15 +0.05 K and p°= 101.325 kPa as -(345.3 +4.7) and -(347.2+ 1.9) kJ mo1-1, respectively. The resulting standard molar enthalpies of formation, AfH°(BaCmO3, cr) = -(1517.8 + 7.1) kJ mol-1 and AfH°(BaCfO3, cr) = -(1477.9 + 5.6) kJ mo1-1, together with other corresponding experimental values for several lanthanide, actinide and transition metal complex oxides with barium and strontium, are used to estimate the molar enthalpies of formation of a number of homologous actinide compounds. The present results also provide additional information on the standard molar enthalpy of formation of CfO2 and on the Cf4+/Cf 3÷ standard potential.

Sorption of Strontium to Uraninite and Uranium(IV)–Silicate Nanoparticles

“… 49 , 50 Several studies have also shown negligible differences in the thermodynamics of formation of SrUO 3 compared to those in the binary oxides UO 2 and SrO, suggesting that SrUO 3 formation is possible and perhaps thermodynamically favored in the presence of excess UO 2 . 51 − 54 Additionally, in the current study, the high surface area of the nanoparticulate UO 2 may promote the Sr reaction at the UO 2 surface. The split shell and high O coordination number in the EXAFS fits for both pH 10 and 12 samples certainly suggest that the Sr coordination environment is very different from that of the absorbed Sr and is perovskite-like.…”

“…This proposed surface incorporation mechanism for Sr is novel; however, Sr–U-oxides have been formed previously at high temperatures. ,, Mixed Sr–U-oxides have been observed at T > 1000 K as either Sr 2+ substituted into U sites within UO 2 or via formation of a perovskite SrU­(IV)­O 3 structure. , Several studies have also shown negligible differences in the thermodynamics of formation of SrUO 3 compared to those in the binary oxides UO 2 and SrO, suggesting that SrUO 3 formation is possible and perhaps thermodynamically favored in the presence of excess UO 2 . − Additionally, in the current study, the high surface area of the nanoparticulate UO 2 may promote the Sr reaction at the UO 2 surface. The split shell and high O coordination number in the EXAFS fits for both pH 10 and 12 samples certainly suggest that the Sr coordination environment is very different from that of the absorbed Sr and is perovskite-like. , Indeed, within the perovskite structure of Ca 1– x Sr x TiO 3 , Sr has 12 O atoms at an average distance of 2.72 Å in the first coordination shell .…”

Standard molar enthalpies of formation of PrO2and SrPrO3: the unusual thermodynamic stability of APrO3(A = Sr, Ba)

“…This linear molar-enthalpy-against-tolerance-factor relation may be extended to other AMO 3 systems, where A is an alkaline-earth metal cation and M is a tetravalent cation, as shown previously by Fuger and co-workers. (5,17) Deviations from this linear behavior occur only for BaMoO 3 6 ) appear to fit the linear tolerance-factor relation quite well. However, it is clear that there may indeed be reasons for the deviation of 4f 1 from the expected behavior which could be elucidated by an investigation of the electronic structures of these compounds.…”