Phase of ice

Figure A1.12 shows the phase diagram for ice. (The pressures are so large that steam appears only at the extreme upper left.) There are eight different solid phases of ice, each with a different crystal structure. 

Problem At what temperature will water freeze to ice if the pressure is (a) 2 kbar, (b) 10 kbar What phase of ice is formed in each case ... 

Forms of ice designated as IV, IX, X, and XI have also been reported in the literature. See P. W. Hobbs, Ice Physics, Clarendon Press, Oxford, 1974, pp. 60-67 and C. Lobban, J. L. Finney, and W. F. Kuhs, The Structure of a New Phase of Ice , Nature, 391, 268-270 (1998). These phases are not shown in Figure 13.7, since they are metastable, not yet well-defined, or occur at pressure and temperature extremes beyond those given in the figure. 

These amorphous phases of ice can be of interest for creation on their basis of adjustable stores hydrogen fuel in the form of methane and other. Progress in understanding nature of ice amorphism has been made using developments of fine experiments. But data about formation hydrate methane in amorphous ice are scarce. For quite some time now the scientists have not been trying to identify ways to resolve this problem by studying different samples of ice and learning what combinations of pressure and temperature keep the methane locked up. Other party to problem is how the methane can be extracted. 

In a given work computer simulations devoted to study of nanostructure of abovementioned cryogenic amorphous phases of ice, mechanisms of their transformations, and properties to accumulate methane and hydrogen was realized within the theoretical concepts thermo field dynamics [5] and quantum-field chemistry [6-9]. We developed two models of nanostructures corresponding to HDA-ice and LDA-ice, respectively. Some computations of energetic barriers locking molecules CH4 and H2 inside of amorphous ice were fulfilled. 

In particular for cryogenic amorphous phase of ice share of physical intermolecular /-bonds is negligible component. In such case formulas for equilibrium share sizes come to expressions ... 

Mishima, O., Calvert, L. D. Whalley, E. (1985) An apparently First-order transition between two amorphous phases of ice induced by pressure. Nature 314,76-78. 

In addition to positive aspects, numerous flavor and textural defects may be associated with the fat phase of ice cream. Such flavor defects are usually related to either autoxidation of the fat, resulting in oxidized flavors (cardboardy, painty, metallic) or, especially in the case of milk-fat, lipolysis of free fatty acids from triglycerides by the action of lipases (referred to as hydrolytic rancidity). A significant content of free butyric acid gives rise to very undesirable rancid flavors. These defects tend to be present in the raw ingredients used in ice cream manufacture, rather than promoted by the ice cream manufacturing process itself. However, processing... 

Transferability from the solid state to the liquid state is equally problematic. A truly transferable potential in this region of the phase diagram must reproduce not only the freezing point, but also the temperature of maximum density and the relative stability of the various phases of ice. This goal remains out of reach at present, and few existing models demonstrate acceptable transferability from solid to liquid phases.One feature of water that has been demonstrated by both an EE model study and an ab initio study °° is that the dipole moments of the liquid and the solid are different, so polarization is likely to be important for an accurate reproduction of both phases. In addition, while many nonpolarizable water models exhibit a computed temperature of maximum density for the liquid, the temperature is not near the experimental value of 277 Eor example, TIP4P and... 

The structural correlations are strongly enhanced in the under-cooled state as the temperature is reduced towaids the metastable limit of -40°C (to D2O) and various thermoph ical properties exhibit diverged behaviour [8]. The exact nature of this anomaly is still the subject of some controversy. However, the difiraction pattern indicates that the stmcture is evolving towards that of amorphous ice which is characterised as a continuous random networit of tetrahedral hydrogen-bonds [9]. Recent neutron measurements on amorphous ice [10] have re-infor the earlier conjectures tuid shown that the structure is similar to that of hyper-quenched glassy water produced by rapid cooling of micron-sized water droplets. It can now be realised that the CRN mo l for the disordered phase of ice is effectively the limiting stmcture of water at low temperatures. 

This happened because of our investigation of the rate of nucleation of ice in deeply supercooled water. Previous laboratory studies of the freezing of water occurred in substantially warmer water and were blind to the phase of ice obtained. We studied water undergoing nucleation at roughly the temperature of nucleation in cirrus clouds, I believe. I understand that what happens in cirrus clouds has an important effect on the climate. Moreover, we showed directly that the ice first nucleated was the metastable cubic ice, not the ordinary hexagonal ice. Atmospheric scientists had inferred that result from indirect evidence. Previously it had not been possible to carry out experiments like ours in the laboratory, which is why our work attracted the attention of atmospheric scientists. 

Alley R. B., Brook E. J., and Anandakrishnan S. (2002) A northern lead in the orbital band north-south phasing of ice-age events. Quat. Sci. Rev. 21, 431—441. 

Here we should note that the dispersion curve calculation has provided all the information required to obtain the response from a single crystal sample aligned along a specific direction in Q. Indeed, if such an experiment were realistically feasible it would be the preferred technique. This is because the dispersion curves would be measured directly and the detailed information about the force field could be extracted. However, this is often not practical, at least for the exotic phases of ice and powdered samples were used. For ice Ih, single crystals are widely available (but a large crystal of ice Ic has not been obtained), after many attempts [49,55], reliable dispersion curves have yet to be obtained. This is due to the proton disordering in the structure of ice Ih and hence all the optic modes are localised. 

We have shown, in later sections, how precise INS measurements of the DOS provide the most stringent means of testing the model potential functions that lie at the heart of any LD or MD simulation. In the last a few years, we have systematically studied the vibrational dynamics of a large verity of phases of ice using above instruments at ISIS. These spectra were obtained at very low temperatures (< 15 K) on the recoverable high-pressure phases of ice and a few forms of amorphous forms of ice, in order to reduce the Debye-Waller factor and avoid multiphonon excitations. Hence the one-phonon spectra, g(co), can be extracted from the experimental data for the theoretical simulations. 

Ideally, the measurement of the g(a>) for normal ice (Ih) at different pressures would provide the information about the hydrogen bond interaction V(r) as a function of r. The difficulty with such measurements is that the structure of ice Ih readily transforms at only modest pressures, less than 3 kbar, and below this pressure there is little change in the hydrogen bond lengths. Hence, pressure measurements have to be performed on other phases of ice, such as ice II, III, V, VI and VIII in order to cover an extended pressure range. On the other hand, in these ice structures, the 0-0 distance varies even at the ambient pressure from 2.76 A to 2.965 A and the tetrahedral 0-0-0 angle also changes, from 83.8 to... 

The structures of the range of exotic crystalline phases of ice have been, for the most part, well known for many decades [9] and provide a suitable framework for the theoretical modelling. Moreover, by suitably choosing the... 

The spectra obtained for ice Ih, LDA and HDA, using the TFXA spectrometer at 10K [53] is shown in Fig. 11. Ice Ih is the most common and readily obtainable phase of ice which has now been well studied [14,15,48,49]. Its spectrum has a very simple structure, the translational modes below 40 meV are well separated from the librational modes (or hindered rotations) in the energy region between 65-125 meV (very few system shows similar behaviour and this is due to the large mass difference between O and H). The observed acoustic phonon peak is at 7 meV. The two sharp peaks at 28 and 37 meV are the optic-phonon bands and have an unusual triangular-shape. In contrast, only a single feature appears in the IR spectrum, at 27 meV, and the Raman spectrum has an additional shoulder at 36 meV (see Fig. 10). 

Fig. 13. Neutron spectra for a number of recovered exotic phases of ice and ice Ih (H2O) were measured using HET spectrometer on ISIS with incident energy of Ei = 600 meV at temperature T 10 K. The data show very small differences among the different phases, indicating there is little effect to the intramolecular frequencies from the external structures.

Figure 9.3 Phase diagram of H2O up to the pressure 2.5 GPa The closed circles indicate the surface temperatures of the icy satellites of Jupiter (100 K) and Saturn (75 K). Interior pressures in large satellites, such as Ganymede, Callisto, and Titan, are likely to reach several GPa, indicating that some high-pressure phases of ice may exist in them. (Figure from Kirby et al. [41].)...

The mix emulsion is subsequently foamed in the continuous ice cream freezer, creating a dispersed phase of air bubbles, and is concomitantly frozen, forming another dispersed phase of ice crystals. Air bubbles and ice crystals are usually in... 

The freezing process influences the building of the phases of ice, air and fat. The maximum size of ice crystals may not exceed 60 pm, otherwise the crystals could be detected by the consumer. 

It seems that the method to fix the size parameter of the Leonard-Jones potential to match the density of ambient water is unable to predict the internal energy of the high density phases of ice. 

Ice Ih, the proton-disordered hexagonal phase of water, has been by far the most studied phase of ice, however, a complete understanding of many of its properties still remains elusive. The role played by crystal defects is among the important issues requiring better comprehension. It is in fact quite remarkable that not even the most basic disruptions of crystalline order, the molecular vacancy and self-interstitial, are well understood. ... 

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