Galvanostatic Pulse Measurements Research Articles

Finite Modeling and Simulation of the Effects of Neutral Electrolytic Pickling Process Parameters on EN 1.4404 Steel Strips

Surface treatment via neutral electrolytic pickling (NEP) aims to remove oxide layers and scaling from stainless steel. The objective of this study was to investigate the factors that affect the energy efficiency of the process. This study developed a COMSOL Multiphysics model for the distribution of current across a bipolar steel strip by controlling the following parameters: Na2SO4 concentration, temperature, electrode-to-strip distance, and inter-electrode distance. Full factorial measurements of the electrolyte’s conductivity as well as the steel strip’s and the electrode’s polarization were conducted to provide data for the NEP model. Galvanostatic pulse measurements were performed to calculate transient times during pickling. According to the model, an applied voltage of less than 11 V was insufficient to polarize the steel strip to the potentials needed on both the anodic and cathodic sides. A higher voltage of 11–15 V resulted in anodic current densities of 600–1600 A m−2 and cathodic current densities of 700–2000 A m−2 on the steel strip. These current densities are within the range of previous experimental studies and industrial practices. The model showed that when a steel strip acts as a bipolar electrode, the current’s efficiency decreases, as only a fraction of the strip facing the anodes or cathodes is polarized sufficiently. The galvanostatic tests showed that anodic polarization of the steel strip is easier than cathodic polarization. The slow polarization in the cathodic direction can be improved by using a higher current density. The time needed to polarize stainless steel indicates that the strip’s velocity should be less than 1 m s−1 to give enough time for polarizing the steel strip.

A new perspective on measuring the corrosion rate of localized corrosion

AbstractMany corrosion phenomena are nonuniform, which means that anodic and cathodic locations are spatially separated. An example is macrocell corrosion of steel in concrete. Under these conditions, determining the corrosion rate from polarization resistance measurements and using the Stern–Geary equation is fundamentally not possible. We present a novel theoretical approach for the interpretation of galvanostatic pulse measurements, to make them applicable as a method for corrosion rate measurements in situations of localized corrosion. Experiments show that it is important to consider that (a) only a fraction of the applied current flows through the anode of the macrocell, and (b) this current is not constant over time. We propose an approach to quantify and consider these two effects, based on information generally accessible in condition assessment of concrete structures. Our results show that galvanostatic pulse measurements are a robust method to determine the corrosion current. With the traditional empirical approach, the measurement error was generally below factor 3, and occasionally up to factor 10. With the novel approach, this error could be reduced to a factor of maximum 2 in all cases.

Use of galvanostatic pulse measurements on active reinforcing steel in concrete to assess corrosion rates

This paper reports the results of galvanostatic pulse transient response experiments to determine the corrosion parameters associated with actively corroding reinforcing steel in concrete. Galvanostatic pulse measurements have been conducted on a number of short 100 mm sections of steel reinforcing bar embedded in chloride contaminated concrete. The duration of the applied galvanostatic pulse was 90 s and the lateral distance of the point of measurement from the bar varied from zero to 400 mm. All of the bars monitored were conditioned so that they were actively corroding at different rates. Analysis of the galvanostatic pulse transient response has enabled the separate components that make up the measured transients to be isolated and evaluated. These components display a range of resistivities and capacitances, dependent on the corrosion condition of the reinforcing steel, which may be attributed to the corrosion process, to effects within the concrete cover, or to film effects on the surface of the concrete. Other investigators using this technique have evaluated the corrosion rate by summation of the separate corrosion components, i.e. simply summing all of the resistance values to obtain an aggregated corrosion resistance. However, it is possible that not all resistances identified are associated with the loss of steel from the surface of the reinforcement. Significant variations in corrosion rates have been observed dependent on the assignment of the separate components to either corrosion or to other processes. The data indicate that it is not feasible to assign the component based solely on the capacitance. An inappropriate selection of measurement time or equilibrium time may result in part of the resistance associated with the corrosion process being left out or an additional resistance not controlling the rate of corrosion being included.

Galvanostatic Pulse Measurements of Passive and Active Reinforcing Steel in Concrete

Results of galvanostatic pulse transient response experiments were reported to determine the corrosion parameters associated with passive and actively corroding reinforcing steel in concrete. Galvanostatic pulse measurements were conducted on a number of short sections of steel-reinforcing bar embedded in concrete. The duration of the applied galvanostatic pulse varied from 45 s to 600 s. The bars displayed a range of corrosion rates, from passive steel to highly active corrosion. Analysis of the galvanostatic pulse transient enabled separate components, which made up the measured transient, to be isolated. These components displayed a range of resistances and associated capacitances, dependent upon the corrosion state of the reinforcing steel, which may be attributed to the corrosion process or other effects within the bulk concrete. The corrosion rate was calculated from the summation of the separate resistive components and compared with the corrosion rate determined from linear polarization resistance (LPR) measurements on the same specimens. Results from the galvanostatic pulse transient analysis showed that significant errors in evaluating corrosion rates using the LPR method may be incurred if the usual 30-s equilibrium period was used for measuring actively corroding steel bars.

Kinetics of electrochemical n-doping of polyacetylene investigated by impedance and galvanostatic pulse measurements

The characteristics of n- and p-doping of polyacetylene in different solvents were investigated by potentiostatic and galvanostatic charge/discharge curves, the fast Fourier transform impedance method and the galvanostatic pulse technique. The intercalated ions were Li +, Na +, ClO 4 − and BF 4 −. From the impedance measurements a rapid determination of electrochemical parameters like double-layer capacitance, electrolyte resistance and polarization resistance at different states of charge and discharge were obtained. Similarly, electrode kinetics and diffusion behaviour were determined by the galvanostatic pulse technique. The doping characteristics were additionally monitored by in situ resonance Raman scattering experiments. We found strong evidence for solvent coinsertion during the doping process. Ion diffusion is rate controlling to a much higher degree for undoping compared to n-doping.

The double layer at the interface between two immiscible electrolyte solutions: Part III. Capacitance of the water/1,2-dichloroethane interface

From ac impedance and galvanostatic pulse measurements the capacitance of the interface between solutions of LiCl in water and tetrabutylammonium tetraphenylborate in 1,2-dichloroethane has been evaluated at various electrolyte concentrations. The experimental data have been interpreted on the basis of the modified Verwey-Niessen model, according to which a layer of oriented solvent molecules (inner layer) separates two space charge regions (diffuse double layer). As for the water/nitrobenzene interface, the interfacial potential difference is spread mainly within the diffuse double layer. In the sequence nitrobenzene < 1,2-dichloroethane, the effects of the ion association, finite ion size and image forces, which modify the double-layer structure, become more pronounced. The latter two effects have been estimated by means of the weak-coupling and hypernetted chain theories, respectively. No evidence for the specific adsorption of ions or ion pairs was found.

The double layer at the interface between two immiscible electrolyte solutions: Part II. Structure of the water/nitrobenzene interface in the presence of 1:1 and 2:2 electrolytes

From fast galvanostatic pulse measurements at 25°C the capacitance of the water/nitrobenzene interface was evaluated as a function of the interfacial potential difference Δ o wϕ for systems consisting of NaBr, LiCl or MgSO 4 in water and tetrabutylammonium tetraphenylborate, tetraphenylarsonium tetraphenylborate or tetraphenylarsonium dicarbollylcobaltate in nitrobenzene. The modified Verwey—Niessen model, in which an inner layer of solvent molecules separates two space-charge regions (the diffuse double layer), describes the structure of the water/nitrobenzene interface well at electrolyte concentrations above ca. 0.02 mol dm −3, provided that the ions are allowed to penetrate into the inner layer over some distance. For all the systems studied the zero-charge potential difference was found at Δ w oϕ pzc ≈ 0 on the basis of the standard potential difference Δ w oϕ 0 TMA + = 0.035 V for tetramethylammonium cation which was used as a reference ion. At zero surface charge a comparison was made with the theoretical capacitance calculated using the mean spherical approximation for a model consisting of two ion and dipole mixtures facing each other. The effect of ion penetration on the interfacial capacitance was estimated from the solution of the linearized Poisson-Boltzmann equation for a triple dielectric model with a continuous distribution of the point ions. The concentration-independent inner layer potential difference and capacitance can only be inferred from the capacitance data if the ion size effect is taken into account. A non-iterative procedure based on the hypernetted-chain equation was used for the evaluation of the potential drop across the diffuse double layer. The extend of the penetration into the inner layer appears to be a function of ion solvation, e.g. the more hydrated ion the less extensive ion penetration is likely.

Ellipsometer Studies of Surface Layers on Lithium

The growth of surface layers on lithium in propylene carbonate solutions can be followed by ellipsometry, although the refractive indexes of many potential film materials are close to those of the electrolyte. Film thicknesses calculated from ellipsometer measurements increase over periods of several days at open circuit; they are several times larger than those derived from galvanostatic pulse measurements. Films are found to be inhomogeneous with properties continuously varying as a function of distance from the substrate; compact regions are located adjacent to the metal and porous regions are located adjacent to the solution. Electrode capacitance measurements are sensitive to the thin compact region, which can also be generated by reaction with water vapor. Ellipsometer measurements are primarily affected by the thicker, porous region, which may be formed by the precipitation of decomposition products of the solution.

Surface films on lithium in acetonitrile-sulphur dioxide solutions

The growth of the passive film on Li in acetonitrile-sulphur dioxide solutions of LiBr, LiAsF 6, LiAlCl 4 and LiClO 4 with time has been followed by galvanostatic pulse measurements and SEM observations. It was found that the specific conductivity of the primary film on Li in ANSO 2LiBr solutions ( k = 4 × 10 −9 ohm −1 cm −1) is practically insensitive to changes in concentration of SO 2 and LiBr. The substitution of Br − by AsF 6 − anions in ANSO 2 electrolytes significantly changes the properties of the film; the rate of growth and the “steady state” value of the polarization resistance are much higher as compared with those of films obtained on Li in Br −-containing electrolytes. Water contamination above 1000 ppm enhances the growth of the passive film as compared with that in “dry” electrolytes.

Anodic behaviour of tin in neutral phosphate solution

The oxidation behaviour of tin in neutral phosphate solution at 37°C (pH = 6.7) has been examined by means of cyclic voltammetry, potentiostatic and galvanostatic pulse measurements. The results showed that the anodic reaction is controlled by diffusion. The passivation can be brought about by precipitation of soluble species and by nucleation and growth process at more anodic potential. Analysis of the passive layer indicated that it consists of a mixture of tin hydroxide and tin phosphate, or of tin hydroxide containing adsorbed phosphate species.

ChemInform Abstract: INVESTIGATION OF THE PROCESSES ON IRON AND NICKEL ELECTRODES AT HIGH CORROSION CURRENT DENSITIES IN SOLUTIONS OF HIGH CHLORIDE CONTENT

AbstractIm Anfangsbereich der Strom‐Spannungs‐Kurven findet keine Passivierung der Metalloberfläche statt (Bildung einer CF‐Adsorptionsschicht oder einer nur sehr dünnen Salzschicht).

Investigation of the processes on iron and nickel electrodes at high corrosion current densities in solutions of high chloride content

Iron and nickel anodic dissolution has been examined by galvanostatic pulse measurements in solutions of high chloride concentrations with current densities in the range 1–100 A/cm 2. The transition time τ for the formation of salt layers was determined at different compositions of the electrolyte and current densities i. The relation of Sand viz i √τ = 1 2 Z MF √ π D ( c s — c) could be applied to the results. The increase of the electrode potential by some volts at t ⩾ τ is explained by a poreless salt layer directly on the metal surface. This layer is non-electron-conducting and prevents the chlorine or oxygen evolution though the electrode potential is very positive. The measured additional ohmic drop U Ω, p at t ≥ τ is explained by a porous precipitated salt layer formed on the poreless film. at times t > τ potential oscillations for both metals and electropolishing of nickel was observed.

Diffusion and electromigration in solid Na 2WO 4

The differential equation for the case of one-dimensional diffusion/electromigration of silver ions in solid Na 2WO 4 is solved for the case of galvanostatic electrolysis of the cell system Ag/Na 2WO 4/Ag. Galvanostatic pulse measurements and silver ion concentration profile measurements (by microscan analysis) of sectioned electrolyzed Ag/Na 2WO 4/Ag cell arrangements were performed. The theory is not in quantitative accordance with the experiments, the reasons of which are discussed. According to the present study, the diffusion of Ag + in ∝-Na 2 WO 4 (high temperature phase, 589–694°C) can be given by: ▪

ChemInform Abstract: THE INFLUENCE OF THE TUNNEL PROBABILITY ON THE ANODIC OXYGEN EVOLUTION AND OTHER REDOX REACTIONS AT OXIDE COVERED PLATINUM ELECTRODES

AbstractPotentiostatische und galvanostatische Impulsmessungen wurden vorgenommen, um die anodische Sauerstoffentwicklung an Pt‐Elektroden in In H2SO4 in Abhängigkeit von Oxidschichtdicke und Elektrodenpotential zu untersuchen.

The influence of the tunnel probability on the anodic oxygen evolution and other redox reactions at oxide covered platinum electrodes

Potentiostatic and galvanostatic pulse measurements were carried out to investigate the anodic oxygen evolution at platinum electrodes in 1N H 2SO 4 in dependence on the oxide layer thickness d and the electrode potential ε. The thickness d (1·5–10 Å) was obtained from cathodic charging curves. Further, the temperature dependence (0°–81°C) was evaluated from Bowden's measurements. Summarizing, the current i o2 follows the relation, log i = A - ( E 0 a - α Fη)/2·3 RT - d/d o. The experimental activation energy E o = E o a = α Fη decreases linearly with increasing overvoltage η. The linear decrease of log i with increasing d, which is given by the term d/d o, is correlated to the probability of the quantum mechanical tunnel transition of the electron from adsorbed ions, OH − ad or O 2− ad respectively, through the oxide layer to the metal. Similar effects of the oxide layer thickness on the current density were observed in the case of the oxygen evolution at iridium, the CO-oxidation on platinum, and the reduction of Cl − and Ce 4+ at platinum. In these cases a rate determining electron transfer through the oxide layer is also assumed.

Etude De La Rupture De Passivite De Certains Metaux Electrochimiquement Actifs

The anodic behaviour of a group of metals (manganese, zinc, cadmium, copper) in borate buffer solutions containing different aggressive anions was studied. The breakdown of the passivity was examined by means of stationary potentiostatic and transient galvanostatic pulse measurements. The literature on the passivity breakdown is briefly reviewed at the same time as the results are discussed.

The kinetics of the electrochemical formation and reduction of monomolecular oxide layers on platinum in 0.5 M H 2SO 4: Part II. Galvanostatic pulse measurements and the model of oxide growth

The formation and reduction of platinum oxide layers in 0.5 M H2SO4 was investigated by galvanostatic pulse measurements. The results led to the conclusion that the properties of the layer are dependent on the formation conditions of the layer, i.e. the formation rate, the ageing of the layer, and the method of the setting of the coverage (anodic/increase or cathodic/decrease). At constant formation conditions, ϑ-dependent Tafel equations, log i+=A++(ε−E+)/b+, are obtained for the anodic layer growth, and log |i−|=A−−(ε−E−)/b− for the cathodic reduction. The anodic b+-factor is dependent on the coverage according to the equation b+=b+0(1+1.0 ϑ), whereas the cathodic b−-factor is almost constant, b−≈60 mV. The double layer capacity CD decrease with oxide formation according to a similar equation, 1/CD=(1/Ci)(1+1.2 ϑ). The kinetics of the layer formation can be explained by the following model: oxygen ions are chemisorbed from the electrolyte solution in an equilibrium reaction, H2O(aq)⇌O2− (ad)+2H+ (aq). The coverage of these ions does not, however, exceed a few percent. Then the adsorbed oxygen ions are exchanged for platinum ions from the first atomic layers. This process is rate-determining and dependent on the field strength. It takes place in the inner Helmholtz layer, thereby forming an epitaxial surface oxide. Somewhat thicker oxide layers (ϑ=1–2.5) are formed in a similar place exchange reaction at the metal/oxide and oxide/electrolyte interfaces, followed by a migration of platinum and oxygen ions over vacancies or interstitial positions in a high electric field. The oxide is reduced according to the same mechanism, though only at the edges of oxide islands. The b−-factor is therefore nearly independent of ϑ. A three-layer structure has been assumed for the double layer. It is composed of the outer and inner Helmholtz layer (adsorption layer) and the charge-free oxide layer. With increasing coverage, the potential drop in the oxide layer also increases, causing an ascending anodic charging curve at constant current density, a decrease of the current density at constant potential, and a dependence of the b-factors and of the double layer capacity on the layer thickness.

The kinetics of the electrochemical formation and reduction of monomolecular oxide layers on platinum in 0.5 M H2SO4 Part II. Galvanostatic pulse measurements and the model of oxide growth*1

The kinetics of the electrochemical formation and reduction of monomolecular oxide layers on platinum in 0.5 M H2SO4 Part II. Galvanostatic pulse measurements and the model of oxide growth*1

A new analysis of data obtained with galvanostatic and coulostatic single pulses

Summary Methods of analyzing experimental data from coulostatic and galvanostatic pulse measurements are given, by which it is possible to determine the three parameters involved in the electrode process, i.e. , double-layer capacity, kinetic and diffusional parameters, in the presence of the electroactive species. This method does not require such a stringent condition for the charging of the double layer in the coulostatic pulse method, as previous methods of analysis of data.