Product

Iron(III) oxide in its α-phase, commonly known by its mineral name hematite, is the most stable and abundant form of iron oxide and the most industrially significant iron compound on Earth. It is a reddish-brown solid with the systematic name diiron trioxide, and it occurs both as a widely mined natural mineral and as a synthetically produced chemical compound.​

Crystal Structure

α-Fe₂O₃ crystallises in the rhombohedral lattice system with a corundum-type structure, in which Fe³⁺ cations occupy two-thirds of the octahedral interstitial sites within a hexagonally close-packed array of O²⁻ anions. Each Fe³⁺ ion is coordinated by six oxygen atoms in a distorted octahedral geometry. The unit cell contains six formula units. The compound is antiferromagnetic below its Morin transition temperature (~260 K) and weakly ferromagnetic (canted antiferromagnetic) between the Morin temperature and its Néel temperature (~955 K), above which it becomes paramagnetic.

Physical & Chemical Properties

α-Fe₂O₃ is chemically stable under ambient conditions, non-toxic, and highly resistant to corrosion, which underpins its widespread practical use. It is a small band-gap semiconductor (1.9–2.6 eV), making it responsive to visible light and relevant for photoelectrochemical applications. It is insoluble in water but dissolves in strong acids. Upon heating above ~1400°C it partially reduces to Fe₃O₄, and at very high temperatures further to FeO.

Natural Occurrence

α-Fe₂O₃ occurs naturally as the mineral hematite, one of the most abundant iron minerals in Earth's crust. It is the primary constituent of major iron ore deposits globally, including the banded iron formations (BIFs) of the Pilbara region (Australia), the Carajás deposit (Brazil), and Kiruna (Sweden). Natural hematite ores typically carry Fe grades of 58–62%.

Synthesis

Synthetic α-Fe₂O₃ is produced by several routes:

• Thermal decomposition of iron(III) hydroxide or goethite (α-FeOOH) above ~300°C
• Precipitation from iron salt solutions followed by calcination
• Oxidation of magnetite (Fe₃O₄) at elevated temperatures
• Sol-gel, hydrothermal, and co-precipitation methods for nanoparticle production

Industrial Applications

α-Fe₂O₃ is the most broadly applied iron oxide across industry:

• Iron & steel production — the dominant iron ore mineral, reduced in blast furnaces via Fe₂O₃ → Fe₃O₄ → FeO → Fe
• Pigments — synthetic hematite is the primary red iron oxide pigment (PR101), used in paints, coatings, concrete, plastics, ceramics, and cosmetics; approved food colorant (E172)
• Catalysis — used as a catalyst and catalyst support in the Haber–Bosch process (ammonia synthesis), Fischer–Tropsch synthesis, and dehydrogenation reactions
• Thermite welding — reacts exothermically with aluminium to produce molten iron for rail welding and structural joining
• Gas sensing — its semiconductor properties make it sensitive to CO, LPG, and ethanol vapours
• Photoelectrochemistry — investigated as a photoanode material for solar-driven water splitting due to its visible-light band gap

References

1. BragitOff (Aug 8, 2017)). Alpha – Fe2O3 [HEMATITE]
2. Naveas, N., Pulido, R., Marini, C., Hernández-Montelongo, J., & Silván, M. M. (Feb 17, 2023). First-principles calculations of hematite (α-Fe₂O₃) by self-consistent DFT+U+V. iScience, 26(2), 106033. DOI: 10.1016/j.isci.2023.106033
3. Zadeh J., Discovery Alert (Apr 3, 2025). Hematite vs Magnetite: Understanding Types of Iron Ore in 2025
4. Rasheed, R. T., Al-Algawi, S. D., Kareem, H. H., & Mansoor, H. S. (Nov 28, 2018). Preparation and characterization of hematite iron oxide (α-Fe₂O₃) by sol-gel method. Chemical Sciences Journal, 9(4), 197