Structure transformations of copper chromite under reduction-reoxidation conditions

Structure transformations accompanying reoxidation preliminary reduced at 2 70 degrees C copper chromite were studied using X-ray powder diffraction me thod, and comparison of the structures of the initial and reoxidized copper chromite was carried out. Conditions under which cation-deficient spinel, stabilized with hydrogen and epitaxially bonded with its surface Cu particl es (derived from reduction of copper chromite by hydrogen) forms copper chr omite with the tetragonal spinel structure are revealed. It is shown that t he reoxidized spinel is non-stoichiometric and possibly contains some amoun t of hydrogen in the form of protons bonded to the lattice oxygen. Differen ces of reversible phase transformation of copper chromite under reduction-r eoxidation conditions from reversible polymorphism of copper chromite with temperature variations are analyzed. (C) 2000 Elsevier Science B.V. All rig hts reserved.