Cathodic Polarization Curves Research Articles

Effect of pH Value on Electroless Deposition of Copper Graphite Powders

The effect of pH value on the electroless deposition of copper coated graphite powders (Cu@GPs) was investigated in this paper. The cathodic and anodic polarization curves were determined by linear sweep voltammetry in the plating at various pH value. pH value increasing can reduce the initial oxidation potential of formaldehyde, increase peak current density and accelerate electroless copper nuclei generated by the reduction reaction. With increasing pH value Cu+ disproportionation reaction was inhibited. Through the complexation competition and discharge competition among them, Na2EDTA, –OH and TART affect the reduction of cupric ions. The increasing pH value promote the formation of copper nuclei on the surface of graphite powders. Uniform Cu@GPs were fabricated by optimizing the pH 12.5~13. The copper plating layer is tightly combined with graphite, and the coating is complete.

Effect of Thiourea on Electrodeposited Co–Mg–Nd Alloy Coating in Deep Eutectic Solvents

Potentiostatic technique was used to investigate the effect of additive thiourea on the deposition mechanism of Co2+ in choline chloride–urea eutectic solvent system. The Co–Mg–Nd ternary alloy coating was prepared by linear scanning technique which was used to study the electrochemical behavior of Co2+, Mg2+ and Nd3+ in the system and the corrosion resistance of alloy coatings. The results show that Co2+ follows the growth mechanism of three-dimensional continuous nucleation in choline chloride–urea eutectic system. When the amount of thiourea added exceeds 300 mg, the nucleation mode of Co2+ approaches the three-dimensional instantaneous nucleation. The cathodic polarization curves of Co2+, Mg2+, and Nd3+ in the choline chloride–urea system shows a trend of weakening first and then increasing with the increase of thiourea content. At the addition of 100 mg, the cathodic polarization of the films was the strongest, which was conducive to deposite. According to the Ecorr and Icorr obtained by tafel curve, it is found that adding thiourea in the plating solution system could change the corrosion resistance of the coating. When the content was less than 100 mg, the corrosion resistance of the coating is the best. With the thiourea content increasing, the corrosion resistance of the coating is gradually weakening. It is found that the plating solution with 100 mg thiourea added can prepare Co–Mg–Nd ternary alloy coating with excellent coating morphology, high rare earth content and stable compound, by SEM, EDX and XRD analysis.

Secondary Reduction of Refractory Metal near Smooth Cathode during the Salt Melt Electrolysis. 3. Numerical Reproducing of Natural Experiment with the Nb Cathodic Reduction in KNaCl2–NaF–K3NbF7 Melt

In terms of the model of steady-state process of a refractory-metal ion secondary reduction with an alkali (or alkali-earth) metal formed on a smooth cathode during salt melt electrolysis, numerical reproducing of a natural experiment is carried out. The model calculations are based on the polarization measured during the cathodic reduction of Nb in chloride―fluoride melt: [Nb] = 2.4 mol %, 800°C, current density i up to 5.4 A/cm2. On a smooth cathode in the overvoltage range from 0.21 to 0.41 V (i = 0.75―1.17 A/cm2), the reduction mechanism is shown to completely change from primary to the secondary reduction. The secondary reduction zone is located inside the diffusion layer and moves away from the cathode with increasing i. Even at maximal i, this zone remains inside δ (δ is the thickness of the diffusion layer): with i = 0.96 A/cm2, the coordinate of the maximum of the secondary reduction rate xm = 0; with i = 5.4 A/cm2, xm = 0.93δ (in the experiment, the value of i at which xm ≥ δ was not achieved). At i = 5.4 A/cm2, the fraction of secondary reduction in the bulk is insignificant, ≈10−5 A/cm2. The δ vs. E curve is calculated: when E is shifted from the equilibrium value toward the negative values, |i| increased from zero and higher, whereas δ first decreased by an order of magnitude and then increased. Correspondingly, the limiting diffusion current is not constant at a constant Nb concentration in the bulk. This is the reason of uncertain limiting current on steady-state cathodic polarization curves during the electrolysis of metals in melts. A hypothesis is proposed on the dependence of the Nernst diffusion layer thickness near the cathode on the current density exceeding the limiting diffusion current density under the conditions of secondary reduction.

Effect of Ni Content on the Initial Corrosion Resistance of Steel in Atmospheric Environment

Weathering steels with a protective rust layer are well known to exhibit high corrosion resistance in mild corrosive environment for a long time even if it is used without paint. However, they do not generally show high corrosion performance in coastal area. Therefore, there have been numerous reports on the corrosion resistance and corrosion mechanism of weathering steel by exposure tests, electrochemical measurements, and rust analysis. However, the detailed effects of additive elements such as Ni and Cr on corrosion resistance have not been clarified. In this study, we focused on Ni as an additive element, and investigated the effect of Ni addition on the initial corrosion resistance of Fe-Ni alloy with different amounts of Ni by corrosion monitoring and electrochemical measurement under atmospheric corrosion environment. Fe (Fe : 99.7%), Fe-3mass% Ni, and Fe-5mass% Ni (Fe, 3Ni, and 5Ni) were used as the samples. The concentric ring type corrosion sensors (corrosion sensor) and the electrodes embedded in an epoxy resin were prepared for an atmospheric corrosion monitoring and for an electrochemical measurement, respectively. The wet and dry cyclic corrosion test was conducted in the chamber set at 25°C and 60% RH after adding 100 µL droplet of a 0.01 mol dm-3 NaCl solution. During the corrosion test, the atmospheric corrosion behavior was monitored by continuously measuring the impedance at low frequency (10 mHz) and high frequency (10 kHz) by a corrosion monitor. On the other hand, polarization curves were measured with a three-electrode system from the immersion potential. The scanning rate was set at 0.5 mV / s. In addition, the electrochemical impedance measurements were performed for the samples with and without passive film, in order to investigate the characteristic of the sample surface. The impedances were measured at 10mV of applied potential with the frequency range from 100 kHz to 10 mHz. The corrosion rate of the steel content Ni in the first cycle was less than one-tenth that of Fe, and was almost the same for 3Ni and 5Ni. However, the corrosion rate after the second cycle decreased with increasing Ni content, and 5Ni showed a low value for a long time. This indicates that the Ni-content steel shows high corrosion resistance in the initial corrosion process. Almost the same oxygen diffusion limited current was observed in the cathodic polarization curves of all samples. On the other hand, the anodic currents of 3Ni and 5Ni, which are considered to correspond to the dissolution of Fe, were about one digit smaller than that of Fe. The impedance of Ni-content steels was larger than that of Fe. However, this result was not agreement with the corrosion monitoring results. Furthermore, the result of surface alalysis will be introduced in our poster.

Pseudo-passivation mechanism of CoCrFeNiMo0.01 high-entropy alloy in H2S-containing acid solutions

The pseudo-passivation mechanism of CoCrFeNiMo0.01 high-entropy alloy (HEA) in H2S-containing acid solutions was investigated. The results showed that HEA displayed pseudo-passive behaviour in the H2S environment. The reduction reactions of H2S and HS− occurred, leading to a diffusion-controlled region in the cathodic polarization curve. The massive formation of Cr substances on HEA resulted in the transition from active to pseudo-passive corrosion. The film broke down at high potential due to the instability of sulphides. The pseudo-passivation mechanism of HEA in H2S environments was discussed.

Microwave absorption properties of spheres-assembled flake-like FeNi3 particles prepared by electrodeposition

Flake-like FeNi3 particles based on submicrometre spheres self-assembly were prepared by electrodeposition method using cetyltrimethylammonium bromide (CTAB) as the morphology modifier. To explore the formation mechanism of the novel flaky structures, three different concentrations of CTAB were employed to electrodeposit FeNi3 particles in the experiment. Linear sweep voltammetry were conducted to measure cathodic polarization curves of the corresponding three solutions. The crystal structure, morphology and electromagnetic properties of corresponding three samples were characterized by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometry, vector network analysis. The effects of CTAB on the morphologies and structures of the FeNi3 particles were investigated. When the concentration of CTAB is 1.0 g/L, the prepared sample exhibited the best microwave absorption properties as a consequence of better electromagnetic impedance matching. The effective absorption bandwidth (RL < −10 dB) increases with decreasing thickness, reaching 4.32 GHz (13.2–17.52 GHz) when the absorber thickness is only 1.3 mm. The minimum reflection loss (RL) reaches −50.42 dB at 3.44 GHz. The absorbent with thickness of 1.3–2.5 mm obtains RL values exceeding −10 dB over a wide frequency range of 4.40–17.52 GHz, which covers almost the whole C, X and Ku-band (4–18 GHz). The microwave absorption properties of as-prepared FeNi3 particles possess the advantage of broad absorption bandwidth especially at thin thickness.

Investigation of color and anticorrosive properties of pigments in the Fe-Al-Mg-O-H system by the simplex lattice method

PurposeThe purpose of this paper is to study the patterns of formation of anti-corrosion properties, the development of compositions for pigments by using the method of co-precipitation and subsequent heat treatment.Design/methodology/approachTo obtain co-precipitated hydroxides, aqueous solutions of salts were used. The conditions of synthesis varied according to the following parameters: the nature of the starting salts of metals; and the ratio of metal cations. The anticorrosive activity of the pigments was evaluated by the potentiodynamic method, by comparing the anodic and cathodic polarization curves, and calculated potentials and corrosion currents on the basis of regions of Tafel on curves. Polarization curves were obtained by using Potentiostat/Galvanostat/ZRA Gamry, which connected to the PC, and by using the program Gamry Framework. The measurement results were processed by using the method of simplex-lattice planning. X-ray diffractograms of pigments were recorded on a DRON – 2.0 diffractometer (monochromatic copper radiation with a nickel filter).FindingsThe paper deals with the results of research the dependence of colour characteristics and anticorrosion properties of synthesized compositions on their nature and composition. The presence of aluminium cations leads to the formation of solid solutions of ferrum and aluminium oxyhydroxides.Originality/valueThe main technological properties of pigments are determined by the anionic and cationic composition. Colour characteristics are determined by the cation-chromophore. The anti-corrosive properties of non-calcined pigments are determined to a greater extent by the presence of the formed hydroxyl ions and the composition of the compounds. The greatest protective effect is observed when using double compounds of metals, the dissociation constants of which differ significantly. The protective effect is mainly determined by the slowdown of the anode process. Anions containing aluminium atoms accelerate the corrosion processes.

Insight into the Adsorption and Inhibitive Effect of Spironolactone Drug on C38 Carbon Steel Corrosion in Hydrochloric Acid Environment

The inhibitive effect of spironolactone drug (SPR) on C38 carbon steel corrosion in 10% hydrochloric acid solution was investigated using weight loss and two electrochemical techniques, namely electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP), in the temperature range between 30 and 60 °C. Spironolactone was found to act as an inhibitor for the acid corrosion of C38 carbon steel. Inhibition efficiency of the drug increased with an increase in concentration of SPR but decreased with increase in temperature. The maximum inhibition efficiencies obtained with 7.2 × 10–3 M SPR at 30 °C were 98.1%, 95.0% and 95.8% for weight loss, EIS and PDP technique, respectively. Anodic and cathodic polarization curves reveal that SPR is a mixed-type inhibitor. Impedance data show that charge transfer process controlled the mechanism of corrosion. The adsorption of SPR on the C38 steel surface was found to be spontaneous and obeyed Langmuir isotherm at all studied temperatures. The adsorption is a mixed adsorption involving both chemisorption and physisorption. The carbon steel surface was assessed using scanning electron microscopy (SEM), which also revealed the protective ability of the drug for C38 carbon steel in 10% HCl solution. Quantum chemical calculations in the framework of the density functional theory were undertaken to theoretically describe the adsorption and inhibition action of SPR on the C38 steel surface.

EFFECT OF POLYVINYLPYRROLIDONE ON THE SYNTHESIS AND CATALYTIC PROPERTIES OF PLATINUM-CONTAINING OXYGEN ELECTROREDUCTION CATALYSTS

Results of the work on the synthesis of highly effective nanocomposite platinum-containing oxygen reduction electrocatalysts for hydrogen-oxygen fuel cells are presented and ways of increasing their activity are considered. Fuel cells (FCs) represent the most promising renewable and environmentally friendly energy sources that can operate at low temperatures with high efficiency and with low or zero levels of hazardous waste. The main problem of fuel cells is that the oxygen reduction reaction is slowed down in relation to the hydrogen oxidation reaction, which leads to an increase in the overvoltage at the cathode and, as a result, to a decrease in the productivity of FCs. To solve this problem, the new methods are being developed for the synthesis of highly efficient platinum electrocatalysts, which currently have the best performance, since platinum has the highest specific catalytic activity among other materials used in low temperature FCs. The purpose of this work is to determine the optimal composition of reaction mixture and conditions for the preparation of a platinum based catalyst for oxygen electroreduction where Vulcan XC-72 nanodispersed carbon black is used as a carrier. We have worked out 6 methods for preparing Pt (40 %)/XC-72 catalysts. To evaluate the activity of the prepared catalysts and to determine the kinetic parameters of the oxygen reduction on them, cathodic stationary polarization curves were recorded in a 0.5 M H2SO4 solution on a floating gas diffusion electrode superficially modified by the catalysts. For preparation of all electrocatalysts we are used 3.6 ml of a hexachloroplatinic acid (H2PtCl6) solution, containing 18.8 mg Pt/ml, 100 ml of ethylene glycol or its mixture with deionized water (3 : 1) and 100 mg of Vulcan XC-72 carbon black, previously oxidized in HNO3 solution. 1 M NaOH or KOH solutions were used to create the necessary medium (pH = 11). Some Pt(40 %)/XC-72 electrocatalysts were prepared when additions of polyvinylpyrrolidone (PVP) (100 mg or 300 mg) and/or 60 ml of formaldehyde were introduced into reaction mixture. Temperature during syntheses was in the range 75 - 160 °C. It was shown that reducing the synthesis temperature from 160 to 75 °C and introduction of PVP together with formaldehyde into reaction mixture had a positive effect on the activity of obtained nanocomposite platinum-containing catalysts Pt(40 %)/XC-72 for oxygen electroreduction.The sizes of the obtained platinum clusters on the surface of carbon black nanoparticles were in the range of 1.7 - 5.7 nm, and under optimal synthesis conditions they were evenly and densely distributed on the surface of the carbon carrier. The obtained kinetic characteristics of oxygen electroreduction on the studied catalysts indicate that the mechanism of this process depended on both the current density and the method of catalyst synthesis.

Formation of porous Ni surface by electrodeposition and dissolution in molten salt

In a NaCl–KCl-3.5 mol%AlF3 molten salt bath, Al deposition and Al dissolution were performed at the bath temperatures of 750 °C and 900 °C to form a porous Ni surface. Furthermore, in order to investigate the hydrogen evolution behavior of the prepared porous Ni, the cathode polarization curve was measured in 10% KOH.When the Al was dissolved after the Al deposition, a porous layer was formed on the Ni surface of the substrate. When the electrodeposition potential of Al was lowered, it formed a thicker layer. Observations of the porous surface showed that the sample at 900 °C had a finer morphology than at 750 °C.The cathode polarization curve in an alkaline aqueous solution was measured. The porous Ni showed a higher cathode current density at a potential higher than the untreated Ni. The cathode current density increased in the order of untreated Ni, 750 °C treatment, and 900 °C treatment. Therefore, it was found that the 900 °C treatment generated the most hydrogen. The sample with the higher porosity showed a higher cathode current density based on the cathode polarization curve.The activation energies for the hydrogen evolution reaction were 10.3 kJ/mol for the untreated Ni, 10.1 kJ/mol at 750 °C, and 11 kJ/mol at 900 °C. There is no difference in the reaction mechanism, and it is considered that the performance was improved by increasing the surface area.

An Electrochemical Simulation and Treatment Study for the Carbonate and Chloride Based Corrosion of Heritage Silver–Copper Alloys

ABSTRACT This study aimed to investigate the corrosion of a group of historic silver–copper alloy coins and their conservation treatment on defined parameters by potentiostatic methods. Basic copper carbonates and silver chloride were identified on the surface of the coins by a combination of scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray diffraction (XRD) analyses. The carbonate and chloride-based corrosion mechanisms were synthetically simulated on modern silver–copper alloy samples (Ag72/Cu28) by anodic polarisation measured by linear sweep voltammetry (LSV) in sodium bicarbonate (NaHCO3) and sodium chloride (NaCl) solutions. Cathodic polarisation curves, measured by LSV, were used to identify the working conditions to reduce the corrosion products on the corroded samples and to treat the actual coins. The reduction process was then monitored by chronoamperometry. Following the potentiostatic reduction process, the metallic copper spots on the treated samples were wiped with cotton swabs moistened with a diluted solution of silver nitrate (AgNO3) to obtain a silvery appearance, and the treatment was completed by a gentle rubbing of the redeposited silver with a cotton swab moistened with a calcium carbonate (CaCO3) suspension followed by rinsing and drying. The corrosion products identified on the synthetically corroded samples indicated that the deterioration mechanisms were dominated by selective attack on the copper-rich phases of the (Ag72/Cu28) alloy, which is consistent with an internal galvanic corrosion phenomenon. The potentiostatic methods showed excellent effectiveness in determining treatment parameters and monitoring the reduction process of the corrosion products on the coins, which helped to preserve surface details in the cleaning process and to prevent over-treatment.

Effects of Zn content on surface deformability and corrosion resistance of MgZnMnCa alloys

Abstract The effects of the Zn content on the mechanical and corrosion properties of MgZnMnCa alloys were investigated. The results revealed that with increasing Zn content up to 4 wt.%, the Mg-4Zn-0.2Mn-0.2Ca (wt.%) alloy after solution treatment at 400°C for 24 h (ZM40-S) exhibited a volume fraction of 1.56 ± 0.05 (vol.%) of secondary phases with an average grain size of 83.6 ± 1.6 µm. This alloy in the at-cast condition exhibited indentation hardness (Hit) of 657.1 ± 17.8 MPa, which increased to 723.5 ± 29.8 MPa after solution treatments. In addition, the alloy also exhibited a Vickers hardness value of 66.8 ± 2.7 HV and an elastic modulus of 33.8 ± 0.6 GPa, close to the values for human bone. Further, the corrosion properties of this alloy were analyzed: it exhibited a cathodic polarization curve attributed to a hydrogen evolution reaction and an anodic curve corresponding to a passivation tendency, indicating the formation of an oxide layer at the surface; further, its corrosion rate was 0.23 mm/year.

Effects of Zn content on surface deformability and corrosion resistance of MgZnMnCa alloys

Abstract The effects of the Zn content on the mechanical and corrosion properties of MgZnMnCa alloys were investigated. The results revealed that with increasing Zn content up to 4 wt.%, the Mg-4Zn-0.2Mn-0.2Ca (wt.%) alloy after solution treatment at 400°C for 24 h (ZM40-S) exhibited a volume fraction of 1.56 ± 0.05 (vol.%) of secondary phases with an average grain size of 83.6 ± 1.6 µm. This alloy in the at-cast condition exhibited indentation hardness (Hit) of 657.1 ± 17.8 MPa, which increased to 723.5 ± 29.8 MPa after solution treatments. In addition, the alloy also exhibited a Vickers hardness value of 66.8 ± 2.7 HV and an elastic modulus of 33.8 ± 0.6 GPa, close to the values for human bone. Further, the corrosion properties of this alloy were analyzed: it exhibited a cathodic polarization curve attributed to a hydrogen evolution reaction and an anodic curve corresponding to a passivation tendency, indicating the formation of an oxide layer at the surface; further, its corrosion rate was 0.23 mm/year.

Effect of Zn2+ on Cathodic Reaction of Carbon Steel in Aqueous MgCl2 Solutions

We have shown that zinc dissolution is accelerated in relatively high concentrations of MgCl2 during the galvanic corrosion process consisting of zinc and carbon steel. In this study, in order to understand further the galvanic corrosion process of zinc and carbon steel in MgCl2, the cathode reaction on carbon steel was investigated in MgCl2 aqueous solution with and without Zn2+ which is generated during the galvanic corrosion process.The sample used for the experiment was carbon steel SS400 (Fe-0.12C-0.60Mn-0.011P-0.019S) machined to a shape of 1.5 × 1.5 × 0.3 cm3. One side of this sample was ground up to #2000 grit with SiC abrasive papers and then degreased and washed in acetone before use in the following experiments. The test solutions were mixtures of 0.25 M MgCl2 and x mM ZnCl2 (x = 2.5, 5 mM, Mg / Zn molar ratio: 100, 50) and they were used at room temperature under a naturally aerated condition. As reference solutions, the mixtures of 0.5 M NaCl and y mM ZnCl2 (x = 5, 10 mM, Na / Zn molar ratio: 100, 50) with the same Cl- concentration were used. The cathodic polarization curve measurements were done by a conventional three-electrode method with a platinum wire as a counter electrode and an Ag / AgCl electrode (saturated KCl, SSE) as a reference electrode. The potential sweep rate was 0.5 mV/sOn the cathodic polarization curves for carbon steel measured in an aqueous MgCl2 solution containing Zn2+, the diffusion-limiting current region due to the cathodic reduction reaction of dissolved oxygen (ORR) was observed from -0.6 V to -0.8 V, and the magnitude of the limiting currents were almost the same regardless of the Zn2+ concentration. Furthermore, the cathodic polarization curves showed that an increase in the current due to the hydrogen evolution reaction (HER) occurred in the MgCl2 solution without Zn2+. By comparison with the cathodic polarization curve measured in the NaCl solution without Zn2+ showed a diffusion-limiting current of ORR was comparable to that in the MgCl2 solution, but the overvoltage of HER was increased by about 0.1 V. These results indicated that in the MgCl2 solution, HER on carbon steel was enhanced more than that in NaCl aqueous solution.On the other hand, in the MgCl2 solutions containing Zn2+, a shoulder was observed in the cathode polarization curve at around -0.95 V, and the the current due to HER was decreased with increasing the Zn2+ concentration. It was shown that HER was suppressed in MgCl2 solutions by the presence of Zn2+. This may be attributed to the precipitation of zinc corrosion products formed during cathodic polarization.

Electrochemical Study of External Corrosion of Three API Steels Exposed to Seawater and Sediment from Seabed of the Gulf of México

An electrochemical study of three API steels: X52, X65, and X80, exposed to seawater and sediment from seabed is presented. Two seabed samples were collected at 60 meters depth near a platform (seabed A) and at a distance of 500 m (seabed B) from the same platform of the Sonda of Campeche, Mexico. In both samples, the seawater and sediment were separated in order to characterize their corrosiveness in an electrochemical cell of 100 mL. The physicochemical and electrochemical responses were determined in the water and sediment. Electrochemical impedance spectra and polarization curves for both water and sediment from the two seabed samples were carried out. A cathodic protection analysis for the three steel surfaces exposed to sediment was proposed based on cathodic polarization curves. Corrosion rates for the three studied low carbon steels could be attributed to their physicochemical properties and low temperatures from a specific seabed area. Thus, high susceptibility to corrosion was identified when three API steels were in contact with seabed B. A corrosive gas fixation and discharges of produced water into the seabed that are able to conduct the corrosion process were suggested. In order to study the activation energies of corrosion for the API steels exposed to sediment, a low temperature dependence was taken into account using the Arrhenius equation and Rct values from impedance data. Activation energy values were Ea = 23.06, 31.7, and 43.2 J mol–1 in X52, X80, and X65 steels, respectively.

Effect of AC interference on hydrogen evolution reaction of x80 steel

PurposeThe purpose of this paper is to quantify the influence of alternating current (AC) interference on hydrogen evolution reaction of X80 steel.Design/methodology/approachThe hydrogen evolution potential was obtained by cathodic potentiodynamic polarization curve. The instantaneous potential under AC interference was obtained by high-frequency acquisition with three-electrode system. Electrochemical impedance spectroscopy and Tafel polarization curves were used to study the influence mechanism of AC interference on instantaneous potential.FindingsIt was concluded that the hydrogen evolution reaction could occur on X80 steel under AC interference. There were critical AC current densities of about 100 to 200 A/m2, beyond which the cathode reaction of X80 steel changed from oxygen absorption to hydrogen evolution. Besides the pH value, the initial polarization potential EZ and impedance module of the steel/electrolyte interface under AC interference were also the factors that affected the critical AC densities in different solutions.Originality/valueThis research quantified the hydrogen evolution capacity of X80 steel under AC interference, which could be applied to clear the effect of AC interference on hydrogen evolution reaction.

The corrosion of aluminum alloy and release of hydrogen in nuclear reactor emergency core coolant: Implications for deflagration and explosion risk

Hydrogen evolution (HE) accompanying the corrosion of aluminum alloy in the sump water formed after a loss-of-coolant accident (LOCA) influences the safety of reactor containments due to the deflagration and explosion risk of the air-hydrogen mixture. In experiments examining the corrosion of Al alloy 6061 in borated solutions simulating the water chemistry of post-LOCA sump water, HE rates were evaluated by analyzing the potentiodynamic cathodic polarization curves from rotating cylinder electrodes, and an empirical formula predicting the HE rates as a function of solution pH was proposed based on the evaluation results. At pH 7, the dominant cathodic reaction during free corrosion was found to be the oxygen reduction reaction and the HE rate was slow; however, the HE reaction became increasingly significant as the solution pH progressively increased to 11. The HE sources on the alloy surface were inferred to be mainly the bulk matrix, which was covered with a less protective hydroxide film in more alkaline solution, as well as the trenches formed by the intense anodic dissolution of the matrix around electrochemically more noble Fe-bearing intermetallic particles. Local alkalization due to preferential oxygen reduction on these intermetallic particles may also contribute to the formation of such trenches and HE; however, this mechanism should have been mostly suppressed by the buffering capacity of the borated solutions.

Sustainable Development of Corrosion Inhibitors from Electronic Scrap: Synthesis and Electrochemical Performance

Due to its high content of rare earths, the use of permanent magnets can be a sustainable alternative for the synthesis of environmentally friendly corrosion inhibitors in order to replace the use of highly toxic inhibitors, as well as the use of rare earth salts of high purity and high cost. In this study, the recovery of rare earths from permanent magnet wastes and their synthesis to chloride salts were carried out. Rare earth chlorides were evaluated as corrosion inhibitors by electrochemical techniques on API X70 steel in a 3.5% NaCl solution. Both anodic and cathodic polarization curves were made, and measurements of both open-circuit potential, linear polarization resistance, and electrochemical impedance were made. Results show that the inhibitor synthesized is a mixture of Nd and Pr chloride. Its performance as a corrosion inhibitor is superior to that of high purity Nd chloride (analytical reagent). The results show that the use of electronic scrap is a sustainable source for the synthesis of green corrosion inhibitors with low carbon footprint.

Influence Mechanism of Sulfide Ions during Manganese Electrodeposition

Influence mechanism of sulfide ions (S2-) during manganese electrodeposition from sulphate electrolyte was investigated. Under the experimental conditions, S2- ion concentration and electrolyte pH represented significant multiple effects on the cathode current efficiency. Scanning electron microscope (SEM) indicated that electrodeposition manganese layer (EML) became refinement as S2- ion concentration was increased. X-ray Diffraction (XRD) displayed that S2- ion had negligible influence on the preferred orientation of the crystalline layer of the EML. S2- ion had no influence on the chemical composition of EML. S2- ion could improve the corrosion resistance of EML. The interaction mechanism of S2- ion with manganese electrodeposition was systematically explored by analysing E-pH diagram, cyclic voltammetry curve, cathode polarization curve and electrochemical impedance method.

Cathodic Kinetics on High Resistance and Low Alloy Steels with Corrosion Inhibitors

This paper presents a study of the cathodic kinetics of high resistance and low carbon steel by the potentiodynamic cathodic polarization curves. In this study, the steel was immersed in a NACE brine with 50 ppm of corrosion inhibitor dissolved under turbulent flow conditions, room temperature and atmospheric pressure of the Veracruz Port. In order to simulate the hydrodynamic conditions, a Rotating Cylinder Electrode (RCE) with different rotation speeds was used. Electroactive species to be reduced were determined using the Eisenberg equation, as well as an analysis with dimensionless numbers was made in order to complement this study. The analysis of cathodic kinetics shown that the system under turbulent flow conditions is dominated by a mass transfer process, this is due to the diffusion of the oxygen from the bulk of the solution toward to metallic surface. According to the comparison of the experimental and the theoretical , attained by the Eisenberg equation, it can be established that the cathodic kinetics of the process is dominated by an oxygen reduction reaction.