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article imageJapanese physicists grow helium crystals in zero gravity

By Angela Norwood     Dec 13, 2012 in Science
Helium crystals are grown under zero gravity conditions by a team of Japanese physicists with the help of a phenomenon called parabolic flight.
A team of Japanese physicists have grown helium crystals in zero gravity conditions. The experiments took place in a small jet under parabolic flight conditions. During parabolic flight, zero gravity was achieved for a duration of 20 seconds. During the two-hour flight, approximately eight experiments were conducted.
Using low temperatures and high pressures, the crystals were grown and splashed with a superfluid. Superfluids are a form of quantum matter which contain zero viscosity and maintain the behavior of a fluid, flowing friction-free through miniscule gaps.
"Helium crystals can grow from a superfluid extremely fast because the helium atoms are carried by a swift superflow, so it cannot hinder the crystallization process. It has been an ideal material to study the fundamental issues of crystal shape because the crystals form so quickly,” says lead author Professor Ryuji Nomura from The Tokyo Institute of Technology.
Nomura states that helium crystals grow from superfluids rapidly because the atoms are carried by a “swift superflow” that does not interfere with crystallization. He adds that because the crystals form so fast, superfluids are an “ideal material” to study crystal shape.
"It can take thousands of years for ordinary classic crystals to reach their final shape; however, at very low temperatures helium crystals can reach their final shape within a second. When helium crystals grow larger than 1 mm they can be easily deformed by gravity, which is why we did our experiments on a plane,” says Nomura.
A small refrigerator fitted with observation windows was taken on the plane. A high-pressure chamber was used to hold large crystals which were then crushed into small pieces with an acoustic wave. A helium-4 superfluid was then applied to the crystal pieces. After being crushed, the tiny crystals were melted, causing larger crystals to grow quickly, with one surviving 10 mm crystal. The other crystals melted in seconds.
The process under which the crystal was grown is called Ostwald ripening. This phenomenon can be seen on ice cream when it’s been in the freezer too long. Large ice crystals form over time, a process commonly known as “freezer burn.”
"Ostwald ripening is usually a very slow process and has never been seen in such huge crystals in a very short period," says Nomura.
The results of the experiments were presented December 13 in the German Physical Society’s New Journal of Physics and the Institute of Physics.
Researchers believe the results of the helium crystal experiments may uncover the fundamentals behind crystal development without the hindrance of gravity.
More about Physics, helium crystals, Zero gravity
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