Cubic structure, water

According to these authors all gas hydrates crystallize in either of two cubic structures (I and II) in which the hydrated molecules are situated in cavities formed by a framework of water molecules linked together by hydrogen bonds. The numbers and sizes of the cavities differ for the two structures, but in both the water molecules are tetrahedrally coordinated as in ordinary ice. Apparently gas hydrates are clathrate compounds. 

Larsson, K., Cubic lipid-water phases Structures and biomembrane aspects. J. Phys. Chem. 1989,93,7304. 

Golden yellow, soft and ductile metal body-centered cubic structure density 1.93 g/cm melts at 28.44°C vaporizes at 671°C vapor pressure 1 torr at 280°C electrical resistivity 36.6 microhm-cm (at 30°C) reacts with water dissolves in liquid ammonia forming a blue solution. 

Black sulfide is a black amorphous powder or crystalline substance (beta form) cubic structure metastable at ordinary temperatures converts to red sulfide by sublimation at ordinary pressure density 7.73 g/cm melts at 583.5°C insoluble in water, alcohol and nitric acid soluble in aqua regia, alkalies, and solutions of alkali metal sulfides. 

Silvery metal body-centered cubic structure imparts crimson-red color to flame density 0.862g/cm3 at 20°C melts at 63.25°C density of hquid potassium at 100°C is 0.819 g/cm and 0.771g/cm3 at 300°C vaporizes at 760°C vapor pressure 123 torr at 587°C electrical resistivity 6.1 microhm-cm at 0°C and 15.31 microhm-cm at 100°C viscosity 0.25 centipoise at 250°C surface tension 86 dynes/cm at 100°C thermal neutron absorption cross section 2.07 barns reacts violently with water and acids reacts with alcohol dissolves in liquid ammonia and mercury... 

Colorless crystals or white crystalline sohd cubic structure salty taste density 1.984 g/cm melts at 770°C subhmes at 1,500°C soluble in water 34.4 g/lOOmL at 20°C, 56.7 g/lOOmL at 100°C soluble in ether, glycerol and alkalies shghtly soluble in alcohol. 

Exists in two adotropic modifications. Crystalline sihcon is made up of grayish-black lustrous needle-hke crystals or octahedral platelets cubic structure Amorphous sdicon is a brown powder. Other physical properties are density 2.33g/cm3 at 25°C melts at 1,414°C high purity liquid silicon has density 2.533 g/cm at its melting point vaporizes at 3,265°C vapor pressure 0.76 torr at 2,067°C Mohs hardness 6.5. Brinell hardness 250 poor conductor of electricity dielectiric constant 13 critical temperature 4°C calculated critical pressure 530 atm magnetic susceptibility (containing 0.085%Fe) 0.13x10 insoluble in water dissolves in hydrofluoric acid or a mixture of hydrofluoric and nitric acids soluble in molten alkalies. 

White granular crystals or powder large crystals are colorless, transparent, or translucent saline taste cubic structure refractive index 1.5442 density 2.165 g/cm3 melts at 801°C vaporizes at 1,413°C soluble in water, 35.7g/100mL at 0°C and 39.1 g/lOOmL at 100°C aqueous solution neutral soluble in glycerol, ethylene glycol, and formic acid sparingly soluble in... 

Silvery-white metal when freshly cut rapidly turns yellow on exposure to air forming a thin oxide coating face-centered cubic structure malleable, ductile, and somewhat softer than calcium density 2.64 g/cm melts at 777°C vaporizes at 1,382°C vapor pressure 5 torr at 847°C and 20 torr at 953°C electrical resistivity 23 microhm-cm at 20°C thermal neutron absorption cross section 1.21 barns reacts with water soluble in ethanol. Thermochemical Properties... 

A bright white metal soft and ductile body-centered cubic structure index of refraction 3.03 density 5.96 g/cm melts at 1,910°C vaporizes at 3,407°C electrical resistivity, 18.1 microhm-cm at 0°C and 20.1 microhm-cm at 25°C magnetic susceptibility 1.4x10 cgs units modulus of elasticity 18-19x10 psi shear modulus 6.73xl0 psi Poisson s ratio 0.36 thermal neutron absorption cross section 5 barns/atom insoluble in water, dilute sulfuric acid, and hydrochloric acid at all concentrations soluble in nitric acid, aqua regia, and concentrated sulfuric acid insoluble in alkalies. 

White powder body-centered cubic structure density 5.03 g/cm melts at 2,436°C insoluble in water soluble in dilute acids. 

Gray metallic soM cubic structure very hard, hardness > 8.0 Mohs density 6.73 g/cm3 melts at 3,532°C insoluble in water slightly soluble in concentrated sulfuric acid soluble in hydrofluoric acid and oxidizing acids, such as nitric and perchloric acids attacked by oxidizers... 

Many single-chain amphiphiles form cubic phases when added to water in a given composition. Two of the most well known are didodecyl-phosphatidyl ethanolamine, and mono-olein. Figure 9.18 shows some idealized bicontinous cubic structures of the former, including typical inverse ones. This is also highly viscous and optically transparent as are most of the other cubic phases. 

Figure 6. Cubic structures in lipid-water systems based on space-filling polyhedra. The data from the monoglyceride-water cubic phases fit with the body-centered structure to the right.

All common natural gas hydrates belong to the three crystal structures, cubic structure I (si), cubic structure II (sll), or hexagonal structure H (sH) shown in Figure 1.5. This chapter details the structures of these three types of hydrate and compares hydrates with the most common water solid, hexagonal ice Ih. The major contrast is that ice forms as a pure component, while hydrates will not form without guests of the proper size. 

H3PW12O40 is one of the most common heteropoly compounds. A distinct X-ray diffraction pattern is seen for H3PWi2O40.6H2O, where the Keggin units are linked by H+(H20)2 bridges, resulting in a body-centered cubic structure and hence the X-ray diffraction pattern. The water molecules can be easily replaced by a number of polar molecules such as alcohols and amines (Misono, 1987). 

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