Dehydration of γ-FeOOH: Direct Observation of the Mechanism

Abstract

The dehydration of γ-FeOOH to γ-Fe₂O₃ has been investigated by thermoanalytical, electron microscopic and X-ray diffraction methods, using single crystals of suitably small size as a starting material, in order to maintain short diffusion paths. While kinetical data alone are not conclusive, the electron micrographs show unambiguously how the reaction proceeds in the crystals: Strings of perfectly oriented γ-Fe₂O₃ crystallites of about 70 Å diameter and disordered lithium site vacancies extend into the undecomposed matrix crystal which can be distinguished from decomposed parts by direct imaging of the (120) lattice planes of 3 Å spacing. An atomistic interpretation of this result is given.