Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCubic ice Ic free from stacking defects synthesized from ice XVII
116
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Among the over eighteen different forms of water ice, only the common hexagonal phase and a cubic phase are present in nature on Earth. The existence of these two polytypes, almost degenerate in energy, represents one of the most important and unresolved topics in the physics of ice. It is now widely recognised that all the samples of cubic ice obtained so far are instead a stacking-disordered form of ice I (i.e. ice Isd), in which both hexagonal and cubic stacking sequences of hydrogen-bonded water molecules are present. Here we describe a new method to obtain cubic ice Ic in large quantities, and demonstrate its unprecedented structural purity from two independent neutron diffraction experiments performed on two of the leading neutron diffraction instruments in Europe.
rate research
Read More
Water freezes below 0 {deg}C at ambient pressure, ordinarily to ice Ih with an ABAB... hexagonal stacking sequence. However, it is also known to produce ice Ic nominally with an ABCABC... cubic stacking sequence under certain conditions1, and its existence in Earths atmosphere, or in comets is debated. Ice Ic, or called as cubic ice, was first identified in 1943 by Konig, who used electron microscopy to study the condensation of ice from water vapor to a cold substrate. Subsequently, many different routes to ice Ic have been established, such as the dissociation of gas hydrates, warming amorphous ices or annealing high-pressure ices recovered at ambient pressure, freezing of $mu$- or nano-confined water. Despite the numerous studies on ice Ic, its structure has not been fully verified, because the diffraction patterns of ice Ic show signatures of stacking-disorder, and ideal ice Ic without stacking-disorder had not been formed until very recently. Here we demonstrate a route to obtain ice Ic without stacking-disorder by degassing hydrogen from the high-pressure form of hydrogen hydrate, C$_2$, which has a host framework that is isostructural with ice Ic. Surprisingly, the stacking-disorder free ice Ic is formed from C$_2$ via an intermediate amorphous or nano-crystalline form under decompression, unlike the direct transformations that occur in the cases of recently discovered ice XVI from neon hydrate, or ice XVII from hydrogen hydrate. The obtained ice Ic shows remarkable thermal stability until the phase transition to ice Ih at 250 K; this thermal stability originates from the lack of dislocations, which promote changes in the stacking sequence. This discovery of ideal ice Ic will promote understanding of the role of stacking-disorder on the physical properties of ice as a counter end-member of ice Ih.
We report results of MD simulations of amorphous ice in the pressure range 0 - 22.5 kbar. The high-density amorphous ice (HDA) prepared by compression of Ih ice at T = 80 K is annealed to T = 170 K at intermediate pressures in order to generate relaxed states. We confirm the existence of recently observed phenomena, the very high-density amorphous ice and a continuum of HDA forms. We suggest that both phenomena have their origin in the evolution of the network topology of the annealed HDA phase with decreasing volume, resulting at low temperatures in the metastability of a range of densities.
Ice growth from liquid phase has been extensively investigated in various conditions, especially for ice freely grown in undercooled water and aqueous solutions. Although unidirectional ice growth plays a significant role in sea ice and freeze casting, the detailed pattern formation of unidirectionally grown ice in an aqueous solution remains elusive. For the first time, we in situ proved a crossover from lamellar to spongy ice morphologies of a single ice crystal via unidirectional freezing of an aqueous solution. The spongy ice morphology originates from the intersect of tilted lamellar ice and is observed in a single ice crystal, which is intrinsically different from the competitive growth of bi-crystal composed of two differently orientated grains in directional solidification. These results provide a complete physical picture of unidirectionally grown ice from aqueous solution and are believed to promote our understanding of various pattern of ice in many relevant domains where pattern formation of ice crystal is vital.
Recently, significant interest has emerged in fabricated systems that mimic the behavior of geometrically-frustrated materials. We present the full realization of such an artificial spin ice system on a two-dimensional kagome lattice and demonstrate rigid adherence to the local ice rule by directly counting individual pseudo-spins. The resulting spin configurations show not only local ice rules and long-range disorder, but also correlations consistent with spin ice Monte Carlo calculations. Our results suggest that dipolar corrections are significant in this system, as in pyrochlore spin ice, and they open a door to further studies of frustration in general.
Heterogeneous ice nucleation is one of the most common and important process in the physical environment. AgI has been proved to be an effective ice nucleating agent in the process of ice nucleation. However, the microscopic mechanism of AgI in heterogeneous ice nucleation has not been fully understood. Molecular dynamics simulations are applied to investigate the ability of which kinds of $gamma$-AgI substrate can promote ice nucleation by changing the dipole of $gamma$-AgI on the substrate, we conclude that the dipole of $gamma$-AgI on the substrate can affect the conformation of ice nucleation. The surface ions with positive charge on the substrate may promote ice nucleation, while there is no ice nucleation founded on the surface ions with negative charge. $gamma$-AgI substrates affect ice nucleation through adjust the orientations of water molecules near the surfaces.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
