In situ probing and microstructural evolution mechanisms of hydrogen-derived manganosite (MnO) during oxidative cooling

This study first revealed the oxidation pathways and microstructural evolution mechanisms of hydrogen-reduced MnO during air cooling. The results demonstrated that when the oxygen concentration was 9% and the cooling time was 15 min, the cooling temperature range in which MnO was most easily oxidized was from 200 to 400 °C, oxidation rate increased from 7.23 to 34.41%. When the cooling temperature was 300 °C and the oxygen concentration was 9%, MnO had the fastest oxidation rate within 1 –7 min, the oxidation rate rapidly rose from 5.12 to 22.70%. Under controlled cooling conditions (300 °C, 7 min), the MnO oxidation rate was effectively maintained below 15.78% at 5% oxygen concentration. Thermodynamic analysis, thermogravimetric analysis and in-situ XRD indicated that the oxidation reaction sequence of MnO was as follows: MnO → Mn₃O₄ → Mn₂O₃. Notably, the maximum weight gain rate emerged at 345 °C. XPS analysis confirmed the MnO → Mn₃O₄ transformation during oxidation, while SEM-EDS provided direct evidence through the observed gradual decrease in Mn/O ratios during cooling. BET analysis indicated that higher cooling temperatures decreased particle specific surface area and pore volume, shifting pore distribution from macropores to mesopores through pore occlusion by manganese oxides. This reduced leaching interfacial area and MnO recovery, underscoring the necessity to control MnO oxidation for efficient extraction. Therefore, the oxidation of newborn manganosite should be controlled to the least extent possible.