Indian (element)

Indium is a chemical element with atomic number 49 located in group 13 and period 5 of the periodic table of elements. Its symbol is In. It is a scarcely abundant, malleable, easily meltable metal, chemically similar to aluminum and gallium, but more similar to zinc (in fact, the main source of obtaining this metal is from zinc ores). Its main application is in touch screens, in the form of indium and tin oxide.

History

Indium was discovered by Ferdinand Reich and Theodor Richter in 1863 when they were investigating the presence of thallium in zinc ores using a spectrograph. It was isolated by Richter in 1867.

Properties

Physics

The Indian wets the glass surface of a test tube.

Indium is a silvery-white, highly ductile post-transition metal with a brilliant luster. It is so soft (Mohs hardness 1.2) that, like sodium, it can be cut with a knife. It also leaves a visible line on the paper. It is a member of group 13 on the periodic table and its properties are mainly intermediate between its upright neighbors gallium and thallium. Like tin, when indium is bent a high-pitched scream is heard, a crackling sound due to the twinning of crystals. Like gallium, indium is capable of wetting glass. Like both, indium has a low melting point, 156.60 °C (313.88 °F); higher than its lighter counterpart, gallium, but lower than its heavier counterpart, thallium, and lower than tin. The boiling point is 2,072 °C (3,762 °F), higher than tin. of thallium, but lower than that of gallium, in reverse of the general trend in melting points, but similar to the downward trends of the other post-transition metal groups due to weak metallic bonding with few delocalized electrons.

The density of indium, 7.31 g/cm³, is higher than that of gallium, but lower than that of thallium. Below the critical temperature, 3.41 K, indium is a superconductor. Indium crystallizes in a body-centered tetragonal crystal system structure in the space group I4/mmm (lattice parameters: a = 325 pm, c = 495 pm): which forms a slightly distorted face-centered cubic crystal structure, where each indium atom has four neighbors at a distance of 324 pm and eight neighbors a little further away far (336 pm). Indium has a greater solubility in liquid mercury than in any other metal (greater than 50 mass percent indium at 0 °C). Indium exhibits a ductile viscoplastic response, which is independent of size in tension and compression.. However, it has a size effect to bending and indentation, associated with a length scale of the order of 50–100 µm, significantly large when compared to other metals.

Chemicals

Indium has 49 electrons, with an electron configuration of [Kr]4d¹⁰5s²5p¹. In compounds, indium typically donates the outer three electrons to become indium(III), In³⁺. In some cases, the 5s pair of electrons are not donated, resulting in indium(I), In⁺. The stabilization of the monovalent state of valence (chemistry) is attributed to the inert pair effect, in which the relativistic effects of relativistic quantum chemistry stabilize the 5s orbital, observed in heavier elements. Thallium (indium's heavier homologue) shows an even stronger effect, making oxidation to thallium(I) more likely than to thallium(III), while gallium (indium's lighter homologue) usually In general, it only has a +3 oxidation state. Thus, although thallium(III) is a moderately strong oxidizing agent, indium(III) is not, and many indium(I) compounds are powerful reducing agents. While the energy required to include the s electrons in the chemical bonding is lowest for indium among the group 13 metals, bond energies decrease down the group, so for indium, the energy released by forming two additional bonds and reaching the +3 state is not always enough to offset the energy needed to engage the 5s electrons. Indium(I) oxide and hydroxide are more basic, and indium(III) oxide and hydroxide are more acidic.

A number of standard electrode potentials, depending on the reaction involved, are reported for indium, reflecting the decreased stability of the +3 oxidation state:

In2+ + e−	In+	E0 = −0.40 V
In3+ + e−	In2+	E0 = −0.49 V
In3+ + 2 e−	In+	E0 = −0.443 V
In3+ + 3 e−	In	E0 = −0.3382 V
In+ + e−	In	E0 = −0.14 V

Metallic indium does not react with water, but is oxidized by stronger oxidizing agents, such as the halogens, to give indium(III) compounds. It does not form boride, silicide, or carbide, and the hydride InH₃ has, at best, a transient existence in ethereal solutions at low temperatures, being unstable enough to spontaneously polymerize without coordination. Indium is quite basic in aqueous solution, showing only slight amphoteric characteristics, and unlike its lighter counterparts aluminum and gallium, it is insoluble in alkaline aqueous solutions.

Isotopes

Indium has 39 known isotopes, ranging in mass number from 97 to 135. Only two isotopes occur naturally as primordial nuclides: indium-113, the only stable isotope, and indium-115, which has a half-life of 4.41×10¹⁴ years, four orders of magnitude greater than the age of the Universe and almost 30,000 times greater than that of natural thorium. The half-life of ¹¹⁵In is very long because it decays by beta to ¹¹⁵Sn is spin-forbidden. Indium-115 makes up 95.7% of all the Indian. Indium is one of three known elements (the others are tellurium and rhenium) whose stable isotope is less abundant in nature than the long-lived primordial radioisotopes.

The most stable artificial isotope is indium-111, with a half-life of about 2.8 days. All other isotopes have half-lives of less than 5 hours. Indium also has 47 metastates, among which indium-114m1 (half-life about 49.51 days) is the most stable, more stable than the ground state of any non-primordial indium isotope. Everything decays by isomeric transition. Indium isotopes lighter than ¹¹⁵In decay predominantly through electron capture or positron emission to form cadmium isotopes, whereas the other indium isotopes of ¹¹⁵ In and major predominantly decay via beta-minus decay to form isotopes of tin.

Main features

Indian lingote.

Indium is a very soft, silvery-white metal with a brilliant luster. When the metal is bent it emits a characteristic sound.

Its most characteristic oxidation state is +3, although it also presents +2 in some compounds.

Applications

It was used mainly during World War II as a coating in high-performance aeronautical engines. After this, it has been used for new applications in alloys, in welding and in the electronics industry.

In the mid to late 1980's The use of semiconductor indium sulfides and indium tin oxide thin films for the development of liquid crystal displays (LIDs) aroused interest. This is because the use of indium allowed obtaining the blue color in LEDs, which had been resisted for years.

Other applications:

• In the manufacture of low melting point alloys. A alloy with 24% Indian and 76% gallon is liquid at room temperature.
• To make photoconductors, germanium transistors, rectifiers and thermoistors.
• It can be deposited on other metals and evaporated on a glass forming a mirror as good as the made with silver, but more resistant to corrosion.
• Its oxide is used in the manufacture of luminiscent electro panels.
• Indian and tin oxide is used abundantly for the manufacture of transparent electrodes such as those on touch screens, such as mobile phones or tablets.
• In nuclear medicine a radioisotope of In, the 111 In associated with monoclone antibodies (Capromab) is used against the membrane-specific prostatic antigen for imaging of prostate cancer.

Abundance and production

Trend in global production

It is estimated that there is about 0.24 ppm of indium in the earth's crust (approximately as abundant as silver). The main producer of indium is China, which produced 300 tons in 2002. It is expected that indium will run out before 2050, so, taking into account the situation that existed in 2011, investment in research into substitute materials is important. to produce transparent and conductive electrodes for tactile devices, such as those present in mobile phones, tablets or didactic screens. It is thought that very thin sheets of graphene could replace indium tin oxide for this function. The Korean company Samsung has already made some prototypes of touch screens with graphene, although there is still a lot to be investigated to achieve the same performance as with indium tin oxide.

Indium minerals are rare, so they are not used as an industrial source. The most representative are the roquesite (CuInS₂) and the dzhalindite [In(OH)₃].

Indium is produced exclusively as a by-product during the processing of ores from other metals. Its main source material is sulfidic zinc ores, where it is hosted primarily in sphalerite. Lesser amounts of sulfidic copper ores are probably mined as well. During the zinc smelting process, indium accumulates in the iron-rich waste. It can be extracted from them in different ways. It can also be recovered directly from process solutions. Subsequent purification is done by electrolysis. The exact process varies depending on the mode of operation of the foundry.

Its status as a by-product means that indium production is limited by the amount of zinc (and copper) sulfide ores that are mined each year. Therefore, its availability must be analyzed in terms of supply potential. The supply potential of a by-product is defined as the amount that is economically extractable from its host materials per year under current market conditions (ie technology and price). Reserves and resources are not relevant for by-products, as they cannot be mined independently of the main products. Recent estimates put indium supply potential at a minimum of 1,300 t/y from sulfidic zinc ores and 20 t/year from sulfidic copper ores. These figures are significantly higher than current production (655 t in 2016). Therefore, it will be possible for future significant increases in indium by-product production to occur without significant increases in production costs or in production. the price. The average price of indium in 2016 was $240/kg, down from $705/kg in 2014.

China is one of the top producers of indium (290 tons in 2016), followed by South Korea (195 tons), Japan (70 tons), and Canada (65 tons). The Teck Resources refinery in Trail, Columbia British, is a large single-source producer of indium, with production of 32.5 tons in 2005, 41.8 tons in 2004 and 36.1 tons in 2003.

The main consumption of indium in the world is the production of liquid crystal displays (LCDs). Demand increased rapidly from the late 1990s to 2010 with the popularity of LCD computer monitors and televisions, now accounting for 50% of Indian consumption. Increased manufacturing and recycling efficiencies (especially in Japan) maintain the balance between demand and supply. According to UNEP, the recycling rate for indium at the end of its useful life is less than 1%. The average price of indium in 2000 was $188 per kilogram.

Precautions

There is some unconfirmed evidence to suggest that indium has low toxicity. However, in the semiconductor and welding industry, where exposures are relatively high, there have been no reports of side effects. It would be necessary to carry out studies in this regard.