A group of physicists from Japan have taken to the skies to grow crystals under zero gravity.
Presenting their results today, 13 December, in the Institute of Physics and German Physical Society's New Journal of Physics, they've overcome the limitations of the laboratory to examine the peculiar dynamics of helium crystals on a much larger scale than can be achieved with ordinary materials.
Their results could help researchers reveal the fundamental physics behind the development of crystals, whilst also unveiling phenomena that are usually hidden by gravity.
The helium crystals were grown using high pressures, extremely low temperatures (0.6K/-272°C) and by splashing them with a superfluid - a state of quantum matter which behaves like a fluid but has zero viscosity, meaning it has complete resistance to stress. Superfluids can also flow through extremely tiny gaps without any friction.
Footage from their zero-gravity flight, which also shows the formation of the crystals close up, can be viewed here.
Lead author of the study, Professor Ryuji Nomura from the Tokyo Institute of Technology, said: "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.
"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."
The experiments were carried out in a small jet plane in cooperation with the Japan Aerospace Exploration Agency (JAXA). When on a specific trajectory, known as parabolic flight, the jet plane provided zero gravity conditions for 20 seconds. Around eight experiments were performed during a two-hour flight.
A small, specially designed refrigerator was taken on board the plane, which was fitted with windows so the formation of the crystals could be observed. Large helium crystals were placed at the bottom of a high-pressure chamber and then zapped with an acoustic wave to crush them into tiny pieces; they were then splashed with a helium-4 superfluid. Once crushed, the smaller crystals were melted and larger ones grew rapidly until only one 10 mm crystal survived.
The crystal grew under a process known as Ostwald ripening. This is commonly seen in ice cream when it becomes gritty and crunchy as it gets older - larger ice crystals begin to grow at the expense of smaller ice crystals.
"Ostwald ripening is usually a very slow process and has never been seen in such huge crystals in a very short period," continued Professor Nomura.
Notes to Editors
1. For further information, a full draft of the journal paper or contact with one of the researchers, contact IOP Press Officer, Michael Bishop:
Tel: 0117 930 1032
Ripening of 4He crystals by acoustic waves with and without gravity
2. The published version of the paper "Ripening of 4He crystals by acoustic waves with and without gravity" (Takahashi T et al 2012 New J. Phys. 14 123023) will be freely available online from Thursday 13 December.
New Journal of Physics
3. New Journal of Physics publishes across the whole of physics, encompassing pure, applied, theoretical and experimental research, as well as interdisciplinary topics where physics forms the central theme. All content is permanently free to read and the journal is funded by an article publication charge.
4. IOP Publishing provides publications through which leading-edge scientific research is distributed worldwide. IOP Publishing is central to the Institute of Physics (IOP), a not-for-profit society. Any financial surplus earned by IOP Publishing goes to support science through the activities of IOP. Beyond our traditional journals programme, we make high-value scientific information easily accessible through an ever-evolving portfolio of community websites, magazines, conference proceedings and a multitude of electronic services. Focused on making the most of new technologies, we're continually improving our electronic interfaces to make it easier for researchers to find exactly what they need, when they need it, in the format that suits them best. Go to http://ioppublishing.
The Institute of Physics
5. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 45,000, working together to advance physics education, research and application. We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
The German Physical Society
6. The German Physical Society (DPG), with a tradition extending back to 1845, is the largest physical society in the world with more than 59,000 members. The DPG sees itself as the forum and mouthpiece for physics and is a non-profit organisation that does not pursue financial interests. It supports the sharing of ideas and thoughts within the scientific community, fosters physics teaching and would also like to open a window to physics for all those with a healthy curiosity.