An illustration of the ice’s molecular configuration.
Uni of Nebraska-Lincoln-led research team has predicted a new molecular form of the slippery stuff that even Mother Nature has never borne. The proposed ice would be 25% less dense than a record-low form synthesized by a European team in 2014. If synthesized, it would become the 18th known crystalline form of water—and the 1st discovered in the US since before World War II, lowest-density ice to date.
This newest finding represents the latest in a long line of ice-related research from Zeng, who previously discovered a 2D “Nebraska Ice” that contracts rather than expands when frozen under certain conditions.
This new study used a computational algorithm and molecular simulation to determine the ranges of extreme pressure and temperature under which water would freeze into the predicted configuration. That configuration takes the form of a clathrate— a series of water molecules that form an interlocking cage-like structure.
It was long believed that these cages could maintain their structural integrity only when housing “guest molecules” such as methane, which fills an abundance of natural clathrates found on the ocean floor and in permafrost. Like the European team before them, however, Zeng and his colleagues have calculated their clathrate would retain its stability even after its guest molecules have been evicted.
Synthesizing the clathrate will take effort. The new ice will form only when water molecules are placed inside an enclosed space at -10F, surrounded by expansion pressure 4X greater than at the Pacific Ocean’s deepest trench. At -460, that pressure would need to be even greater— the same amount experienced by a person shouldering 300 jumbo jets at sea level. The guest molecules would then need to be extracted via a vacuuming process pioneered by the European team.
“Water and ice are forever interesting because they have such relevance to human beings and life,” Zeng said. “If you think about it, the low density of natural ice protects the water below it; if it were denser, water would freeze from the bottom up, and no living species could survive. So Mother Nature’s combination is just so perfect.” If confirmed, the new form of ice will be called “Ice XVII,” a naming quirk that resulted from scientists terming the first two identified forms “Ice I.”
http://news.unl.edu/newsrooms/unltoday/article/scientists-reveal-new-ice-with-record-low-density/
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