Spontaneous convection in the ice–water system was investigated with temperature and concentration measurements. Earlier work had shown that mild convection causes an apparent concentration dependence of the distribution coefficient that masks any real concentration dependence. Convection was found to be determined primarily by the density inversion at the 4 C isotherm. A simple method of evaluating the height of convection cells was developed which enables one to obtain an order-of-magnitude estimate of the distribution coefficient. Forced convection (stirring at 300 or 1000 rpm) and improved sampling and analysis techniques were used to redetermine the distribution coefficients of chlorides in ice. Solutions of HCl, LiCl, NaCl, KCl, RbCl, CsCl, and NH4Cl were investigated in the concentration range 10−6–10−2M. For the hydrogen and alkali chlorides no effect of the different cations on the chloride distribution coefficient was evident. Its average value is 2.7×10−3. For the ammonium chloride, the distribution coefficient is 1.4×10−2. The chloride distribution coefficient is not affected by solution pH, nor by an electrical interface potential. The chloride distribution coefficient is nearly or completely independent of concentration. This contrasts with the distribution coefficients of alkali fluorides which are strongly concentration dependent and much greater than those of the chlorides. These results point to different structural relationships of chloride and fluoride impurities with the ice lattice. However, dielectric relaxation and electrical conductivity of ice containing chloride and fluoride, respectively, are quite similar. According to a classical concept, each solute particle introduces into the ice lattice electrical point defects of specific type and number. The distribution coefficient enables one to determine these defects. We conclude from our results that this concept needs to be re-examined.
Dilute solutions of about 50 typical salts, acids, and bases in the concentration range 10 -8 to 10-~M were frozen at nonequilibrium rates. The freezing potential, charge separation across the phase boundary, and chemical composition of the phases were measured. The charge separation is a function of ionic species present in the solution, their concentration, and the freezing rate. It is caused by a differential transfer of ion constituents across the phase boundary. Hydrogen and hydroxyl ions neutralize the charge as the phase boundary advances. The solution pH greatly affects the charge separation, other conditions held constant.x Present address: California State Polytechnic College, San Luis Obispo, California.Key words: interracial electrical effects, ice/water system, freezing potentials, differential solute incorporation in ice, ice/water interface potentials, charge separation at the advancing ice/water interface.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.129.182.74 Downloaded on 2014-11-19 to IP Vol. 116, No. 6 INTERFACIAL ELECTRICAL EFFECTS 797 ~Plotinum wire electrode ~ -Thin-wolled Teflon cylinder Platinum bose ~'onnection for ground wire 5 inch cylindrical copper b~ock Idi~ /7"/7"/7-/72 protruding from deep freeze J oopoer ~~ oopper fins fins ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.129.182.74 Downloaded on 2014-11-19 to IP
Three-terminal dielectric bridge measurements (in the range 20 Hz to 100 kHz between — 5°C and —90 to — 120°C) have been made of ice doped with (a) conductivity-enhancing ionic impurities (HCl, HF, NaCl, KF, NH4F) and (b) conductivity-depressing solutes (NH4OH, NH4Cl, NH5CO3, NaHCO3). Blocking electrodes were used for the first group. The true ice parameters were extracted from linearized plots of the Debye equations. Chlorides and fluorides showed very similar characteristics in their spectra and static conductivity. The results suggest that static conductivity is controlled by extrinsic protons. On the other hand, bases, or solutes that impart a positive freezing potential to the ice, suppress extrinsic protons. In this case, the static conductivity was not, or only weakly, temperature dependent and lower than in the first group. A conductivity cross-over was observed in neither case. The dielectric conductivity contribution is strongly dependent on impurity concentration but apparently less affected than the static conductivity by the nature of the solute. The principal relaxation time is reduced by most solutes, exceptions are pure (bicarbonate-free) bases, sodium bicarbonate, and carbon dioxide.
Trace inorganic impurities cause specific changes in the con ductivity, dielectric constant and dielectric relaxation, ther moelectric power, mechanical relaxation, and the microstruc ture of ice. Most of these effects are explained by changes in the populations of ion defects and valence defects. The freezing potential (Workman-Reynolds effect) occurs when trace amounts (10 -6 M to 10 -3 M) of many inorganic and some organic salts are present in a freezing solution. Selec tive ion incorporation induces a charge layer at the advanc ing phase boundary. Its effect on the overall distribution of impurities between the phases is probably small. The dis tribution coefficient increases with freezing rate. For a given ion species and freezing rate it is a function of all im purity species present in solution, their concentrations, and the shape and surface structure of the phase boundary. Typical values of distribution coefficients for ionic solutes in ice range from 10 -5 to 10 -3 . Traceinorganics are the cause of specific electrochemical phenomena at the phase boundary of growing ice; these are the freezing potential and the preferential incorporation into the solid phase of certain ions over others. The physical and chemical properties of the phases are more or less deeply affected by such interface processes. These processes raise fundamental questions concerning the mechanisms by which solute ions are incorporated into the ice structure and what their positions and effects are once they get there. This paper proposes to review these phenomena, the experimental evidence available, and the theories that have been formulated to account for them. A major difficulty in the critical evaluation of the data is their great sensitivity to the experimental conditions, which are difficult to define completely in most instances.
Dilute solutions (2.5×10−4 M) of potassium fluoride, cesium fluoride, and lithium iodide were frozen at rates from approximately 1 to 20 μ/sec. A chemical analysis of the melted ice and of the supernatant liquid was made, and the electrical potentials or currents generated were measured. During the freezing, ionic transfer processes take place at the ice‐solution interface which are a function of ionic species present, their concentration, and the freezing rate. These processes are ionic rejection and incorporation, ionic separation, and ionic neutralization. In all three solutions, the anion is incorporated in greater numbers than the cation, regardless of the relative ionic sizes. The difference between incorporated halogen anions and incorporated alkali cations is made up with hydrogen ions, supplied either from the freezing base (shunt case) or from the liquid (open‐circuit case) or both. The relation between the rates of freezing and of ionic transfer determines the extent of this replacement. Ice samples grown from potassium‐ and cesium‐fluoride solutions with a low‐resistance external shunt show a direct‐current conductivity on the average about four times greater than samples grown without a shunt. Trace impurities, growth rate, and phase‐boundary conditions during growth are determining factors of the electrical bulk properties of ice.
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