Since early humans began painting on cave walls, iron oxide pigments have been used as colorants. Several iron oxide minerals are used to make natural pigments: Hematite is the source of red pigments. Limonite is the source of yellow and brown pigments such as ochres, sierras, and umbers. Magnetite is a source of black iron oxide pigment. Micaceous iron oxide is a type of hematite that occurs in the form of thin metallic gray platelets or flakes. Synthetic pigments are manufactured under controlled conditions in order to accurately replicate particle size, distribution, and shape, resulting in superior uniformity, color quality, and chemical purity.
Iron oxide pigments are low-cost materials that resist color change due to sunlight exposure, have good chemical resistance, and are stable under normal environmental conditions. Pigments are primarily used in paints, coatings, and construction materials such as concrete, mortar, paving stones, and roofing tiles. Natural pigments are used in primers and undercoats where color consistency isn't as important, whereas synthetic pigments are used in topcoat paints where color consistency is critical.
Micaceous iron oxide gives paints and coatings unique properties because the flaky particles align in such a way that moisture and gases cannot penetrate. These coatings can protect metals from corrosion and rusting while also resisting blistering, cracking, and peeling.
Steelmaking also results in the production of iron oxide pigments. When steel is treated with hydrochloric acid to remove surface oxides, the acid is regenerated and iron oxide is formed. Regenerated iron oxides are used in a wide range of filters, inductors, and transformers in electronic household appliances and industrial equipment, as well as flexible magnets, generators, loudspeakers, and electric car motors.
Recent advancements in the synthetic iron oxide pigment industry include granular forms of iron oxides and new versions of nano-sized materials, which are used in computer disk drives and high-performance loud speakers, as well as biology and medicine, including nuclear magnetic resonance imaging.
