Effect of acetic acid on CO2 corrosion of carbon steel in NaCl solution

Potentiodynamic sweep and electrochemical impedance spectroscopy measurements were applied to investigate the effects of both temperature and acetic acid (HAc) on the anodic and cathodic reactions in CO₂ corrosion of P110 steel in 3.5% NaCl solution. The temperatures were controlled at 30 and 60 °C. The concentrations of HAc were controlled at 0, 1000, 3000 and 5000 ppm. In this work, the corrosion parameters of polarization curves, such as corrosion potential (E_corr), corrosion current density (i_corr), and anodic and cathodic branch slopes (b_a and b_c), are presented and discussed in detail. In addition, the equivalent circuit models and ZsimpWin software were utilized to discuss the Nyquist plots. The plots showed that the E_corr values shifted in the positive direction as the HAc concentration increased. The i_corr values increased with the increase in HAc concentration, indicating that HAc could accelerate the corrosion. The impedance spectra measured at 30 and 60 °C have different time constants and characterization. The coverage fraction θ and the thickness L of corrosion film are two most important controlled variables that influence and control the CO₂ corrosion mechanisms. Copyright © 2010 John Wiley & Sons, Ltd.     

Formation of artificial micro‐pits on Al alloy with the photon rupture method and the localized corrosion behavior of the formed pits

An in situ artificial micro‐pit fabrication method with an area selective electrochemical measurement technique was applied to investigate the effect of the geometry of artificially formed pits on their localized corrosion behavior in anodized 1000 series aluminum. This technique enables the fabrication of artificial micro‐pits with different aspect ratios (pit depth/pit diameter) in solutions. The aspect ratios of the fabricated artificial micro‐pits in this experiment could be varied from 0.13 to 1.83 by controlling the irradiation time of the focused pulsed YAG laser beam. By applying a constant potential to the final laser‐beam‐irradiated spot in chloride environments, localized dissolution occurred only at the laser beam irradiated area, because the anodic oxide film acted as an insulator. The corrosion current and charge increase with increasing aspect ratio at any applied potential. Copyright © 2010 John Wiley & Sons, Ltd.     

Pitting behavior on super 13Cr stainless steel in 3.5% NaCl solution in the presence of acetic acid

The pitting behavior was investigated on super 13Cr stainless steels in 3.5% NaCl solution in the presence of HAc. The electrochemical measurements including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and chronoamperometric experiments were carried out, as well as the SEM surface analysis. The parameters such as E _corr and I _corr were obtained by fitting technique. Moreover, the equivalent circuit model was applied in the analysis of Nyquist plots, and ZsimWin software was used to analyze the EIS data. The results indicate that the pitting corrosion is accelerated with increasing the amounts of HAc. In addition, pitting nucleation and growth mechanisms were described in this work.     

Effect of Acetic Acid on Saccharomyces Carlsbergensis ATCC 6269 Batch Ethanol Production Monitored by Flow Cytometry

Bioethanol produced from lignocellulosic materials has been considered a sustainable alternative fuel. Such type of raw materials have a huge potential, but their hydrolysis into mono-sugars releases toxic compounds such as weak acids, which affect the microorganisms' physiology, inhibiting the growth and ethanol production. Acetic acid (HAc) is the most abundant weak acid in the lignocellulosic materials hydrolysates. In order to understand the physiological changes of Saccharomyces carlsbergensis when fermenting in the presence of different acetic acid (HAc) concentrations, the yeast growth was monitored by multi-parameter flow cytometry at same time that the ethanol production was assessed. The membrane potential stain DiOC₆(3) fluorescence intensity decreased as the HAc concentration increased, which was attributed to the plasmic membrane potential reduction as a result of the toxic effect of the HAc undissociated form. Nevertheless, the proportion of cells with permeabilized membrane did not increase with the HAc concentration increase. Fermentations ending at lower external pH and higher ethanol concentrations depicted the highest proportions of permeabilized cells and cells with increased reactive oxygen species levels. Flow cytometry allowed monitoring, near real time (at-line), the physiological states of the yeast during the fermentations. The information obtained can be used to optimize culture conditions to improve bioethanol production.     

Influence of caffeine and temperature on corrosion-resistance of CoCrMo alloy

The inhibitory activity of caffeine (1,3,7-trimethyl xanthine) on artificial saliva was studied on a CoCrMo alloy using different electrochemical methods: open circuit potential (OCP), potentiodynamic measurements and electrochemical impedance spectroscopy (EIS). The results show that caffeine produces an inhibitory effect on the anodic currents due to its adsorption on the surface of the alloy. Temperature is another parameter with an influence on corrosion processes, so thermodynamic data were obtained from Arrhenius plots and Langmuir adsorption isotherms. The protective action of caffeine is enhanced at high temperatures at OCP, while for potentiodynamic experiments high temperatures block the inhibitory activity of caffeine and the corrosion rate increases. The process may also be studied by a simulation, determining the functional dependence between OCP, corrosion current density (i _corr), corrosion potential (E _corr), breakdown potential (E _bd) and temperature and amount of caffeine in artificial saliva, for Heraenium® CE. The neural network-based methodology applied in this work provides accurate results, thus proving to be an efficient modelling technique.     

Morphological studies of the mechanism of pit growth of pure aluminum in sulfate ion- or nitrate ion-containing 0.1 M NaCl solutions

The mechanism of pit growth of pure aluminum (Al) in sulfate ion (SO₄ ^2–)- or nitrate ion (NO₃ ^–)-containing 0.1 M sodium chloride solutions has been studied in terms of the morphological changes of artificial pits using potentiodynamic polarization experiment, potentiostatic current transient technique and optical microscopy. The increase in SO₄ ^2– and NO₃ ^– ion concentrations in NaCl solution raised the pitting potential E _pit of pure Al, which is ascribed to the impediment to pit initiation on pure Al by the addition of SO₄ ^2– or NO₃ ^– ions. From the potentiostatic current transients of artificial pits in aqueous 0.1 M NaCl solution, the average value of the pit current was observed to increase with increasing SO₄ ^2– ion concentration, whereas that value of the pit current in the presence of NO₃ ^– ions increased up to ca. 0.4 M NO₃ ^– ion concentration and then decreased abruptly with increasing NO₃ ^– ion concentration. From observations of the morphologies of the pits, it appears that the pit grows preferentially in the lateral direction or in the downward direction by adding SO₄ ^2– or NO₃ ^– ions to aqueous 0.1 M NaCl solution, respectively. Based upon the experimental results, two different pit growth mechanisms by anion additives can be proposed: (1) pit growth by the preferential attack of both SO₄ ^2– and Cl^– to the pit wall in SO₄ ^2–-containing solutions; (2) pit growth by the creation of an aggressive environment at the pit bottom up to 0.4 M NO₃ ^– ion concentration due to the lower mobility of NO₃ ^– than Cl^– in NO₃ ^–-containing solutions. Electronic Publication     

The effects of film thickness and incorporated anions on pitting corrosion of aluminum with barrier-type oxide films formed in neutral borate and phosphate electrolytes

The pitting corrosion behavior of high-purity aluminum covered with barrier-type anodic films, which are formed in neutral borate and phosphate electrolytes, has been examined in 0.5 mol dm^?3 NaCl solution at an applied potential of ?0.6 V versus Ag/AgCl, which is slightly nobler than the pitting potential of ?0.64 V in the same solution. The pitting current density, i _p, increased with time after an incubation time, t _i. The double logarithmic plot of i _p and polarization time, t, reveal two straight lines, which are separated at the time, τ. The slope becomes larger after τ for the specimens anodized in the phosphate electrolyte, while it becomes smaller for those in the borate electrolyte. Both the t _i and τ increase with the thickness of the anodic films, and at the similar film thickness, they are much larger for the anodic films formed in the phosphate electrolyte than for those in the borate electrolyte. The corrosion process can be divided into three stages: the incubation period up to t _i, the pit nucleation period before τ, and the pit growth period after τ. We have discussed the different pitting corrosion behavior of the aluminum specimens covered with the anodic films formed in the borate and phosphate electrolytes in terms of ion selectivity of the anodic films.     

Electrochemical instabilities due to pitting corrosion of iron

Electrochemical instabilities induced by chlorides and bromides due to pitting corrosion of iron in sulfuric acid solutions are investigated. Analysis of the electrochemical instabilities as a function of the applied potential and the nature and concentration of the aggressive chemical species shows that the system exhibits a transition from aperiodic bursting of large-amplitude to small-amplitude chaotic oscillations at a critical potential (bifurcation potential, E _bif). The E _bif is determined by the halide concentration inside the pits and coincides with the repassivation potential defined in corrosion studies to explain pit repassivation due to changes in pit chemistry. Surface observations show that, at E < E _bif, an active-passive state dissolution (etching) occurs, while at E > E _bif, a polishing state dissolution is reached. Spatial interactions between early initiated pits and the adjacent electrode surface, oxide film alteration, aggressive species accumulation around active pits, and formation of ferrous salt layers in front of the Fe electrode are all considered to be associated with electrochemical instabilities emerging during pitting corrosion of iron under different dissolution states. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 535–550. The text was submitted by the authors in English.     

Corrosion mitigation on orthodontic wire made of SS 18/8 alloy using esomeprazole tablet (Esiloc-40 mg) in artificial saliva

The corrosion inhibition of orthodontic wire made of SS 18/8 alloy in artificial saliva, with and without the presence of tablet esomeprazole − 40 mg has been investigated by electrochemical analysis. Polarisation study indicates that in the presence of the mentioned tablet, polarisation resistance (R_p) value increases and corrosion current (I_corr) decreases. That is, the corrosion resistance of SS 18/8 alloy in artificial saliva increases. AC impedance spectroscopy reveals that charge transfer resistance value (R_ct) value increases and double layer capacitance value (C_dl) decreases. The open circuit potential (OCP) values for the inhibited system are more negative than that of the uninhibited blank system. The vibration peaks obtained from the FTIR spectra indicates the presence of functional group in esomeprazole pill and these characteristic peaks are slightly shifted in the analyzed scratched film from the surface of the orthodontic wire after immersion. AFM micrograph image of the polished specimen sample immersed in artificial saliva (AS) with esomeprazole tablet solution shows lesser degree of surface deterioration than those for SS 18/8 specimen immersed only in artificial saliva. From the present work, it is reported that people clipped with orthodontic wire made of SS 18/8 alloy need not worry about orthodontic corrosion for taking esomeprazole tablet for the treatment of gastro esophageal reflux disease and other medicinal purpose.     

Pitting Corrosion Mechanisms and Characteristics of Aluminum in Solar Heating Systems

The complex characteristics and mechanisms of aluminum pitting corrosion in a solar heating system were studied by the chemical immersion method and electrochemical techniques as well as fractal theory. The results showed that pitting corrosion of Al occurred in a tap water environment due to the local enrichment of Cl^? ions. The higher the Cl^? ions concentration, the more negative the critical pitting potential (E_b) of Al. A linear relationship between E_b and the logarithm of Cl^? ions concentration was observed. The pitting corrosion mechanism of Al in neutral water was explained in terms of complexation corrosion theory. The corrosion surface images of aluminum immersed in tap water were captured and analyzed by image processing technique and box‐dimension method. The fractal characteristics of pit distribution, described by fractal dimension, have been identified. The fractal dimension of the pit distribution increased with the increase of immersion time and had the same trend as that of the weight loss. Fractal dimension can, thus, be used as an important parameter for quantitative evaluation of pitting corrosion of aluminum.     

Surface characteristics of titanium–silver alloys in artificial saliva

Titanium and its alloys are widely used in biomedical and dental fields because of their excellent corrosion resistance and biocompatibility. It is well known that titanium is protected from corrosion because of the stability of the passive film that controls and determines the corrosion resistance and biocompatibility of titanium and its alloys. The purpose of this study was to evaluate the electrochemical properties of titanium–silver alloys and the surface characteristics of passive film in artificial saliva. We designed titanium–silver alloys with silver contents ranging from 0 to 5 at.%, in 1% increments. These alloys were arc‐melted, homogenized, hot‐rolled to 2 mm thickness, and finally solution heat‐treated for 1 h and quenched. Potentiostatic testing was performed, and the open circuit potentials of the alloys were measured in artificial saliva, at 37 °C. The passive films of the titanium–silver alloys were analyzed via XPS. Titanium–silver alloys maintained low current density and showed stable passive region and also had high open circuit potential as compared with pure titanium. The open circuit potential of titanium–silver alloys increased as silver addition increased. With regard to the fraction of oxygen species, a component of over 80% was found to be comprised of oxide. Therefore, the titanium surface mainly consisted of titanium oxide and, on the titanium–silver alloys, this film was composed of TiO₂, Ti₂O₃, and TiO. As silver content increased, the TiO₂ fraction also increased, as did the thickness of the titanium oxide layer formed. Copyright © 2005 John Wiley & Sons, Ltd.     

Electrochemical and dissolution behavior of the Ti-alloy VT-9 in H2SO4 solution in the presence of the organic inhibitor (2-phenyl-4-[(E)-1-(4-solphanylanilino)methylyden]-1,3-oxazole-5(4H)-one

This investigation potentiodynamically evaluates the corrosion behavior of a high strength titanium alloy, VT-9, in 4 M sulfuric acid solution containing different concentrations (10, 20, 30 ppm) of the organic inhibitor, 2-phenyl-4-[(E)-1-(4-sulfanylanilino)methylidene]-1,3-oxazole-5(4H)-one (L-SH), at different temperatures (293, 303 and 313 ± 1 K). The open circuit potential values noted before and after each experiment varied appreciably with time. These values, in the presence of L-SH, were negative before polarization, but after completion of the experiment turned positive and remained stable over a long period of time. The cathodic current density values increased with increasing cathodic potential (more negative). The corrosion potential (E_corr) increased remarkably with the addition of L-SH. The corrosion current densities (I_corr), critical current density (I_cr), and passive current density (I_p) all decreased when L-SH was used. However, only the decrease in the I_corr with increasing amounts of inhibitor was significant compared to that of I_cr and I_p. L-SH expanded the range of the passive potential. SEM micrographs and open circuit potential measurements revealed the formation of a uniform and protective film on the alloy surface in the presence of L-SH, which acted as an efficient inhibitor.     

Constant-distance mode AC-SECM for the visualisation of corrosion pits

The local visualisation of corrosion pits has so far failed to convincingly prove the advantage of scanning microscopy in overcoming Abbey’s Limit. Thus, for imaging pit initiation and instant pit growth the resolution of the methods used for detecting the related changes in local electrochemical activity has to be significantly improved. Progress into this direction has been achieved by combining shear force based constant-distance mode scanning electrochemical microscopy (SECM) with the alternating current mode of this technique (AC-SECM). A very small corrosion pit was generated by inducing active corrosion underneath an accurately positioned 5 μm diameter Pt disk SECM tip that served as counter electrode in the direct mode of SECM. Before and after pit initiation, constant-distance mode AC-SECM images were recorded and subsequently used to identify the area of broken passivity. The results demonstrate the feasibility of the suggested approach to image actively corroding sites with overall dimensions of only a few micrometers. Combination of constant-distance scanning with AC-SECM is an important prerequisite for further improving spatial resolution by employing smaller-diameter micro- or even nano-electrodes as SECM tips.     

Surface characteristics of AZ91D alloy anodized with various conditions

Anodic oxidation of an AZ91D magnesium alloy was carried out in an attempt to increase the corrosion resistance. The alloy was placed in an electrolyte containing 0.1 M sodium silicate (Na₂SiO₃), 2.0 M sodium hydroxide (NaOH) and 0.1 M sodium phosphate (Na₃PO₄), and treated with a current density of 100–400 mA/cm² for 1 to 4 min. After the anodic oxidation treatment, the surface characteristics were analyzed by SEM, X‐ray diffraction (XRD) and a surface roughness tester. The corrosion resistance was determined by measuring the corrosion potential and corrosion current density using potentiodynamic polarization in a 3.5 wt% NaCl electrolyte solution. Although the anodic oxidation treatment with the base electrolyte resulted in an arrival voltage ranging from 60 to 70 V, the addition of silicate tended to reduce this arrival voltage by approximately 10–20 V and decrease the critical voltage required for the formation of a porous oxide film. The pore size and film thickness increased with increasing applied current and treatment time. The addition of silicate to the electrolyte resulted in films with a homogeneous pore size and a film thickness increasing with the increasing applied current and treatment time. XRD showed the formation of a new MgO and Mg₂SiO₄ phase. The formation of Mg₂SiO₄ was attributed to the presence of SiO₄^4? in the film. After the addition of silicate, the corrosion potential increased and corrosion current decreased, resulting in improved corrosion resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrochemical corrosion kinetics of tin and tin amalgams in NaCl aqueous solutions

Electrochemical techniques were used to determine the corrosion rate of pure tin metal as compared to 80 Sn/20 Hg tin amalgam. X-ray diagrams showed that this amalgam was a crystalline γ₂ phase, whereas a 50 Sn/50 Hg amalgam contained liquid alloy embedded in the same γ₂ phase. Open circuit potential measurements, combined with narrow range potential scanning voltammetry, lead to the conclusion that amalgamation resulted in enhancement of the corrosion current, mainly by increasing the cathodic electron transfer reaction kinetics both in deaerated and in oxygen-saturated NaCl solution. When maintained at zero current potential in a solution containing dissolved O₂ gas, the samples were gradually covered with an insulating oxide layer which was identified by a series of electrochemical impedance diagrams recorded at different time intervals. The oxide layer was firmly adherent to the bulk tin metal but was poor at protecting the amalgam electrode. Finally, at potential values where the anodic current reached a few mA/cm², the pure tin metal surface was suddenly deteriorated by the formation of extremely deep pinhole corrosion pits, while this effect was smoothed down by amalgamation. Electronic Publication     

Fractal analysis of pit morphology of Inconel alloy 600 in sulphate,nitrate and bicarbonate ion-containing sodium chloride solution at temperatures of 25–100 °C

Pit morphology of Inconel alloy 600 in sulphate (SO₄ ^2-), nitrate (NO₃ ^-) and bicarbonate (HCO₃ ^-) ion-containing 0.5 M sodium chloride (NaCl) solution was analysed in terms of fractal geometry as functions of solution temperature and anion concentration using the potentiostatic current transient technique, scanning electron microscopy, image analysis and ac-impedance spectroscopy. Potentiostatic current transients revealed that the pitting corrosion is facilitated by the increase in solution temperature, irrespective of anion additives, and that it is hindered by the increase in NO₃ ^- and HCO₃ ^- ion concentration, regardless of solution temperature. Above 60 °C, it was also found that the addition of SO₄ ^2- ions impedes pit initiation, but enhances pit growth. The value of fractal dimension D _f of the pits increased with increasing solution temperature and with decreasing NO₃ ^- and HCO₃ ^- ion concentration. Moreover, the value of D _f increased above 60 °C with increasing SO₄ ^2- ion concentration. This is caused by the increase in the ratio of pit perimeter to pit area, implying the formation of pits with micro-branched shape due to the acceleration of the local attack in the pits. From the decrease of the depression parameter with increasing solution temperature, it is inferred that the roughness of the pits increased with increasing solution temperature. In addition, the depression parameter was found to increase with increasing NO₃ ^- and HCO₃ ^- ion concentration. But, above 60 °C, in the case of SO₄ ^2- ion addition, the depression parameter decreased with increasing SO₄ ^2- ion concentration. From the experimental findings, the three-dimensional pit morphology is discussed in terms of the values of D _f of the pits and the depression parameter, with respect to anion concentration and solution temperature.     

Effect of Ta on the corrosion performance of Mo<Subscript>3</Subscript>Si intermetallic in NaCl solutions

The effect of Ta contents on the corrosion performance of Mo₃Si intermetallic in 0.5 M NaCl has been evaluated. Materials included Mo₃Si plus 5, 17, 53, 60, and 74 at% Ta. Techniques included potentiodynamic polarization curves and linear polarization resistance curves. Except for 74 at% Ta, additions of Ta induced a passive region, decreasing the anodic current density, the free corrosion potential, the pitting potential, and the corrosion current density.     

The electrochemical behaviour of polycrystalline silver electrodes in Na2CO3 solution and the effect of ClO− 4 ions

The electrochemical behaviour of polycrystalline silver electrodes in Na₂CO₃ solutions was studied under potentiodynamic and potentiostatic conditions and complemented with X-ray diffraction analysis. Potentiodynamic E/i anodic curves exhibit active passive transition prior to an oxygen evolution reaction. The active region involves a small peak AI followed by a major peak AII before the passive region. Peak AI is assigned to the formation of an Ag₂O layer while peak AII is due to the formation of an Ag₂CO₃ layer. The height of the anodic peaks increases with increasing Na₂CO₃ concentration, scan rate and temperature. The effect of increasing additions of NaClO₄ on the electrochemical behaviour of Ag in Na₂CO₃ solutions was investigated. The perchlorate ions stimulate the active dissolution of Ag, presumably as a result of the formation of soluble AgClO₄ salt. In the passive region, ClO⁻ ₄ ions tend to break down the dual passive film, leading to pitting corrosion at a certain critical pitting potential. The pitting potential decreases with ClO⁻ ₄ concentration. Potentiostatic current/time transients showed that the formation of Ag₂O and Ag₂CO₃ layers involves a nucleation and growth mechanism under diffusion control. However, in the presence of ClO⁻ ₄ ions, the incubation time for pit initiation decreases on increasing the anodic potential step. Received: 3 July 1998 / Accepted: 10 March 1999     

Application of Polytyramine Nanoparticles to the Corrosion Protection of Copper

Electrochemical polymerization of tyramine was achieved on copper electrode surface from tyramine in 0.3 M oxalic acid (pH=1.2) solution by using cyclic voltammetry technique. The formation of polytyramine nanoparicles (PTN) were characterized by cyclic voltammetry (CV), fourier transform infrared‐attenuated total reflectance (FTIR‐ATR) spectroscopy and scanning electron microscopy (SEM). The corrosion behavior of PTN coated copper was investigated by means of the change of open circuit potential with exposure time (E_ocp t), electrochemical impedance spectroscopy (EIS) and anodic polarization curves in 3.5 % NaCl solutions at room temperature. The obtained results showed the shift of corrosion potential toward positive values for electropolymerized copper and a significant decrease in corrosion current and corrosion rate in comparison with bare copper, so that the PTNs coating could be used as an important protection against corrosion of copper.     

苯酚苯胺共聚物在304不锈钢电极表面的电化学合成及成膜微观结构分析

Electrochemical copolymerization of phenol and aniline was achieved on 304 stainless steel anodes in neutral water solution with an electrolyte of Na₂SO₄O₄. Compared with pit corro-sion potential of different copolymer coatings, the best solution composition was 0.09 mol/L phenol and 0.01 mol/L aniline. Through infrared spectrum analysis, polyaniline structure was proved in phenol-aniline copolymer, as well as more side chains. Scanning electron mi-croscope was used to analyze microstructure of copolymer coating, taking advantage of part solubility of phenol-aniline copolymer in tetrahydrofuran, the bifurcate network structure was observed. The copolymer coating microstructure was summarized, compared with the performance of polyphenol coatings, the reasons of corrosion resistance enhancement with the addition of aniline in electropolymerization reaction was assumed as well.