Corrosion Inhibition and Adsorption Behavior of Sodium Lauryl Ether Sulfate on L80 Carbon Steel in Acetic Acid Solution and Its Synergism with Ethanol

The application of sodium lauryl ether sulfate (SLES) as an anionic surfactant and its synergistic combination with ethanol for inhibition of corrosion of L80 carbon steel in acetic acid solutions were investigated by means of potentiodynamic polarization measurements, scanning electron microscopy (SEM), X‐ray diffraction (XRD), and energy‐dispersive X‐ray (EDX) investigations. The inhibition efficiency increases with an increase in concentration of SLES. The adsorption of SLES on the surface of L80 carbon steel obeys the Freundlich isotherm. SLES acts predominately as an anodic inhibitor. XRD, EDX, and SEM examinations of the electrode surface confirmed the adsorption of SLES on the electrode surface. The addition of ethanol with SLES significantly enhances the inhibition effectiveness and generates a strong synergistic effect.     

Corrosion protection of carbon steel by thin films of poly(3-alkyl thiophenes) in 0.5 M H2SO4

Poly(3-octyl thiophene) (P3OT) and poly(3-hexylthiophene) (P3HT) dissolved in toluene were deposited onto 1018 carbon steel and corroded in 0.5 M H₂SO₄. P3OT and P3HT films were chemically deposited by drop casting onto 1018-type carbon steel with two surface finishing, i.e. abraded with 600-emery paper and with alumina (Al₂O₃) particles of 1.0 μm in diameter (mirror finish). Their corrosion resistance was estimated by using potentiodynamic polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy, EIS, techniques. In all cases, polymeric films protected the substrate against corrosion, but the protection was improved if the surface was polished with Al₂O₃ particles of 1.0 μm in diameter. The polymer which gave the best protection was P3HT because the amount of defects was much lower than that for the P3OT films. The polymers did not act only as a barrier layer against aggressive environment, but they improved the passive film properties by decreasing the critical current necessary to passivate the substrate, increasing the pitting potential and broadening the passive interval.     

Investigation of alkylamine self-assembled films on iron electrodes by SEM, FT-IR, EIS and molecular simulations

Alkylamine were used to form self-assembled films for the inhibition of the corrosion of iron in 0.5 M H₂SO₄ solution. The films were characterized by electrochemical impedance spectroscopy (EIS) and surface analysis techniques including SEM and FT-IR. EIS results indicate that the inhibition ability of these alkylamine self-assembled films depends on the immersion time and the alky chain length of the adsorbate. Both longer immersion time of the electrode in the solution and longer alky chain will result in stronger inhibition ability of the films. However, when the immersion time was increased over some critical point, the inhibition ability was almost invariable. Also when the chain length reached a certain degree such as 14 carbon atoms, the inhibition ability decreased on the contrary. The ability of the corrosion inhibition of the tetradecylamine and dodecylthiol mixed films improved remarkably comparing with the tetradecylamine or dodecylthiol single films. In addition, molecular simulation was used to discuss the adsorption mechanism and good agreement with electrochemical results was obtained.     

Electrochemical synthesis of poly(5-nitroindole) on 316L-stainless steel in LiClO4-acetonitrile solution and its corrosion performance

The preparation of poly(5-nitroindole) (P5NI) coating was achieved on 316L-stainless steel (SS). Poly(5-nitroindole) was deposited via anodic oxidation of the corresponding monomer in acetonitrile (ACN) solution containing LiClO₄. The influence of P5NI coating against SS corrosion was studied in 3.5% NaCl solution by electrochemical impedance spectroscopy (EIS), anodic polarization curves and the open circuit potential–time (E_ocp–t) diagrams. The results obtained suggest that P5NI coating forms a sacrificial layer but the efficiency against corrosion is limited with increasing time.     

Testing and evaluation of nonchromated coating systems for aerospace applications

The advanced corrosion resistant aircraft coatings program (ACRAC) is part of the Air Force strategy to improve performance and reduce environmental impact of coatings used on Air Force weapon systems. The program addresses the Air Force near and mid-term strategies to eliminate chromate corrosion inhibitors and reduce steps in the outer mold line coating process. Evaluation of the coating process (surface preparation, conversion coating, primer, topcoat) as a system is a key feature of the ACRAC program. Results to date indicate that the current-state-of-the-art nonchromated coating systems are significantly less effective than those with chromate. A chromate conversion coating is required for the nonchromate primer system to meet minimum requirements. Sol–gel-process based conversion coatings can replace chromate conversion coatings provided a chromated primer is used. Several approaches to incorporating inhibitors into sol–gel coatings are discussed. Electrochemical methods for testing coating performance are discussed and a new procedure based on impedance spectroscopy for evaluating active damage repair is presented.     

Resistance of metallic substrates protected by an organic coating containing glass flakes

The resistance against corrosion of an epoxy-polyamine-based coating immersed in a 3 wt.% sodium chloride solution was investigated by electrochemical impedance spectroscopy (EIS). The organic coating contained glass flakes as pigment in order to enhance its barrier characteristics. The data show that this coating is more strongly adhered and exhibits higher protection characteristics when applied onto carbon steel substrates than on galvanized steel. Though the capacitance of the coating (C_C) does not show any appreciable variation with immersion time, the resistance (R_PO) of the film is observed to increase with time upon immersion. The analysis of the data sustains that the organic film behaves as a porous, non-barrier coating. Two time constants are observed even at earlier exposures, and the improved corrosion resistance developed after the coating system was exposed to the test electrolyte is considered to originate from the precipitation of corrosion products within the pores in the film.     

Eco friendly inhibitor for corrosion inhibition of mild steel in phosphoric acid medium

The inhibition effect of Zenthoxylum alatum plant extract on the corrosion of mild steel in 20, 50 and 88% aqueous orthophosphoric acid has been investigated by weight loss and electrochemical impedance spectroscopy (EIS). Plant extract is able to reduce the corrosion of steel more effectively in 88% phosphoric acid than in 20% phosphoric acid. The effect of temperature on the corrosion behaviour of mild steel in 20, 50 and 88% phosphoric acid with addition of plant extract was studied in the temperature range 50-80 °C. Results on corrosion rate and inhibition efficiency have indicated that this extract is effective up to 70 °C in 88% phosphoric acid medium. Surface analysis (XPS and FT-IR) was also carried out to establish the mechanism of corrosion inhibition of mild steel in phosphoric acid medium.     

Electrodeposition of bilayered polypyrrole on 316 L stainless steel for corrosion prevention

The electropolymerization of pyrrole in aqueous solutions of salicylate leads to the formation of hollow rectangular-sectioned microtubes. With the aim to develop a coating with this morphology but with better anticorrosive properties we synthesized a bilayer system by depositing a polypyrrole underlayer electropolymerized in the presence of molybdate and nitrate and a polypyrrole film formed by the microtubes as a top layer. The corrosion performance of the coatings was monitored by following the open circuit potentials, polarization curves and electrochemical impedance spectroscopy in acid and neutral chloride solutions. The bilayers have the capacity to protect the steel against uniform as well as against pitting corrosion during long exposure times. The system with the inner layer formed in alkaline solution was the most protective coating in this study. The results are discussed in terms of the galvanic interaction between the polymer and the substrate and the role played by the dopant anions.     

Potentiostatic transient technique, a simple approach to estimate the corrosion current density and Stern-Geary constant of reinforcing steel in concrete

The linear polarization resistance (LPR) method, introduced by Stern and Geary, is widely used in determining corrosion rates of steel bars in concrete or synthetic pore solution. The major limitation of this method is that the value of the Tafel slopes, and consequently the Stern-Geary constant (B), is necessary for accurate calculation of the corrosion rate. This paper proposes a simple method for determining the corrosion current density and the Stern-Geary constant, using the results of the potentiostatic transient technique. The effect of the Stern-Geary constant on the corrosion rate of steel bar in concrete is also discussed. Results of this study show that potentiostatic transient method can be used successfully to determine the corrosion rate of steel bars in concrete without using the pre-assumed value of B.     

Effect of Al content on the corrosion behavior of Mg-Al alloys in aqueous solutions of different pH

The effect of systematic increase of Al content on the electrochemical behavior of the Mg-Al alloys in aqueous solutions of different pH was investigated. Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy, EIS, were used to investigate the electrochemical behavior of the alloys in aqueous solutions. The results have shown that Mg-5Al is easily corroded due to the microgalvanic effect between α-phase and β-phase, its corrosion rate is even higher than that of Mg itself. The increase of Al content increases the corrosion resistance of the alloy due to the formation of the β-phase (Mg₁₇Al₁₂) together with the Mg α-phase. The ranking of the corrosion rate of these alloys was Mg-5Al > Mg > Mg-10Al ≅ Mg-15Al. The corrosion rates of the alloys in acidic solutions are pronouncedly high compared to those measured in neutral or basic solutions. The impedance measurements are in consistence with the polarization techniques and the impedance data were fitted to theoretical data obtained according to an equivalent circuit model describing the electrode/electrolyte interface.     

Corrosion behavior of different alloys exposed to continuous flowing seawater by electrochemical impedance spectroscopy (EIS)

The corrosion of four types of alloys, under a dynamic condition, has been studied in continuous fresh seawater system using electrochemical impedance spectroscopy (EIS) technique. The materials used in this study were stainless steel 304, Cu-Ni 70-30, Hastelloy G-30, and titanium. The total exposure time of the test was 180 days, in continuous fresh seawater of the Gulf in Kuwait. The EIS tests were carried out by using EG&G software and hardware instrument. Electrochemical parameters such as the polarization resistance (R_P), solution resistance (R_Sol), and the double layer capacitance (C_dL) of these alloys were determined. Then the obtained EIS parameters were used to study the effect of the seasonal change of the Gulf seawater on the corrosion behavior of the tested materials. All the obtained EIS parameters showed that the seasonal changes of the Gulf seawater have a significant effect on controlling the rate of the formation of the marine bio-film on the surface of tested materials. Consequently, the corrosion behavior of the materials tends to vary as a function of the rate formation of the marine bio-film on the surface of tested materials.     

Identification of inductive behavior for polyaniline via electrochemical impedance spectroscopy

Polyaniline (PANI) film electrodeposited in HCl medium using cyclic voltammetry (CV) with an upper potential limit of 0.90 V, exhibited an inductive behavior. PANI films deposited with different conditions were subjected to various applied potentials and the impedance characteristics were recorded through electrochemical impedance spectroscopy (EIS). The impedance results clearly reveal the existence of inductive behavior to PANI. Inductive behavior was observed for PANI films deposited with conditions which favor benzoquinone/hydroquinone (BQ/HQ) formation and further evidenced by X-ray photoelectron spectroscopy (XPS). A comparative analysis of the EIS and XPS results of PANI films prepared under similar conditions with the upper potential limits of 0.75 and 0.90 V, respectively, clearly documented that the presence of BQ/HQ, the degradation product of PANI, formed during the electrochemical polymerization at the upper potential limits causes inductive behavior to PANI.     

Electrochemical noise and impedance study of aluminium in weakly acid chloride solution

The electrochemical noise (EN) characteristics of pure aluminium in unbuffered potassium chloride solution and with acetic acid/sodium acetate buffer at pH 5.4 and 4.3 have been analysed to throw light on the influence of pH and of the presence of buffer at the aluminium surface on chloride ion-induced corrosion. Comparison has been made with results obtained by electrochemical impedance spectroscopy (EIS) and quantitative deductions made concerning the values of the noise resistance and the magnitude of the electrochemical impedance. Deviations between results obtained by the two experimental techniques are discussed.     

可剥蓝胶的成分分析

采用各种分离、测试手段剖析可剥蓝胶的成分及含量。首先借助红外光谱(FT-IR)法确定其基体树脂为氯醋树脂,再通过核磁氢谱(1H-NMR)法确定其固化体系和基体树脂的成分,随后用凝胶渗透色谱(GPC)法验证了基体树脂和固化体系的成分及含量;此外,利用X射线荧光光谱法确定了润滑体系和颜填料体系的成分及含量;最后通过热失重分析(TGA)法将各成分的含量进一步细化。结果表明:该可剥蓝胶中各成分及含量(以质量分数计)分别为氯醋树脂60%~65%、环氧树脂(EP)10%~12%、甲阶酚醛树脂8%~10%、邻苯二甲酸酯8%~10%、硬脂酸钡1%~2%、磷酸三苯酯1%~3%、碳酸钙1%~2%、二氧化硅1%~2%和酞菁蓝0.5%~1%;还原试验证明各种分析结果有效可靠。     

Electrochemical and anticorrosion behavior of functionalized graphite nanoplatelets epoxy coating

Functionalized graphite nanoplatelets (FGNP) were used as efficient and compatible nano-particles to produce homogenous epoxy nano-coating with impressive anticorrosion behavior for carbon steel. The characterizations of the nano-particle and nano-coating were carried out by SEM, FT-IR, XRD, TEM and pull-off test. Fine distribution of nano-particles in the cured nano-coating with particle sizes of 20–40 nm was obtained. Electrochemical experiments, salt spray and X-ray fluorescence showed that the nano-coatings protect the metal substrate by formation of passive layer and physical barrier characteristics. Three samples (0.25%, 0.5% and 1%) of FGNP-epoxy coatings were prepared that 0.5% showed better anticorrosion properties.     

Effect of benzotriazole (BTA) addition on Polypyrrole film formation on copper and its corrosion protection

Benzotriazole (BTA) was added in a conducting Polypyrrole (PPy) film prepared on copper in oxalic acid aqueous solution containing pyrrole monomer to improve corrosion protection by the PPy film and reduce copper corrosion. When BTA was added in the preparation solution, the copper surface was covered by a BTA–Cu complex layer before the anodic polymerization of PPy was started. On the copper surface with the BTA layer, the initial dissolution of copper was inhibited and the PPy polymerization-deposition was started immediately after the anodic current was imposed. The PPy film thus formed was doped with oxalic ions and ionized BTA and was homogeneous in thickness and strongly adhesive. The PPy film containing BTA protected the copper from corrosion in 3.5 wt.% NaCl solution. In 400 h of immersion, copper dissolution was inhibited with 80% protection efficiency relative to that of bare copper.     

Plasma interface engineered coating systems for magnesium alloys

In this study, a dc low-temperature plasma technique, including plasma treatment and plasma polymerization, was used to create interface engineered coating systems with a structure of Mg/plasma interlayer/cathodic electrocoating (E-coat) for machined AZ31B magnesium (Mg) alloy panels. The plasma interlayer deposited from trimethylsilane (TMS) precursor had a nano-scale thickness of ∼65 nm and well-controlled surface properties through subsequent plasma treatments in order to achieve different level of interfacial adhesion between the E-coat and the Mg substrates. The surface wettability of the plasma interlayer was monitored by water surface contact angle measurement. The interface adhesion of the coating system was evaluated using N-methylpyrrolidinone (NMP) paint removal test and ASTM tape test conducted under dry and wet conditions. Electrochemical impedance spectroscopy (EIS) was employed to investigate the effects of plasma interlayer properties including surface wettability and adhesion enhancement on corrosion protection properties of the coating systems. It was found that a more wettable interface enhanced the electrolyte penetration through the coating and thus reduced the corrosion resistance of the coating system. On the other hands, the improved interface adhesion had little effects on EIS results mainly due to the high chemical reactivity of the Mg alloy substrates.