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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The chemistry of the AgI-HaI-water system has been studied by
Burkardt, et al. (1968), Mossop and Tuck-Lee (1968), Davis (1969),
Burkardt and Finnegan (1970), St.-Amand, et al., (1971), Chen et al.
(1972), and Johnson and Davis (1972). X-ray diffraction analysis of
samples prepared by evaporating AgI-RaI solutions of various ratios
indicated AgI-RaI was always complexed and hydrated. Formation of the
hydrated complex appeared to be preceeded by hydration of the RaI
(Burkardt, et al., 1968). Mossop and Tuck-Lee (1968) performed more
detailed X-ray diffraction analysis and concluded that aerosol particles
of AgI-Ral greater than 0.05 diameter produced by combustion of an
2.5AgI-Ral-acetone solution are composed of ~-~I and RaI'2H20.
By using the _ple chamber of the X-ray diffractometer as an
environmental chamber Davis (1969) determined the phase diagram for a
2.5:1 mole ratio of AgI to RaI, produced by acetone solution combustion,
as a function of temperature and water vapor pressure. At room
temperature, in an initially dry lIixture of AgI and NaI crystals, the
RaI forms the two lIole hydrate, RaI'2H20, at approximately 16~ relative
humidity. At about 28.5'1t relative bumidity a three or four IIOle bydrate
of AgI'NaI forms. At 421 relative bumidity solid AgI and a water
solution of AgI and NaI results. Similar sequences of hydration and
complexing occur at 100C and OOC with somewhat higher relative
humidities required for transitions.
The three mole hydrated complex, 2AgI'NaI'3H20, was observed by
Burkardt and Finnegan (1970) when water was evaporated from bulk samples
of AgI-HaI solutions in X-ray diffraction analysis. They present
several mechanisms for the formation of tbis complex in tbe presence of
excess water vapor. all of which include or begin with RaI'2H20, as