مجله علوم و مهندسی خوردگی
سال سوم شماره 4 (پیاپی 10، زمستان 1392)

Corrosion behavior of Nickel-Aluminum bronze alloy was studied in 3.5%NaCl aqueous solution in the absence and presence of sulfide anion using a common experiment setup of electrochemical noise. Data were recorded during 7 days at ambient temperature and were transferred into time and frequency domains. Also, localization index and noise resistance were investigatedas a function of time in the solutions containing 50 and 100ppm sulfide anion. Morphology of the surface destruction was studied using scanning electron microscope equipped with energy dispersive X-ray spectroscopy. Localization index was constant value of 1 in all cases that confirmed it cannot be used as a reliable parameter for determining of corrosion category. Increasing and decreasing of Roll-Off slope could be attributed respectively to the breakdown and repair of the passive film. In the presence of 50ppm sulfide ions, Roll- Off Slope of the potential power spectral density plots of the potential noise was increased and approached pitting corrosion. Small increase resistance noise and Roll-off power spectrum densities curves in 100ppm concentration of sulfide ions after 7days immersion might be attributed to the formation of a porous film. Increasing of power spectrum densities curves showed increasing of tendency to corrosion. Surface analysis of nickel-aluminum bronze in 50ppm concentration showed surface tears and some corrosion in film passive and in the presence of 100ppm sulfide ions;a porous sulfide film was formed.

In this paper, Cr-TiO2 nanocomposite coatings with various contents of TiO2 nanoparticles were prepared by electroplating method on low carbon steel substrate from St.37 plate substance. The nanocomposite coatings were obtained by codeposition of TiO2 nanoparticles with the average particle size of 21 nm, 99.5% purity degree and anatase crystal structure prepared from Evonik Company with Chromium during plating process. The coating thickness average was 30 μm on low carbon steel substrate from St.37 plate substance. The influences of the TiO2 nanoparticles concentration in the plating bath,the current density and the stirring rate on the chemical composition of Cr-TiO2 nanocomposite coatings were investigated. The surface morphology and composition of coatings was investigated by scanning electron microscope (SEM) with energy dispersive analyzer system (EDX). The wear behavior of the pure Chromium and Cr-TiO2 nanocomposite coatings were evaluated by a pin-on-disc tribometer and The worn surface of coatings was observed using a scanning electron microscope (SEM). The electrochemical behavior of the coatings in the corrosive solutions such as 0.5M NaCl, 1M NaOH and 1M HNO3 was investigated by potentiodynamic polarization method at 25±1 °C temperature. It was found that The Cr-TiO2 nanocomposite coating surface morphology is smoother, more uniform and compact surface in appearance compare to that of pure Chromium coating and The codeposited TiO2 nanoparticles were uniformly distributed in the Chromium matrix. The microhardness and wear resistance of the nanocomposite coatings increase with increasing of TiO2 nanoparticles content in the coating. The worn surface morphologies show that the Cr-TiO2 nanocomposite coatings exhibit less abrasive width and depth and less tendency for plastic deformation when compare to that of pure Chromium coating. It is obvious that with increasing of TiO2 nanoparticles content in coating, the corrosion current density decreased and the corrosion potential of the coatings shifted to more positive potential values in 0. M NaCl and 1M NaOH solutions. Also, The Polarization resistance (Rp) increased with increasing of TiO2 nanoparticles content in coating. As Cr-8.3wt.%TiO2 nanocomposite coating polarization resistance in 0.5M NaCl and 1M NaOH solutions reached to 3.954 and 5.631 MΩ.cm2 respectively. It can be concluded that the codeposited TiO nanoparticles in Chromium matrix of coating increase the corrosion resistance and decrease the corrosion rate in salty and alkaline solutions. In anodic region of polarization curves of pure Chromium coating and Cr-TiO2 nanocomposite coatings in 1M HNO3 solution, Passive layer formation is observed. Passive layer formation current density of Cr TiO2 nanocomposite coatings (about 0.02A/cm2) is less than that of pure Chromium coating (about 0.03A/c 2). On the other hand, passive layer formation potential of Cr-TiO2 nanocomposite coatings (about 288mv) is more negative compare to that of pure Chromium coating (about 478mv). It can be concluded that presence of Ti 2 nanoparticles in Chromium matrix of coating aids to formation of passive layer. The passive current density of Cr-TiO nanocomposite coatings (about 10-4A/cm2) is more than that of pure Chromium coating (about 10-5 A/cm2). It means that passive layer corrosion rate of Cr-TiO2 nanocomposite coatings is more than pure Chromium coating because of The presence of TiO2 nanoparticles in the coating surface disturbs the continuity of nanocomposite coating passive layer and accelerates the destruction of passive layer which causes to increasing of corrosion rate. It can be concluded that Cr-TiO2 nanocomposite coatings is not a proper coating in HNO3 solution.

Laboratory (lab) simulation is a suitable method to apply theoretical principles in order to identify effective parameters in stray direct current (DC) influenced corrosion. Simulation techniques can be utilized for various mitigation methods applied in a small scales for selection of the most efficient method with regards to field applications. In this research, laboratory simulation of potential fluctuations caused by DC stray currents on a cathodically protected pipeline was investigated. A lab model capable of generating DC static and dynamic stray currents and simulating its effects on cathodically protected samples were developed. Stray current pick-up and discharge areas on an influenced structure were simulated by inducing fluctuations in the coupon stationary potential (cathodic protection (CP) potential), which normally happens as a dynamic stray current interference. An equivalent electrical circuit was also developed for the lab model. Mitigation methods for DC stray current interference on buried structures such as application of both sacrificial anodes as preferred discharge point for DC stray current and potential controlled cathodic protection system (namely intelligently controlled CP for structures with induced DC dynamic potentials) were investigated. Results showed that the latter technique could decrease interference more effectively and to a larger degree than that of the former one.

In recent years, the pulse current has been received much attention in electrolysiss process such as electroplating, electrodeposition, anodziing and electrosynthesis of metal oxide and composites. The mechanical, chemical and other properties of the electrolsiys products can be improved by using Pulse current. In electrolysis, mass transfer and electrocrystalization phenomena are affected by the pulse current. This paper reviews the effects of pulse current on the electrolysis and related phenomena such as current distribution, composition, structure and properties of the products of electrolysis.

In this paper, alumina hybrid nanostructured coating involving different amount of nano encapsulated organic inhibitor, Benzotriazole, such as, 1.8, 3.6 and 5.4 % has been applied by sol-gel method through a dip-coating process on Aluminium alloy 2024 as a substrate. Phase structural, morphologicalproperties, Corrosion behavior and nano-mechanical properties have been evaluated by using GIXRD, SEM and FESEM, tafle polarization according to ASTM G59 standard and electrochemical impedance spectroscopy in 3.5% NaCl solution, nano indentation and nanoscratch analyses, respectively. The results showed the homogeneity and uniformity of the coating and increasing in the resistance corrosion of Aluminium 2024 by preventing nucleation and growth of cracks through a migration of Benzotriazole inhibitors from the nano-containers, and also improving hardness and ductility, especially at optimum amount 3.6% of Benzotriazole.

In this paper, current requirement for cathodic protection of low carbon steel that coated by coal tar polyamide coating under synergistic effect of environmental parameter has been studied. This project is mainly focused on the effect of temperature, velocity, salinity and pH, which are the most important factors, that can affect on protective current from corrosion. Assess the percentage of cumulative and individual effect of factors on protective current was computed by the analysis of variance (ANOVA) via full two-level factorial experiment. Moreover, qualitative analysis has been studied to predict the path variation of current required for cathodic protection under individual and cumulative parameters. The overall results, that get from these two analysis of individual and cumulative effect of parameters on protective current, was shown that cumulative effect of parameters are more important and effective than individual effect of parameters on current requirement for cathodic protection in seawater. Considerable, according to the results, among the factors, temperature is the most affecting factors on protective current for cathodic protection and coal tar polyamide coating has shown good resistance against pH variations.

In this paper, the electrodeposition of DLC films on carbon steel from aqueous acetic acid solutions is investigated. The process is performed at room temperature at relatively low cell voltages with entirely green chemicals. Electrodeposition has been followed by current transient measurements, yielding mechanistic information on the time-dependence of the growth process. Qualitative and quantitative evaluation of C hybridisation type has been performed by Raman spectroscopy. Microhardness and adhesion of the supported electrodeposited films have been measured by micro-indentation and scratch-testing. Notably, ductile failure was found in correspondence of a wide range of film growth conditions. The corrosion resistance of DLC-coated steel has been assessed by electrochemical impedance spectrometry in neutral chloride solution. Optimal electrodeposition conditions were identified for the formation of high-quality DLC films ca. 250 nm thick with a high content of diamondcoordinated carbon and an ideal combination of hardness and adhesion; films formed under these conditions also confer some degree of corrosion protection to the carbon steel substrate.