Silver clusters from nozzle expansions

This note reports on the first successfull experiments to generate silver clusters (N≦100) in supersonic nozzle flows. A mixture of argon/silver-vapor was used expanding from a conical nozzle (0.35 mm, 10° full cone angle, 17 mm long conical section). Source temperature and total pressure ranged up to 2200 K/300 kPa, and silver partial pressure up to 25 kPa. The data confirm the scaling laws developed to compare clustering of metals with that of rare gases.     

A coated tubular solid-state chloride-selective electrode in flow-injection analysis

The construction, suitability and behaviour of a coated tubular solid-state chloride ion-selective electrode in continuous flow analysis are discussed. The flow-through cell is constructed easily from Tygon tubing and silver foil, which is treated to give a silver/silver chloride electrode. The optimum contact area is obtained with a tube 5 mm long and of 2 mm internal diameter, for a total flow rate of 4.7 cm³ min^?1; the carrier streams are 1.0 mol dm³ potassium nitrate. Response times are fast (3–4 s for 95% response). With 30-μl samples, the working range covers 5–5000 mg dm³ chloride with a reproducibility better than 1.7% (relative standard deviation); the stability of the system is excellent. Interferences are similar to those found in batch analysis with Ag/AgCl electrodes, but are less severe in the flow system; pH has no effect in the range 2–12. Results obtained for chloride in waters at a sample throughput rate of about 120 h^?1 agree well with results by a standard spectrophotometric automated method.     

High Ethene/Ethane Selectivity in 2,2′‐Bipyridine‐Based Silver(I) Complexes by Removal of Coordinated Solvent

Following removal of coordinated CH₃CN, the resulting complexes [Ag^I(2,2′‐bipyridine)][BF₄] ( 1 ) and [Ag^I(6,6′‐dimethyl‐2,2′‐bipyridine)][OTf] ( 2 ) show ethene/ethane sorption selectivities of 390 and 340, respectively, and corresponding ethene sorption capacities of 2.38 and 2.18 mmol g^?1 when tested at an applied gas pressure of 90 kPa and a temperature of (20±1) °C. These ethene/ethane selectivities are 13 times higher than those reported for known solid sorbents for ethene/ethane separation. For 2 , ethene sorption reached 90 % of equilibrium capacity within 15 minutes, and this equilibrium capacity was maintained over the three sorption/desorption cycles tested. The rates of ethene sorption were also measured. To our knowledge, these are the first complexes, designed for olefin/paraffin separations, which have open silver(I) sites. The high selectivities arise from these open silver(I) sites and the relatively low molecular surface areas of the complexes.     

Adsorption isotherms for oxygen chemisorbed on silver powder

Adsorption isotherms have been measured on cleaned silver powder from 178 to 339°C at oxygen pressures of 0.226 Pa to 40 kPa using a vacuum ultramicrobalance. Adsorption equilibrium was found at all temperatures and pressures studied. The surface was prepared for the reproducible chemisorption studies using an established method of cyclic outgassing, oxygen adsorption and reduction in carbon monoxide. Seven isotherms were measured that spanned fractional surface coverages from 0.17 to 1.1. The isosteric heat of adsorption q was determined at constant values of θ. After decreasing from 42 to 17.7 kcal mol^?1 at the lower coverages, q remains constant at 18.4 ± 0.8 kcal mol^?1 from θ of 0.33 to about 0.90 and then decreases to zero at the highest coverages and temperatures. The initial drop in q is attributed to the formation of islands of a two-dimensional surface silver oxide. The constant value of q results then from the completion of the oxide layer and molecular adsorption on and/or through the oxide. The decrease in q to zero at the highest coverages results from repulsions in the adlayer at T ≤ 275°C and absorption into silver at T > 302°C.     

Indirect potentiometric flow-injection determination of silver in photographic fixing solutions

The thiosulfate present in fixing solutions was destroyed on-line by acidification and the undissolved gaseous products were separated from the flow stream by use of polytetrafluoroethylene microporous tubing. The silver was precipitated with an excess of sulfide, and the excess was measured with a silver/silver sulfide electrode. Silver was determined in several ranges from 1 mg 1^?1 to 10 g l^?1.     

Kinetics of gas-phase decomposition of oxetan and oxetan-2,2-d2

The pressure dependence of the first-order rate coefficient of oxetan and oxetan-2,2-d₂ decomposition has been studied in the pressure range from about 7 kPa down to 0.01 kPa at various temperatures between 673 and 758 K. Experimental data were analyzed using RRKM theory. Interpretation of the fall-off curves lends support to the high-pressure Arrhenius parameters A = 10^15.42s^?1 and E_A = 259.5 kJ/mol derived from measurements made in the pressure-independent range. Decomposition of oxetan is found to occur via biradical intermediates. Data for the kinetic isotope effect were used to derive kinetic parameters for the ring-opening elementary steps in oxetan and oxetan-d₂ decomposition.     

Rate Constants and Sticking Coefficients for H2 and He Obtained by Analysis of Agglomeration in a Nozzle Beam

Cluster–cluster reaction rate constants are obtained from measurements of coalescence in nozzle‐beam expansions. Coalescence is described by the Smoluchowski equations, modified to accommodate changes in volume and temperature. The asymptotic form of the cluster size distribution can reveal the scaling of the second‐order rate constants K_jk with the sizes of colliding particles. Scalings derived in the past are demonstrably incorrect and physically unjustifiable. Here, we use the physically reasonable scaling, K_jk = K₁₁j^μk^μ, to study H₂ coalescence in a nozzle beam. Experimental size distributions fit the predicted asymptotic form, N_k = Ak^ae^?bk, very well, with deviations identifying magic numbers. We obtain the base agglomeration cross section K₁₁ and the parameter μ, and thus all the rate constants, for H₂. By comparing with products of geometric cross section and relative velocity, we find sticking coefficients. Experimental results for a nozzle‐beam expansion of He are analyzed similarly, to yield K₁₁ and μ, and hence sticking coefficients, for He. These are compared to those for H₂.     

Capacity and kinetic measurements of methane and nitrogen adsorption on H+-mordenite at 243–303 K and pressures to 900 kPa using a dynamic column breakthrough apparatus

A dynamic column breakthrough (DCB) apparatus was used to measure the capacity and kinetics of CH₄ and N₂ adsorption on zeolite H⁺-mordenite at temperatures in the range 243.8–302.9 K and pressures up to 903 kPa. Equilibrium adsorption capacities of pure CH₄ and pure N₂ were determined by these dynamic experiments and Langmuir isotherm models were regressed to these pure fluid data over the ranges of temperature and pressure measured. A linear driving force-based model of adsorption in a fixed bed was developed to extract the mass transfer coefficients (MTCs) for CH₄ and N₂ from the pure gas experimental data. The MTCs determined from single adsorbate experiments were used to successfully predict the component breakthroughs for experiments with equimolar CH₄ + N₂ gas mixtures in the DCB apparatus. The MTC of CH₄ on H⁺-mordenite at 902 kPa was 0.013 s^?1 at 302.9 K and 0.004 s^?1 at 243.6 K. The MTC of N₂ on H⁺-mordenite at 902 kPa was 0.011 s^?1 at 302.9 K and 0.005 s^?1 at 243.5 K. The values of the MTCs measured for each gas at a constant feed gas flow rate were observed to increase in a linear trend with the inverse of pressure. However, the apparent MTCs obtained at the lowest pressures studied (≈105 kPa) were systematically below this linear trend, because of the slightly longer residence time of helium in the mass spectrometer used to monitor effluent composition. Nevertheless, the pure fluid dynamic breakthrough data at these lowest pressures could still be reasonably well described using MTC values estimated from the linear trend. Furthermore, the results of dynamic breakthrough experiments with mixtures were all reliably predicted using the capacity and MTC correlations developed for the pure fluids.     

Selective determination of silver in solution by adsorption on a piezoelectric quartz crystal

Electrodeposition of metal ions on the crystal is eliminated by using a specially constructed transistorized oscillator. When tartrate, citrate, EDTA or their mixtures are present, silver adsorption occurs. The frequency change is proportional to the silver concentration in the range 2 × 10^?7?1 × 10^?5 M after adsorption for 10 min from a 1 mM EDTA/3 mM tartrate solution. No significant interferences are caused by other metal ions. On the basis of cyclic voltammetric studies, it is suggested that silver is adsorbed as a silver (I) complex.     

Simple Infrared Cell for Corrosive Gases

Abstract

A simple infrared cell that can be used for corrosive gases is described. The cell consists of a Kel-F tube with silver chloride windows sealed on with Kel-F wax. Evacuation of the cell to 10^?5 mm is possible.     

Time‐Dependent Surface Plasmon Resonance Spectroscopy of Silver Nanoprisms in the Presence of Halide Ions

Herein, we find that the surface plasmon resonance (SPR) spectra of silver nanoprisms in the presence of halide ions change gradually with reaction time. The changes in the spectra correspond to the shape transformation of silver nanoprisms. There are threshold concentrations of halide ions that initiate the shape‐transformation reaction. The threshold concentrations for Cl^?, Br^?, and I^? are about 3×10^?4 M , 1×10^?6 M , and 1.5×10^?6 M , respectively. Any concentrations of the added halide ions above these thresholds can eventually etch the silver nanoprisms into nanodisks if the reaction time is long enough. The higher the concentration of the halide ions, the higher the etching rate will be. The kinetics of the shape transformation of the silver nanoprisms can be studied by recording their time‐dependent surface plasmon resonance (SPR) spectra on a commercial UV/Vis–NIR spectrometer. The peak positions of in‐plane dipole SPR bands of silver colloids in the presence of chloride and bromide ions can be fitted very well with the biexponential functions. We propose that the fast components of the biexponential behaviors should correlate to the truncating effect on the corners of silver nanoprisms, and the slow component should correlate to the redeposition of the truncated residues onto the basal plane of the nanoplates.     

Kinetics of the reaction of OH radicals with t-amyl methyl ether revisited

The kinetics of the reaction of OH radicals with t-amyl methyl ether (TAME) have been reinvestigated using both absolute (flash photolysis resonance fluorescence) and relative rate techniques. Relative rate experiments were conducted at 295 K in 99 kPa (740 torr) of synthetic air using ethyl t-butyl ether, cyclohexane, and di-isopropyl ether as reference compounds. Absolute rate experiments were performed over the temperature range 240–400 K at a total pressure of 4.7 kPa (35 torr) of argon. Rate constant determinations from both techniques are in good agreement and can be represented by k₁=(6.32 ± 0.72) × 10^?12 exp[(?40 ± 70)/T] cm³ molecule^?1 s^?1. Quoted errors represent 2σ from the least squares analysis and do not include any estimate of systematic errors. We show that results from the previous kinetic study of reaction (1) are in error due to the presence of a reactive impurity. Results are discussed in terms of the atmospheric chemistry of TAME. © 1993 John Wiley & Sons, Inc.     

Direct determination of traces of silver in mercury by voltammetry at the hanging mercury drop electrode in acetonitrile medium

A direct method for the determination of silver in mercury is described. The sample of mercury is introduced into the container of the hanging mercury drop electrode and the anodic voltammograms are recorded in a 0.1 M lithium perchlorate solution in acetonitrile. The anodic peak of silver obtained under these conditions is well separated from the mercury dissolution current. The peak height is proportional to silver concentration over the wide range 2 × 10^?6 mol dm^?3 (1.6 × 10^?6%) to at least 2.0 × 10^?2 mol dm^?3. No prior separation is needed; the procedure requires less than 20 min. The diffusion coefficient of silver in mercury was determined at several temperatures. It was found that silver in mercury does not form intermetallic compounds with copper, lead, thallium, cadmium, tin and bismuth.     

Transparent Electronic Skin Device Based on Microstructured Silver Nanowire Electrode

Transparent, flexible electronic skin holds a wide range of applications in robotics, humanmachine interfaces, artificial intelligence, prosthetics, and health monitoring. Silver nanowire are mechanically flexible and robust, which exhibit great potential in transparent and electricconducting thin film. Herein, we report on a silver-nanowire spray-coating and electrodemicrostructure replicating strategy to construct a transparent, flexible, and sensitive electronic skin device. The electronic skin device shows highly sensitive piezo-capacitance response to pressure. It is found that micropatterning the surface of dielectric layer polyurethane elastomer by replicating from microstructures of natural-existing surfaces such as lotus leaf, silk, and frosted glass can greatly enhance the piezo-capacitance performance of the device. The microstructured pressure sensors based on silver nanowire exhibit good transparency, excellent flexibility, wide pressure detection range (0-150 kPa), and high sensitivity (1.28 kPa^-1).     

Novel Flow Injection/Potentiometric Measurement of Slightly Soluble Salts in Small Volumes: Determination of Solubility Product Constants of Some Silver Salts

Abstract

The flow injection technique is shown to provide fast, reliable and sensitive determination of solubility product constants of silver acetate, silver sulfate, silver oxide, silver bromate and silver chloride in microliter volume samples. Potentiometric detection using electrodes of the first kind and second kind was used for measuring silver ions and chloride ions, respectively. The solubilities were determined from measurement of the silver ion concentration in the saturated solutions. In the case of silver chloride, the solubility product constant was calculated from the concentrations corresponding to the intersection of the silver ion calibration curve and the chloride ion calibration curve, i.e., where the potentials of the two electrodes are equal. Tenth-molar sodium nitrate was used for all solutions to maintain constant ionic strength. At a concentration range of 1.00 × 10^?2 ? 1.00 × 10^?5 M silver, and 1.00 × 10^?2 ? 1.00 × 10^?4 M chloride, a Nernstian response of 60 m V per decade was obtained. At a sampling rate of 50–70 samples per hour, with 50 μl sample injections, high reproducibility of measurements was achieved, with a -pL 2% relative standard deviation in measured concentrations. The scope and applications of this system are discussed.     

Vapor pressure measurements of ferrocene,mono- and 1,1′-di-acetyl ferrocene

By using different techniques the vapor pressure of ferrocene, mono-acetyl ferrocene and 1,1′-di-acetyl ferrocene was measured. The following pressure—temperature equations were derived ferrocene log P(kPa)= 9.78 ± 0.14 ? (3805 ± 46)/T mono-acetyl ferrocene log P(kPa) = 14.83 ± 0.14 ? (5916 ± 48)/T 1,1′-di-acetyl ferrocene log P(kPa) = 8.82 ± 0.11 ? (4289 ± 44)/T By second- and third-law treatment of the vapor data the ΔH⁰_sub,298 = 74.0 ± 2.0 kJ mole^?1 for the sublimation process of ferrocene was calculated and compared with the literature data. For the sublimation enthalpy of mono- and 1,1′-di-acetyl ferrocene the values ΔH⁰_sub,298 = 115.6 ± 2.5 kJ mole^?1 and ΔH⁰_sub,298 = 91.9 ± 2.5 kJ mole^?1 were derived by second-law treatment. Thermal functions of these compounds were also estimated.     

Kinetics of silver electrodeposition from thiocarbamide solutions at a regular surface coverage with sulfide ions

Kinetics of silver electrodeposition in the presence of sulfide ions is studied on electrodes renewed by cutting off a thin surface layer, at a controlled time of contact of the “fresh” surface with the electrolyte. Solutions containing 10^?2 M AgNO₃, 0.1 M thiocarbamide, 0.5 M HClO₄, and from 2 × 10^?6 to 1.5 × 10^?5 M Na₂S are studied. It is shown that under the studied conditions, the effect of silver electrodeposition on the surface concentration of sulfide ions is insignificant. As the concentration of sulfide ions in solution and their coverage on the electrode surface θ increase, the cathodic polarization decreases. Tafel curves plotted for θ = const are used in estimating the exchange current i ₀ and the transfer coefficient α. It is shown that α ≈ 0.5 and weakly depends on θ, whereas the exchange current increases with the increase in θ by an approximately linear law from 10^?5 A/cm² at θ ? 0 to 10^?4 A/cm² at θ = 0.43. The obtained data are compared with the results of kinetic studies of silver anodic dissolution in similar solutions.     

Study on the chemisorption kinetics of Methylene Blue using SERS technique

SERS technique was used to study the chemisorption kinetics of Methylene Blue (MB) on the HNO3-etched silver surface. The adsorption kinetic parameters were deduced from different vibrational modes at a low concentration of 3.5×10-6 mol/L, and it showed that MB adsorbed uniformly (monolayerly) on silver surface. However, the adsorptive behavior turned anomalous at relatively higher concentrations and a possible explanation was suggested. In addition, the influence of Cl- ions on the adsorption states of MB was investigated, and it was shown that MB molecules, adsorbed on the silver surface, tended to transform from the "lying-down" state to the "end- on"4 state after Cl- ions were added.     

Evaluation of food-processing conditions of various particle sizes of <Emphasis Type="Italic">Tremella fuciformis</Emphasis> powder via DSC and TG analyses

Tremella fuciformis (Berk.), also known as silver ear, has a high economic value due to being a valuable edible and medicinal mushroom. The focus of this study was on the various particle sizes of 80–300 mesh (particle diameters from 2 mm to 250 μm) for freeze-drying silver ear powder in order to determine the water-holding capacity, viscosity, and crude polysaccharide content of various particle sizes. Our aim was to determine the possible conditions for silver ear powder for food processing under the conditions of oxidation/non-oxidation and heat treatment. Overall, we obtained various particle sizes of silver ear powder, the water-holding capacity decreased from 21.84 to 14.82 g g^?1, the viscosity increased from 8.53 to 71.20 cP, and the content of crude polysaccharides, which remained almost constant, was approximately 300 mg g^?1. In addition, the smaller the particle size of silver ear powder, the greater the thermal stability of the particles by differential scanning calorimetry (DSC) and thermogravimetric (TG) tests. The results for various particle sizes of silver ear powder in food processing are never more than ca. 240 °C by DSC tests. Moreover, comparing the results of thermal decomposition using TG analyzer under nitrogen and air conditions, in nitrogen, the various particle sizes have better preservation for storage conditions and the smaller particle size powders retained good thermal decomposition characteristics.     

Thermodynamics of silver-thiosemicarbazide complexation

The stability constants of the complexes formed by the silver ion with thiosemicarbazide (tsc) are determined by a potentiometric method using a silver electrode, in a wide range of silver-ion overall concentration (from 10^?4 to 9 × 10^?3 mol dm^?3). Calorimetric measurements gave access to the enthalpy changes accompanying the formation of the species Ag(tsc)⁺, Ag₂(tsc)₃²⁺, Agtsc)₂⁺, and Ag(tsc)₃⁺, and the corresponding entropy changes have been calculated.