Thermodynamics of formation for zirconolite (CaZrTi2O7) from T=298.15K to T=1500K

Zirconolite (CaZrTi2O7) has been proposed as a ceramic host for the long-term disposal of excess weapons-grade plutonium. Using high-temperature oxide-melt solution calorimetry, the standard molar enthalpy of formation at T = 298.15 K for zirconolite, Delta(f)H(m)(o) = -(3713.7 +/- 4.5) kJ.mol(-1) has been obtained. In combination with the third-law entropy Delta(0)(298.15) S-K(m)o obtained by using adiabatic calorimetry on the same sample, the standard molar Gibbs free energy of formation at T = 298.15 K, Delta(f)G(m)(o) = -(3514.5 +/- 4.5) kJ.mol(-1), has also been obtained. The formation enthalpies, free energies, and third-law entropies Delta(0)(T) S-m are reported from T = 298.15 K to T = 1500 K. Also reported for ZrTiO4, a compound of interest with respect to the (CaO, TiO2, ZrO2) phase diagram containing zirconolite, are the first estimates of the standard molar enthalpy and Gibbs free energy of formation, Delta(f)H(m)(o)(ZrTiO4) = -(2048.7 +/- 5.0) kJ.mol(-1), and Delta(f)G(m)(o)(ZrTiO4) = -(1935.7 +/- 5.0) kJ.mol(-1). (C) 1999 Academic Press.