The existence of gallium was predicted by Dmitri Mendeleev, inventor of the periodic table. His table had a gap below aluminum where a new metal ought to reside. In 1875, French chemist Lecoq de Boisbaurdran detected an unknown element spectroscopically in a zinc ore. He isolated the metal later that year and named it gallium after his native country ("Gaul" in Latin).
Mining and Production
Gallium only occurs as a trace element in ores of other metals. It can be extracted from bauxite (aluminum ore), coal, zinc ore, and other minerals. Bauxite is the most common source.
Gallium can be extracted from mineral ores by conventional industrial chemical means. Most gallium goes for use in the semiconductor industry. Therefore, standard extraction is often followed by melting and crystalizing the gallium, which produces the very high purity (99.9999%) required.
The principal gallium producers are China, Germany, Japan, and Ukraine. World production in 2014 was estimated to be 440 tonnes.
Properties and Uses
Gallium is a silvery metal with an extremely low melting point; in fact, it melts in the hand (30°C). Gag spoons were once available for stirring coffee – the bowl of the spoon would melt in the cup, leaving one holding the stem.
Gallium has several properties that make it inconvenient to store. It wets glass, it expands when it freezes like water, and it leaks into the crystalline structure of other metals. Viewed another way, this last property makes it a useful component of metal alloys. For example, gallium is a component of low-melting-point alloys such as solder.
Gallium can replace toxic mercury in high-temperature thermometers.
The two largest applications of gallium by far are in photoelectric devices and electronics. Gallium arsenide is a high-performance semiconductor used in light-emitting diodes (LEDs, below) and integrated circuits. Gallium nitride is the key component of blue LEDs used in Blu-ray DVD players.
Gallium is used in solar cells in the form of gallium arsenide, indium gallium arsenide, and other compounds. Silicon is cheaper, but pure crystalline silicon was in short supply for several years. Gallium is also a component of new copper indium gallium diselenide solar thin films.