A metal that melts in the hand
Gallium is a silvery-gray metal with a bluish tinge, and is quite brittle. It is not encountered in nature in pure form and is a trace element. The average content of gallium in the earth’s crust is 19 g/t. Gallium is contained in minerals, primarily sphalerite, magnetite, cassiterite, garnet, beryl, tourmaline, spodumene, phlogopite, biotite, muscovite, sericite, lepidolite, chlorite, feldspars, nephelite, hackmanite and natrolite. Gallite, CuGaS₂ is a rather rare metal that is used to extract pure gallium, Additionally, gallium can be obtained as a secondary product in processing bauxites.
Gallium melts at just 29.76 °C, so it even melts in the hand. At around room temperature, another three metals also melt: mercury, caesium and rubidium. But because of their high toxicity or reactivity, unlike gallium they must not be held in the hand.
How gallium was discovered
The existence of gallium was predicted by D. I. Mendeleev in 1871 on the basis of the Periodic Law that he formulated.
Mendeleev named this element “ekaaluminum” and predicted such properties as its density and melting point. Mendeleev also predicted:
- the nature of its oxide,
- its bond in compounds with chlorine
- that the metal would slowly dissolve in acids and alkalis;
- it would not react with air
- eka-aluminum oxide M₂O₃ should react with acids with the formation of the salts MX₃;
- that it should form base salts;
- its chloride would have greater volatility than ZnCl₂;
- that the element would be discovered by spectroscope.
Mendeleev proved to be a Nostradamus of chemistry: when gallium was obtained, all the properties that he had predicted were confirmed!
In 1875, the French chemist Paul-Émile Lecoq de Boisbaudran studied sphalerite using spectroscopy and found two purple lines that belonged to a new element. A year later the scientist extracted a new element using electrolysis. Boisbaudran named this element after the Latin name of France – Gallia. There is a legend that the scientist also placed another meaning in this name. Lecoq sounds like le coq in French, i.e. “rooster” (gallus in Latin). So as if by chance, Boisbaudran immortalized his name in the name of the new element.
Studying the gallium obtained, Boisbaudran determined that the density differed from Mendeleev’s predictions. When Mendeleev found out about this, he wrote to his French colleague, recommending that he check his results again. And as it turned out, he was quite right to do so: Boisbaudran’s initial findings were indeed incorrect.
Field of application of gallium
Most gallium produced is used for the manufacturer of semiconductors. Arsenide (GaAs) and gallium nitride (GaN) are used in electronic components of many devices, to make integrated circuits, high-performance processors and microwave amplifiers. Gallium arsenide is used in various electrooptic infra-red devices. Gallium-aluminum arsenide is used to make infra-red laser diodes of high power. On the basis of gallium nitride and indium-gallium nitride, blue and purple laser diodes are manufactured. Incidentally, a laser with gallium nitride is used in the Blu-ray disc drives.
Photoelements on the basis of gallium arsenide and indium-gallium phosphide and arsenide are used in satellites and Mars rovers.
Gallium has an interesting feature: it greatly reduces the melting point of alloys in which it is contained. The temperature becomes lower than each component of the alloy individually (eutectic properties). The alloy Gallistan (68.5% gallium, 21.5% indium and 10% tin) has a melting point of -19°С and is used in some thermometers instead of mercury.
Gallium is also used in medicine. In general, the metal is characterized by a low toxicity and does not perform any natural biological function. So medicine containing gallium can be used in treating and diagnosing cancerous diseases (the isotopes gallium-67 and -68). Gallium is also used in treating several bacterial infections: the ion Ga³⁺ displaces Fe³⁺ on the metabolic pathways of bacterial respiration, causing the bacteria to die. Medicine containing gallium can also be used to treat malaria. Gallium helps to detect neutrino particles emanating from the sun. Detecting these particles is usually a very complex and laborious process. Gallium in the registration mixture increases the sensitivity of the analysis, and accordingly helps to detect neutrinos. The GALLEX detectors at the Laboratori Nazionali del Gran-Sasso contain 12.2 tons of gallium-71. They detect neutrinos emanated by the sun, and transform them into radioactive isotopes, the radiation of which can be recorded. Similar studies are also carried out at the Baksan neutrino observatory (Kabardino-Balkaria), where the neutrino detectors contain 5 tons of liquid gallium.
Thermometers can be tested using the melting temperature of gallium! This figure - 302.9146 K (29.7646 °C) – is used as a standard by the International Bureau of Weights and Measures. In 2007, a focused gallium ion beam with a thickness of 7 nm was used at Simon Fraser University to print the smallest book in the world – “Teeny Ted from Turnip Town”. The size of the book is 0.07 by 0.10 mm.
Gallium has another amusing use: gallium spoon, which look identical to aluminum ones, are used to play a trick with a disappearing spoon. In hot tea or coffee, this spoon simply melts!