EFFECTS OF DIFFERENT METHODS OF PREPARATION OF ICE MANTLES OF TRIPLE POINT OF WATER CELLS ON THE TEMPORAL BEHAVIOR OF THE TRIPLE-POINT TEMPERATURES

We report results of an investigation of the temporal variation of the temperature of triple point of water (TPW) cells, in which the ice ma ntles were prepared by four different techniques using: (i) solid CO2, (ii) an immersion cooler, (iii) liquid-nitrogen-cooled rods, and (iv) liquid nitrogen (LN), first passing cold nitrogen vapours and then LN directly into the wells of the cells. The temperature of the TPW cell water was either approximately 274 K or 295 K when the freezing of th e ice mantle was started. No visible cracks formed during the preparat ion of any of the mantles using the crushed solid-CO2 or the immersion -cooler method, but all of the ice mantles cracked when prepared using the LN-cooled-rod and LN techniques. The cracked mantles, however, so on healed. Initially, the temperatures of the mantles prepared by the four methods varied, but after about three or four days they agreed to within 0,1 mK; after one week they agreed to within 0,03 mK, except f or mantles prepared by the LN technique, for which nine days were once required for one of the mantles; after eleven days, the results were practically the same. It appears that the temperature variations obser ved during the first few days following the preparation of mantles cou ld be caused by a combination of (i) temperature decrease due to intro duction of strains in the ice and to formation of fine ice crystals du ring the preparation of the mantle and (ii) temperature increase due t o the relief of strains and the gradual conversion of fine ice crystal s to larger ice crystals. Mantles that underwent severe cracking there by released most of the energy associated with the large strains intro duced during preparation of the mantle.