Potentiostatic Pulse Technique Research Articles

Technique for Detecting Sensitization in Austenitic Stainless Steel

Abstract A potentiostatic pulse technique has been proposed for detecting sensitization of austenitic stainless steel. Compared with conventional electrochemical potentiokinetic reactivation (EPR) test, this technique has some advantages: The detection of sensitization of stainless steel with this technique can be conducted at greater speed and with smaller destruction. A potentiostatic pulse test is generally completed within five minutes. It is almost nondestructive. The experimental results indicate that the sensitization of austenitic stainless steel can be detected with this technique.

Potentiostatic pulse technique to determine the efficiency of hydrogen absorption by alloys

A potentiostatic pulse technique was used to determine the efficiency of hydrogen entry and trapping in two precipitation-hardened (Inconel 718 and Incoloy 925) and two work-hardened (Inconel 625 and Hastelloy C-276) nickel-base alloys in an acetate buffer (1 M acetic acid/1 M sodium acetate) containing 15 p.p.m. As2O3. The data were examined as a function of charging time and overpotential. The trapping efficiency increases with charging time (f c) and is linearly dependent on (t c)1/2 for sufficiently short times. The range of linearity is determined by the apparent trapping constant for the alloy. The entry efficiency is independent of charging time but it can vary with overpotential depending on the value of the charge transfer coefficient (α) for the hydrogen evolution reaction. In the case of Inconel 718 and Hastelloy C-276, the value of α was 1.4, which is consistent with a mechanism for hydrogen evolution involving fast discharge followed by slow electrochemical desorption.

Identification of intermetallic compounds in thin layers of electrodeposited Cu–Cd alloys using electrochemical techniques

AbstractAn attempt was made to analyse the phase structure of thin layers of electrodeposited Cu–Cd alloys using anodic linear sweep voltammetry combined with a potentiostatic pulse technique (ALSV–PPT). The results were compared with data obtained using conventional techniques for phase structure analysis. It was found that application of the conventional X-ray technique (Guinier analysis) is limited, because the grain size of the alloy constituents is too small for compounds to be revealed by X-ray peaks. Electrodeposited alloys could be successfully analysed using that method only after subsequent thermal treatment. Diffraction patterns from transmission electron micrographs of very thin foils (of the order of 20–50 nm) of electrodeposited 75Cd–25Cu (at.-%) alloy revealed the presence of CuCd3 intermetallic compound having a grain size of ~20 nm. By comparing all the results, the distribution of the various intermetallic compounds present at various stages in the electrodeposition of thin (up to 10 μm)...

Hydrogen trapping in work-hardened alloys

The ingress of hydrogen in two work-hardened nickel-base alloys (Inconel 625 and Hastelloy C-276) exposed to an acetate electrolyte (1 mol L −1HAc/1 mol L −1 NaAc where Ac = acetate) was studied using a potentiostatic pulse technique. The data were shown to fit a diffusion/trapping model under interface control, and values were determined for the irreversible trapping constants ( k) and the flux of hydrogen into the alloys. The density of irreversible trap defects in Inconel 625 was calculated from k and found to be in excellent agreement with concentration of NbTi(C) particles. Hastelloy C-276 was characterized by two trapping constants; one is associated with quasi-irreversible traps that saturate, leaving only irreversible traps. The density of irreversible traps was shown to agree with the concentration of phosphorus segregated at grain boundaries. The irreversible trapping constants for these alloys are consistent with their relative susceptibilities to hydrogen embrittlement.

Electrodeposition of CdTe by potentiostatic and periodic pulse techniques

Cadmium telluride was electrodeposited from an aqueous solution containing the species CdCl 2 and TeO 2 by potentiostatic and periodic pulse techniques. The effect of different parameters such as concentration of the individual species, hydrogen ion concentration, applied potential and temperature are analysed to obtain optimum conditions for codeposition. X-ray diffractograms, X-ray microprobe analysis, scanning electron microscopy and voltammetry were employed to understand the crystalline nature, elemental composition and surface properties of the deposited films. A theoretical model has been developed for the electrodeposition of CdTe to understant the mechanism involved in the process. The results are discussed.

Prediction of bending fatigue behaviour by the reference stress approach : Megahed, M.M.Fatigue Fract. Eng. Mater. Struct. 1990 13, (4), 361–374

Hydrogen trapping in two precipitation-hardened alloys — 18Ni (250) maraging steel and alloy X-750 — was studied using a potentiostatic pulse technique. Irreversible trapping constants (k) and hydrogen entry fluxes were determined for these alloys in 1 mol l−1 acetic acid/1 mol l−1 sodium acetate. The values of k for stress-equalized and stress-equalized/aged alloy X-750 were higher than those for three other hardened Ni-base alloys (625, 718, and 925) but were considerably lower than the value for the aged 18Ni steel. A correlation was found between k and the observed resistance to hydrogen embrittlement for three groups of aged alloys: X-750 and 718; 18Ni (250) and 718; and 18Ni (250), 18Ni (300), and 4340 steels.

A procedure for estimation of fatigue strength for general multiaxial stress states : Clorman, U.H. and Simon, G.Stahlbau May 1990 59, (5), 149–154

Hydrogen trapping in two precipitation-hardened alloys — 18Ni (250) maraging steel and alloy X-750 — was studied using a potentiostatic pulse technique. Irreversible trapping constants (k) and hydrogen entry fluxes were determined for these alloys in 1 mol l−1 acetic acid/1 mol l−1 sodium acetate. The values of k for stress-equalized and stress-equalized/aged alloy X-750 were higher than those for three other hardened Ni-base alloys (625, 718, and 925) but were considerably lower than the value for the aged 18Ni steel. A correlation was found between k and the observed resistance to hydrogen embrittlement for three groups of aged alloys: X-750 and 718; 18Ni (250) and 718; and 18Ni (250), 18Ni (300), and 4340 steels.

Crack layer analysis of fatigue fracture of a β-titanium alloy : Mostafa, I.M.Diss. Abstr. Int. June 1990 50, (12), 203 pp

Hydrogen trapping in two precipitation-hardened alloys — 18Ni (250) maraging steel and alloy X-750 — was studied using a potentiostatic pulse technique. Irreversible trapping constants (k) and hydrogen entry fluxes were determined for these alloys in 1 mol l−1 acetic acid/1 mol l−1 sodium acetate. The values of k for stress-equalized and stress-equalized/aged alloy X-750 were higher than those for three other hardened Ni-base alloys (625, 718, and 925) but were considerably lower than the value for the aged 18Ni steel. A correlation was found between k and the observed resistance to hydrogen embrittlement for three groups of aged alloys: X-750 and 718; 18Ni (250) and 718; and 18Ni (250), 18Ni (300), and 4340 steels.

Electrodeposition of CdSe xTe 1 − x by periodic pulse technique

Cadmium chalcogenides have been electrodeposited from an aqueous solution on titanium and graphite substrates by potentiostatic and periodic pulse techniques. Deposits have been characterized with X-ray diffractograms, surface micrographs, X-ray microprobe analysis and voltammetry. The mechanism and deposition kinetics of CdSe x Te 1 − x have been determined. The results are discussed.

Thin film deposition and characterization of CuInSe 2

Thin film CuInSe 2 was successfully electrodeposited from an aqueous solution containing CuSO 4, In 2(SO 4) 3 and SeO 2 onto titanium and graphite substrates by the potentiostatic and periodic pulse technique. The deposited material was characterized by X-ray photoelectron spectroscopy and voltammetry. A theoretical model was developed to construct the linear sweep voltammograms. This model, which is based on Butler-Volmer kinetics, was successfully employed to construct the voltammograms for various values of activity and rate constants of the species and pH and temperature of the electrolyte. The results obtained are discussed.

Hydrogen Ingress in Titanium

Abstract A potentiostatic pulse technique was used to study the ingress of hydrogen in titanium (pure and grade 2) in an acetate buffer. Hydrogen ingress did not occur with pure titanium, indicating that the surface oxide is an effective barrier to hydrogen entry. In contrast, the data for Ti grade 2 (UNS R50400) were shown to fit a model for hydrogen diffusion and trapping, allowing values to be determined for the irreversible trapping constant (k) and the flux of hydrogen into the metal. Two values of k were obtained, depending on the level of hydrogen present in the metal. The density of irreversible traps calculated from k for low hydrogen levels suggests that the principal irreversible traps may be interstitial nitrogen, but grain boundaries are another possibility. The additional trapping constant obtained for high hydrogen levels is thought to be associated with hydride formation. The irreversible trapping constants for Ti grade 2 are consistent with its susceptibility to hydrogen embrittlement rel...

Hydrogen trapping in precipitation-hardened alloys

The ingress of hydrogen in three precipitation-hardened alloys (Inconel 718, Incoloy 925, and 18 Ni maraging steel) exposed to an acetate electrolyte (1 mol L −1 HAc/1 mol L −1 NaAc where Ac = acetate) was studied using a potentiostatic pulse technique. The data were shown to fit a diffusion/trapping model under interface control, and values were determined for the irreversible trapping constants ( k) and the flux of hydrogen into the alloys. The density of irreversible trap defects in Inconel 718 and Incoloy 925 was calculated from k and found to be in excellent agreement with the concentration of NbTi(CN) and TiC particles, respectively. The maraging steel was characterized by two trapping constants; one is associated with quasi-irreversible traps that saturate, leaving only irreversible traps thought to be TiC/Ti(CN) particles. The irreversible trapping constants for these alloys are consistent with their relative susceptibilities to hydrogen embrittlement. Moreover, a comparison of the trapping constants with those for AISI 4340 steel and two other nickel-base alloys (Monel K-500 and MP35N) indicates that a strong correlation exists between hydrogen embrittlement susceptibility and trapping capability over all the alloys.

Electrode reactions at extremely negative potentials: Part IV. Kinetics and thermodynamics of the Ca(II)/Ca(Hg) system in water

The electrode reactions of the Ca(II)/Ca(Hg) system in aqueous 0.10–2.0 mol dm −3 Ca(ClO 4) 2 solutions were investigated using potentiostatic pulse techniques and dc polarography. The reduction of Ca(II) was found to be irreversible under polarographic conditions and accompanied by hydrogen evolution. It was shown, however, that the water reduction process does not influence the kinetics of Ca amalgam formation. The oxidation of in situ generated diluted Ca amalgam was found to be controlled both by diffusion and charge transfer kinetics. In various solutions standard rate constants not reported earlier in the literature (−log k app s = 4.08–4.20) and formal potentials (− E o = 2.200-2.143 V vs. SSCE) for the Ca(II)/Ca(Hg) couple were determined and discussed critically. Possible mechanisms of H 2O reduction are discussed.

The extraction of heterogeneous kinetic parameters from combined chronoamperometric and chronocoulometric data by a multiple regression procedure

A new method for extracting kinetic parameters from heterogeneous electrochemical reactions without distortion of the data and with a reliable calculus of uncertainty in the parameters has been devised. It consists of the application of a statistical multivariable regression procedure to combined current ( i)-charge ( q) transient data obtained from the potentiostatic pulse technique. The procedure was tested on theoretical i- q transients, both on pure faradaic data and on faradaic data admixed with Gaussian noise and typical double-layer component values. It was also satisfactorily checked on real systems, i.e. from the typical irreversible Fe 2+ oxidation on a glassy carbon electrode in acidic medium (I), through the “slow” quasi-reversible oxidation of Fe(CN) 4− 6 in neutral aqueous solution on a glassy carbon electrode (II), to the “fast” quasi-reversible N, N, N', N'-tetramethyl- p-phenylendiamine oxidation on a platinum electrode in acetonitrile (III). A method for recovering the diffusion coefficients of electroactive substances from combined kinetic data is also proposed. This method also proved to be a good internal check of the whole procedure.

Aluminium electrodeposition from AlCl3-NaCl melts on glassy carbon, platinum and gold electrodes

The electrochemical deposition and dissolution of aluminium on glassy carbon, platinum and gold electrodes in chloraluminate melts have been investigated using linear sweep voltammetry and potentiostatic pulse techniques. It was shown that deposition of aluminium on the glassy carbon electrode at low overpotentials takes place by 3-D progressive nucleation and growth, with the incorporation of atoms in the crystal lattice as the rate-determining step. At overpotentials higher than −100 mV vs Al, in the melts containing more than 52 mol % of AlCl3, diffusion of Al2Cl7−, takes over the control of deposition of aluminium. Alloying of platinum and gold electrodes with aluminium from the melt occurs in the underpotential region.

A method of obtaining a small number of nucleation sites and growing large crystal grains

Abstract Optical microscopy was used in situ for the investigation of granular metal growth in electrochemical depositions of silver from a silver nitrate solution on a glassy carbon substrate. Incomplete dissolution of silver upon anodic polarization was observed and explained in terms of “undercutting”. A triple potentiostatic (or galvanostatic) pulse technique was developed for obtaining a small number (between 1 and 10) of nuclei in the field of vision, and growing them into large crystal grains. The pulse train consists first of a negative pulse to deposit silver crystallites, then a positive one to dissolve them all, but a few, which then serve as sites for growth in the third negative step.

ChemInform Abstract: A POTENTIOSTATIC PULSE STUDY OF OXYGEN EVOLUTION ON TEFLON‐BONDED NICKEL‐COBALT OXIDE ELECTRODES

AbstractAus stationären Messungen der O2‐Entwicklung an einer Reihe Teflon‐gebundener NiyCoxO4‐Elektroden bei 25°C, 5 N KOH geht hervor, daß NiCo2O4 die höchste Aktivität und die niedrigste Aktivierungsenergie besitzt.

A Potentiostatic Pulse Study of Oxygen Evolution on Teflon‐Bonded Nickel‐Cobalt Oxide Electrodes

Steady‐state oxygen evolution measurements on a series of Teflon‐bonded electrodes at 25°C, showed that had the highest activity. Tafel plots on such electrodes are complicated by the formation of higher oxides, gas bubbles, and emptying of the electrocatalyst pores, and it is suggested that potentiostatic pulse techniques can give more reliable results, provided the electrodes are fully preanodized to form the higher metal oxide.

Galvanostatic and potentiostatic measurements on iron dissolution in the range between active and passive state

The kinetics of anodic iron dissolution in sulphate ions containing solutions, which are free of oxygen, were investigated in the range between active and passive states of the metal at pH ⋍ 5. The measurements were carried out at fixed electrodes under mechanical stirring of the electrolyte at T = 298K using galvanostatic as well as potentiostatic pulse technique. In the prepassive range the obtained transients indicate transition states, which can be attributed to parallel reactions to the active metal dissolution. The mechanism of the metal dissolution in the prepassive range is discussed.

The anodic behaviour of copper in static and flowing hydrochloric acid solutions

The dissolution of copper in 0·36 to 3·6 HCl was studied both in static and in flowing solutions using flow rates between 0·098 and 1·14 ms −1, all in the region of laminar flow. Steady state anode potential current curves, potentiodynamic sweep and potentiostatic pulse techniques and impedance measurements, in the range of 0·02–7 kHz, were used. In both static and flowing solutions dissolution of copper occurs to a monovalent state, as chloro-complexes CuCl − 2 and CuCl 2− with exchange currents for the two reactions of ∼ 1·9 × 10 −5 A mm −2 and ∼ 8 × 10 −7 Amm −2 respectively in 1·44 MHCl. The cuprous chloride layer first forms a monolayer and subsequently grows to considerable thicknesses. The double layer capacity is constant at ∼ 0·17 ± 0·03 μFmm −2 at potentials below multilayer formation and this is interpreted as implying that there is no specific adsorption of chloride ions prior to formation of the cuprous chloride layer. As the flow rate increases the film becomes thinner so delaying the formation of the film of critical thickness required for passivation.