Papers by Masoud Zakeri
Corrosion Science, 2011
Inhibitive performance of some synthesized thiophenol derivatives on corrosion behavior of mild s... more Inhibitive performance of some synthesized thiophenol derivatives on corrosion behavior of mild steel in 0.1M HCl solution was investigated by means of electrochemical techniques, quantum chemical and optical microscopy. The increase in concentration and immersion time shows a positive effect on inhibition efficiency while temperature has a negative effect. Inhibitor molecules directly adsorb at surface on the basis of donor–acceptor
The transition potential and the repassivation potential of AISI type 316 stainless steel was inv... more The transition potential and the repassivation potential of AISI type 316 stainless steel was investigated in the absence and the presence of 0.01 M thiosulfate in chloride containing media. The pencil electrode method was employed to explore the key factors affecting the pit transition potential and the repassivation potential in thiosulfate containing solution. Using this method the pit chemistry at various temperatures was also evaluated. A good correlation was found between the pitting potential and the pit transition potential at various temperatures. Moreover, there was a significant decrease in the repassivation potential by addition of 0.01 M thiosulfate. The results were in accordance with the theory suggesting that the chemistry of the pit governs the pit repassivation potential.
The effect of dichromate ions on the corrosion behaviour of 316 stainless steel was investigated ... more The effect of dichromate ions on the corrosion behaviour of 316 stainless steel was investigated in 0.1 M NaCl solution by electrochemical measurements and electron microscopy. The results revealed that the addition of dichromate increases the resistance to pitting corrosion as the pitting corrosion does not occur in the presence of 0.05 M dichromate ions at room temperature. The mechanistic studies showed that the increase in pitting corrosion resistance in presence of Cr2 O7 2 is due to the decrease in the meta-stable pit initiation, lower kinetics of metastable pit dissolution and increase in the survival probability of the pit formation.
The influence of grain size on pitting corrosion of 304L stainless steel in 3.5 wt.% NaCl solution... more The influence of grain size on pitting corrosion of 304L stainless steel in 3.5 wt.% NaCl solution was investigated by electrochemical methods employing the statistical approach. The potentiodynamic results revealed that grain refinement has no effect on the pitting potential. To understand the reason of ineffec-tiveness of grain size on pitting potential of 304L stainless steel, potentiostatic tests were conducted. Evaluation of current transients observed in potentiostatic tests revealed that the frequency of meta-stable pit initiation decreases with grain refinement. However, grain size reduction increases the kinetics of metastable pits dissolution and the probability of transition from metastable pitting to stability.
This article provides a better understand ing of dichr omate effect on the critical pitting tempe... more This article provides a better understand ing of dichr omate effect on the critical pitting temperature (CPT)
of 316 SS in chloride solution. Potentiostatic measure ments revealed that dichromate effectively
improves the CPT. In the presence of dichromate ion, a remarkable decrease in the anodic dissolution
in simulated pit environmen t and a slight decrease in the saturation concentration of cations in pit solu-tion were defined in pencil electrode experiments. Scanning electron microscopy showed that, in com-pare with pure chlor ide solution, the pits formed on the metal surface in dichromate containing
solution, have finer lacy covers.
In the present part of study, the effect of thiosulfate ion on pitting corrosion of AISI 316 stai... more In the present part of study, the effect of thiosulfate ion on pitting corrosion of AISI 316 stainless steel in 0.1 M NaCl solution was investigated. In order to elucidate the effect of thiosulfate on pitting corrosion, the metastable pitting has been studied in more details. The results showed that the thiosulfate addition increased susceptibility to pit initiation and increased the dissolution kinetics of metastable growing pits in a fashion that facilitates the transition from metastability to stability. Consequently, the pitting potential of the stainless steel was decreased in the presence of thiosulfate ion.
In this research, the effect of thiosulfate ion on pitting corrosion behavior of 316 stainless st... more In this research, the effect of thiosulfate ion on pitting corrosion behavior of 316 stainless steel was studied. Part I of this work deals with the influence of thiosulfate on the critical pitting temperature of 316 SS in 0.1 M chloride solution and studies the effect of this ion on the pit chemistry. Electrochemical experiments performed in absence and presence of 0.01 M thiosulfate ion revealed that thiosulfate deteriorates the CPT. Pencil electrode studies showed that thiosulfate addition decreases both saturation concentration of metal cations necessary to metal salt precipitate at the pit bottom (CS) (the value of diffusion controlled limiting current density (iLim) was decreased) and the ratio of C*/CS (where C* is the critical concentration of metal cations in pit solution essential for a pit to remain stable) while it increases the anodic dissolution rate in a simulated pit solution. Furthermore, scanning electron microscopy showed that the lacy cover formed over the pits mouth has coarser pore structure in the presence of thiosulfate ion.
Investigation on influence of the nitrate ion on critical pitting temperature (CPT) of DSS 2205 i... more Investigation on influence of the nitrate ion on critical pitting temperature (CPT) of DSS 2205 in 0.6 M NaCl media is the aim of this research. Results revealed that 0.01 M NO3 has negligible effect on CPT, while 0.1 M NO3 causes CPT to shift to a value more than 85 C. Then, a mechanistic approach using pencil electrode was sought based on proposed theory defining CPT as a temperature at which critical current density necessary for passivity (icrit) equals to limiting current density (ilim). Results indicate that nitrate ion increases CPT by increment in ilim and slight decrement in icrit.
In this study critical pitting temperature (CPT) of two stainless steels is compared using EIS, p... more In this study critical pitting temperature (CPT) of two stainless steels is compared using EIS, potentiodynamic and potentiostatic techniques. Two types of stainless steels including DSS2205 and 20Cr–28Ni were chosen. EIS measurements were carried at anodic potential of 600 mV/SCE and the results were compared with those of potentiodynamic and potentiostatic polarisations. The results revealed that the CPT of DSS2205 and 20Cr–28Ni was between 45–55 C and 35–45 C in potentiodynamic polarisation, respectively. It was 60 and 55 C for potentiostatic method and between 55–60 C and 45–55 C in EIS method for DSS2205 and 20Cr–28Ni, respectively.
Inhibitive performance of some synthesized thiophenol derivatives on corrosion behavior of mild s... more Inhibitive performance of some synthesized thiophenol derivatives on corrosion behavior of mild steel in 0.1 M HCl solution was investigated by means of electrochemical techniques, quantum chemical and optical microscopy. The increase in concentration and immersion time shows a positive effect on inhibition efficiency while temperature has a negative effect. Inhibitor molecules directly adsorb at surface on the basis of donor–acceptor interactions between the p-electrons of benzene, sulfur and nitrogen atoms and the vacant d-orbitals of iron atoms. According to the thermodynamic parameters, present inhibitors adsorb physically. Optical microscopy examinations demonstrate a decrease in corrosion attacks in presence of inhibitors.
Conference Presentations by Masoud Zakeri
Critical pitting temperature (CPT) has been defined by Salinas-Bravo and Newman as a temperature ... more Critical pitting temperature (CPT) has been defined by Salinas-Bravo and Newman as a temperature at which i lim =i crit where i lim is the diffusion limiting current density as a result of salt precipitation and i crit is the critical (maximum) current density necessary for passivity in pit solution (1). The positive effect of nitrate ion on CPT of 2205 by increasing it towards higher temperatures due to its increasing effect on i lim was presented in detail elsewhere(2). The objective of this work is to validate the theory mentioned above by investigating the effect of nitrate ion addition in chloride containing solution on critical current density of a 2205 duplex stainless steel (DSS 2205). Potentiodynamic polarization tests were conducted on 200 μm diameter DSS 2205 in a 5M HCl solution assuming creates simulated pit environment(3). To identify the effect of nitrate ion addition to the solution containing chloride ion, the critical current density for passivation on a DSS 2205 specimen annealed at 1050°C was measured in 5M HCl and 5M HCl+0.1M NaNO 3 solutions. Mentioning that addition of 0.1M NaNO3 to a 0.6M NaCl solution causes an increase of 30°C in CPT of DSS 2205(4). Typical anodic polarization curves of specimen annealed at 1050°C obtained in 5M HCl and 5M HCl+0.1M NaNO 3 solutions at different temperatures are illustrated in (a) and . Depicted curves show that passivity occurs at temperatures up to 45°C and 55°C for 5M HCl and nitrate containing solution respectively. At temperatures higher than 45°C and 55°C, passivity does not occur and after a maximum current density g salt film precipitates and a diffusion controlled dissolution (dissolution under the salt) is established. The fluctuations in current density observed at diffusion control region is believed to be due to localized passivation followed by rapid reactivation under the salt film(5). An increasing trend of Maximum current densities is observed for all conditions shown in fig 2. It is obvious that critical current density is marginally affected by nitrate ion addition and its values and also the slope of i crit vs. temperature curve is slightly changed for nitrate containing solution in comparison with ones without nitrate. According to the effect of nitrate ion addition on both limiting current density (i lim )(2) and critical current density (i crit ) of DSS 2205, it can be concluded that increase in critical pitting temperature (CPT) of DSS 2205 is a consequence of change mainly in i lim rather than i crit values. These results are in a good agreement with CPT theory proposed by Salinas-Bravo and Newman . According to their proposed mechanism for CPT, the CPT can be affect by change in diffusion limiting current density, pit critical current density for passivation or both. The effect of addition of nitrate in increasing CPT can be related to an increase on diffusion limiting current density, although its addition has also changed marginally on critical current density. Figure 1. Potentiodynamic polarization curves of DSS 2205 alloy solution annealed at 1050°C mV in a) 5M HCl and b) 5M HCl+0.1M NaNO 3 solutions at different temperatures. Scan rate is 5 mV/Sec Figure 2. Critical current density vs. temperature obtained from potentiodynamic polarization curves of DSS 2205 alloy.
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Papers by Masoud Zakeri
of 316 SS in chloride solution. Potentiostatic measure ments revealed that dichromate effectively
improves the CPT. In the presence of dichromate ion, a remarkable decrease in the anodic dissolution
in simulated pit environmen t and a slight decrease in the saturation concentration of cations in pit solu-tion were defined in pencil electrode experiments. Scanning electron microscopy showed that, in com-pare with pure chlor ide solution, the pits formed on the metal surface in dichromate containing
solution, have finer lacy covers.
Conference Presentations by Masoud Zakeri
of 316 SS in chloride solution. Potentiostatic measure ments revealed that dichromate effectively
improves the CPT. In the presence of dichromate ion, a remarkable decrease in the anodic dissolution
in simulated pit environmen t and a slight decrease in the saturation concentration of cations in pit solu-tion were defined in pencil electrode experiments. Scanning electron microscopy showed that, in com-pare with pure chlor ide solution, the pits formed on the metal surface in dichromate containing
solution, have finer lacy covers.