Supercooled water riddle is solved

2011-11-24 08:09

Paris - At what temperature does water have to freeze?

The answer: Not necessarily at 0°C.

Water can exist in liquid form well below this threshold, notably in a so-called "supercooled" state that is well into the minus zone.

The reason: if you want to form ice from liquid water, you need a "seed" of ice from the liquid - a crystal that becomes the nucleus around which other crystals form.

But in very pure water, which has no contaminants or particles around which the critical nucleus can form, this can be difficult to achieve because of the unusual thermodynamics of H20.

Until now, supercooled water has been measured right down to around -41°C, although scientists have long suspected that the temperature at which it unconditionally has to freeze is somewhat lower.

They have been unable to find out for sure because ice crystallises so fast at this temperature that it is impossible to measure accurately the properties of the remaining liquid.

Chemists Valeria Molinero and Emily Moore at the University of Utah used computer modelling to simulate the behaviour of supercooled water at the microscopic level.

Their programme mimicked what would happen when 32 768 water molecules were cooled, factoring in the heat capacity of water, its density and compressibility.

After thousands of computer hours, the answer came back.

The temperature at which water absolutely must freeze, no questions asked, is -48°C.

When water approaches this temperature, it becomes less dense and becomes easier to compress and its structure changes.

As a result, each molecule links up loosely with four others to form tetrahedron, or pyramid-like, shapes.

The investigators describe this as an "intermediate ice" that is halfway between the structure of the liquid and halfway between the full structure of ice.

The research, published on Wednesday in the British journal Nature, is more than an exercise in scientific curiosity.

Atmospheric scientists delving into global warming need to know temperatures and rates at which water freezes and crystallises into ice. Water as chill as -40°C has been found in clouds.

"You need that to predict how much water in the atmosphere is in the liquid state or crystal state," Molinero said. "This is important for predictions of global climate."

Read more on:    nature  |  france  |  research  |  climate change  |  water
NEXT ON NEWS24X

Read News24’s Comments Policy

24.com publishes all comments posted on articles provided that they adhere to our Comments Policy. Should you wish to report a comment for editorial review, please do so by clicking the 'Report Comment' button to the right of each comment.

Comment on this story
49 comments
Add your comment
Comment 0 characters remaining
 

Inside News24

 
 

Zuma: Pray for peaceful polls

President Jacob Zuma has asked members of the Universal Church of the Kingdom of God to pray for peaceful elections on 7 May.

 
 

Latest elections multimedia

Why Jack Parow wants you to vote on 7 May
The ad the SABC doesn't want to air
Elections 2014 in one cartoon
This year's election posters
 
Traffic
Lottery
 
  • Friday Grabouw - 11:32 AM
    Road name: N2 Eastbound
    DELAYS between Sir Lowrys Pass and Grabouw
  • Friday Cape Town - 10:14 AM
    Road name: M3 Inbound
    EVENT - left lane closed between Rhodes Avenue and UCT
 
More traffic reports...
 

Jobs in Cape Town [change area]

Property [change area]

Travel - Look, Book, Go!

Escape winter, head to Mauritius

Escape winter by spending 7 nights in Mauritius' tropical bliss from R13 215 per person sharing. Includes return flights, airport transfers and accommodation. Book now!

Kalahari.com - shop online today

Get many eggs in one basket!

Gaming bundles: 2 Super Hits games for R99, 3 Disney games for R99 and more + exclusive accessory bundles only available on kalahari.com. While stocks last. Shop now!

25% off bestselling books!

The Real Meal Revolution by Tim Noakes, Jeffrey Archer’s Be Careful What You Wish for, Man’s Search for Meaning by Victor E. Frank and many more titles. Shop now!

Up to 25% off electronics

Buy top electronics and save up to 25%. Such as kalahari.com’s 1# selling product the gobii eReader, Patriot X Porter flash drive, Asus Nexus 7” 3G tablet, Samsung Galaxy SIII, Lenovo G580 Notebook and many more. Shop now!

DStv HD PVR Decoder now R949

The DStv HD PVR Decoder has further revolutionised the television experience with lifelike viewing, sharper images, more vibrant colours and precision picture quality. Now R949, save R550. Offer valid while stocks last. Shop now!

Up to 30% off appliances & homeware

Save up to 30% on appliances and homeware this Easter! Offer valid while stocks last. Shop now.

OLX Free Classifieds [change area]

Samsung Galaxy s4

Mobile, Cell Phones in South Africa, Western Cape, Cape Town. Date October 24

Best bargain in big bay

Real Estate, Houses - Apartments for Sale in South Africa, Western Cape, Cape Town. Date October 25

VW Golf 6, 1.6 Trendline (Excellent condition)

Vehicles, Cars in South Africa, Western Cape, Cape Town. Date October 25

BlackBerry Curve 9360

The BlackBerry Curve 9360 smartphone comes preloaded with Blackberry OS7...

From R1595.00

I'm shopping for:

Horoscopes
Aquarius
Aquarius

Self-indulgence may be strong today. You may want to enjoy yourself to the fullest and share it with those that make you feel...read more

There are new stories on the homepage. Click here to see them.
 
English
Afrikaans
isiZulu

Hello 

Create Profile

Creating your profile will enable you to submit photos and stories to get published on News24.


Please provide a username for your profile page:

This username must be unique, cannot be edited and will be used in the URL to your profile page across the entire 24.com network.

Settings

Location Settings

News24 allows you to edit the display of certain components based on a location. If you wish to personalise the page based on your preferences, please select a location for each component and click "Submit" in order for the changes to take affect.








Facebook Sign-In

Hi News addict,

Join the News24 Community to be involved in breaking the news.

Log in with Facebook to comment and personalise news, weather and listings.