Cathodic Polarization Curves Research Articles

Evaluation of Effect of Welding Methods to Corrosion and Hardness Characteristics of Welded Zone

Recently a fuel oil of the diesel engine in the merchant ship has been changed with heavy oil of low quality as the oil price is getting higher and higher .Therefore, the wear and corrosion against all parts of the engine are significantly increased with using of heavy oil of low quality. In particular, the degree of wear and corrosion in between spindle and seat ring of exhaust valve are more serious compared to the other parts of the engine due to severe environment such as the high temperature of exhaust gas and repeating impact. Thus, repair welding is a unique method to prolong their lifetime in an economical point of view. In this study, an effect of welding methods to corrosion and mechanical properties of both weld and base metal zone was investigated with some electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram and AC impedance etc. in. The hardness of the weld metal zones exhibited comparatively higher values than that of the base metal zone. And their corrosion resistances were also increased compared to the base metal. The weld metal zone of P1F( plasma welding with 1 pass) showed a relatively good corrosion resistance as well as the hardness compared to the other welding methods. Consequently, it is considered that plasma welding method is a desirable method compared to other welding methods for both better corrosion and hardness properties.

Effect of Relative Humidity on the Initial Atmospheric Corrosion Behavior of Zinc during Drying

The effects of relative humidity on the initial atmospheric corrosion of zinc during drying of chloride-contained absorbed thin electrolyte layer was investigated by mass loss, scanning electron microscopy (SEM), cathodic polarization curves, pre-Tafel polarization curves fitting method and electrochemical impedance spectroscopy (EIS). The results showed that the zinc corrosion rate decreased with increasing relative humidity in the first 2 h. After 72 h of exposure, the corrosion rates of zinc were ranked as: 75% RH < 85% RH < 97% RH. And the morphology of corrosion products at 75% RH appeared more compact than that of 85% and 97% RH.

Environmentally friendly chromium electrodeposition: effect of pre-electrolysis on a Cr(iii) bath in an anion-exchange membrane reactor

In order to tackle the problem of high energy consumption and toxic substances produced in Cr(III) electrodeposition, a pre-electrolysis method was proposed, and its effects on the current efficiency and stability of the cathodic electrolyte were studied. The results show that pre-electrolysis had a remarkable influence on the pH of the Cr(III) bath. Pre-electrolysis can accelerate the hydrolysis of [Cr(H2O)6]3+, and this can be considered to provide sufficient electrochemically active Cr(III) complexes for electrowinning. Different pretreatment methods influence the cathodic polarization. Without pre-electrolysis, the cathodic polarization curve has one plateau, corresponding to the evolution of hydrogen. After pre-electrolysis, three plateaus in the polarization curve were found, corresponding to the evolution of hydrogen, the reduction of [Cr(H2O)nLm]3−m to [Cr(H2O)nLm]2−m, and the electrodeposition of chromium from [Cr(H2O)nLm]2−m. Moreover, the cathodic potential shifts towards a negative value with the increase of pH. The secondary adjustment of pH after pre-electrolysis has a significant influence on the current efficiency of Cr(III) electrolysis. When the pH is less than 1.3, no chromium is produced; when the pH is 1.6, the current efficiency reaches the highest value of 75.4%. With the extension of electrolysis time, the average current efficiency decreases. However, the average current efficiency is still able to reach more than 50% in an 8 h test, which should be attributed to the effects of pre-electrolysis. For the separation characteristics of an ion-exchange membrane reactor, the problems of toxicant produced on both of the electrodes were solved.

Preliminary studies on the electrochemical recovery of Zn and Cd from effluent produced by a zinc refinery plant using a filterpress reactor

BACKGROUND Fundamental studies are reported investigating the electrochemical deposition of cadmium and zinc contained in solutions from a zinc electro-refining plant. This work also analyzes the performance of a filterpress electrochemical reactor used in the recovery of zinc and cadmium from this effluent. RESULTS The cathodic polarization curves showed electrochemical processes with mixed control for 304 SS and Al. The cyclic voltammetry studies on stainless steel revealed the presence of metal deposits at low current densities, whereas Zn and Cd were preferentially deposited at high overpotentials. The greatest recovery of cadmium (19%) and zinc (24%) at jap = 4 mA cm-2 was obtained with a 304 SS cathode and t = 180 min. The SEM micrographs of cathode plates confirmed the presence of cadmium and zinc deposits. In addition, EDS analyses revealed that the composition of such deposits depends on the deposition time and the cathode material. CONCLUSION A continuous filterpress electrochemical reactor with 304 SS and Al cathodes exhibited a promising performance level for cadmium and zinc recovery from industrial solutions.

Corrosion mechanisms in aqueous solutions containing dissolved H2S. Part 1: Characterisation of H2S reduction on a 316L rotating disc electrode

This paper compares the cathodic reactions occurring on steel in aqueous solution containing dissolved H2S or CO2. In aqueous solutions containing these weak acids, the rate of the cathodic reaction is enhanced in comparison with strong acid solutions at the same pH. In the case of dissolved CO2, this phenomenon is fully explained by a buffer effect, contributing to the transport of proton at the steel surface. In the case of H2S containing solutions, this chemical mechanism is no more sufficient to explain the cathodic polarization curves. An additional electrochemical reaction is clearly observed, with strong links with H2S concentration.

Soft magnetic properties of Ni–Cr and Co–Cr alloy thin films electrodeposited from aqueous solutions containing trivalent chromium ions and glycine

Ferromagnetic Ni–Cr and Co–Cr alloy thin films were electrodeposited from aqueous solution containing trivalent chromium (Cr3+) ions and glycine. According to the Tafel slopes obtained from the cathode polarization curves for Ni–Cr and Co–Cr alloy deposition, it was estimated that Cr3+ ions inhibited Ni2+ and Co2+ ions from electrodepositing. Ni and Co preferentially electrodeposited rather than Cr and the electrodeposition process of Ni–Cr and Co–Cr was categorized to “normal co-deposition type.” At the cathode potential of −1.8 V versus Ag/AgCl/KCl sat., Ni—9.5 %Cr and Co—8.4 %Cr alloy deposits were obtained. X-ray diffraction patterns of the electrodeposits revealed that pure Ni and pure Co consist of large crystal grains, while Ni—9.5 %Cr and Co—8.4 %Cr alloys were composed of a solid solution phase with fine crystal grains. Magnetization of Ni—9.5 %Cr and Co—8.4 %Cr alloy thin films with fine crystalline phase reached to saturation at ca. 2.5 kOe in perpendicular direction to the film plane, while pure Ni and pure Co thin film with large crystal grains were hardly magnetized in the perpendicular direction. Soft magnetic properties were improved with increasing Cr content in the deposits.

Local degradation analysis of a real long-term operated DMFC stack MEA

Understanding degradation of the membrane–electrode assembly (MEA) of direct methanol fuel cells (DMFC) is important technically and scientifically for the advancement of this technology. In this work, we carry out a spatially resolved investigation of the degradation of an MEA, which has been degraded through its operation lifetime. The MEA has an active area of 320cm2 and has been used in operation of a DMFC stack for more than 3000h to power a lift truck. The analysis of degradation with respect to the local position of the flow field pattern was carried out by cutting the MEA into small pieces that are characterized in a 1cm2 sized test cell with a reference electrode setup. The characterization techniques involved measurement of anode and cathode polarization curves, electrode potential relaxation curves after current interruption, MeOH-stripping voltammograms, cyclic voltammetry and SEM/EDX analysis. The MEA pieces were prepared by Laser ablation technique to realize the reference electrodes. The analysis yielded an independence of performance from the local position of the MEAs within the stack in terms of the anode and cathode flow fields.

Study of Initial Corrosion Behaviors of Pure Copper under Simulated Marine Atmosphere

The corrosion behaviors of pure copper were studied in initial exposure to a simulated marine atmosphere. A two-electrode cell system with two identical pure copper plates had been employed in electrochemical tests of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The copper electrodes were deposited with 70 µg cm-2 NaCl particles and then exposed in a humidified pure air of 97% RH at 25 °C. The time-evolution of corrosion current density obtained from the cathodic polarization curves had a trend of firstly decreasing, then increasing and finally getting a relative stable stage. The EIS data showed that the transition of two time constants corrosion stage to three time constants corrosion stage. The initial atmospheric corrosion behaviors of pure copper could be divided into three stages, including rapid corrosion stage, diminished corrosion stage and balanced corrosion stage.

Plug-In Specimens for Measurement of the Corrosion Rate of Mg Alloys

Magnesium alloy corrosion is often nonlinear. The corrosion rate accelerates to steady state after an initial period of low corrosion. Plug-in specimens permit simultaneous measurement of the corrosion rate using hydrogen evolution, PH, and Tafel extrapolation of cathodic polarization curves, Pi. Moreover, weight loss allows independent verification. PH is consistently greater than Pi. The data, for short exposure periods up to 10 days, are consistent with the unipositive Mg+ ion being a short-lived intermediate. Tafel extrapolation needs to be used with caution for estimation of Mg corrosion, as the measured corrosion rate can have a significant contribution from crevice corrosion. Furthermore, measurements made at short immersion times may not reflect the steady-state corrosion rate, and the corrosion reaction at the Mg surface may be decoupled from the electrochemical measurement.

Cathodic polarization curves of the oxygen reduction reaction on various structural materials of boiling water reactors in high temperature–high purity water

Cathodic polarization curves of the O2 reduction reaction were measured by using electrodes made from typical structural materials of boiling water reactors (BWRs) to evaluate the effects of kind of material on the electrochemical corrosion potential (ECP) calculation. To estimate ECPs at any region in the BWRs on the basis of the BWR environmental conditions, anodic and cathodic polarization curves should be obtained in advance under relevant conditions. The concentration of oxidants such as O2 and H2O2 in coolant changes depending on the region in which they exist. As well, reduction reaction rates might differ depending on the kind of materials. In this work, the cathodic polarization curves of type 316L stainless steel (316L SS) and Alloy 182 were measured in high purity water at 553 K with different O2 concentrations and compared with those of type 304 SS (304 SS). The results showed that the cathodic polarization curves differed depending on the kind of materials at the activation-controlled region. But, the difference in the ECP vs. O2 concentration relationship was small when the ECPs were calculated by using both anodic and cathodic polarization curves measured on the objective material.

In-situ investigation of atmospheric corrosion behavior of bronze under thin electrolyte layers using electrochemical technique

The atmospheric corrosion behavior of bronze under thin electrolyte layer (TEL) with different thicknesses was monitored using cathodic polarization curves, open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). Cathodic polarization result indicates that the cathodic limiting current density increases with decreasing the TEL thickness. EIS result shows that the corrosion rate increases with decreasing the TEL thickness at the initial stage because the corrosion is dominated by the cathodic process, whereas after long immersion time, the corrosion degree with the TEL thickness is in the sequence of 150 μm > 310 μm >100 μm ≈ bulk solution > 57 μm. The measurements of OCP and EIS present in-situ electrochemical corrosion information and their results are in good agreement with that of physical characterizations.

Corrosion behaviour of a nominally high purity Mg ingot produced by permanent mould direct chill casting

The corrosion behaviour was characterized using hydrogen evolution, weight loss, electrochemical impedance spectroscopy (EIS) and cathodic polarization curves, in 3.5% NaCl saturated with Mg(OH)2, with tests lasting up to 14days, and compared with the corrosion behaviour of the HP Mg used in our prior research at UQ. The corrosion behaviour was consistent with the uni-positive Mg+ ion Mg corrosion mechanism, particularly the fact that the corrosion rate measured using electrochemical techniques was consistently lower than that measured independently by weight loss or hydrogen evolution, as predicted by the uni-positive Mg+ ion Mg corrosion mechanism.

Mechanism of Zinc Phosphating Solution at Low Temperature

In our studied phosphating system, the morphology, chemical composition, phase and corrosion resistance of the phosphate film were characterized by EDS, AES, XRD and cathodic polarization curves. Test results indicated that the phosphate coating was made of the two kinds of Zn3(PO4)2•4H2O and Fe2Zn(PO4)2•4H2O crystals composed. On this basis, we came up the film-forming mechanism of low temperature phosphating technology.

Electrochemical Study of the Additive-Effect on Sn Electrodeposition in a Methansulfonate Acid Electrolyte

The effect of three organic additives in stannous methanesulfonate baths on cathodic overpotential and Faradaic impedance of tin-electrodeposition were studied by measuring cathodic polarization curves, galvanostatic responses and electrochemical impedance spectroscopy. The results show that the composite additive consisting of three organic compounds can significantly increase the cathodic polarization, crystallization overpotential and charge transfer resistance, which is very beneficial to improve coating quality and result in a fine-grained and smooth matt tin coating.

Electrodeposition of iron‐enriched nanocrystalline Fe‐Ni alloy foil from chloride‐sulfate solutions

PurposeThe purpose of this paper is to obtain iron‐enriched Fe‐Ni alloy foil on Ti substrates with good quality from a chloride‐sulfate bath used in a normal DC plating mode. The effects of iron content on the hardness, surface morphology and microstructure of the foil were clarified.Design/methodology/approachFe‐Ni alloy foil was prepared by electrodeposition in a chloride‐sulfate based solution. The effects of current density, temperature, stirring rate and sodium propargyl sulfonate concentration on the iron contents of the Fe‐Ni alloy foils were studied. The phase composition and surface morphology with various iron contents were characterized by X‐ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Cathodic polarization curves were used to evaluate the role of sodium propargyl sulfonate (PS).FindingsNanocrystalline Fe‐Ni alloy foil containing up to 64 wt. percent iron can be obtained from a chloride‐sulfate based solution. The foil converts from a face‐centered cubic (fcc) Fe3Ni2 phase to a mixture of fcc and body‐centered cubic (bcc) Fe7Ni3 with increase in iron content from 55.0 wt. percent to 63.5 wt. percent. AFM studies revealed that the foil had a fine grain structure with a roughness of 30 nm and grain size of 30 nm. With iron increasing to 63.5 wt. percent some islands appeared on the surface. This structure was related to the development of a (200) fiber texture in the BCC phase. Sodium propargyl sulfonate accelerates the discharge of nickel and inhibits the discharge of Fe.Practical implicationsThe foil has many industrial applications in the area of memory devices for computers, laser components and precise instruments.Originality/valueThe paper presents a process to produce a foil with iron up to 64 wt. percent from a chloride‐sulfate based solution used in normal DC mode. The dependence of microstructure and surface morphology on iron contents also is presented. Until now, there has been little research or reports on this subject.

Plasma Immersion Ion Implantation for the Prevention of Metal Ion Release From CoCrMo Alloys

Surface modifications of biomaterials by plasma immersion ion implantation (PI3) are innovative methods to improve the biocompatibility of these materials. In this paper, the modification of the ion-releasing behavior of a LC forged ASTM F-799 CoCrMo alloy after implantation with N and O in a plasma immersion ion implantation process is described. Corrosion behavior in bovine serum was measured by open circuit potential and cathodic potentiodynamic polarization curves. After corrosion tests, metal ion release was estimated comparing GDOES analysis results in treated samples before and after corrosion tests. They showed a good relation between both studies. Better results in corrosion tests indicate important reduction in Co and Cr ions release rates. Conclusions about corrosion improvement of CoCrMo alloys after N or O implantation are presented.

Effect of cyclic hydrostatic pressure on the sacrificial anode cathodic protection

PurposeThe purpose of this paper is to study the effect of cyclic hydrostatic pressure on the protective performance of cathodic protection (CP) system consisting of Zn‐Bi sacrificial anode and Ni‐Cr‐Mo‐V steel.Design/methodology/approachThe anode and cathode polarization curves of the driving potential and current for CP were investigated in case of cyclic hydrostatic pressure (0‐3.5 MPa) and compared with that at atmospheric pressure. The morphologies of the anode material with and without corrosion products were observed by scanning electron microscopy.FindingsThe experimental results revealed that the cyclic hydrostatic pressure had significant influence on the CP system. The anode potential instantaneously responded to the cyclic hydrostatic pressure and the discharge performance decreased due to the deposition of corrosion product. Also, the CP system exhibited higher slope parameter under cyclic hydrostatic pressure, indicating that the CP system cannot provide adequate protection for Ni‐Cr‐Mo‐V steel.Originality/valueThe results presented in this paper clearly show the effect of cyclic hydrostatic pressure on the sacrificial anode CP system, and present a foundation for further research on the practical application of sacrificial anode under cyclic hydrostatic pressure environment.

Effects of Temperature on Corrosion Behavior of X70 Steel in Halons

The corrosion behavior of X70 pipeline steel in 0.5% NaC1 solution in different temperature of 25°C、35°C and 55°C was studied by dynamic potential polarization curve and electrochemical impedance spectroscopy（EIS）method. The corrosion topography of X70 pipeline steel in normal temperature and 30°C was also compared in immersion corrosion test after 25 days. The results show that when the temperature rises, the corrosion current density Icorr increases, the linear polarization resistance reduces, cathode polarization curve right shift, caused corrosion rate increases which primarily by the increasing the transmission of reactant in the cathode reaction. Pitting corrosion developed after 25 days immersion corrosion in 30°C solution which proved the promoter action of temperature to pit corrosion, and which is agreed with the electrochemical corrosion test results.

Protective mechanisms occurring on zinc coated steel cut-edges in immersion conditions

Electrochemical processes occurring on the cut-edge of a galvanized steel immersed in NaCl solutions were studied using numerical simulations, and in situ current and pH profiles measured over the cut-edge. These results clearly demonstrate that only the steel surface remote from the zinc coating is cathodically active, oxygen reduction being strongly inhibited in the vicinity of zinc. This trend was confirmed by local polarization curves recorded on these distinct areas. Ex-situ AES and SEM analysis and cathodic polarization curves in solutions containing Zn 2+ ions led to conclude that this cathodic inhibition was related to the fast nucleation of a dense Zn(OH) 2 film on the steel surface. After a long term exposure, a new galvanic coupling takes place between the Zn(OH) 2 covered area, showing an anodic activity, and the remaining steel surface covered by bulky white zinc corrosion products.

Electrocatalytic evolution of hydrogen on the NiCu/Al2O3/nano-carbon network composite electrode

We present a way to fabricate the NiCu/Al2O3/nano-carbon network (NCN) composite electrode by coelectrodepositing NiCu particles, using a novel conductive alumina/NCN composite material as the support. The morphology, crystalline phases, and compositions are characterized by field-emission scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffraction, and Raman spectroscopy. The electrocatalytic behaviors of this NiCu/Al2O3/NCN composite material for hydrogen evolution reaction (HER) in alkaline solution are studied by cathodic polarization curves, electrochemical impedance spectroscopy (EIS), and chronoamperometry. The results show that nickel–copper particles are briefly deposited and uniformly distributed over the carbon layer of the conductive ceramics between alumina grains, in the form of a NiCu solid solution with face-centered cubic structure. The NiCu/Al2O3/NCN composite displays a high electrochemical stability in alkaline solution and relatively high electrocatalytic activity for HER due to its relatively high real surface area and high intrinsic electrocatalytic effect of NiCu alloy particles. The associated kinetic parameters of HER are systematically investigated using EIS.