Iron Oxide refers to several related compounds made of iron and oxygen. The most common forms of Iron Oxide are rust, hematite, magnetite, and the mixed oxides of iron known as limonite and turgite. These compounds make up a significant portion of the Earth’s crust and are important components of rocks and sediments worldwide.

Chemical Composition and Forms

The main forms of Iron Oxide are defined based on the ratio of iron to oxygen they contain. Magnetite (Fe3O4) has an equal ratio of iron and oxygen atoms. Hematite (Fe2O3) is one of the most common forms and contains more oxygen than iron. Rust, scientifically called iron (III) oxide or Iron Oxide (Fe2O3), forms when iron or steel is exposed to oxygen and moisture over time. Goethite (α-FeO(OH)) is an iron oxyhydroxide mineral that contributes to the formation of rust. Limonite is an amorphous, hydrated Iron Oxide mineral containing varying amounts of crystal water.

Physical Properties

The Iron Oxide range in color from gray and black to reddish-brown. Maghemite, an oxidized form of magnetite, is brown in powdered form but appears almost black as particles. Hematite is shiny steel-gray or silvery when freshly fractured but weathers to a dull reddish brown. Rust is most recognizable as the flaky or powdery reddish deposits left behind when iron corrodes. Magnetite possesses strong magnetic properties due to its crystalline structure. Hematite and goethite are weakly magnetic while limonite and rust show little or no magnetism.

Uses of ferric oxide

Several of the Iron Oxide have significant industrial uses. Rust serves mainly as an inhibitor of further corrosion and rusting. Magnetite is mined as the most magnetic of all the naturally-occurring minerals. It is used to make products such as audio tapes, video tapes, and computer disk drives. Hematite, one of the most abundant iron minerals, is an important pigment in paints and is used as an extender in paper. It also has applications in ceramics, plastics, and rubber. Limonite is used as an iron ore source for the production of steel. Additionally, the Iron Oxide are components of pigments and dyes used in cosmetics and for coloring ceramics, cement, paper, plastics, and paints.

Applications in Construction

The reddish-brown pigments created from iron oxide minerals have traditionally been used for centuries in construction materials due to their abundance and low cost. Ochrepigments derived from limonite and goethite are common coloring agents in cement, plaster, stucco, and terra cotta clay products. For example, the reddish pigment added to Roman cement contributed to the distinct coloration seen in ancient Roman architecture. Iron Oxide “rust pigments” also provide aesthetic qualities to aged concrete and masonry structures by inducing a natural reddish patina over time. In modern applications, limonite and hematite pigments color concrete and architectural coatings like stains and seals.

Biomedical Applications

With the development of nanotechnology, Iron Oxide are finding increasing use in biomedical fields due to their magnetic and plasmonic properties at the nanoscale. Superparamagnetic Iron Oxide nanoparticles (SPIONs) that are biocompatible and degradable in vivo are being developed as targeted drug delivery agents and contrast agents for magnetic resonance imaging (MRI). For drug delivery, SPIONs are attached or encapsulated with cancer medications to transport therapeutic drugs directly to tumors using external magnets. As MRI contrast agents, SPIONs increase the contrast between different tissues allowing more precise medical imaging. Research into Iron Oxide for hyperthermia cancer treatments is also emerging where magnetic nanoparticles generate heat under alternating magnetic fields to selectively destroy tumors.