Ferric oxide black, commonly known as iron oxide black, ferrite, black iron oxide, is a black crystal with magnetic properties, so it is also known as magnetic iron oxide. This substance is soluble in acid solution, insoluble in water, alkali solution, ethanol, ether and other organic solvents. Natural Fe3O4 is insoluble in acid solution. It is easy to oxidize to Fe3O4 in humid air. Usually used as pigments and polishes, but also used in the manufacture of audio tapes and telecommunications equipment.
Ferric oxide black is a mixed valence oxide of iron. Its melting point is 1597 C, density is 5.17g/cm3, insoluble in water. It occurs in the form of magnetite in nature. It has strong ferromagnetism and high conductivity at room temperature.
When iron contacts with air, oxide forms on its surface. At this time, the chemical composition of oxide film itself is not uniform. For example, a low carbon steel can be covered by three oxide films: iron oxide in contact with metals, iron oxide in the air on one side, and iron oxide in the middle. More precisely, perhaps a mixture of saturated solid solutions of three oxides forms an oxide film on the surface of steel.
Iron tetroxide has anti-corrosion effect, such as bluing of iron and steel parts (also known as roasted blue and roasted blue) is to form a blue-black or dark-blue iron tetroxide 4 film on the surface of iron and steel parts by oxidation of alkaline oxidizing solution, which can be used to increase corrosion resistance, luster and beauty.