Ice VII is a cubic modification of ice . Its triple point with liquid water and ice VI is located at a temperature of 355 K and a pressure of 2.216 GPa , and the boundary between solid and liquid states extends to at least 715 K and 10 GPa. [one]
It can also be obtained under pressure from ice VI at room temperature . As in most modifications of ice (including the most common - ice I h ), the position of hydrogen atoms in it is not ordered. The structure of ice VII forms a system of hydrogen bonds in the form of two interpenetrating (but not connected) sublattices.
Ice VII is the only of the disordered modifications of ice that can be ordered by simple cooling, thus forming (ordered) ice VIII at temperatures below 273 K and pressures up to ~ 8 GPa. At higher pressures, the temperature of the VII – VIII transition sharply decreases, reaching 0 K at ~ 60 GPa. Thus, ice VII has the greatest stability region compared to other modifications. Cubic oxygen sublattices, which create the structural framework of ice VII, can exist at least up to pressures of about 128 GPa; this pressure is significantly higher than that at which water loses its molecular character, forming ice X.
The density of ice VII at 2.5 GPa pressure is 1.65 g / cm³, the dielectric constant (static) is 150.
Ordinary water ice according to Bridgman's nomenclature belongs to ice I h . In laboratory conditions (at different temperatures and pressures ), various modifications of ice were created: from ice II to ice XVI.
Links
- Chaplin, Martin. Ice-seven (Ice VII) . Water Structure and Science (June 23, 2008). Date of treatment February 23, 2009. Archived May 19, 2012.
- ↑ IAPWS, Release on the pressure along the melting and the sublimation curves of ordinary water substance, 1993 (unreachable link) . Date of treatment February 23, 2009. Archived September 27, 2006.