Silver Iodide Particles Research Articles

The Dispersion of Silver Iodide Particles from Ground-Based Generators over Complex Terrain. Part I: Observations with Acoustic Ice Nucleus Counters

AbstractPart I of this paper presents the results from a series of plume-tracing flights over the Medicine Bow and Sierra Madre Ranges in south-central Wyoming. These flights, conducted during February and early March of 2011, were part of the Wyoming Weather Modification Pilot Project. Effective targeting of ground-based silver iodide plumes to supercooled clouds has long been a problem for winter orographic cloud-seeding projects. Surface-based ice nucleus (IN) measurements made at a fixed location near the Medicine Bow Range target area had confirmed the effective transport of IN plumes in many cases, but not all. Airborne plume tracing, undertaken to further illuminate the processes involved, provided additional insight into the plume behavior while providing physical measurements that were later compared with large-eddy-simulation modeling (Part II). It was found that the plumes were most often encountered along the flight paths set out in the experimental designs and, in the absence of convection, appear to be mostly confined to the lowest 600 m above the highest terrain. All passes above 600 m above ground level revealed IN concentrations greater than background levels, however. An estimate of IN flux measured over the Medicine Bow Range was approximately 85% of that produced by the five ground-based IN generators active at the time.

Mechanical modification of β-AgI nanocrystals

A nanostructured AgI powder has been synthesized. The structure, sizes, and shapes of nanoparticles of the initial powder and a powder modified in a VIBRATOR GM-945B vibration ball mill have been investigated by SEM, X-ray diffraction, and differential thermal analysis. A hypothesis of the structure and microscopic mechanism of structural transformations in the materials under study is proposed. Particular attention is paid to the ac ionic conduction of silver iodide particles.

Collective interactions in the mechanism of adhesion of condensed phase nuclei to a crystal surface. 1. Spatial organization

Self-organization into domains with spontaneous polarization is revealed for an ensemble of water molecules occurring in a contact layer on a defectless polarizable crystal surface. These domains are the sources for specific heteropolarization interactions of condensed phase nuclei with a substrate. The formation of a spatially nonuniform structure is energetically advantageous due to a nonlinear dependence of polarization energy on field strength. Domain sizes equal to several nanometers are governed by the competition between the energy advantage resulting from the coalescence of the domains and the entropy gain caused by their disintegration into smaller fragments. The forces of spontaneous mutual polarization between an adsorbed film divided into domains and a polarized substrate enhance the adhesion to the surface and markedly affect the adsorption mechanism. Computer simulation of the domain formation in a film of water molecules adsorbed on the surface of crystalline silver iodide particles is implemented by the Monte Carlo method with the summation of the long-range electrostatic interactions by means of the Fourier expansion of the field potential. Comparative analysis of the collective behavior of molecules, which underlies the layer-by-layer nucleation, and the indirect signs of domain formation is performed on the basis of experimental data on polarized surfaces with a hexagonal crystalline structure.

Synthesis of High Concentration Colloid Solution of Silica-Coated AgI Nanoparticles

Methods for high concentration silica-coated silver iodide (AgI/SiO2) particles, which could be practically used as X-ray contrast agent, were examined. The first was a single-step method, which was to prepare AgI nanoparticles at an AgI concentration of 5 x 10(-3) M and coat the AgI nanoparticles with silica shell by a Stöber method. The second was a multiple-step method, which was to repeat a step for preparing a AgI/SiO2 particle colloid solution with 10(-3) M AgI 5 times for adjusting a final AgI concentration to 5 x 10(-3) M. In the two methods, dominant particle aggregation took place, though core-shell particles were also produced. The third was a salting-out method, which was to salt out AgI/SiO2 particles in their colloid solution prepared at an AgI concentration of 10(-3) M, remove supernatant by decantation, and redisperse the particles in a fresh solvent. Consequently, AgI/SiO2 particles with an AgI concentration as high as 0.05 M were successfully prepared with the salting-out method, and their core-shell structure was not damaged during the salting-out.

Designing of hollow AgI spheres by ultrasonic spray pyrolysis

A theoretical model which describes the mechanism of droplet formation, structures of the complexes used in the precursor solution and hollow AgI particles prepared by the process of ultrasonic spray pyrolysis (USP) was investigated. Theoretical approaches described very well the properties of silver iodide particles collected and aged in 2-propanol after the USP process. The morphology of hollow silver iodide particles aged in 2-propanol was found to be connected with the mechanism of surface precipitation caused by low precursor density. In addition, the structures of small complexes used are directly connected with structural changes in the synthesized hollow AgI particles. The proposed model and experimental results imply that the structure of the starting thermodynamically stable AgI complexes, used for the first time as a precursor solution, affects the final particle structure.

Iodine-aided palladium-free catalyzation process for durable electroless nickel plating on Kevlar® fiber

We report here a highly durable electroless nickel plating on Kevlar fiber through iodine-aided palladium-free catalyzation process. Kevlar was first treated with an iodine–potassium iodide aqueous solution to impart iodide component into the near fiber surface. The doped iodine was converted to silver iodide particles by treatment with silver nitrate aqueous solution, and subsequently silver iodide was reduced to silver metal particles. After electroless plating, a smooth nickel layer was evenly deposited on the fiber surface, which was resistant against sonication, tape peel-off, and alkaline corrosion tests. The silver particles formed on and near the fiber surface act as an anchor for the plated layer as well as a catalyst for electroless plating. Further investigation revealed that the use of an anionic surfactant during the catalyzation process enhanced the adhesive force of the plated layer with fiber surface. The plated fibers possessed high tensile strength, electrical conductivity, and ferromagnetic properties.

J024031 氷核活性を抑制するポリフェノール化合物の効果

Antifreeze proteins (AFPs) and several synthetic polymers are known as anti-ice nuclei (anti-IN), which inactivate ice nuclei (IN) in water and thus inhibit heterogeneous ice nucleation catalyzed by IN. Recently, it has been found that several types of polyphenol compounds also inhibit heterogeneous ice nucleation. In this study, ice nucleation catalyzed by silver iodide (Agl) particles, which are typical inorganic IN, in emulsified solutions of five different polyphenol compounds (a-oligoglucosyl quercetin 3-O-β-D-glucopyranoside (Q3(Glc)n), epigallocatechin gallate (EGCG), tea catechin, tannic acid, and oligonol) was investigated experimentally. Results showed that the ice nucleating activity of Agl was inactivated by all the polyphenols used here. For Q3(Glc)n and EGCG solutions, in the majority of the emulsified droplets, ice nucleation occurred within a narrow temperature range between -17 and -20℃. On the contrary, for tea catechin, tannic acid, and oligonol solutions, ice nucleation occurred within relatively wide temperature range between -17 and -38 ℃. The highest ice nucleation temperatures in the emulsified droplets of the polyphenol solutions were considerably lower than those of AFP and synthetic polymer solutions. Especially, the highest ice nucleation temperature for oligonol solution was -19.4 ℃. Such anti-ice nucleating activities of the polyphenols available at relatively high temperatures would be promising for practical applications in various fields.

Field measurements suggest the mechanism of laser-assisted water condensation

Because of the potential impact on agriculture and other key human activities, efforts have been dedicated to the local control of precipitation. The most common approach consists of dispersing small particles of dry ice, silver iodide, or other salts in the atmosphere. Here we show, using field experiments conducted under various atmospheric conditions, that laser filaments can induce water condensation and fast droplet growth up to several μm in diameter in the atmosphere as soon as the relative humidity exceeds 70%. We propose that this effect relies mainly on photochemical formation of p.p.m.-range concentrations of hygroscopic HNO3, allowing efficient binary HNO3–H2O condensation in the laser filaments. Thermodynamic, as well as kinetic, numerical modelling based on this scenario semiquantitatively reproduces the experimental results, suggesting that particle stabilization by HNO3 has a substantial role in the laser-induced condensation.

Synthesis of Silica-Coated AgI Nanoparticles and Immobilization of Proteins on Them

This paper describes a method for preparing silica-coated silver iodide (AgI/SiO2) particles and immobilizing proteins on the AgI/SiO2 particles. Colloid solution of AgI particles was prepared by mixing AgClO4 aqueous solution and KI aqueous solution. Silica-coating of the AgI particles was performed by adding 3-mercaptopropyltrimethoxysilane, tetraethylorthosilicate/ethanol solution and NaOH aqueous solution successively to the AgI colloid solution. TEM observation revealed that the AgI nanoparticles were coated with uniform silica shell. The AgI/SiO2 particles were surface-modified with 3-aminopropyltrimethoxysilane and succinic anhydride. It was confirmed by XPS measurement that amino group or carboxyl group was introduced onto the AgI/SiO2 particles. Protein-immobilization was performed in aqueous solution with bovine serum albumin (BSA) in the presence of the surface-modified AgI/SiO2 particles. UV-VIS absorption spectroscopy revealed that the BSA was adsorbed on the surface-modified particles.

Anomalous Conductivity Behavior of AgI-Vycor7930 Nanocomposites

Using the electrocrystallization process, silver iodide particles were embedded into bulk Vycor7930 porous glass (VPG) to obtain ionic conductor composite. X-ray microdiffraction (μXRD) was carried out on the composite. AgI was found to be in its β-form with nanometric crystallite size. Microstructure has also been investigated by scanning electron microscopy (SEM). The ionic conductor was found to be embedded in the center of the VPG disk, into the 4 nm diameter pore network. Electron probe for micro analysis (EPMA) has shown the homogeneity of the silver iodide precipitate inside the VPG. Electrical conductivity was measured by complex impedance spectroscopy (CIS). A large hysteresis phenomenon in the conductivity versus temperature curve at a temperature close to the transition β ↔ α-AgI was observed. At low temperature, the conductivity of the composite was found to be higher than that of pure β-AgI by 1 order of magnitude.

Conductivity and structure of a polyamide/silver iodide nanocomposite

AbstractIn this study, the structure and properties of an organic–inorganic composite material prepared from nylon 6 doped with fine particles of silver iodide (AgI) were examined. The preparation of the composite involved the complexation of nylon 6 with polyiodide ions such as I and I by immersion in an iodine/potassium iodide (I2–KI) aqueous solution followed by reaction in a silver nitrate (AgNO3) aqueous solution; this resulted in the in situ formation of β‐AgI fine particles within the nylon 6 matrix. The AgI content formed in the composite was dependent on the immersion temperatures of the I2–KI and AgNO3 solutions. Lower solution temperatures resulted in larger amounts of AgI in the composite. This method readily provided a composite with a high content of AgI in nylon 6 and a conductivity of approximately 10−5 Ω−1 cm−1. In a uniaxially oriented nylon 6 matrix, AgI particles precipitated with anisotropic shape, which was caused by the orientation of the precursor polyiodide ions. The structure of the oriented composite provided the anisotropic conductivity. Additionally, the composite exhibited high antibacterial properties. The procedure used in this study is considered a unique method for the preparation of organic–inorganic composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The Zurich Ice Nucleation Chamber (ZINC)-A New Instrument to Investigate Atmospheric Ice Formation

A new instrument to study ice nucleation, the Zurich Ice Nucleation Chamber (ZINC), has been constructed. It is a continuous flow diffusion chamber following the design by Rogers (1988) but has a flat parallel plate geometry. The instrument can operate at temperatures as low as 236 K with the current setup with ice supersaturations of up to 50%. The typical sample flow is 1 lpm with a total flow of 10 lpm using twice 4.5 lpm for sheath flows. FLUENT simulations were performed and are presented to discuss the flow, temperature, and humidity profiles within the main chamber. Activation experiments with silver iodide particles were used to validate the instrument against literature data. We report the onset of freezing for an activated fraction of 2% of all particles. The data exhibit an almost linear trend between 257 K (111.5% RHi) and 237 K (119% RHi) with very good agreement with literature data.

Fabrication of Nylon 6 / Silver Iodide Composite Fiber from Polymer-Iodine Complex

In this study, the structure and properties of an organic-inorganic composite fiber, prepared from nylon 6 doped with fine particles of silver iodide (AgI), were examined. The preparation of the composite fiber involved the complexation of nylon 6 with polyiodide ions such as I3. and I5. by immersion in an iodine-potassium iodide(I2-KI) aqueous solution, followed by reaction in an AgNO3 aqueous solution, resulting in the in-situ precipitation of Beta-AgI fine particles within the nylon 6 fiber. AgI was formed as anisotropic particles, and displayed crystallite orientation in the oriented nylon 6 fiber. This is attributed to the orientation of polyiodide ions, as the precursor of AgI, in the orientated nylon 6 chain. The composite exhibited conductivity of approximately 10.5 ohm-1 cm-1.

Influence of solvent on the structural and morphological properties of AgI particles prepared using ultrasonic spray pyrolysis

Silver iodide particles were synthesized in the process of ultrasonic spray pyrolysis using aqueous solutions of thermodynamically stable silver iodide clusters as precursor. The AgI particles were collected in solvents of different polarities such as water, 2-propanol and toluene. In order to study influence of solvent and aging time on the morphological and structural properties of the AgI particles ultra-filtration was employed to isolate solid material from solution. The scanning electron microscopy showed that morphology of the AgI particles is different for different solvents. The AgI particles with hexagonal/triangular shape were obtained in water and toluene, while in 2-propanol hollow spheres were formed. The X-ray diffraction analysis, besides wurtzite hexagonal and zinc blende cubic phases, revealed appearance of tetragonal high-pressure AgI modification for sample collected in toluene and for sample aged in 2-propanol. The aging in toluene induced transformation of all three modifications into single phase with one preferred orientation.

Photothermographic Materials with Nanoparticles of Silver Iodide

We have found that nanoparticles of silver iodide have high sensitivity for blue light and are fixed during thermal development in photothermographic materials. Silver iodide particles exhibit high sensitivity and weak LIRF in photothermographic materials, as they do in conventional materials with higher silver ion concentration than usual, and have their sensitivity further improved by reducing agents adsorptive to the particles. The sensitivity of photothermographic materials with nanoparticles of silver iodide for blue laser light could be comparable to that of the materials with silver iodobromide for red laser light. Silver iodide particles are slowly fixed during thermal development in photothermographic materials with existence of either silver carboxylate or phthalazine, and rapidly fixed with coexistence of these two compounds. Fog density of developed layers of photothermographic materials with nanoparticles of silver iodide does not increase under room light illumination.

Formation of silver iodide particles from thermodynamically stable clusters using ultrasonic spray pyrolysis

Silver iodide particles in the submicronic size domain were synthesized in the process of ultrasonic spray pyrolysis (USP) using aqueous solutions of thermodynamically stable silver iodide clusters as precursor. After the process of USP, the AgI particles were collected in water. In order to study influence of aging time on the morphological and structural properties of the AgI particles, ultra-filtration was employed to isolate solid material from solution. The scanning electron microscopy showed change from spherical to hexagonal/triangular shape and increase of average particle size of the AgI particles as a function of aging time, which is characteristic for the Ostwald ripening growth mechanism. The X-ray diffraction measurements revealed the presence of wurtzite hexagonal and zinc blende cubic AgI modifications whose abundance is also dependent on the aging time.

A Comparison of Wasteforms and Processes for the Immobilisation of Iodine-129

ABSTRACTA range of potential wasteforms for the immobilisation of iodine-129 have been synthesised and compared. The work used both iodosodalite and iodovanadinite, as identified in previous studies, as baseline iodine host phases. Syntheses of related compounds using alternative precursors had varying degrees of success. In addition it was shown that iodine could potentially be isolated in a simple composite wasteform of silver iodide particles in a rutile or anatase matrix. Preliminary leaching studies suggest that iodosodalite dissolves congruently whilst iodovanadinite shows preferential release of iodine at a rate approximately ten times that of matrix alteration.

Surface chemistry of colloidal silver: surface plasmon damping by chemisorbed iodide, hydrosulfide (SH-), and phenylthiolate

The optical changes that occur upon the addition of iodide, iodine, and colloidal silver iodide to a colloidal solution of silver particles (6-nm mean diameter) were monitored spectrophotometrically. For small concentrations of added I - and I 2 (formation of less than a monolayer of adsorbate), the changes in the shape of the silver plasmon absorption band are practically identical. Silver iodide particles in contact with silver particles affect the plasmon band only slightly. It is concluded that the AgI molecules formed by the surface oxidation of the Ag particles by iodine do not possess the properties of bulk AgI

Semiconductor photophysics. 5. Charge carrier trapping in ultrasmall silver iodide particles and kinetics of formation of silver atom clusters

Reactions of reducing species from acetonitrile media with silver iodide particles ({approximately}25-{angstrom} diameter) have been investigated by pulse radiolysis techniques. Injection of electrons into these ultrasmall particles leads to transient bleaching of the adsorption of AgI at wavelengths close to the onset of absorption ({approximately}400 nm) with the concomitant reduction of AgI to metallic silver. The reduction of Ag{sup +} ions and formation of silver atoms and/or dimeric Ag{sub 2} molecules on three different size AgI particles ({approximately}100, 35, and {approximately}25 {angstrom}) have also been examined by picosecond laser spectroscopy.

Kinetics of ice nucleation on aerosol particles in supercooled fog—I. The influence of water vapour depletion

The kinetics of heterogeneous nucleation of ice on aerosol particles has been experimentally studied in supercooled fog. Two cloud chambers of 0.018 and 0.25 m 3, constructed so as to avoid local supersaturations of hot vapour in cold air, have been employed to study kinetics dependencies. Particles of silver iodide, mass-mean radii of 4–100 nm, and of copper acetyl acetonate, 80–120 nm, have been used as ice-forming nuclei. At the supercooled fog temperatures of 268, 263 and 253 K the ice nucleation constant has been shown to be practically independent on the aerosol particles size. The effect of ice crystal concentrations in fog on the frequency of ice nucleation on particles has been observed.