Saturday, May 11, 2019

          THEY DON'T MAKE ICE AGES LIKE THEY USED TO   

ROBERT FROST CAN HAVE IT BOTH WAYS WITH WHITE-HOT ICE XVIII   

   ICE CREAM FROM HELL
The discovery of superionic ice potentially solves the puzzle of what giant icy planets like Uranus and Neptune are made of. They’re now thought to have gaseous, mixed-chemical outer shells, a liquid layer of ionized water below that, a solid layer of superionic ice comprising the bulk of their interiors, and rocky centers. @iammoteh for Quanta Magazine

Nanosecond X-ray diffraction of shock-compressed superionic water ice








Abstract
Since Bridgman’s discovery of five solid water (H2O) ice phases1 in 1912, studies on the extraordinary polymorphism of H2O have documented more than seventeen crystalline and several amorphous ice structures, as well as rich metastability and kinetic effects. This unique behaviour is due in part to the geometrical frustration of the weak intermolecular hydrogen bonds and the sizeable quantum motion of the light hydrogen ions (protons). Particularly intriguing is the prediction that H2O becomes superionic—with liquid-like protons diffusing through the solid lattice of oxygen—when subjected to extreme pressures exceeding 100 gigapascals and high temperatures above 2,000 kelvin. Numerical simulations suggest that the characteristic diffusion of the protons through the empty sites of the oxygen solid lattice (1) gives rise to a surprisingly high ionic conductivity above 100 Siemens per centimetre, that is, almost as high as typical metallic (electronic) conductivity, (2) greatly increases the ice melting temperature  to several thousand kelvin, and (3) favours new ice structures with a close-packed oxygen lattice. Because confining such hot and dense H2O in the laboratory is extremely challenging, experimental data are scarce... Here we use laser-driven shockwaves to simultaneously compress and heat liquid water samples to 100–400 gigapascals and 2,000–3,000 kelvin. In situ X-ray diffraction measurements show that under these conditions, water solidifies within a few nanoseconds into nanometre-sized ice grains that exhibit unambiguous evidence for the crystalline oxygen lattice of superionic water ice. 

The X-ray diffraction data also allow us to document the compressibility of ice at these extreme conditions and a temperature- and pressure-induced phase transformation from a body-centred-cubic ice phase (probably ice X) to a novel face-centred-cubic, superionic ice phase, which we name ice XVIII.
NATURE  Letter