We continue to review some of the most important materials in heat treatment and metallurgy.
Gallium (chemical symbol: Ga)
Gallium is a soft, silvery, glass-like metal used primarily in electronic circuits, semiconductors and light-emitting diodes (LEDs). Although very hard and brittle as a solid, gallium melts near room temperature. It has one of the largest liquid ranges of any metal – with a melting point of 85.57°F (29.76°C) and a boiling point of 3999°F (2204°C). As a result, this unusual element is used in high-temperature thermometers. It is also commonly used in pharmaceuticals and nuclear medicine tests.
First postulated by pioneering Russian chemist Dmitri Mendeleyev in 1871, he predicted gallium’s properties and its location below aluminum on the periodic table. He named the hypothetical element eka-aluminum.
Gallium was discovered spectroscopically in 1875 by the French chemist Paul-Émile Lecoq de Boisbaudran. He had extracted several milligrams of gallium chloride from a sample of 52 kg of mineral ore. Identified by its characteristic spectrum (two violet lines), de Boisbaudran recognized it as a new element. He later produced pure gallium through the electrolysis of a solution of gallium hydroxide (Ga(OH)3) in potassium hydroxide (KOH). He was a pioneer in the field of spectroscopy, the study of the interaction between matter and electromagnetic radiation, and is also credited with the discovery of the elements samarium (1880), dysprosium (1886) and europium (1890), as well as being the first to isolate gadolinium (1886).
Gallium is an abundant element on earth and is found primarily in combination with zinc and aluminum ores. Most gallium is extracted from the crude aluminum-hydroxide solution of the Bayer process that produces alumina and aluminum. A moderately reactive element, gallium combines with most non-metals at high temperatures and easily alloys with many metals.
Gallium’s most common uses are in the electronics industry. About 95% of all gallium produced is used to make the compound gallium arsenide (GaAs), which is used in microwave and infrared circuits, semiconductors and blue and violet LEDs. Another use of gallium arsenide is to produce high-performance solar panels, such as the ones used on the Mars Exploration Rover (Fig. 2), because they offer higher efficiency and better low-light performance than their silicon counterparts. The compound gallium nitride (GaN) is used as a semiconductor in Blu-ray technology, mobile phones and pressure sensors for touch switches. Gallium is also used in small quantities as a plutonium crystal stabilizer in the plutonium cores of nuclear bombs.
Here are some interesting facts about gallium.
- Atomic number: 31
- Atomic weight: 69.723
- Melting point: 302.91 K (29.76°C or 85.57°F)
- Boiling point: 2477 K (2204°C or 3999°F)
- Density: 5.91 grams per cubic centimeter
- Phase at room temperature: Solid
- Element classification: Metal