Crystal Structure Evolution of Magnetite Ferrofluids: Effect of Heating Treatment

Abstract

This work aimed at investigating the crystal evolution, crystallite phase, morphology, and particle size of the magnetite ferrofluids as the effects of heating temperature. The iron sand was used to prepare magnetite ferrofluids by employing a simple chemical method. The high-resolution transmission microscopy characterization presented that the particle size and morphology were expanded from small to bigger size in nanometric size with aggregation. The electron and X-ray diffractions patterns exhibited that the magnetite particles in the fluids evolved from Fe3O4 (cubic structure) structure to α-Fe2O3 (rhombohedral structure) as the effect of heating treatment. At a temperature of 500 °C, the magnetite particles had a mixed crystallite phases consisting of α-Fe2O3 and Fe3O4 structures. Interestingly, at the temperature of 600 °C or higher, the magnetite particles in the fluids changed to the pure α-Fe2O3 structure. Such evolution phenomenon gives significant information in designing new sophisticated application of the magnetite ferrofluids, especially for the temperature sensor.