Thermodynamic Properties for Nd2(MoO4)3 Formed in the Nuclear Fuel Waste Glasses

The thermodynamic properties for Nd-2(MoO4)(3) were investigated. Nd-2(MoO4)(3) is one of the end member of the yellow phases which are known as hygroscopic harmful phases in the nuclear fuel waste glasses. The standard molar entropy, Delta S-T(0)m degrees, at 298.15K of Nd-2(MoO4)(3) was determined by measuring its isobaric heat capacities, C-p,C-m degrees, from 2K via the fitting functions including the Debye-Einstein formula and electronic-as well as magnetic terms. The Neel temperature, T-N, estimated by extrapolating the magnetic-term in the fitting function. Its standard Gibbs energy of formation, Delta(f)G(m)degrees, was determined by combining Delta S-T(0)m degrees datum with the standard enthalpy of formation, Delta H-f(m)degrees, which were estimated from ones for Ce-2(MoO4)(3) and Sm-2(MoO4)(3). The unknown standard Gibbs energy of solution, Delta(sol)G(m)degrees, at 298.15K of Nd-2(MoO4)(3) was predicted from the reference data for MoO42- (aq) and Nd3+(aq). The obtained thermodynamic values are as follows: Delta S-T(0)m degrees (Nd-2(MoO4)(3)(cr), 298.15 K)/(JK(-1)mol(-1)) = 439.29 +/- 4.39 Delta(f)G(m)degrees (Nd-2(MoO4)(3)(cr), 298.15 K)/(kJ mol(-1)) = -4072.13 +/- 6.14 Delta(sol)G(m)degrees (Nd-2(MoO4)(3), 298.15 K)/(kJ (mol of MoO42- (aq))(-1)) = 73.12 +/- 2.33 T-N/K = 1.55 +/- 0.16 The data obtained in the present work are expected to be useful for geochemical simulations of the diffusion of radioactive elements through underground water.