Indium

49 cadmium ← indium → tin Ga ↑ In ↓ Tl periodic table
General
Name, Symbol, Number	indium, In, 49
Chemical series	poor metals
Group, Period, Block	13, 5, p
Appearance	silvery lustrous gray
Atomic mass	114.818(3) g/mol
Electron configuration	[Kr] 4d10 5s2 5p1
Electrons per shell	2, 8, 18, 18, 3
Physical properties
Phase	solid
Density (near r.t.)	7.31 g/cm³
Liquid density at m.p.	7.02 g/cm³
Melting point	429.75 K (156.60 °C, 313.88 °F)
Boiling point	2345 K (2072 °C, 3762 °F)
Heat of fusion	3.281 kJ/mol
Heat of vaporization	231.8 kJ/mol
Heat capacity	(25 °C) 26.74 J/(mol·K)
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 1196 1325 1485 1690 1962 2340
Atomic properties
Crystal structure	tetragonal
Oxidation states	3 (amphoteric oxide)
Electronegativity	1.78 (Pauling scale)
Ionization energies (more)	1st: 558.3 kJ/mol
	2nd: 1820.7 kJ/mol
	3rd: 2704 kJ/mol
Atomic radius	155 pm
Atomic radius (calc.)	156 pm
Covalent radius	144 pm
Van der Waals radius	193 pm
Miscellaneous
Magnetic ordering	no data
Electrical resistivity	(20 °C) 83.7 nΩ·m
Thermal conductivity	(300 K) 81.8 W/(m·K)
Thermal expansion	(25 °C) 32.1 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 1215 m/s
Speed of sound (thin rod)	(r.t.) 11 m/s
Mohs hardness	1.2
Brinell hardness	8.83 MPa
CAS registry number	7440-74-6
Notable isotopes
Main article: Isotopes of indium iso NA half-life DM DE (MeV) DP 113In 4.3% In is stable with 64 neutrons 115In 95.7% 4.41×1014y Beta- 0.495 115Sn

Indium (chemical symbol In, atomic number 49) is a rare, soft, malleable and easily fusible metal. It is chemically similar to aluminum and gallium, but it looks more like zinc. Zinc ores are also the primary source of this metal. Its current primary application is to form transparent electrodes from indium tin oxide in liquid crystal displays (LCDs). It is also widely used in thin films, to form lubricated layers. During World War II, it was widely used to coat bearings in high-performance aircraft.

Occurrence

Ductile Indium wire

Indium is produced mainly from residues generated during zinc ore processing, but it is also found in iron, lead, and copper ores. The amount of indium consumed is largely a function of worldwide LCD production. Increased manufacturing efficiency and recycling (especially in Japan) maintain a balance between demand and supply. Demand increased as the metal is used in LCDs and televisions, and supply decreased when a number of Chinese mining concerns stopped extracting indium from their zinc tailings.

Up until 1924, there was only about one gram of isolated indium on the planet. The Earth is estimated to contain about 0.1 parts per million (ppm) of indium. This means it is about as abundant as silver, but indium is nearly three times more expensive by weight. Canada is a leading producer of indium. Worldwide production is typically over 300 tonnes per year, but demand has risen rapidly with the increased popularity of LCD computer monitors and television sets.

History

Indium was discovered by Ferdinand Reich and Hieronymous Theodor Richter in 1863, when they were testing zinc ores with a spectrograph in search of thallium. The element was named after the indigo line in its atomic spectrum. It is interesting to note that most elements were discovered while searching for other elements. Richter went on to isolate the metal in 1867.

Notable characteristics

In the periodic table, indium lies in group 13 (former group 3A), between gallium and thallium, and in the same group as aluminum. Consequently, its properties resemble those of these three elements. In addition, it is situated in period 5, between cadmium and tin.

Indium is a very soft, silvery-white metal, with a bright luster. As a pure metal, it emits a high-pitched "cry" when bent. This element and gallium are able to wet glass.

Isotopes

One unusual property of indium is that its most common isotope, ¹¹⁵In, is slightly radioactive—it decays very slowly by beta emission to tin. The estimated abundance of ¹¹⁵In is about 95.7%, while that of the stable isotope, ¹¹³In, is 4.3%.

The radioactivity of ¹¹⁵In is not considered hazardous, mainly because its decay rate is nearly 50,000 times slower than that of natural thorium, with a half-life of 4×10¹⁴ years. Also, indium is not a notorious cumulative poison, like its neighbor cadmium, and is relatively rare.

Numerous other radioactive isotopes of indium are known, but most of them are extremely short-lived.

Applications

The first large-scale application for indium was as a coating for bearings in high-performance aircraft engines during World War II. Afterwards, production gradually increased as new uses were found in fusible alloys, solders, and electronics. In the middle and late 1980s, the development of indium phosphide semiconductors and indium-tin-oxide thin films for liquid crystal displays (LCD) aroused much interest. By 1992, the thin-film application had become the largest end use. Other uses;

• Used in the manufacture of low-melting-temperature alloys. An alloy consisting of 24% indium and 76% gallium is liquid at room temperature.
• Some indium compounds such as indium antimonide, indium phosphide, and indium nitride are semiconductors with useful properties
• Used as a semiconductor dopant
• Can also be plated onto metals and evaporated onto glass which forms a mirror which is as good as those made with silver but has higher corrosion resistance.
• Its oxide is used in the making of electroluminescent panels.
• Used as a light filter in Low pressure sodium vapor lamps
• Indium's freezing point of 429.7485 K (156.5985 °C) is a defining fixed point on the international temperature scale ITS-90.
• Sometimes used as a component of nuclear control rods.
• Very small amounts used in aluminium alloy sacrificial anodes (for salt water applications) to prevent passivation of the aluminium

Precautions

Pure indium in metal form is considered non-toxic by most sources. This may not be the case with indium compounds: there is some unconfirmed evidence that suggests that indium has a low level of toxicity. However, in the welding and semiconductor industries, where indium exposure is relatively high, there have been no reports of any toxic side-effects. Other sources are more definite about indium compounds' toxicity - for example, the WebElements website states that "All indium compounds should be regarded as highly toxic. Indium compounds damage the heart, kidney, and liver, and may be teratogenic." For example, indium trichloride anhydrous (InCl3) is quite toxic, while indium phosphide (InP) is both toxic and a suspected carcinogen.

See also

• Chemical element
• Metal
• Periodic table

References

ISBN links support NWE through referral fees

• Los Alamos National Laboratory – Indium

External links

• WebElements.com – Indium
• The Indium Corporation
• Reducing Agents > Indium low valent

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