جستجوی مقالات مرتبط با کلیدواژه « پلاریزاسیون » در نشریات گروه « مواد و متالورژی »

Chromium coated zirconium alloys are one of the promising options for accident resistant fuel cladding (ATF) tubes for light water reactors (LWRs). In this study, the oxidation behavior of the chromium coating deposited by the physical vapor coating method on the zirconium substrate was investigated. The scanning electron microscope image of the cross-section of the samples and the atomic force microscope image of the sample surface show that a chromium layer with an approximate thickness of 20 nm and a lower surface roughness of 680 nm is formed on the surface. The results of EIS and PDP spectroscopic tests, in the aqueous environment of 3.5 wt% NaCl, show that the corrosion potential and current from -0.371 V and 5.85 ×10-8 A for the uncoated sample to -0.354 V And A has changed 0.65×10-8 , which indicates the improvement of oxidation resistance of the sample coated with Cr.

In order to strengthen the epoxy phenolic coating, glass flakes and cerium nitrate have been used. For this purpose, 6 samples with different combinations of cerium nitrate and glass flake were prepared and applied on ST37 steel. The self-healing properties of the samples at the scratch site were investigated by field emission scanning electron microscope (FESEM), elemental map analysis (MAP), and energy dispersive spectroscopy (EDS). According to the results, 58.52% of the complexes formed in the scratch area are composed of cerium nitrate (in sample EP2CN1.5G-04). In order to measure the anti-corrosion performance, electrochemical impedance spectroscopy (EIS), polarization and salt spray tests were performed. The obtained results showed a significant improvement in the protective performance of coatings containing glass flake and cerium nitrate compared to the pure epoxy. The results indicated that the presence of glass flakes and the combination of its protective mechanism with the self-healing properties of cerium nitrate increased Rct (charge transfer resistance) in sample 04 compared to sample 01 by 11.2 and 4.8 times, respectively, after 18 days of immersion. This sample also had the highest RP and the lowest icorr compared to other under-studed samples. These results prove the release of cerium nitrate in addition to the barrier properties of glass flakes. According to the results, it was observed that the EP2CN1.5G04 sample had better anti-corrosion performance than other samples.

Solvent and water-based polyester resins are used in many different applications; one of them is the automotive paints' primary layers. In this research, a water-reducible polyester resin curable with melamine was synthesized (PS1). This resin was cured for 30 minutes with a temperature of 120 ̊C. The final product is a water-reducible resin, which was synthesized, neutralized and diluted with water, and consequently, a milky white water-based dispersion was obtained. The indicating peaks of the Fourier Transform Infrared (FTIR) test alongside the results of the Differential Scanning Calorimetry (DSC) test were proof to confirm the control over the polyester resin synthesis. To evaluate the anti-corrosion and adhesion properties, the synthesized resin in a full-coating system was compared with a commercial resin. The pull-off test was used to check the adhesion strengths. PS1 (polyester resin) coating system revealed an adhesion strength value of 2.05 MPa compared to 2.51 MPa for RW100. Digital images taken from the samples' surface in the salt spray test showed that after one month in a corrosive environment, synthesized resin has better anti-corrosion resistance than commercial sample. Electrochemical Impedance Spectroscopy (EIS) test indicated that after 15 weeks of immersion in the 3.5% sodium chloride electrolyte solution, the synthesized resin system indicated an impedance resistance at low frequency of 4.05 ×109 ohm.cm2, which is more than the Daotan VTW 1225 (2.75 ×106 ohm.cm2).

According to the widespread use of aluminum alloys in the oil and gas and petrochemical industries and their low corrosion resistance in corrosive environments, it is necessary to make the surface of these alloys resistant to corrosion using a appropriate coating method. In this research, the coating method in an aqueous environment in an autoclave on the surface of 6061 aluminum alloy was used and its corrosion resistance was investigated. The cleaned samples were placed in an autoclave. Then, by controlling the temperature, time and pressure, an oxide / hydroxide coating was created on the surface. X-ray diffraction (XRD) patterns showed that the coating generally contained an AlO(OH) phase. Scanning electron microscopy (SEM ) images of the coating surface showed that the cubic nanocrystals were densely formed throughout the surface. Vickers microhardness test also showed that the coating was soft and had no effect on the surface hardness. However, the polarization curves show that the corrosion current density of the generated substrates is significantly reduced and the corrosion potential is more positive. As the parameters of autoclave temperature, time and pressure increase, the coating thickness increases and the corrosion current density decreases. It was also concluded that the coating method in the aqueous environment inside the autoclave in liquid and immersed state is a more desirable method due to the higher autoclave pressure than the water vapor state. This indicates that the corrosion resistance of 6061 aluminum alloy has been significantly increased by the use of steam coating.

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, three nickel-based superalloys consist of Colmonoy 6 ،Inconel 625 and Hastelloy C276 was coated by GTAW process method on 310 stainless steel. Evaluation of hardness, wear behavior and wear mechanism of samples was performed with Vickers, pin-on-disc method and using SEM images, respectively. The high temperature oxidation behavior was also studied at 1050°C in 8 cycles of 24hours. Also, to investigate corrosion behavior of samples, potentiodynamic polarization test was used in a solution of sulfuric acid and sodium chloride. The surface hardness results showed higher hardness of the Hastelloy C276 (727 HV) and Colmonoy 6 (612 HV) than the Inconel 625 (338 HV) and the steel substrate (217 HV). The best wear behavior was related to Hastelloy C276 with friction coefficient of 0.28. Surface morphology studies of the samples show a change in the wear-resistance mechanism from sliding to adhesive by applying nickel-base coatings on 310 stainless steel. In high temperature oxidation test, minimum weight gain was calculated for Hastelloy C276 (0.5mg/cm2). Corrosion test shows that fabrication of coatings improved 310 stainless steel corrosion resistance which maximum corrosion potential (-119/9 mV) and minimum corrosion current density (0.14 µA.cm-2) was owned by Hastelloy C276. Finally with considering the results, it seems that Hastelloy C276 be as the most desirable option with the aim of coating on 310 stainless steel in high-temperature conditions.

CO2 corrosion controlling was surveyed on carbon steel (API-5L X60) in NaCl 3.5 % (wt.) Solution saturated with CO2 by 2-Mercaptobenzoxazole (2MBO) and 2-Aminobenzimidazole (2ABI). Inhibition effects of these compounds were investigated by Scanning Kelvin Probe (SKP) as a new method and other techniques include; Weight loss, Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) in 50, 100, 200, 300 and 400 ppm concentration at 25, 40 and 60 oC in static condition. Weight loss results did not confirm effective efficiency for 2-Aminobenzimidazole as corrosion inhibitor on API-5L X60 in CO2 media but all tests results revealed 2-Mercaptobenzoxazoleacts as an effective inhibitor in this media on API-5L X60. The highest inhibition efficiency of 95%, 90% and 83.8% was obtained according to EIS, Potentiodynamic polarization and Weight loss tests, respectively at the concentration of 400ppm and 25oC. Adsorption isotherms of 2-Mercaptobenzoxazole showed physical and chemical adsorption process takes place on API-5LX60 surface. 2-Mercaptobenzoxazole adsorption obeys Langmuir isotherm model and affects on anodic and cathodic processes on metal surface so it’s performance is known as a mixed type inhibitor. Increasing of media temperature has reductive effect on 2-Mercaptobenzoxazole efficiency. Results of Scanning Kelvin Probe tests revealed surface potential of API-5L X60 is increased by 2-Mercaptobenzoxazole molecules that form a film on metal surface. This phenomena confirms that adsorption of 2-Mercaptobenzoxazole, more over the cathodic reactions, limits the metal surface affinity for anodic reactions of Fe atoms. Local corrosion potential on specimen surface was surveyed by use of surface potential maps (SKP map).

Hydroxyapatite (HA, Ca10(PO4)6(OH)2) has been widely used as a coating material for dental implants for many years, due to its close similarity of chemical composition with bone material and its ability to bond with bone. In this study, a hydroxyapatite coating was formed on Ti substrate, employing the electrochemical coating method of cyclic voltammetry, in order to enhance the corrosion resistance. Formation of Hydroxyapatite on Ti is confirmed by the XRD and SEM analyses. Polarization curves revealed a substantial improvement in the corrosion potential from -289 to -193 mV (Ag/AgCl) and decrease in corrosion-current density, for the hydroxyapatite coatings in artificial saliva compared with pure titanium that showed positive role of HA on Ti corrosion behavior.

Nickel field composite coatings have a high ability to improve surface properties, such as increased corrosion resistance and abrasion resistance. In this study, Ni-P-TiO2-ZrO2 composite coating on AISI 316L steel substrate was deposited by direct current flow method and the effects of different pH 3, 3.5, 4 and 4.5 on coating morphology and corrosion resistance were investigated. Scanning electron microscopy (SEM) was used to investigate the microstructure. In order to investigate the corrosion behavior of the coatings, a potentiodynamic polarization test was used in 3.5% NaCl solution. The results of SEM and EDX analysis showed that the coating produced at pH = 4 had the highest uniformity and the highest amount of titanium oxide and zirconium oxide particles was related to this pH. Also, the polarization results showed that the highest corrosion resistance is related to the precipitation produced in pH = 4. At low pH and more than pH=4, the coating was not continuous and in some parts of the coating crack and pit were observed.

In this study, the effect of strainin thermomechanical two-step aging heat treatment on mechanical properties and electrochemical corrosion resistance of Al-2024 alloy has been investigated. These results were compared with normal aging T6. For this research, samples of Al-2024 alloys were placed at ambient temperature during normal aging under different percentages of strain, and then aging treatment was completed. Four strains of 10%, 30%, 50% and 65% were applied on the samples by rolling machine. The results of tensile test with low strain rate, potentiodynamic polarization curves and optical microscopy indicated that the sample with 50% strain offered optimum combination of microstructure, mechanical strength and corrosion resistance. This is due to the fine and uniform distribution of precipitates that cause increasing of yield strength, tensile strength and corrosion resistance by 27%, 10%, and 83%, respectively, in comparison with T6 heat treated[MP2D1] . Therefore applying strain of 50%, can increase the corrosion resistance with maintaining high strength in two-step aging and thermomechanical heat treatments.

In this study, a novel Schiff base compound based on chromone was synthesized and its inhibition efficiency on corrosion of carbon steel in the hydrochloric acid was investigated. In this regard, the inhibition efficiency of the compound were investigated by weight loss methods, UV-Vis test, electrochemical methods such as electrochemical impedance spectroscopy (EIS) and polarization, scanning electron microscopy (SEM), X-ray diffraction spectroscopy (EDX) and absorption isotherm. The results of the studies indicated good inhibition efficiency with an efficiency above 92% for the synthesized Schiff base in the acidic media. Concentrations of 0.5, 1, 1.5 and 2 mM were investigated for the inhibitor, and the best result was obtained at concentration of 1 mM. SEM-EDX results showed that in the presence of inhibitor, the adsorption amount of chloride ions on the steel surface decreased to 90% and according to the adsorption isotherm, Inhibitor absorption on the steel surface follows Langmuir adsorption isotherm.

Composite coatings with nickel matrix and ceramic reinforcement particles have high ability to improve surface properties, such as good corrosion and abrasion resistance. In this study, Ni-P composite coating was coated with ZrO2 and TiO2 ceramic particles on the AISI 316 steel substrate through direct current plating method. The effect of the current densities of 20, 30, 40 and 50 mA/cm2 on the microstructure and corrosion resistance was investigated. Scanning electron microscopy (SEM) was used to investigate the microstructure. In order to investigate the corrosion behavior of the coatings, potentiodynamic polarization test was used in aqueous NaCl solution of 3.5%. The results of SEM and EDX analysis showed that the coating produced at current density of 40 mA/cm2 was more uniform and had more deposition of titanium oxide and zirconium oxide particles. Also, the polarization results showed that the corrosion resistance of the coated specimen in the current density of 40 mA/cm2 (Rp = 12.3030 MΩ) was higher than that of the coated in current density of 20 (Rp = 12.1950 KΩ), 30 (Rp = 22.2710KΩ) and 50 mA/cm2 (Rp = 8.34020 KΩ). In the higher or less current densities, the coatings were not uniform.

Conversion Coatings are one of the effective ways for improving adhesion of organic coatings to metallic substrates and consequently increasing anti-corrosion performance of a fully coated system. In the current research, multi-cationic conversion coating formed from sources such as hexafluorotitanic acid, sodium molybdate, phytic acid and nickel sulphate was studied and investigated. Results obtained from electrochemical impedance spectroscopy and polarization revealed that conversion coating which formed in the presence of sodium molybdate has not appropriate polarization resistance and the reason for this weak performance investigated by field emission scanning electron microscope. Obtained results showed that in the presence of sodium molybdate, there were abundant micro-cracks on the surface of the coating. After optimizing the multicationic conversion coating, an epoxy coating applied on the surface of bare steel and conversion coated one. The results obtained from adhesion and salt-spray tests indicated that the multi-cationic conversion coating causes improvement in adhesion strength of epoxy coating to steel substrate and finally increased the anti-corrosion performance of the system.

The presence of organic molecules containing active groups in the aqueous extract of Kiwi fruit shell converted it as a low cost and rich source of green inhibitors in corrosion control of carbon steel. In the present study, the synergistic inhibition effect of Kiwi fruit shell extract and zinc nitrate on the corrosion behavior of carbon steel in 3.5 wt.% NaCl solution was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. By means of scanning electron microscopy (SEM) the morphology and chemistry of surface were investigated. In addition, the Fourier transform infrared (FT-IR) spectroscopy was applied to recognize the functional groups of Kiwi fruit shell extract and its mixture with zinc nitrate. The EIS results indicated that after 24 h immersion of steel sample in NaCl solution containing 200 ppm Kiwi fruit shell extract and 600 ppm zinc nitrate the maximum inhibition efficiency of 85% was achieved. The potentiodynamic polarization analysis demonstrated that the corrosion inhibition dominantly occurred through anodic half-reactions. The interactions and complex formation of organic molecules of Kiwi fruit shell extract with iron cations and also the zinc cations adsorption on the cathodic sites resulted in the deposition of effective corrosion resistant film on the mild steel surface. Moreover, the images obtained from SEM analysis proved that the increase in the concentration of zinc nitrate resulted in the steel surface corrosion resistance increment so that with addition of 600 ppm zinc nitrate to the solution a uniform layer with less porosity was formed over the surface. These observations confirm the successful adsorption of inhibitor molecules on mild steel surface.

In this research, a uniform film of polypyrrole/CNT/cadmium oxide nanocomposite was produced to protect the austenitic stainless steel 304 against corrosion in 0.5 molar hydrochloric acid medium. For this purpose, the chemical deposition method was used for CNT / CdO synthesis. Electrochemical synthesis method was used to coat the stainless steel and to find optimal coating conditions. Polarization tests were used to find the optimum amount of reinforcement nanocomposite. Optical microscope and scanning electron microscope (SEM) were used to study the morphology of coating. Results showed that the final nano composite had a remarkable corrosion resistance and the presence of CNT / CdO reduced the porosities in the final polymer film. Also coating results showed that the optimum amount of apply current density and pH for electropolymerization were 4mA/cm2 and 9 respectively. The 0.5% weight-volumetric functionalized carbon nanotube with Cadmium Oxide was determined as optimum amount of nano composite reinforcement using a polypyrrole matrix. Polypyrrole Carbon nanotube/Cadmium Oxide nanocomposite coating on the surface of austenitic stainless steel 304 protected more than 98% against corrosion in a 0.5 M solution hydrochloric acid.

In this research, the electrochemical behavior of AISI 430 ferritic stainless steel at presence of Al, Ti and simultaneous co-deposition of Al-Ti diffusional coatings were studied in the simulated marine environment (NaCl 3.5%). To determine the microstructure and phases of the coatings, scanning electron microscopy (SEM) and X-ray diffraction (XRD) was used. To evaluate the corrosion resistance of coatings, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods were used. Electrochemical polarization results showed that co-deposition of Al-Ti coating has better corrosion resistance (4.55×10-4 μA.cm-2) in comparison to Al (3.21×10-2 μA.cm-2) and Ti (3.6×10-2 μA.cm-2) coatings. Also the results of electrochemical impedance showed that co-deposition of Al and Ti have higher charge transfer resistance of electric double-layer in comparison with Al and Ti coatings.

In most industrial processes, acidic solution are commonly used for the pickling, industrial acid cleaning, acid descaling, oil well acidifying, etc. Corrosion prevention systems favor the use of corrosion inhibitors with low or zero environmental impacts. In this work, the inhibition ability of 2-Mercaptobenzothiazole (MBT) and 2-amino-5-nitrothiazole (Nitramine) (two thiazole derivatives) against the corrosion of AISI steel 4130 in 1 M HCl solution were evaluated by polarization and electrochemical impedance spectroscopy (EIS). Polarization studies indicated that MBT retards both the cathodic and anodic reaction and Nitramine retards anodic reaction through chemical adsorption and blocking the active corrosion sites. EIS data was analyzed to equivalent circuit model shows that as the inhibitor concentration increased the charge transfer resistance of steel increased whilst double layer capacitance decreased. Thermodynamic parameters such as activation energy, enthalpy, entropy and free energy of adsorption were calculated and Atomic force microscopy (AFM) was used to study the steel surface with and without inhibitors.