FUNDAMENTAL RESEARCH ON FREEZING OF SUPERCOOLED WATER WITH HETEROGENEOUS NUCLEATING SUBSTANCE

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Fundamental research on freezing of supercooed water with heterogeneous nucleating substance was investigated experimentally and analytically, and the following results were obtained.(1) The effect of solid particles on the freezing of the supercooled water was investigated. Silver iodide was selected as the solid particle, and several types of contaminants were prepared. The size of the particle and wet-ability of the surface were varied to three, and to two types, respectively. The amount of the particle was also varied. The sample water was put into a test tube and cooled at a constant cooling rate until the water solidified. The relationship between the degree of supercooling at freezing and various variables were investigated. Then, analytical method to predict the results was introduced. It was found that the results agreed quite well with the experiments. Hence, it was concluded that the freezing temperature does not depend upon the size of the solid particle nor its amount, but is decided by the total area exposed to the water.(2) Heterogeneous nucleation of water was investigated using Molecular Dynamics method. Solid with fcc (111) surface was placed at the bottom of a cell consisting of 864 water molecules. ST2 model was used. The interaction between water and the solid were based on the equations proposed by Spohr. It was found that the only one layer of water molecules was adsorbed in a case of flat surface, whereas ice nucleation occurred by changing the surface to 3-point surface. Modifying the Spohr interaction so that the dipole moment of water becomes unti-ferroelectric increased the ice growth further. The effect of lattice constant of solid on nucleation was also investigated.