Indium — low-melting, very soft and ductile silver tint metal. 49th element of fifth period of table of chemical elements, where it is indicated by symbol In (Indium). In its qualities, it is close to aluminum and gallium, in appearance — to zinc. Name comes from shade of spectral line inherent in indium — indigo.
|Atomic number||Atomic (molar) mass g/mol||Oxidation state||
|Melting point t °С||Boiling point t °С||Heat of fusion kJ/kg|
|№ 49||114,8||1, 3||7,362||256°С||2072°С||3,24|
In 1863, German scientists Reich and Richter obtained spectroscopic study of zinc blende in spectrum of indigo color line. Scientists were looking for gallium, which gives green spectral line, but instead discovered new element. Isolated in pure form, indium was very ductile — much softer than lead, 20 times softer than gold. Tiny ingot of new metal in form of pencil about hundred grams, French Academy of Sciences estimated at 80 thousand dollars. Four years later, at 1867 World’s Fair, India was represented by half kilogram ingot. Today, cost of this metal is about $700 per kg. India’s global consumption grows annually. In 2010, it reached 900 tons.
Indium in form of dispersed impurities is found in number of minerals. Its content in high-iron sphalerite is several grams per kilogram, in chalcopyrite and stannine — ten times less, and in cassiterite and pyrrhotite — even less, as well as in pyrite, arsenopyrite, tungsten — grams per ton. Total indium content in earth’s crust is approximately 0.25 g/t. In seawater it’s even more — 18 g/t.
Chemistry is believed to have no useless waste. Proof of this is technology for producing indium from industrial wastes. Very history of its discovery is associated with ore called «zinc blende». Currently, indium is obtained from intermediate wastes from production of zinc, tin, copper and lead. Although indium is contained there in scanty amounts — up to 0.1%, and its separation from related elements — cadmium, zinc, copper, antimony and others — is rather difficult task, but it is worth it: indium is necessary. At first stage of concentration, it is separated from copper, zinc and cadmium. Feed is treated with sulfuric acid, which dissolves metals, and concentrate is isolated by hydrolytic precipitation. This is achieved by changing acidity of solution. Cadmium hydroxide precipitates at pH of about 8, zinc and copper hydroxides — at 6. To «precipitate» indium hydroxide, pH of solution must be brought up to 4. «Indium rough» concentrate is extracted by cementation on zinc and aluminum. «Fine Indium» is obtained by refining using zone melting.
Since January 1, 1997, interstate standard GOST 10 297−94 has been in force on territory of former Soviet Union, regulating quality of indium in bars, pyramids and bars. According to standard, this metal is produced in five purity classes, depending on percentage of element. So, In0000 brand contains this element in amount of 99.9999%. In In000, share of pure indium is 99.9995%. In In00 — 99.999%. In0 has chemical purity of 99.998%. Brand In2 — 99.97%.
Density of indium at 20 °C is 7.362 g/cm³. If magnesium ignites at 623 °C, then indium withstands heating to 800 °C, after which it flashes with violet-blue flame to form oxide. This metal is soluble in almost all acids, faster in inorganic (especially easy in perchloric and nitric). It is stable in solutions of alkalis, but it reacts with bromine and chlorine, and when heated, with iodine, sulfur vapor of phosphorus. Critical temperature of indium superconductivity = 3.405 °K.
- As acceptor additive to silicon and germanium in microelectronics.
- For fusible solders. Exceptional adhesion of indium to many materials allows soldering, for example, metal with glass.
- In manufacture of glass for liquid crystal monitors.
- Indium coating of mirrors and car headlights gives reflectivity at silver level, while resistance to atmospheric influences is higher.
- For graduation of thermocouples.
- For photocells.
- Like phosphor.
- Indium coating of aluminum diesel piston skirts reduces wear.
- Indium arsenide — high-temperature high-performance thermoelectric, 10% indium phosphide is still doped to increase efficiency.
- 111 In and 113 In isotopes are used in radioisotope diagnostics.
- Indium isotope 115 In — for detecting neutrinos with threshold energy of 120 keV: 115In + νe → 115Sn+e-+2γ
- Indium is part of «blue gold».
In the 21st century, world indium consumption is growing rapidly and in 2009 reached 900 tons. It is indispensable in high vacuum technology as sealant (gaskets, coatings); in particular, when sealing spaceships and particle accelerators. Indium mercury oxide electrochemical system is used to create high specific energy consumption batteries. Alloy of indium with silver is resistant to hydrogen sulfide and is used to create high-quality reflective coatings. Its alloys with gallium, tin and zinc melt at room temperature and can be liquid metal coolants. Indium absorbs thermal neutrons and can serve to control nuclear reaction. Even better in this role is its combination with other elements that capture neutrons. Thermal neutron absorbing glass is made from indium oxide. Most famous composition of such glass is indium oxide (12%), boron oxide (33%), cadmium oxide (55%). Indium having low melting point is indispensable in production of liquid crystal screens and as component of fusible solders and alloys. Indium orthophosphate is part of dental cements.
Indium delivered by indoor transport. Lot is transported by rail per one recipient 1 package. In000 and In00 brands are transported in form of ingots or pyramids weighing from 50 grams to 1 kg. For other brands — up to 3 kg. If necessary, In000 ingots can weigh 20 — 50 grams, and elongated according to Czochralski method — up to 2.5 kg. In00 grade is supplied with bars of Ø 21−25 mm and length of 50 — 70 mm or Ø 22−24 mm and length of 63 — 67 mm.
On surface of samples minor defects are permissible, not exceeding limits specified by standard. Each bar is marked. Indium ingots In000 and In0000 each are packed separately in plastic packaging. In00 and In0 ingots can be packaged in pairs. In2 ingots are packed either in plastic film or in waxed paper.
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