Gallium

• 1. Introduction

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  Gallium is a silvery metal that can vanish in a person's hand. Its melting point is 29.7646 degrees Celsius, and the human body sits at 37. Chemists have turned this into a practical joke. They fashion spoons from the metal, which looks much like its lighter cousin aluminium, and serve tea to unsuspecting guests. The spoons melt in the hot cup.

  Behind the prank is the element with atomic number 31 and the symbol Ga. It has no known natural role in biology, and it does not exist as a free element anywhere in the Earth's crust. Yet it now sits at the heart of modern electronics.

  This documentary asks how a metal could be described on paper before anyone had held it. It asks why gallium behaves so differently from its neighbours on the periodic table. And it asks how a trace by-product of other metals' ores became the subject of a global contest over who controls the supply.

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• 2. A Predicted Metal

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  In 1871, the Russian chemist Dmitri Mendeleev left a gap in his periodic table for an element no one had found. He called it eka-aluminium, after the slot it would fill. He forecast its density, its melting point, the character of its oxide and the bonding in its chloride. He expected it to turn up under a spectroscope, to dissolve slowly in both acids and alkalis, and to ignore air. He also expected its sulfate to form alums. Every one of these predictions later proved accurate.

  In 1875, in Paris, the French chemist Paul-Émile Lecoq de Boisbaudran found it. He was examining a sample of sphalerite when he saw a spectrum with two violet lines. Later that year he produced the free metal by passing an electric current through the hydroxide dissolved in a potassium hydroxide solution.

  Mendeleev's forecast for atomic weight was about 68, and the real figure is 69.723. His forecast for the density of the oxide was 5.5 grams per cubic centimetre, against an actual 5.88. Only one number clashed badly. Lecoq first measured the density of the metal as 4.7, the single property that failed to match.

  Mendeleev wrote to him and suggested that he measure it again. The new value came out at 5.9, exactly what Mendeleev had predicted.

  Lecoq named the element gallia, from the Latin Gallia, meaning Gaul, an old name for his native France. Later, a rumour spread that he had also named it after himself. Le coq is French for the rooster, and the Latin word for rooster is gallus. The pun was of a kind favoured by 19th century men of science. In an 1877 article, Lecoq denied the conjecture.

  The new metal then waited for its real career. Until the age of semiconductors arrived, it served mainly in high-temperature thermometers and in alloys prized for stability or an easy melt.

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• 3. An Anomalous Metal

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  The International Temperature Scale of 1990 uses the melting point of gallium as one of its formal reference points. The scale was established by the International Bureau of Weights and Measures. The US National Institute of Standards and Technology prefers a slightly different marker, the triple point, at 302.9166 kelvin.

  Only four non-radioactive metals are liquid at or near room temperature: caesium, rubidium, mercury and gallium. Caesium and rubidium are violently reactive, and mercury is highly toxic. Gallium is neither, which is why it can fill high-temperature thermometers made of metal and glass. It also has one of the largest liquid ranges of any metal. Its boiling point of 2676 kelvin is nearly nine times its melting point on the absolute scale, the greatest such ratio of any element. Unlike mercury, it also has a low vapour pressure at high temperatures.

  Liquid gallium has an awkward habit. It wets glass and skin, along with most other materials. Quartz, graphite, gallium oxide and PTFE are the exceptions. Painted onto glass, it makes a brilliant mirror. Samples are usually shipped in polyethylene packets inside other containers. That also guards against a hazard of freezing. The volume grows by 3.10% as the liquid turns solid, and a rigid container can rupture. Water, silicon, germanium, bismuth, lead and plutonium share this trait of being denser as liquids.

  Gallium can also refuse to freeze at all. Micrometre-sized droplets can be cooled to as low as 150 kelvin and stay liquid. Nanoparticles remain liquid below 90 kelvin. Seeding with a crystal helps freezing begin. In another trick, liquid gallium seeps into cracks and grain boundaries of aluminium and steel, causing a sharp loss of strength called liquid metal embrittlement.

  The explanation starts in the solid. Its stable phase, called Ga-I, is a complex orthorhombic structure with eight atoms in the conventional unit cell. Each atom has only one nearest neighbour, at a distance of 244 picometres. The other six neighbours sit 27, 30 and 39 picometres farther away, in pairs. The bond between the closest two is covalent, so pairs of atoms called Ga2 dimers are the building blocks of the crystal. This helps explain a low melting point compared with its neighbours aluminium and indium. The arrangement closely resembles that of iodine. In the liquid, those dimers break apart, and each atom is surrounded by 10 others instead of the 11-12 typical of liquid metals.

  Squeezing the metal reveals even more. Gallium has one of the most complex phase diagrams of any elemental metal. Compressed to 0.5 gigapascals at room temperature, the solid melts, which is a negative melting curve. At 2 gigapascals the liquid crystallizes into a simple body-centred tetragonal phase called Ga-III. Compressing Ga-I below 273 kelvin yields Ga-II, with 103 atoms in its orthorhombic cell. At around 120 gigapascals a face-centred cubic phase, Ga-IV, finally appears.

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• 4. Light and Chips

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  The 1960s brought the arrival of gallium arsenide as a direct bandgap semiconductor, and it changed the metal's fortunes. By the late 1960s the electronics industry was using gallium on a commercial scale to make light-emitting diodes, photovoltaics and semiconductors. The metals industry used it to lower the melting point of alloys.

  Blue light proved far harder. The first blue gallium nitride LEDs were developed in 1971-1973, but they were feeble. In the early 1990s Shuji Nakamura combined gallium nitride with indium gallium nitride and built the modern blue LED. It became the basis of the ubiquitous white LED, which Nichia commercialized in 1993. Nakamura and two other Japanese scientists shared a Nobel Prize in Physics in 2014 for this work.

  Semiconductors now account for 98% of commercial demand for gallium. In 2022-44% of world use went to light fixtures and 36% to integrated circuits. Photovoltaics and magnets took about 7% each. Gallium arsenide alone makes up 95% of annual global consumption. It was worth $7.5 billion in 2016, with 53% of that tied to cell phones and 27% to wireless communications. The rest went to automotive, consumer, fibre-optic and military uses. The jump came from 3G and 4G smartphones, which use up to 10 times as much gallium arsenide as older models.

  Optoelectronic devices built on these compounds had a market of $15.3 billion in 2015 and $18.5 billion in 2016. Aluminium gallium arsenide drives high-power infrared laser diodes. Gallium nitride diode lasers at 405 nanometres supply the violet light for higher-density Blu-ray drives. Gallium nitride also appears in cable television transmission, wireless infrastructure, power electronics and satellites.

  In space, multijunction solar cells made from thin films of gallium arsenide and related compounds power satellites. The Mars Exploration Rovers run on triple-junction gallium arsenide cells grown on germanium.

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• 5. Alloys and Odd Jobs

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  The alloy Galinstan takes its trade name from gallium, indium and stannum, the Latin word for tin. It melts at -19 degrees Celsius, or -2.2 degrees Fahrenheit. That figure may actually be a freezing point lowered by supercooling. Galinstan is a room-temperature liquid used in medical thermometers as a non-toxic alternative to mercury. The same family of alloys can cool computer chips in place of water, and can replace thermal paste in high-performance computing.

  Dentists have evaluated gallium alloys as substitutes for mercury amalgams, but they have not won wide acceptance. Liquid alloys of mostly gallium and indium have been found to turn gaseous carbon dioxide into solid carbon. Researchers are exploring them for carbon capture. Their high surface tension and deformability also allow actuators that move by controlling surface tension, and researchers have shown them working as artificial muscle in robotics. Where the wetting of glass is unwanted, as in Galinstan thermometers, a transparent layer of gallium oxide protects the glass.

  The plutonium in nuclear weapon pits is stabilized in its delta phase, and made machinable, by alloying it with gallium.

  Underground in Russia, the Baksan Neutrino Observatory holds possibly the largest amount of pure gallium ever gathered in one place. The detector of the SAGE experiment contains 55-57 tonnes of liquid gallium, about 9 cubic metres. In the early 1990s, the GALLEX detector in an Italian mountain tunnel held 12.2 tons of watered gallium-71. Solar neutrinos turned a few atoms of gallium-71 into radioactive germanium-71, and these were counted. The result showed that the flux of solar neutrinos was 40% lower than theory predicted. This solar neutrino problem stayed unexplained until better detectors and theories came along.

  Smaller jobs abound. A focused beam of gallium ions was used to carve Teeny Ted from Turnip Town, the world's smallest book. Gallium also serves as an additive in glide wax for skis. Where gallium breaks the protective oxide layer on aluminium, water can react with the metal to make hydrogen gas. Materials scientists speculate that its properties could suit flexible and wearable devices.

  In the sea, advances in trace testing have found dissolved gallium in the Atlantic and Pacific Oceans and in the Beaufort Sea. Pacific concentrations typically run 4-6 picomoles per kilogram at depths above about 150 metres. Because gallium is chemically similar to aluminium, it can trace aluminium and also the dust that delivers iron. In the northwest Pacific, low gallium in subpolar surface waters points to little dust input. That may explain the region's high-nutrient, low-chlorophyll waters.

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• 6. The Iron Impostor

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  Researchers noticed that 67Ga citrate, injected into tumor-bearing animals, collected at the tumor sites. That observation launched interest in gallium as medicine. The reason is that gallium ions behave in the body much like iron(III), and the body handles them in similar ways. The ions gather in areas of inflammation, such as infection, and in areas of rapid cell division.

  That behaviour powers the nuclear medicine technique called the gallium scan. The radioactive isotope gallium-67 has the longest half-life among the radioactive isotopes, at 3.2617 days. The exact salt does not matter. Gallium has 30 known isotopes, ranging in mass number from 60 to 89, but only two are stable and natural. Gallium-69 makes up about 60.1% of natural gallium, and gallium-71 the remaining 39.9%.

  Gallium-68 has a half-life of about 68 minutes. This positron emitter is used in PET-CT scans when linked to drugs such as DOTATOC and DOTA-TATE. Those compounds help investigate neuroendocrine tumors and their metastases, including some lung cancers. It comes from gallium-68 generators, where it is eluted from germanium-68, a synthetic radioisotope.

  As treatment, gallium nitrate, sold as Ganite, is given intravenously for hypercalcemia linked to tumors spreading to bone. It is thought to interfere with osteoclast function, and may work when other treatments have failed. Clinical trials have shown gallium nitrate to be active against non-Hodgkin's lymphoma and urothelial cancers. A newer generation includes tris(8-quinolinolato)gallium(III), known as KP46, and gallium maltolate. Gallium maltolate is a highly absorbable oral form. It is anti-proliferative to cancer cells and to some bacteria that accept it in place of ferric iron.

  Bacteria such as Pseudomonas that mistake gallium for iron(III) suffer for it. Iron is redox-active, so it passes electrons during respiration, while gallium is redox-inactive. The ions interfere with respiration and the bacteria die. A compound called MR045 is selectively toxic to malaria parasites resistant to chloroquine. Both it and chloroquine work by blocking crystallization of hemozoin, a waste product of the parasites' digestion of blood.

  Metallic gallium is not toxic, though several of its compounds are. In large injected doses, the Ga3+ ion forms an insoluble hydroxide, and its precipitation caused kidney damage in animals. At lower doses it is tolerated well and leaves mostly through urine. Excretion has two phases, with biological half-lives of 1 hour and 25 hours. Inhaled gallium oxide particles are probably toxic.

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• 7. A Metal Without Mines

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  At 16.9 parts per million, gallium is the 34th most abundant element in the Earth's crust. That is comparable to lead, cobalt and niobium. Yet unlike those, it never forms ore deposits of its own above 0.1% by weight. A rare mineral called gallite, CuGaS2, is too scarce to serve as a source. Gallium shows no strong enrichment in the processes that build most ore deposits. It sits instead at trace levels in zinc ores, and at around 50 parts per million in aluminium ores.

  Bauxite, the chief ore of aluminium, supplies most of it. The US Geological Survey estimates that known reserves of bauxite and zinc ores hold more than 1 million tons of gallium. Some coal flue dusts carry less than 1% by weight, and in the past certain coals were an important source. None of this can be mined independently, so supply depends on how much bauxite, zinc ore and coal is extracted for other reasons.

  In the Bayer process, which turns bauxite into alumina, gallium builds up in the sodium hydroxide liquor. The most recent way to pull it out uses ion-exchange resin. At a typical feed concentration of 50 parts per million, only about 15% of the gallium is extractable. The rest ends up in the red mud and aluminium hydroxide streams. Electrolysis then yields the metal. For chips, zone melting or the Czochralski process purifies it further, and purities of 99.9999% are routinely available.

  Because it is a by-product, the useful measure is supply potential, the amount economically extractable each year. Recent estimates put it at a minimum of 2,100 tons per year from bauxite and 85 from sulfidic zinc ores. Coal could add potentially 590. Actual production was 375 tons in 2016, so output could rise without large cost increases. Low-grade gallium averaged $120 per kilogram in 2016 and $135-140 in 2017.

  In 2017, world production of low-grade gallium was about 315 tons, a drop of 15%. The leading producers were China, Japan, South Korea, Russia and Ukraine. Germany had stopped primary production the year before. High-purity output was about 180 tons, against a capacity of 320.

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• 8. The Chokehold

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  China produced about 250 tons of low-grade gallium in 2016 and about 300 tons in 2017. It also accounted for more than half of global LED production. By July 2023 its share of gallium production stood between 80% and 95%. The Critical Raw Materials Alliance reported in August 2023 that China made 80% of the world's gallium and 60% of its germanium. China began restricting exports of both, as a so-called chip war with the United States intensified. Both materials are key to the semiconductor industry.

  By 2024, the US Geological Survey put China's share of low-purity gallium at 98 percent. Global output had crept up from several tens of tons per year in the 1970s to pass 100 tons around 2010. It then accelerated, reaching about 450 tons per year by 2024.

  In July 2025, the Center for Strategic and International Studies, a US think tank, wrote: "China is increasingly weaponizing its chokehold over critical minerals amid intensifying economic and technological competition with the United States." It added that gallium, which is crucial to defense supply chains and new energy technologies, had been at the front line of that strategy.

  Also in 2025, Rio Tinto and Indium Corporation partnered to mine the first primary gallium in North America. For a metal long recovered only as a by-product, the project was a notable break from the pattern.

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