مجله علوم و مهندسی خوردگی
سال دوازدهم شماره 3 (پیاپی 45، پاییز 1401)

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 study, magnetic nanoparticles of MnFe2O4@SiO2 activated with N-phosphonomethyl amino di-acetic acid were synthesized with a core-shell structure. Moreover, the characteristics of surface functional groups, crystal structure, magnetic properties, size and surface morphology of these nanoparticles were investigated by using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), microscope Scanning electrons (FESEM, Thermal Weight Analysis (TGA) and vibrating sample magnetometer(VSM). In this study, the antiscalant effect of precipitation for magnetic nanoparticles MnFe2O4@SiO2 were examined according to the reference test (NACE TM0374) by using 5 ppm MnFe2O4@SiO2. In this experiment, the precipitation effect of calcium sulfate and calcium carbonate on the surface of carbon steel was investigated. For this purpose, in one test a piece of carbon steel is placed in the presence of the precipitative compound and absence of antiscalant (control test) and in the other test of carbon steel is placed in precipitative compound with the antiscalant (main test) for a certain period of time. Afterwards, the amount of precipitation of the control and main experiment for carbon steel in the similar environment of the cooling tower of thermal power plants containing 1000 ppm sulfate and 500 ppm chloride were investigated. The tafel polarization test and impedance spectroscopy were used to measure the amount of fouling on the surface of the control and main carbon steel samples. The results indicate that the rate of precipitation formation is greatly reduced in the presence of antiscalant.

Copper has long been widely used by humans and due to its properties, such as excellent ductility, high thermal conductivity, antimicrobial properties, and also the highest electrical conductivity after silver, it has gained this high position of consumption. This metal has been used in cases such as power transmission wires, copper pipes, laboratory equipment, electromagnetic motors, kitchen utensils, extensive alloying with gold, etc. This study investigated the corrosion behavior of copper metal in a solution of 1.0 M HCl and the inhibitory effect of Silybum marianum oil (SMO). The test method is that the corrosion behavior of copper in a solution of 1.0 M HCl was first measured using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. one and two gr of SMO were measured in liters. The results show that according to the potentiodynamic polarization diagrams and electrochemical impedance spectroscopy of the sample a solution containing one gr of SMO in one liter of 1.0 M HCl solution has higher corrosion resistance and higher corrosion potential and lower corrosion current density than the solution. It is oil-free. Also, the sample in a solution containing 2 g of SMO in one liter of 1.0 M HCl solution has much better corrosion resistance, lower corrosion rate, and more noble behavior. Therefore, it can be concluded that SMO as a green inhibitor has an acceptable inhibitory effect on the copper piece in the solution, and with increasing the amount of oil, the inhibition increases.

In this research, the corrosion inhibition of X70 steel in HCl containing 2-amino-5-nitrothiazole as an inhibitor has been investigated by Tafel polarization technique. The electrochemical measurements showed that this compound is a suitable corrosion inhibitor for mild steel and the inhibition efficiency increased with inhibitor concentration. The effect of temperature on the corrosion behavior of mild steel was studied. As the temperature increases, the corrosion current density increases and the inhibition efficiency decreases. Different adsorption models were investigated and the results showed that the adsorption of this inhibitor follows the Langmuir adsorption isotherm. The values of the thermodynamic parameters were calculated by the corrosion currents at different temperatures and using the adsorption isotherm. The negative sign of Gibbs free energy indicated spontaneous adsorption of inhibitor on steel surface. Thermodynamic investigations showed that corrosion of steel X70 is exothermic and the molecules of inhibitor are adsorbed on the steel surface by the process of chemisorption and physisorption.

In the present work, it was tried to improve the electrochemical efficiency of aluminum base sacrificial anodes with Al-Zn-Mn-Fe alloy by two mechanical and chemical methods and to compare the effect of these methods. In this regard, the melt shearing process at 0, 2 and 4 minutes was used as a mechanical method and the addition of bismuth, lithium and tin elements was used as a chemical method. The results of the microstructure investigation using optical (OM) and transmission electron (SEM) microscopes revealed that the melt shearing process leads to grain refinement, increasing the number of equiaxed grains and reducing the size of intermetallic compounds. With increasing the melt shearing time, the effect of microstructure modification increased and therefore the electrochemical efficiency of the samples increased so that the 4 minute sample showed the most modification of structure and the highest electrochemical efficiency. Also, the results showed that among the additive elements, adding Bi caused the best electrochemical efficiency. The results of comparing the effect of mechanical modification and chemical modification demonstrated that the effect of chemical modification is far better than the mechanical modification. The electrochemical efficiency of the mentioned alloy without melt cutting and chemical additives was 11%, but by applying melt cutting in 4 minutes, the efficiency increased to 15%, while due to the addition of bismuth, the electrochemical efficiency increased from 15% to 68%.