Synthesis of Nanoscale γ-Fe2O3 Powders with Hydrates via Microwave-Assisted Heat Treatment

Herein, the effect of microwave irradiation on the formation of gamma-Fe2O3 phase was investigated. The structural and chemical features of the gamma-Fe2O3 synthesized via microwave-assisted heat treatment (MWH) were examined in terms of precursors. Three different types of precursors, i.e., FeC2O4 center dot 2H(2)O (FH), FeOOH, and Fe3O4, were used, and each precursor was heated in a temperature range of 100-300 degrees C via MWH. Nanocrystalline gamma-Fe2O3 powders with a crystallite size of similar to 19 nm were synthesized when the source FH was heat-treated at 120 degrees C for 20 min by MWH. The activation energy required for the formation of gamma-Fe2O3 powders was 21.4 kJ/mol, which is approximately one-third or one-quarter of the activation energy (68.5 and 87.9 kJ/mol) reported for the synthesis of gamma-Fe2O3 via conventional heating. The lattice parameter of the synthesized gamma-Fe2O3 phase expanded to 8.360 angstrom at 120 degrees C, whereas it contracted to 8.351 angstrom at 200 degrees C. This variation can be attributed to the content of the surface-absorbed OH group. The values of the saturated magnetization and coercive force of the powders increased by approximately threefold with increasing crystallinity. [GRAPHICS] .