Marvellous Metals – Meet Gallium
6061 aluminium plate, 7075 aluminium round bar, brass round bar cz121, aluminium extrusion, it’s all familiar stuff. But look deeper and science has discovered some very odd metals indeed, with very strange properties. Let’s explore the ins and outs of Gallium.
Gallium comes with the atomic number 31. When solid it’s a blue-grey colour, and when very pure it’s silvery. You can’t find the pure metal naturally and it can’t be extracted from the earth. It’s actually a by-product of iron pyrites, zinc blende, germanite, and bauxite. The metal is soft enough to cut with a knife and has a very low melting point of 30C. It expands when solid and supercools very well. Solid at room temperature, when you heat it slightly and it comes into contact with cesium, rubidium and mercury, it turns into a liquid.
Gallium is widely used in Blue-ray tech, to make blue and green LED lights, in mobile phones, and in the sensors used in touch switches. It is useful in high-temperature thermometers, barometers, and in pharmaceuticals. And it sits at the heart of some of the most unusual and exiting scientific developments in recent years.
Weird metals and their properties – Liquid Gallium
In 2018 scientists discovered that zapping liquid Gallium makes it move in a way that powers wheels. The team, from the University of Wollongong in Australia, placed a drop of the liquid metal inside a 5cm diameter wheel made from plastic, very like a car tyre. A pair of electrodes sat in front and behind a platform that slid along the wheel’s walls. When switched on the voltage they created pushed the drop of metal towards one of the electrodes, like a hamster on a wheel. The idea is to use the discovery to power robots that can travel like tumbleweed over difficult terrain.
Also in 2018, scientists made Gallium droplets that can beat like tiny hearts, with the potential to eventually power artificial muscles.
More fun with Gallium – Making bendy audio speakers
In 2019 scientists made a bendy audio speaker out of the liquid heavy metal Gallium in a bid to bring the next generation of wearable technology closer. A team at Korea University developed a loudspeaker that plays a range of sounds even when you bend it. It was made using a couple of strips of Gallium in a liquid electrolyte solution. Under that there were two strips of copper transmitting an alternating current. The current flowing through the copper distorted the gallium alloy, and the fast expansion and contraction of the liquid strips generated sound.
A liquid metal alloy less dense than water – It’s Gallium again
Injecting the material with glass beads could make it perfect for manufacturing light exoskeletons and transformable robots that change with the temperature.
Liquid metal alloys don’t go solid at room temperature. They’re eutectic too, melting at a lower temperature than the melting points of the metals they’re made from. In 2020 a team at China’s Tsinghua University mixed pure gallium with indium to make a new liquid metal alloy with a melting point of just 15.7°C. Decreasing the density of the material with air-filled glass beads cut the gallium-indium alloy’s density by an impressive 97%. The resulting material conducts electricity very well and can be both reformed and shaped without breaking.
Also in 2020, electronic blood vessels made from a blend of metal and plastic were created, intended to eventually replace damaged arteries in people with cardiovascular disease. A team at the Southern University of Science and Technology in Shenzhen, China, printed a layer of liquid metal ink containing Gallium and Indium onto a flexible membrane where it acted like an electrode. Then they rolled it up to make a tiny 2mm wide tube
When they sent electrical pulses to the electrode it made live endothelial cells from the inside of blood vessels collect and stick to the inside of the vessel. The idea is that these vessels will be less likely to lead to blood clots than other treatments.
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