1. Physical Properties
Appearance and shape
Silvery-white metal sheet or plate, the surface has a metallic luster.
Brittle, high hardness (Mohs hardness about 5~6), poor ductility, easy to break during processing.
Density and melting point
Density: 7.2~7.4 g/cm³ (close to the density of iron, but heavier than aluminum).
Melting point: 1244°C, boiling point about 1962°C, volatile at high temperature.
Conductivity and magnetism
Good electrical conductivity (conductivity about 7.8×10⁶ S/m), but lower than that of copper and aluminum.
Paramagnetic, but the magnetic properties are weak, not suitable for strong magnetic materials.
Crystal Structure
A cubic crystal system (α-Mn), a complex cubic structure at room temperature, at high temperature (>727°C) transforms into a cubic structure centered in the body (β-Mn).
2. Chemical Properties
(1) Oxidation Reaction
Oxidation at room temperature:
A brown oxide film (MnO₂ or Mn₃O₄) forms on the surface in humid air, reaction equation:
2Mn+3O2→2MnO2 The oxide film is dense and slows down further corrosion, but prolonged exposure results in chalking of the lamellar structure.
High temperature oxidation:
When heated above 500°C, rapid oxidation occurs to form Mn₃O₄ or MnO:
3Mn+2O2ΔMn3O4
(2) Reactions With Acids
Dilute acids:
Easily soluble in dilute sulfuric and hydrochloric acids, releases hydrogen and forms a solution of Mn²⁺:
Mn + H2SO4 → MnSO4 + H2↑ The reaction is violent, the concentration of the acid must be controlled (to avoid passivation by concentrated acid).
Concentrated acid:
The reaction stops in concentrated sulfuric acid or concentrated nitric acid due to passivation (the formation of an oxide film on the surface).
(3) Reaction With Alkali
It does not react with strong bases (e.g., NaOH) at room temperature, but may react slowly at high temperatures to form manganates:
2Mn+4NaOH+3O2Δ2Na2MnO4+2H2O
(4) Other Reactions
Reacts with halogens: When heated,
it reacts violently with Cl₂ and Br₂ to form manganese halides (e.g. MnCl₂).
Reaction with sulphur: At high temperatures,
manganese sulfide (MnS) is formed, which is used for the desulphurization of iron and steel:
Mn+SΔMnS
Reducing properties:
Acts as a strong reducing agent, displacing metals from salts of highly valent metals (e.g., reducing Fe³⁺ to Fe²⁺).
3. Key Chemical Behavior In Applications
Steel smelting
Deoxidation: combines with oxygen in the molten steel to form MnO, which floats into the slag for removal:
Mn+O→MnO
Десульфуризация: соединяется с серой, образуя MnS, снижая содержание серы в стали и повышая ее прочность.
Материалы для аккумуляторов
В литий-ионных батареях стабильность манганата лития (LiMn₂O₄) зависит от антиоксидантной способности марганца и стабильности решетчатой структуры.
Устойчивость к коррозии
Легко окисляется сам по себе, но при использовании в качестве легирующей добавки (например, в алюминиевых сплавах) образует защитную оксидную пленку.