Calorimetric study of nickel molybdate: Heat capacity, enthalpy, and Gibbs energy of formation

The thermodynamic properties of the alpha and beta polymorphs of NiMoO4 were directly investigated by calorimetry. The standard entropies of formation, Delta(f)S(T)degrees, of alpha and beta were determined from measuring the molar heat capacity, Cp,m, from near absolute zero (2 K) to high temperature (1380 K) by a relaxation method and differential scanning calorimetry. The standard enthalpies of formation, Delta(f)H(T)degreesof alpha and beta were T determined by combining C-p,C-m with the standard enthalpy of formation, Delta(f)H(298)degrees, at 298 K obtained from drop solution 2 calorimetry in molten sodium molybdate at 973 K. The standard Gibbs energies of formation, Delta(f)G(T)degrees of alpha and beta were T determined from their Delta(f)S(T)degrees and Delta(f)H(T)degrees values. The Delta(f)G(T)degrees values T T T indicate that the polymorphic transformation from alpha to occurs at 1000 K, consistent with the observed phase transformation at 1000 K.