A Laboratory Study On Nucleating Properties And Microstructure Of AgI Artificial Ice Nuclei

Two formulations(WMC-IN-001 and WMC-IN-002) of high efficient AgI-type pyrotechnics used in weather modification have been obtained after a number of screen tests carried out in CAMS 1m3 isothermal cloud chamber. The foreign pyrotechnic was made according to the formulation of silver-spare(USSR). The ice nucleating properties of Silver-spare and other five formulations of AgI-type pyrotechnics mainly used in weather modification in 2011 have been tested in the same chamber for comparison with the new pyrotechnics. The properties such as ice nucleation effectiveness, nucleating rate and nucleation mechanisms have been detected. And the nuclei chemical and physical properties of WMC-IN-001 have been analysed by the aerosol static setting sampler of ice nuclei(ASSI) and JSM-6701 F cold field emission scanning electron microscope(FESEM).According to the ice nucleating property testing results, the ice nucleation effectivenesses of five formulations of AgI-type pyrotechnics in the marketplace in 2011 are generally low, which can only achieve 1012/g AgI at a temperature of-15 ℃. The ice nucleation effectivenesses of WMC-IN-001 and WMC-IN-002 are generally high, which can reach up to 1015 /g AgI at a temperature of-15 ℃. Especially at a temperature of-7 ℃, the ice nucleation effectiveness of WMC-IN-001 can also reach up to 1014 /g AgI, which increases of up to two orders of magnitude over that of silver-spare. Influenced by the fog supplement, the nucleating rates of WMC-IN-001 and WMC-IN-002 are in the range of 40-55 min, which are relatively slow and have minor difference at different temperatures. Based on the high ice nucleation effectivenesses and high sensitivity to fog supplement, it is deduced that the nucleation mechanisms give priority to condensation freezing.The aerosol particles produced by WMC-IN-001 have been identified by FESEM. The particle sizes are between 0.02~0.60μm in diameter, whose peaks are 0.025μm and 0.13μm, and the mean cube-root diameter is 0.2472μm. Synthesizing the the relationships between size distributions and ice nucleating properties of some other AgI-type pyrotechnics, it is found that the ice nucleation effectiveness and nucleating rate do not show the simple law of increasing or decreasing with the enlargement of mean cube-root diameter or spectral width. The meancube-root diameter, spectral width or peak diameter of AgI aerosols can not influence the ice nucleating properties independently, but they are resulted from several factors.