Preparation And Icing Performance Of Nanometer-sized Powders As Ice-nucleatent In Weather Modification

In this dissertation, nano-meter-sized silver iodide (n-AgI) and nano-meter-sized silver-copper iodide n-Ag_1-xCu_xI(x=0.10, 0.20, 0.25, 0.40) composite powder materials wereprepared by using liquid precipitation method, nano-meter-sized Cr_2-xAl_xO₃(x=0-1) compositesolid solution (n-CrB_2-xAl_xO₃(x=0-1)) powders were prepared by using sol-gel method.The microstructural and crystalline structures and properties of these powder materials werecharacterized and analyzed by using scanning electron microscopy (SEM), transmissionelectron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscope(XPS), Brunner-Emmett-Teller (BET), pore size analyzer and differential thermal analysis(TG/DTA) instruments (TG/DTA). 20L separated-body mixed cloud chamber and 1200Lisothermal cloud chamber were designed and manufactured and the icing performance ofn-AgI powders was measured using the explosion method of rainfall balls. The followingmain research results and conclusions were drawn from this dissertation work:1. The n-AgI powders prepared by liquid precipitation method have a uniform grain sizedistribution, do not show significant agglomeration, have aβ-type crystalline structureand is closer to the crystalline structure of ice crystal than the commonly used micro-meter-sized AgI (m-AgI) powders. The n-AgI powders have much higher specialsurface area than the m-AgI powders. The ability absorbing moisture of the n-AgI powdersincreases as the grain size decreases. The transition temperature of the solid-solidphase of the n-AgI powders is similar to that of the m-AgI powders, but the transitiontemperature of the solid-liquid phase of the n-AgI powders is 100°C higher than them-AgI powders. The n-AgI powders with different grain sizes can be obtained by controllingthe concentrations of complexing agent and dispersant, solution dropping rateand stirring speed, drying temperature and time, the smallest grain size prepared canreach ³0nm. 2. The n-Ag_1-xCu_xI(x=0.10, 0.20, 0.25, 0.40) composite powders have aβ-type crystallinestructure and do not show significant agglomeration. The grain size of then-Ag_1-xCu_xI(x=0.10, 0.20, 0.25, 0.40) composite powders decreases as the Cu additionincreases. The lattice constants of the n-Ag_1-xCu_xI(x=0.10, 0.20, 0.25, 0.40) compositepowders decrease and are gradually close to those of ice crystal. Then-Ag_1-xCu_xI(x=0.10, 0.20, 0.25, 0.40) composite powders would become the new, effectiveand low cost catalyst applied in weather modification.3. The n-Cr_2-xAl_xO₃(x=0-1) powders prepared by using sol-gel method with can crystallizedcalcined at 800°C. The lattice constants, lattice volume and the mean grain size ofthe CrB2B-xAlxOB3B (x=0-1) powders become small as Al₂O₃ Baddition increases.4. The 20L cloud chamber can send directly cool fog to the chamber, the temperature disturbancecan be reduced, the ice nucleation rate can be measured below -8°C due to theinstallation of a temperature-controllable collection device, the thermal insulation ismuch better due to the installation of an electric heating device. The 1200L cloudchamber has high temperature stability and high measurement efficiency due to the usesof a refrigerant samdwich device and an electric temperature controller. The super-coolfog can be produced the fog system can send super-cool fog to the chamber and the fogamount can be controlled and fog can be supplied continuously, which ensure the temperatureand moisture conditions for high activation rate of ice nucleation and growthand reduce the temperature disturbance caused by the injection of cool fog. The 1200Lhas good thermal insulation property and no temperature gradient, the measurement stabilityin different temperature regions and the measurement efficiency are improved.The ice nucleation rate can be measured below -5.7°C due to the installation of a temperature-controllable collection device and data is stable, repeatable and reliable.5. The ice nucleation rate of the n-AgI powders is high than that of the m-AgI powders by1 to 2 orders of magnitude. The ice nucleation rate can reach 10P14P at the nucleation temperaturebelow -20°C and is 10P11P in a relatively high negative temperature region. Thethreshold nucleation temperature of the n-AgI powders is significantly higher than that of the m-AgI powders. The activation and nucleation rates of the n-AgI powders are faster than that of the m-AgI powders under the same catalyst conditions.