Oxidation of the hexagonal Zr(Cr 0.4Fe 0.6) 2 Laves phase

Abstract

The hexagonal (C14-type) Laves phase Zr(Cr 0.40Fe 0.60) 2 when oxidized in an open furnace was studied by X-ray diffraction and Mössbauer spectroscopy techniques. Oxidation modified part of the original Laves phase and Zr oxides, Cr oxides, α-Cr, (Fe, Cr) oxides, α-Fe and α-Fe 2O 3 appeared. The behaviour of these phases, particularly the Fe-bearing phases, is described in detail through a two stage process (stage I from 0 to ∼7 wt% O 2 and stage II up to 22 wt% O 2). A very small amount of O 2 (stage I) is enough to induce the formation of α-Fe upon oxidation, sustaining a model previously suggested for the oxidation of the Laves phases. This α-Fe is highly Cr-substituted. Oxidation proceeds through the increasing presence of α-Fe 2O 3 and through the structural evolution of Zr oxides (formation of monoclinic, tetragonal and cubic ZrO 2).