The diffusion of ferrocyanide and ferricyanide ions in aqueous solutions of potassium hydroxide

The diffusion of ferro- and ferricyanide ions in potassium hydroxide solutions has been studied with the rotating disk electrode between 24 and 50°C. The quotient Dη/T was satisfactorily constant and temperature-independent. A comparison with previous results obtained for solutions containing sodium hydroxide and potassium chloride as supporting electrolytes is made.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

The diffusion of ferrocyanide and ferricyanide ions in aqueous solutions of potassium hydroxide

The diffusion of ferro- and ferricyanide ions in potassium hydroxide solutions has been studied with the rotating disk electrode between 24 and 50°C. The quotient Dη/T was satisfactorily constant and temperature-independent. A comparison with previous results obtained for solutions containing sodium hydroxide and potassium chloride as supporting electrolytes is made.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Diffusional flow under non-isothermal laminar free convection at a thermal convective electrode

A theoretical solution for the set of differential equations related to laminar free convection under simultaneous concentration and thermal gradients, at an ideal vertical plate electrode, is attempted. The rate equation comprises the limiting case of isothermal free convection and presents a relationship between the maximum average flux and the temperature gradient that is qualitatively coincident with previous experimental results. Velocity and concentration distributions in the boundary layer are evaluated.On a tenté une solution théorique des équations différentielles compliquées par dans un électrode ideale plane et verticale avec convection libre et gradients thermique et de concentration simultanés. On a évalué les distributions de concentration et de vitesse dans des couches limites. L'équation de débit comprend le cas limite de convection libre isothermique et elle présente une dépendence de la vitesse moyenne du procassus avec le gradient de température qui montre une concordance qualitative avec des données experimentales préalables.Es wird versucht, eine theoretische Lösung für die Differentialgleichungen der laminaren freien Konvektion an einer idealen senkrechten Plattenelektrode, an welcher gleichzeitige Konzentrations- und Wärmegradienten, vorhanden sind aufzustellen. Die Geschwindigkeitsgleichung schliesst den Grenzfall der isothermien freien Konvektion ein und zeigt eine Beziehung zwischen dem maximalen mittleren Fluss und dem Temperaturgradienten, welche qualitativ mit vorhergehenden experimentellen Resultaten übereinstimmt. Die Geschwindigkeits- und Konzentrationsverteilungen in der Grenzschicht wurden abgeschätzt.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Ionic mass transfer on fixed disk and conical electrodes under streaming solutions : I. Theoretical approach

A solution of the convective-diffusion differential equation for the case of disk and conical electrodes axially placed in laminar flow is attempted. The integration of the equations is done with an approximate streaming function which is valid for values of the function up to 0·3 within an error of one per cent. The rate equation for a steady convective-diffusion process on the disk electrode is [fórmula en el documento]. The type of solution is then extended to the case of conical electrodes with axial symmetry. A similar equation is thus obtained and the numerical coefficients for the average rate equation are in agreement with the one of the above equation, within 4 per cent, and are independent of the cone angle. The latter result agrees also with a previous equation deduced by analogy with the corresponding heat-transfer problem.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Diffusional flow under non-isothermal laminar free convection : II. Experimental approach

The rate of a non-isothermal free convection process has been measured at different temperature gradients in an electrochemical cell having parallel vertical plate copper electrodes, the reaction being the electrodeposition of copper from a copper-sulphate-sulphuric-acid solution. Results agree with the theoretical equation derived previously. They are correlated in a way similar to isothermal free convection in terms of dimensionless ratios, and an equivalence between thermal gradient and rate of stirring under laminar forced convection is established.On a mesuré la vitessed 'un processus à convection naturelle non-isothermique a différents gradients de temperature dans une cellule électrochimique avec des électrodes verticales et parallèles de cuivre, où la réaction étudiée est l'électrodéposition de cuivre dans des solutions de sulfate de cuivre-acide sulfurique. Les données expérimentales sont en concordance avec l'équation théorique obtenue dans une étude antérieure. Les résultats sont présentés d'une manière analogue à ceux de la convection naturelle isothermique avec emploi des relations adimensionelles. On a établi la relation entre l'effet du gradient thermique et la vitesse d'agitation déduite pour la convection forcée en régime laminaire.Man bestimmte die Geschwindigkeit eines Prozesses mit nichtisothermer natürlicher Konvektion. Zu diesem Zweck wurde die Kupferabscheidung in einer Zelle mit parallelen senkrechten Elektroden bei verschiedenen Temperaturgradienten untersucht. Die Ergebnisse bestätigen die früher abgeleitete theoretische Beziehung. Sie können durch eine dimensionslose Korrelation, ähnlich wie fur den isothermen Fall, ausgedrückt werden. Es konnte ein Zusammenhang zwischen dem Temperaturgradienten und der Rührintensität bei erzwungener laminarer Konvektion gefunden werden.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Sieving Effect of Agarose on Quasi-2D Silver Pattern Electroformation : A Pinning-Depinning-like Transition Resulting from Gelled Silver Plating Solutions

New features of silver patterns grown in quasi-2D electrochemical cells of parallel plate cathode/anode design utilizing sol and gel aqueous silver plating solutions are reported. Morphology transitions in the silver growth patterns that depend on the composition of plating solutions are observed. These transitions are explained by both a sieving effect due to the presence of agarose and the change in the relative contribution of diffusion and advection to the mass-transport-controlled electrochemical process. Characteristic scaling lengths from growth patterns are related to both the gel structure and the geometry of electrodeposits. Gels consist of a percolated network of gel and randomly distributed colloidal particles, their size and velocity being represented by hyperbolic distribution functions. For silver plating gels a pinning-depinning transition in growth patterns is also observed. From the dynamic scaling analysis of growth pattern 2D profiles, the critical growth and roughness exponent as well as the characteristic lengths of the environment were evaluated. Values of these exponents approach those predicted either by the Kardar, Parisi, and Zhang (KPZ) deterministic equation, or by the cellular automata lattice model that has been proposed for the dynamics of a driven interface in a medium with random pinning forces.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Non-isothermal ionic mass transfer at vertical parallel plate electrodes under natural convection : Comparison and validity range of dimensionless correlations

For non-isothermal ionic mass transport-controlled electrochemical reactions on vertical parallel plate electrodes under steady state natural convection, the dimensionless correlation Sh=0.9 (ScGr*)1/4, Sh, Sc and Gr* being Sherwood, Schmidt and Grashof number, respectively, earlier proposed (Electrochim. Acta 13 (1968) 1657; 14 (1969) 741), was extended covering almost two decades of (ScGr*)1/4. Data from different test reactions in the range −10≤ΔT′≤15 °C, utilising cells of similar geometry and cathode height in the range 0.025≤X≤1 cm were considered. Using the above correlation as reference, other dimensionless correlations later derived, considering data from the same test reactions and using electrochemical cells of approximately the same design, were critically reviewed. The validity range of these correlations covered a smaller range of (ScGr*)1/4 than the reference correlation, and their differences were explained in terms of cell designs and operating conditions.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Modelling of pulsating diffusional boundary layers : I. A reversible metal—metal ion electrochemical reaction under symmetric square wave perturbing potentials at a plane electrode

The concentration profiles of reacting species at the electrode—solution interface under a periodic square wave perturbing potential are calculated by solving the diffusion equation for the case of a fast reversible metal—metal ion reaction. This situation is particularly interesting in the electrochemical facetting of metals. The model explains the dependence of current density and charge density on the frequency and number of cycles of the perturbing potential.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The diffusion of ferrocyanide and ferricyanide ions in aqueous solutions of potassium hydroxide

The diffusion of ferro- and ferricyanide ions in potassium hydroxide solutions has been studied with the rotating disk electrode between 24 and 50°C. The quotient Dη/T was satisfactorily constant and temperature-independent. A comparison with previous results obtained for solutions containing sodium hydroxide and potassium chloride as supporting electrolytes is made.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Ionic mass transfer on fixed disk and conical electrodes under streaming solutions : III. A second experimental approach and kinetic application

The rate of ionic mass transfer on fixed disk electrodes under streaming solutions was studied avoiding as far as possible any wall effect on the mass-transfer rate. Nickel electrodes, previously activated, and platinum and graphite electrodes with solutions of potassium ferro- and ferricyanide in sodium hydroxide were used. The geometry of the cell and other variables of the system were conveniently changed. The experimental rate equation agrees with that found by solving the Navier-Stokes and Fick's differential equations, for results with activated nickel electrodes, the fluid velocity being properly defined. Results obtained with platinum and graphite electrodes present a deviation from those equations, a fact which is interpreted in terms of an electrochemical reaction with intermediate kinetics. The kinetic parameters of the corresponding electrochemical reactions are evaluated.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada