Determination of Standard Gibbs Free Energy of Formation of NiW₂B₂ and Activity of Ni-W Binary System by EMF Measurement

Abstract

The standard Gibbs free energy of formation of NiW₂B₂ was determined in the temperature range from 1273 K to 1423 K by measuring electromotive forces of a galvanic cell having a solid oxide electrolyte. Also, the standard Gibbs free energies of formation of WO₂ and WO_49/18 and the Gibbs free energy of mixing of the Ni-W binary system, which were necessary to determine the standard Gibbs free energy of formation of NiW₂B₂, were determined. The results obtained are as follows:
(1) ΔG°f(NiW₂B₂)=-199000+3.08T±1000J/mol (1273-1423 K).
(2) ΔG°f(WO₂)=-573100+167.0T±100J/mol (1223-1473 K).
(3) ΔG°f(WO_49/18)=-755400+213.2 T+200J/mol (1223-1423 K).
(4) The Gibbs free energy of mixing of the Ni-W solid solution (Ni-16.4 mol%W), which is in equilibrium with NiW₂B₂, is:
ΔGm(Ni-16.4 mol%W)=-4040+0.280T±3J/mol (1273-1423 K).