Manganese dioxide
- Pyrolusite
- Polianit
- Braunstein
- Magnesia nigra
Black - brown solid
Fixed
5.03 g · cm -3
535 ° C ( decomposition)
Insoluble in water
Attention
0.5 mg · m-3
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Manganese (IV ) oxide, also manganese dioxide or manganese dioxide, is an oxide of manganese with the formula MnO2. Manganese is present here in the oxidation state 4. Because of its appearance (dark brown, matt, silky, granular to earthy ), it is also referred to magnesia nigra, black magnesia, or somewhat imprecise as Braunstein. However, manganese dioxide is a manganese group of minerals whose main component is manganese dioxide.
History
Manganese (IV ) oxide was formerly known under craftsmen as " glassmakers soap " because it could discolor discolored by iron ( III) silicates glass melts. Even in the glasses of the ancient Egyptians and Romans can be found about 2% manganese oxides. Probably has already been used at that time Braunstein for decolorization of the glasses.
Occurrence
Manganese (IV ) oxide can be found as a rhombic crystalline pyrolusite ( Weichmanganerz ) and tetragonal crystalline Polianit a large scale in the southern Urals and in South Africa. Together with other iron compounds, it is often a major component of the Umbraerden and the other brown, dark-colored earth.
Production and representation
Manganese ( IV) oxide (II ) nitrate in air to above 500 ° C prepared by grinding pyrolusite or by heating manganese.
Today, however, manganese (IV ) oxide is mainly obtained by electrolysis of a solution of manganese (II ) sulfate. Divalent manganese ions (Mn 2 ) to the anode to oxidize trivalent Mn3 ions then Mn2 - disproportionation and Mn4 ions. Here, Braunstein is deposited on the anode.
Properties
Manganese ( IV) oxide is a brown-black powder, which is insoluble in water. Moreover, no reaction takes place with cold sulfuric or nitric acid.
Reactions
By heating above 450 ° C (III ) oxide ( Mn2O3 ) is formed under oxygen release manganese.
By heating above 600 ° C under oxygen delivery manganese (II, III ) oxide ( Mn3O4 ) is formed; Mn3O4 contains 72 % manganese.
Heating with addition of sulfuric acid leads to the elimination of oxygen with the formation of manganese ( II) sulfate.
Hydrogen peroxide decomposes in the presence of manganese dioxide oxygen delivery. The manganese dioxide acts as a catalyst.
Hydrochloric acid with manganese dioxide reacted with chlorine evolution to manganese (II ) chloride. This implementation had as Weldon process importance for the production of chlorine.
Use
Due to its oxidizing action, manganese dioxide is often used as the oxidant. It is for example used in organic synthesis of hydroquinone from aniline. Manganese dioxide, the active component of the catalyst paste for sealants based on polysulfides and causes oxidative linkage via the SH- groups of the Polysulfidpräpolymers. In fireworks it is used as the oxidant. It's also used in the laboratory for the preparation of halogens from corresponding hydrogen halides.
It is also known as " glassmakers soap " in glass manufacturing. Glass melting, (III) silicates often with small amounts of iron are colored yellow-green, manganese dioxide is added in small amounts to neutralize the discoloration. Here manganese ( III) silicates are formed, the color is purple. However, yellow green and purple are complementary colors, so the melt flow ( greyish to almost colorless) appears in a neutral shade.
In batteries used as a cathode material. In zinc - carbon and alkaline - manganese batteries is either
- Naturally occurring manganese dioxide ( " NMD " ),
- Chemically synthesized manganese dioxide ( "CMD" ) or
- Produced by electrolysis manganese dioxide ( " EMD " ) are used.
Other uses are as a colorant for bricks, part of the gas cleaning in gas masks and as an additive in the manufacture of varnishes and driers. It also acts in the catalytic decomposition of hydrogen peroxide and serves as the vapor - and oxygen production.
Mangandioxidhydrat
Mangandioxidhydrat ( manganese ( IV) oxide-hydroxide ) is obtained by oxidative precipitation of manganese (II ) salt solutions with sodium hydroxide and hydrogen peroxide or with sodium peroxide as a dark brown precipitate:
The significance of this connection because, in contrast to the anhydrous manganese dioxide has a greater reactivity as an oxidant.