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Non-equilibrium phase synthesis in $Al_2O_3-Y_2O_3$ by spray pyrolysis of nitrate precursors

Ullal, CK and Balasubramaniam, KR and Gandhi, AS and Jayaram, V (2001) Non-equilibrium phase synthesis in $Al_2O_3-Y_2O_3$ by spray pyrolysis of nitrate precursors. In: Acta Materialia, 49 (14). pp. 2691-2699.

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Abstract

The phase evolution in the $Al_2O_3-Y_2O_3$ system has been studied for 4, 10, 15 and 37.5% $Y_2O_3$ amorphous powders prepared by spray pyrolysis of nitrate precursor solutions. Two distinct metastable transformation sequences were identified for the amorphous powders upon heat treatment. Crystallisation accompanied by partitioning leads to a mixture of hexagonal $YAlO_3$ and $\gamma-Al_2O_3$ (spinel structure). Partitionless crystallisation, on the other hand, leads directly to a $\gamma-Al_2O_3$ solid solution in dilute alloys, and garnet at temperatures as low as 800°C in the stoichiometric composition provided segregation is avoided during decomposition. Further heat treatment of a yttria-supersaturated $\gamma-Al_2O_3$ leads to the precipitation of the orthorhombic $YAlO_3$ that is stable up to temperatures as high as 1600°C, while hexagonal $YAlO_3$ converts to garnet, $Y_3Al_5O_1_2$. A rationalisation of the phase evolution sequence has been attempted on the basis of kinetic considerations, cation coordination and semi-quantitative free energy–composition curves for the various competing phases.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Elsevier.
Keywords: Chemical synthesis;Ceramics;Amorphous materials;Phase transformations;Non-equilibrium processing
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 30 Mar 2007
Last Modified: 19 Sep 2010 04:37
URI: http://eprints.iisc.ernet.in/id/eprint/10590

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