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2-D Pressure-Temperature-Density graph, liquid-gas data derived from ref 540

Water Density


The density anomalies of water are described elsewhere. The liquid-vapor density data used in the graphs opposite and below were obtained from the IAPWS-95 equations [540]. Such data for liquid water has been reviewed [2329 ] and extended [2342 ]. The density at higher temperatures and at high pressure has been investigated using laser-driven shock compression [2318].


Other phase diagrams for water are presented elsewhere [681]. The density of supercooled (emulsified) water under pressure has recently been determined [1685 ].

The two graphs below show the variation in the density of liquid, gaseous and supercritical water with temperature and pressure. The density of liquid water increases with increasing pressure and decreases with increasing temperature.

Variation in the density of liquid, gaseous and supercritical water with temperature and pressure


Density of liquid and solid water along the phase line. C.Pt = critical point


Seen opposite is the density of liquid and solid (that is the ices) water along the liquid-solid phase line. Note that temperature varies along this phase line (as shown dashed red). Hexagonal ice is less dense than liquid water whereas the other ices found in equilibrium with water are all denser with phase changes occurring on the approach of the liquid and solid densities.

the volume of ambient  water as  the pressure changes; the dashed lines are estimates



The molar volume of water is shown left at 300K (approximately ambient temperature) as the pressure changes. At positive pressures, two phase changes occur, with liquid water first changing to ice VI at about 0.99 GPa and then changing to ice VII at about 2.13 GPa (at equilibrium). The liquid curve is from IAPWS-95 whereas the ice pressure volume data is from [2337 ]. At negative pressures (metastably stretching the liquid water without vapor formation, if physically possible), the liquid water will change to ice XVI at about -0.2 GPa.

As pressure increases, the ice phases become denser. They achieve this by initially bending bonds, forming tighter ring or helical networks, and finally including greater amounts of network inter-penetration. This is particularly evident when comparing ice-five with the metastable ices (ice-four and ice-twelve) that may exist in its phase space.

3-D Pressure-Temperature-volume graph


3-D Pressure-Temperature-Density graph, liquid-gas data derived from ref 540

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This page was established in 2015 and last updated by Martin Chaplin on 15 August, 2016

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