Water/Freezing point: Difference between revisions
imported>Johan Förberg (Further de-degreeification) |
imported>Milton Beychok m (Testing) |
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<includeonly>Not measurable*</includeonly> | <includeonly>Not measurable*</includeonly> | ||
<noinclude>Not measurable</noinclude> | <noinclude>Not measurable</noinclude> | ||
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Note: The freezing point of "pure" water is not measurable, whereas the melting point is. This is because pure water does not freeze without help of a solid crystallization kernel.<ref>http://www.newton.dep.anl.gov/askasci/gen01/gen01672.htm</ref> Very cold (metastable) ''pure liquid water'' can be obtained by "[[supercooling]]" pure water. Pure liquid water has been reported to be possible down to various extremely low temperatures: (-38°C to -45°C<ref>http://polymer.bu.edu/hes/articles/ms98.pdf</ref>) and (231 K=-43.9°C<ref>http://polymer.bu.edu/hes/articles/ds03.pdf</ref>). | Note: The freezing point of "pure" water is not measurable, whereas the melting point is. This is because pure water does not freeze without help of a solid crystallization kernel.<ref>http://www.newton.dep.anl.gov/askasci/gen01/gen01672.htm</ref> Very cold (metastable) ''pure liquid water'' can be obtained by "[[supercooling]]" pure water. Pure liquid water has been reported to be possible down to various extremely low temperatures: (-38°C to -45°C<ref>http://polymer.bu.edu/hes/articles/ms98.pdf</ref>) and (231 K=-43.9°C<ref>http://polymer.bu.edu/hes/articles/ds03.pdf</ref>). | ||
The standard unit of thermodynamic temperature, currently defined in the [[SI system]] as K (Kelvin), selects as the fundamental fixed point the [[triple point]] of water. One Kelvin, and therefore 1°C ([[Celsius]]), is specified by multiple standards bodies<ref>http://www.bipm.org/en/si/si_brochure/chapter2/2-1/kelvin.html</ref><ref>http://physics.nist.gov/cuu/Units/kelvin.html</ref> as the fraction 1/273.16 of waters triple point. Formerly (until 1954<ref>http://physics.nist.gov/cuu/Units/kelvin.html</ref>) the definition developed by [[Anders Celsius]] had fixed the 0°C point at the "freezing point" of water.<ref>http://www.energyquest.ca.gov/scientists/celsius.html</ref> It is now generally accepted that while the [[phase transition]] from solid to liquid water occurs at a predictable temperature (namely 0°C), the transition from liquid to solid water does not. This is because the actual "Freezing" is dependent upon the previously mentioned [[nucleation]] as well as the temperature.{{Reflist}}</noinclude> | The standard unit of thermodynamic temperature, currently defined in the [[SI system]] as K (Kelvin), selects as the fundamental fixed point the [[triple point]] of water. One Kelvin, and therefore 1°C ([[Celsius]]), is specified by multiple standards bodies<ref>http://www.bipm.org/en/si/si_brochure/chapter2/2-1/kelvin.html</ref><ref>http://physics.nist.gov/cuu/Units/kelvin.html</ref> as the fraction 1/273.16 of waters triple point. Formerly (until 1954<ref>http://physics.nist.gov/cuu/Units/kelvin.html</ref>) the definition developed by [[Anders Celsius]] had fixed the 0°C point at the "freezing point" of water.<ref>http://www.energyquest.ca.gov/scientists/celsius.html</ref> It is now generally accepted that while the [[phase transition]] from solid to liquid water occurs at a predictable temperature (namely 0°C), the transition from liquid to solid water does not. This is because the actual "Freezing" is dependent upon the previously mentioned [[nucleation]] as well as the temperature.{{Reflist}}</noinclude> | ||
Revision as of 16:30, 28 July 2010
Not measurable
Note: The freezing point of "pure" water is not measurable, whereas the melting point is. This is because pure water does not freeze without help of a solid crystallization kernel.[1] Very cold (metastable) pure liquid water can be obtained by "supercooling" pure water. Pure liquid water has been reported to be possible down to various extremely low temperatures: (-38°C to -45°C[2]) and (231 K=-43.9°C[3]).
The standard unit of thermodynamic temperature, currently defined in the SI system as K (Kelvin), selects as the fundamental fixed point the triple point of water. One Kelvin, and therefore 1°C (Celsius), is specified by multiple standards bodies[4][5] as the fraction 1/273.16 of waters triple point. Formerly (until 1954[6]) the definition developed by Anders Celsius had fixed the 0°C point at the "freezing point" of water.[7] It is now generally accepted that while the phase transition from solid to liquid water occurs at a predictable temperature (namely 0°C), the transition from liquid to solid water does not. This is because the actual "Freezing" is dependent upon the previously mentioned nucleation as well as the temperature.
- ↑ http://www.newton.dep.anl.gov/askasci/gen01/gen01672.htm
- ↑ http://polymer.bu.edu/hes/articles/ms98.pdf
- ↑ http://polymer.bu.edu/hes/articles/ds03.pdf
- ↑ http://www.bipm.org/en/si/si_brochure/chapter2/2-1/kelvin.html
- ↑ http://physics.nist.gov/cuu/Units/kelvin.html
- ↑ http://physics.nist.gov/cuu/Units/kelvin.html
- ↑ http://www.energyquest.ca.gov/scientists/celsius.html