Showing papers on "Overpotential published in 1971"
TL;DR: In this paper, the nature and characteristics of the overpotential in cells of the type were determined from 700° to 1100°C over a wide range of oxygen pressures, and based on the present results and adsorption data, a mechanism was proposed for the cathode reaction.
Abstract: The nature and characteristics of the overpotential in cells of the type were determined from 700° to 1100°C over a wide range of oxygen pressures. Porous Pt black electrodes were deposited on impervious tubes. Almost pure resistance polarization is observed when or mixtures are present at the anode. However, for mixtures dilute in at the cathode, diffusion overpotential readily appears and limiting currents are eventually reached. Limiting currents, proportional to , are controlled by the diffusion of gaseous oxygen in the pores of the Pt electrode. Based on the present results and adsorption data, a mechanism is proposed for the cathode reaction. For mixtures, transition overpotential associated with the reaction is observed. The transition factor is about 0.5 and exchange current densities are in the vicinity of 1 mA/cm2. Equations relating exchange current density to , , and the amount of adsorbed on the electrolyte are derived and compared with the experimental results. It is concluded that either gaseous or adsorbed and gaseous are directly involved in the electrochemical step of the reaction.
160 citations
TL;DR: In this paper, the internal fugacity of cavities in equilibrium with surfaces on which H 2 is being evolved is examined in terms of electrochemical kinetics, and it is shown that depending upon the mechanism of hydrogen evolution, the situation may be less embrittling, i.e., the fugacity set up by a given η is less than given by (1).
104 citations
TL;DR: The anodic oxidation of platinum in is studied by using open-circuit transients to determine Tafel slopes and by following film growth optically with an ellipsometer.
Abstract: The anodic oxidation of platinum in is studied by using open‐circuit transients to determine Tafel slopes and by following film growth optically with an ellipsometer. The Tafel slope values are found to be proportional to the film thicknesses measured with the ellipsometer. This result is interpreted in terms of an ionic conduction model in which the overpotential appears across the anodic oxide film, and the logarithm of the ionic current density is proportional to the field in the oxide. The results are compared with the results of similar measurements on iron and tantalum. Although platinum, iron, and tantalum have quite different chemical properties, and their oxides span a thickness range from a monolayer to several thousand angstroms, it is concluded that the same basic process is responsible for the anodic oxidation of the three metals.
53 citations
TL;DR: In this article, the anodic behavior of zinc in aqueous potassium hydroxide has been investigated at very high cds (1−10 A/cm2), and no evidence was found for a change in the mode of passivation.
29 citations
01 Dec 1971-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the magnitude of the overpotential resulting from concentration polarization at these interfaces, in the case of pure iron/CaF2+Al2O3, CaF2 +CaO slags using a galvanostatic pulsing technique in an electrolytic cell, has been determined.
Abstract: It is evident from the known ionic properties of the slags used in electroslag melting, that the dc melting process must be accompanied by Faradaic reactions on the slag/ingot and slag/electrode interfaces. The present work has determined the magnitude of the overpotentials resulting from concentration polarization at these interfaces, in the case of pure iron/CaF2+Al2O3, CaF2+CaO slags using a galvanostatic pulsing technique in an electrolytic cell. The polarization overpotential existing on an electrode in an operating ESR unit has been measured by the same technique. It is found that the potentials observed on the ESR electrode agree well with the results from the electrolytic cell. The primary anodic process is postulated to be the corrosion of iron, leading to an Fe2+-saturated layer on the anode surface at sufficiently high current densities. The cathodic process is suggested to be the Faradaic reduction of Al3+ or Ca2+, to give a concentration of [Al]Fe or (Ca)slag in the cathode interface region. This observation is supported by the fact that the cathodic potentials with respect to a C/CO reference electrode are close to those predicted from the reactions: (Al2O3)+3C=3CO(g)+2Al(l) or (CaO)+C=CO(g)+Ca(g) At very high current densities both the anodic and cathodic processes may convert to arcs, leading to process instability. The chemical and thermal effects of the overpotentials are briefly discussed and compared with the present results on ESR ingots of pure iron.
22 citations
22 citations
TL;DR: In this paper, the effect of overpotential, cd and the rotation rate of a disk electrode on the process of copper electrocrystallization on the (111) plane of a single-crystal copper cathode in sulphate solution was investigated.
16 citations
12 citations
TL;DR: In this paper, the reduction of oxygen in 1 M NaOH at 25°C with a fluidized bed electrode of solid silver spheres and of silver coated glass spheres of different diameter was examined.
11 citations
TL;DR: In this article, a study has been made of the passivating process at a zinc electrode in KOH solutions, where the zinc electrodes were passivated at a constant overpotential and the current response during passivation was measured.
Abstract: A study has been made of the passivating process at a zinc electrode in KOH solutions. Zinc electrodes were passivated at a constant overpotential and the current response during passivation was measured. The potential response after the passivating potential was removed was also measured.
11 citations
TL;DR: In this paper, a linear variation of the separation factor of hydrogen isotopes with overpotential is observed only on the high over-potential metals, where the discharge step is rate-determining, and seems to depend upon a change in shape of the potential-energy barrier of the rate determining discharge step with potential.
01 Oct 1971
TL;DR: The behavior of the liquid silver electrode in the cell (Ar-O2,O(in Ag)/ZrO2-CaO/O2 (+) was studied as a function of the oxygen activity in silver and the temperature as discussed by the authors.
Abstract: The behavior of the liquid silver electrode in the cell (–) Ar-O2,O(in Ag)/ZrO2-CaO/O2 (+) was studied as a function of the oxygen activity in silver and the temperature. The liquid metal was contained inside an impervious tube of ZrO2+10 mole pct CaO. The cell discharges reversibly from 1000° to 1200°C. However, when the liquid silver electrode is made the cathode, diffusion overpotential appears due to a depletion of dissolved oxygen at the silver-electrolyte interface. Limiting currents are eventually observed which are directly proportional to the concentration of dissolved oxygen from 0.01 to 0.24 at. pct O.
TL;DR: In this paper, the variation of overpotential with time on iron membranes cathodically polarised in M/3 sulphuric acid has been found to be due to the formation of an adsorbed layer of hydrogen.
Abstract: The variation of overpotential with time on iron membranes cathodically polarised in M/3 sulphuric acid has been found to be due to the formation of an adsorbed layer of hydrogen. This layer decays with time but it can be removed by the application of an alternating current.Anomalous time-lag curves, permeation maxima and the formation of ‘barriers’ in the course of diffusion of electrolytic hydrogen reported in the literature can be largely attributed to the surface adsorbed hydrogen.Hydrogen concentrations determined from diffusivity and permeation values are presented together with an experimental methodfor the determination of hydrogen retained in traps.
TL;DR: In this article, the electromotive force of the cell; Au-Na alloy |Na2CO3| CO2+O2, Pt-Rh, was determined as a function of the temperature and the concentration of sodium in the alloy.
Abstract: The electromotive force of the cell; Au–Na alloy |Na2CO3| CO2+O2, Pt-Rh, was determined as a function of the temperature and the concentration of sodium in the alloy. The results were consistent with the activity values determined previously by the equilibrium method. The overpotential due to the current passing through the Au–Na alloy surface is less than 1 mV per mA/cm2 of the current density at 1400°K. The activity of sodium, referred to the pure liquid standard state, was calculated from the electromotive force of this cell. The activity coefficient of sodium in Au–Na alloy is: logγNa=−2.55⁄T·10−3+0.39±0.05 in the temperature range from 1250°K to 1500°K and in the concentration range of less than 10 atom%Na.
01 Jan 1971