Thermal Decomposition of Manganese Carbonate Supported on Active Alumina

The effect of aluminium oxide support on the thermal behaviour of manganese carbonate was investigated using TG, DTA, dDTA and XRD techniques. The concentrations of MnCO₃ were 0.025, 0.05 and 0.125 mol/mol Al₂O₃. The results obtained showed that the employed support material retards the thermal decomposition of manganese carbonate due to the formation of a manganese/aluminium adduct which decomposes readily at 350°C instead of 250°C in the absence of Al₂O₃, to give γ-MnO₂. This compound decomposed at 500°C into Mn₂O₃ (partridgeite). The produced Mn₂O₃ decomposed at 940°C yielding Mn₃O₄ which interacted with atmospheric oxygen during the cooling processes to give Mn₂O₃. However, Mn₃O₄ formed in the case of unloaded Mn₂O₃ did not interact easily with O₂ and remained stable. The results might indicate the role of Al₂O₃ in increasing the degree of dispersion of the produced manganese oxides thus increasing their reactivity towards reoxidation by O₂. The produced manganese oxide (Mn₂O₃) enhanced markedly the crystallization of aluminium oxide at 800°C into ?-Al₂O₃. Solid-solid interaction between Mn₂O₃ and Al₂O₃ occurred at 800°C giving MnAl₂O₄ which decomposed at 1000°C yielding Mn₂O₃ and α-Al₂O₃ (corundum).