抄録
An experimental stuty has been made to investigate the supercooling solidification of aqueous binary solutions. NaCl aqueous solutions of 0.0 to 22.4wt% in concentration were utilized as the testing solutions. Temperature variations have been measured during solidification, and the shape of growing ice has been observed under microscope for three cases of cooling direction (sidewise, bottom and top cooling). Solidification processes could be clarified into several steps: 1) rapid growth of a number of needle-shaped crystal, 2) melting of the top of needles, 3) at the same time, growing of thin and dense dendrides of which front is parallel to the cold plate, 4) coalescence of both fronts, and 5) stationary growing of dendrites. By the use of the box-counting method, it has been confirmed that the stationary growing dendritic ice patterns are fractals with a property of self-similarity, and their value of fractal dimension D has been obtained as 1.77 for sidewise growth dendrites, which was almost independent of the concentration c. In contrast to this case, smaller values of D were given in the case of upward growth and decreased with increasing c. These difference of D between the sidewise and the upward growth was attributable to the natural convection due to the gravity.
