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Tie-Lines and Mixing Properties of Solid Solutions in the System CaO-SrO-PbO-O at 1100 K

Jacob, KT and Jayadevan, K (2000) Tie-Lines and Mixing Properties of Solid Solutions in the System CaO-SrO-PbO-O at 1100 K. In: Journal of Phase Equilibria and Diffusion, 21 (04). pp. 350-356.

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Abstract

Phase relations in the system CaO-SrO-PbO-O-2 at 1100 K have been determined by equilibrating samples with different compositions in air, oxygen, or evacuated ampoules for 7 days and characterizing quenched specimens by optical and scanning electron microscopy, energy-dispersive analysis of x-rays (EDX), and x-ray diffraction (XRD). There is a solid-state miscibility gap in the pseudo-binary system CaO-SrO, and continuous solid solubility between Ca2PbO4 and Sr2PbO4 at 1100 K. Substitution of Ca for Sr occurs only to a limited extent (similar to 2 mol.%) in SrPbO3. The calcium-rich solid solutions (Ca1-ySry)(2)PbO4 characterized by y less than or equal to 0.255 are in equilibrium with PbO in air; compositions with y greater than or equal to 0.255 coexist with (Ca1-zSrz)PbO3. There is a three-phase region involving the two monoxide solid solutions (Ca1-xSrx)O on either side of the miscibility gap with x = 0.24 and 0.71 and (Ca1-ySry)(2)PbO4 with y = 0.96. Accurately determined are the locations of tie-lines between the solid solutions. Attainment of equilibrium was checked by the conventional tie-line rotation technique. The excess Gibbs energy of mixing of the solid solution with orthorhombic structure is obtained by an analysis of tie-line data; for the mixing of one mole of Ca and Sr represented by (Ca1-ySry)Pb0.5O2, Delta G(E) = y(1 - y) [15,840 - 2950 y] J/mol. The thermodynamic properties suggest the onset of immiscibility in this solid solution below 884 (+/-5) K. The miscibility gap is asymmetric with a critical composition at y = 0.43 (+/-0.02), Inside the triangle (Ca1-ySry)Pb0.5O2 - (Ca1-zSrz)PbO3 - PbO, a small liquid-phase region is present close to the PbO corner, surrounded by three two-phase fields. Each corner of the approximately triangular liquid-phase region is associated with a three-phase field

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Springer.
Department/Centre: Division of Chemical Sciences > Materials Research Centre
Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 20 Nov 2009 06:01
Last Modified: 19 Sep 2010 05:01
URI: http://eprints.iisc.ernet.in/id/eprint/18291

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