Rapid phase mapping in heat-treated powder mixture of alumina and magnesia utilizing cathodoluminescence

Scanning electron microscope–cathodoluminescence (SEM-CL) analysis was carried out for the rapid phase identification of a single particle with the size of approximately 100 µm consisting of alumina (Al₂O₃) and spinel (MgAl₂O₄) phases. We selected this particle as the analyte because Al₂O₃ and MgAl₂O₄ are typical inclusions in steel, and their identification is important for steel production. Samples were prepared by pressing a mixture of Al₂O₃ and magnesia (MgO) powders heated at 1300 °C and copper powder into a pellet. The formation of a MgAl₂O₄ phase in the powder mixture of Al₂O₃ and MgO heated at 1300 °C was confirmed by X-ray diffraction analysis. CL images of samples were obtained using a camera attached to a SEM. We confirmed that Al₂O₃ and MgAl₂O₄ phases in a CL image produced blue and green luminescence, respectively, by comparing the CL image with elemental mappings of aluminum and magnesium in the sample obtained using an energy-dispersive X-ray detector attached to a SEM. We also observed the shift of a phase boundary between Al₂O₃ and MgAl₂O₄ with dozen micrometers scale by obtaining CL images of samples containing a mixture of Al₂O₃ and MgO powders heated at 1300 °C with different heat-treatment durations. The time required to obtain a CL image was 1 s. Thus, SEM-CL analysis will contribute to the rapid phase identification of Al₂O₃ and MgAl₂O₄ in a single particle.