Friday is here, and the 'A Taste of Science for the Weekend' corner is back — number 72.
This time: why gallium is a particularly fascinating element, the challenges of producing it, and why it's dangerous to aircraft.
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Gallium is a silvery element resembling aluminum, with several properties that make it truly remarkable.
It becomes liquid at just under 30 degrees Celsius, yet boils into vapor only above 2,200°C — making it the element with nearly the widest liquid-state range of any element (second only to neptunium).
For this reason, it is now used as a mercury substitute in thermometers.
Gallium is mixed with tin and indium to produce an alloy that remains liquid across virtually any temperature a thermometer would measure.
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Gallium's most interesting applications emerge when it is combined with other elements.
Gallium nitride is made from a mixture of gallium and nitrogen, and its key property is a wide bandgap.
This means the material does not release electrons in an uncontrolled manner at high temperatures and voltages — a fact that makes it highly energy-efficient, since it doesn't waste energy as heat.
For this reason, it can be found in modern laptop chargers, energy converters in electric vehicle batteries, and power supplies for server farms.
Gallium nitride is also the basis for blue and white LED lights, and because it is radiation-resistant, it is ideal for use in satellites as well.
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Gallium arsenide is gallium combined with arsenic.
Its key property is that it allows electrons to flow through it with great efficiency, with low resistance and minimal electromagnetic interference in its surroundings.
It is used for signal processing at exceptionally high speeds and with low noise — for example, in cellular communication signal amplifiers and military radar systems.
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The great challenge with gallium is that it cannot be found in nature in its pure form.
In fact, its existence was predicted from the structure of the periodic table several years before it was first observed in a laboratory.
Gallium is refined as a byproduct of the aluminum production process, in very small quantities.
Bauxite ore contains both aluminum and gallium. The ore is soaked in a strong base (sodium hydroxide), which reacts with the aluminum and gallium and converts them into solution, while the remaining metals stay solid and sink to the bottom.
The solution is then carefully adjusted so that the aluminum crystallizes into a solid and precipitates out, and from the remaining gallium solution, 99.99% pure gallium is extracted via electrolysis.
For the semiconductor industry, this level of purity is insufficient, and the gallium must be further refined through a complex process until 99.99999% pure gallium is obtained.
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A container of gallium leaking in an aircraft's cargo hold would be absorbed into the plane's aluminum body, replacing some of aluminum's strong atomic bonds with gallium's weaker ones — thereby creating a crack that would propagate rapidly and cause the aircraft to break apart in mid-air.
For this reason, gallium is classified as a dangerous material for air transport, despite being neither particularly toxic nor flammable.
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Gallium is a critical material for a range of civilian and military technologies, and is used in cases where silicon cannot handle the required temperatures or clock speeds.
The major challenge is that producing it requires enormous, energy-intensive manufacturing plants that generate millions of tons of aluminum — aluminum that must then be sold to traditional industries such as construction.
For this reason, it is considered a rare and expensive metal, largely controlled by China's massive aluminum production facilities, which has made it a significant flashpoint in the geopolitical rivalry between China and the United States.
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In the video: an RTX facility manufacturing high-quality gallium nitride for military radar systems.
Shabbat Shalom 😊
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