Indium is a chemical element with the atomic number 49 and is represented by the symbol ‘In’ in the periodic table. It is classified as a post-transition metal and belongs to the p-block of group 13 of the periodic table. With almost 0.1 ppm (parts per million) of presence on Earth’s crust is one of the relatively rare metals. Indium is a soft, lustrous silvery-grey metal with a yellowish tint in its appearance.
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History of Indium
- The German chemists Ferdinand Reich and Hieronymus Theodor Richter discovered indium in 1863.
- While in Freiberg, Saxony, Reich, and Richte examined various ores mined nearby. In hydrochloric acid and distilled raw zinc chloride, they dissolve the minerals pyrite, arsenopyrite, galena, and sphalerite.
- When seeking the thallium element, they examined the emission spectrum for lines that appeared green in color. Instead, they discovered a brilliant blue. They hypothesized that a new element was present in the rocks because the blue line did not match any already recognized.
- Indium was named after its bright indigo-blue line in its spectrum.
Occurrence of Indium
- Indium is one of the rare metals on Earth’s crust, with a presence of around 0.1 ppm. This abundance is similar to that of silver. It rarely forms its mineral or occurs naturally on the crust.
- Although there are some indium minerals like roquesite (CuInS2), their low concentration makes extraction costly.
- Indium is extracted as a by-product of commonly available ore minerals, including sphalerite and chalcopyrite. It is found in trace amounts in these ore minerals.
- The majority of indium is extracted as a by-product from zinc mining. It is also found in copper, lead, and iron ore.
- The top producers of indium metal include China, Korea, Canada, and Japan, with China at the top.
Isotopes of Indium
Indium has two naturally occurring stable isotopes: 113In, and 115In.
Natural Isotopes of Indium
| Isotopes | Natural abundance (atom %) |
|---|---|
| 113In | 4.29 (5) |
| 115In | 95.71 (5) |
Elemental Properties of Indium
| Electronic Configuration | [Kr] 4d10 5s25p1 |
| Atomic Number | 49 |
| Atomic Weight | 114.818 g.mol -1 |
| State at 20°C | Solid |
| Group, Period, and Block | 13, 5, p-block |
| Density | 7.31 g.cm -3 at 20 °C |
| Ionic radius | 0.092 nm (+2) |
| Van der Waals radius | 0.162 nm |
| Electron shells | 2, 8, 18, 18, 3 |
| Electrons | 49 |
| Protons | 49 |
| Neutrons in most abundant isotope | 66 |
Physical Properties of Indium
- Indium has an atomic number of 49 and is a silvery-gray metal. It has a melting point of 156.4 °C (313.9 °F) and a boiling point of 2072 °C (3762 °F).
- Indium has a solid phase density of 7.31 gm/cm3 and a liquid or molten phase density of 7.02 gm/cm3.
- It is the softest of non-alkali metal.
- Indium is a malleable metal, which allows it to be easily hit into sheets without any cleavage.
- It is also a ductile metal, which makes it possible to draw thin wires without breaking them.
- It is also a good thermal conductor.
| Color/physical appearance | Silvery-Gray |
| Melting point/freezing point | 429.8 K (156.4 °C, 313.9 °F) |
| Boiling point | 2345 K (2072 °C, 3762 °F) |
| Density | 7.31 g cm-3 at 20° |
| Malleability | Yes |
| Ductility | Yes |
| Electronegativity | 1.78 (Pauling Scale) |
Chemical Properties of Indium
- Indium is stable in water and air. It exhibits slight amorphous characteristics in aqueous solution and it is insoluble in alkaline solutions.
- Indium is only oxidized by stronger oxidizing agents additionally it doesn’t produce silicide, carbide, or boride.
- Indium commonly donates 3 electrons to form indium(III) compounds it undergoes chemical reactions.
Uses of Indium
- Indium was largely used for coating the bearings in aircraft to protect them against damage and corrosion.
- Indium is also used in the electronic industry for soldering, fusible alloys, and other electronic items. Indium beads are also used as emitters and collectors in PNP alloy-junction transistors.
- Indium alloys can be used for the manufacturing of solar cells. Copper indium gallium selenium thin-film solar cells offer the advantages of relatively low manufacturing costs, minimal environmental impact, and low light operation. The photoelectric conversion capacity ranks first among various thin-film solar cells and is acknowledged worldwide as a potential new thin-film solar cell.
- The semiconductor industry is also using indium and its compounds for different reasons, such as dopants, transistors, and rectifiers.
- It is known that alloys employed in dentures mainly consist of gold, silver, and palladium as primary elements and are complemented with 0.5% to 10% indium. After adding a tiny amount of metal indium to the material of dental implants, the ability to resist corrosion and durability of these devices can be considerably enhanced, and the alloy material will not be black.
- Indium has excellent neutron-capture cross-section for thermal neutrons. It is utilized in control rods in nuclear reactors.
- Because of its adhesion and flexibility, it is also employed in cryogenics and other vacuum applications.
- It is also used in screens of different LCD’s and smartphones.
Health Effects of Indium
Indium and its compounds are regarded as toxic. It has the potential to cause damage to the human heart, liver, and kidneys. Some studies have shown its effect on the growth of the fetus and birth abnormalities. The toxicity and in vivo distribution of indium are dependent on its chemical form, dosage, and route of exposure.
Compounds containing indium are recognized as hazardous to health, as they can cause lung cancer and interstitial pneumonia. In addition, they are associated with emphysema, alveolar proteinosis, and cholesterol granuloma.
Workers who handle indium were found to have a higher risk of experiencing respiratory symptoms compared to those who do not handle indium, even though there are stricter regulations in place to limit indium exposure in the workplace. This suggests that additional modifications to the legislation are necessary in order to safeguard the well-being of employees who are exposed to hazardous substances in their work environments.
Environmental Effects of Indium
Elevated levels of indium and gallium in the environment may lead to an increased risk of environmental exposure. However, the extent of this exposure is not yet well understood. There is increasing evidence indicating that indium and gallium may have significant toxicity, particularly in occupational environments.
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References
- W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 1150–151. ISBN 978-0-08-037941-8.
- https://www.rsc.org/periodic-table/element/49/indium
- https://www.britannica.com/science/indium
- https://pubchem.ncbi.nlm.nih.gov/element/Indium
- https://education.jlab.org/itselemental/ele049.html
- Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
- Toshiharu Mitsuhashi. Effects of indium exposure on respiratory symptoms: a retrospective cohort study in Japanese workers using health checkup data: doi: 10.7717/peerj.8413 PMCID: PMC6969551 PMID: 31988812
- Liu, N., Guan, Y., Yu, Y. et al. Pulmonary effects of exposure to indium and its compounds: cross-sectional survey of exposed workers and experimental findings in rodents. Part Fibre Toxicol 19, 69 (2022). https://doi.org/10.1186/s12989-022-00510-w
