Studies of Silver Iodide Ice-Forming Activity: Verification of Theory

Abstract

The dependence of the ice-forming activity on particle radius over the range 50 to 3000 Å at fog temperatures of ?5, ?10 and ?20°C has been obtained. It has been found by diffraction methods that silver iodide particles either have a hexagonal or a cubic low-temperature structure, depending on their size. With these data, the temperature dependences of the threshold particle radius have been obtained for hexagonal and cubic modifications of silver iodide. These dependences are compared to theoretical ones obtained by Fletcher for various models of ice formation. It appears that neither the sublimation nor the freezing models describe the experiment. Taking into account the process of water condensation on silver iodide aerosol particles does not improve the situation. A comparison with the Fletcher theory of ice formation on particles with nonuniform surfaces is carried out. It is shown that there are no values of the theoretical parameters which will give a good fit to theory and experiment.