Oxidation behavior of Mn₅SiB₂powders in flowing air

The oxidation behavior of Mn₅SiB₂powders prepared by self-propagating high-temperature combustion synthesis was investigated in flowing air up to 1100 °C using TG-DSC, XRD, XPS, and SEM/EDS. The oxidation of the Mn₅SiB₂powders with the mean particle size of about 126 μm starts at 650 °C, and completes around 1100 °C. As the temperature increases, the sample mass undergoes a process of increasing, decreasing, increasing, and then decreasing again. This is related to the changes in the surface borosilicate glass system. During this process, the surface transitions from a granular structure to a rippled or flow-patterned morphology. Based on XRD/XPS results, the final products were primarily (Mn₂O₃)₃MnSiO₃and Mn oxides in the +2 and + 3 states. Notably, the mass gain was unusually lower at 800 °C than 700 °C, attributed to the protective silicate-borate layer formed during oxidation.