Indium is a chemical element with atomic number 49 in the periodic table. It occurs in quantities of around 0.1 parts per million (ppm) in Earth’s crust, and it’s a member of the aluminum family with amphoteric properties. The outer shell electrons of indium adopt the oxidation states +1, +2, or +3 when forming compounds with other chemicals.
Chemical and Physical Properties of Indium
|Color||A lustrous silvery-white metal|
|Physical state||Solid at room temperature|
|Half-life||From 5 milliseconds to 4.41×1014 years|
|Density||7.31 g.cm-3 at 20°C|
|Melting point||156.60°C, 313.88°F, 429.75 K|
|Boiling point||2027°C, 3681°F, 2300 K|
|Van der Waals radius||0.162 nm|
|Ionic radius||0.80 nm (+3)|
|Atomic weight||114.818 g.mol-1|
|Most characteristic isotope||113In and 115In|
|Electronic shell||[Kr] 4d10 5s2 5p1|
|The energy of the first ionization||558.2 kJ.mol-1|
|The energy of the second ionization||1820.2 kJ.mol-1|
|The energy of the third ionization||2704 kJ.mol-1|
|Discoverer||Ferdinand Reich and Hieronymous Richter|
|Uses||Used to coat high speed bearings and as an alloy that lowers the melting point of other metals. Relatively small amounts are used in dental items and in electronic semiconductors.|
|Description||Silvery-white, soft, malleable and ductile metal.|
|Covalent Radius||1.44 Å|
|Atomic Radius||2.00 Å|
|Atomic Volume||15.7 cm³/mol|
|Name Origin||Latin: indicum (color indigo), the color it shows in a spectroscope.|
Classified under the In symbol in the periodic table, with an atomic number 49, atomic mass of 114.82 g.mol-1, and electron configuration [Kr] 4d105s25p1, the chemical element indium is a soft, ductile, corrosion-resistant, and malleable metal with a plasticky feel to it.
With its lustrous silvery-white color, it resembles tin in appearance. Easily workable, indium metal can be shaped in many ways and dented with any slightly sharp object. Apart from the alkalis, indium is the softest metal in the periodic system of elements. In fact, even lead is harder than indium metal.
Located between the elements gallium and thallium, indium shares some chemical properties with these two substances. Namely, element 49 also has a low melting point and a property to wet glass. In its molten form, indium easily gets attached to glass and surfaces made of metal, quartz, ceramics, or marble.
Indium reaches its boiling point at 2027°C (3681°F or 2300 K), while the melting point is achieved at 156.60°C (313.88°F or 429.75 K). It adopts a face-centered tetragonal structure and burns violently with a violet flame when exposed to temperatures above its melting point.
Furthermore, this member of the aluminum family of elements in the periodic table has an electronegativity of 2 according to Pauling, whereas the atomic radius according to van der Waals is 0.162 nm. The electron shell of indium remains stable in air and in contact with H2O molecules, but it’s easily dissolved through contact with acids.
How Was Indium Discovered?
In 1863, the German chemists Ferdinand Reich (1799 – 1882) and Hieronymous Theodor Richter (1824 – 1898) were assigned to analyze a sample of mineral zinc blende at the Freiberg University of Mining and Technology where they both were employed. The ore sample was sphalerite (ZnS) obtained from a location near Freiberg, Saxony. They suspected that the sample contained traces of the element thallium, which had been recently discovered at the time.
During their scientific attempts, these two chemists first isolated the pyrite, arsenopyrite, galena, and sphalerite minerals from the ore. Next, they dissolved the minerals in hydrochloric acid and distilled raw zinc chloride, which resulted in a yellow precipitate.
Believing they had produced thallium sulfide, Reich and Richter wanted to confirm their finding by analyzing the isolated product with the spectroscopy method. This brought them to the realization that the color line displayed after the procedure did not belong to the already known element thallium. Unlike the green of thallium, this color line was vibrantly violet and unseen before. This finding convinced them that a new chemical element is contained in the mineral ore.
Hieronymous Theodor Richter continued to further inspect and analyze the new substance. His scientific efforts led him to eventually isolate the pure indium metal in 1864. Finally, an ingot of the new element was presented at the World Fair in 1867.
How Did Indium Get Its Name?
As a result of the luminescent indigo line that can be seen in the indium’s spectrum, the name of element 49 was derived from the Latin word ‘indicium‘, which means “of India”. This is because historically, indigo-colored dye (close to violet) was produced in India and exported from there to the rest of the world.
Where Can You Find Indium?
Indium is as rare as silver, and in similar abundance to bismuth and mercury, so that it’s rarely found in nature in its free elemental form. Typically, it occurs as a trace element in minerals. In the Universe, indium is formed through the slow neutron-capture process (or: the s-process) in stars of low and medium mass, as well as by the rapid neutron-capture process (or: the r-process).
The sphalerite (a sulfidic zinc ore) is the main ore from which indium is obtained as a by-product for commercial uses after its separation from zinc. Polymetallic deposits from mineral ores, and also iron, tin, and copper ores are also great sources for mining indium. Geographically, zinc ore is most exploited for the extraction of the indium metal in China, Australia, the United States, Peru, and Canada.
Until 1924, there was merely a gram of indium metal produced in the entire world. In recent years, the growing popularity of flat-panel LCD televisions and computer monitors and the necessity for indium in their production drastically increased the market demands and led to an annual production of 1000 tonnes of this rare metal through mining. Plus, the recycling and manufacturing efficiency of indium provides an additional 650 tonnes of indium to the world’s available resources of element 49.
Indium in Everyday Life
The first notable use of larger amounts of indium is evidenced during World War II when this rare metal was used as a coating for the bearings of high-performance aircraft engines. Indium was used to prevent damage and corrosion of the planes that participated in the war.
Both the chemical and the physical properties of indium make this element suitable for other versatile applications, mainly in manufacturing industries:
- The production of indium alloys is probably the most significant use of this scarce metal. Its low-melting alloys have a wide range of applications;
- The radioactive indium form 111In (indium pentetreotide) is an FDA-approved IV drug that is applied in nuclear medicine as a radiotracer in order to mark the white blood cells and proteins;
- As a result of its properties, indium is used to produce alloys, manufacture thermistors (thermal resistors), photoconductors, rectifiers, solder germanium transistor parts, and as a substitute for mercury in alkaline batteries, etc.
- Gold and platinum alloys become much harder even when a small quantity of indium is added to them;
- Indium antimonide, indium nitride, and indium phosphide are often used for their semiconducting properties;
- Indium nitride (InN) nanorods are applied in the production of high-speed field-effect transistors and light-emitting diodes (LEDs);
- Indium is one of the essential substances in the making of ITO (indium tin oxide), a part of the manufacturing of electrodes that are used for liquid crystal displays (LCDs), touch screens, flat-screen TVs, etc;
- Copper indium gallium selenide is one of the main constituents in the photovoltaics as the semiconductor used in the making of CIGS solar cells, i.e. the second-generation thin-film solar cells;
- Indium tin oxide (In2-xSnxO3) also obstructs the harmful infrared rays of the sun from passing through an architectural or photovoltaic glass that is coated with this indium-based substance. When a coat of ITO is applied onto the aircraft or automotive windshields, indium makes the glass electrically deiced or demisted which improves the visibility of the vehicle;
- High-speed motors’ bearings are often coated with indium, as this substance achieves even distribution of lubricating oil;
- YInMn blue YIn1−xMnxO3 (also known as Oregon Blue, Mas Blue, or Yin Min Blue) is a non-toxic vibrant blue pigment produced by combining yttrium, indium, and manganese;
- Indium finds application in the control rods. Also, indium foils are used in the measuring process of the thermal neutron flux of nuclear reactors;
- The element 49 is used as a thermal conductor in cryogenics, i.e. in the production of low-temperature systems, such as cryogenic pumps, high vacuum systems, sealing applications, etc.
- Although it’s neither a trace element in the human body nor it is present in the food chain, some dietary supplements do contain indium. These supplements aim to support the function of the endocrine system;
- Indium metal is added to the dental amalgam alloys, thus providing additional hardness and durability for better protection of oral health.
How Dangerous Is Indium?
Indium is considered to be moderately toxic in its pure metal form. A person can be exposed to its toxic effects by ingesting or inhaling the substance. In such an event, indium will be absorbed by the kidneys and the bones which might lead to adverse health effects and damage to the bodily tissues.
Indium toxicity is considered to be chiefly an occupational hazard of the workers in the mining industry or industries that make use of this chemical in the manufacturing of their products.
Environmental Effects of Indium
Since indium is not often found in nature in its free elemental form, there haven’t been any negative environmental effects observed by scientists that could have been triggered by the presence of this chemical in the environment.
Isotopes of Indium
The element 49 has 39 isotopes with atomic mass ranging from indium-97 to indium-137. Among them, there are only two naturally occurring isotopes: indium-113 and indium-115. These two forms comprise the elemental form of indium. The isotope indium-115 takes up 95.72 percent, while indium-113 takes up 4.28 percent in the naturally occurring, pure form of indium.
It’s observed that the formation of indium in the Universe is triggered by the silver-109 neutron capture. After the entire slow neutron capture process is finished, indium remains as a daughter isotope of cadmium-113 decay.
The 115In isotope is slightly radioactive and has a half-life of 4.41×1014 years, while the 113In occurs in only 4.3% of the naturally occurring form of indium.
|Z||N||Isotopic mass (Da)
[n 2][n 3]
[n 6][n 7]
[n 8][n 4]
|Natural abundance (mole fraction)|
|Excitation energy[n 4]||Normal proportion||Range of variation|
|100In||49||51||99.93111(27)||5.9(2) s||β+ (96.1%)||100Cd||(6, 7)+|
|102In||49||53||101.92409(12)||23.3(1) s||β+ (99.99%)||102Cd||(6+)|
|104In||49||55||103.91830(9)||1.80(3) min||β+||104Cd||5, 6(+)|
|111In[n 9]||49||62||110.905103(5)||2.8047(5) d||EC||111Cd||9/2+|
|112In||49||63||111.905532(6)||14.97(10) min||β+ (56%)||112Cd||1+|
|114In||49||65||113.904914(3)||71.9(1) s||β+ (0.5%)||114Cd||1+|
|115In[n 10]||49||66||114.903878(5)||4.41(25)×1014 a||β−||115Sn||9/2+||0.9571(5)|
|127In||49||78||126.91735(4)||1.09(1) s||β− (99.97%)||127mSn||9/2(+)|
|128In||49||79||127.92017(5)||0.84(6) s||β− (99.96%)||128Sn||(3)+|
|129In||49||80||128.92170(5)||611(4) ms||β− (99.75%)||129Sn||9/2+#|
|130In||49||81||129.92497(4)||0.29(2) s||β− (98.35%)||130Sn||1(−)|
|131In||49||82||130.92685(3)||0.28(3) s||β− (97.8%)||131Sn||(9/2+)|
|132In||49||83||131.93299(7)||206(4) ms||β− (94.8%)||132Sn||(7−)|
|133In||49||84||132.93781(32)#||165(3) ms||β−, n (85%)||132Sn||(9/2+)|
|134In||49||85||133.94415(43)#||140(4) ms||β− (79%)||134Sn|
List of Indium Compounds
Element 49 is an amphoteric element. It reacts both as a base and as an acid. When dissolved in acids, indium salts are produced which have a significant application as a transparent conductive coating on surfaces made of glass. On the other hand, indates (oxyanions of indium) are formed when indium reacts with concentrated alkalies.
Although it’s non-reactive with oxygen at a room temperature, indium combines with O2 molecules when exposed to high temperature, forming indium tin oxide (In2-xSnxO3). This compound introduces one of the most important uses of indium as a transparent conductive oxide. In this form, indium helps electric current pass through a device. It also helps light to pass through it.
- Indium(III) Chloride Tetrahydrate
- Indium(III) Bromide
- Indium(III) Hydrogen Phosphate
- Indium Stearate
- Indium(II) Sulfate
- Indium(III) Sulfate Monohydrate
- Indium(III) Acetate
- Indium(III) Nitrate
- Indium(I) Oxide
- Indium(III) Chloride
- Indium(III) Nitrate Pentahydrate
- Indium(III) Telluride
- Indium(II) Chloride
- Indium(III) Iodide
- Indium(III) Carbonate
- Indium(III) Oxide
- Indium(III) Orthophosphate
- Indium(I) Bromate
- Indium(III) Phosphide
- Indium(I) Hypochlorite
- Indium Nitride
- Indium(III) Arsenide
- Indium(I) Bromide
- Indium(III) Chlorite
- Indium(III) Thiosulfate
- Indium Fluoride
- Indium(II) Iodide
- Indium(I) Sulfite
- Indium(III) Antimonide
- Indium(III) Dibromoiodide
- Indium(III) Sulfite
5 Interesting Facts And Explanations
- As he was color blind, Ferdinand Reich could not distinguish the color lines derived by spectroscopy of the substances. That’s why he invited Hieronymous Theodor Richter to aid him in his scientific trials by explaining the resulting colors from the experiments.
- Similarly to indium, tellurium and rhenium also have stable isotopes that occur in lower quantities in nature than the radioactive isotope with the longest life of the element.
- The half-life of the indium-115 isotope amounts to 4.41×1014 years, which is longer than the time in which the Universe has existed (which is nearly 14 billion years)!
- The pure elemental form of indium tightly attaches to other metals.
- When indium metal is bent, it releases a characteristic creaking sound which is interestingly labeled as a “tin cry”.