Internal displacement reactions in multicomponent oxides: Part I. Line compounds with narrow homogeneity range

S. N.S. Reddy, D. N. Leonard, L. B. Wiggins, K. T. Jacob

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

Both polycrystalline and single-crystal materials were used as the starting NiTiO3 Oxide. During the reaction, the Ni in the oxide compound is displaced by Fe and it precipitates as a γ-(Ni-Fe) alloy. The reaction preserves the starting ilmenite structure. The product oxide has a constant Ti concentration across the reaction zone, with variation in the concentration of Fe and Ni, consistent with ilmenite composition. In the case of single-crystal NiTiO3 as the starting oxide, the γ alloy has a "layered structure and the layer separation is suggestive of Liesegang-type precipitation. In the case of polycrystalline NiTiO3 as the starting oxide, the alloy precipitates mainly along grain boundaries, with some particles inside the grains. A concentration gradient exists in the alloy across the reaction zone and the composition is >95 at. pct Ni at the reagtion front. The parabolic rate constant for the reaction is kp = 1.3 × 10-12 m2 s-1 and is nearly the saine for both single-crystal and polycrystalline oxides.

Original languageEnglish
Pages (from-to)2685-2694
Number of pages10
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume36
Issue number10
StatePublished - Oct 2005
Externally publishedYes

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