Thermodynamic insights of ternary compounds of NiO - V2O5 system

We present the first experimental investigation on thermochemical stability of three ternary nickel vanadates, namely, NiV ₂O ₆(s), Ni ₂V ₂O ₇(s) and Ni ₃V ₂O ₈(s) in the NiO-V ₂O ₅ system. The standard molar entropies of formation of the compounds were determined by low temperature heat capacity measurements from 2 to 300 K using relaxation calorimetry. The standard molar enthalpy of formation and molar heat capacities were determined employing high temperature oxide melt solution calorimetry in conjunction with differential scanning calorimetry. Using the experimentally obtained thermochemical data, the standard molar Gibbs energy of formation of these compounds were derived and the corresponding expressions are given as follows: ∆ G f , m ° < Ni V 2 O 6 > ± 1.4 kJ mol − 1 = − 1839.4 + 0.5132 ( T / K ) ( T : 298.15 − 1000 K ) ∆ G f , m ° < Ni 2 V 2 O 7 > ± 1.4 kJ mol − 1 = − 2101.8 + 0.5971 ( T / K ) ( T : 298.15 − 1000 K ) ∆ G f , m ° < Ni 3 V 2 O 8 > ± 3.2 kJ mol − 1 = − 2360.5 + 0.6538 ( T / K ) ( T : 298.15 − 1000 K )