TY - JOUR
T1 - Enthalpies of formation of Ce-pyrochlore
AU - Helean, K. B.
AU - Navrotsky, A.
AU - Vance, E. R.
AU - Carter, M. L.
AU - Ebbinghaus, B.
AU - Krikorian, O.
AU - Lian, J.
AU - Wang, L. M.
AU - Catalano, J. G.
N1 - Funding Information:
The authors would like to thank H. Xu for the synchrotron X-ray data and Rietveld analysis; A. Risbud and J. Majzlan for their assistance in calorimetry. Financial support was provided by Lawrence Livermore National Laboratory, the Department of Energy EMSP grant number 60118 and grant number DE-FG07-97ER45673, the University of California at Davis and by the Office of Basic Energy Sciences, DOE grant (R.C. Ewing) DE-FG02-97ER45656. Portions of this research were carried out at the Stanford Synchrotron Radiation Laboratory, a national user facility operated by Stanford University on behalf of the US Department of Energy, Office of Basic Energy Sciences.
PY - 2002/6
Y1 - 2002/6
N2 - High temperature oxide melt solution calorimetry was used to derive standard enthalpies of formation, ΔHf0 (kJ/mol), for three pyrochlore phases: Ca0.93Ce1.00Ti2.035O7.00 (-3656.0 ± 5.6), Ca1.46U0.234+U0.466+T 1.85O7.00 (-3610.6 ± 4.1) and Gd2Ti2O7 (-3822.5 ± 4.9). Enthalpy of drop solution data, ΔHds, were used to calculate enthalpies of formation with respect to an oxide phase assemblage, ΔHf-ox0: CaO + MO2 + 2TiO2 = CaMTi2O7 or Gd2O3 + 2TiO2 = Gd2Ti2O7, and an oxide/perovskite phase assemblage, ΔHf-pv+ox0: CaTiO3 + MO2 + TiO2 = CaMTi2O7, where M = Ce or U. All three pyrochlore samples were stable in enthalpy relative to an oxide assemblage with ΔHf-ox0 (kJ/mol) (Gd2Ti2O7) = -113.4 ± 2.8; ΔHf-ox0(Ca1.46U0.234+ U0.466+Ti1.85O7.00 = -123.1 ± 3.4; ΔHf-ox0(Ca0.93Ce1.00Ti2.0 35O7.00 = - 54.1 ± 5.2. U-pyrochlore was stable in enthalpy relative to an oxide/perovskite assemblage (ΔHf-pv+ox0 = -5.1 ± 4.0 kJ/mol). Ce-pyrochlore was metastable in enthalpy relative to the oxide/perovskite phase assemblage (ΔHf-pv+ox0 = +21.0 ± 5.5 kJ/mol). A significant metastability field was defined with respect to an oxide/perovskite phase assemblage. However, the proposed waste form baseline composition lies in the stable regions of the phase diagrams.
AB - High temperature oxide melt solution calorimetry was used to derive standard enthalpies of formation, ΔHf0 (kJ/mol), for three pyrochlore phases: Ca0.93Ce1.00Ti2.035O7.00 (-3656.0 ± 5.6), Ca1.46U0.234+U0.466+T 1.85O7.00 (-3610.6 ± 4.1) and Gd2Ti2O7 (-3822.5 ± 4.9). Enthalpy of drop solution data, ΔHds, were used to calculate enthalpies of formation with respect to an oxide phase assemblage, ΔHf-ox0: CaO + MO2 + 2TiO2 = CaMTi2O7 or Gd2O3 + 2TiO2 = Gd2Ti2O7, and an oxide/perovskite phase assemblage, ΔHf-pv+ox0: CaTiO3 + MO2 + TiO2 = CaMTi2O7, where M = Ce or U. All three pyrochlore samples were stable in enthalpy relative to an oxide assemblage with ΔHf-ox0 (kJ/mol) (Gd2Ti2O7) = -113.4 ± 2.8; ΔHf-ox0(Ca1.46U0.234+ U0.466+Ti1.85O7.00 = -123.1 ± 3.4; ΔHf-ox0(Ca0.93Ce1.00Ti2.0 35O7.00 = - 54.1 ± 5.2. U-pyrochlore was stable in enthalpy relative to an oxide/perovskite assemblage (ΔHf-pv+ox0 = -5.1 ± 4.0 kJ/mol). Ce-pyrochlore was metastable in enthalpy relative to the oxide/perovskite phase assemblage (ΔHf-pv+ox0 = +21.0 ± 5.5 kJ/mol). A significant metastability field was defined with respect to an oxide/perovskite phase assemblage. However, the proposed waste form baseline composition lies in the stable regions of the phase diagrams.
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U2 - 10.1016/S0022-3115(02)00795-X
DO - 10.1016/S0022-3115(02)00795-X
M3 - Article
AN - SCOPUS:0036608703
SN - 0022-3115
VL - 303
SP - 226
EP - 239
JO - Journal of Nuclear Materials
JF - Journal of Nuclear Materials
IS - 2-3
ER -