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۱Corrosion Investigation of Polypyrrole–Coated Mild Steel Using Electrochemical Impedance Spectroscopy
نویسنده(ها): ، ،
اطلاعات انتشار: دهمین کنگره ملی خوردگی ایران، سال
تعداد صفحات: ۷
Conductive polymer coatings can be prepared from electro conductive polymers such as polypyrrole. Pyrrole monomer has been proven to be an effective corrosion inhibitor for steel, while its polymer has been shown to protect steel from corrosion in different electrolytes. One of the major variables in the deposition of polypyrro1e coatings on metallic substrates is electro deposition over potential In this research. electrochemical impedance spectroscopy (EIS) was performed during the deposition of polypyrrole on a mild steel substrate at different over potentials. Electro deposition was carried out in aqueoussolution containing 0.1 M oxalic acid and 0.2 M pyrrole. According to the charge transfer resistance of electro deposition at various over potentials, three distinct regions of potentials including 10–60 mY. 60–90 mV and above 90 mV were determined. In each region, the variation of the charge transfer was constant, but different from other regions. Electro deposition of pyrrole was performed galvanostatically at these three potential regions. Corrosion resistance of mild steel substrates coated by polypyrrole in each region was investigated in 0.1 M NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. According to corrosion data. the corrosion resistance of polypyrrole coated mild steel as a function of electro deposition over potential was obtained and presented. In addition, Scanning Electron Microscopy (SEM) was employed to investigate the characteristics ofcoatings produced.<\div>

۲Electrochemical Behavior of drogen Sulfide
نویسنده(ها): ، ، ،
اطلاعات انتشار: دهمین کنگره ملی خوردگی ایران، سال
تعداد صفحات: ۱۱
Electrochemical behavior of A516 Gr60 carbon steel in Diethano1amine (DEA) solutions containing hydrogen sul:fide (lI.2S) at pH=1O.2 was investigated. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS)
techniques were performed at various temperatures within the range of 25°e to 800e and different concentrations of DEA. Results obtained showed that in the presence of H2S, a meta–stable passive sulfide :film is funned on the su.rfilce and corrosion current density is increased. By increasing temperature and amine concentration, corrosion
potential and icon– increased and passive stability region decreased. Nyquist plots from EIS results revealed two time constants fur corrosion processes; a capacitive loop with a depressed semicircle at high frequencies due to charge transfer and a straight line at low frequencies region due to Warburg diffusion. The EIS results were then fitted with
equivalent circuits. Results obtained indicated that diffusion of Fe2+ ions (produced from anodic dissolution) and atomic hydrogen (Hj (produced from reduction of HS· ions) across the sulfide :film is a rate determining step. Warburg coefficient (s) extracted from Randles plots (Zre Vs 0)11l) decreased by increasing the amine concentration and this indicates that compaction of sul:fide film has decreased. By increasing the temperature, the diameter of the first capacitive loop decreased.<\div>

۳Investigation of Pitting Corrosion of Carbon Steel in Rich Diglycolamine Units
نویسنده(ها): ، ،
اطلاعات انتشار: دهمین کنگره ملی خوردگی ایران، سال
تعداد صفحات: ۹
Pitting corrosion of carbon steel in rich diglycolamine solutions from gas sweetening units was investigated using potentiodynamic cyclic anodic polarization. potentiostatic measurements, scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) techniques. The solution used contained 28000 ppm hydrogen sulfide <H2S) and pH was about 8.7. Experiments were done at various temperatures 43, 55, 66 and 80aC for the evaluation of the effects of temperature on the tendency of carbon steel to pitting corrosion. Results obtained showed that a hysteresis loop appeared at reverse scan in cyclic polarization curves, which is evidence on the occurrence of pitting corrosion. SEM observations confirmed the existence of pits on the electrode surface, Plant data from absorption tower and heat exchanger pipes con:finned these results, Increasing the size of hysteresis loop with temperature indicates that tendency to pitting corrosion increases in rich amine solution. Because of the dependence of the values of Epa and ~ to scan rate in cyclic curves, the exact values for pitting potential and protection potential were obtained from potentiostatic curves. By increasing the temperature, E¢t and ~ decreased. EDS micro analysis showed
that there was no :film or very poor :film with low sulfur contents in pits, in compare with the unaffected surface ofpits.<\div>

۴Saccharin Effects on Ni\Co Nanocrystalline Electrodeposited Coati ngs
نویسنده(ها): ، ،
اطلاعات انتشار: دهمین کنگره ملی خوردگی ایران، سال
تعداد صفحات: ۸
A nancrystalline coating ofNilCo was deposited on a carbon steel substrate. This wasdone via electrodeposition in a Watts–type bath using direct current. The current density used was 12mAcm–2 • Grain size and characteristics of the coatings produced were investigated using various techniques including X–ray Diffraction (XRD), Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscopy (SEM). XRD patterns and Scherer fornmla were used to determine the grain size ofthe coated layer. Results obtained showed that the saccharin added to the bath decreases grain size. The effect of saccharin. (I g.rl
) as an additive for grain refining was investigated by (EIS). The EIS results showed that saccharin increases charge transfer resistance, and thus, decreases the surface diffusion of adions. It was also found that saccharin has a significant effect on decreasing the growth kinetics of grains and blocking the active sites of growth as well. Also, SEM observations revealed that saccharin inhibits pyramidal growth, and concomitantly reduces surface roughness and thus, increases surface brightness.<\div>

۵Modified nanosilica\ HDPE–g–MA coating on steel by cast–solution method: Superhydrophobicity and corrosion resistance
نویسنده(ها): ، ، ،
اطلاعات انتشار: دومین کنفرانس بین المللی کامپوزیت، سال
تعداد صفحات: ۶
In this study, polyethylene superhydrophobic coatings containing chemical modified nanosilica on carbon steel were prepared by solution casting method. Silica nanoparticles were modified with vinyl tri methoxy silane (VTMS) by 18 mole ratio of VTMS to surface hydroxyl of nanosilica. Composite mixtures consisting of maleic anhydride grafted high density polyethylene (HDPE–g–MA) and different amounts of modified nanoparticles in xylene were casted on steel surfaces and then coated by evaporation of xylene. Wetting measurement showed that by increasing the amount of modified nanosilica, water contact angle on the surface of coatings increased and sliding angle decreased. So that the maximum contact angle (150.2˚) and the minimum sliding angle (8˚) were achieved at 215 part per hundred gram polymer (phr) of modified nanoparticles. This improved hydrophobicity is attributed to the surface structure of modified nanosilica arises from chemical surface modification. Microstructure of these coatings was investigated by using scanning electron microscopy. Also, it was shown, from the Tafel test, that these coatings on steel surface exhibit an excellent corrosion resistance in chloride containing solution at the room temperature.<\div>

۶Effect of Morphology on the Corrosion Performance of Polypyrrole Conductive Coatings
نویسنده(ها): ، ،
اطلاعات انتشار: چهاردهمین همایش بین المللی نفت، گاز و پتروشیمی، سال
تعداد صفحات: ۱۴
so far electropiolymerization bath for producing polypyrrole coating has consisted of two main constituents; monomer and counter –ion . In the present study polypyrrole was galvanostatically deposited onto carbon steel in aqueous solution containing 0.2 Mpyrrole and 0.1 M oxalic acid with 0.25,0.5,2.5g\l and without saccharin addition estimation of corrosion resistance of coatings emerged in 0.1 M NaCl solution revealed that coating produced with 0.5g\l saccharin addition has more noble corrosion potential and greater corrosion resistance. atomic force microscopy illustrated greater compaction of the coating produced in the presence of 0.5 g\l saccharin. it could be the reason for its higher corrosion resistance. thus adding sasccharin as the third constituent intoduced a new branch in electropolymerization polypyrrole coating with modified surface morphology.<\div>
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