Indium: a metal that can be bitten through
Indium properties and areas of application
Introduction
Indium is a fusible, sparkly, silvery-white metal with a melting point of 157°C (314°F).This temperature is one of the reference points on the international temperature scale.
It is soft enough to cut with a knife or bend with your hands… or even bite through! If you bend a piece of indium, you will hear a crunch – a testament to changes in the metal’s crystal lattice. Indium ions tint flames indigo.
History of discovery
German scientists Ferdinand Reich and Jerome Richter discovered indium in 1863. Reich was studying a zinc ore, sphalerite, hoping it would contain a sample of the newfound element thallium. As Reich was colorblind, he asked his colleague Richter to check the spectrum for him. The scientists were surprised: instead of the green line they were expecting, Richter noticed a rich violet-blue line that had not been seen before. Reich and Richter realized that they had found a new element. They called it the Latin word indicum – "purple" or "indigo." The scientists later quarreled over who discovered this element, with Richter claiming to be the sole discoverer.
Richter continued seeking this metal. Three years later, an indium ingot weighing 0.5 kg was demonstrated at the Paris Universal Exposition.
Nature
Pure indium metal can be found in nature, but most of it is produced as a byproduct when melting zinc ore. Based on current consumption, scientists suggest that its supply will meet human needs for just the next 13 years.
Chemical properties
When heated, indium reacts with sulfur, forming indium (III) sulfide:
2In + 3S = In₂S₃
It dissolves slowly in nitric acid, forming indium (III) nitrate:
In + 4HNO₃ = In(NO₃)₃ + NO + 2H₂O
When indium and gallium touch, they dissolve in each other, forming an alloy that melts at 16°C (61°F). Such alloys are used to substitute for mercury in devices like thermometers.
Application
Indium is added to other metals to produce strong, solid alloys for dentistry and electrics. It increases the wear resistance of parts – the addition of indium reduces the coefficient of friction. Indium is not very toxic and is not metabolized by living organisms. However, prolonged respiration of its salts or indium oxide can lead to lung disease, and injecting it negatively affects the kidneys. The radioactive isotope In-111 emits gamma radiation. It is used in precise medical scanners to recognize osteomyelitis (bone disease).
Indium first found significant use during World War II, where it was used to coat aircraft bearings. Today, indium tin oxide can be found in LCD-TVs, monitors, and smartphone screens. It is a good electrical conductor that can send signals to individual pixels of the screen without interfering with the light from other pixels. Copper-indium-gallium selenide is used as a material for solar batteries.
