No abstract

No abstract

No abstract

Literature is not available on the grain growth in polycrystalline ice. The present paper deals with such grain growth in pure ice and ice doped with sodium chloride. The technique consists in measuring grain size distributions as a function of time and deriving the numberaverage equivalent "diameter", considering the grains as spheres. The functional relntionship between the average diameter and time of growth is, for pure and doped ice, of the same form as that found for met.als. Arrhenius plots show that the energy of activation is higher for doped ice than for pure ice. The results are discussed in terms of interfacial free energy as being ultimately responsible for grain growth. On a molecular scale, processes take place, which lead to diffusion of units consisting of a number of water molecules across the boundaries.Aus der Literatur ist nichts uber das Kornwachstum in polykristallinem Eis bekannt. Uie vorliegende Arbeit beschaftigt sich mit solchem Kornwachstum in reinem und mit Katriumchlorid dotiertem Eis. Die Technik besteht in der Messung der Verteilung der KorngroBe als Fnnktion der Zeit und der Herleitung eines mittleren aquivalenten .,Durchmessers", wobei die Korner als Kugeln angenommen werden. Der funktionelle Zusammenhang zwischen dem mittleren Durchmesser und der Wachstumszeit ist fur reines und dotiertes Eis von der gleichen Form, wie er fur Metalle gefunden wird. Arrheniuskurven zeigen. daB die Aktivierungsenergie fur dotiertes Eis groBer als fur reines Eis ist. Die Ergebnisse werden mit der Annahme erklart, daB die freie Energie der Zwischenflache letztlich fur das Kornwachstum verantwortlich ist. I n einer molekularen Betrachtung finden Prozesse statt, die zu einer Diffusion von Einheiten, die aus einer Anzahl von Wassermolekulen bestehen, durch die Korngrcnzen fiihren. Experimental ApparatusThe apparatus consisted essentially of a constant low-temperature bath for the preparation of ice specimens, a polarizing microscope (Nikon) with photographic attachments and a microscope cold stage. ProcedureThe ice specimens were prepared under rigid standard conditions. A microscope slide was roughened on one side with carborundum. After thorough cleaning, it was placed on a metal block, which was almost fully submerged in the constant temperature, cold bath (ca. [-40 0.21 "C). Doublc distilled, precooled water was then placed on the slide and spread out with the aid of another slide. The surface was smoothed after freezing with a "warm" metal plate and dried quickly with filter paper. The thickness of the ice specimens was about 0.5 mm. Thc doped ice was prepared similarly, but quickly frozen a t -'1 Permanent Address:

No abstract