مجله علوم و مهندسی خوردگی
سال چهارم شماره 3 (پیاپی 13، پاییز 1393)

In this research, the effect of chloride ion concentration on the rate of corrosion protection efficiency of silane coating composition consisting of tetraethoxysilane (TEOS) and (3-mercaptopropyl) trimethoxysilane (MPTMS) were studied on a copper substrate. The silane solution was prepared by dissolving silane agents in a mixture of distilled water and ethanol and the coating on the copper substrates was applied by a simple dip-coating method. Fourier-transform infrared spectroscopy test showed that this coating has bonded well with the copper surface, and the coating has been formed. The protective properties of covered and uncovered copper specimens was investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The Alkoxysilanes Coatings presented excellent inhibition effect to the copper corrosion and stability in water containing Cl−. Furthermore, the surface morphological study by scanning electron microscopy (SEM) showed that the ball like silica particles have been distributed on the copper substrate with particle sizes ranging from 75 to 250nm.

The corrosion behavior of inert titanium anode with ruthenium oxide coating and without coating was studied in molten calcium chloride salt at 950˚C. The Titanium was coated with Ruthenium oxide by the thermal decomposition method. Then, these anodes was placed in the electrolysis cell via the FFC method and cathode was polarized relating to the reference electrode in constant potential value of -1.6v and its corrosion behavior by microscopic studies was investigated. The morphological studies were performed by SEM, the distribution of elements was studied by EDS method. Studies have shown that the coating on the anode, the thickness of the oxide layer formed on the surface of the anode to uncoated anode greatly reduced and the Ti/RuO2 anode made showed two different functions due to exposure to calcium chloride molten salt and during the electrolysis. Part of the coating because of reacting with the released chlorine of molten salt decomposition, was separated from the substrate surface and dissolved in the melt by forming a chloride compound. Also a part of ruthenium during electrolysis and because of diffusion, has penetrated into the titanium of substrate and the intermetallic compound has been formed. So by the time, the ruthenium oxide coating improves the corrosion resistance of the anode by penetrating into the titanium.

In the present work, Ni-W-PCTFE nanocomposite coatings were electrodeposited in the presence of different concentrations of polychlorotrifluoroethylene (PCTFE) from the tartrate bath on the plates of copper. The effect of the concentration of PCTFE was investigated on the corrosion resistance. Surface morphology and composition of the nanocomposite coating were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) measurements. Corrosion resistance of produced coatings were evaluated using open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and polarization techniques in 3.5% wt NaCl solution. The results of these studies show a significant shift in the corrosion potential toward noble potentials, decrease in the corrosion current density and increase in the charge transfer resistance with the incorporating of PCTFE particles in the Ni-W matrix. While The lowest corrosion current (5 ×10-5A cm-2) and the highest charge transfers resistance (19686 Ω cm2) for nanocomposite coatings obtained from the bath containing 4 g/L PCTFE.

Electroless Ni-P coatings have found a variety of applications due to their unique properties. For improvement of the electroless nickel-phosphorous binary coatings qualities, addition of a third element is being developed. Meanwhile, Cobalt as an effective element in improving the coatings characteristics such as corrosion and wear resistance, hardness, electromagnetic properties, etc., has attracted attentions of many researchers. In this study, applying the electroless Ni-Co-P alloy deposit on St37 substrate was considered and the achieved coating was heat treated at 400oC for 1 hour. Influence of bath parameters such as pH, concentration of cobalt sulphate and reducing agent on plating rate was investigated. Morphology and composition of the coatings were characterized by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Corrosion behavior of the binary and ternary alloy deposits were characterized using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) confirming the effect of cobalt addition on improvement of the coatings corrosion resistance.

Phosphate conversion coating is one of the conversion coatings that have high applications indifferent industries due to the good corrosion resistance. In this study, anti-corrosion resistance of the zinc phosphate conversion coatings on cold rolled steel (CRS) with different immersion times (1, 5 and 25 min), different solution temperatures (37-57 ° C) and different pH values (1.7, 2.7, 3.7, 4.7 and 5.7) was studied, using direct current (DC) polarization and electrochemical impedance spectroscopy (EIS). Electrochemical results revealed that the best anti-corrosion resistance from zinc phosphate conversion coating was obtained in 47 °C, immersion time of 25 minutes and pH =2.7. In this point the polarization resistance (Rp) value is 225 times higher than the bare sample polarization resistance (Rp: 0.39 kΩ.cm2). Also the morphology of coated sample in optimum condition by using a field emission scanning electron microscope (FE-SEM) was evaluated. The granular structure and uniform distribution of crystals on the sample surface is a reason to confirm the obtained results from electrochemical tests for optimized sample.

This study investigated the corrosion of low alloy steel weld areas A517 – grade B contains (HAZ-Base-Weld) and the coupling of the areas surveyed. For welding of A517 steel plate welding (SMAW) electrode (E11018 M) then samples were used for cyclic polarization tested, TOEFEL and immersion test was developed and tested. Insomuch this type of steel in the structure of the submarine application and check corrosion levels of welding, especially at depths greater than 250 meters is important, the sensitization of the heat affected zone(HAZ) is not caused by welding but excellent corrosion resistance in the region has created.

In this work, the effect of metallurgical factors on corrosion behavior of Zr-1%Nb in %3.5 NaCl media at 60oC was investigated. After different processes, the microstructure of the treated alloy was analyzed by optical and scanning electron microscopes. Corrosion behavior of the specimens was evaluated by electrochemical impedance spectroscopy (EIS) and potensiodynamic polarization. The results showed that addition of Nb as alloying element, result in increasing both the hardness and polarization resistance of the alloy. While strengthening by deformation process led to refining the grains of the alloy but it had reverse effects on corrosion behavior of the alloy as it decreased the polarization resistance, up to 7 times less than untreated sample. This shows that it is necessary to optimize the conditions of deformation process to access high strength alloy together good corrosion resistance.