The kinetics of silver bromide film formation on the silver anode

The anodic potentiodynamic formation of an AgBr film on an Ag rotating disc electrode was studied in aqueous bromide solutions. As the electron transfer step (1) is intrinsically fast,

and as the film remains porous throughout its growth, the rate of film growth is limited by physical parameters such as ionic diffusion and migration in the solution.The anodic E/I curves for AgBr film formation were calculated quantitatively by computer on the basis of the following model of film growth. Film formation occurs initially by the nucleation of islands of film to a critical thickness, and then these islands spread laterally until only small pores remain between them. As these pores become small, the resistance of the solution within them becomes rate limiting (at the anodic current peak). After the peak, the concentration of bromide ions at the pore base falls to zero and current is then controlled by the diffusion of bromide ions into the lengthening pores of the film.This lateral spreading mechanism and the subsequent retention of the porous film morphology has been substantiated by comprehensive Scanning Electron Microscope investigations.     

Mono- and multilayer formation studies on silver anodic film formation of silver bromide

The mono- and multilayer formation of silver bromide on silver was investigated by cyclic voltammetric and single potential step current-time transient experiments at different concentrations of bromide. A monolayer peak was noticed at potentials more negative than the Ag/AgBr reversible potential. The electrodeposition of AgBr was shown to occur by adorption-desorption and nucleation-growth kinetic processes during mono- and multilayer formation, respectively.     

Mono- and multilayer formation studies of silver iodide on silver electrode from iodide-containing solutions

Cyclic voltammetric and single potential step current-time experiments were carried out on the silver electrode in order to understand the nature of kinetic processes involved during the mono- and multilayer formation of silver iodide. Two pre-peaks were noticed at potentials more negative to the multilayer formation and to the Ag/AgI reversible potential. These pre-peaks were found to arise during the monolayer formation of AgI via the adsorption-desorption processes. On the other hand, the multilayer formation of AgI processes occurs by instantaneous nucleation-growth.     

The kinetics of the anodic formation and reduction of phase silver sulfide films on silver in aqueous sulfide solutions

The kinetics of the potentiodynamic formation and reduction of silver sulfide films on a silver rotating disc electrode in aqueous sulfide solutions were investigated. Due to the inherently fast reaction between silver and the HS⁻ species, the physical processes of migration and diffusion of ions in solution were frequently rate limiting. Only when the rate of HS⁻ transport in solution was very high, did the rate of film growth become limited by the solid-state electromigration of silver ions through the silver sulfide film. By utilizing the low field approximation for field-assisted electromigration, the ionic conductivity of these films was found to be 5.9 × 10⁻⁴ S cm⁻¹. Silver sulfide film reduction occurred by the injection of electrons into the film to the film/electrolyte interface. All of the results have been supported by scanning electron microscope investigations.     

The mechanism of formation of a surface film of silver on a platinum electrode

The mechanism of the growth of thin metal films on inert substrates in potentiostatic metal electrodeposition is given. A possible relation to the porosity of metal deposits is discussed. The effects of pulsating overpotential on the electrodepositon of the first monolayers are described.     

The mechanism of formation of a surface film of silver on a platinum electrode in galvanostatic deposition

A mechanism for the growth of thin metal films on inert substrates in galvanostatic metal deposition is proposed. Qualitative agreement between theoretical and experimental results was obtained.     

Nanocomposites based on silver iodide and aluminum oxide

Nanocomposites based on AgI and Al₂O₃ have been obtained using the techniques of chemical condensation, mechanical treatment, and crystallization. The size of the particles is estimated using the scanning-electron-microscopy technique. After mechanical treatment and crystallization, the AgI composite is composed of nanoparticles of silver iodide, which are localized in the shells of nanocrystalline aluminum oxide. The size of the particles and the thickness of the shells are determined. The results are discussed based on considerations that describe the microscopic mechanisms responsible for the formation of silver iodide nanocrystals in the process of mechanical treatment and crystallization. It is shown that the shape and structure of the composite nanoparticles change depending on the method and conditions of their production.     

纳米级氧化物膜析氧阳极的研究

纳米级氧化物膜析氧阳极是一种新材料,它具有高的电催化活性和长的使用寿命.用溶胶凝胶法和热分解法制备了Ir-Ti二元阳极.讨论了二元阳极制备的某些影响因素,例如原材料的制取,热处理温度和铱中间层,用扫描电镜观察涂层的晶体结构和表面形貌,涂层的表面为无裂缝和纳米级,其晶粒尺寸不大于9.58 nm,并呈丘陵状.     

The electroreduction kinetics of silver sulfite complexes

The electroreduction kinetics of silver sulfite complexes was investigated by rotation disk electrode (RDE) voltammetry, chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). The stability constants of the silver sulfite complexes, pβ₂ = 7.9 and pβ₃ = 8.53 were determined. For the series of isopotential solutions investigated, a reaction order of 0.67 was obtained, the diffusion coefficient of the silver complexes varies in the range of 3.36 × 10⁻⁶ to 5.54 × 10⁻⁶ cm² s⁻¹ and the silver degree of complexation (2.31-2.67) were found. The analysis of the RDE, CP data and EIS spectra indicate the existence of a slow stage of the silver electrocrystallization in the region of the equilibrium potential and at stronger polarization of the electrode at initial time moments.     

The kinetics of thin film polyesterification

The goal of this work was to investigate the increase in the rate of polyesterification that takes place as surface-to-volume ratio is increased. The polymer used in this reaction was derived from the esterification of adipic acid (hexanedioic acid) and propylene glycol (1,2-propanediol). The effect of three variables—film thickness, water concentration of the nitrogen atmosphere, and temperature—was studied to determine their effect on the reaction rate. The water content of the atmosphere was found to severely retard the progress of the esterification and this fact reaffirms that the reverse reaction, hydrolysis, is much more important than was realized by earlier investigators. The reaction in the film was found to have an activation energy of 22,600 cal/mole compared to 12,600 cal/mole in the batch reaction, indicating a possible change in controlling rate from the batch to the film system. New evidence was found which illustrates the possible role of reactant mobility at high conversions. It is suggested that a possible explanation for the change in controlling rate may be due to a complex surface phenomenon such as the alignment of reactive groups at the surface or the orientation of water molecules at the gas–liquid interface.     

The kinetics of ettringite formation

Conversion of hemihydrate to gypsum, and ettringite formation in the system C₃A---CaSO₄·1/2H₂O---H₂O three hydration temperatures using x-ray diffraction. Analysis of the kinetics of gypsum formation suggests that the rate limiting step changes from an initial dependence on the hemihydrate surface area to a dependence on the gypsum growth rate. The formation of ettringite was found to be controlled by diffusion. In accord with the needle-like morphology that ettringite exhibits, a nucleation and growth model predicted one-dimensional growth. An apparent activation energy calculated for ettringite formation is consistent with a diffusionally controlled process.     

Morphological characterization and kinetics study of polyaniline film formation by emulsion polymerization

The kinetics and morphology of polyaniline film prepared by using ammonium persulfate (APS) as oxidant and dodecylbenzoyl sulfonic acid (DBSA) as both emulsifier and dopant were studied in this paper. The kinetics of the formation of polyaniline film was determined by using the quartz crystal microbalance (QCM), and the film morphology was characterized by scanning electron microscopy (SEM). The reaction exhibited half-order kinetics with respect to APS concentration and first-order kinetics with respect to aniline concentration. The activation energy is 41.15 kJ/mol, and the growth rate of PANI film increased with increasing temperature and decreased with increasing concentration of DBSA.     

Electrochemical properties of a new solid electrolyte in the system silver iodide — silver dichromate

A new silver solid electrolyte in the system AgI-Ag₂Cr₂O₇ has been characterized in terms of total and electronic conductivity, silver transport number and activation energy. The electrolyte undergoes a water-catalyzed decomposition reaction but, if kept in dry conditions, may be successfully used for the development of solid-state power sources capable of operating at room temperature.     

Particulate processes in freshly prepared silver iodide hydrosols part III. Disagreement between experimental results and the existing models of silver iodide hydrosols

Silver iodide hydrosols prepared in statu nascendi exhibit some specific effects that cannot be explained on the basis of the existing models of silver iodide hydrosols. These effects are acceleration of a heterogeneous exchange process caused by coagulation of the system, and different aggregation number obtained in the same system applying two different exchange methods. In order to explain these effects, a comparison has been made of the differences between the data calculated on the basis of the existing model of silver iodide hydrosols and the values determined by radiometric, optic, and sedimentation analysis. The previous assumption on the existence of a new structural form of silver iodide, characteristic of stable silver iodide hydrosols, has been confirmed. This new structural form of silver iodide transforms into known hexagonal and cubic modifications during the aggregation of primary particles of silver iodide to secondary ones. The properties of the new structural form of silver iodide are predicted.     

The anode effect in a silver chloride/sodium chloride melt

The anode effect in a silver chloride/sodium chloride melt has been studied using the steady state, potential sweep and galvanostatic methods. Certain theories explaining the onset of the AE are discussed.     

The effect of water on the formation of strongly bound oxygen on silver surfaces

Interaction of water with an oxygenated Ag(111) surface leads to an enhancement of the surface restructuring and an activated formation of hydroxyl groups (OH) located stably on the surface and incorporated in the subsurface region, as evidenced by means of reflection electron microscopy (REM) and in situ Raman spectroscopy. Dehydroxylation of OH_ads at elevated temperatures releases the strongly bound oxygen species labelled O_γ at the surface, and offers an alternative to the energetically less favorable pathway for the direct formation of the O_γ species from molecular oxygen.     

Kinetics of the cathodic decomposition of silver iodide in molten alkaline nitrates

The cathodic decomposition of AgI was studied using a single pulse galvanostatic technique. The working electrode was an AgI-rotating disc immersed in the molten KNO₃-NaNO₃ eutectic. Linear overpotential-log (current density) plots were obtained for varying concentrations of I⁻. Evidence was found for the existence of two different control steps, depending on the iodide concentration. At lower I⁻ concentrations a chemical reaction forming an adsorbed AgI⁻₂ complex ion is postulated as the rate-determining step. At higher I⁻ concentrations the rds is related to the electrochemical reaction AgI + e = Ag° + I⁻. An alternative charge transfer process is suggested corresponding to the transfer of an I⁻ ion between the two ionic media.