جستجوی مقالات مرتبط با کلیدواژه « electrochemical impedance spectroscopy » در نشریات گروه « مواد و متالورژی »

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.

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.

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.

Platinum anodes, including platinum coating on the substrate of niobium, are used for electrolysis of sodium chlorate. Due to the high price of these anodes, their corrosion resistance in this environment is important. In this research the effect of current density has been investigated on corrosion the behavior of Pt/Nb anode. Platinum coating was deposited on the niobium substrate by electrodeposition method. The samples were then exposed to accelerated life test in chlorate electrolysis cell at current densities of 0.5, 1.2 and 2 A/cm2 for 3, 10, 40 and 70 hours at constant temperature of 35°C. Cyclic voltammetry and electrochemical impedance spectroscopy was done on the samples at each time extension. The samples finally were characterized using SEM. The results showed that at any current density, the solution in the vicinity of the anode is acidic and with increasing current density, the corrosion of the coating through the formation of chloroplatin complexes, from local to uniform, is converted at a high rate.As well as, it was revealed that the Pt/Nb anodes are deactivated in to two manners; Spontaneous dissolution of platinum coating and growth of passive layer or dissolution of coating together with passive layer. The electrolysis with current density of 1.2 A/cm2 is the best operating condition in which the platinum anode has its highest corrosion resistance, lowest destruction and optimum catalytic effect.

Polypyrrole modified coatings were coated by ammonium bifluoride doped in the polyethylene glycol (Doped Ppy) on AZ31 alloy using cyclic voltammetry. The result of nuclear magnetic resonance showed that fluoride doping occurred in the glycol molecule. Corrosion performance of the coatings was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization in 0.05 M NaCl solution. Corrosion current density of polypyrrole modified coatings (Doped Ppy) was calculated about 5 µA.cm-2 , which was 5 times lower than the coating with discrete PEG and fluoride ions. It was observed that the modified polypyrrole coatings shows the highest corrosion resistance due to the synergism effect of fluoride and polyethylene glycol. Charge transfer resistance (Rdl) of polypyrrole coating with fluoride and PEG and polypyrrole coating containing ammonium bifluoride doped in the PEG was 5950 and 10050 Ω.cm2 , which was higher about 2.5 and 4.5 compared polypyrrole coating with Rdl of 2250 Ω.cm2 .

In the present study, spark plasma sintering (SPS) technique was used to fabricate Ti-Al2O3-HA composite. Powders were sintered at 40 MPa pressure for 5 min at 1200 and 13000C. Microstructural characterisation was carried out using scanning electron microscopy (SEM). Density, hardness, electrochemical impedance and polarization test were performed to evaluate the properties of the samples. The results showed that by increasing the sintering temperature from 1200 to 1300 0C the density of the samples increases and the apparent prosity decreases. Also with increasing temperature the hardness of the samples increased from 528HV to 612HV. The result of electrochemical impedance test showed the polarization resistance of the sample enhanced from 222 Ωcm2 to 996 Ωcm2 . Furthermore, according to polarization measurements, the corrosion current density was reduced from 16.35 μA/cm2 to 1.47 μA/cm2 . The improvement in the corrosion resistance was attributed to the reduction of prosity and the formation of stronger passive film on the sample surface with increasing sintering temperature.

Nickel-phosphorus coatings (Ni-P) are widely used in industry due to their high hardness, corrosion resistance and very good mechanical and chemical properties. Oxide particles such as TiO2 can be used to increase the wear resistance of these coatings. In this study, the Ni-P-W-TiO2 composite coating was deposited on the AISI 304L steel substrate using the electroplating method. Electroplating was performed at concentrations of 10, 20, and 30 g/L TiO2, and the effect of TiO2 concentrations on the microstructure, corrosion behavior, and wear behavior was investigated. Coatings were characterized by scanning electron microscopy (SEM). In order to investigate corrosion resistance, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were used in 3.5% NaCl aqueous solution. A pin on disk test was used to test the wear resistance of uncoated and coated samples. Sample micro-hardness was also measured by the Vickers hardness test. Examination of the microstructure showed that the best TiO2 concentration for deposition was 20 g/L. The results of Tafel and electrochemical impedance spectroscopy tests were also consistent with microscopic images, and the results showed that the coating formed at concentration of 20 g/L had the highest corrosion resistance compared to other coated and non-coated samples. Also, the results of the wear test showed that increasing the TiO2 concentration increases the micro-hardness and wear resistance.

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.

Corrosion of steel in concrete is the most important reason for the premature destruction of concrete structures. The use of corrosion inhibitors is a suitable way to control the corrosion of reinforcement in concrete. These chemicals are added in small amounts to the corrosive medium to reduce the rate of corrosion by affecting the rate of anodic, cathodic, or both reactions. In this paper, we investigate the corrosion inhibitory effects of disodium hydrogen phosphate, sodium molybdate, and sodium nitrite in simulated concrete pore solution in two concentrations of 1.8% and 3.5% NaCl. Hence according to the tests performed in simulator solution containing 1.8 wt.% NaCl salts, the nitrite, phosphate, and molybdate inhibitors added in 0.2, 0.0002, and 0.15 M, resulted in the efficiencies of 69, 59 and 81 percent, respectively. Also, in scanning electron microscopy micrographs, it was found that the use of these three inhibitors dramatically reduces the number and distance of surface pits compared to the control sample.

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.

AISI 430 ferritic stainless steel is used as interconnects in solid oxide fuel cells. In order to improve the corrosion resistance of this steel under operation conditions of solid oxide fuel cells, a protective and conductive coating layer on the interconnects can be used. In this research, AISI 430 ferritic stainless steel was coated with electrolytic with manganese, cobalt and cerium oxide under different density densities (400, 500, 600 and 700 mA/cm2). The coated specimens were studied by scanning electron microscopy (SEM) with X-ray diffraction spectroscopy (EDX). In order to investigate the corrosion behavior of the coatings, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests was used in aqueous NaCl solution of 3.5%. The results showed that with increasing the current density, the coating became even more uniform. The results of electrochemical polarization showed that the coating produced at a current density of 600 mA/cm2 has a better corrosion resistance (0.186 μA.cm-2) than the coatings produced at current density of 400 (2.06 μA.cm-2), 500 (1.767 μA.cm-2) and 700 (1.02 μA.cm-2). Also the results of electrochemical impedance spectroscopy showed that the capacity of coating produced at current density of 600 mA/cm2 (1.47E-4 Ω-1cm-2Sn) is lower in comparison with the coatings produced at current density of 400 mA/cm2 (2.5E-4 Ω-1cm-2Sn), 500 mA/cm2 (1.6E-4 Ω-1cm-2Sn) and 700 mA/cm2 (2.1E-4 Ω-1cm-2Sn) which indicating better corrosion resistance of produced coating at current density of 600 mA/cm2.

In this research, the effect of inorganic and organic additives of cerium nitrate and adipic acid on anti-corrosion resistance and microstructure of vanadium conversion coating on 2024 aluminum alloy was investigated. First, using the results of electrochemical impedance spectroscopy (EIS) and direct current polarization (DC), optimum value of concentration of both organic and inorganic additives under optimum coating conditions in the absence of additives was determined. Then, in order to properly evaluate the effect of additives, practical process parameters such as immersion time, solution pH and solution temperature were optimized in the presence of additives. Based on the results of direct current polarization and electrochemical impedance spectroscopy, the coated sample with vanadium conversion coating in the presence of 2 gr/lit of cerium nitrate, solution pH of 4, immersion time of 25 minutes and at ambient temperature showed the highest anti-corrosion resistance. This anti-corrosion performance (corrosion current density of 0.026 μA/cm2 and impedance at low frequencies of 85,200 Ω.cm2), displayed significant improvement in anti-corrosion resistance of bare substrate (corrosion current density of 2.28 μA/cm2 and impedance at low frequencies of 18,510 Ω.cm2) by develpoing vanadium conversion coating in the percense of cerium nitrate. Also, in the presence of adipic acid additive the anti-corrosion resistance of substrate increased. In order to investigate the surface characteristics of the vanadium conversion coating in the presence of additives, water contact angle measurment, scanning electron microscopy and energy dispersive X-ray spectroscopy were used.

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.