Elsevier

Minerals Engineering

Volume 16, Issue 10, October 2003, Pages 921-929
Minerals Engineering

Gallium: the backbone of the electronics industry

https://doi.org/10.1016/j.mineng.2003.08.003Get rights and content

Abstract

Gallium is a silvery blue and soft metallic element that enjoys vast application in optoelectronics (e.g., LED’s), telecommunication, aerospace, and many commercial and household items such as alloys, computers and DVD’s. Albeit that gallium represents a small annual tonnage of material, its important impact as the backbone of the worldwide electronics sector goes unnoticed by the popularity of key base metals such as Cu/Ni/Co and attraction of the platinum group metals. Although gallite is a host mineral, gallium occurrence is associated with aluminosilicates such as bauxite and clays, plus zinc-bearing ores (e.g., sphalerite). Gallium is extracted primarily from the residue obtained during the processing of aluminum and secondly via electrolytic zinc. Other sources include fly ash collected from burning coal. Whilst countries such as Australia, China, Germany, Kazakhstan, Japan and Russia are the main suppliers of primary (i.e., virgin) gallium, France is the largest single source of refined gallium in the world. GEO Chemicals in France accounted for the lion’s share of the world’s annual production of refined gallium in recent years. At present, 60 companies located in 18 countries are actively engaged in the supply of gallium products. The majority of gallium is employed to produce gallium arsenide (GaAS) wafers for the electronics industry. The supply and demand of gallium-bearing products has gradually declined during the past decade. This was mainly attributed to bursting of the technology bubble worldwide while also being subject to swings in market price in relation to purity. The mandate of the paper was to simply pinpoint the salient facts regarding gallium globally and identify applicable sources of information thereby creating an ideal reference document.

Introduction

Gallium was discovered by the French chemist, Paul-Émile Lecoq de Boisbaudran in 1875 after initial spectroscopic discovery then upon isolating the element as a free metal by electrolysis of a solution of gallium hydroxide in potassium hydroxide (Mineral Information Institute, 2003). The French researcher had first observed the principal spectral lines while examining a substance separated from sphalerite. Several years earlier Mendeleyev had predicted the existence of a metal with properties and chemical behaviour similar to aluminum. Some individuals consider that the name gallium was derived from the Latin word for France, “Gallia”. Another theory is that the discoverer perhaps used his own name (Lecoq) and took the Latin translation of a cock which is “gallum”. The soft and silvery blue metal gallium, symbol “Ga” within group 13, has an atomic weight of 69.723, a 1.5 mohs hardness, and a specific gravity (i.e., density) of 5.904 and 6.905 g/cm3 for the solid and liquid phases respectively (Jefferson Lab, 2003). Gallium is a metallic element in Group IIIa of the periodic table. A solid piece of gallium will liquify when placed in ones hand. The 31st element in Dmitri Mendeleyev’s periodic table exhibits an unusually large liquid range of any element and/or metal due its melting point of 302.98 K and boiling point of 2676 K (Gallium, 2003). Gallium has a low vapour pressure even at high temperatures (CRC, 2003). Solid gallium has an orthorhombic crystal structure and displays a conchoidal fracture similar to glass. Gallium can exist in the form of six isotopes of which only two are stable (Chemical Elements, 2003). According to Greber (1989) gallium normally has a valency of three with its compounds while the two stable isotopes are 69Ga (60.4%) and 71Ga (39.6%). Gallium can form many substances such as bromides, chlorides, hydrides, iodides, nitrides, oxides, selenides, sulphides and tellurides (Chemistry, 2003).

The industrial usage of gallium began in the 1940s within the USA upon inception of recovery processes. The metal attracted more interest in the 1970s when it was discovered that gallium combined with elements of group 15 displayed semiconducting properties (Ullmanns, 2002). Apart from cesium, mercury and rubidium, gallium is the only metal which can be in liquid form near room temperatures and hence is suited for high-temperature thermometers (Chemistry, 2003). Since gallium remains in the liquid state over a wide range of temperatures from about 30–2237 °C it is also suited as a lubricant for high-temperature applications (AMM, 2003). Since the metal expands by 3.1% upon solidification, care must be taken with respect to the type of storage container. Solid gallium is less dense than liquid gallium and is characteristic of water which also expands when it freezes. Seeding may be required to initiate solidification since gallium tends to supercool below its freezing point. Consequently, special regulations apply when storing and transporting gallium by conventional carriers such as truck, rail and air. The actual quantity shipped by air freight is limited while gallium must be contained within seven layers of packing in the event of an accident since the structural metal of the aeroplane would be attacked by liquid gallium (Ullmanns, 2002). Both the physical and electrical properties of gallium are strongly anisotropic. A thin oxide coating is characteristic of gallium material since it slowly oxidizes in moist air until formation of a protective film. Although the element is stable with water it reacts vigorously with halogens even at low temperatures. Metallic gallium slowly dissolves in dilute mineral acids and solutions of hydrogen halides in ether. High-purity gallium is slowly attacked by mineral acids (Shaoguian, 2003). The element rapidly dissolves in either aqua regia or concentrated sodium hydroxide in an aqueous medium (Ullmanns, 2002). It also reacts with strong bases and oxidants (Recapture Metals, 2003). Gallium forms a brilliant mirror when it is painted on glass and it wets both glass and porcelain. The element is suited to readily form alloys (e.g., eutectic alloys) with most metals in conjunction with being a component in low-melting alloys. Dental alloys containing 3% gallium are used in dentistry in lieu of mercury. Magnesium gallate featuring divalent impurities (e.g., Mn+2) finds application in commercial ultraviolet-activated phosphor powders (CRC, 2003).

Gallium arsenide (GaAs) and gallium nitride (GaN) are valuable compounds employed in advanced semiconductors for microwave transceivers, DVD’s, laser diodes in compact discs and other electronic applications. The chemical analysis of gallium used to manufacture semiconductors varies from six (6N) to eight nines (8N) purity (i.e., 99.999999%). Metallic gallium is magnetic and an excellent conductor of both heat and electricity (AMM, 2003). Since gallium arsenide (GaAs) is capable of converting electrical power into coherent laser light the compound is a key component of light emitting diodes (LED’s). It is noteworthy that Furukawa Co. Ltd. in Japan is the world’s largest producer of high quality arsenic after increasing output from 9 to 15 tonnes per annum (tpa) at its Iwaki facility (USGS, 2002). Significant capital for new technological development of gallium nitride (GaN) was only invested during the past few years since uses for this compound are not as advanced as for the arsenides. RF Micro Devices (former RF Nitro Communication Inc.) headquartered in Charlotte, NC, operates a dedicated facility for production of GaN used in wafer processing. The modern plant features both class 10 and class 1000 clean rooms and associated systems to fabricate heteroepitaxial structures and power transistors (USGS, 2002). As an example of a complex electronic chip produced for light emitting diodes, AXT, Inc., located in the United States markets high-flux AlInGaN (aluminum/indium/gallium nitride) chips in blue, cyan and green for many applications such as automobiles. These LED’s range from 35 to 350 mW output power rating with varying lumens per watt efficiency. Gallium phosphide is a secondary source for light emitting diodes (ACTED, 2003). Gallium is employed as a doping material for semiconductors and used to manufacture solid-state items such as transistors (Jefferson Lab, 2003).

LED’s consume less than one quarter of the energy required for an incandescent bulb. Minute amounts of gallium are employed in cell phone circuitry while medical applications are being developed at present. Gallium arsenide applications are highly specialized and thereby do not have a substitute. Silicon is acceptable as a substitute of GaAs in solar cells. Photovoltaic cells (PV) are able to directly convert solar power into electrical energy (EECA, 2001). Semiconducting materials such as gallium arsenide and indium phosphide in single crystal form are used in solar cells. Albeit the high cost single crystal GaAs was exclusively used in space exploration, these solar cells with high conversion efficiency are now available for terrestrial applications. An alternate includes amorphous forms comprised of silicon or silicon/germanium alloys. Multi- or polycrystalline substances such as Si, CdTe, CuIn and gallium diselenide provide another alternative source for development of solar cells. Companies engaged in development include BP Solarex (Australia), Canon-Unisolar (USA) and BP Solar (Europe). Organic compounds may be used as substitutes to fabricate liquid crystals in visual displays in LED’s (USGS, 2003). Indium phosphide (InP) may replace gallium arsenide within infrared diodes while helium–neon lasers compete with GaAs in visible diode applications. The enhanced properties of gallium arsenide based analog integrated circuits (IC’s) in defence related applications are preferred in lieu of silicon (Mineral Commodities Summaries, 1992). It is interesting that gallium arsenide solar cells were incorporated within the Hubble space telescope. It was reported that gallium arsenide products account for about 95% of the annual global gallium consumption (Mineral Information Institute, 2003).

A large quantity of gallium chloride (GaCl3) was provided during the construction of the Gallium Neutrino Observatory in Italy to study atomic particles called neutrinos. About 90 tonnes of gallium were used in the experiments to detect solar neutrinos. A neutrino collection system employing heavy water as a media was commissioned in the Sudbury, Ontario, region deep underground to measure these minute invisible particles produced inside the sun during nuclear fusion. Although the toxicity of gallium apparently is of a low order, the element should be handled with care until further data becomes available. The metallic substance may cause skin and eye irritation while some suggest that gallium may cause dermatitis. It is surprising that gallium is used as a replacement for mercury in dental amalgams. To date no respirable hazards have been identified. Consequently, good industrial hygiene is recommended for airborne particulates (MSDS, 2003). Ultra pure gallium of seven nines quality (99.99999%), which has a beautiful appearance, may be commercially supplied at a nominal cost of $3 per gram (Gallium, 2003). Prices for gallium have fallen from a peak of US$70 per ounce to about $32 per ounce due to the worldwide collapse of the tech bubble. As an example, PMC-Sierra Inc., which makes chips for telecommunications equipment, traded above US$200 a share in the year 2000. The stock ended 2002 at US$5.56 and ended June 2003 with an advance equivalent to about a 140% gain (National Post, 2003). Low-purity gallium from China fetched approximately $250 per kilogram during mid-2002 while high-purity material commanded a range of $400–500 per kilogram. July 2003 prices for gallium metal ingots ranged from US$225–450 per kilogram depending upon purity (Market Prices, 2003). The writer plans a companion paper regarding germanium entitled “Worldwide Review of Germanium Processing” as a sequel since this element is closely associated with gallium in nature and interacts as a competitor within the electronics industry.

Section snippets

Sources of gallium

Gallium is considered one of the rarer elements in the Earth’s crust since its concentration is 16 parts per million (ppm). The annual commodity trading of gallium worldwide historically approached 100 metric tonnes. However, the global primary production dropped from 75 to 61 metric tonnes in 2002. As an example of the disparity between suppliers and refiners, crude gallium production in 2001 was 81 tonnes while refined gallium amounted to 107 tonnes. Recycling of gallium scrap accounted for

Recovery methods for gallium

In the Bayer process, gallium is normally recovered in conjunction with aluminum oxide (i.e., alumina). Upon cooling and seeding a solution of sodium aluminate, the alumina trihydrate is crystallized. The gallium hydroxide fraction accumulates in the liquor phase. After concentration of the liquor and adjustment of pH pure gallium may be electrolytically recovered (Gallium, 2002). This extraction technique to recover gallium from an alkaline medium was suggested in 1937 by V.M. Goldschmidt. The

Discussion

On a world basis analysts estimated an annual growth rate of 6.5% per annum for gallium to reach 350 tonnes. However, Roskill (2002) forecast a more sustainable annual growth rate in the range of 8–10% which should result in a global output of 290 metric tonnes by the year 2008. A surge in demand for consumer items such as mobile phones and white LED’s have the potential to generate double digit growth rates. Wireless communications appear to be the main sector attributing growth in gallium

Acknowledgements

The author thanks Dr. A.M. Alfantazi, a professor at the University of British Columbia in Canada, for his contribution to this work and others by supplying technical articles and texts from the university library service. Akram’s assistance was welcomed in proof reading and processing the manuscript with an established publisher.

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