Reduction mechanism of uniform iron oxide nanoparticles to metal used as recording media

Uniform and stable α-Fe nanoparticles of around 40 nm in width and axial ratios from 5 to 7 have been obtained from hematite (α-Fe2O3) without any additive. The precursor was synthesized by forced hydrolysis of a Fe(ClO4)3 solution in the presence of urea and different amounts of NaH2PO4. These particles have been reduced to metal α-Fe by heating under a hydrogen flow and the best conditions of temperature, hydrogen flow and time to preserve the morphology have been established. There is a minimum temperature (400 °C) and a minimum hydrogen flow (20 l/h) to reduce the hematite particles to metal in a reasonable time (4 h), preserving the size and the shape of the particles. The main change in the material is related to the crystallite size of the metal particles, which increases as the reduction proceeds. A detailed analysis of the magnetic properties of these particles during the reduction process and the influence of the particle axial ratio has been carried out.