Iron Oxide

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What is Iron Oxide?

Iron oxide, which is also called ferric oxide, is an inorganic compound having the chemical formula Fe2O3. It is one of the 3 major oxides of iron, and the remaining two being iron(II) oxide (FeO), which is the rare iron (II, and III) oxide (Fe3O4), and also naturally takes place as the mineral magnetite. Since the mineral is referred to as hematite, Fe2O3 is iron’s primary source for the steel industry and is readily attacked by acids. Often, iron oxide can be referred to as rust. This label is useful to some extent because rust shares many properties and has the same composition. But, in chemistry, rust is considered an ill-defined material, which can be described as Hydrous ferric oxide.


Iron Oxide Structure Fe2O3

Fe2O3 is obtained in various polymorphs. As the primary one, α, iron adopts the octahedral coordination geometry. It means each Fe centre is bound to 6 oxygen ligands. In the γ polymorph, a few of the Fe sits on the tetrahedral sites, with 4 oxygen ligands.

Let us look at the iron oxide structure Fe2O3.

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Properties of Iron Oxide

IUPAC name of Fe2O3

Iron oxide

Molecular Weight or Molar Mass

159.69 g/mol

Density

5.24 g/cm³

Boiling Point

3,414 °C

Melting Point

1,565 °C

Chemical Formula

Fe2O3


Physical Properties of Iron Oxide Fe2O3

Odour

Odourless

Covalently-Bonded Unit

5

Hydrogen Bond Donor

3

Oxidation state

+3

Appearance

Red-brown solid

Solubility

Soluble in strong acid and insoluble in water


Chemical Properties of Iron Oxide Fe2O3

  • The iron oxide will react with water and form iron hydroxide.

Fe2O3 + H2O → Fe(OH)3

  • The iron oxide will react with the sulphuric acid to form water and iron(III) sulfate.

Fe2O3 + H2SO4 → Fe2(SO4)3 + H2O

Preparation of Iron Oxide

  • Iron(III) oxide is the oxidation of the iron products, where it can be prepared in the laboratory by electrolyzing sodium bicarbonate solution, which is an inert electrolyte including an iron anode:

4Fe + 3O2 + 2H2O → 4 FeO(OH)

  • The resultant hydrated iron(III) oxide can be written as FeO(OH), which dehydrates around 200 °C.

2 FeO(OH) → Fe2O3 + H2O 

Reactions

One of the most important reactions of iron oxides is its carbothermal reduction that gives iron, used in steel-making:

Fe2O3 + 3CO → 2Fe + 3CO2

The other redox reaction is with aluminium, which is an extremely exothermic thermite reaction.

2 Al + Fe2O3 → 2 Fe + AI2O3

We can use this process to weld the thick metals including rails of train tracks with the help of a ceramic container to funnel the molten iron in between 2 sections of the rail. Thermite can also be used in making small-scale cast-iron sculptures, weapons, and tools.

Partial reduction, along with the hydrogen compound at around 400 °C will produce magnetite, which is referred to as a black magnetic material. It contains both Fe(III) and Fe(II):

3 Fe2O3 + H2 → 2 Fe3O₄ + H2O  

The Iron(III) oxide results insoluble in water, but it readily dissolves in strong acid. For example, sulfuric and hydrochloric acids. It also dissolves well in the solutions of chelating agents like oxalic acid and EDTA.

Heating the iron(III) oxide with other carbonates or metal oxides yields materials called ferrates (ferrate (III)):

ZnO + Fe2O3 → Zn(FeO2)2  


Uses of Iron Oxide Fe2O3

Let us look at the uses of iron oxide in various industries, listed below.


Iron Industry

The overwhelming iron(III) oxide application is the feedstock of the iron and steel industries. For example, the production of steel, iron, and several alloys.


Polishing

A very fine powder of the ferric oxide is called "red rouge," "jeweller’s rouge," or just as a rouge. It can be used to put the final polish on the lenses and metallic pieces of jewellery, and historically, as a cosmetic. This rouge cuts more slowly than a few modern polishes, like cerium(IV) oxide, but still, it is used by jewellers for the superior finish it can produce and in the optics fabrication. The rouge slightly stains the gold when polishing gold, which contributes to the appearance of the finished piece.


Pigment

Iron oxide can also be used as a pigment, under the names "Pigment Brown 6", "Pigment Brown 7", "Pigment Red 101". A few of them as examples are Pigment Brown 6, Pigment Red 101, which are approved by the US Food & Drug Administration - FDA, for cosmetics use. In addition, iron oxides can be used as pigments in dental composites alongside titanium oxides.

Hematite is one of the characteristic components of the Swedish paint colour Falu red.


Medicine

Calamine lotion, which is used to treat mild itchiness, is chiefly composed of a combination of zinc oxide, by acting as astringent, and around 0.5% iron(III) oxide, the active ingredient of the product, acting as an antipruritic. The red colour iron(III) oxide is also primarily and widely responsible for the familiar pink colour lotion.

FAQ (Frequently Asked Questions)

Q1. Explain the Difference Between Fe₂O₃ and Fe₃O₄?

Ans. Both of these compounds are ferrous oxides. Therefore, Fe₂O₃ can be given as a simple oxide, where Fe in Ferric oxide results only +3 in the oxidation state, and hence, Fe₃O₄ is a mixed oxide, where the Fe in Ferrous oxide exists in both +2 and +3 oxidation states. Although, we can compose Fe₃O₄ as FeO. And, Fe₂O₃ can be written as iron oxide (II), whereas, Fe₃O₄ can be written as iron oxide (II, III).

Q2. Explain if the Iron Oxide is Toxic to Humans?

Ans. When we breathe iron oxide, it will impact us. Exposure to the fumes from Iron Oxide may cause fever from metal fumes. This is explained as a flu-like condition with metallic taste signs, aches, fever and chills, cough, and chest tightness. However, Ferrous Oxide (FeO) is highly flammable and reactive and can combust spontaneously in the air.

Q3. What is the Black Iron Oxide Used for?

Ans. Black iron oxide, which is also called magnetite, can be used for resistance and as well as corrosion. Black iron oxide can often be used in anti-corrosion paints, which is found in several bridges and also in Eiffel Tower. These are used to shorten the proton relaxation times (T1, T2, and T2) as a contrast agent in the imaging of magnetic resonance.

Q4. What is Iron Oxide Made of?

Ans. The iron oxide compounds are composed of both iron and oxygen. There exist 17 known iron oxides and oxyhydroxides, where the best known is rust, which is a type of iron oxide(III). Also, oxyhydroxides and iron oxides are common in nature and play a vital role in several processes, both biological and geological.