High-pressure ices

Ice, high pressure form Solid hydropen, high. 

Figure 35 (a) Comparison of the filled-ice high-pressure crystalline polymorph of... 

Perhydrodlpyrldlno(l,2-a][l, 2 -c]-pyrlmldlne (2). (a) To an ice-cooled solution of 2-(2-(pipendyl)ethyll pipendine 1 (3.2 g, 10 2 mmol) in EtaO (200 mL) was added N-chlorosuccinimlde (NCS) (1.7 g, 12 7 mmol) Under stirring, the reaction mixture was inadated with a 300 W high pressure mercury lamp under N2 for 5 h. The precipitate was filtered, dryed and extracted with n-pentane Evaporation of the solvent and distillation gave 1.0 g of 2 (50%). bp 140 C (20 torr)... 

Many of the high-pressure forms of ice are also based on silica structures (Table 14.9) and in ice II, VIII and IX the protons are ordered, the last 2 being low-temperature forms of ice VII and III respectively in which the protons are disordered. Note also that the high-pressure polymorphs VI and VII can exist at temperatures as high as 80°C and that, as expected, the high-pressure forms have substantially greater densities than that for ice I. A vitreous form of ice can be obtained by condensing water vapour at temperatures of — 160°C or below. 

A solution of a 3-azidopyridine (0.5-1.0 g) in a mixture of MeOH (75 mL) and dioxane (75 mL) containing NaOMe (2.5-3.0g, large excess) was irradiated under N2 with a 400-W high-pressure Hg lamp with a Pyrcx filter. When TLC indicated that no azidopyridine was left (1 —2 h), the solvents were removed in vacuo, ice-water (10-25 mL) was added to the residue and the mixture was extracted with hexane. The extract was washed with H20, dried and evaporated under reduced pressure and the residue was chromatographed (Sephadex, hexane) to give the products as colorless oils. 

Azido-2-methylquinoline (4, R - Me 0.500 g, 2.7 mmol) and NaOMc (4.0 g. large excess) in a mixture of MeOH (70 mL) and dioxane (70 mL) was irradiated for 30 min with a 400-W high pressure Hg lamp (Pyrex filter). The solvents were removed in vacuo and ice-water (20 mL) was added. The mixture was extracted with CH2C12 and the extract was washed with H20, dried and evaporated. The residue was chromatographed (silica gel, 1 % acetone/CH2Cl2) to give 5a yield 0.194 g (38%) pale-yellow prisms (acetone/hexanes) mp 78-79 C. 

Ice I is one of at least nine polymorphic forms of ice. Ices II to VII are crystalline modifications of various types, formed at high pressures ice VIII is a low-temperature modification of ice VII. Many of these polymorphs exist metastably at liquid nitrogen temperature and atmospheric pressure, and hence it has been possible to study their structures without undue difficulty. In addition to these crystalline polymorphs, so-called vitreous ice has been found within the low-temperature field of ice I. It is not a polymorph, however, since it is a glass, i.e. a highly supercooled liquid. It is formed when water vapour condenses on surfaces cooled to below — 160°C. 

High-pressure freezing Specimens are subjected to a pressure of 2100 bar, which depresses the melting point of water, reduces the formation of ice nuclei, and retards the growth rate of crystals... 

There are few models with automatic test capability. Testing is usually limited to hand held devices only 2 meters (7 ft.) from the detector or directly on the lens test unit. It can be ineffective if ice forms on the lens. It is sensitive to modulated emissions from hot black body sources. Most of the detectors have fixed sensitivities. The standard being under five seconds to a petroleum fire of 0.1 square meter (1.08 sq. ft.) located 20 meters (66 ft.) from the device. Response times increase as the distance increases. It cannot be used in locations where the ambient temperatures could reach up to 75 °C (167 °F). It is resistant to contaminants that could affect a UV detector. Its response is dependent on fires possessing a flicker characteristic so that detection of high pressure gas flames may be difficult. 

Figure 5.10 Phase diagram of water. Inset applying a high pressure from p (here p ) to pi causes the melting temperature of the ice to decrease from temperature T (here 0 °C) to 7i...

Kalichevsky, M.T., Knorr, D., and Lillford, PJ. 1995. Potential food applications of high-pressure effects in ice-water transitions. Trends Food Sci. Technol. 6, 253-259. 

More recent quantum-based MD simulations were performed at temperatures up to 2000 K and pressures up to 30 GPa.73,74 Under these conditions, it was found that the molecular ions H30+ and OH are the major charge carriers in a fluid phase, in contrast to the bcc crystal predicted for the superionic phase. The fluid high-pressure phase has been confirmed by X-ray diffraction results of water melting at ca. 1000 K and up to 40 GPa of pressure.66,75,76 In addition, extrapolations of the proton diffusion constant of ice into the superionic region were found to be far lower than a commonly used criterion for superionic phases of 10 4cm2/s.77 A great need exists for additional work to resolve the apparently conflicting data. 

Properties and extraction processes At high pressures and low temperatures, water and gas form an ice-like mixture, called gas hydrate, also known as clathrate or simply hydrate. Hydrates are a crystalline, solid substance composed largely of water... 

---