High-temperature phase chemistry of the system Gd-Pd-O

Jacob, Thomas K and Lwin, Kay Thi and Waseda, Yahio (2002) High-temperature phase chemistry of the system Gd-Pd-O. In: Science and Technology of Advanced Materials, 3 (2). pp. 75-84.

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Abstract

An isothermal section of the phase diagram for the system Gd–Pd–O at 1223 K has been established by equilibration of samples and phase identification after quenching by optical and scanning electron microscopy, X-ray powder diffraction, and energy dispersive spectroscopy. Three ternary oxides $Gd_4PdO_7$, $Gd_2PdO_4$ and $Gd_2Pd_2O_5$ were identified. Liquid alloys, the four inter-metallic compounds and Pd-rich solid solution were found to be in equilibrium with $Gd_2O_3$. Based on the phase relations, four solid-state cells were designed to measure the Gibbs energies of formation of the three ternary oxides in the temperature range from 920 to 1320 K. Although three cells are sufficient to obtain the properties of the three compounds, the fourth cell was deployed to cross check the data. An advanced version of the solid-state cell incorporating a buffer electrode with yttria-stabilized zirconia solid electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode was used for high-temperature thermodynamic measurements. The standard Gibbs energy of formation of the inter-oxide compounds from their component binary oxides can be represented by the following equations: $Gd_4PdO_7(s):\triangle f_{(ox)}G^ 0/Jmol^ - ^ 1=−25,030+0.33T (\pm 140)$, $Gd_2PdO_4(s):\triangle f_{(ox)}G^ 0/Jmol^ - ^ 1=−25,350+0.84T (\pm 135)$, $Gd_2Pd_2O_7(s):\triangle f_{(ox)}G^ 0/Jmol^ - ^ 1=−48,700+0.38T (\pm 270)$, Based on the thermodynamic information, isothermal chemical potential diagrams and isobaric phase diagrams for the system Gd–Pd–O are developed.

Item Type:	Journal Article
Publication:	Science and Technology of Advanced Materials
Publisher:	Elsevier
Additional Information:	Copyright of this article belongs to Elsevier.
Keywords:	Phase diagram;Gibbs energy;Enthalpy;Entropy;Gd4PdO7;Gd2PdO4;Gd2Pd2O5
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	02 Jun 2006
Last Modified:	19 Sep 2010 04:29
URI:	http://eprints.iisc.ac.in/id/eprint/7497

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