# Phase equilibria and thermodynamic properties in the system $Ni-Mo-O$

Jacob, KT and Kale, GM and Iyengar, GNK (1987) Phase equilibria and thermodynamic properties in the system $Ni-Mo-O$. In: Journal of Materials Science, 22 (12). pp. 4274-4280.

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## Abstract

Coexisting phases in the $Ni-M0-O$ ternary system at 1373 K have been identified by X-ray diffraction, optical microscopy and scanning electron microscopy. The samples were equilibrated in evacuated quartz capsules. Only one ternary phase, $NiMoO_4$, was found to exist in the system. The reversible e.m.f, values of the following solid-state galvanic cells were measured in the temperature range 900 to 1500 K: (I) $Pt, Ni + NiO/(CaO) ZrO_2/NiO + MoO_2 + NiMoO_4, Pt$; (II) $Pt, Mo + MoO_2/(CaO) ZrO_2/O_2, Pt$; and (III) $Pt, Mo + MoO_2/(CaO) ZrO_2/Ni-Mo + MoO_2, Pt$. The Gibbs energies of formation of $NiMoO_4$ and $MoO_2$ and activities in $Ni-Mo$ alloys were derived from the e.m.f, data. For the reaction $<NiO> + <MoO_2> + 1/2(O_2) \rightarrow <NiMoO_4>$ we obtain $\Delta G^0_r = -201 195 + 69.70T (\pm400) J mol^{-1}$; for $<Mo> + (0_2) \rightarrow <MoO_2>$ we obtain $\Delta G^0_f = -578880 + 168.5T (\pm 500) J mol^{-1}$. Based on the information from phase identification studies and thermodynamic stabilities, the isothermal section and oxygen potential diagram for the $Ni-Mo-O$ system at 1373 K have been developed.

Item Type: Journal Article Copyright of this article belongs to Springer. Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy) 10 Apr 2008 19 Sep 2010 04:44 http://eprints.iisc.ernet.in/id/eprint/13722