Indium Facts – In or Element 49

Indium is a chemical element with the symbol In and atomic number 49. It is a soft, malleable metal that is silvery-white in color and resembles tin. Chemically, it behaves like its homologues on the periodic table: gallium and thallium.

Discovery and Naming

Indium was discovered in 1863 by the German chemists Ferdinand Reich and Hieronymous Theodor Richter. They named the element after the indigo blue line in its spectrum. The name “indium” is derived from the Latin word “indicum,” meaning “indigo.” Reich was colorblind and had Richter interpret colored spectral lines. Reich isolated the pure element in 1864 and present an ingot of the pure metal at the 1867 World Fair.

Appearance and Properties

Indium is a shiny, silvery-white metal. While not very reactive, it eventually oxidizes to a darker color after exposure in air. It is a soft solid at room temperature that is highly ductile and malleable. It is a good conductor of heat and electricity.

Isotopes

Indium has two naturally occurring isotopes: ¹¹³In and ¹¹⁵In. Of these, ¹¹⁵In is the most abundant, making up about 95.7% of naturally occurring indium. The remaining 4.3% consists of ¹¹³In. Indium-113 is stable. Technically, indium-115 is a radioactive isotope, but its half-life is 4.41×10¹⁴ years, which is over four times longer than the age of the universe. There are several (37) other synthetic isotopes of indium, but they have short half-lives and are not commonly found in nature. The most stable is indium-111, which has a half-life of 2.8 days.

Abundance and Sources

Indium is a rare element that does not occur in its pure form in nature. It is the 68th most abundant element in the Earth’s curst, comparable in abundance to bismuth and mercury. It is a primordial element that comes from the slow neutron capture process in stars with low to medium mass. Indium also forms from radioactive decay of cadmium-115. The metal mainly occurs in association with zinc ores. Canada, China, and South Korea are some of the primary producers of indium.

Uses of Indium

Indium stabilizes non-iron metals, so its first significant application was as a coating on bearings to protect against damage and corrosion. Today, the element serves many uses:

• Touchscreens and LCDs: Indium tin oxide is a transparent conductor in touchscreens and LCD displays.
• Soldering: Because of its low melting point, indium is an important solder.
• Sealants: Indium wire is a vacuum seal and a gasket in cryogenics.
• Thermometers: Because of its low melting point, the indium allow galinstan replaces mercury in some thermometers.
• Photovoltaic cells: Indium is a component of thin-film solar cells.
• Batteries: Indium replaces mercury as a less-toxic option for preventing zinc corrosion in alkaline batteries.
• Electronics: Indium phosphide finds use in high-frequency and high-power electronics.
• Nuclear Reactors: Because of its high neutron capture cross-section, indium finds use in nuclear reactor control rods.
• Pigments: YInMn blue is an intense blue pigment that is non-toxic and fade-resistant.
• Mirrors: Because it wets glass, it readily forms a corrosion-resistant mirror.

Oxidation States

Indium exhibit several oxidation states (-5, -2, -1, 0, +1, +2, +3), but the most common is +3. The element is most stable in this state.

Biological Role, Health Effects, and Toxicity

Indium has no known biological role in the human body or any other organism. Prolonged exposure to indium compounds causes health problems, especially in the respiratory system. “Indium lung” is a condition involving pulmonary alveolar proteinosis and pulmonary fibrosis. Indium tin oxide, in particular, is toxic if ingested or inhaled in large amounts. Tiny quantities of radioactive indium find use in nuclear medicine and as tracers for white blood cells and proteins.

Key Indium Facts for Chemists

Here is the atomic data and a collection of indium physical properties:

Interesting Indium Facts

Here are more interesting indium facts:

• Superconductivity: When cooled to cryogenic temperatures, indium becomes superconductive.
• No Biological Need: Although indium occurs in trace amounts in all living organisms, there’s no evidence to suggest that it serves any biological purpose or is essential for life.
• Sound of Freshness: When bent, pure indium produces a characteristic “cry” sound, similar to the cry of tin. This sound results from the metal’s crystal structure reforming.
• Flame Test: Indium turns flames an indigo to violet color.
• Low Abundance: Indium is rarer in Earth’s crust than silver, gold, or mercury.
• Radioactive Isotope: Activating the isotope ¹¹⁵In produces the metastable isotope ^116mIn, which is a radioisotope used in some types of nuclear medicine imaging.
• Indium Beads: Molten indium droplets form a pattern of beads when they solidify that resemble water droplets on a surface.
• Compounds with Colors: Some compounds of indium are colorful. For instance, indium(III) chloride is yellow, while indium(III) sulfide is red.
• Wetting Properties: Indium has the unique ability to “wet” many non-metallic surfaces, including glass and ceramics. This makes it particularly valuable in sealing applications.
• Indium vs. Corrosion: Indium resists corrosion when exposed to water, but it does not resist acidic and alkaline solutions.
• Gallium-Indium Alloy: An alloy of gallium and indium remains liquid at room temperature, making it a non-toxic replacement for mercury.

References

• Alfantazi, A. M.; Moskalyk, R. R. (2003). “Processing of Indium: A Review”. Minerals Engineering. 16 (8): 687–694. doi:10.1016/S0892-6875(03)00168-7
• Emsley, John (2011). Nature’s Building Blocks: An A-Z Guide to the Elements. Oxford University Press. ISBN 978-0-19-960563-7.
• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
• Hammond, C. R. (2004). The Elements, in Handbook of Chemistry and Physics (81st ed.). CRC press. ISBN 978-0-8493-0485-9.
• Iliev, S. P.; Chen, X.; Pathan, M. V.; Tagarielli, V. L. (2017). “Measurements of the mechanical response of Indium and of its size dependence in bending and indentation”. Materials Science and Engineering: A. 683: 244–251. doi:10.1016/j.msea.2016.12.017
• Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. ISBN 0-8493-0464-4.