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Determination of thermodynamic properties of $Ca_{4}PtO_{6}$ and $CaPtO_{3}$ using solid state cells with buffer electrodes

Jacob, KT and Okabe, TH and Uda, T and Waseda, Y (1999) Determination of thermodynamic properties of $Ca_{4}PtO_{6}$ and $CaPtO_{3}$ using solid state cells with buffer electrodes. In: Zeitschrift Fur Metallkunde, 90 (7). pp. 491-498.

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Abstract

The standard Gibbs energies of formation of CaPtO3 and Ca4PtO6 have been measured in the temperature range from 940 to 1400 K using solid-state cells with (Y2O3) ZrO2 as the electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode. For the de sign of appropriate working electrodes, phase relations in the ternary system Ca-Pt-O were investigated at 1250 and 1350 K. Two ternary oxides, CaPtO3 and Ca4PtO6, compositions of which fall on the join CaO-PtO2. were found to be stable. Each of the oxides coexisted with pure metal Pt. Therefore, two working electrodes were pre pared consisting of mixtures of Pt + CaO + Ca4PtO6 and Pt + Ca4PtO6 + CaPtO3. These mixtures unambiguously define unique oxygen chemical potentials under isothermal and isobaric conditions. A novel apparatus, incorporating a buffer electrode between reference and working electrodes to absorb the electrochemical flux of oxygen through the solid electrolyte, was used for measurement. The buffer electrode prevented polarization of the measuring electrode and ensured accurate data. The standard Gibbs energies of formation Delta(f) G(o) of the ternary compounds from elements in their stable form can be obtained from the emfs; the results are represented by the equations: Ca4PtO6 : Delta(f)G(o)/J mol(-1) = -2,774,240 + 582,86 T (+/-4,500)[940 to 1,115 K] = -2,808,600 + 613,66 T (+/-4,500)[1,115 to 1,400 K] CaPtO3 : Delta(f)G(o)/J mol(-1) = -852,875 + 271,57 T (+/-1,200) [940 to 1,115 K] = -861,465 + 279,27 T (+/-1200) [1,115 to 1,260 K] Based on the thermodynamic information, chemical potential diagrams for the Ca-Pt-O system are developed.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Carl Hanser Verlag.
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 01 Jun 2009 05:15
Last Modified: 01 Jun 2009 05:15
URI: http://eprints.iisc.ernet.in/id/eprint/18395

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