PREPARATION OF POLYCRYSTALLINE ICE SPECIMENS FOR LABORATORY EXPERIMENTS

A perennial problem in preparing fine grained ice specimens is the convenient production of low porosity material which is homogeneous, of random c-axis orientation and of controlled grain size. A review of the nature of bubble formation in ice leads directly to the two factors which must be controlled in order to minimize gas bubble formation, and thus porosity. The factors are (1) reduction of the number of bubble nucleation sites and (2) reduction of the amount of dissolved gas available at the freezing front. An ice specimen preparation technique developed at CRREL addresses both these factors. Two techniques have proven effective in reducing the number of nucleation sites; (1) a purge technique using carbon dioxide gas and (2) a vacuum technique. A newly developed flushing technique reduces the amount of dissolved gas in the pore water during freezing. The resulting material is optically clear with some very small bubbles dispersed throughout. The radial freezing technique employed occasionally results in a narrow column of fine bubbles along the central axis of the specimen. The density is 0.917 ± 0.002 Mg/m3. An overview of techniques for forming, flooding and freezing ice specimens is presented and several major preparation methods are reviewed in detail. © 1979.