Microwave-induced phase transformations of iron oxide particles

The article presents results of study of α-Fe₂O₃ response on microwave treatment. Microwave influence on iron oxides constituting nature occurring kaolinite clay were studied by a complex of methods. The original sample S0 was made from fine-dispersed Fe₂O₃ iron oxide particles. Sample S1 was produced via treatment with 2.45 GHz microwave field. Microwave treatment induced structure changes in iron oxides which manifest themselves through polymorphic changes. X-ray phase analysis shown that a deformation polymorphic transformation α-Fe₂O₃→γ-Fe₂O₃ takes place and two-phase hematite-maghemite state is formed. Problem of faint and overlapping diffraction peaks resolution is solved with wavelet transformation skeleton technique. Crystal particles of S0 sample are α-Fe₂O₃ hematite particles with rhombohedral lattice. After microwave treatment sample S1 developed new diffraction peaks corresponding to cubic γ-Fe₂O₃ maghemite crystal system. Polymorphic transition is accompanied with morphological changes. After the treatment surfaces of large particles are covered with smaller particles which are proved by the increase of samples fractal dimension from 2.83 to 2.85. Powder color changes from red-orange to dark brown which results in changes of all color parameters; the red component experience the biggest suppression and it is suppressed by the factor 2. (paper)