Laser-Induced Hematite/Magnetite Phase Transformation

The goal of this work was to demonstrate the viability of using laser irradiation to promote the development of a magnetite/hematite bi-layer structure. Local heating by laser irradiation induces a hematite redox mechanism, promoting a phase transition of hematite (Fe2O3) into magnetite (Fe3O4). A relationship between laser feed rate, laser power and the top layer grain size was established. The average grain size increased from 3 mu m to 10 mu m when the laser power increased from 50 W to 100 W. Raman spectroscopy results demonstrated that residual hematite coexists on the magnetite top layer, distributed mostly along the grain boundaries. Electrical conductivity measurements of the irradiated regions confirmed the effectiveness of the laser surface treatment in promoting the local phase transformation of hematite into magnetite, with consequent enhancement of electrical conductivity. The maximum conductivity, 2.8 mS/m, was thus reached for the highest laser power used, 100 W. This phase transformation can be used on other materials to produce bi-layer structure, presenting an important factor for future applications and development using this technique.