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Phase Relations in the System Cu-Gd-O and Gibbs Energy of Formation of CuGd204

Jacob, KT and Mathews, Tom and Hajra, JP (1993) Phase Relations in the System Cu-Gd-O and Gibbs Energy of Formation of CuGd204. In: Metallurgical Transactions. Physical Metallurgy and Material, 24 (7). pp. 1655-1660.

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Abstract

The phase relations in the system Cu-Gd-O have been determined at 1273 K by X-ray diffrac- tion, optical microscopy, and electron microprobe analysis of samples equilibrated in quartz ampules and in pure oxygen. Only one ternary compound, CuGd2O4, was found to be stable. The Gibbs free energy of formation of this compound has been measured using the solid-state cell Pt, Cu2O + CuGd2O4 + Gd2O3 // (Y2O3) ZrO2 // CuO + Cu2O, Pt in the temperature range of 900 to 1350 K. For the formation of CuGd2O4 from its binary component oxides, CuO (s) + Gd2O3 (s) → CuGd2O4 (s) ΔG° = 8230 - 11.2T (±50) J mol-1 Since the formation is endothermic, CuGd2O4 becomes thermodynamically unstable with respect to CuO and Gd2O3 below 735 K. When the oxygen partial pressure over CuGd2O4 is lowered, it decomposes according to the reaction 4CuGd2O4 (s) → 4Gd2O3 (s) + 2Cu2O (s) + O2 (g) for which the equilibrium oxygen potential is given by Δμo 2 = −227,970 + 143.2T (±500) J mol−1 An oxygen potential diagram for the system Cu-Gd-O at 1273 K is presented.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Minerals Metals Materials Soc.
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 18 Feb 2011 07:36
Last Modified: 18 Feb 2011 07:36
URI: http://eprints.iisc.ernet.in/id/eprint/35670

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