Activities and immiscibility in the system Cu-Rh

Priya, Shashank ; Jacob, K. T. (2000) Activities and immiscibility in the system Cu-Rh Journal of Phase Equilibria, 21 (4). pp. 342-349. ISSN 1054-9714

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Official URL: http://link.springer.com/article/10.1361%2F1054971...

Related URL: http://dx.doi.org/10.1361/105497100770339860

Abstract

The thermodynamic activity of rhodium in solid Cu-Rh alloys is measured by the electromotive force method in the temperature range from 1050 to 1325 K with a solid-state cell: Rh,Cu+Cu2O//(Y2O3)ZrO2//Cu−Rh+Cu2O,Rh The activity of copper and the Gibbs energy, enthalpy, and entropy of mixing of the solid solution are derived. Activities exhibit large positive deviation from Raoult’s law. The mixing properties can be represented by a pseudo-subregular solution model in which excess entropy has the same type of functional dependence on composition as the enthalpy of mixing: ΔH=XRh(1−XRh)[41,340+12,670XRh]Jmol−1 ΔSE=XRh(1−XRh)[15.46+4.72XRh]Jmol−1K−1 The results predict a solid-state miscibility gap with Tc=1408 (±5) K at XRh=0.59 (±0.02). The computed critical temperature is 15 K lower than that reported in the literature. The coherent spinodal, calculated using Cahn’s model, is characterized by T′c=983 (±5) K and X′Rh=0.43 (±0.02). The large difference between the coherent and chemical spinodal is caused by the relatively large difference in lattice parameters of Cu and Rh and high Young’s modulus of the alloy. The positive enthalpy of mixing obtained in this study contrasts with the negative values predicted by Miedema’s model. Thermodynamic properties of liquid alloys are estimated from the data for solid alloys obtained in this study and the approximate location of the liquidus available in the literature.

Item Type:Article
Source:Copyright of this article belongs to John Wiley and Sons.
ID Code:95003
Deposited On:11 Oct 2012 11:06
Last Modified:11 Oct 2012 11:06

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