Indium

Indium, with the symbol In and atomic number 49, is a shiny, silvery-white metal that, although not highly reactive, gradually oxidises and darkens when exposed to air. It is a soft, highly ductile, and malleable solid at room temperature, and it efficiently conducts heat and electricity.

1.0Introduction

Indium is named after the bright indigo line observed in its spectrum. Like gallium, it remains liquid over a broad temperature range. When heated above its melting point, indium burns with a violet flame, forming yellow sesquioxide (In₂O₃).

Indium liquid adheres to glass and similar surfaces. Indium remains stable when exposed to water and air but dissolves in acids. When heated above its melting point, it burns with a violet-coloured flame.

Chemically, indium behaves similarly to its periodic table homologues, gallium and thallium. Indium liquid adheres to glass and similar surfaces. In compounds, indium primarily exists in the +3 oxidation state.

2.0Physical  Properties of Indium

• Appearance: Silvery-white, lustrous metal.
• State at Room Temperature: Solid.
• Density: 7.31 g/cm³; relatively low density for a metal.
• Melting Point: 156.6°C; one of the lowest melting points among metals.
• Boiling Point: 2,072°C.
• Electrical Conductivity: Highly conductive; used in electronics.
• Thermal Conductivity: Moderately high; efficient in heat transfer.
• Malleability and Ductility: Highly malleable and ductile; easily formed into various shapes.
• Crystal Structure: Tetragonal; typical for post-transition metals.
• Hardness: Relatively soft; can be cut with a knife.
• Reflectivity: Highly reflective, particularly in thin films.

3.0Chemical Properties of Indium

Indium is a rare post-transition metal known for its softness and malleability. Its chemical properties are similar to those of its group members, gallium and thallium.

• Reactivity: Indium is not highly reactive at room temperature. It does not react with water but gradually oxidises in air, forming a protective layer of indium(III) oxide on its surface.

4In + 3O₂ → 2In₂O₃

• Reaction with Acids: Indium reacts with acids like hydrochloric acid, producing indium(III) chloride and hydrogen gas.

2In + 6HCl → 2InCl₃ + 3H₂

• Alloys: Indium readily forms alloys with various metals, significantly lowering their melting points. This property is essential in applications like fusible alloys, solders, and thermal interface materials.
• Oxidation States: Indium primarily exhibits the +3 oxidation state, though it can also form the less stable +1 oxidation state in certain compounds.
• Compounds: Indium forms various compounds, including indium tin oxide (ITO), valued for its electrical conductivity and optical transparency in touchscreens and liquid crystal displays.
• ITO Synthesis Equation:  In₂O₃ + SnO₂ → ITO
• Isotopes: Indium has two naturally occurring isotopes: ¹¹³ In and ¹¹⁵In. While ¹¹⁵In is mildly radioactive, its long half-life poses negligible radiological risk.

4.0Compounds of Indium

Indium(III) Oxide (In₂O₃)

• Equation: 4In+3O₂→2In₂O₃
• Uses: Employed in touch screens and flat-panel displays for their electrical conductivity and transparency.

Indium Tin Oxide (ITO)

• Equation: In₂O₃+SnO₂→ITO
• Uses: A combination of indium(III) oxide and tin oxide, ITO is essential for transparent conductive coatings in touchscreens and solar cells.

Indium(III) Chloride (InCl₃)

• Equation: 2In + 3Cl₂ → 2InCl₃
• Uses: It serves as a precursor for synthesising other indium compounds and is used in organic synthesis and electronics.

Indium(III) Sulfide (In₂S₃)

• Equation: 2In+3S → In₂S₃
• Uses: Utilized in semiconductor manufacturing and as a photocatalyst in water splitting.

Indium Phosphide (InP)

• Equation: In + P→ InP
• Uses: Employed in high-speed and high-frequency electronics due to its superior electron mobility.

Indium Antimonide (InSb)

• Equation: In+Sb→InSb
• Uses: This semiconductor, known for its rapid electron transport properties, is used in infrared detectors and Hall effect devices.

5.0Uses of Indium

Indium has a range of applications due to its unique properties:

• Touchscreens and LCDs: Indium tin oxide (ITO) is a transparent conductor in touchscreens and LCDs.
• Soldering: Indium’s low melting point is important in soldering materials.
• Thermometers: Due to their low melting point, indium alloys, such as Galinstan, replace mercury in some thermometers.
• Photovoltaic Cells: Indium is used in the production of thin-film solar cells.
• Batteries: Indium is a less-toxic alternative to mercury to prevent zinc corrosion in alkaline batteries.
• Electronics: Indium phosphide is employed in high-frequency and high-power electronic devices.
• Mirrors: Indium’s ability to wet glass makes it suitable for creating corrosion-resistant mirrors.