Supercooled water can stay liquid far belowits normal freezing point

                                     

Very-sub-zero water

Supercooled water can stay liquid far below its normal freezing point

Cold water has hit a new low. Droplets can avoid freezing — at least for a short while — at

temperatures as low as –46° Celsius (–50.8° Fahrenheit), a new study shows.

“It’s a world record, and it’s hard to imagine it will ever fall,” H. Eugene Stanley told Science

News. This physicist at Boston University, in Massachusetts, did not take part in the new study.

Water's normal freezing point is 0° C (32° F). But under some conditions, even colder water can

remain liquid. It’s something scientists have long known. Such “supercooled” water stays liquid as

long as it doesn't touch anything, such as a dust particle or an ice cube tray. Once it does, it turns

to ice.

The previous record for supercooled water was -38° C (-36.4° F). However, scientists suspected

water could go colder still.

At really low temperatures, water’s behaviour turns quirky. Both its ability to absorb heat — and to

be squished — change at extreme lows.

“If you understand water there, you understand it everywhere,” Anders Nilsson told Science News.

He’s the new study’s leader. A physicist, he works at Stanford University and the SLAC National16/8/2014 Very-sub-zero water | Science News for Students

       Nilsson’s team used a small squirt gun to fire droplets of water into a vacuum chamber. The

droplets were as small as red blood cells. As each droplet sped through the chamber, some of its

molecules evaporated, or turned to gas. That process released heat. Each time this happened,

the droplet grew a bit colder.

Using a laser, the researchers fired X-ray pulses at the droplets. Those X-rays traveled right

through each droplet. By measuring changes in the X-ray pulses as they passed through a

droplet, the scientists could calculate the water’s temperature.

And a droplet’s temperature fell by as much as 10° C every millisecond, the tests showed. But the

drops could remain at the record low temp for only a millisecond. Then they turned to ice. The

scientists shared their findings June 19 in Nature.

The X-rays also destroyed each droplet as they took its temperature. “It’s like a hit-and-run,”

Nilsson explained to Science News.

Chemical engineer Pablo Debenedetti from Princeton University in New Jersey did not work on

the new study. He notes that the droplets remained liquid far longer than some researchers had

predicted. That’s why, he concludes, “It’s a major experimental accomplishment.”