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TOPIC: How Ice Melts:

Blobrana

L

Posts: 131433

Date: Mar 23 01:39 2007

water	Permalink

Look around you module 2 water __________________

Blobrana

L

Posts: 131433

Date: Mar 20 21:48 2007

Giant snowflakes	Permalink

Since at least the 19th century, people have periodically claimed to see giant snowflakes falling from the sky — big ones the size of saucers and plates or even larger, their edges turned up, their heaviness making them descend faster than small flakes. But the evidence was always sketchy and, because of the fragile nature of snowflakes, fleeting. The giant flakes were not quite in the category of sea monsters or U.F.O.’s. Even so, sceptics noted the human fondness for exaggeration, as well as the lack of convincing photographs. Read more __________________

Blobrana

L

Posts: 131433

Date: Oct 4 18:04 2006

Water at extreme temperatures and pressures	Permalink

Supercomputer simulations by two Sandia researchers have significantly altered the theoretical diagram universally used by scientists to understand the characteristics of water at extreme temperatures and pressures. The new computational model also expands the known range of water’s electrical conductivity. The Sandia theoretical work showed that phase boundaries for “metallic water” — water with its electrons able to migrate like a metal’s — should be lowered from 7,000 to 4,000 kelvin and from 250 to 100 gigapascals. Read more __________________

Blobrana

L

Posts: 131433

Date: Aug 31 07:01 2006

Metallic Water	Permalink

Metallic Water, an electrically conducting form of water, might exist under just the right conditions of temperature and pressures on gas giant planets like Jupiter or ice giants like Neptune. Ice on Earth comes in many forms---the normal hexagonal ice (manifested as crystalline ice or as six-sided snowflakes), cubic ice (which is rare; it can form as tiny crystallites high in the atmosphere), and other types which vary according to pressure conditions. A new theoretical study by physicists at Sandia National Lab shows that a conducting phase of water could occur at a temperature of 4000 K and a pressure of 100 gigapascals, which are much more forgiving than the previous estimates---7000 K and 250 GPa, respectively---and thought to exist inside Jupiter and Neptune. Furthermore, the new work shows, unexpectedly, that on a pressure-vs-temperature phase diagram the conducting phase of water ice should sit right next to electrically insulating ice, also called “superionic” ice, since in that case a water molecule’s two hydrogen atoms are free to move about while the oxygen atoms remain frozen in place. Source __________________

Blobrana

L

Posts: 131433

Date: Jul 2 09:32 2005

How Ice Melts:	Permalink

How Ice Melts: A breakthrough new study, supports a leading theory that melting starts when the fundamental structure of matter begins to crack. Melting is considered a basic phenomenon in physics. An understanding of how it works is crucial to gaining a firm grasp on the physical world. "Yet major details about the mechanisms that drive the melting of an ice cube are missing. Superficially, the principle is straightforward. As a solid heats up, molecules within the ice acquire more energy and jiggle around more, driving the transition from a solid to a liquid. This is true in part, but reality is richer and more complex." - Arjun Yodh, University of Pennsylvania. The problem is that the earliest phase of melting has never been seen. Scientists can't see the atoms involved because they are so small and because they are hidden in the structure of solid material. So Yodh's team made some big atoms. Specifically, they made see-through crystals that are like small beads and are visible in an optical microscope. "The spheres swell or collapse significantly with small changes in temperature, and they exhibit other useful properties that allow them to behave like enormous versions of atoms for the purpose of our experiment" - Ahmed Alsayed, University of Pennsylvania doctoral student and lead author of a paper on the results in the July 1 issue of the journal Science. A premelting occurs in spots where atoms within solid crystals are not perfectly aligned, and they begin to move. The changes are seen in pictures taken as the material was heated. The imperfections are much like the differences seen in wood grain. "These motions then spread into the more ordered parts of the crystal. We could see that the amount of premelting depended on the type of crystal defect and on the distance from the defect" - Ahmed Alsayed. Nature could inspire technology as the process is investigated further. "The existence of premelting inside solid materials implies that liquids exist within crystals before their melting temperature is reached. Understanding this effect will provide insight for the design of strong materials that are more or less impervious to temperature changes and could also apply to our theories of how natural materials, such as water, evolve in our environment" - Arjun Yodh. __________________

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