Linear Polarization Method Research Articles

Hybrid Flow Battery/Mediator Supercapacitor Using Iron Cyanide Redox Materials

Flow batteries have very high specific energy but low specific power and slow response while mediator supercapacitors give high specific power and fast response but relatively low specific energy. A hybrid flow-battery/supercapacitor is fabricated and operated under different conditions in order to provide both high specific energy and power. The porous electrodes of the consisted of catalysts for redox reactions (Ni, Pt, Ru, etc.), mediators (NaI/I2, VOSO4, K4Fe(CN)6, etc.), and polymer electrolytes as binders. An ion exchange membrane was used as the separator. An array of complex iron cyanide compound were synthesized and used as the redox materials in slurry reservoirs. This investigation focuses on the effects of flow rate, temperature, pressure, and mediator concentration on the performance of the energy storage device. Cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) measurements were conducted under a wide range of flow rate and mediator concentration. The redox potential of the slurry was monitored using an electrochemical redox sensor. The electrochemical kinetics of the mediators and redox materials were evaluated using linear polarization methods. The results indicate that at a given scan rate for CV or current for GCD, both flow rate and mediator concentration greatly impact the charge/discharge behaviour, the total energy, and efficiency. There is a critical flow rate at which a capacitor-like behaviour transits to battery-like behaviour. A simple numerical model is created to analyse the experimental data and provide an explanation of the observations.

Development of Metallic Bipolar Plate for PEFC By Coating Carbon Thin Film on Stainless Steel

Introduction The polymer electrolyte fuel cell (PEFC) has characteristics that it can operate at a relatively low temperature and can be downsized. Therefore, development is proceeding in a wide field such as a stationary power supply and a power supply for electric vehicles. It is required to reduce the size and weight of the fuel cell as well as to lower the price. For example, it is a method to solve by changing the separator material from a conventional carbon material to a metallic material. Therefore, in this research we proposed the following method aiming at the development of simple and low cost production method. The method is to coat the surface of stainless steel with a resin thin film and then carbonize it at low temperature. We observed the surface and cross section of the obtained carbon film using high resolution SEM. We also examined its applicability as a fuel cell separator by measuring Raman spectroscopy, TG-DTA, XRD, XPS and so on. Experimental method The substrate materials used were austenitic SUS304 stainless steel with various thicknesses. Surface pretreatment of the specimen was polished with wet emery paper up to #600. Also, it was used without pretreatment. In the experiment, specimens were used which was rinsed with water after degreasing with acetone before use. The resin coating on the specimen surface was carried out by electrodeposition coating method using various cationic resins. Electrodeposition coating was carried out with varying electrolytic voltage and time at 303K. Carbonization of the resin film was performed in an electric furnace under a nitrogen atmosphere. Sintering temperature was 673K to 1173K for 2 hours. The electrical properties of the carbon-coated film were evaluated by measurement of electrical conductivity. Electrochemical properties were evaluated by measurement of polarization curve. The polarization curves were measured by linear sweep polarization method with sweep rate of 20 mV / min at room temperature in 0.5M H2SO4 solution by a three electrode system using a working(specimen) electrode, a platinum plate as a counter electrode and Hg/Hg2SO4 electrode as a reference electrode. The electric resistance of the carbon film formed on the specimen surface by the carbonization treatment was measured and evaluated by the four-terminal sensing method. Results and discussion Figure 1 shows resin coated and its converted carbon film deposited on the specimen surface and cross section SEM photographs. The thickness of resin coated film with about 40 µm was reduced about 2 µm when sintered at 873K. The carbonized film had a smooth surface and no defects were observed. As a result of the tape peeling resistance test, resistance to the adhesion between the carbonized coating film to the substrate had a sufficient ability. This result seems to be due to the formation of the third layer which improves the adhesion at the interface between the substrate metal and the formed carbon film. Figure 2 shows the relationship between the electrical conductivity of the carbon film obtained by heat-treating the resin film formed on the specimen surface of various resin materials at 773 to 1173K and sintering temperature. The electrical resistance of sintered film decreased with increasing heat treatment temperature. And it showed under 10 mΩ·cm at 1073K. In order to improve the electrical conductivity at lower temperature treatment, a coating was prepared by mixing various kinds of carbon powder with resin. As a result, even in the heat treatment at 873K, a value of 10 mΩ·cm or less was obtained. Figure 3 shows polarization curves of specimens that are raw materials and covered by carbon thin film on specimen surface. The polarization curve of the untreated specimen showed an immersion potential of about 0.0 V(vs. SHE) and a passivation current density of 20 µA/cm2. On the other hand, the immersion potential in all carbon-coated specimens was 0.5 to 0.8 V(vs. SHE) and shifted in the noble direction and the anode current became 10 µA/cm2 or less. It was revealed that sufficient corrosion resistance and electric conductivity are exhibited by giving carbon coating treatment. The power generation test was carried out for 180 hours by connecting a load resistance of 0.1 Ω with a carbon film coated separator, as the result the generated voltage was approximately constant value of about 0.7 V during the test period. Therefore, it was clarified that the prepared separator is effective as a fuel cell separator. We intend to make a detailed presentation on the relation between the electrical conductivity and the corrosion resistance. This work was carried out with the assistance of the NEDO. Figure 1

The anticorrosion properties of pigments based on molybdates and tungstates surface-modified with conducting polymers

AbstractThe objective of this work was to examine the properties of molybdate or tungstate based pigments whose surface has been coated with a conductive polymer, viz. either polyaniline phosphate (PANI) or polypyrrole phosphate (PPY), if used as pigments in organic coating materials. The anticorrosion pigments were prepared by high-temperature solid-state synthesis from the respective oxides, carbonates. The composite pigments (pigment/conductive polymer) were dispersed in a solvent-type epoxy-ester resin binder to obtain a series of paints whose anticorrosion properties were assessed by means of corrosion tests in accelerated corrosion test and by the linear polarisation method. Focus was on the anticorrosion properties of the paints depending on the pigment surface treatment, initial pigment composition, and pigment volume concentration (PVC) in the paint. The surface-treated pigment particles were expected to have a favourable effect on the anticorrosion and the mechanical properties of epoxy-ester resin based paints.

Measurement and Analysis of Exchange Current Density for U/U3+ Reaction in LiCl-KCl Eutectic Salt via Various Electrochemical Techniques

Electrochemical impedance spectroscopy (EIS), linear polarization (LP), Tafel and cyclic voltammetry (CV) were performed to investigate the exchange current density (i0) of U/U3+ reaction in LiCl-KCl eutectic salt under different UCl3 concentrations (0.5wt%–4wt%) and temperature conditions (723K–798K). The EIS spectra were measured by applying minimum overpotential from equilibrium potential and fitted to the proposed equivalent circuit. From the EIS experiments, the calculated values of i0 were varied from 0.0054Acm−2 to 0.102Acm−2. For the LP and Tafel methods, i0 values were determined from the linear fitting at small and large overpotential ranges of the current-potential curves. The measurement for i0 via CV was done analogously to the LP method. All i0 values have the linear trend with the change of concentration and temperature; however, these values measured by LP, Tafel, and CV methods are greatly influenced by the change in electrode surface area. Overall, i0 agreed within 33% relative error range with the EIS method being the most consistent and accurate in comparison to reported literature values. Dimensionless analysis was done on the EIS data sets providing insightful correlations for prediction of i0 under various experimental conditions.

Exchange Current Densities and Charge-Transfer Coefficients of Chromium and Iron Dissolution in Molten LiF-NaF-KF Eutectic

The exchange current density (i0) and charge-transfer coefficient (α) for Cr2+/Cr0 and Fe2+/Fe0 couples are studied in molten LiF-NaF-KF eutectic. These two parameters are important for understanding the metal dissolution kinetics and development of corrosion model for applications using LiF-NaF-KF eutectic as coolant or electrolyte. The values are obtained by the optimized fitting of the polarization curves, the Tafel method, and the linear polarization method. The values of i0 of Fe2+/Fe0 couple are about 1 order of magnitude larger than that of Cr2+/Cr0 couple. The exchange current density increases with temperature and obeys the Arrhenius law. The activation energy for the exchange current density is evaluated to be 91 ± 19 kJ/mol for Cr2+/Cr0, and 93 ± 6 kJ/mol for Fe2+/Fe0 in the temperature ranging from 600°C to 750°C. The charge-transfer coefficient of Cr2+/Cr0 couple slightly decreases with the temperature, while the α of Fe2+/Fe0 couple shows little temperature dependence.

Effects on corrosion resistance of rebar subjected to deep cryogenic treatment

An attempt has been made to evaluate the effect of deep cryogenic treatment on the corrosion resistance of rebar. Corrosion behavior of samples subjected to deep cryogenic treatment and samples tempered after deep cryogenic treatment was studied by linear polarization method. The Vickers hardness and ultimate tensile strength of the samples were also measured. The possible mechanism for increase in corrosion resistance has been explained based on Scanning electron micrographs (SEM) and X-Ray diffraction (XRD) study. The morphology of the corroded surfaces of the samples was studied using Atomic force microscopy (AFM). It was found that there is 69 % improvement in corrosion resistance because of deep cryogenic treatment, further it was seen that the increase in corrosion resistance was due to the contribution of increased pearlite phase. Deep cryogenic treatment had no adverse effect on ultimate tensile strength and hardness, which are crucial properties to be considered for rebar.

Experimental Study of the Interaction of Solanum Tuberosum Fluid as Additive in Electrodeposition Bath in the Presence of Zn-Tio2 on Mild Steel

Enhancing mild steel properties is necessary to meet global competiveness and performance during application. In this study, we report the effect of Solanum tuberosum as additive to Zn-TiO2 sulphate bath coating by electrodeposition method on low carbon steel. The interfacial and structural characteristics of the produced coating were examined by means of scanning electron microscopy equipped with energy dispersive spectroscopy (SEM/EDS). The corrosion resistance properties of the deposited coatings were assessed in 3.65% NaCl using linear polarization method and characterized by optical microscope (OPM). Diamond based microhardness tester was used to measure hardness of the composites. From the results, it is evident that Zn-TiO2-solanum coating resulted in improved performance as compared to Zn-TiO2 coating; both in hardness properties and corrosion resistance properties propagation as a result of its embedded structural build up.

Corrosion Susceptibility of a 0.35%C Steel in Seawater Electrolyte Using the Electrochemical Method

The Tafel extrapolation and linear polarization methods were used as effective measures for determining the corrosion susceptibility of a spheroidized 0.35%C steel with sea water as the electrolyte. Eight pieces of steel were machined to length 5mm by 10mm in diameter. Two pieces each were heat treated at 600°C, 700°C and 800°C respectively and two pieces left as control. Electro-chemical experiments were carried out to obtain the best potential and anodic current of samples immersed in an electrolyte (seawater) at varying anodic potential of-0.7mv, -0.6mv, -0.5mv and-0.4mv respectively. The results showed that the sample with the least corrosion rate were the samples spheroidized at 700°C. They appeared to have the highest electrode potential value of-0.6mv and 800°C spheroidized samples had the least electrode potential value of-0.65mv at the end of 2000seconds respectively. From the results obtained, the samples spheroidized at 700°C appeared to be most suitable for seawater environment.

Dye-surfactant aggregates as corrosion inhibitor for mild steel in NaCl medium: Experimental and theoretical studies

Abstract The corrosion inhibition efficiency of tetradecyltrimethylammonium bromide (TTAB) in presence of Sunset Yellow (SY) was investigated in NaCl corrosive medium using Tafel linear polarization method, electrochemical impedance spectroscopy (EIS), gravimetric measurement, and Density functional theory (DFT) calculations. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and UV–visible spectroscopy techniques were also employed to study the morphology of corrected surface and the nature of adsorbed layer. It was revealed that TTAB micelles exhibit low corrosion inhibition efficiency at high concentration for mild steel in NaCl, while the inhibition efficiency was drastically increased in TTAB-SY mixed system, reaching higher than 90% in the presence of 100 uM TTAB- SY(1:1). Different corrosion mechanisms were proposed in the presence and absence of dye. A noticeable Warburg resistance was observed in the absence of dye while no Warburg was seen in the presence of dye indicating that the mechanism is mainly changed. Also, the results indicated that TTAB-SY ion pairs act as mixed-type inhibitors. Finally, from the optimized geometry of TTAB, SY, and TTAB-SY complexes and also electron distribution in HOMO and LUMO, possible modes of interaction of TTAB-SY complexes with mild steel surface have been predicted.

Theoretical and experimental studies on the corrosion inhibition potentials of 3-nitrobenzoic acid for mild steel in 0.1 M H2SO4

AbstractThe inhibition of the corrosion of mild steel in 0.1 M H2SO4 by 3-nitrobenzoic acid was studied using weight loss, electrochemical impedance spectroscopy (EIS), linear polarization resistant, potentiodynamic polarization, scanning electron microscopy, Fourier transformed infra-red spectroscopy and quantum chemical techniques. The results obtained indicated that 3-nitrobenzoic acid inhibited the corrosion of mild steel in solution of H2SO4. Maximum inhibition efficiency obtained from weight loss, potentiodynamic, linear polarization and EIS methods were 87.15, 90.51, 95.42 and 99.40% at inhibitor’s concentration of 0.01 M respectfully. The activation energies (which ranged from 26.02 to 59.02 J/mol) supported the mechanism of charge transfer from charged inhibitor to charged metal surface, which favours the mechanism of physical adsorption. The adsorption of the inhibitor was found to be exothermic and spontaneous. Although the adsorption characteristics of the inhibitor fitted the Langmuir adsorpt...

Comparison of Electrochemical Methods for the Evaluation of Cast AZ91 Magnesium Alloy.

Linear polarization is a potentiodynamic method used for electrochemical characterization of materials. Obtained values of corrosion potential and corrosion current density offer information about material behavior in corrosion environments from the thermodynamic and kinetic points of view, respectively. The present study offers a comparison of applications of the linear polarization method (from −100 mV to +200 mV vs. EOCP), the cathodic polarization of the specimen (−100 mV vs. EOCP), and the anodic polarization of the specimen (+100 mV vs. EOCP), and a discussion of the differences in the obtained values of the electrochemical characteristics of cast AZ91 magnesium alloy. The corrosion current density obtained by cathodic polarization was similar to the corrosion current density obtained by linear polarization, while a lower value was obtained by anodic polarization. Signs of corrosion attack were observed only in the case of linear polarization including cathodic and anodic polarization of the specimen.

Corrosion behaviour of single and double layer hydroxyapatite coatings on 316L stainless steel by plasma spray

AISI316L stainless steel is extensively used in orthopedic and dental applications. However, this alloy exhibits low integration behaviour when it comes in contact with surrounding bone tissue and implant healing duration can be as much as few months. The aim of this study is the fabrication of biocompatible hydroxyapatite (HA) coatings on stainless steel substrate in order to accelerate the process of osseointegration of implants. The biocompatible single layer of Titania (TiO2), Hydroxyapatite and bi-layer TiO2/HA coatings were deposited by atmospheric plasma spray on 316L stainless steel. Coated and uncoated stainless steel specimens were incubated in simulated body fluids and 0.9% NaCl solutions for 1h and 7 days. In vitro electrochemical-corrosion evaluation of coated and uncoated stainless steel specimens have been investigated by Tafel extrapolation and linear polarization methods. Results indicates that corrosion resistance of single layer HA coated stainless steel specimens are superior to single layer TiO2 and bi-layer HA/TiO2 coated stainless steel specimens.

EXTRACT OF COMBRETUM MICRANTHUM AS CORROSION INHIBITOR FOR AL – SI – MG ALLOY IN SIMULATED SEA WATER ENVIRONMENT

The leaf extract of Combretum micranthum (CM) was tested as green corrosion inhibitor for Al-Si-Mg alloy in 3.5wt% NaCl solution using gravimetric and linear polarization methods at 30 0 C, 50 0 C and 70 0 C, from 1, 2, 3, 4, 5 hours of exposure time with concentration of the extract 0, 0.2, 0.4, 0.6, 0.8 and 1.0 v/v respectively. The result obtained indicate that the leaf extract of CM is a good corrosion inhibitor in the simulated sea water medium. The inhibition efficiency of the extract increased with an increase in concentration of the CM extract and decreased with increase in temperature. On the other hand, inhibition efficiency (IE%) synergistically decreased on addition of surfactant (Monoethylamine). The adsorption of the inhibitor on Al-Si-Mg surface is exothermic, Spontaneous and is best described by Langmuir, Freundlick and El-Awady adsorption models. The calculated values of activation energy, enthalpy of activation entropy of activation, free energy of process is by physical adsorption. Equally, methanol extract CM is a good adsorption inhibitor for the corrosion of Al-Si-Mg in 3.5wt% NaCl solution. Tafel polarization analysis indicates that the studied plant extract is a mixed type inhibitor. http://dx.doi.org/10.4314/njt.v35i4.25

Studies on the Inhibitive Properties of Boscia senegalensis in Aluminium-HCl environment

The extracts of Boscia senegalensis was study as corrosion inhibitors for Aluminium in 1M HCl environment using gravimetric and linear polarization methods. The result shows that the extract inhibits the corrosion of aluminium by elongating the latency periods of the metal beyond in the absence of the inhibitor. The results from gravimetric measurements illustrate increase in inhibition efficiency with increment in extract concentration. Linear polarization plots show that the mode of inhibition was mixed type. The observed decrease in corrosion rate was due to adsorption of the extracts on the surface of the metal which obey the Langmuir adsorption isotherm. Adsorption of the extract depends on its chemical composition which showed the presence of various phytochemicals like flavonoids, steroids, tannins and phenolic compounds etc. which has oxygen atoms with lone pair electrons for co-ordinate bonding with metal.

Novel electrical resistance method to measure underdeposit corrosion and its inhibition in pipeline steels

In this work, the evaluation of under deposit corrosion (UDC) behaviour of X65 pipeline steel and its inhibition in oxygen corrosion conditions were studied. In the fundamental experimental study, a three-electrode electrochemical system was used to measure the corrosion rates and polarisation curves by linear polarisation resistance and potentiodynamic polarisation methods. The galvanic effect caused by the deposit was also studied by the zero resistance ammeter technique. An 8 in X65 pipeline internal corrosion monitoring system based on the ring pair electrical resistance sensor (RPERS) was established for further research of UDC. The underdeposit corrosion rate and its inhibitory effect in the pipeline were also monitored by RPERS. Electrochemical test results showed that the corrosion inhibitor amino trimethylenephosphonic acid (ATMP) would result an accelerate corrosion for UDC. A nearly 1.7 times increase was found on the galvanic current when ATMP was introduced into the solution. The inhibitor imidazoline had a good performance on UDC for both corrosion inhibiting and the reduction of the galvanic current. Through the monitoring results of RPERS, the UDC status in the pipeline and the effect of the inhibitors were studied. The monitoring results have a consistency with the fundamental experiment.

Corrosion Behavior of New Dental Co-Cr-Nb-Mo-Zr Alloy

This paper presents a complete and complex characterization of the new Co-Cr-Nb-Mo-Zr alloy in comparison with the commercial CoCrMo (Heraenium CE) alloy. The alloy microstructure was showed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS); the composition and thickness of the native passive film were identified by X-ray photoelectron spectroscopy (XPS). Also, the surface roughness was revealed by atomic force microscopy (AFM) and the contact angle evinced the alloys hydrophilic properties. The amounts of ions released in artificial Carter-Brugirard saliva were evaluated by the inductively coupled plasma-mass spectroscopy (ICP-MS) technique. The corrosion rate was obtained by the linear polarization method. The cast new Co-Cr-Nb-Mo-Zr alloy is characterized by a multicomponent, fine dendritic structure with typical interdendritic distances of few microns. EDS spectra detected the alloying elements, Co, Cr, Nb, Mo, Mn, Si, etc. EDS elemental analysis quantified that Mo, Nb, Si and C are enriched in the interdendritic regions. XPS survey spectrum for the new Co-Cr-Nb-Mo-Zr alloy surface showed a complex feature that included the peaks for Co 2p, Cr 2p, Nb 3d, Mo 3d, Zr 3d, o 1s; this film is composed from chromium, niobium, molybdenum, zirconium, manganese, silicon oxides and is thicker (6.5 nm – 8.0 nm), more compact and enhanced with oxides as compared with that of commercial Co-Cr-Mo alloy. The topography and roughness parameters (AFM data) are similar for the two studied alloys and very proper for the cell adhesion. An increase in the contact angle value for the new Co-Cr-Nb-Mo-Zr alloy has been observed as compared to the commercial Heraenium CE alloy. The increase from 75.920 to 86.790 values indicates that the both alloys have hydrophilic character but the stronger one is for the commercial alloy. The quantity of ions (determined by ICP-MS method) released in artificial saliva for the both alloys is relatively small, but for the new alloy, the amount is significant lower. The quantified amounts in ppb (parts-per-billion, 10−9) sustain increased stability for the new alloy. The evolution of open circuit potentials in time for the both alloys depicts a trend to steady state sooner after immersion in the both cases; it is a specific aspect for passivity due to the protective oxides formed on the surface of the both alloys. The open circuit potentials tend to more electropositive values, indicating an increase of passive film thickness. The Tafel results showed that the new alloy is included in conventional stability scale „Perfect Stable” while the commercial alloy in “Very Stable” in the corrosion resistance group (corrosion classification). With the increase of immersion time, the penetration index, corrosion rate decreased. Also, the polarization resistance, Rp values for the new alloy increased in time as result of the passive film thickening; for the commercial alloy, polarization resistance decreased in time, denoting some dissolution and repassivation processes. Rp have higher values from about 8 times to 175 times than those of Heraenium CE alloy; correlating with the lower values of the corrosion current densities, it results a better corrosion resistance, a more resistant passive film for the new alloy due to its passive film that contains beside chromium oxide, niobium (Nb2O5, 49.8%) and zirconium oxides (ZrO2, 54.9%), as was showed by XPS analysis. In conclusion, the new Co-Cr-Nb-Mo-Zr alloy displayed an increased corrosion resistance as compared with the commercial Heraenium CE alloy.

Electrochemical behavior of mesh and plate oxide coated anodes during zinc electrowinning

The catalytic performance of two oxides coated anodes (OCSs) meshes and one OCA plate was investigated in a zinc electrowinning electrolyte at 38 °C. Their electrochemical behaviors were compared with that of a conventional Pb–0.7%Ag alloy anode. Electrochemical measurements such as cyclic voltammetric, galvanostatic, potentiodynamic, open-circuit potential (OCP) and in situ electrochemical noise measurements were considered. After 2 h of OCP test, the linear polarization shows that the corrosion current density of the Ti/(IrO2–Ta2O5) mesh electrode is the lowest (3.37 μA/cm2) among the three OCAs and shows excellent performance. Additionally, after 24 h of galvanostatic polarization at 50 mA/cm2 and 38 °C, the Ti/MnO2 mesh anode has the highest potential (1.799 V), followed by the Ti/(IrO2–Ta2O5) plate (1.775 V) and Ti/(IrO2–Ta2O5) mesh (1.705 V) anodes. After 24 h of galvanostatic polarization followed by 16 h of decay, the linear polarization method confirms the sequence obtained after 2 h of OCP test, and the Ti/(IrO2–Ta2O5) mesh attains the lowest corrosion current density. The Ti/(IrO2–Ta2O5) mesh anode also shows better performance after 24 h of galvanostatic polarization with the overpotential lower than that of the conventional Pb–Ag anode by about 245 mV.

Corrosion rate determination of austenic steels in calcium hypochlorite solutions

This paper presents the results of testing the corrosion resistance of austenitic chromium-nickel steel X6 CrNiTi 18-10 and X6 CrNiNb 18-10 in solutions of calcium hypochlorite. For the tests were used potentiodynamic measurement methods. By graphical method of linear polarization, corrosion currents and corrosion potential were obtained on the intersection of the Tafel real E = f(log i) on the basis of potentiodynamic curves for the examined steels. The comparative method to determine the corrosion current density is the polarization resistance method. Based on corrosion currents were calculated corrosion rate of tested steel. Anodic polarization curves for both austenitic steel in the investigated solutions were shot in the interval of stationary potential of up to + 2.5V, to determine the areas of activity. Test results show that with increasing of calcium hypochlorite solution concentration, increase the pH of the solution and the concentration of active chlorine which causes a reduction in the corrosion resistance of the tested steel. These steels are resistant to corrosion in a 1% solution, stable in 10% solutions, and less resistant in 50% suspensions of calcium hypochlorite.

Microstructural, mechanical and anticorrosion characterisation of new CoCrNbMoZr alloy

In this paper, the microstructure, mechanical and anticorrosive properties of the new CoCrNbMoZr alloy were studied in comparison with those of the commercial CoCrMo, Heraenium CE alloy. SEM and XRD techniques were used to evince the microstructure, and the morphology of the two alloys. Electrochemical linear and potentiodynamic polarisation and electrochemical impedance spectroscopy methods showed the electrochemical and corrosion behaviour of the alloys in artificial Carter‐Brugirard saliva of different composition (doped with NaF, pH = 8.21 and undoped) and pH values (3.83; 7.84; 9.11) simulating the various functional conditions from the oral cavity. The new CoCrNbMoZr alloy showed self‐passivation, more favourable values of the corrosion, passivation and transpassive potentials and tendency to passivation than those of the commercial Heraenium CE alloy and lower values of the passive current density; the values of the corrosion current densities and corrosion rates are lower and polarisation resistances are higher comparing with those of the reference alloy. EIS spectra revealed a passive film, a compact, resistant layer formed especially by the chromium, cobalt, niobium and zirconium oxides. Taking into consideration the microstructural features, electrochemical behaviour, corrosion resistance, and mechanical characteristics, it results that the new CoCrNbMoZr alloy is recommended for the dental applications.

Electrochemical corrosion behavior of Ni-containing hypoeutectic Al-Si alloy

Electrochemical corrosion characteristics of the thermally treated 2 wt % Ni-containing Al-6Si-0.5Mg alloy were studied in NaCl solutions. The corrosion behavior of thermally treated (T6) Al-6Si-0.5Mg (-2Ni) alloys in 0.1 M NaCl solution was investigated by electrochemical potentiodynamic polarization technique consisting of linear polarization method using the fit of Tafel plot and electrochemical impedance spectroscopy (EIS) techniques. Generally, linear polarization experiments revealed a decrease of the corrosion rate at thermal treated Al-6Si-0.5Mg-2Ni alloy. The EIS test results showed that there is no significant change in charge transfer resistance (R ct ) after addition of Ni to Al-6Si-0.5Mg alloy. The magnitude of the positive shift in the open circuit potential (OCP), corrosion potential (E corr ) and pitting corrosion potential (E pit ) increased with the addition of Ni to Al-6Si-0.5Mg alloy. The forms of corrosion in the studied Al-6Si-0.5Mg alloy (except Al-6Si-0.5Mg-2Ni alloy) are pitting corrosion as obtained from the scanning electron microscopy (SEM) study.