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Ice IV
Ice IV is a metastable high-pressure phase of ice. It is formed when liquid water is compressed with an immense force. Preparation Several organic nucleating reagents had been proposed to selectively crystallize ice IV from liquid water, but even with such reagents, the crystallization of ice IV from liquid water was very difficult and seemed to be a random event. In 2001, Salzmann and his coworkers reported a whole new method to prepare ice IV ''reproducibly''; when high-density amorphous ice (HDA) is heated at a rate of 0.4 K/min and a pressure of 0.81 GPa, ice IV is crystallized at about 165 K. What governs the crystallization products is the heating rate; fast heating (over 10 K/min) results in the formation of single-phase ice XII. Crystal structure The crystal structure of ice IV was elucidated by Engelhardt and Kamb in 1981 by low-temperature single-crystal X-ray diffraction. Its structure is described by a rhombohedral unit cell with a space group of R-3c. The hydr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High Density Amorphous Ice
Amorphous ice (non-crystalline or "vitreous" ice) is an amorphous solid form of water. Common ice is a crystalline material wherein the molecules are regularly arranged in a hexagonal lattice, whereas amorphous ice has a lack of long-range order in its molecular arrangement. Amorphous ice is produced either by rapid cooling of liquid water (so the molecules do not have enough time to form a crystal lattice), or by compressing ordinary ice at low temperatures. Although almost all water ice on Earth is the familiar crystalline ice Ih, amorphous ice dominates in the depths of interstellar medium, making this likely the most common structure for H2O in the universe at large. Just as there are many different crystalline forms of ice (currently more than seventeen are known), there are also different forms of amorphous ice, distinguished principally by their densities. Formation The production of amorphous ice hinges on the fast rate of cooling. Liquid water must be cooled to i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ice XII
Ice XII is a metastable, dense, crystalline phase of solid water, a type of ice. Ice XII was first reported in 1996 by C. Lobban, J.L. Finney and W.F. Kuhs and, after initial caution, was properly identified in 1998. It was first obtained by cooling liquid water to at a pressure of . Ice XII was discovered existing within the phase stability region of ice V. Later research showed that ice XII could be created outside that range. Pure ice XII can be created from ice Ih at by rapid compression (0.81-1.00 GPa/min) or by warming high density amorphous ice at pressures between . While it is similar in density (1.29 g/cm at ) to ice IV (also found in the ice V space) it exists as a tetragonal crystal. Topologically it is a mix of seven- and eight-membered rings, a 4-connected net (4-coordinate sphere packing)—the densest possible arrangement without hydrogen bond interpenetration. Ordinary water ice is known as ice Ih, (in the Bridgman nomenclature). Different types of ice, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ice Ic
Ice Ic (pronounced "ice one c" or "ice I see") is a metastable cubic crystalline variant of ice. Hans König was the first to identify and deduce the structure of ice Ic. The oxygen atoms in ice Ic are arranged in a diamond structure; it is extremely similar to ice Ih having nearly identical densities and the same lattice constant along the hexagonal puckered-planes. It forms at temperatures between upon cooling, and can exist up to upon warming, when it transforms into ice Ih. Apart from forming from supercooled water, ice Ic has also been reported to form from amorphous ice as well as from the high-pressure ices II, III and V. It can form in and is occasionally present in the upper atmosphere and is believed to be responsible for the observation of Scheiner's halo, a rare ring that occurs near 28 degrees from the Sun or the Moon. Ordinary water ice is known as ice Ih (in the Bridgman nomenclature). Different types of ice, from ice II to ice XIX, have been created in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ice Ih
Photograph showing details of an ice cube under magnification. Ice Ih is the form of ice commonly seen on Earth. Phase space of ice Ih with respect to other ice phases. Ice Ih (hexagonal ice crystal) (pronounced: ice one h, also known as ice-phase-one) is the hexagonal crystal form of ordinary ice, or frozen water. Virtually all ice in the biosphere is ice Ih, with the exception only of a small amount of ice Ic that is occasionally present in the upper atmosphere. Ice Ih exhibits many peculiar properties that are relevant to the existence of life and regulation of global climate. For a description of these properties, see ''Ice'', which deals primarily with ice Ih. The crystal structure is characterized by the oxygen atoms forming hexagonal symmetry with near tetrahedral bonding angles. Ice Ih is stable down to , as evidenced by x-ray diffraction and extremely high resolution thermal expansion measurements. Ice Ih is also stable under applied pressures of up to about where i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
