Indium, In, Atomic number 49


Indium is a chemical element with the symbol In and atomic number 49. In the periodic table of the elements, it is in the 5. Period and is the fourth element of 3. Main group (according to new census group 13) or boron group. Indium is a rare, silver-white and soft heavy metal. Its frequency in the earth's crust is comparable to that of silver. Indium is not essential to the human body, nor are known toxic effects. The metal is processed today for the most part to indium tin oxide, which is used as a transparent conductor for flat panel displays and touch screens. Since the turn of the millennium, the associated increase in demand to a significant increase in Indiumpreise and discussions about the scope of resources out.

Indium was 1863 discovered by the German chemists Ferdinand Reich and Theodor Richter at the Bergakademie Freiberg. They investigated a found around sphalerite sample after thallium. They found in the absorption spectrum instead of the expected thallium lines, a previously unknown indigo spectral line and thus a previously unknown element. After this, the new element was later given its name. A short time later, they were initially, and indium oxide, by reduction of indium oxide with hydrogen and the metal. A larger amount of indium was first at the World Exhibition 1867 shown in Paris.

After a first application 1933 as an alloying element in dental gold began the extensive use of indium with the Second World War. The United States implemented it as a coating in highly loaded bearings Aircraft. After the Second World War, indium was mainly in the electronics industry, used as solder and in low-melting alloys. The use in control rods in nuclear reactors became important with the increasing use of nuclear energy. This led to 1980 to a strong rise in the first Indiumpreises. After the nuclear accident at Three Mile Iceland Went but both demand and prices significantly.

From 1987 Two new indium compounds, developed the semiconductor indium phosphide and the conductive and transparent in thin layers of indium tin oxide. Especially indium tin oxide, with the development vonFlüssigkristallbildschirmen technically interesting. Is due to the high demand for 1992 the major part of the indium further processed to indium tin oxide.


Indium is a rare element, its share of the continental crust is only 0,05 ppm. It is thus similar incidence of silver and mercury. In dignified state of indium has only been found in a single discovery in eastern Siberia. There are only a few indium minerals known. These are mainly sulphide minerals such as finely Indite2S4 und roquesi Cuina2. However, these are rare and do not play a role in the recovery of indium. The largest deposits of indium in zinc ores are, especially sphalerite. The theoretical reserves are on 16.000 Tons valued, are economically mineable, of which about 11.000 Tons. The largest deposits are located in Canada, China and Peru. Indium-containing ores but also in Australia, Bolivia, Brazil, Japan, Russia, South Africa, USA, Found Afghanistan and some European countries. In Germany deposits are located in the Ore Mountains (Freiberg, Marienberg, Geyer) and the Rammelsberg in the Harz.

Extraction and representation

Indium is obtained almost exclusively as a by-product in the production of zinc or lead. An economic recovery is possible, if at certain points of the production process indium accumulates. This is about fly ash, that occur during the roasting of zinc sulfide and residues, which remain in the electrolysis during the wet method of zinc production. They are reacted with sulfuric acid or hydrochloric acid and then brought into solution. Since the concentration is too low of indium in the acid, it must be enriched. This is done by extraction with tributyl about or indium phosphate precipitation as.

The actual Indiumgewinnung carried out electrolytically. For this, a solution of indium(III)-chloride in hydrochloric acid used. This is implemented with the help of mercury to elemental indium electrodes. In the electrolysis is to make sure, that the solution contains no more thallium, because the standard potentials of the two elements are very similar.

\mathrm{In^{3+} + 3\ e^- \ \xrightarrow{Hg-Elektr.} \ In}

By suitable methods such as zone melting method or multiple electrolysis of indium(I)-chloride salt melts the crude product can be further purified and so on 99,99 % pure indium are obtained.


The primary production (Mine production) of indium was in 2006 between 500 and 580 Tons. Due to the limited supplies of natural 11.000 Tons with high demand among the scarcest commodities to indium on earth. In 2008 China grew especially for the information on the natural reserves of indium 280 on 8.000 Tons, what the static range of previously 6 on 19 Prolonged years. The secondary production, also das Recycling, exceed the primary production, and was in 2008 at 800 Tons.

Refinery production of Indium by country

The Indiumproduktion in China has increasingly taken place only recently. In 1994 was the amount produced even at 10 Tons. Since then, China's share of world production increased to 60 % in 2005. Production in other countries such as Japan, Canada and France could be increased only marginally or decreased by depletion of the deposits. Thus, 2006 Japanese Toyoha mine closed, thereby reducing the local production significantly.

Temporal development of indium production

As the demand for indium has risen faster than production, resulted in a sharp increase of price of indium 97 Dollar 2002 on 827 Dollars per kilogram in 2005. Recycling of indium is done before all through recycling of residues from the sputtering. The only country, in the currently recovered in larger amounts of indium, ist Japan.

With further increases in demand and the consequent high price is also the recycling of materials with little of indium profitable. Likewise, it is now economically feasible, also exploit ores with lower Indiumgehalten. This will probably be possible, the drying up of resources to delay.

Indium may indeed be replaced in most applications by other substances, However, it often deteriorate the properties of the product or the cost of production. Thus, for example indium phosphide are replaced by gallium arsenide and indium are also some - albeit of lower quality - possible substitutes.


Physical Properties

Crystallographic Data[22]
Crystal system tetragonal
Space group I4/mmm \;
Lattice parameters


a = (b) = 325 pm

c = 495 pm

Number (The) the

Formula units

Z = 2

Unit cell of indium coordination sphere of the central Indiumatoms

Coordination polyhedra of a Indiumatoms from 4 + 8 = 12 Neighboring atoms in the form of a distorted cuboctahedron

Indium is a silvery-white metal with a low melting point of 156,5985 ° C. Have a lower melting point among metals only mercury, Gallium and most of the alkali metals. Over a very wide area of ​​nearly 2000 K is the liquid metal. Liquid indium leaves a thin film on glass permanently (Wetting). The same property has the similar gallium.

The metal has a high ductility and very low hardness (Mohs hardness: 1,2). It is therefore possible, To cut with a knife as sodium indium. At the same time it leaves a visible line on paper. Below a critical temperature of 3,41 Kelvin indium is superconductive. A special feature of the indium, it has in common with the tin, are the characteristic noise, which can be heard during bending of indium ("Zinngeschrei").

Indium only one crystalline modification is known under normal conditions, in the tetragonal crystal system, space group I4/mmm \; and thus in a tetragonal body-centered lattice with the lattice parameters a = 325 pm and c = 495 crystallized pm and two formula units in the unit cell.

An indium atom is surrounded in the crystal structure of twelve other atoms, wherein four adjacent cells are derived from the elementary and a smaller distance (325 pm; Red Ties ) ) than the eight having at the corners of the unit cell located atoms (337 pm; green bonds). As coordination polyhedra obtained by the coordination number 4 + 8 = 12 a verzerrtesKuboktaeder. The crystal structure can therefore act as a tetragonally distorted, cubic closest packing of spheres are described.

In high-pressure experiments, a further modification discovered, the above 45 GPa is stable and in the orthorhombic crystal system, space group Fmmm crystallized.

Chemical Properties

The chemical properties similar to those of the indium gallium and thallium group neighbors. Thus, indium as the other two elements, a base element, which can react at high temperatures with many non-metals. In the air it is stable at room temperature, as forming a dense oxide layer as in aluminum, which protects the material from further oxidation by passivation. Only at high temperatures, the reaction takes place to indium(III)-oxidstatt.

While indium mineral acids such as nitric acid or sulfuric acid is attacked, It is not soluble in hot water, Bases, and most organic acids. Also, salt water does not affect indium. Indium at room temperature, the mercury in the most soluble metal.


Are of indium 38 different isotopes and more 45 Kernisomere von 97Add to 135In known. In nature, which are found only two isotopes, 113In (64 Neutron) with 4,29 % and 115In (66 Neutron) with 95,71 % Proportion of the natural isotope distribution. The common isotope 115In is slightly radioactive, it is a beta emitter with a half-life of 4,41 · 1014 Years. Both natural isotope can be detected by NMR spectroscopy. The most stable artificial isotopes 111In and 114mIn have half-lives of several days, 113mIn only about one and a half hours. 111In and 113mIn nuclear medicine be used.



Is indium in Indiumdichtungenverwendet.

Indium is versatile, its use is limited by the scarcity and high price. The largest part of the produced indium is not used as metal, but further processed into a series of compounds. Alone for the production of indium tin oxide were in 2000 65 % out of a total production of indium. Other compounds, such as indium phosphide and indium arsenide be recovered from the produced indium. More details on the use of indium compounds found in the section Connections.

Metallic workpieces may be protected by electrically abgeschiedenene Indiumüberzüge. Thus coated materials such as steel, Lead or cadmium, are thereafter or salt solutions resistant to corrosion by organic acids and especially abrasion. Indiumschutzschichten were formerly often used for sliding bearings in automobiles or aircraft. Since the significant increase in Indiumpreises but this is no longer economically. Coated with indium surfaces have a high and uniform reflectivity over all colors of time and can therefore be used as a mirror.

The melting point of indium is relatively low and is very accurately determined. For this reason, he is one of the strong points in drawing up the temperature scale. This property is also for calibration in the Differential Scanning Calorimetry (DSC) used.

Because of the high Einfangquerschnittes for both slow and fast neutron Indium is a suitable material for control rods in nuclear reactors. As neutron detectors indium foils can be used. Indium is gas-tight and easy to deform even at low temperatures and is therefore used in so-called Indiumdichtungen in cryostat.

Also known as Lot for many materials plays indium due to some specific characteristics play a role. It is deformed when cooled only to a limited extent. This is especially important when soldering semiconductors for transistors important. Also plays a role, that indium is able, to solder and non-metallic materials such as glass and ceramics.

With "Indiumpillen" germanium wafers were on both sides anlegiert, produce first transistors.


Indium can be alloyed with many metals. Many of these alloys, especially with the metals bismuth, Zinn, Cadmium and lead, have a low melting point of 50 to 100 ° C. As a result of potential applications for example in sprinkler, Thermostats and fuses. Also usable as the lead is toxic, Indium is used as non-hazardous substitutes. The purpose of these alloys is that, that they contribute to high ambient temperatures, caused by fire or high current, melt. Is then interrupted by the melting of the circuit or activated the sprinkler system. Indium-gallium alloys often have even lower melting points and are included in high-temperature thermometers. A special gallium-indium-tin alloy is galinstan. This is liquid at room temperature and is used as non-hazardous substitute for mercury or sodium-potassium alloys.

There are a few other indium alloys, used in different areas. Indium is with copper, Manganese and magnesium is used as an alloy component of magnetic materials. Occasionally, indium (maximum 5 %) with silver, Zinn, copper, Used mercury and zinc as an additive in amalgam fillings. In the storage layer of a CD-RW, inter alia indium is contained.


A possible chemical detection is the precipitation of indium ions with 8-hydroxyquinoline from an acetic acid solution. Usually indium is not detected by chemical means, but on appropriate spectroscopic methods. Light is indium on the characteristic spectral lines at 451,14 nm and 410,18 nm prove. Since these are in the blue spectral range, results in the characteristic blue flame color. For a more precise quantitative determination itself provide X-ray fluorescence analysis and dieMassenspektrometrie as a research method.

Toxicity and safety

While aware of indium metal, no toxic effects are, However, it was, have that indium ions in animal studies with rats and rabbits, embryo toxic and teratogenic effects. When a single dose of 0,4 mg * kg-1 Incl3 observed in pregnant rats konntenMissbildungen such as cleft palate and Oligodactyly. These symptoms were more frequently noted, when the indium at the 10. Of pregnancy has been applied. In mice, however, no abnormalities were observed. For indium, a toxicity to aquatic organisms (aquatic toxicity) found.

Compact indium metal is not flammable. The finely divided state as a powder or dust, it is, however, how many metals and highly inflammable. Burning indium may not be extinguished with water because of the risk of explosion due to hydrogen formed, but rather with metal fire extinguishers (Class D) be deleted.


Indium forms a series of compounds. In them, the metal usually has the oxidation state III. The state I is rare and unstable. The oxidation state of II does not exist, Connections, which occurs formally divalent indium, are in fact mixed compounds from a- and trivalent indium.


Indium(III)-oxide is a yellow, stable salt. Pure indium(III)-oxide is little used, in the art, most of indium tin oxide is further processed to. It is to indium(III)-oxide, the with a small amount of tin(IV)-oxide is doped. Thereby, the connection to a transparent and conductive oxide (TCO-Material). This combination of properties, that few other materials have, requires a broad application. In particular, as a conductor in liquid crystal displays (LCD), organic light emitting diodes(OLED), Touch screens and solar cells indium tin oxide is used. In other applications such as heated car windows and solar cells, the expensive indium tin oxide could be replaced by cheaper aluminum-doped zinc oxide.

Compound semiconductor

Many indium compounds are compound semiconductor with characteristic band gaps. This relates especially to compounds with elements of 15. and 16. Main group, such as phosphorus, Arsenic and sulfur. Those elements with the 15. Main group are counted as III-V compound semiconductors, those with chalcogens of the III-VI compound semiconductors. The number varies according to the number of valence electrons in the two connection components. Indiumnitrid, Indiumphosphid, Indium arsenide and indium antimonide have different applications in different diodes, such as light-emitting diodes (LED), Photo diodes or laser diodes. The exact application depends on the required bandgap. Indium(III)-sulphide (In2S3) is a III-VI semiconductor having a band gap of 2 eV, is used instead of solar cells Cadmiumsulfidin. Some of these compounds - especially indium phosphide and indium arsenide - play a role in nanotechnology. Indium phosphide nanowires have a strongly anisotropic photoluminescence and may possibly be used in highly sensitive photodetectors or optical switches.

In addition to the simple compound semiconductors, there are semiconducting compounds, the more than one metal contained. An example is indium gallium arsenide (InxGa1-xAs) a ternary semiconductor with a decreased compared to gallium arsenide band gap. Kupferindiumdiselenid(CuInSe2) has a high absorption coefficient for light and is therefore used in thin film solar cells (CIGS-Solarzelle).

More indium

With the halogens fluorine, Chlorine, Bromine and iodine indium forms a series of compounds. Lewis acids and they are formed with suitable donors complexes. An important indium is indium(III)-chloride. This is used, inter alia, as a catalyst for the reduction of organic compounds.

There are also organic indium compounds having the general formulas InR3 and InR. Sie sind wie viele metallorganische Verbindungen empfindlich gegen Sauerstoff und Wasser. Indiumorganische Verbindungen werden als Dotierungsreagenz bei der Produktion von Halbleitern genutzt.

Name, Symbol,Atomic number Indium, In, 49
Series Metals
group, Period, Block 13, 5, p
Appearance silvery gray
CAS-Nummer 7440-74-6
Mass fraction of derErdhülle 0,1 ppm
Atomic mass 114,818 you
Atomradius (calculated) 155 (156) pm
Kovalenter Radius 144 pm
Van-der-Waals-radius 193 pm
Electron configuration [Kr] 4d105s25p1
1. Ionization 558,3 kJ / mol
2. Ionization 1820,7 kJ / mol
3. Ionization 2704 kJ / mol
Physical State fixed
Crystal structure tetragonal
Density 7,31 g/cm3
Mohs 1,2
Magnetism diamagnetisch (\chi_{m} = −5,1 · 10−5)
Melting point 429,7485[4] K (156,5985 ° C)
Boiling point 2345 K (2072 ° C)
Molar Volume 15,76 · 10−6 m3/mol
Heat of vaporization 231,8 kJ / mol
Schmelzwärme 3,26 kJ / mol
Vapor Pressure 1 Pa bei 1196 K
Speed ​​of sound 1215 m / s at 293,15 K
Specific heat capacity 233 J/(kg · K)
Electrical conductivity 12,5 · 106 A/(In · m)
Thermal conductivity 81,6 W /(m · K)
Oxidation states 3, 1
Normalpotential −0,343 V (In3+ + 3and → In)
Electronegativity 1,78 (Pauling-Scale)
Isotope NH t1/2 ZA ZE (MeV) ZP
111In {a son.} 2,8047 d e 0,865 111Cd
113In 4,3 % Stable
114In {a son.} 71,9 s b 1,989 114Sn
e 1,452 114Cd
115In 95,7 % 4,41 · 1014 a b 0,495 115Sn
NMR properties
Spin γ in
Itr(1H) fThe at
B = 4,7 T
in MHz
113In 9/2 5,8845 · 107 0,0151 21,87
115In 9/2 5.8972 · 107 0,271 38,86
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