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Phase relationships in the system Ni-W-O and thermodynamic properties of NiWO4

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Abstract

The phase diagram of the Ni-W-O system at 1200 K was established by metallographic and X-ray identification of the phases present after equilibration at controlled oxygen potentials. The oxygen partial pressures over the samples were fixed by metered streams of CO+CO2 gas mixtures. There was only one ternary oxide, nickel tungstate (NiWO4), in the Ni-W-O system at a total pressure of 1 atm, and this compound decomposed to a mixture of Ni+WO2.72 on lowering the oxygen potential. The Gibbs' free energy of formation of NiWO4 was determined from the measurement of the e.m.f. of the solid oxide galvanic cell, Pt, Ni+NiWO4+WO2.72/CaO-ZrO2/Ni+NiO, Pt and thermodynamic properties of tungsten and nickel oxides available in the literature. For the reaction, NiO(s)+WO3(s)→NiWO4(s) ΔG°=−10500−0.708 T (±250) cal mol−1.

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  1. Department of Metallurgy and Materials Science, University of Toronto, Toronto, Canada

    K. T. Jacob

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  1. K. T. Jacob
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Jacob, K.T. Phase relationships in the system Ni-W-O and thermodynamic properties of NiWO4 . J Mater Sci 12, 1647–1652 (1977). https://doi.org/10.1007/BF00542815

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