Structure and synthetic method of Manganese Oxide Mn2O3
What is Manganese Oxide Mn2O3?
Manganese Oxide Mn2O3 is an oxide with a chemical formula of Mn2O3 and a molecular weight of 157.88. It is a black cubic crystal, insoluble in water, acetic acid, and ammonium chloride solution, but soluble in other inorganic acids. Manganese Oxide Mn2O3 dissolves in cold hydrochloric acid to form a brown solution, turns into a red solution in hot dilute sulfuric acid or concentrated sulfuric acid, decomposes into MnO₂, and manganese nitrate in hot nitric acid, and decomposes into Mn3O4 by heating and releases O₂. Manganese Oxide Mn2O3 exists in two forms: α-Mn2O3 and γ-Mn2O3. The α-type is obtained by decomposing divalent manganese nitrates, carbonates or chlorides, and hydrides in the air to 600-800°C. The γ-type is produced by heating MnO2 at 500°C for 78 hours in a vacuum. Manganese Oxide Mn2O3 can be used in the printing and dyeing process of cloth. It can also be used to synthesize soft magnetic materials, or as an important base material for the synthesis of lithium-ion batteries.
Manganese Oxide Mn2O3 Structure
Manganese Oxide Mn2O3 is unlike many other transition metal oxides in that it does not adopt the corundum (Al2O3) structure. Two forms are generally recognized, α-Mn2O3 and γ-Mn2O3, although a high-pressure form with the CaIrO3 structure has been reported too.
α-Mn2O3 has a cubic bixbyite structure, which is an example of a C-type rare earth sesquioxide. The bixbyite structure is stabilized by the presence of small amounts of Fe3+, pure Mn2O3 has an orthorhombic structure. α-Mn2O3 undergoes antiferromagnetic transition at 80 K.
γ-Mn2O3 has a structure related to the spinel structure of Mn3O4 where the oxide ions are cubic close-packed. This is similar to the relationship between γ-Fe2O3 and Fe3O4.γ-Mn2O3 is ferrimagnetic with a Néel temperature of 39 K.
Manganese Oxide Mn2O3 synthetic method
Preparation of α-Mn2O3
α-Mn2O3 can be further oxidized or reduced by manganese oxide. It also can be prepared by heating divalent manganese salt in the air at 600-800°C. The easiest way is to heat manganese nitrate hexahydrate or pure β-MnO2 in the air at 650°C to constant weight. When manganese nitrate hexahydrate is used as raw material, it needs to be heated at 190°C in advance to make a solid, then crush it and heat it at 650°C.
Preparation of γ-Mn2O3
In 350 mL of a solution in which 2.2 g of manganese sulfate tetrahydrate is dissolved, under vigorous stirring, 34 mL of 3% hydrogen peroxide solution is added dropwise. Then add 50mL 0.2mol·dm-3 ammonia water to generate γ-MnO(OH). The dark brown or black suspension that emits oxygen is quickly boiled by heating. After boiling for 4 minutes, filter and separate, wash the solid with 1.5L hot water and put it in a vacuum desiccator containing phosphorus pentoxide at a temperature below 100°C After drying, γ-MnO(OH) is obtained. This γ-MnO(OH) is carefully dehydrated at 250°C under reduced pressure for 3 days to produce γ-Mn2O3. In addition, γ-MnO2 can also be heated at 500°C for 78 hours under reduced pressure to prepare γ-Mn2O3.
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