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ferent impurities (Delmas et al,,14Petit et all5). 90% of the insoluble microparticles seem to be aluminosilicates with a diameter around 1 km and a maximum concentration of 2 X lo5 particles per gram of ice (0.1 ppm, 6 X lo-’ m2/g). Soluble particles with diameters lower than 0.1 pm may also exist in these ices (Aitken particles). The other interfaces formed by bubbles and grain boundaries normally give a specific surface area of 0.06 m2/g. The highly mobile signal of the Antarctic sample probably develop at the interfaces in the interior of the bulk ice. As the number of highly mobile protons diminishes abrubtly (for temperatures near the melting point and after one annealing cycle) we think that a fraction of water molecules at the interface, initially distorted, reach the bulk ice structure. For the protons of the residual water molecules that remain near the interface, the chemical environment is different after ageing. One of the causes might be impurities initially confined at the interfaces (as in grain boundaries) that segregate after ageing. Another cause might be that the interface itself changes its original structure. Conclusion The main conclusions may be summarized as follows: unfrozen water was observed to exist for different kinds of solid-ice interfaces. Interfaces very actives as icesilica interfaces influence the structuring of water over distances as greater as 500 A. This influence diminishes when the distance between the particles of silica increases. On the other hand, the mobility of protons increases toward a (14)R. Delmas, J. M. Ascencio, and M. Legrand, Nature (London), 284, 155 (1980). (15)J. R. Petit, M. Briat, and A. Royer, Nature (London),293,391 (1981).
saturation value with increasing temperatures. Pearson* suggested that water in the bodies of silica pores freezes for diameters greater than 120 A. However, we observe a highly mobility of protons for distances as greater as lo3 A between silica particles. For less active interfaces such as icePVC interfaces, the mobility of protons increases exponentially reaching the proton mobility of the “quasi-liquid layer” near the melting point. The main difference between water-solid surfaces and ice-solid surfaces seems to be the rate of restructuring elements. The original interface in the first stage of ice sample preparation seems to be the same. Antarctic samples initially show only the broad signal of bulk ice. We think that water molecules at the interfaces are ordered in the first stage showing an equilibrium state properly of the aged antarctic samples (20 X 103years old). This equilibrium is thermally disturbed in the second stage giving as a result the appearance of a narrow peak belonging to the “quasi-liquid layer”. After this, a new equilibrium state is building up with time in order to diminish the extent of this layer. The preliminary work on Antarctic ices has to be completed by detailed geochemical analysis and of systematic physical measurements in order to understand the anomalous behavior of these ices.
Acknowledgment. This work has been sponsored by the French “Institut National d’Astronomie et de GBophysique-CNRS”ATP Planetologie, Grant 37-86, and the “Commission des CommunautBs EuropBennes”,Grant CLI 013-F(G). The authors thank all the colleagues of the Glaciological Laboratory in Grenoble for the very interesting discussion on this subject. We also thank M. Gey (C.E.R.M.O. Grenoble) who helped us to overcome the numerus difficulties in the NMR experiments. Registry No. Water, 7732-18-5; proton, 12586-59-3.
Discussion of Papers Presented at the Symposium Formation and Annihilation of Stacking Faults i n P u r e Ice (T. Hondoh) E. M.Schukon: Would you please comment on the role of the high interstitial concentration on the mechanical behavior of ice Ih? In particular, would you indicate the likely effect of the interstitials on the case of dislocation slip? Thank you. Hondoh: The high concentration affects the mechanical behavior as follows: (1) The deformation due to dislocation climb becomes important. (2) Glide dislocations are pinned at jogs generated by precipitation of interstitials into the core. (3) High concentrationsmay affect the reorientation mechanism of water molecules at the core. S. H. Kirby: Do the excess interstitials which precipitate into partial and perfect prismatic loops result from supersaturation during cooling or are they taken up in a nonequilibrium way at the growth interface by a “burial” process during fast growth? If it is the second case, these defects might be avoided by growing at lower rates. Hondoh: During crystal growth, excess interstitials are generated both by supersaturation due to cooling and nonequilibrium at the interface. Since the concentration of the excess interstitiah generated by these processes increases with the growth rate, the number of prismatic dislocation loops formed during growth can
be lowered by growing at lower rates.
J. Perez: You have shown that dislocations can be generated on certain parts of grain boundaries, and linear defects then will accumulate in the vicinity of the grain boundary. We have done internal friction measurements on annealed and stressed bicrystals: the peak due to the movement of the grain boundary is observed in the former case but not in the latter (Phys.Status Solidi 1979). Can you explain that by reference to your work? Hondoh: I think that the origin of the internal friction peak owing to grain boundary observed in bicrystals is grain boundary sliding which is caused by applied shear stress and is stopped by stress concentrations due to the nonplanar shape of the grain boundary. A possible mechanism to interpret your experiments is as follows: since irregularity of the grain boundary shape must increase with loading time, sliding displacement will be inhibited. Then the peak height may be lowered.
Study of Lattice Defects i n Ice Ih by Very Low Frequencies Internal Friction Measurements (J. Perez) T. Hondoh: A small bump seems to exist near the main peak in your measurements of internal friction. Could you explain the origin of the bump? Perez: When this peak is observed with high frequencies internal friction measurements (-1000 Hz) it exhibits a single 0 1903 American Chemical Society
