Characteristics of Silver Iodide Ice Nuclei Originating from Anhydrous Ammonia-Silver Iodide Complexes: Part I

Abstract

Two methods of generating silver iodide ice nuclei have been investigated, neither employing thermal processing. A 3000-liter isothermal cloud chamber controllable over the range of 0 to ?20 ± 0.1C was designed and fabricated to study nucleation processes along with other support equipment. Anhydrous ammonia as the AgI carrier was employed since solution preparation is simple and direct, high concentrations (60 per cent of AgI by mass) can be used, and corrosion and deposition problems are virtually nonexistent. In a simple system in which the complex is sprayed into ambient air via a commercial nozzle, the results are negative with 1012 nuclei gm?1 at ?20C. Another system, using Dautrebande's principle of obligatory filtration, shows promise. Performance at ?13C is 3 ? 1014 nuclei gm?1. The threshold temperature of both non-thermal systems is about 5C lower than for other dispersion methods. Ultra pure silver iodide is a poorer nucleant than the commercial materials. The electron microscope was used to study the effluents from both generators. The shape and physical characteristics of effective particles are quite different from those found in thermal generators. The marked difference in effectiveness between thermal and non-thermal systems is attributed to impurities.