Kinetic decomposition of {Ni_2SiO_4} in oxygen potential gradients

Jacob, KT and Shukla, AK (1987) Kinetic decomposition of {Ni_2SiO_4} in oxygen potential gradients. In: Journal of Materials Research, 2 (3). pp. 338-344.

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Abstract

Nickel orthosilicate {(Ni_2SiO_4)} has been found to decompose into its component binary oxides in oxygen potential gradients at 1373 K. Nickel oxide was formed at the high oxygen potential boundary, while silica was detected at the low oxygen potential side. Significant porosity and fissures were observed near the {Ni_2SiO_4/SiO_2} interface and the {SiO_2} layer. The critical oxygen partial pressure ratio required for decomposition varied from 1.63 to 2.15 as the oxygen pressures were altered from 1.01 ? 105 to 2.7X 10-4 Pa, well above the dissociation pressure of {Ni_2SiO_4}. Platinum markers placed at the boundaries of the {Ni_2SiO_4} sample indicated growth of NiO at the higher oxygen potential boundary, without any apparent transport of material to the low oxygen potential side. However, significant movement of the bulk {Ni_2SiO_4} crystal with respect to the marker was not observed. The decomposition of the silicate occurs due to the unequal rates of transport of Ni and Si. The critical oxygen partial pressure ratio required for decomposition is related both to the thermodynamic stability of {Ni_2SiO_4} with respect to component oxides and the ratio of diffusivities of nickel and silicon. Kinetic decomposition of multicomponent oxides, first discovered by Schmalzried, Laqua, and co-workers [H. Schmalzried, W. Laqua, and P. L. Lin, Z. Natur Forsch. Teil A 34, 192 (1979); H. Schmalzried and W. Laqua, Oxid. Met. 15, 339 (1981); W. Laqua and H. Schmalzried, Chemical Metallurgy—A Tribute to Carl Wagner (Metallurgical Society of the AIME, New York, 1981), p. 29] has important consequences for their use at high temperatures and in geochemistry.

Item Type:	Journal Article
Publication:	Journal of Materials Research
Publisher:	Materials Research Society
Additional Information:	Copyright of this article belongs to the Materials Research Society
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	13 Jun 2008
Last Modified:	19 Sep 2010 04:45
URI:	http://eprints.iisc.ac.in/id/eprint/14316

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