WMOD00300

• Title: Characterization of Silver Iodide-Sodium Iodide Ice Nuclei Using Chemical Kinetic Methodology
• Date: 5/1/1985
• State: CO
• Weather Modification - Doc Type: Report

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observed by Davis (1969). Later work (Chen, et al., 1972 and Johnson
and Davis, 1972) favored the existence of the 4 mole hydrate,
AgI'NaI'4H20. The 4 mole hydrated phase (Johnson and Davis, 1972) was
particularly difficult to examine at subzero temperatures and near water
saturation. Experimental error in the technique of measuring the extent
of hydration was estimated to be 25' for compounds at subzero
temperatures. It was proposed that water was physically, rather than
chemically adsorbing on the surface of the compound. In water
supersaturated environments 19I'NaI'4H20 broke down to Nal solution and
solid Agl (Johnson and Davis, 1972). A similar sequence of hydration
was observed by St.-Amand, et al, (1971) for the 2AgI'NaI compound.
A distinction can be made between the time required for hydrate
tormation and the rate of supply of water vapor to the compound as the
oontrolling factor in chemical transformation in the AgI-NaI-water
system. Chen, et al, (1972) estimated diffusion of water vapor through
pores and over surfaces of 2AgI'NaI complexes in a water supersaturated
environment. Hygroscopicity of the material was neglected but was noted
to speed the prooess. Diffusion was estimated to require less than six
seconds. Measured rates of transformation of the chemical compounds
studied (hydrates of AgI-NaI) required between 5 and 20 minutes time.
It was concluded that the rate, or kinetics, of the chemical reaction is
the oontolling tactor in hydrate formation and breakup, not the supply
of water vapor.
Using the phase diagram in St.-Amand, et al, (1971) and solubility
tables for 2.5Agl'NaI Mossop and Jayaweera (1969) found the proportion
of AgI dissolved in water reaches a maximum of 21~ when the particle has
taken up 101 by weight of water. Considering a particle of 0.01 ~m

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