Physical Properties
Black tetragonal crystal; exhibits two allotropic modifications—a stable alpha phase, occurring in tetragonal crystalline form (as hausmannite) and an unstable beta modification; Moh’s hardness 5.5; insoluble in water; soluble in hydrochloric acid.
Occurrence and Use
Manganese(II,III) oxide occurs in nature as the mineral hausmannite [1309-55-3]. It is used to make ferrites and thermistors. The oxide also is used in the thermite process for producing manganese.
Preparation
Manganese(II,III) oxide is made by heating manganese(IV) oxide, MnO2, or manganese(III) oxide, Mn2O3, above 950°C. When Mn2O3 is heated in air, the temperature should be above 940°C, but if heated in oxygen, the temperature should be above 1,090°C. Also, heating manganese(III) oxide at 230°C in hydrogen yields Mn3O4. However, further heating above 300°C converts Mn3O4 formed to green manganese(II) oxide, MnO.
Manganese(II,III) oxide also is obtained by heating the dioxide, MnO2, with carbon at 600 to 700°C.
Reactions
Manganese(II,III) oxide reacts with dilute acids forming the corresponding manganous salt and manganese(IV) oxide, MnO2:
Mn3O4 + 2H2SO4 → 2MnSO4 + MnO2 + 2H2O
The oxide, however, dissolves slowly in cold sulfuric acid forming a red solution that also contains manganic sulfate, Mn2(SO4)3:
Mn3O4 + 4H2SO4 → MnSO4 + Mn2(SO4)3 + 4H2O
Reaction with acetic acid yields manganese(II) acetate and manganese(III) oxide:
Mn3O4 + 2CH3COOH → Mn(CH3COO)2 + Mn2O3 + H2O
Manganese(II,III) oxide is reduced to manganese metal when heated with powdered aluminum (the Thermite process). The reaction is vigorous and exothermic:
3Mn3O4 + 8Al → 4Al2O3 + 9Mn
Chemical Properties
Grass-green powder.
but converted to Mn
3O4 if heated in air. Soluble in
acids; insoluble in water. Noncombustible.
Uses
Textile printing, analytical chemistry, catalyst
in manufacture of allyl alcohol, ceramics, paints,
colored glass, bleaching tallow, animal feeds, fertilizers, food additive and dietary supplement.
General Description
Manganese(II,III) oxide is a transition metal oxide that is formed by annealing manganese oxide in the air above 1000°C. It can be used for a variety of applications such as catalysis, electrochromic devices, and other energy storage applications.
Reactivity Profile
Trimanganese tetraoxide is non-combustible but decomposes, generating toxic fumes when strongly heated strongly in the air. A good oxidizing agent. Reacts with hydrochloric acid to form gaseous chlorine and soluble manganese salts.
Hazard
Chronic manganese poisoning and pulmonary effects.
Health Hazard
Manganese tetroxide affects the
central nervous system, and toxicity occurs
mostly in chronic form (manganism).
Flammability and Explosibility
Non flammable
Safety Profile
Experimental reproductive effects. Reacts violently @ <l00℃. See also MANGANESE COMPOUNDS.
