Difference Between Fe2O3 and Fe3O4

Main Difference – Fe₂O₃ vs Fe₃O₄

Fe₂O₃ and Fe₃O₄ are two common oxides of iron that can be found naturally along with some impurities. Fe₂O₃ is also known as hematite, a mineral from which pure Fe₂O₃ can be obtained via processing and Fe₃O₄ is known as magnetite for the same reason. These minerals are the feedstock for pure metal iron production. There are many physical and structural difference between Fe₂O₃ and Fe₃O₄. The main difference between Fe₂O₃ and Fe₃O₄ is that Fe₂O₃ is a paramagnetic mineral having only Fe²⁺ oxidation state whereas Fe₃O₄ is a ferromagnetic material having both Fe²⁺ and Fe³⁺ oxidation states.

Key Areas Covered

1. What is Fe₂O₃
     – Definition, Properties and Applications
2. What is Fe₃O₄
     – Definition, Chemical Properties
3. What is the Difference Between Fe₂O₃ and Fe₃O₄
     – Comparison of Key Differences

Key Terms: Ferromagnetic, Hematite, Iron, Magnetite, Oxidation States, Oxide, Paramagnetic, Rust

What is Fe₂O₃

Fe₂O₃ is iron(III) oxide. It is an inorganic compound (one of the three major iron oxides). Fe₂O₃ is found in nature as the mineral hematite. Hematite is the major source of iron for the steel industry. Fe₂O₃ appears as a dark red (brick red) colored solid which is odorless. Fe₂O₃ is paramagnetic. This means it can be attracted to a strong, external magnetic field. This compound is readily attacked by acids. An alternative name for Fe₂O₃ is “rust”.

Figure 1: Pure Fe₂O₃ Particles

The molar mass of Fe₂O₃ is 159.687 g/mol. The melting point of this compound is 1565^oC; at higher temperatures, it usually decomposes. Fe₂O₃ is readily soluble in acids and sugar solutions. It is insoluble in water.

Fe₂O₃ exists in two major polymorphs; alpha phase and gamma phase. Alpha Fe₂O₃ has a rhombohedral structure. This structure is the most common form of Fe₂O₃. It is the form in which hematite exist.  The gamma Fe₂O₃ has a cubic structure and is less common. This structure is formed from the alpha phase at high temperatures. The other phases of Fe₂O₃ include beta phase, epsilon phase, etc., which are rarely found.

The major application of Fe₂O₃ is in iron production. There, Fe₂O₃ is used as the feedstock for the blast furnace (In which iron is produced in the form of molten iron). In addition, very fine particles of Fe₂O₃, known as rouge in common, is used in polishing jewelry to get the final finishing of the product.

What is Fe₃O₄

Fe₃O₄ is iron(II,III) oxide. It is named as such since it contains both Fe²⁺ and Fe³⁺ ions. This makes Fe₃O₄ ferromagnetic. This means Fe₃O₄ can be attracted to even a weak, external magnetic field. The mineralogical name of Fe₃O₄ is magnetite. It is one of the major iron oxides found naturally on earth.

Figure 2: Pure Fe3O4 Particles

Fe₃O₄ has a dark (black) color. The molar mass of Fe₃O₄ is 231.531 g/mol. The melting point of this compound is 1597^oC, and the boiling point is 2623^oC. At room temperature, it is a solid black powder which is odorless. When considering the crystal system of Fe₃O₄, it has a cubic, inverse spinel structure.

Fe₃O₄ is a good electrical conductor (the conductivity is about 10⁶ times higher than that of Fe₂O₃). When properly induced, Fe₃O₄ particles can act like tiny magnets. This compound is used as a black pigment and is known as Mars black. It is used as a catalyst in Haber process (for the production of ammonia). Nano- Fe₃O₄ particles are used in MRI scanning (as contrast agents).  

Difference Between Fe₂O₃ and Fe₃O₄

Definition

Fe₂O₃: Fe₂O₃ is iron(III) oxide, also known as hematite.

Fe₃O₄: Fe₃O₄ is iron(II,III) oxide, also known as magnetite.

Appearance

Fe₂O₃: Fe₂O₃ appears as dark red or brick red solid powder.

Fe₃O₄: Fe₃O₄ appears as a black solid powder.

Oxidation State of Iron

Fe₂O₃: Fe₂O₃ has Fe³⁺ oxidation state.

Fe₃O₄: Fe₃O₄ has both Fe²⁺ and Fe³⁺ oxidation states.

Molar Mass

Fe₂O₃: The molar mass of Fe₂O₃ is 159.687 g/mol.

Fe₃O₄: The molar mass of Fe₃O₄ is 231.531 g/mol.

Melting Point

Fe₂O₃: Melting point of Fe₂O₃ is 1565°C

Fe₃O₄: Melting point of Fe₃O₄ is 1597°C

Boiling Point

Fe₂O₃: Fe₂O₃ decomposes at high temperatures.

Fe₃O₄: The boiling point of Fe₃O₄ is 2623°C.

Magnetic Properties

Fe₂O₃: Fe₂O₃ is paramagnetic.

Fe₃O₄: Fe₃O₄ is ferromagnetic.

Attraction Towards a Magnetic Field

Fe₂O₃: Fe₂O₃ can be attracted to a strong, external magnetic field.

Fe₃O₄: Fe₃O₄ can be attracted to even a weak, external magnetic field.

Crystal Structure

Fe₂O₃: Fe₂O₃ exist in two major polymorphs; alpha phase, gamma phase and some other phases. Alpha phase has rhombohedral structure, and gamma Fe₂O₃ has a cubic structure.

Fe₃O₄: Fe₃O₄ has a cubic, inverse spinel structure.

Electrical Conductivity

Fe₂O₃: Fe₂O₃ is less electrical conductive when compared to Fe₃O₄.

Fe₃O₄: Fe₃O₄ is a good electrical conductor, and the conductivity is about 10⁶ times higher than that of Fe₂O₃.

Conclusion

Hematite and magnetite are the major sources of iron in industrial metal iron production processes. These mineral are used as the feedstock for this production. Hematite mainly contains iron in the form of Fe₂O₃ whereas magnetite contains iron in the form of Fe₃O₄. These compounds are the major oxides of irons that can be found in nature. The main difference between Fe₂O₃ and Fe₃O₄ is that Fe₂O₃ is a paramagnetic mineral having only Fe²⁺ oxidation state whereas Fe₃O₄ is a ferromagnetic material having both Fe²⁺ and Fe³⁺ oxidation states.

Reference:

1. “Iron(III) oxide.” Wikipedia, Wikimedia Foundation, 11 Feb. 2018, Available here.
2. “Iron(II,III) oxide.” Wikipedia, Wikimedia Foundation, 10 Feb. 2018, Available here.

Image Courtesy:

1. “Iron(III)-oxide-sample” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia
2. “Fe3O4″By Leiem – Own work (CC BY-SA 4.0) via Commons Wikimedia