Potential-time Curves Research Articles

Reversal and Cyclic Chronopotentiometry with Exponential Current-Time Functions at Spherical Electrodes. Reversibility Effects and Experimental Verification

General analytical solutions for the potential-time curves corresponding to a slow charge transfer reaction in reversal and cyclic chronopotentiometry with exponential current-time functions, I(t) = I0ewt, have been deduced. For obtaining these equations, the superposition principle can be applied. Our results are valid for planar and spherical electrodes of any size. We have evaluated the effects of electrode sphericity and of the reversibility of the process on the potential-time curves. The analysis of the successive potential-time responses allows to obtain accurate values of the thermodynamic and kinetic parameters of the process under study as well as to detect any possible kinetic complication. The validity of the theoretical solutions has been experimentally tested with the iron(III) trioxalate complex in aqueous solutions.

Anodic Behaviour of Antimony and Antimony-Tin Alloys in Alkaline Solutions

Abstract The electrochemical and corrosive behaviour of antimony and antimony-tin alloys (Alloy No./Sb(wt. %); I/90, II/80, III/65, IV/50) as anodes in various aqueous concentrations of KOH have been investigated using galvanostatic, potentiodynamic and potentiostatic techniques. Galvanostatic potential–time curves at 4 mA cm−2 revealed that passivation of both antimony and antimony tin alloys is inhibited by an increase in KOH concentration. The opposite effect was observed with an increase in Sn content in the alloy. At high Sn content and low [OH−] a pseudo passivation potential was observed. (Abnormal early passivation occurring in the active anodic region due to the formation of tin oxides, which dissolve in alkali. Then, potential decreases.) The alloy with 50% Sn exhibited immediate passivation. The potentiodynamic curves were swept from Eo.c up to +1000 mV vs SCE. The results showed an increase in the peak current (Ip) for antimony and its alloys with increasing [OH−] on the oxide film. The first three alloys showed two anodic peaks at −780 and −450 mV, but the forth traced a third peak at −940 mV. X-ray diffraction and SEM micrographs detailed the electrochemical results and morphology of the electrode surface.

3302 Ni 電析薄膜形成における電極反応の動力学

A method is described for the study of the kinetics of electrode reactions on the basis of analytical solutions of three transient electrochemical processes induding diffusion of ions in electrolyte, charge-transfer reactions and a charging process of an electrochemical double-layer. Multi-pulse currents are applied to a working electrode of a (110) single-crystalline nickel disk in nickel sulfamate and the potentials between the working and counter electrodes are recorded. The measured potential-time curves well agree with those predicted by the analytical solution. The kinetic constant, exchange current density and double-layer capacitance characterizing the kinetics of the electrode reactions are determinedfrom the measured potentialtime curves using the analytical solution.

Anodic oxide films on nickel electrode in borate solutions

The effect of different concentrations of sodium borate, current densities, pH and temperature on the anodic oxidation of nickel was studied using galvanostatic polarization technique. The anodic potential-time curves showed four regions: the charging of the anodic double layer, an arrest corresponding to anodic dissolution and/or oxide film formation, linear rise in the potential due to the formation of barrier oxide film and finally deviation from linearity to reach steady-state potential value attributed to oxygen evolution reaction. The duration time of the arrest decreases with increasing current density and concentration of borate anion while the rate of oxide film formation increases. On the other hand, the duration time of the arrest increases with increasing pH and temperature of the solution while the rate of oxide film formation decreases. Increasing the borate concentration and pH of the solution shifted the starting potential of the arrest towards more negative values. Linear relationships were obtained between the starting potential of the arrest and both borate concentration and pH.

Determination of the kinetics of the hydrogen evolution reaction by the galvanostatic step technique

The galvanostatic step technique was used to study the kinetics of the hydrogen evolution reaction (her). A mathematical model and a numerical procedure allowing approximation of the potential–time curves and determination of the rate constants of the Volmer and Heyrovsky reactions were developed. This model was successfully applied for studying the kinetics of the her on polycrystalline and porous nickel electrodes in alkaline solutions. Results obtained are in good agreement with those determined by the open circuit potential decay and electrochemical impedance spectroscopy combined with Tafel curves.

Synthesis of poly(O‐anisidine) coatings on low carbon steel by electrochemical polymerization of O‐anisidine

AbstractThe poly(O‐anisidine) (POA) coatings have been synthesized on low carbon steel (LCS) substrates by electrochemical polymerization (ECP) of O‐anisidine. The synthesis of POA coatings was carried out under cyclic voltammetric and galvanostatic conditions from an aqueous solution of oxalic acid. It has been observed that the formation of POA coatings on LCS occurs after the passivation of its surface via the formation of polycrystalline iron oxalate (FeC2O4·2H2O) interphase. The formation of iron oxalate interphase is confirmed by fourier transform infrared spectroscopy, glancing angle x‐ray diffraction (GAXRD) measurements and scanning electron microscopy (SEM). Uniform, granular, and strongly adherent dark green POA coatings were obtained on the LCS substrate by ECP of O‐anisidine. These coatings were characterized by cyclic voltammetry (CV), potential–time (E–t) curves, UV‐visible absorption spectroscopy and SEM. The potential–time curve is characterized by an induction time before the ECP of O‐anisidine. The induction time is found to be dependent on the applied current density. The optical absorption spectroscopy study reveals the formation of conducting emeraldine salt phase of POA. Our results reveal that the oxalic acid is a suitable medium for the ECP of O‐anisidine on the LCS substrate and it favors the formation of emeraldine salt (ES) phase of POA. © 2002 John Wiley & Sons, Inc. Adv Polym Techn 21: 33–43, 2002; DOI 10.1002/adv.10006

Galvanostatic and microscopic studies of nodulation during copper electrolysis

The galvanostatic technique on a laboratory scale has been shown to be a useful tool in detecting the presence of nodules on the cathode during copper electrodeposition by using the value of the starting electrolytic potential and by the presence of a cathodic polarization peak on the potential–time curve. Studying the morphology of the deposit with a scanning electron microscope at various magnifications confirmed the galvanostatic results. It is postulated that inappropriate concentrations and/or ratios of the additives (thiourea, gelatin and chloride ions) are associated with a certain current density that generates intergranular microcracks due to adsorption of the additives and leads to the formation of nodules at the macroscale.

Effects of nitrogen ion implantation on the surface characteristics of iron aluminides

Iron aluminides are of considerable interest for low to intermediate temperature structural applications in which low cost, low density and good corrosion or oxidation resistance are required. However, their application is currently limited by room temperature brittleness and low corrosion resistance. In this study, in order to improve the wear and corrosion resistance of iron aluminides in acidic solutions, steel containing Mo and Cr were fabricated and nitrogen ion implanted on the surface of samples with doses of 3.0×10 17 ions/cm 2 at an energy of 150 keV. The effects of nitrogen ion implantation on the electrochemical characteristics of samples were investigated using various electrochemical methods in H 2SO 4+KSCN and HCl solutions. AlN, CrN and Fe 4N were formed in the surface by the nitrogen ion implantion. The grain boundary activation (DOS, degree of sensitization), the active current density (I a) and reactivation current density (I r) were significantly decreased by the nitrogen ion implantation in H 2SO 4+KSCN solution. Nitrogen implantation promoted the corrosion potential, pitting potential, repassivation potential and E hys value for iron aluminides containing Mo. Whereas, the pitting and repassivation potential for iron aluminides containing B was reduced in comparison with iron aluminides containing Cr and Mo in HCl solution. From current and potential–time curves, pitting resistance and passive film stability of the nitrogen implanted iron aluminides containing Mo was higher than that of the unimplanted iron aluminides. The nitrogen ion implanted iron aluminides containing B and Mo showed rounded pit shapes in comparison with irregular pit shape of ion implanted iron aluminides without B and Mo additions. In conclusion, it is considered that the corrosion problem of iron aluminides could be solved, to some extent, by the addition of Mo and Cr to iron aluminides and nitrogen implantation on the surface of iron aluminides.

Chronopotentiometry at a microband electrode: simulation study using a Rosenbrock time integration scheme for differential–algebraic equations and a direct sparse solver

Two-dimensional digital simulation of chronopotentiometry at a microband electrode cannot be performed by conventional alternating direction implicit finite-difference simulation methods, as a result of non-local boundary conditions at the electrode. It is also potentially troublesome for iterative Krylov algorithms for solving linear algebraic equations that result from implicit temporal integration schemes. These difficulties can be avoided by representing the spatially discretised initial boundary value problem in the form of a set of differential–algebraic equations, to which a suitable integration scheme, such as the Rosenbrock ROWDA3 scheme, can be applied. The resulting linear algebraic equations can be solved unfailingly by a general direct sparse algorithm such as Y12M. Using this technique it has been found that the chronopotentiometric potential–time curves and transition time characteristics of a single charge transfer reaction at a microband electrode resemble those for a microhemicylinder electrode of the same surface area, although transition times are somewhat shorter. The simulation reveals also that the assumption of a uniform flux of the concentration at the electrode, encountered in the literature in the context of the two-dimensional theories of chronopotentiometry at microelectrodes, is not adequate, owing to non-negligible edge effects observed.

Kinetic Effect of Halide Ions on the Anodic Behaviour of Antimony and Its Tin Alloys

The anodic behaviour of antimony and antimony-tin alloys in 0.2 kmol/m 3 KOH solution containing various concentrations of Cl - , Br - and I - ions was investigated. Galvanostatic, potentiodynamic and potentiostatic techniques were used. Galvanostatic potential-time curves at 50 A/m 2 reveal that the value of passivation time of Sb electrode decreases with increasing [Cl - ]. On the other hand the opposite effect on its alloys was observed, that the passivation time of the first three alloys (65, 80, 90% Sb) increases with increasing [Cl - ] up to a critical concentration. The passivation time of Sb and its first three alloys is unaffected by the progressive addition of Br - ion, while with increasing [I - ] up to a critical concentration it increases, then I - ion starts to promote the achievement of passivation. The potentiodynamic data exhibited inhibition of the active dissolution of Sb and its alloys, denoted by decreasing the value of peak current, as a result of adding Cl - , Br - and I - ions. However, on increasing [Cl - ] it causes very rapid increase in the value of current density at the permanent passivation region especially in case of Sn-rich alloys, This indicated the breakdown of the thin oxide film followed by pit formation, The potentiostatic-current density-time transients at a constant potential within the permanent passivation region (+2000 mV) have been investigated, and the results supported the potentiodynamic studies, SEM photographs supplement the results.

Cyclic reciprocal derivative chronopotentiometry. Applications to the detection and characterisation of adsorption processes

Cyclic reciprocal derivative chronopotentiometry (CRDC) is applied to the characterisation of different electrode processes in which the adsorption of the reactant and/or the product takes place. The d t/d E– E curves have been obtained by making the analytical or numerical reciprocal of the time derivative of the analytical equations corresponding to the chronopotentiograms (potential time curves) deduced in a previous paper in cyclic chronopotentiometry. The expressions corresponding to the simpler case of strong adsorption of both species have been deduced as a limit case of these general equations. When two successive cathodic and anodic currents (one cycle) are applied, the d t/d E– E response presents two peaks whose ratio of the heights and difference between their potentials afford simple diagnosis criteria to characterise different adsorption processes. Moreover, these processes can be further confirmed through the use of more than one current cycle. Methods for determining adsorption parameters are also proposed.

Formation of Al–Zr composite oxide films on aluminum by sol–gel coating and anodizing

Al specimens were covered with zirconium oxide film by sol–gel coating using zirconium alkoxide, and then anodized galvanostatically in a neutral borate solution. The time-variation in anode potential during anodizing was followed, and the structure and dielectric properties of the anodic oxide film were examined by TEM, EDX, RBS, and impedance measurements. It was found that the anode potential increases during anodizing, and that the slope of the potential–time curve becomes steeper with increasing number of dippings in sol–gel solution. An anodic oxide film was formed at the interface between zirconium oxide and the aluminum substrate during anodizing. This anodic oxide film was composed of an inner Al2O3 layer and an outer Al–Zr composite oxide layer. The capacitance of anodic oxide films formed after sol–gel Zr-oxide coating and anodizing was about 20% higher than without Zr-oxide coating.

Chronopotentiometric and open circuit potential analisys of the redox process in poly(3-methylthiophene) (PMT)

Abstract Chronopotentiometric measurements for PMT samples show that, for film previously in the reduced state, a maximum in the potentialtime curves was observed. The maximum occurs for times between 1 and 70 ms, the exact value depends on the anodic current density applied. It is followed by a potential minimum between 100 and 1500 μCcm −2 and finally by smooth increase of the potential. For samples lightly oxidized, Q = 6.25 μCcm −2 , the maximum potential disappears. In the reduction process, the decrease in the potentials is always linear. The open circuit potential (Eoc) as function of the oxidation charge curves show a strong increase in the Eoc for oxidation charge up to 1000 μCcm −2 followed by a linear increase for higher charges. Otherwise, the reduction process presents only one linear region.

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Cyclic chronopotentiometry with non-linear current-time functions at an SMDE Amalgamation and reversibility effects and experimental verification

Abstract The general analytical equations corresponding to the potential-time response obtained for a charge transfer reaction in cyclic chronopotentiometry with power current-time functions at a static mercury drop electrode are presented. The superposition principle can be applied in this case in spite of the fact that the successive applied currents are non-linear functions of time. These theoretical equations have been tested experimentally in the following cases: (a) for reversible systems in order to quantify the amalgamation product effects; (b) for non-reversible systems pointing out that a given electrode process becomes more irreversible the lower the power of time in the applied current; (c) to analyse the influence of the electrode kinetics on the potential-time curves by using solutions of Cd 2+ with different concentrations of n -pentanol by determining kinetic parameters of tie charge transfer reaction. The sensitivity obtained in the characterisation of amalgamation processes is similar to that of voltammetric stripping techniques. Moreover, the analysis of the different cycles of the potential-time response allows us to obtain accurate values of kinetic parameters, as well as to detect possible complications in the charge transfer reaction.

A study of abrasive-metallic lapping tools : A. Barylski. (Technical University of Gdansk, Gdansk, Poland.)

Repassivation behaviour of Al-1 wt.%Si-0.5 wt.%Cu alloy has been investigated as a function of applied potential in 0.5 M Na2SO4 solutions containing various chloride ion concentrations ranging from 0 to 0.5 M in terms of potentiostatic current transients by using an abrading electrode technique. The current transients obtained were found to be classified into three groups. The anodic processes included in each group are as follows: 1.(i) only repassivation related to the formation of passivating oxide in low concentrations (0–0.01 M);2.(ii) competition between oxide repassivation and film breakdown, the growth of a stable pit after an induction time of tm, followed by a uniform metal dissolution through aluminium salt film in intermediate concentrations (0.05–0.3 M);3.(iii) only a uniform metal dissolution through aluminium salt film in high concentrations (> 0.3 M). Transition from (i) to (ii) occurs at 0.05 M Cl−, regardless of applied potential and (ii) to (iii) transition does at −0.1V/sce and 0.3 M Cl−. In connection with the results of the current-time curves, potential-time curves measured on oxide-covered Al alloy in various halide (F−, Cl−, Br− and I−) solutions demonstrated that the attack by halide ions occurs on the bare metal surface simultaneously with the formation of anodic oxide film.

Shock sintering and properties of cubic boron nitride : C. Cline. (Dynamic Consolidation Technology, Inc., USA.)

Repassivation behaviour of Al-1 wt.%Si-0.5 wt.%Cu alloy has been investigated as a function of applied potential in 0.5 M Na2SO4 solutions containing various chloride ion concentrations ranging from 0 to 0.5 M in terms of potentiostatic current transients by using an abrading electrode technique. The current transients obtained were found to be classified into three groups. The anodic processes included in each group are as follows: 1.(i) only repassivation related to the formation of passivating oxide in low concentrations (0–0.01 M);2.(ii) competition between oxide repassivation and film breakdown, the growth of a stable pit after an induction time of tm, followed by a uniform metal dissolution through aluminium salt film in intermediate concentrations (0.05–0.3 M);3.(iii) only a uniform metal dissolution through aluminium salt film in high concentrations (> 0.3 M). Transition from (i) to (ii) occurs at 0.05 M Cl−, regardless of applied potential and (ii) to (iii) transition does at −0.1V/sce and 0.3 M Cl−. In connection with the results of the current-time curves, potential-time curves measured on oxide-covered Al alloy in various halide (F−, Cl−, Br− and I−) solutions demonstrated that the attack by halide ions occurs on the bare metal surface simultaneously with the formation of anodic oxide film.

Biofilm formation on stainless steels in Arabian Gulf water

Metals immersed in natural seawater are covered with a thin, slimy film of micro-organisms and their biological secretion commonly referred to as biofilm. Biofilms cause the ennobling of the free corrosion potentials and increase the susceptibility of pitting- and crevice corrosion. Biofilm formation from Arabian Gulf water has not been reported before. Biofilm formation on 7 different types of Mo-containing stainless steels and on type 304 steel from Arabian Gulf water was examined in detail. Film formation was followed by measuring the variation of the open circuit, free corrosion potentials in fresh seawater. Stages in the potential-time curves were assigned to oxide thickening and biofilm formation. Coverage with the biofilm occurred within 12–15 days of immersion and was independent of the chemical composition of the steels. Oxygen reduction on biofilmed metals was accelerated and the process involved the intermediate formation of H 2O 2. Cathodization retarded film growth and reduced the catalytic activity of the film. Complementary anodic polarization experiments showed a change in behaviour and increased attack at the transpassive region. Biofilm formation thrived with rise in temperature till ca 42°C whereafter the micro-organisms were killed. No film formed in pre-boiled and cooled seawater. Some factors influencing the activity of the biofilm were identified and examined in some detail. These comprised temperature, dryness, sterilization of the water and the eventual use of biocides.

Aluminium fluoride complexation and its ecological importance in the aquatic environment

A potentiometric investigation of the rate and mechanism of the reaction between aluminium (III) ions and fluoride ions in buffered aqueous solution (pH values 2 and 5) is described. Potential-time curves recorded during the reaction, using fluoride-ion selective electrode, constitute the primary data in this study. The rate of aluminium fluoride complexation is calculated under different experimental conditions. In the solutions where the analytical ratios between fluoride and aluminium are > 6, the calculated average number of fluoride ligands bound by aluminium are in the range 1.8–3.7.

Effect of halide ion and applied potential on repassivation behaviour of Al-1 wt.%Si-0.5 wt.%Cu alloy

Repassivation behaviour of Al-1 wt.%Si-0.5 wt.%Cu alloy has been investigated as a function of applied potential in 0.5 M Na 2SO 4 solutions containing various chloride ion concentrations ranging from 0 to 0.5 M in terms of potentiostatic current transients by using an abrading electrode technique. The current transients obtained were found to be classified into three groups. The anodic processes included in each group are as follows: 1. (i) only repassivation related to the formation of passivating oxide in low concentrations (0–0.01 M); 2. (ii) competition between oxide repassivation and film breakdown, the growth of a stable pit after an induction time of t m , followed by a uniform metal dissolution through aluminium salt film in intermediate concentrations (0.05–0.3 M); 3. (iii) only a uniform metal dissolution through aluminium salt film in high concentrations (> 0.3 M). Transition from (i) to (ii) occurs at 0.05 M Cl −, regardless of applied potential and (ii) to (iii) transition does at −0.1V/ sce and 0.3 M Cl −. In connection with the results of the current-time curves, potential-time curves measured on oxide-covered Al alloy in various halide (F −, Cl −, Br − and I −) solutions demonstrated that the attack by halide ions occurs on the bare metal surface simultaneously with the formation of anodic oxide film.