Dielectric properties of ice

Molecular reorientations at Bjerrum fault sites are responsible for the dielectric properties of ice. A second type of fault (proton jumps from one molecule to a neighbor) accounts for the electrical conductivity of ice, but cannot account for the high dielectric constant of ice. Further discussion of such ice faults is provided by Franks (1973), Franks and Reid (1973), Onsager and Runnels (1969), and Geil et al. (2005), who note that interstitial migration is a likely self-diffusion mechanism. 

In this paper, we discuss the relaxation process in ice samples grown from the liquid or vapor phase, and attempt to reveal differences in dielectric behavior between ice samples grown by the different processes. There is a possibility that the dielectric properties of ice are affected by the process by which it grew. 

Clathrate ice samples. Prior to the results reported by Auty and Cole, researchers had faced difficulties obtaining reproducible results for the dielectric properties of ice. The use of well-degassed ice samples has enabled the obtainment of reproducible results. This indicates that the existence of gas molecules in ice affects the dielectric properties. Clathrate ice shows a short relaxation time and low activation energy... 

Polar deep ice. Polar deep ice is made of snow under a compressing process. The dielectric properties of polar ice core samples have been reported as having small values of relaxation time rand activation energy.The observation of small rvalues for the core ice samples suggests that Bjerrum defects are more numerous in polar ice than in ordinary ice. The impurity concentration of polar ice is not sufficiently high to decrease the rvalue the HCl concentration is about 2x10 mol/1 for Byrd core ice. Since we know that polar deep ice has structures of clathrate gas hydrate, imperfection in the structures and the existence of gas molecules in the ice lattice seem to affect the dielectric properties.It is well known that the dielectric properties of ice samples derived from polar deep ice that has melted and refrozen are similar to those of ordinary ice. ... 

Dielectric Measurements. The dielectric properties of ice can be understood on the basis of Pauling s model (21) in which a central water molecule is tetrahedrally surroundeiHiy four others with which hydrogen bonds are formed. Depending on how its two protons are directed towards the four neighbors, the central molecule can occupy six positions. On applying an... 

The dielectric properties of most foods, at least near 2450 MH2, parallel those of water, the principal lossy constituent of food (Fig. 1). The dielectric properties of free water are well known (30), and presumably serve as the basis for absorption in most foods as the dipole of the water molecule interacts with the microwave electric field. By comparison, ice and water of crystaUi2ation absorb very Httie microwave energy. Adsorbed water, however, can retain its Hquid character below 0°C and absorb microwaves (126). 

S. Zaromb and R. Brill. J. Chem. Phys. 24, 895-902 (1956). Dielectric properties of solid solutions of ice and NHar. 

It has since been shown by a variety of physical techniques that in some of the high-pressure forms of ice the protons are ordered and in others disordered, in particular, the low-temperature forms IX and VIII are the ordered forms of ice-IIl and ice-vII respectively. The nature of the far infrared absorption bands indicates that the protons are ordered in ii and ix (sharp bands) but disordered in v (diffuse bands). The dielectric properties of all the following forms of ice have been studied ic ii, iii, v, and vi, vii and viii, and the conclusions as to proton order/disorder are included in Table 15.1. 

L2 Impure ice sample. Dielectric properties of impure ice have been reported by... 

Crushed ice samples. Figure 2 shows the dielectric properties of samples consisting of packed crushed ice particles, which were prepared by crushing single crystal... 

A convincing but indirect proof indicating a close connection between the motions of hydrogen atoms and the dielectric properties of aqueous fluids follows from the comparison of the static dielectric permittivity ss of ice Ih and ice II. In the former, where the proton disorder is emphasized, ss 100, while in the latter, where such a disorder is lacking, ss = 3.66 [17]. 

The TV-dielectric relaxation mechanism allows us to (i) remove the THz deficit of loss e" inherent in previous (see GT2) theoretical studies, (ii) explain the THz loss and absorption spectra in supercooled (SC) water, (iii) describe, in agreement with the experiment, the low- and high-frequency tails of the two bands of ice H20 located in the range 10-300 cm-1, and (iv) describe the nonresonance loss spectrum in ice in the submillimetric region of wavelengths. Specific THz dielectric properties of SC water are ascribed to association of water molecules, revealed in our study by transverse vibration of the HB charged molecules. 

Solids and dipole relaxation of defects in crystals lattices Molecules which become locked in a solid or rigid lattice cannot contribute to orientational polarization. For polar liquids such as water, an abrupt fall in dielectric permittivity and dielectric loss occur on freezing. Ice is quite transparent at 2.45 GHz. At 273 °K, although the permittivity is very similar (water, 87.9 ice, 91.5) the relaxation times differ by a factor of 10 (water, 18.7 x 10 s ice, 18.7 x 10 s). Molecular behavior in ordinary ice and a feature which may be relevant to a wide variety of solids has been further illuminated by the systematic study of the dielectric properties of the nu-... 

The dielectric properties of a material are properly specified by a symmetric second-rank tensor relating the three components of the electrical displacement vector D to those of the field E. By choosing axes naturally related to the crystal structure the six independent components of this tensor can be reduced to three and, taking account of the hexagonal symmetry of the ice crystal, only two independent components remain. These are the relative permittivities parallel and perpendicular to the unique c-axis direction and we shall denote them by e, and e. We shall discuss the experimental determination of these quantities when we come to consider dielectric relaxation, since some difficulties are involved. For the present we simply note the results which are shown in fig. 9.2. The often-quoted careful measurements of Auty Cole (1952) were made with polycrystalline samples and removed many of the uncertainties in earlier work. They represent, however, a weighted mean of the values of e, and Humbel et al. (1953 [Pg.201]

In most supramolecular structures, the temperature dependence of the characteristic dielectric relaxation time follows the Arrhenius equation, r = Toexp(A dip/ T). where tq is the preexponential factor that is often of the magnitude of the vibrational time scale and A dip is the activation energy of the dipolar process.The dipolar process of the host lattice and the trapped molecules follows this behavior, but A trapped molecules is less than that for the host lattice molecules. In ice ciathrates, the dipolar processes of the water molecules that form the host lattice and the guest molecules inside the cages of this lattice occur at widely different time scales. This allows for a reliable attribution of the dielectric spectra features to water molecules and to the guest molecules. As an example of the magnitude of the dielectric properties of supiainolecular structures, the data on selected ice clathrates and other inclusion compounds are summarized in Tables 1 and 2. 

PARTI. THE SIGNIFICANT STRUCTURE THEORY APPLIED TO LIQUID WATER AND HEAVY WATER. PART II. DIELECTRICAL PROPERTIES OF LIQUID WATER AND VARIOUS FORMS OF ICE. PART III. THE SIGNIFICANT STRUCTURE THEORY OF ISOMERIC EFFECTS. PH. D. THESIS. 

An interesting property of ice is its response to an external electric field. The dielectric constant of any polar medium is a measure of the ability of the molecules to reorient in the electric field. It is believed that in ice the... 

The common form of ice at ambient pressure is hexagon2il ice, designated as ice Ih (see phase diagram in Section 12). The data given here refer to that form, at standard atmospheric pressure (101.325 kPa). Data have been taken from the references indicated, which in most cases are formulations based on critical evaluation of available experimental data. Most properties are sensitive to the method of preparation of the sample, because air and other gases are sometimes occluded. For this reason, there is often disagreement among values in the literature. For all properties except the dielectric constant of ice, the cited reference contains information on the uncertainty of the property. 

Dielectric studies of ice are important, because moisture absorbed in many plastics well above 0°C may have reduced mobility and some of the characteristics of ice. It is apparent from studies (62) of the influence of moisture on the electrical properties (see Figs. 45 and 46) that moisture is absorbed (or adsorbed) in different ways. A well-cured, as-molded resin (containing a small quantity of water from the condensation reaction) is compared with a sample of the same resin that has been extensively dried for about 40 days at 100° C in vacuum. In... 

The Structure of Ice and Water. It has not yet been necessary to consider in detail the properties of particular solvents. In Table 1 we gave a list of values for the dielectric constants of various solvents but apart from this we have not yet paid attention to the observed properties of solvents or of the ions which are commonly dissolved in them. Before continuing the discussion which was in progress in Sec. 23, it will be useful to review in some detail the state of our knowledge of the liquids which are used as solvents, and of the species of ions which are most often studied in solution. Although non-aqueous solutions are of great interest for the sake of comparison, nevertheless aqueous solutions are still of paramount importance, and we shall pay most of our attention to H20 and D20 and to ions dissolved in these liquids. 

Changes to the physical properties of a compound or material can have a dramatic influence on the susceptibility to microwave radiation. For example, ice has dielectric properties (e, 3.2 tan 8, 0.0009 e", 0.0029) that differ significantly from those of liquid water at 25 °C (s, 78 tan <5, 0.16 e", 12.48) [31], rendering it essentially microwave-transparent. Although liquid water absorbs microwave energy efficiently, the dielectric constant decreases with increasing temperature and supercritical water (Tc 374 °C) is also microwave-transparent. 

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