Potentiostatic Current-time Curves Research Articles

Influence of Extrusion Temperature on the Corrosion Behavior in Sodium Chloride Solution of Solid State Recycled Aluminum Alloy 6061 Chips

In the present work, aluminum alloy 6061 (AA6061) device chips were subjected to cold compaction monitored by an extrusion procedure at an extrusion ratio of 5:2 and elevated temperatures of 350, 425, and 500 °C, respectively. The influence of changing temperature on the corrosion of the extruded alloys after 1 h and 24 h in 3.5% NaCl solutions was studied. The polarization (cyclic potentiodynamic polarization, CPP) results indicated that the corrosion decreases with the increase of extrusion temperature of AA6061 from 350 to 500 °C. Impedance (electrochemical impedance spectroscopy, EIS) experiments provided a remarkable increase in the corrosion resistance with rising the extrusion temperature. Potentiostatic current-time (PCT) curves indicated that the current initially increased then decreased for all alloys after 1 h measurements. Prolonging the exposure time to 24 h was observed to decrease the rate of corrosion for all AA6061 alloys as proved by CPP and EIS data. This effect was found to increase the pitting corrosion as indicated by the measured PCT curves and by the scanning electron microscopy (SEM) images for the surface of the alloys. The surface layers formed on AA6061 alloys were mostly composed of aluminum oxide as presented by the spectra of the energy dispersive X-ray analyzer (EDX). All results indicated that the increase of the temperature of extrusion increased the corrosion resistance via decreasing the corrosion current and corrosion rate, and that this effect was found remarkably increased when the immersion time increased from 1 to 24 h exposure to the chloride test solution.

Technical Note: Suppression of Anodic Kinetics of Stainless Steels During Biofilm Development in Natural Seawater

The anodic kinetics of three stainless steels, viz. UNS S31600, S44660, and N08367, in gently flowing natural seawater was investigated. Potentiodynamic anodic polarization showed two distinct passive regimes emerging with biofilm development. A dramatic decrease of anodic current densities (p < 10−4) was recorded in the lower passive region near the ennobled open-circuit potential, accompanied by an increase of the breakdown potential by over 0.2 V for Alloy S31600. However, significant broadening of the transpassive region was observed on all the three alloys tested. Further, for Alloys S44660 and N08367, the second passive region was altered during biofilm growth, which resulted in enhanced peak current densities. These seemingly undesired effects, nonetheless, were detected far beyond the domain of practical significance. Potentiostatic current-time curves for Alloy N08367 further confirmed the suppression of anodic kinetics in the lower passive region. Evans diagrams constructed from actual polarization curves provided fundamentally important insights that passivity promotion can be independent of microbially enhanced cathodic kinetics.

Effect of Nickel Content on the Corrosion Resistance of Iron-Nickel Alloys in Concentrated Hydrochloric Acid Pickling Solutions

The effect of Ni content on the resistance against corrosion of Fe-36% Ni and Fe-45% Ni alloys in 1 M hydrochloric acid pickling solution was reported. Various electrochemical and spectroscopic techniques such as potentiodynamic cyclic polarization (CPP), open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiostatic current-time (PCT), and scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) have been employed. CPP measurements indicated that the corrosion current and corrosion rate recorded lower values for the alloy that had higher nickel content. OCP curves proved that the presence of high Ni content shifts the absolute potential to the positive potential direction. EIS results revealed that the surface and polarization resistances were much higher for the alloy with higher Ni content. PCT curves also showed that the absolute currents were lower for Fe-45% Ni alloy. All results were in good agreement with others and confirmed clearly that the corrosion resistance in HCl solutions for Fe-45% Ni alloy was higher than that obtained for Fe-45% Ni alloy.

The effects of sodium fluoride as the electrolyte additive on the electrochemical performances of magnesium–8lithium–0.5zinc electrode in sodium chloride solution

The electrochemical performance of Mg–8Li–0.5Zn electrode in 0.7 mol L−1 NaCl solution with different concentrations of NaF (0.0, 0.2, 0.5, 0.8, 1.0, 1.2 and 1.5 mmol L−1) was investigated by means of potentiodynamic polarization, potentiostatic current–time curves, electrochemical impedance spectroscopy, scanning electron microscopy and utilization efficiencies. The findings indicate that Mg–8Li–0.5Zn electrode in 0.7 mol L−1 NaCl solution with 1.0 mmol L−1 NaF has a higher discharge current density than that in 0.7 mol L−1 NaCl solution with the other concentrations of NaF that were investigated. The addition of 1.0 mmol L−1 NaF to the NaCl electrolyte solution loosens the product film and the oxidation products on the alloy surfaces of the electrode, which produces deeper and larger channels, as observed by the SEM investigation, compared with those in 0.7 mol L−1 NaCl solution without any NaF. The addition of 1.0 mmol L−1 NaF in 0.7 mol L−1 NaCl solution improves the continuous discharging utilization efficiency of Mg–8Li–0.5Zn electrode by more than 18.80%, and enhances the interval discharge utilization efficiency of Mg–8Li–0.5Zn electrode by more than 27.90%.

The electrochemical behaviors of the Mg-7.5Li-3.5Al and Mg-7.5Li-3.5Al-1Y electrodes in sodium chloride solution

Mg-7.5Li-3.5Al and Mg-7.5Li-3.5Al-1Y alloys are prepared, and their electrochemical performances are investigated by potentiodynamic polarization, potentiostatic current-time curves, electrochemical impedance spectroscopy, scanning electron microscopy (SEM), varying load performances, and utilization efficiencies. The performances of the Mg-H2O2 semi-fuel cells with the above alloy anodes are also determined. It is found that the Mg-7.5Li-3.5Al-1Y electrode has higher discharge activity and better corrosion resistance than Mg-7.5Li-3.5Al electrode in 0.7 mol L−1 NaCl solution. SEM studies indicate that the alloying element Y prevents the formation of dense oxide film on the alloy surface and facilitates peeling off of the oxidation products. The utilization efficiencies of the alloys increase in the order: Mg-7.5Li-3.5Al < Mg-7.5Li-3.5Al-1Y. The Mg-H2O2 semi-fuel cell with Mg-7.5Li-3.5Al-1Y alloy as the anode presents a maximum power density of 92 mW cm−2 at room temperature, which is higher than that with Mg-7.5Li-3.5Al anode (85 mW cm−2). Y is a “promotion element” in the alloy, and the Mg-7.5Li-3.5Al-1Y alloy electrode exhibits better performances comparing to the Mg-7.5Li-3.5Al alloy electrode.

The effect of different concentrations of Na2SnO3 on the electrochemical behaviors of the Mg-8Li electrode

In this research, the effect of the different concentrations of NaSnO3 as the electrolyte additive in 0.7 mol L−1 NaCl solution on the electrochemical performances of the magnesium-8lithium (Mg-8Li) electrode are investigated by methods of potentiodynamic polarization, potentiostatic current-time, electrochemical impedance technique, and scanning electron microscopy (SEM). The corrosion resistance of the Mg-8Li electrode is improved when Na2SnO3 is added into the electrolyte solution. The potentiostatic current-time curves show that the electrochemical behaviors of the Mg-8Li electrode in the electrolyte solution containing 0.20 mmol L−1 Na2SnO3 is the best. The electrochemical impedance spectroscopy results indicate that the polarization resistance of the Mg-8Li electrode decreases in the following order with the concentrations of Na2SnO3: 0.05 mmol L−1 > 0.00 mmol L−1 > 0.30 mmol L−1 > 0.10 mmol L−1 > 0.20 mmol L−1. The scanning electron microscopy studies indicate that the electrolyte additive prevents the formation of the dense oxide film on the alloy surface and facilitates the peeling off of the oxidation products.

Comparative Study on the Inhibition of Iron Corrosion in Aerated Stagnant 3.5 wt % Sodium Chloride Solutions by 5-Phenyl-1H-tetrazole and 3-Amino-1,2,4-triazole

A comparative study on the inhibition of iron corrosion in 3.5 wt % NaCl solutions by 5-phenyl-1H-tetrazole (PHTA) and 3-amino-1,2,4-triazole (ATA) was investigated using a variety of electrochemical measurements. The potential-time curves revealed that PHTA and ATA shift the potential of iron toward the positive values. Electrochemical impedance spectroscopy measurements indicated that the presence of PHTA and ATA and the increase of their concentrations decrease the iron corrosion by increasing the solution and polarization resistances. This effect also decreases the corrosion current and corrosion rate for iron as confirmed by potentiodynamic polarization data. Potentiostatic current–time curves indicated that the presence of PHTA and ATA molecules decreases the absolute current and severity of pitting corrosion of iron in the test solutions. In situ Raman spectra for iron in chloride solution containing PHTA and ATA confirmed that the inhibition of iron corrosion is achieved by the adsorption of PHTA and ATA molecules onto its surface.

Improving the Stability and Ethanol Electro‐Oxidation Activity of Pt Catalysts by Selectively Anchoring Pt Particles on Carbon‐Nanotubes‐Supported‐SnO2

AbstractTo improve the stability and activity of Pt catalysts for ethanol electro‐oxidation, Pt nanoparticles were selectively deposited on carbon‐nanotubes (CNTs)‐supported‐SnO2 to prepare Pt/SnO2/CNTs and Pt/CNTs was prepared by impregnation method for reference study. X‐ray diffraction (XRD) was used to confirm the crystalline structures of Pt/SnO2/CNTs and Pt/CNTs. The stabilities of Pt/SnO2/CNTs and Pt/CNTs were compared by analyzing the Pt size increase amplitude using transmission electron microscopy (TEM) images recorded before and after cyclic voltammetry (CV) sweeping. The results showed that the Pt size increase amplitude is evidently smaller for Pt/SnO2/CNTs, indicating the higher stability of Pt/SnO2/CNTs. Although both catalysts exhibit degradation of electrochemical active surface area (EAS) after CV sweeping, the EAS degradation for the former is lower, further confirming the higher stability of Pt/SnO2/CNTs. CV and potentiostatic current–time curves were recorded for ethanol electro‐oxidation on both catalysts before and after CV sweeping and the results showed that the mass specific activity of Pt/CNTs increases more than that of Pt/SnO2/CNTs, indicating that Pt/CNTs experiences more severe evolution and is less stable. The calculated area specific activity of Pt/SnO2/CNTs is larger than that of Pt/CNTs, indicating SnO2 can co‐catalyze Pt due to plenty of interfaces between SnO2 and Pt.

Inhibition Effects of Amides on the Corrosion of Copper in 1.0 M HCl: Theoretical and Experimental Studies

Abstract The corrosion inhibition effects of benzamide (BA) and 4-aminobenzenesulfonamide (ABSA) for copper in 1.0 M hydrochloric acid (HCl) solution were investigated using potentiodynamic polarization, cyclic voltammetry (CV), and potentiostatic current-time curves. The Langmuir adsorption isotherms of the inhibitors were used to explain the adsorption behavior. In addition, surface analysis of copper was investigated using scanning electron microscopy (SEM). The results showed that the inhibition efficiency of ABSA was much better than those of BA. The theoretical study on the corrosion inhibition efficiencies for neutral and protonated forms of the BA and ABSA molecules were performed using density functional theory (DFT) and MP2 method in gas and water phases.

Cathodic polarization behavior of self-supporting polyaniline film electrode

The preparation method of a self-supporting doped-polyaniline film electrode and its open-circuit potential (OCP) in NaClO4 and Na2SO4 solutions with different pH value as well as cathodic polarization behavior have been investigated for the purpose of discussing the corrosion electrochemical behavior of polyaniline (PANI) in the acid solution. X-ray photoelectron spectroscopy (XPS) reveals that the lower pH corresponds to higher doping level of H+ in the film and a more positive OCP of PANI film electrode. OCP of the PANI film reached 0.35 V vs. SCE in 1M H2SO4, which is more positive than that of most metals, suggests that PANI would act as cathode when it couples with these metals. The cathodic polarization experiments indicate that the dominating cathodic polarization process of PANI is reversible doping and dedoping reaction and the reduction of dissolve oxygen has very little contribution to it. The potentiostatic current-time curves exhibit a large transient current density at initial stage of polarization, which should be attributed to the charge stored in the film and a relative less steady state current density at the subsequent stage of polarization, which is provided by its doping/dedoping equilibrium activity. Such a current characteristic of PANI electrode might be the force of PANI to provide the passivation protection for some active-passive metals.

Deterioration in critical pitting temperature of 904L stainless steel by addition of sulfate ions

This paper deals with the effect of adding sulfate on the critical pitting temperature (CPT) of highly alloyed austenitic stainless steel. A large number of potentiodynamic CPT measurements and potentiostatic current–time curves were obtained in 1 M NaCl containing 0, 0.2, 0.5 and 0.75 M Na 2SO 4. Provided the CPT is defined as the first temperature where stable pitting occurs at intermediate potentials, such as 600 mV (Ag/AgCl), addition of sulfate is shown to have the unexpected effect of lowering the CPT. The growing pits formed in sulfate-containing solution passivate anodically as the potential is increased, perhaps via salt precipitation. The effect of sulfate on pitting kinetics was studied using 50 μm-dia. 302SS wire in 1 M NaCl and 1 M NaCl + 0.5 M Na 2SO 4 at 40 °C. Sulfate increases the critical concentration of metal salt in the pit, expressed as a fraction of the saturation concentration, that is required to sustain pit dissolution. Provided this fraction does not exceed 100% of saturation, passivation is enhanced just inside the pit rim, allowing earlier undercutting of the metal surface and a finer pore structure in the lacy metal cover over the pit. The pitting potential measured above the CPT is increased by sulfate addition, but the CPT itself is lowered. Related examples are cited where pitting shows an unusual dependence on some variable such as anion concentration or temperature.

Anodic electrochemistry of chalcopyrite

The anodic behaviour of chalcopyrite in 1 M H2SO4 and 1 M HCl was studied by linear sweep voltammetry and potentiostatic electrolysis. Voltammograms with a fresh surface showed a small prewave, attributed to a surface oxidation process, followed by a region of active dissolution characterized by a steeply rising anodic current. At still higher potentials the behaviour differed in the two electrolytes, but, contrary to a previous report, there was no evidence of a photosensitive limiting current. Anodic characteristics of chalcopyrite specimens from different sources, including synthetic material, were similar. The anode reaction was found to involve 6·7±0·3 F per mole of chalcopyrite, from which it was calculated that 86% of the sulphide sulphur was oxidized to the elemental form (some of which was plastic sulphur) and 14% to sulphate. The surfaces of oxidized electrodes were examined and photographed after varying periods of potentiostatic electrolysis. Chalcopyrite dissolution occurred at localized sites, the number of which depended strongly on potential. Current-voltage and potentiostatic current-time curves were interpreted in terms of the kinetics of nucleation, growth and overlap of these discrete corrosion centres.

General analysis of potentiostatic current-time curves for cylindrical electrodes

General analysis of potentiostatic current-time curves for cylindrical electrodes

塩酸中におけるチタンのアノード分極とアノード防食

The anodic polarization behavior of commercially pure titanium in hydrochloric acid was investigated and the availability of anodic protection was examined. Acid concentrations ranging from 10 to 30% were used in the temperature range 35° to 90°C. In this electrode system, the potentiostatic current-time curves in a passive range generally showed the following characteristic change; the current decreased at first with rapidity and then gradually to a minimum value, following which it began to increase to attain a maximum and after showing some decrease, reached a steady state. The shapes and relative positions of these curves were affected by set potentials, acid concentrations, temperature, etc., and the effect of set potentials was most significant.In hydrochloric acid, the anodic oxide film of titanium is unstable as stated above, and furthermore titanium exposed to the vapor of hydrochloric acid cannot be protected by anodic polarization. From the above considerations, the applications of anodic protection to titanium in hydrochloric acid should encounter a number of questions, contraly to the views of other researchers.

Analysis of potentiostatic current-time curves for spherical electrodes

A general analytical method was devised for evaluating the exchange current and transfer coefficient for the electrode reaction from experimental current-time curves obtained with a spherical electrode, for conditions in which the charge-transfer process and diffusion both control the electrode reaction rate. The method involved development of an approximate equation to describe the current time behaviour. Examples are presented to illustrate the inherent accuracy and generality of the method.

Influence of heterogeneous chemical reactions upon potentiostatic current-time curves

Influence of heterogeneous chemical reactions upon potentiostatic current-time curves

The calculation of potentiostatic current—time curves

The calculation of potentiostatic current—time curves

The calculation of potentiostatic current-time curves

It is shown how a complex electrochemical situation involving surface diffusion can be calculated. The current-time transient depends critically on the value of the surface diffusion coefficient, D a , and the distance between step lines, 2l . Evidence for a surface diffusion mechanism will only be obtainable when D a and l have suitable values. Possible experimental systems for comparing theory with experiment are discussed.

The calculation of potentiostatic current-time curves for the electrocrystallisation of metals

The shape of the current-time transient during electrocrystallisation is predicted for potentiostatic conditions, when electro chemical formation of adatoms is followed by diffusion to crystal-growth sites. This is an extension of the equations proposed by fleischmann and thirsk to the case where a finite rate of crystal growth is allowed.

Elektrochemische untersuchungen von weichem kohlenstoffstahl unter mechanischer belastung in ätzalkali- und nitratlösungen

Potentiostatic current-time curves are better suited for the study of corrosion under stress than galvanostatic potential-time curves. Peaks in the curves were shown to be related to the stepwises elongation of the specimen. In the passive range, the specimens show a higher tensile strength than in the active or transpassive range. In the active potential range, the life of wire specimens exhibits a sharp minimum. However, the longest life was obtained at quite negative potentials, although the resulting hydrogen evolution caused some embrittlement (lowering of elongation). These results seem to indicate that the well-known phenomenon of caustic cracking is a case of stress corrosion and not of hydrogen embrittlement.