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The '''maximum density''' of a [[Chemical substance|substance]] is the highest attainable [[density]] of the substance under given conditions.

==Attaining maximum density==
Almost all known substances undergo [[thermal expansion]] in response to heating, meaning that a given mass of substance contracts to a low volume at low [[temperature]]s, when little [[thermal energy]] is present.  Substances, especially [[fluid]]s in which [[intermolecular force]]s are weak, also undergo [[Physical compression|compression]] upon the application of [[pressure]].  Nearly all substances therefore reach a density maximum at very low temperatures and very high pressures, characteristic properties of the [[solid]] [[State of matter|state]] of [[matter]].

==Irregular maximum densities==
A few substances break the typical thermal expansion rules, instead [[Negative thermal expansion|contracting]] in response to increased temperature.  An example of such a substance is [[zirconium tungstate]] in the cubic [[Phase (matter)|phase]], which contracts continuously up to 1050 [[Kelvin|K]].  Cubic zirconium tungstate's maximum density would be reached at the temperature where either contraction stops (that is, where the sample's volume stops decreasing) or the substance decomposes.

==Maximum density of water==
<!-- Citation help is here http://www.google.com/search?&q=Wetzel+3.98+Density-of-water --> {{Fact|date=March 2007}}
An especially notable irregular maximum density is that of [[water]], which reaches a density peak at 3.98 °[[Celsius|C]] under standard conditions of pressure because of the low-density [[crystal structure]] of [[Ice Ih|typical ice]].  This has important ramifications in Earth's [[ecosystem]]; see [[Water (molecule)#Density of water and ice]].

==References==
{{Unreferenced|date=December 2006}}
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==See also==

* [[List of elements by density]]
* [[Density]]
* [[Specific Gravity]]
* [[Specific weight]]
* [[Charge density]]
* [[Buoyancy]]
* [[Hydrometer]]

[[Category:Density]]
[[Category:Condensed matter physics]]
[[Category:Physical chemistry]]
[[Category:Physical quantity]]


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