Study of dielectric properties of nanophase silver iodide

Dielectric properties of nanophase AgI are studied over the frequency range from 100 kHz to 3 MHz at different temperatures. The values ofε, tanδ andσ _ac are considerably larger than those reported for crystalline pellets of AgI, but they show a similar trend in variation with frequency and temperature. The increase in these values are attributed to the defect structure of the nano-particles.     

A new chemical method of formation of silver iodide thin films

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Preparation of silver iodide nanoparticles using laser ablation in liquid for antibacterial applications

In this study, the authors reported the first synthesis process of silver iodide (AgI) nanoparticles (NPs) by pulsed laser ablation of the AgI target in deionised distilled water. The optical and structural properties of AgI NPs were investigated by using UV–vis absorption, X‐ray diffraction, scanning electron microscope (SEM), energy dispersive X‐ray, Fourier transform infrared spectroscopy, and transmission electron microscope (TEM). The optical data showed the presence of plasmon peak at 434 nm and the optical bandgap was found to be 2.6 eV at room temperature. SEM results confirm the agglomeration and aggregation of synthesised AgI NPs. TEM investigation showed that AgI NPs have a spherical shape and the average particle size was around 20 nm. The particle size distribution was the Gaussian type. The results showed that the synthesised AgI NPs have antibacterial activities against both bacterial strains and the activities were more potent against gram‐negative bacteria.Inspec keywords: antibacterial activity, nanoparticles, X‐ray chemical analysis, particle size, transmission electron microscopy, X‐ray diffraction, nanofabrication, scanning electron microscopy, visible spectra, ultraviolet spectra, silver compounds, pulsed laser deposition, Fourier transform infrared spectra, optical constants, energy gap, aggregationOther keywords: synthesis process, pulsed laser ablation, AgI target, deionised distilled water, optical properties, structural properties, UV–vis absorption, X‐ray diffraction, transmission electron microscope, optical data, optical bandgap, antibacterial activities, silver iodide nanoparticles, energy dispersive X‐ray analysis, SEM, wavelength 434.0 nm, temperature 293 K to 298 K, AgI     

Electrodeless growth of silver iodide nanowires in a polycarbonate membrane using chemical reaction

We report the fabrication, structural and optical characterization of Silver iodide (AgI) nanowires. Large scale uniform nanowires with lengths 40 m and diameter 100 nm were grown using the simple chemical reaction technique. Morphological study of AgI nanowires was done using scanning electron microscopy. X-ray diffraction studies show the crystalline structure of AgI nanowires. Energy dispersive X-ray fluorescence technique was used to study the composition of AgI nanowires. UV–Vis absorption studies were made to calculate the optical band gap of AgI nanowires. Photo-luminescence spectrum shows a broad emission peak around 460 nm.     

Hydrogen-induced sensitization,photochromism, and giant IR absorption in thin silver iodide films

New effects related to the behavior of atomic hydrogen in thin silver iodide (AgI) films have been observed. Hydrogen-induced sensitization produced simultaneously with illumination of the AgI film surface leads to a deep photolysis of the halide compound, which leads to the formation of silver clusters and colloids and produces a sharp change in the optical properties of the material (photochromism). The average diameter of the photolytic colloidal particles formed in AgI films does not exceed 20 nm, which accounts for their large specific surface. The adsorption of hydrogen-donor molecules used for the photosensitization on silver colloids gives rise to the giant IR absorption, which is related to the oscillations of atoms in adsorbed molecules. This phenomenon offers a probe for the investigation of atomic hydrogen photodetachment involved in AgI photosensitization.     

Influence of Topical Fluorides on corrosion behaviour of silver amalgam alloys

Potentiodynamic polarization and cyclic voltametry measurements were employed to study the effect of topical fluoride preparations on corrosion of silver amalgam alloy in synthetic saliva and aqueous fluoride solutions. Results support that small amounts of copper and indium alloyed to silver – tin amalgam enhance corrosion resistance considerably. Indiloy shifts both the open circuit potential and the anodic polarization curve to more positive potential values, this lead to a decreases in the current density. The weak activity of Indiloy as compared with Spheraloy is attributed to the fact that the amount of γ₂ phase (tin–mercury) present in the former is much lesser than that present in the latter. Findings also show that fluoride solutions (NaF, SnF and SnF + HCI) enhance the dissolution rate of the investigasted alloys and the polarization curves illustrate the appearance of an active – passive transitions. This behaviour was discussed on the basis of complex formation. Cyclic voltammograms confirm the results obtained from the potentiodynamic polarization measurements and elucidate the anodic oxidation peaks of silver oxide and copper verifying the proposed mechanism.     

Fatigue behaviour of metallic fibre-reinforced materials: a study of steel fibre-reinforced silver

Low-cycle fatigue tests were performed on silver matrix-steel-fibre-reinforced composites (FRC) with unidirectionally aligned fibres of constant volume-fraction,V _f=0.35. The influence of various material parameters, namely the fibre and matrix strengths, the interfacial bond strength and the mean fibre diameter, was examined. Low-cycle fatigue hardening and softening of FRCs deviate from the behaviour expected from the properties of the components. The differences are mainly based on a specific deformation or recrystallization structure of the composite matrix. The shapes of the stress—strain hysteresis loops are discussed qualitatively and compared to the experimental results. The comparison of fatigue life for different material conditions shows that the design of low-cycle fatigue-resistant metallic-fibre composites requires material criteria similar to those known to be responsible for high ultimate tensile strengths. The criteria may be varied if the composites are subjected to high-cycle fatigue loading.     

Age-hardening behaviour and microstructure of a silver alloy with high Cu content for dental application

Age-hardening behaviour and the related microstructural changes of a silver alloy with relatively high Cu content were elucidated by means of hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) observations and electron probe microanalysis (EPMA). The microstructure of the solution-treated specimen was composed of the Ag-rich matrix, the Cu-rich particle-like structures containing Pd, and the lamellar structure of both phases. By the age-hardening heat-treatment, the Cu element began to precipitate from the Ag-rich matrix by the solubility limit, and the very fine Cu-rich precipitates became coarsened by further aging. The silver alloy with relatively high Cu content showed apparent age-hardenability. The hardness of the solution-treated specimen began to increase and reached a maximum value with increasing aging time, and then the hardness decreased gradually after maintaining the maximum value for short periods of time. The early stage of precipitation of the Cu-rich phase from the Ag-rich matrix seemed to have caused the increase in hardness. The decrease in hardness was attributed to the coarsening of the Cu-rich precipitates in the later stage of the age-hardening process.     

Effect of static charge on the tarnishing behaviour of silver in iodine atmosphere at low temperatures

The kinetics of Agl film growth on silver under the action of applied static charge of both the polarities, as well as under normal iodination conditions in the temperature range of 294 to 338 K and in the iodine partial pressure range of 0.03 to 0.22kPa, conform to parabolic rate law. Compared to normal iodination, an enhancement in rate under both positive and negative surface charge conditions at the Ag/Agl interface and a decrease in rate under either surface charge condition at the Agl/l₂ interface have been observed. The increased rate with negative charge at the Ag/Agl interface and the decreased rate with same kind of charge at the Agl/l₂ interface, compared to normal iodination, can be explained on the basis of positive hole transport, while the observed effects with positive charge at either of the interfaces receive reasonable support from cation migration as the rate limiting factor during the film growth process.     

Antimicrobial activity of UV-irradiated nylon film for packaging applications

Antimicrobial packaging could enhance food storage life and safety. An antimicrobial moiety that is permanently bound to the polymer surface and does not leach has particular appeal. The use of 193 nm UV irradiation to convert amide groups on the surface of nylon to amines having antimicrobial activity has been reported previously. We prepared materials accordingly and explored their mode of action and activity against pathogens. Three food related bacterial strains, Staphylococcus aureus, Pseudomonas fluorescens and Enterococcus faecalis were exposed to antimicrobial film in 0.2 M sodium phosphate buffer (pH 7.0). Samples were held shaken at 100 r.p.m. in a 25°C incubator. The antimicrobial film was effective in reduction of microbial concentration in the bulk fluid for all food-related bacteria tested. The effectiveness was dependent on the bacterial strain. Adsorption of bacterial cells diminished the effectiveness of amine groups. Experimental results indicate that the decrease in concentration of bacterial cells in bulk fluid is more likely to be the bactericidal action than adsorption of live cells. © 1998 John Wiley & Sons, Ltd.     

Electrical behaviour of discontinuous silver films deposited on compatible Polystyrene/Poly (2-vinylpyridine) composite

Polystyrene (PS) and Poly (2-vinylpyridine) (P2VP) was melt blended. The compatibility of PS/P2VP was investigated by differential scanning calorimetry (DSC), Fourier transmission Infrared (FTIR) and scanning electron microscopy (SEM). The results indicated the single glass transition temperature for the blend. Results of the studies carried out on the electrical behaviour of silver island films deposited on the composite of PS and P2VP are presented here. The substrates were held at 457 K, much above the glass transition temperature of the polymers to ensure sufficient polymer fluidity during deposition, to obtain a sub-surface particulate film. A constant deposition rate of 0.4 nm/s was used through out the study. Silver films deposited on softened PS give rise to a very high room temperature resistance approaching that of the substrate resistance due to the formation of a highly agglomerated structure. On the other hand, films on softened P2VP gives rise to a room temperature resistance in the range of tens to a few hundred MΩ/□ which is desirable for device applications. The composite of PS and P2VP show resistances at room temperature. The films show an increase in resistance, when they are exposed to atmosphere. This is attributed to the oxidation of silver islands. The film resistances in the desired range could be obtained even, after exposure to atmosphere with PS concentration of 50%.     

Electrical behaviour of discontinuous silver films deposited on softened polystyrene and poly (4-vinylpyridine) blends

Results of the studies carried out on the electrical behaviour of silver island films deposited on the blends of polystyrene (PS) and poly (4-vinylpyridine) (P4VP) are presented here. The substrates were held at 457 K, much above the glass transition temperature of both the polymers to ensure sufficient polymer fluidity during deposition, to obtain a sub-surface particulate film. A constant deposition rate of 0.4 nm/s was used throughout the study. Films on softened PS gives rise to a very high room temperature resistance approaching that of the substrate resistance due to the formation of a highly agglomerated structure. On the other hand, films on softened P4VP gives rise to a room temperature resistance in the range of a few tens to a few hundred MΩ/, which is desirable for device applications. The blends of PS and P4VP show room temperature resistances in the desirable range even at a PS/P4VP ratio of 75:25. The films show an increase in resistance when they are exposed to atmosphere. This is attributed to the oxidation of silver islands. The film resistances in the desired range could be obtained even after exposure to atmosphere up to a PS concentration of 50%.     

Diffusion of silver in silver vanadium bronzes

Diffusion constants of silver in silver vanadium bronzes Ag_xV₂O₅ are given as a function of x in the temperature range 200 – 450 °C. The measurements were done by means of a galvanostatic pulse technique. The results indicate a very slow diffusion of the silver (e.g. D_Ag⁺ = 10^?12 cm²s^?1 at 400 °C, x=0.30).     

Synthesis of sub-micron silver and silver sulfide particles via solvothermal silver azide decomposition

Many transition-metal azides are thermodynamically unstable with respect to the elements and thus, may serve as energetic precursor sources in nanoscale metal particle synthesis. This report describes the use of silver azide (AgN₃) in nonaqueous, solvothermal decomposition reactions to produce crystalline sub-micron silver particles and interconnected structures. The thermal decomposition of AgN₃ directly produces silver and N₂ and no secondary chemical reducing agent is required. This solvothermal conversion was examined in toluene, tetrahydrofuran (THF), and trioctylamine below 250 °C. The coordinating solvents produced the smallest particles (150-500 nm), while the toluene reaction products were near 1 μm in size. The addition of soluble elemental sulfur to the THF reaction results in the growth of silver sulfide particles near 1 μm in size. The silver and Ag₂S products are crystalline by X-ray diffraction and show some faceting by scanning electron microscopy.     

全氟乙基碘制备新工艺

简要介绍了全氟乙基碘合成技术中催化剂、工艺方法、原料路线等方面的进展。     

Optical properties of thallium mercury iodide

We investigated the growth conditions and obtained Tl₄HgI₆ nonlinear crystals of red and black phases. We also measured the dispersion of the black-phase crystal refractive indices and analyzed possible nonlinear three-frequency processes.     

The crystal growth of bismuth iodide

The growth of platelet crystals of bismuth iodide 1 to 10 microns thick by an open flow sublimation technique is described. The best crystals were prepared in a Pyrex glass apparatus by passing argon, at a flow rate of 40 cc/min. over iodine at 25°C. and reacting this gas mixture with elemental bismuth heated to 310°C. Bismuth iodide crystals, suitable for optical absorption measurements grew in a temperature gradient ranging from 210°C. to 90°C. The optical properties of the crystals were dependent on the growth temperature.