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IceIce is the solid form of water. The phase transition occurs when liquid water is cooled below 0 °C (273 K, 32 °F) at standard atmospheric pressure. Ice can be formed at higher temperatures in pressurized environments, and water will remain a liquid or gas until -30 °C at lower pressures. Ice formed at high pressure has a different crystal structure and density than ordinary ice.
Ice, water and water vapour can coexist at the triple point, which for this system is 273.16 K at a pressure of 611.73 Pa. An unusual feature of ice frozen at a pressure of one atmosphere is that the solid is less dense than liquid water (10 % less). This is due to hydrogen bonds between the water molecules, which line up molecules less efficiently (in terms of volume) when water is frozen. The result of this is that ice floats on liquid water, an important factor in Earth's climate. Types of iceEveryday ice and snow is Ice Ih, or hexagonal ice. Subjected to higher pressures and varying temperatures, ice can form in roughly a dozen different phases. Only a little less stable (metastable) than Ih is cubic structure ice (Ic). But cooling Ih causes a different arrangement to form in which the protons move, XI. With both cooling and pressure more types exist. Rime is a type of ice formed by fog freezing on cold objects. It contains a high proportion of trapped air, making it appear white rather than transparent, and giving it a density about one quarter of that of pure ice.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ice" and from http://www.white-on.com also see:
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