مجله علوم و مهندسی خوردگی
سال دهم شماره 4 (پیاپی 38، زمستان 1399)

Researchers and industries have considered Electroless nickel boron coatings due to their appropriate corrosion and wear properties. In this study, the effect of thickness on corrosion behavior of the nickel-boron electroless coating was evaluated before and after heat treatment. The coating was performed in three different thicknesses of 40, 20 and 60 micrometers. The samples were heat treated at 450 ° C for one hour. Scanning electron microscopy was used to evaluate the coating surface. Potentiodynamic polarization and electrochemical impedance spectroscopy tests were used to study the corrosion behavior. The results showed that the coated sample with a thickness of 40 microns after heat treatment shows better corrosion behavior than other samples. SEM images obtained from the surface of produced coatings showed the larger cauliflower-type structure having better corrosion behavior due to fewer grain boundaries.

In this study, the inhibitory effects of two organic corrosion inhibitors, 2-amino-5-nitrothiazole (Enheptin) and 2- Aminoethanesulfonic acid on carbon steel 4130 in hydrochloric acid solution were investigated using Tafel polarization tests and Density Function Theory (DFT) (using Gaussian 09W software). The results showed that with increasing the concentration of inhibitors in acidic environment, the percentage of inhibition increases and both organic inhibitors affect the cathodic (hydrogen reduction) and anodic (metal dissolution) reactions so can be classified as mixed inhibitors. With increasing concentration of inhibitors, the inhibitor efficiency of Enheptin was more than 2-Aminoethanesulfonic acid. The results and parameters derived from the DFT also showed the more chemical and electron affinity of the of the Enheptin atomic orbitals in comparison with 2- Aminoethanesulfonic.

In this study, the chronoamperometry technique was used to investigate the electrodeposition mechanism of copper/ nickel-phosphor multilayer coatings using the single-bath method. In this regard, the influence of bath components on current transients was studied by fitting two and three-dimensional nucleation and growth models. In the potential range of nickel reduction, hydrogen evolution reaction co-occurs; Therefore, the current contribution of this process, as well as surface absorption and charge of the electric double layer current densities, were considered in these fittings. The reduction mechanism from the final bath was instantaneous nucleation with three-dimensional diffusion-controlled growth. Fitting results reveal that the existence of copper and phosphorus in the bath had an incentive role in the three-dimensional deposition of nickel-rich layers. Although copper-nickel citrate baths are commonly employed for alloy deposition, AAS and EDX analyses revealed that deposition of nickel-rich layers at potentials less than -0.8 V is achievable, and phosphorus co-deposits with nickel. Finally, FE-SEM analysis was used to investigate the morphology of copper-rich and nickel-rich monolayers, which revealed the formation of uniform and spherical deposits, and confirmed the results of the chronoamperometry approach. The potentials of -0.3 and -1.1 V vs. SCE were the most appropriate potentials for generating copperrich and nickel-rich layers, respectively, in terms of particle shape, size, and uniformity.

Corrosion is one of the most costly problems for the industry, which causes a lot of waste of time and manpower in this field. These costs can be directly related to the use of paints and inhibitors in the corrosion process, repair of metal parts or the use of steel, or indirectly affect the costs of damage, environmental hazards, closure or failure of a plant. . The aim of this study was to investigate the effect of temperature on the corrosion behavior of X70 micro-alloy steel in a sour environment in a solution of one molar of sulfuric acid in the presence of benzomidazole and methicbenzomidazole. With increasing temperature from 25 to 45 and 65° C, in the case of benzomidazole inhibitor, the protective layer formed on the surface is broken and less is formed at 25° C, as a result of this phenomenon, better adsorption is formed on the passive layer. The electron transfer is delayed, then the benzomidazole inhibitor is changed and subjected to an increase in temperature to 65° C, so that the protective layer increases again and the corrosion current does not decrease. From this decrease and increase of corrosion flow, a protective layer is formed at 45° C, which has relative adhesion and strength, and with increasing temperature up to 65° C, a protective layer begins to form at a lower potential. However, the protective layer is not recommended at all for this inhibitor. This is especially evident in X70 micro-alloy steel. Best Operating Temperatures Benzomidazole and methyl benzomidazole at room temperature are both inhibitors that improve corrosion resistance by increasing their amount in corrosion solution.

In this study, camphor sulfonic acid doped polyaniline (CSA PANi) and its nanocomposite with α-Fe2O3 nanoparticles were synthesized using in situ oxidative polymerization and were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Field Emission Scanning Electron Microscopy (FESEM). The paste was prepared from synthesized compounds and applied to the pre-treated titanium substrates (sanded and etched) by Dr. Blade method and used as the photoanode for photoelectrochemical cathodic protection of mild steel. The Mott-Schottky analysis was performed to study the type of semiconductor compounds as well as the density of charge carriers. The performance of the prepared photoanodes in the photoelectrochemical cathodic protection of mild steel was studied using electrochemical impedance spectroscopy (EIS) and Tafel polarization. The results showed that the corrosion potential (Ecorr) of mild steel decreased from -706 mV in the case without photoanode connection to -842 mV in the case of connection to Ti / CSA PANI-Fe photoanode under light irradiation, indicating the flux of produced electrons from the photoanode to the surface of mild steel and its cathodic protection. The EIS results also showed that the charge transfer resistance (Rct) for Ti / CSA PANI-Fe was 578.6 Ωcm2 which is less compared to Ti / α-Fe2O3 (874.9 Ωcm2 ) and Ti / CSA PANi (693.4 Ωcm2 ), confirming the low recombination rate of electrons and holes and more flux of electrons to the surface of mild steel and the proper performance of Ti / CSA PANI-Fe photoanode in photoelectrochemical cathodic protection.

It is important to produce cost-effective electrocatalysts that can produce hydrogen at a lower cost and higher purity. In this study, nanostructure Ni-P electrocatalysts were generated by cyclic voltammetry electrochemical deposition method on copper sheet and its electrocatalytic activity was investigated for oxygen evolution reactions. FESEM were used for microstructural investigations and electrochemical tests were used to study the electrocatalytic behavior. The results of this study showed that the number of coating cycles is effective on microstructural and coating morphology and with increasing the number of coating cycles from 15 to 25 and then up to 40 nanostructured surface cycles are almost eliminated and flat surface is created. The results of electrocatalytic activity analysis showed that by increasing the number of coating cycles the electrocatalytic behavior is improved first and then by further increase in the number of cycles the activity decreases and the best electrocatalytic activity of the sample created in the number of cycles. 25, which requires an overpotential of 230 mV to produce a current density of 10 mA.cm-2 due to improved surface active area and improvement of intrinsic electrocatalytic activity. OER reactions also showed that the electrode produced showed excellent behavior compared to other electrodes reported in references.