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Activities and Immiscibility in the System Cu-Rh

Priya, Shashank and Jacob, KT (2000) Activities and Immiscibility in the System Cu-Rh. In: Journal of Phase Equilibria, 21 (04). p. 342.

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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 1 Cu2O//(Y2O3)ZrO2//Cu-Rh 1 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: DH 5 XRh(1 2 XRh)[41,340 1 12,670 XRh] J mol21 DSE 5 XRh(1 2 XRh)[15.46 1 4.72 XRh] J mol21 K21 The results predict a solid-state miscibility gap with Tc 5 1408 (65) K at XRh 5 0.59 (60.02). 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 T8c 5 983 (65) K and X8Rh 5 0.43 (60.02). 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: Journal Article
Publication: Journal of Phase Equilibria
Publisher: Springer Boston
Additional Information: Copyright of this article belongs to Springer Boston
Keywords: Thermodynamic activity;System Cu-Rh;Immiscibility
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 02 Dec 2008 10:46
Last Modified: 02 Dec 2008 10:46
URI: http://eprints.iisc.ac.in/id/eprint/16561

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