جستجوی مقالات مرتبط با کلیدواژه « طیف سنجی امپدانس الکتروشیمیایی » در نشریات گروه « مواد و متالورژی »

The scanning Kelvin probe (SKP) is a non-destructive and non-contact method for surface inspection, which is widely used in evaluating the performance of corrosion inhibitors, investigating the mechanism of inhibition, determining the optimal concentration, and evaluating the effectiveness of inhibitors in different environments. This method provides information about the electrochemical behavior of the surface based on the measurement of the contact potential difference (CPD) between the sample surface and the reference electrode. A more comprehensive understanding of the corrosion process can be achieved by using the SKP method and comparing its results with electrochemical measurements such as electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP). In this research, the inhibition behavior of quaternary ammonium salts (QAS) against the corrosion of X65 carbon steel in the sour environment (H2S) at 60 °C was investigated using EIS and PDP tests, then the results were confirmed with the scanning Kelvin probe.

The effects of 0.7-3 ppm thiourea on the structure and corrosion properties of electroless nickel-phosphorus coatings were evaluated. SEM, AFM and EDS analyses were used to investigate the morphology, topography of the coatings and their elemental composition, respectively. A micro hardness test was performed to evaluate the hardness of the coatings. The corrosion behavior of the coatings was evaluated in in 3.5 wt.% NaCl aqueous solution using Tafel polarization test and electrochemical impedance spectroscopy method. It was observed that at 0.7 ppm concentration of thiourea, the solution was decomposed after 10 minutes, but electroless solution containing 1-3 ppm thiourea was stable during the deposition for one hour. The solution containing 1 ppm had the highest coating speed (10.21 m/hµ), which was decreased with increase of thiourea concentration to 3 ppm (2.5 m/hµ). In addition, by increasing the concentration of thiourea from 1 ppm to 3 ppm, the amount of phosphorus was decreased from 12.64 to 2.4 wt.%, which caused a change in the crystallographic structure from amorphous to crystalline and a decrease in hardness from 610 ± 15 Vickers to 198 ± 20 Vickers. By increasing the amount of thiourea in the electroless bath from 1 ppm to 3 ppm, the corrosion resistance was decreased so that the corrosion current density was increased from 6.91 × 10-7 A.cm-2 to 4.07 × 10-6 A.cm-2 and the charge transfer resistance for nickel-phosphorus electroless coatings was decreased from 3151 Ω.cm2 to 625.3 Ω.cm2 . The obtained results can be due to the absorption of thiourea on the surface of the substrate or nickel-phosphorus coating and preventing the continuation of the electroless process.

Plasma electrolytic oxidation coating has emerged as a relatively new method to increase the corrosion resistance of metals. This research aims to improve the corrosion resistance of coatings applied on pure titanium substrate by optimizing the parameters of the coating process. For this purpose, the experiments were designed using the fractional factorial design method to determine the determinants of a response. The main factors of the process include electrolyte concentration, electrical parameters (current density, frequency and duty cycle) and treatment time at two different levels. The microstructural and phase analysis of the coating were carried out using Scanning Electron Microscopy and X-Ray Diffraction (XRD). Corrosion behavior of coatings in 3.5 wt% NaCl solution was studied by electrochemical impedance spectroscopy analyze. Statistical analysis showed that the optimal conditions can be obtained in the concentration of 5 g/L sodium phosphate, 4 g/L potassium hydroxide, current density 6 amps/square meter, duty cycle 80%, frequency 1000 Hz, and treatment time of 10 min.

In this research, a two-component anti-corrosion coating based on polyurethane was made using polyacrylic resin and isocyanate hardener with different NCO/OH ratios. The anti-corrosion performance of these coatings was investigated using electrochemical impedance spectroscopy (EIS) with time in 1 M sulfuric acid. Equivalent circuit models were used to quantitatively compare the effect of the NCO/OH ratio on the anti-corrosion performance of polyurethane coatings. The results showed that with increasing the amount of hardener, the corrosion resistance of the coating first increases and then decreases and hence the best anti-corrosion performance of the coating was obtained at NCO/OH ratio of 1.2.

The DP980, DP590, and IF steels are used in the construction of car bodies due to their unique mechanical properties. In this paper, the corrosion behavior and microstructure of the DP980, DP590, and IF steels which are used in the automotive industry are investigated and evaluated. In order to evaluate the corrosion behavior of all three alloys, the electrochemical impedance spectroscopy and potentiodynamic polarization were evaluated in 0.1 M NaCl + 0.1 M H2SO4 and 0.1 M NaCl + 0.1 M NaOH environments. The corrosion evaluations of all three alloys show much better corrosion behavior in the alkaline environment than in the acidic environment due to the formation of the passive layer. While these alloys show much less corrosion resistance in the 0.1 M NaCl + 0.1 M H2SO4 environment, the uniform corrosion occurs while there is no evidence of the passive layer formation. The DP980 and DP590 dual-phase steels show lower corrosion resistance than the IF steel due to the presence of the ferrite and martensite phases and the possibility of galvanic cell formation at the interface between the two phases. The DP980 dual-phase steel has a better corrosion behavior than the DP590 due to the lower martensite content in both acidic and alkaline solutions, but the corrosion behavior of these two sheets of steel is very close to each other.

In this study, the effect of bacterium clostridium sp. as ananaerobic sulfate-reducing bacteria on the corrosion behavior ofAPI X42 micro-alloyed pipeline steel was evaluated in a saline simulated soil solution at different immersion times (varying from 3 days to 40 days) under biotic condition. In this process, a soil sample containing sludge was used as a source of production sulfate-reducing bacteria and a saline soil sample was used as the basis of the saline simulated soil solution. The corrosion behavior and microstructure of the corrosion products were evaluated as a function of immersion time. Microstructural examinations show the accumulation of bacteria on the steel surface after 7 days. By further immersed times to the middle times (21-24 days), a biofilm comprised of the dense extracellular polymeric substances was formed. After that, biofilm exfoliation was observed showing physical biofilm breakdown. This microstructural variation is associated with aremarkable variation in corrosion resistance. At first, the corrosion resistance decreases sharply from 1019Ω.cm2at 3 days to 274Ω.cm2at 7 days due to the metabolic bacterial activity. As a result of this high corrosion rate, a densely packed biofilm was formed at the middle times in such a way that corrosion resistance rises sharply to 7330Ω.cm2at 21 days. However, the dense protective biofilm formed at the surface was unstable and biofilm was degraded rapidly; consequently, the corrosion resistance decreases to 480 Ω.cm2at 40 days.

The study of superfluid levels due to the importance of these levels in many applications has been considered. In this study, nickel-copper alloy coatings were created using a two-step electrochemical deposition method-the surface energy reduction and microstructure and corrosion resistance were investigated. Surface morphology was investigated using scanning electron microscopy and XRD for field publishing and fuzzy structure. Corrosion resistance was investigated using potentiodynamic polarization method as well as electrochemical impedance spectroscopy. The results of this study showed that by increasing the concentration of Modidium crystal in the coating bath, the nanostructured coating was obtained and at a concentration of 200 grams per liter, a hieratic hierarchy coating was obtained. XRD data showed that only the nickel phase was created and a solid solution was created by the entry of copper atoms into the structure. Corrosion behavior studies showed that with the formation of coating, the corrosion density decreased from 6.2 to 0.12 mA/cm2 , and corrosion potential from-273 to -171 also decreased. The reason for this was the capture of trapped air in the coating, thereby preventing the entry of corrosive ions into the substrate as well as the Laplace pressure.

Anti-corrosion coatings based on the epoxy resin belnding with different extenders including talc, silicon dioxide and barium sulfate were prepared and applied on the carbon steel surface. The corrosion behavior of these coating systems versus the immersion time in 1M sulfuric acid was investigated by using electrochemical impedance spectroscopy (EIS) method. The anti-corrosion behavior of the coatings was simulated using EIS data and the approperiate equivalent circuit models. Variation of the coating and double layer parameters showed that the protective strenght of the epoxy coating blending with different extenders against corrosion is as the following sequence: Talc > Silicon dioxide > without extender > Barium sulfate

In this study, the effect of coating time on the microstructure and corrosion behavior of AZ31 Mg alloy coated by plasma electrolytic oxidation (PEO) method has been investigated. For this purpose, phosphate-based electrolyte containing hydroxyapatite nanoparticles was used at different times of 5, 10 and 15 minutes. The surface properties and chemical composition of the coatings were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD) pattern. The corrosion properties of coatings in the simulated body fluid have been studied by potentiodynamic polarization and electrochemical impedance spectroscopy tests. The results of this study showed that with increasing the coating time to 15 minutes, the size of the pores and the thickness of the coatings increased. The coating created in 10 minutes has the lowest percentage of porosity among the samples. The results also showed that the coating created in 10 minutes had the lowest corrosion current density (2.33 × 10-8 A/cm2) among the samples.

In the present study, the effect of different concentrations of calcium acetate (10 and 20 g/l) and potassium hydroxide (1 and 3 g/l) salts in electrolyte of the plasma electrolytic oxidation process on corrosion resistance of coatings formed on pure titanium has been investigated. After observation the surface structure of the coatings, it was found that the lowest porosity (about 4.86%) was related to the coating formed in the electrolyte containing 20 g/l calcium acetate and 1 g/l potassium hydroxide. This coating also showed the highest contact angle with water droplets (67.89 degrees) or in other words, the lowest wettability. The results of evaluation of corrosion behavior of coatings using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests after 48 hours of immersion in Ringer's solution indicated that the mentioned coating had the lowest corrosion current density (3.06 × 10-8 Ω/cm2 ) and the highest corrosion resistance (448272 Ω cm2 ) among all coatings. The high resistance of this coating against corrosion was due to low porosity percentage and thus reducing the penetration of corrosive ions into the substrate and also low wettability.

In this study, the effects of Tri-sodium citrate, Sodium potassium tartrate and Ethylene di-amine tetra-acetic acid as organic corrosion inhibitors on the corrosion behavior of carbon steel in a simulated concrete pore solution contaminated with 3.5 wt% NaCl, were investigated through open circuit potential, Electrochemical impedance spectroscopy and Cyclic polarization analysis. Morphology and surface roughness of the specimens was evaluated by scanning electron microscopy. EIS analysis showed that after 48 hours of exposure to NaCl solution, the citrate and tartrate were able to achieve 91.2% and 87.3% corrosion inhibition efficiency at their best performance respectively. Inhibition Mechanism of each inhibitor was analyzed Based on the parameters obtained from the EIS tests. According to Cyclic polarization results, the dominant mechanism of inhibition is through aggregating on anodic sites and consequently limiting the anodic reactions. SEM images showed that the addition of 0.1 M of citrate or tartrate to the corrosive medium, causes a relatively persistent layer on the surface of the metal with low porosity level which immunes the carbon steel from pitting corrosion to a large extent.

In this research, UNS S42000 martensitic stainless steel (SS) samples were subjected to tempering heat treatment at constant temperature of 550 oC for different time duration, ranging between 0.5 and 24 h, so as to assess the intergranular corrosion (IGC) behavior of the alloy. The microstructural characteristics and electrochemical properties of the alloys were evaluated using scanning electron microscopy (SEM) and anodic polarization method, respectively. The localized attack of the samples was investigated by potentiodynamic electrochemical impedance spectroscopy (PD-EIS) in the transpassive potential region. The results indicated that tempering up to 2 h would be followed by severe intergranular attack at martensite lath interfaces; however, the effect of tempering on corrosion performance of the alloys would be suppressed at prolonged tempering due to desensitization. Moreover, the PD-EIS results revealed that the charge transfer resistance (Rct) values of specimens at 1.10 V can be employed as a primary criterion in order to assess the localized attack of the martensitic SS. In this regard, the lower the Rct value at this DC bias potential, the lower the corrosion resistance to the IGC. These results were in good agreement with the SEM morphologies from the surfaces of corroded samples, indicating uniform corrosion, severe attack and desensitization for samples experiencing no-tempering, short tempering time and prolonged tempering, respectively.

Corrosion of steel bars in reinforcement concrete is the most important factor in the destruction of concrete structures. Till now, several protection methods for reducing the rate of corrosion of steel in reinforced concrete structures have been used, which corrosion inhibitors due to economical, easy to apply and efficiency, compared to other methods, faced with more attention. In this study, the effects of the simultaneous use of sodium nitrite and sodium-potassium tartrate inhibitors have been investigated. For this purpose, open circuit potential tests, electrochemical impedance spectroscopy and cyclic polarization were used in simulated concrete pore solution. This study aims to reduce the consumption of sodium nitrite due to environmental problems reported for it and also its destructive effects on the mechanical properties of concrete. Electrochemical impedance spectroscopy showed that the combination of these two inhibitors, improves the corrosion resistance by 91%. This rate is higher than the best performance of each of them, and finally, the synergistic parameter of 2/2 was calculated for this combination. According to the scanning electron microscopy images and the parameters obtained from the fitting of the Electrochemical impedance spectroscopy data, it seems that the simultaneous use of these two inhibitors at appropriate concentrations leads to the formation of a flat, uniform and chloride-resistant layer. Also, according to the results of the cyclic polarization test, the simultaneous use of these two inhibitors increases the pitting potential to 691 mV. Generally, it improves the resistance of steel specimens to pitting corrosion.

In this study, the inhibition effect of a Schiff base with three C=N groups and three aromatic rings on corrosion of 1018 carbon steel in 0.1 M hydrochloric acid is investigated by two electrochemical methods, impedance spectroscopy and polarization, at 25 °C. The inhibition efficiency increases by increasing the concentration of Schiff base from 100 to 500 ppm and the highest inhibition efficiency was about 96% at 25 °C for the concentration of 500 ppm of Schiff base. The results of the polarization method showed that the Schiff base in acidic solution acts as a mixed inhibitor. The charge transfer resistance (Rct) for 1.0 M HCl solution increases from 39.5 Ω.cm2 to 949.7 Ω.cm2 by adding 500 ppm of Schiff base. The effect of temperature on the inhibitor performance is investigated by electrochemical polarization method in the range of 25-65 °C and it shows decreasing of inhibition efficiency with increasing temperature. The adsorption of Schiff base molecules on the surface of 1018 carbon steel at all temperatures follows the Langmuir adsorption isotherm. The values of ΔGads obtain -32.122 kJ and -35.124 kJ mol-1 at 25 °C and 65 °C, respectively, which shows increment in its absolute value. These results show that the adsorption of Schiff base molecules on the surface of 1018 carbon steel is a physico-chemical adsorption.

In this study, the nanocomposite coatings of Ni-W-P/SiO2 were produced by electrochemical co-deposition of SiO2 nanoparticles with Ni-W-P alloy in solutions with different amounts of these nanoparticles on the copper surface. The composition and structure of the coatings were studied with Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive Spectroscopy (EDS). The results showed that the incorporation of SiO2 particles in the Ni-W-P/SiO2 composite coatings increases the surface uniformity and smoothness of the coating. The open circuit potential (OCP), electrochemical Impedance (EIS) and potentiodynamic polarization (Tafel) techniques were used to evaluate the corrosion resistance of the coatings in 3.5% NaCl solution. The corrosion results showed that the Ni-W-P/SiO2 nanocomposite coatings were much higher corrosion resistance than pure Ni-W-P coating. By adding SiO2 nanoparticles to the solution, first the corrosion resistance increases and then decreases due to the agglomeration of the nanoparticles. The highest corrosion resistance was obtained for the synthesized composite coating from a solution containing 9 g/L SiO2 nanoparticles. The main reasons for the high corrosion resistance of this coating are the maximum amount of SiO2 reinforcing particles in metal matrix, nanometer structure without surface defects and micro-cracks.

In this paper, zirconium oxide coating was produced on Zircaloy-4 alloy using plasma electrolytic oxidation (PEO). Sodium silicate and sodium pyrophosphate based electrolyte was selected in PEO process and the effects of concentration of sodium pyrophosphate (0, 2.5, 5, 7.5, and 10 g/L) on the microstructure and the behavior of electrochemical corrosion of formed coatings was studied. In order to examine the morphology and phase structure of coatings, scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used respectively. The corrosion behavior of the coated samples was evaluated by electrochemical impedance spectroscopy (EIS) in 0.5 M LiOH solution. The results show that, ZrO2 coating causes an increase in corrosion resistance inner layer from 0.61 MΩ.cm-2 for the bare sample to 126 MΩ.cm-2 for the sample which was coated in an electrolyte with the combination of 10g/L Na2SiO3 and 5g/L Na4P2O7 (sample S5). This corrosion behavior was related to the coating characteristics. So that in the electrolyte of 5g/L Na4P2O7 (S5) has compact/uniform structure in comparison to other coatings. Also, this sample contains the monoclinic ZrO2 phase of 94% and the tetragonal ZrO2 phase of 6% respectively.