Polycrystalline ice

NMR Measurement of The Residual Water. The residual water obtained in Experiments No. 5 and No. 6 was measured with a broadline NMR spectrometer, in which, proton signal of the water gives a very broad line. The full width at half height of the NMR signal is 15750 Hz and 18000 Hz for samples obtained in Experiments No. 5 and No. 6, respectively. The line width for liquid water is normally less than 5 Hz while the line width for polycrystalline ice is 56000 Hz (39). Therefore, the residual water is expected to have a mobility closer to ice than to liquid water. The wider line given by sample obtained in Experiment No. 6 seems to agree with the expectation that the water is more immobile at higher electrolyte concentration. 

In most of the early studies 9> of H20(as) the vapor was condensed on metal surfaces in the temperature range 77 K diffraction data, supplemented by new experimental studies, convinced Olander and Rice that most deposits obtained at or above 77 K are likely contaminated with crystalline ice. They established conditions for the deposition of pure H20(as) on a variety of substrates 10>. Briefly put, the temperature of the substrate should be low, preferably below 55 K, and the rate of deposition very small (a few mg/hour). There is evidence that H20(as) can be deposited on a substrate at 77 K if the deposition is slow enough. The use of high deposition rates at 77 K leads to polycrystalline ice Ic mixed with H20(as). A sample of pure H20(as) is stable indefinitely long (at least several months) if maintained below 20 K. At about 135 K, with some variation from sample to sample, the amorphous solid transforms spontaneously and irreversibly to ice Ic. 

For comparison purposes they also studied the diffraction pattern of polycrystalline ice Ih at 77 K. We shall discuss these data in detail, drawing heavily on Ref. 27>. It is convenient to begin with the case of poly crystalline ice Ih, and discuss in turn H20(as) deposited at 77 K, H20(as) deposited at 10 K, and the comparison with the neutron diffraction data. 

Fig. 7 a. Structure function of polycrystalline ice Ih prepared by vapor deposition at 77 K from X-ray diffraction (from Ref. 27>)... 

Correlation functions hoo(R) for the amorphous deposit prepared and studied at 77 K are shown in Fig. 7b together with the curve for polycrystalline ice Ih. As in the crystalline phase, the nearest-neighbor oxygen-oxygen correlations in H20(as) occur in an exceptionally narrow band centered at 2.76 A, with rms-deviation 0.114 A. The distance ratio for second and first neighbors indicates tetrahedral coordination on the average, but the second neighbor peak near... 

Fig. 9. Spectrum of energy losses in polycrystalline ice (taken from Ref. 85).

Figure 6 Absolute vaporization rate of D2O and H2O ice. Different symbols represent the data obtained with polycrystalline ice samples of various thermal histories.

In order to demonstrate that Fast Thermal Desorption spectroscopy can be used successfully to study reactions in volatile polycrystalline materials and to gain insights into nanoscale molecular transport in polycrystalline ice, we have conducted preliminary studies of H/D exchange kinetics near ice melting point. Figure 7 illustrates our approach. 

Figure 8 shows the H/D exchange kinetics between 50 nm thick D2O layer and the surrounding H20 polycrystalline ice at -5 C. As shown in the figure, only half of the initial D2O layer is converted into HDO on the time scale of our FTDS experiment. Analysis of the isothermal desorption spectra of HDO along with the observed reaction kinetics for D2O layers of various thickness show that the H/D exchange is controlled by... 

Several experiments reviewed in this article illustrate just a small fraction of opportunities for research into the fundamental physical and chemical properties of ice offered by our experimental approach. We emphasize that our core method, i.e., the FTDS can be combined with a variety analytical techniques. For instance, the existing apparatus can be equipped with an FTIR spectrometer for better initial characterization of phase and chemical composition of ice films during deposition. At the present time we are also developing an optical system that would allow us to conduct studies of photochemical reactions in polycrystalline ice. While our USC measurements were conducted with a fixed heating rate, further improvement of this particular component of our apparatus will make... 

LI Pure ice sample. Figure 1(a) shows results of the relaxation time r by Auty and Cole, whose data for polycrystalline ice have been some of the most quoted reproducible results reported, the results reported by von Hippel et al whose data for single crystal ice comprise the third component in six dielectric dispersions analyzed by computer, and... 

Tensile fracture stress reading at a certain temperature. For polycrystalline ice with a grain size of 10 mm one finds a fracture stress of about 800 kPa at -10 °C reported in the literature for high strain rates. This finding is consistent with the observed fracture stress in this study of about 700 kPa at 263 K. 

A technique has been developed that investigates the effect of the growth rate of a polycrystalline ice hemisphere from solution on the incorporation levels of solutes into the ice phase. The technique uses an adaptation of apparatus designed by Charles Rnight to determine ice-binding sites for peptides (Rnight, 1991). 

Takahashi (143) obtained less clear-cut charge separation effects when an ice rod was broken. This effect occurred even if no temperature gradient was present, and its magnitude depended on crystallinity (mono-or polycrystalline ice), bubble content, and temperature gradient. 

D.c. conductivity measurements at — 15°C. for polycrystalline ice doped with HF (Figure 20 and Ref. 67) show substantially the same square root of concentration dependence, and so do Steinemann s 140) low-frequency results. 

The book by Douzou on cryobiochemistry provides an excellent discussion of the types of solvents that are suitable for low-temperature studies. The need for investigating the effects of low temperatures on various solvents other than water was for cryoprotection of the dissolved proteins and the requirement for optically transparent samples. Samples even as thin as around 0.1 cm polycrystalline ice do not transmit light well however, if glycerol is added to about 60-75% (v/v), a clear glass is formed at about 200 K. 

Fig, 6.6. Thermal conductivity of polycrystalline ice as determined by Jakob Erk (1929), A RatclifFe (1962), I and Dean Timmerhaus (1963), O. The behaviour suggested by theory is shown as a broken interpolation curve. 

Since it is often of practical consequence to know the elastic behaviour of polycrystalline ice, particularly under static loading. 

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