Silver Iodide Particles Research Articles

Velocity Map Imaging Photoelectron Spectroscopy of Silver Iodide Aerosol Particles.

The valence band electronic structure of isolated silver iodide nanoparticles (AgI NP) was investigated by vacuum-ultraviolet aerosol photoelectron spectroscopy using the velocity map imaging technique (VUV VMI-PES). The VUV VMI-PES results were obtained for polydisperse aerosol produced by aggregation of hydrocolloid of silver iodide particles 8-15 nm in size. The ionization energy of the AgI particles was found to be 6.0±0.1 eV with respect to the vacuum level. The DFT calculations showed that the main contribution to the density of AgI electronic states in the valence region originates from I 5p orbitals. The dependence of the asymmetry parameter on the electron energy showed that the value of the characteristic energy loss of excited photoelectrons was 2.7 eV, which coincided with the band gap of the nanomaterial.

Исследования льдообразующих свойств кластеров из нанотрубок оксида цинка

Introduction. In recent years, the volume of funds used in the practice of weather modification has been growing in the world. Silver, the main component of weather modification funds, is a rather expensive metal. Therefore, the issue of reducing the silver content in the formulations of pyrotechnic compositions or the use of other effective ice-forming agents is relevant. Zinc oxide, like silver iodide, has ice-forming properties. When zinc is sublimated in water vapor, clusters of nanotubes of various sizes are formed. In this regard, experimental studies of the mechanism of ice formation on clusters of zinc oxide nanotubes seem to be an urgent task. The results of these studies are presented in this article. Materials and research methods. During thermal sublimation of reagents nanoscale particles are formed. These particles combine into clusters. The shape and size of these clusters, as well as their ice-forming properties, depend on the thermodynamic state of the medium in which they are formed. Tests of the ice-forming efficiency of such reagents should be carried out in conditions in clouds. This article presents the results of laboratory modeling of the formation of ice crystals during the interaction of zinc oxide clusters consisting of nanotubes, and the results of their comparison with the pyrotechnic composition AD–1 used in practice of weather modification, which is used in anti-hail products of the type «Alazan–6» and «Alazan–9» [1]. Research results and their discussion. The article presents the equipment and methods of performing experiments to study the ice-forming properties of clusters of zinc oxide nanotubes obtained in a cloud chamber during zinc sublimation in the presence of water vapor. The experiments were carried out on laboratory installations in the temperature range from –3 to –14 °C. The effectiveness of a reagent based on clusters of zinc oxide nanotubes has been investigated and compared with the effectiveness of the pyrotechnic composition of AD–1. The research results are presented in Tables 1–6 and Figures 2–7. Conclusions. In the course of laboratory experiments, a method for studying the ice-forming properties of clusters of zinc oxide nanotubes has been developed. When the pyrotechnic composition of AD–1 is sublimated, particles with a diameter from 20 nm to 400 nm with a modal value of 70 nm are formed. Zinc oxide clusters have a porous, loose structure, low density and larger sizes, almost two orders of magnitude larger than the sizes of silver iodide particles. Large ice crystals are formed on them. The total area of crystals formed on clusters of zinc oxide nanotubes is an order of magnitude larger than the total area of crystals formed on particles of the pyrotechnic composition AD–1. The reagent consisting of zinc oxide clusters is comparable in ice-forming characteristics to the pyrotechnic composition of AD–1 and can be recommended for practical use.

The moment of initial crystallization captured on functionalized nanoparticles

Even if a liquid is cooled below its melting point, the liquid state can be maintained under certain conditions. This state is called supercooling. Spraying fine particles of dry ice or silver iodide induces a phase change from supercooled droplets to ice grains. However, the mechanism by which crystallization seeds diminish supercooling is not well understood. Here, we captured the moment when a cluster, which is the smallest structural unit of a crystal, envelops a silver nanoparticle. As a result of observing the structure of a supercooled aqueous solution of a clathrate hydrate, we found that silver nanoparticles accelerate the formation of clusters, whereas the noble metals palladium, gold and iridium likewise form nanoparticles but do not promote crystallization. Our discoveries elucidate the mechanism of heterogeneous nucleation during a phase change in clathrate hydrates. We anticipate our discovery to be the starting point for the control of supercooling, a technique that can be applied to enhance the production efficiency and quality of manufactured products.

Ordered Hydrogen Bonding Structure of Water Molecules Adsorbed on Silver Iodide Particles under Subsaturated Conditions

Silver iodide (AgI) is an efficient ice-nucleating material. This has been related to the close lattice match to hexagonal ice, which helps to nucleate ice crystals on its surface under supersaturated conditions. In turn, the structure of water molecules adsorbed on its surface, embodied in the coordination of hydrogen bonds, has not been addressed so far. We suspected that AgI may induce ice-like coordination among adsorbed water molecules already under subsaturated conditions. X-ray photoelectron spectroscopy was used to probe the structure and composition at the AgI surface. We determined the chemical properties of the surface, the thickness of adsorbed water, and the amount of contaminating carbon species. Auger electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to assess the hydrogen bonding (HB) structure. The O K-edge NEXAFS spectra indicated that the HB structure of the adsorbed water on AgI under subsaturated conditions showed similarity to that of ice, which helps facilitate the stabilization of ice embryos at saturation. The approach used here opens up important perspectives for characterizing adsorbed water molecules on a wide variety of solids, which provides an important basis for understanding ice nucleation and other interfacial processes at the molecular level.

Study of Distribution Ice-Forming reagent in the Boundary layer of the atmosphere When Exposed by Ground Aerosol Generators NAG-07M

The paper describes the technical means, methods, and results of experimental studies of the spread of ice-forming agents in the boundary layer of the atmosphere under the action of ground-based aerosol generator NAG-07M. Comparison of the data on sampling by an AVA 3-240-01S probe mounted aboard Vilga-35A aircraft with aerosol propagation calculations using a 3-D SeedDisp model shows 1. The concentration of silver iodide measured in the atmosphere was above background one to a height of 1200 m at distances of 3 to 9 km from the place of the generator installation. 2. The developed SeedDisp numerical model in general qualitatively correctly describes the distribution of silver iodide aerosols in the boundary layer and the free atmosphere under the action of ground-based aerosol generator NAG-07M. Thus, the coefficient of correlation of the measured and calculated by model values of the silver iodide particles concentration in the sub-cloud layer exceeded the value of 0.7.

ESTUDIO DE LA COAGULACIÓN DE PARTÍCULAS COLOIDALES DE AgI POR INFLUENCIA DE QUITOSANO CON SULFATO DE ALUMINIO

El objetivo del presente trabajo fue determinar las condiciones óptimas de la coagulación de partículas suspendidas de yoduro de plata de carga negativa por la acción de soluciones de quitosano, sulfato de aluminio, así como la acción mixta de ambos coagulantes. La suspensión de partículas coloidales de AgI se obtuvo mediante la mezcla de soluciones diluidas de KI y AgNO3 en exceso de KI. En todos los experimentos el volumen del sistema coloidal fue de 600 mL y pH= 6. Los parámetros óptimos del proceso de coagulación se determinó a base del método de Test de Jarras. Para la solución de quitosano los parámetros óptimos fueron: concentración 0,01 %, pH=4,5 y un volumen de 25 mL; para el sulfato de aluminio: concentración 30 ppm, pH=4,0 y un volumen 25 mL. En el caso de la acción mixta de ambos coagulantes los parámetros óptimos fueron 5 mL de una solución al 30 ppm de sulfato de aluminio a pH 4,0 y 20 mL de una solución de quitosano al 0,01 % a pH=4,5 . A base de estos parámetros, se estudió la cinética del proceso de coagulación de la suspensión de AgI mediante el método de turbidimetría y se determinó que el proceso de coagulación fue rápido y culminó aproximadamente a los 3 minutos de haber empezado el proceso.

Atomistic Simulation of Ice Nucleation on Silver Iodide (0001) Surfaces with Defects

Small particles of silver iodide (AgI) are known to have excellent ice nucleating capabilities and have been used in rain seeding applications. It is widely believed that the silver-terminated (0001) surface of β-AgI acts as a template for the basal plane of hexagonal ice. However, the (0001) surface of ionic crystals with the wurtzite structure is polar and will therefore exhibit reconstructions and defects. Here, we use atomistic molecular dynamics simulations to study how the presence of defects on AgI(0001) affects the rates and mechanism of heterogeneous ice nucleation at moderate supercooling at −10 °C. We consider AgI(0001) surfaces exhibiting vacancies, step edges, terraces, and pits and compare them to simulations of the corresponding ideal surface. We find that, while point defects have no significant effect on ice nucleation rates, step edges, terraces, and pits reduce both the nucleation and growth rates by up to an order of magnitude. The reduction of the ice nucleation rate correlates well with the fraction of the surface area around the defects where perturbations of the hydration layer hinder the formation of a critical ice nucleus.

Water-vapor clustering on the surface of β-AgI crystal in the field of defects with a disordered structure

The Monte Carlo method has been employed to simulate the nucleation of condensed water phase from vapor at 260 K on a crystalline silver-iodide surface containing a defect in the form of a nanoscopic spot with a random distribution of ions. The free energy and work of formation of a nucleus have been calculated in the bicanonical ensemble at the molecular level as functions of nucleus size; computer images and spatial correlation functions of molecules have been obtained. The presence of a defect with a disordered (amorphous) structure, on the one hand, entails local destructions of a monomolecular film, but, on the other hand, shifts the onset of the adsorption process toward lower vapor pressures by several orders of magnitude. Under the conditions of a growing condensate film, the defect leads to its thermodynamic stabilization and a decrease in the barrier of the formation of subsequent layers, thereby weakening the known effect of the hydrophobicity of monomolecular films on crystalline surfaces with hexagonal structures. The factors that predetermine the abnormally high efficiency of silver-iodide particles as stimulators for atmospheric-moisture nucleation at negative Celsius temperatures seem to be the presence of extended defects on the surface of aerosol particles in combination with the hexagonal structure of their crystal lattice, the optimum magnitude of direct interactions between water molecules with ions of the crystal surface layer, and the collective domain-formation effects that result from a relatively high polarizability of iodine ions.

Polyethylenimine complexes with silver ions in aqueous solutions as precursors for synthesis of monodisperse silver iodide particles

The conditions of formation and composition of polyethylenimine complexes with silver ions in aqueous solutions are found. The complex is formed according to the model of a uniform distribution of ions throughout the macromolecule, and the composition of the complex may vary depending on pH of the medium. The size parameters are determined and the volume fractions of polyethylenimine macromolecular coils in solution are calculated. The synthesis of silver iodide particles is carried out under conditions where the silver ions are bound in the complex with polyethylenimine macromolecules and are distributed homogeneously over the volume of solution. The use of the polyethyleneimine complex with silver ions as a precursor of silver iodide allows the preparation of particles 1.2 nm in diameter with a narrow size distribution.

Evaluation of Orographic Cloud Seeding Using a Bin Microphysics Scheme: Two-Dimensional Approach

AbstractA new version of a bin microphysical scheme implemented into the Weather Research and Forecasting (WRF) Model was used to study the effect of glaciogenic seeding on precipitation formation in orographic clouds. The tracking of silver iodide (AgI) particles inside of water drops allows the proper simulation of the immersion nucleation. The ice formations by deposition, condensational freezing, and contact nucleation of AgI particles are also simulated in the scheme. Cloud formation—both stably stratified and convective—and the spread of AgI particles were simulated by idealized flow over a two-dimensional (2D) bell-shaped mountain. The results of numerical experiments show the following: (i) Only the airborne seeding enhances precipitation in stably stratified layer clouds. Seeding can reduce or enhance precipitation in convective clouds. AgI seeding can significantly affect the spatial distribution of the surface precipitation in orographic clouds. (ii) The positive seeding effect is primarily due to additional diffusional growth of AgI-nucleated ice crystals in layer clouds. In convective clouds, seeding-induced changes of both diffusion and riming processes determine the seeding effect. (iii) The seeding effect is inversely related to the natural precipitation efficiency. (iv) Bulk seeding parameterization is adequate to simulate AgI seeding impacts on wintertime orographic clouds. More uncertainties of ground-seeding effects are found between bulk and bin simulations.

Study on the Preparation and Characteristics of Cellulose/Silver Iodide Nanocomposite Film.

In this study, the structure and properties of an organic-inorganic composite material prepared from cellulose doped with fine particles of silver iodide (AgI) were examined. The preparation of the composite involved the complexation of cellulose with polyiodide ions, such as I- and 13-, by immersion in iodine/potassium iodide (I2/KI: 0.2, 0.4, 0.6, 0.8, 1.0 M) or potassium iodide (KI: 0.6, 1.2, 1.8, 2.4, 3.0 M) aqueous solutions followed by reaction in a silver nitrate (AgNO3:1.0 M) aqueous solution. These procedures resulted in the in situ formation of fine β-AgI particles within the cellulose matrix. The characteristics and conductivities of prepared cellulose/silver iodide (AgI) nanocomposite films with different I2/KI and KI concentrations were investigated. AgI particle formation and aggregation increased on increasing I2/KI and KI concentrations as determined by SEM. X-ray results showed that KI could penetrate the cellulose crystal region and form AgI particles. The electrical conductivities of nanocomposite films treated with KI were higher than that of I2/KI at < 1.0 M of I2/KI and 3 M of KI, although the weight gain by AgI formation was lower than that of I2/KI. This was also attributed to the formation of smaller AgI particles and crystal defects. Highest electrical conductivity (3.8 x 10(-7) Ω(-1) cm(-1)) was obtained from the cellulose films (1.25 x 10(-11) Ω(-1) cm(-1)) treated with the aqueous solutions of 1.0 M I2/KI and 1.0 M AgNO3.

Firm footing for cloud seeding

The pilots at Weather Modification Inc. were standing by on alert on Aug. 12, 2012, when they got word from their staff meteorologist to jump in their planes and head toward a budding thunderstorm just west of Calgary, Alberta. Their mission: to prevent the formation of crop-destroying, car-denting hail by shooting flares loaded with silver iodide into cumulus clouds. Some of the pilots headed for the smooth, rain-free base of the clouds at 2,000 meters, where updrafts could pull the inorganic compound in. Other pilots flew to 5,500 meters, penetrating the tops of the billowy formations. Once in position, the aviators ejected the flares mounted on their planes. Theoretically, the silver iodide particles that spewed forth would catalyze supercooled water droplets in the clouds to freeze at a warmer temperature and more abundantly than they might have otherwise. The pilots hoped that this maneuver would redistribute the water vapor in

Comparison of measured and calculated collision efficiencies at low temperatures

Abstract. Interactions of atmospheric aerosols with clouds influence cloud properties and modify the aerosol life cycle. Aerosol particles act as cloud condensation nuclei and ice nucleating particles or become incorporated into cloud droplets by scavenging. For an accurate description of aerosol scavenging and ice nucleation in contact mode, collision efficiency between droplets and aerosol particles needs to be known. This study derives the collision rate from experimental contact freezing data obtained with the ETH CoLlision Ice Nucleation CHamber (CLINCH). Freely falling 80 μm diameter water droplets are exposed to an aerosol consisting of 200 and 400 nm diameter silver iodide particles of concentrations from 500 to 5000 and 500 to 2000 cm−3, respectively, which act as ice nucleating particles in contact mode. The experimental data used to derive collision efficiency are in a temperature range of 238–245 K, where each collision of silver iodide particles with droplets can be assumed to result in the freezing of the droplet. An upper and lower limit of collision efficiency is also estimated for 800 nm diameter kaolinite particles. The chamber is kept at ice saturation at a temperature range of 236 to 261 K, leading to the slow evaporation of water droplets giving rise to thermophoresis and diffusiophoresis. Droplets and particles bear charges inducing electrophoresis. The experimentally derived collision efficiency values of 0.13, 0.07 and 0.047–0.11 for 200, 400 and 800 nm particles are around 1 order of magnitude higher than theoretical formulations which include Brownian diffusion, impaction, interception, thermophoretic, diffusiophoretic and electric forces. This discrepancy is most probably due to uncertainties and inaccuracies in the description of thermophoretic and diffusiophoretic processes acting together. This is, to the authors' knowledge, the first data set of collision efficiencies acquired below 273 K. More such experiments with different droplet and particle diameters are needed to improve our understanding of collision processes acting together.

Study on formulas of manual interventional glaze aerosols agents and their combustion properties

Based on the theory of silver iodide particles released by combustion of solid propellant, the aerosol agent that was appropriate for manual interventional glaze of power grid was prepared by pouring process in different prescriptions. The burning rate was studies to obtain the combustion properties of the ingredient, and component analysis of solid combustion products was tested by X-ray photoelectron emission microscopy. Otherwise, scanning electron microscope was implemented to study the particle size and distribution of solid combustion products. The mechanisms of solid combustion products were analysed by the combustion test results. The results showed that the formula of manual interventional glaze aerosols agents are environmentally friendly, and the technology of preparation is easy-going. Otherwise, the combustion process is stable, and the aerosol particles generated by combustion are small and distributed narrow. The prepared aerosols could satisfy the demands of power grid to eliminate the glaze.

Electron-stimulated desorption of the surface of mechanically modified silver-iodide particles

The interaction of electrons with the surface of AgI particles resulting from the exchange reaction of aqueous solutions of AgNO3 and KI is studied. The AgI powder is modified in a VIBRATOR GM-945B vibratory ball mill. The change in the surface topography of the AgI particles revealed by scanning electron microscopy is attributed to the desorption of atoms or ions from the surface of silver iodide under the action of an electron beam.

Capture of iodine from the vapour phase and immobilisation as sodalite

The work reports a study to investigate practical methods by which iodine capture from the vapour phase and subsequent conversion to stable wasteforms may be achieved. Iodine loaded commercial silver exchanged zeolite has been shown to convert to silver sodalite after hot isostatic pressing. The composition of the fully iodine loaded material is such that an excess of silver iodide particles forms during thermal conversion. Attempts to fabricate a mixed sodium silver sodalite have been unsuccessful.

Response of Natural Ice Nuclei to Deposited Silver Iodide

Aim: To demonstrate that deposition of silver iodide particles on the ground creates secondary ice nuclei and that these interfere with analyses of experiments designed to increase rainfall. Methods: Measurements of ice nucleus concentrations following the cessation of deposition of silver iodide during cloud seeding show that persistent secondary nuclei had been generated. The information is used to predict the effects on analyses of cloud seeding experiments. Effects on rainfall in large areas surrounding cloud seeding operations are then examined. Results: The predictions have explained effects such as a decrease in seeding effects with increasing application of silver iodide or with the duration of its application. Widespread downwind increases in rainfall appear to have accompanied all cloud seeding experiments. The explanation offered is that silver iodide increases the airborne concentration of ice nucleating bacteria or their properties. The secondary nuclei appear to be more efficient in stimulating rainfall than the silver iodide nuclei. Conclusions: Attempts to increase precipitation from clouds by seeding with silver iodide ice nuclei has been motivated by water shortages in many parts of the world. This paper has indicated that the frequent apparent slight or negligible success of such operations may have been due to the influence of the silver on ice nuclei of microbiological origin. An understanding of that influence is urgently required. Much larger and more widespread gains in rainfall than have been found in the past might then be obtained. Original Research Article

Numerical simulation of airborne cloud seeding over Greece, using a convective cloud model

An extensive work has been done by the Department of Meteorology and Climatology at Aristotle University of Thessaloniki and others using a three-dimensional cloud resolving model to simulate AgI seeding by aircraft of three distinct hailstorm cases occurred over Greece in period 2007-2009. The seeding criterion for silver iodide glaciogenic seeding from air is based on the beneficial competition mechanism. According to thermodynamic analysis and classification proposed by Marwitz (1972a, b, and c) and based on their structural and evolutionary properties we classified them in three groups as singlecell, multicell and supercell hailstorms. The seeding optimization for each selected case is conducted by analysis of the thermodynamic characteristics of the meteorological environment as well as radar reflectivity fields observed by the state of the art Thunderstorm Identification, Tracking, Analysis and Nowcasting (TITAN) software applied in the Greek National Hail Suppression Program (GNHSP). Results of this comprehensive study have shown positive effects with respect to hailfall decrease after successful seeding as our primarily objective. All three cases have illustrated 15-20% decrease in accumulated hailfall at the ground Seeded clouds have exhibited earlier development of precipitation and slight dynamical enhancement of the updraft and rainfall increase of ~10- 12.5%. The results have emphasized a strong interaction between cloud dynamics and microphysics, especially the subgrid scale processes that have impact on agent transport and diffusion in a complex environment. Comparisons between modelled and observed radar reflectivity also show a relatively good agreement. Simulated cloud seeding follows the operational aircraft seeding for hail suppression. The ability of silver-iodide particles to act as ice nuclei has been used to perform airborne cloud seeding, under controlled conditions of temperature and humidity. The seeding effects depend upon applying the seeding methodology in proper seeding time, right placement and agent dose rate.

Modification of silver iodide particles caused by a flow of electrons

A crystalline powder of AgI has been synthesized using an exchange reaction of aqueous solutions of AgNO3 and KI. The size and shape of the crystals are determined with the help of scanning electron microscopy. It is shown that nanocrystalline silver particles (30–70 nm) are formed at the surface of monocrystalline AgI particles (500–2000 nm) under the action of a focused bunch of electrons.

The Dispersion of Silver Iodide Particles from Ground-Based Generators over Complex Terrain. Part II: WRF Large-Eddy Simulations versus Observations

AbstractA numerical modeling study has been conducted to explore the ability of the Weather Research and Forecasting (WRF) model-based large-eddy simulation (LES) with 100-m grid spacing to reproduce silver iodide (AgI) particle dispersion by comparing the model results with measurements made on 16 February 2011 over the Medicine Bow Mountains in Wyoming. Xue et al.'s recently developed AgI cloud-seeding parameterization was applied in this study to simulate AgI release from ground-based generators. Qualitative and quantitative comparisons between the LES results and observed AgI concentrations were conducted. Analyses of turbulent kinetic energy (TKE) features within the planetary boundary layer (PBL) and comparisons between the 100-m LES and simulations with 500-m grid spacing were performed as well. The results showed the following: 1) Despite the moist bias close to the ground and above 4 km AGL, the LES with 100-m grid spacing captured the essential environmental conditions except for a slightly more stable PBL relative to the observed soundings. 2) Wind shear is the dominant TKE production mechanism in wintertime PBL over complex terrain and generates a PBL of about 1000-m depth. The terrain-induced turbulent eddies are primarily responsible for the vertical dispersion of AgI particles. 3) The LES-simulated AgI plumes were shallow and narrow, in agreement with observations. The LES overestimated AgI concentrations close to the ground, which is consistent with the higher static stability in the model than is observed. 4) Non-LES simulations using PBL schemes had difficulty in capturing the shear-dominant turbulent PBL structure over complex terrain in wintertime. Therefore, LES of wintertime orographic clouds with grid spacing close to 500 m or finer are recommended.