Editor's note: The crystal growth process is also called "Ostwaldripening" (Ostwaldripening), that is, in solution, the smaller crystals will be dissolved and deposited on the larger crystals again. Normally, it is not easy to generate helium crystals. Not only does it need to convert liquid helium-4 to the freezing temperature of the solid, but it must also pressurize the liquid helium-4 to at least 25 standard atmospheres. In addition, when the helium crystal grows more than 1 mm, it will be deformed by the action of gravity. Japanese physicists have created a unique way to generate helium crystals up to 10 millimeters long under zero gravity on the plane. This is a breakthrough.
According to the physicist organization network on December 13 (Beijing time), recently, Japanese physicists broke through the laboratory conditions during the study of crystal growth under zero-gravity conditions and used helium-4 supercurrent on the aircraft The liquid produced helium crystals up to 10 mm long, and examined the special kinetics of helium crystals growing under a wider range of conditions, which is impossible for ordinary materials. Related papers were published in the "New Physics Journal" on the same day.
The helium crystal is grown by means of high pressure at a very low temperature of 0.6K (approximately minus 272 ° C) with a super-fluid splash. Superfluid is a kind of quantum state substance. Its properties are like liquid but its viscosity is zero, so it can flow smoothly under high pressure. The superfluid can flow through very small gaps without any frictional resistance.
The crystal growth process is also called "Ostwaldripening" (Ostwaldripening), that is, in solution, the smaller crystals will dissolve and deposit again on the larger crystals. "Osterwald ripening is usually a very slow process and can hardly be seen in larger crystals in a short period of time," said Ryuji Nomura, a leading author of the paper and a professor at Tokyo Institute of Technology. "For ordinary tradition Crystals, it may take thousands of years to form the final fixed shape. Low-temperature helium crystals can reach their final shape in 1 second. Generally, when the helium crystal grows more than 1 mm, it will be deformed due to gravity, which is also The reason why we are doing this experiment on the plane. "
When the plane is flying on a special trajectory, that is, along a parabola, the gravity on the plane is zero. The researchers collaborated with Japan Aviation Research and Development Agency (JAXA) to conduct experiments on a small jet. The aircraft can provide a zero-gravity condition of 20 seconds, and can perform about 8 experiments in a two-hour flight.
They designed a dedicated small refrigerator on the plane with a window to observe the crystal formation. They put a large helium crystal in a high-pressure chamber, shattered it into tiny particles with sound waves, and then poured it into helium-4 superfluid. The smaller particles melted, and the larger ones grew quickly and formed quickly. A 10 mm long independent crystal.
"Helium crystals can grow out of superfluid very quickly, because helium atoms are carried by very sensitive and fast superfluid, and the crystallization process is not hindered. This is an ideal material to study the basic problems of crystal formation, The crystallization speed is extremely fast, "Long Si said. This research helps people understand the basic physical mechanism behind crystal growth and also reveals some phenomena hidden under gravity.
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