Indium is a valuable, expensive and rare metal. Man has learned to
use every natural material with great benefit for himself. But they all
differ in quantity, importance, complexity of extraction and processing.
Indium melting point 156.59 ºC = 429.74 K is the defining point on the ITS-90 temperature scale.
Natural element - indium
In its pure form, 99.97-99.99% indium is a white shiny metal, resembling zinc in appearance, but according to its technical characteristics it is closest to aluminum and gallium. When bent, it emits a characteristic crisp sound, this is due to the deformation of the crystal lattice.
This element acquired its name at the time of its discovery: when studying the spectral analysis of zinc blende, a line of indigo color (blue tint) was discovered, as a result of which the element was named Indigo. On the cut, the ingot also has a beautiful blue tint.
This material is being studied to this day. In nature, this element occurs in the form of 2 isotopes of indium-113 and indium-115 (with weak β-radioactivity), the decay period of which is 6 * 1015 years. A total of 37 isotopes with different decay times are known.
Indium is a very soft metal (20 times softer than gold), with a density of 7.362 g / cm³. It can be cut with a knife, leaves marks when pressed on the paper. Melted at 156.7 ºC, boils at 2072 ºC.
But when the mass is reduced to a critical value, the melting point drops to 40 ºC; raising the temperature to 800 ºC reacts with oxygen, and a violet flame can be observed.
Up to this temperature limit, indium does not tarnish in air or oxidize.
Inert towards alkalis, even when boiling. Let's dissolve in acids:
reacts quickly with chlorine and nitrogen;
reacts slowly with saline and sulfuric.
Reacts with bromine, chlorine, when heated with sulfur, sulfur dioxide, selenium, tellurium, iodine.
Indium is characterized by high electrical conductivity and is a semiconductor: even its small concentration in alloys with other metals increases this characteristic.
Therefore, the main fields of application are engineering, electronics, optoelectronics. In addition to electrical conductivity, indium increases corrosion resistance and durability.
Less commonly used in jewelry and dentistry.
60-80% of the total production is used for the production of LCD displays and solar panels. Indium oxide is applied as transparent film electrodes.
It is included in the compositions of solders and alloys with a high degree of adhesion and high thermal conductivity. Allows you to connect dissimilar substances by soldering, for example, glass + metal.
In an alloy with silver, it is used for mirror coating. Practiced in optical technology for photocells and phosphors, in the manufacture of headlights, reflectors, astronomical mirrors (with zero distortion).
In the automotive industry: applied to the skirts of aluminum pistons in diesel engines, which increases their wear resistance.
Compounds of indium with arsenic (indium arsenide) is a refractory compound with indium phosphide, used as a thermoelectric material.
Some isotopes of indium are used in radiopharmaceutical, dental (dental cements) preparations.
It is used in space technologies as seals, gaskets, coatings.
It is part of a special glass used in nuclear power engineering that absorbs thermal neutrons (boron oxide 3%; silicon oxide 55%; indium oxide 12%).
It is part of the "blue gold".
The main raw materials for the production of indium are the ores of lead, zinc, tin, copper, or dust obtained from the processing of cuprous shale. Indium is a by-product of the processing of lead-zinc, tin or polymetallic ores. For processing materials are used with an indium content of 0.1%, not less.
The indium processing method is multistage and consists of 3 stages:
Obtaining a concentrate enriched with indium;
Processing of concentrate and obtaining a crude composition;
Cleaning of rough metal, i.e. refining.
The production is complicated by the fact that there are a large number of chemical reactions that are used selectively, depending on the composition of the concentrate. In addition, at the firing stage, the concentrate is enriched with zinc, lead, cadmium, etc.
The technology for obtaining and the market for indium is closely related, since the amount of material is limited, its extraction and processing are multistage and very expensive.