Grain Growth In Ice Research Articles

Dynamical mechanism of antifreeze proteins to prevent ice growth.

The fascinating ability of algae, insects, and fishes to survive at temperatures below normal freezing is realized by antifreeze proteins (AFPs). These are surface-active molecules and interact with the diffusive water-ice interface thus preventing complete solidification. We propose a dynamical mechanism on how these proteins inhibit the freezing of water. We apply a Ginzburg-Landau-type approach to describe the phase separation in the two-component system (ice, AFP). The free-energy density involves two fields: one for the ice phase with a low AFP concentration and one for liquid water with a high AFP concentration. The time evolution of the ice reveals microstructures resulting from phase separation in the presence of AFPs. We observed a faster clustering of pre-ice structure connected to a locking of grain size by the action of AFP, which is an essentially dynamical process. The adsorption of additional water molecules is inhibited and the further growth of ice grains stopped. The interfacial energy between ice and water is lowered allowing the AFPs to form smaller critical ice nuclei. Similar to a hysteresis in magnetic materials we observe a thermodynamic hysteresis leading to a nonlinear density dependence of the freezing point depression in agreement with the experiments.

Influence of bubbles on grain growth in ice

Numerical static grain growth simulations of ice with air bubbles as a second phase show a significant drop in grain-growth rate compared to bubble-free ice. The magnitude of this drop in growth rate is dependent on the bubble boundary mobility, the volume fraction of air, the average bubble size and the bubble size distribution. The rate of grain growth decreases at first, as the microstructure evolves towards a steady state. Only then does grain growth follow the expected linear increase of mean grain area with time. In experiments, this decrease in growth rate could erroneously be interpreted as growth with a deviating growth exponent.

Meteoric and marine ice crystal orientation fabrics from the Amery Ice Shelf, East Antarctica

AbstractThe northwestern sector of the Amery Ice Shelf, East Antarctica, has a layered structure, due to the presence of both meteoric ice and a marine ice layer resulting from sub-shelf freezing processes. Crystal orientation fabric and grain-size data are presented for ice cores obtained from two boreholes ˜70 km apart on approximately the same flowline. Multiple-maxima crystal orientation fabrics and large mean grain sizes in the meteoric ice are indicative of stress relaxation and subsequent grain growth in ice that has flowed into the Amery Ice Shelf. Strongly anisotropic single-maximum crystal orientation fabrics and rectangular textures near the base of the ˜200 m thick marine ice layer suggest accretion occurs by the accumulation of frazil ice platelets. Crystal orientation fabrics in older marine ice exhibit vertical large circle girdle patterns, influenced by the complex stress configurations that exist towards the margins of the ice shelf. Post-accumulation grain growth and fabric development in the marine ice layer are restricted by a high concentration of brine and insoluble particulate inclusions. Differences in the meteoric and marine ice crystallography are indicative of the contrasting rheological properties of these layers, which must be considered in relation to large-scale ice-shelf dynamics.

水分子吸着による人工衛星光学硝材の透過率変動計測

Gas adsorption onto optical surfaces equipped in satellites is one of the causes of signal degradation occurred in orbit and water is one of the most potent ad-molecules. To estimate the degradation caused by water adsorption onto optical glass surface, the transmittance measurements were carried out in UV-VIS (200--800nm) and IR (1.7--20μm) wavelength ranges. Five kinds of glasses, SiO2, BK7, Al2O3, CaF2, and ZnSe, which are typically used for satellite optics, were selected as glass samples. In IR wavelength range, a local absorption feature was appeared at λ=3.1μm when a glass temperature was below 200K. The phase change of adsorbed water from vapor to solid may account for the newly appeared absorption. In UV-VIS region, there was no local absorption feature but broad transmittance decrease. BK7 and ZnSe, which are hydrophobic, showed little transmittance decrease and it was hard to find the wavelength dependence for their transmittance spectra. On the other hand, the transmittance spectra of hydrophilic glasses, SiO2, Al2O3, and CaF2, showed wavelength dependence and had the local minimal value. From our computation, it is found that the growth of ice grains on a glass surface makes it possible to reproduct the spectral transmittance degradation detected for hydrophilic glasses.

Effects of impurities and their redistribution during recrystallization of ice crystals

AbstractIn order to examine the effects of solutes on recrystallization and subsequent grain growth in ice, both doped and undoped ice single crystals were extruded through a 120° equal-channel angular extrusion jig, in order to impart a large shear strain (∼1.15). Upon subsequent annealing at −3°C, the original single crystals recrystallized, in most cases to a new single crystal with a different orientation. Increasing the solute concentration (for H2SO4 to ∼200–300 ppb, and for NaCl, KCl and MgSO4 to >5 ppm) was found to significantly retard the growth and possibly, for H2SO4-doped ice, the nucleation of new grains in the strained ice single crystals. This is indicative of how soluble impurities can retard grain growth in ice cores. It was also found that the migrating grain boundaries surrounding the newly formed grains contained large concentrations of impurities, often observed as filaments. These could have formed by the grain boundaries sweeping up impurities from the lattice into the boundary or by their diffusion to the boundary – mechanisms whereby impurities could be concentrated into the grain boundaries in ice cores – although the latter mechanism seems unlikely since it would require very high diffusion rates.

The Gibbs–Thomson effect and intergranular melting in ice emulsions: Interpreting the anomalous heat capacity and volume of supercooled water

Calculations for the Gibbs–Thomson effect and the intergranular melting of the ice droplets in (water) emulsions at temperatures below 273.16 K show that water and ice coexist at thermodynamic equilibrium in an apparently frozen emulsion. The fraction of water at this equilibrium increases on heating, which alters further the thermodynamic properties of the emulsion. As some of the ice in the emulsion has already melted, the increase in the enthalpy, H, and heat capacity, Cp, and the decrease in the volume measured on the normal melting at 273.16 K, are less than the values anticipated. The ratio of this increase in H, or Cp, on melting of the emulsion to the corresponding value for pure ice, underestimates the emulsion’s water content which, when used for scaling the difference between the Cp of the unfrozen and frozen emulsion at lower temperatures, as in earlier studies, leads to a larger Cp of supercooled water than the actual value. Similar scaling of the corresponding difference between the volume leads to higher volume, or lower density, than the actual value. A formalism for this premelting effect is given for both the adiabatic and differential scanning calorimetry (DSC), and its magnitude is calculated. New experiments show that the rise in the DSC signal, or equivalently in the apparent Cp observed on heating the frozen emulsion, occurs over a temperature range much wider than the Gibbs–Thomson effect and intergranular melting predict, for which reasons are given. It is shown that Cp of the dispersant phase is also affected by the melting of ice droplets. There are four consequences of the premelting effects for all finely dispersed materials, for frozen water emulsions below 273.16 K: (i) water and ice coexist in the emulsion, (ii) its apparent Cp will increase with increase in the heat input used to measure it, (iii) the apparent Cp will increase with decrease in the average size of the droplets, and (iv) the apparent Cp will decrease on annealing the frozen emulsion for a period long enough to allow the ice-grain growth in the frozen droplets. Calorimetry of emulsions has verified consequences (i) and (iv). The corresponding effects on the molar volume are briefly discussed. A substantial fraction of the anomalously high Cp and volume of supercooled water is due to the observed premelting effects.

Effect of Bubbles on Grain Growth in Ice

Grain growth is studied in artificial samples of pure ice. It is shown that the mean grain diameter D can be represented by the equation D2 = D02 + 4kt, both in bubble free ice and in growth regimes where bubbles are present on boundaries. In the second case it is found k ≪ ki, where ki is the intrinsic grain growth rate obtained for bubble free ice. This behavior is explained by considering that the drag effect Pb of migration bubbles on boundaries occurs in the low-velocity regime, where Pb = ν/Mb with ν and Mb the migrate velocity and mobility of bubbles, respectively. From the values of ki, the free boundary mobility M is calculated and the values of Mb are derived from the equation k = ki(1 + M/Mb)-1. The results obtained by different authors for k, both in artificial and glacial ice, are compared in an Arrhenius plot. It is shown that the results for glacial ice and for bubbly laboratory ice can be grouped in the same region where k ≪ ki. These results are interpreted by assuming that also in glacial ice grain growth is affected by migrating bubble drag. It is noted that this interpretation is not in contradiction with the fact that in glacial ice bubbles gradually separate from boundaries, i.e., that the phenomenon would occur in the high-velocity regime. Correlation between the experimental and theoretical values of Mb, the latter calculated on the basis of molecular diffusion processes, is discussed.

Grain Growth in Ice

Grain Growth in Ice

Grain Growth in Polar Ice: I. Theory

AbstractMany observations regarding grain growth in ice sheets are glaciologically interesting but imperfectly understood. Here we develop the theory of grain growth in ice that is not deforming rapidly, and in the succeeding paper we use this theory to explain observations from glacial ice. In the absence of significant strain energy, the driving force for grain growth arises from grain-boundary curvature. Grain growth is slowed by the interaction of grain boundaries with extrinsic materials (microparticles, bubbles, and dissolved impurities). If the driving force for growth is not large enough to cause boundaries to separate from an extrinsic material, then the grain-boundary velocity is determined by the velocity characteristic of the extrinsic material (low-velocity regime). If the driving force is large enough to cause separation, then boundaries migrate more rapidly than the extrinsic material (high-velocity regime) but the net driving force is reduced through transient pinning by the extrinsic material. Polar ice is typically in the low-velocity regime relative to dissolved impurities and the high-velocity regime relative to microparticles and bubbles. Cross-sectional area of grains is predicted to increase linearly with time under most but not all circumstances.

Grain Growth in Polar Ice: I. Theory

AbstractMany observations regarding grain growth in ice sheets are glaciologically interesting but imperfectly understood. Here we develop the theory of grain growth in ice that is not deforming rapidly, and in the succeeding paper we use this theory to explain observations from glacial ice. In the absence of significant strain energy, the driving force for grain growth arises from grain-boundary curvature. Grain growth is slowed by the interaction of grain boundaries with extrinsic materials (microparticles, bubbles, and dissolved impurities). If the driving force for growth is not large enough to cause boundaries to separate from an extrinsic material, then the grain-boundary velocity is determined by the velocity characteristic of the extrinsic material (low-velocity regime). If the driving force is large enough to cause separation, then boundaries migrate more rapidly than the extrinsic material (high-velocity regime) but the net driving force is reduced through transient pinning by the extrinsic material. Polar ice is typically in the low-velocity regime relative to dissolved impurities and the high-velocity regime relative to microparticles and bubbles. Cross-sectional area of grains is predicted to increase linearly with time under most but not all circumstances.

Grain growth in ice

Grain growth is studied in polycrystalline ice, consisting of elongated grains, of (200÷300) μm mean width\(\bar w\) and (2÷3) mm mean length\(\bar l\). The samples are annealed at different temperatures, between 0°C and −10°C. It is found that\(\bar l\) is not affected by annealing, while\(\bar w\) increases with the annealing time. Below the melting point,\(\bar w\)(t) tends to a limit value\(\bar w_s \). This behaviour is related to the pinning action of air bubbles, which would be similar to that found for solid inclusions in metals. By assuming\(\bar w_s = {{\bar d} \mathord{\left/ {\vphantom {{\bar d} f}} \right. \kern-\nulldelimiterspace} f}\) where\(\bar d\) is the mean bubble diameter andf is the volume fraction of air dissolved in water, reasonable values are found for\(\bar d\). The activation energy of the phenomenon is evaluated on the basis of the present and of Jellinek and Gouda's results. It is foundQ=0.6 eV, which value approximately coincides with that for bulk self-diffusion as it occurs for metals, several degrees below the melting point. This coincidence suggests that, for ice, grain growth would be controlled by bulk impurity diffusion up to the very melting point.

Two-Dimensional Grain Growth in Ice

The rate of grain growth in thin sections of polycrystalline ice was found to be practically the same at temperatures between 0°C. and −1°C. and not to depend to a great extent upon initial average grain size. In general, several hundred hours of annealing at 0°C. reduced the number of grains by a factor of about 3. The growth rate of certain grains was much greater than the average and these increased about a hundredfold in area. The rate of change of the average diameter was approximately inversely proportional to the annealing time. Grain boundary angles tended to average 120° irrespective of the number of sides per grain. Both grain shapes and crystallographic orientations were found to influence boundary migration rates. After long periods of annealing there was a strong tendency for the surviving grains to have theirc-axes oriented parallel to the plane of the ice surface.

Two-Dimensional Grain Growth in Ice

The rate of grain growth in thin sections of polycrystalline ice was found to be practically the same at temperatures between 0°C. and −1°C. and not to depend to a great extent upon initial average grain size. In general, several hundred hours of annealing at 0°C. reduced the number of grains by a factor of about 3. The growth rate of certain grains was much greater than the average and these increased about a hundredfold in area. The rate of change of the average diameter was approximately inversely proportional to the annealing time. Grain boundary angles tended to average 120° irrespective of the number of sides per grain. Both grain shapes and crystallographic orientations were found to influence boundary migration rates. After long periods of annealing there was a strong tendency for the surviving grains to have their c -axes oriented parallel to the plane of the ice surface.