WATER FREEZES WHEN HEATED

da http://news.discovery.com/tech/water-freezes-when-heated.html

Usually water freezes at 32 degrees Fahrenheit and temperatures below that. But now scientists – reporting today in the journal Science — have found a way to keep water in a liquid form at -40 degrees F. What’s more, the scientists have found another way to make the water freeze when it’s heated. It’s a curious phenomenon to say the least, but the results could have implications for computer climate modeling.

Igor Lubomirsky and his colleagues from Israel’s Weizmann Institute of Science achieved this unusual feat using dust-free water on materials called pyroelectric amorphous solids, which change their electrical charge depending on their temperature.

One of the materials the scientists looked at was lithium tantalate. At 12 degrees F, the material has a negative charge. But raise the temperature to 17.6 degrees F, and it has a positive charge.

When the scientists put dust-free water on the material, the freezing point no longer was the normal 32 degrees. In fact, the freezing point depended on the charge. The scientists were able to supercool the water down -40 F without it freezing.

A negative charge did the opposite. So when they applied a negative charge to the surface, thereby raising the temperature to 17, the “heated” water froze.

Another strange thing happened: on a positively charged surface, the water froze from the bottom up, and on a negatively charged surface, the water froze from the top down.

Lubomirsky told NPR that he wasn’t sure yet why any of this happened.

But the implications of the roll of dust in water should be considered in climate modeling, Franz Geiger, a physical chemist at Northwestern University in Illinois, told NPR. Ice in the atmosphere forms on dust particles and dust particles can have different electrical charges. That could influence temperatures, so it’s a variable that could be taken into consideration in computer models of climate.

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