Effect of sodium molybdate on the corrosion behavior of cold rolled steel in peracetic acid solution

The effect of sodium molybdate (Na₂MoO₄) on the corrosion of cold rolled steel (CRS) in peracetic acid (PAA) solution was investigated by gravimetric measurements, Tafel polarization curves, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). All the data indicate that Na₂MoO₄ acts as a very good inhibitor in PAA solution. The inhibition efficiency increases with increasing concentration of Na₂MoO₄ and immersion time. The inhibition efficiencies, calculated from gravimetric measurements, Tafel polarization curves and electrochemical impedance spectroscopy, are in reasonably good agreement and are very similar in the three cases. Furthermore, polarization data show that Na₂MoO₄ behaves as an anodic passive type inhibitor. Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) were used to characterize the corrosion surface. A probable mechanism is presented to explain the experimental results.     

Corrosion behaviors of a γ-toughened Cr13Ni5Si2/Cr3Ni5Si2 multi-phase ternary metal silicide alloy in NaCl solution

Corrosion behaviors of a novel corrosion-resistant γ-toughened Cr₁₃Ni₅Si₂/Cr₃Ni₅Si₂ multi-phase ternary metal silicide alloy and properties of the passive film formed in NaCl solution were examined by anodic polarization, cyclic polarization and electrochemical impedance spectroscopy (EIS) experiments as well as X-ray photoelectron spectroscopy (XPS) and potentiostatic polarization measurements. Effects of immersion time and chloride ion concentration on corrosion behaviors of the alloy were also evaluated. Results indicated that the alloy exhibited excellent corrosion resistance in NaCl solution due to the spontaneous formation of a compact and protective passive film composed mainly of chromium (III) oxide as well as the high chemical stability and strong inter-atomic bonds inherent to Cr₁₃Ni₅Si₂ and Cr₃Ni₅Si₂ intermetallic phases. Moreover, corrosion resistance of the alloy was quite insensitive to the increase of chloride ion concentration and was improved noticeably with the increasing immersion time.     

The Influence of Ni Content on the Stability of Copper—Nickel Alloys in Alkaline Sulphate Solutions

The electrochemical behaviour of copper–nickel alloys with different Ni content (5–65%) in sulphate solutions of pH 12 was investigated. The effects of temperature, immersion time, and concentration of sulphate ions were also studied. Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used. Potentiodynamic measurements reveal that the increase in nickel content increases the corrosion rate of the alloy in sulphate solution linearly. Nevertheless, an increase in the nickel content along with increase in immersion time improves the stability of the Cu–Ni alloys due to the formation of a stable passive film. An equivalent circuit model for the electrode/electrolyte interface under different conditions was proposed. The experimental impedance data were fitted to theoretical data according to the proposed model. The relevance of the model to the corrosion/passivation phenomena occurring at the electrode/solution interface was discussed.     

Self-assembled 1-octadecyl-1H-1,2,4-triazole films on copper for corrosion protection

A film of 1-octadecyl-1H-1,2,4-triazole (OTA) was formed on a fresh copper surface by self-assembly technique. The optimum concentration of OTA and immersion time for the formation of a protective OTA film have been established using electrochemical impedance spectroscopy (EIS). These are (i) 15 mM concentration of OTA in methanol and (ii) immersion period of 48 h. X-ray photoelectron spectroscopy (XPS), reflection absorption FTIR spectroscopy, atomic force microscopy (AFM), and contact angle measurements have been used to characterize the OTA film on copper surface. The efficiency of OTA film to protect copper from corrosion in aqueous NaCl environment has been investigated using EIS, potentiodynamic polarization studies, cyclic voltammetry and weight-loss studies. All these studies showed that the OTA film affords excellent protection against corrosion of copper.     

Study on the effect of vanillin on the corrosion inhibition of aluminum alloy

The effect of vanillin on the corrosion inhibition of aluminum (Al) alloy in seawater was studied by potentiodynamic polarization (PP), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) techniques. The surface morphology after its exposure to seawater with and without vanillin was examined by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). All the studied parameters showed good inhibitive characteristics against the corrosion of Al alloy in the tested solution, and their performance was observed to increase with the inhibitor concentration. Polarization data indicated that the studied inhibitor is a mixed-type inhibitor. Linear polarization and EIS studies showed that there were significant increases in the overall resistance after the addition of vanillin. The adsorption of inhibitor on Al alloy was found to obey the Langmuir adsorption isotherm. The analysis of SEM and EDS confirmed the formation of precipitates of vanillin on the metal surface, which reduced the overall corrosion reaction.     

The use of polyindole for mild steel protection

Synthesis of polyindole was achieved on mild steel electrode previously coated with a very thin polypyrrole layer (PPy). Cyclic voltammetry technique was used for both syntheses; oxalic acid solution was used for synthesis of primer PPy coating and polyindole film (PI) was obtained from LiClO₄ containing acetonitrile medium. The corrosion performance of this PPy/PI coating was investigated properly in 3.5% NaCl solution by using anodic polarization and open circuit potential (E_ocp)–time curves and electrochemical impedance spectroscopy (EIS). This coating exhibited excellent barrier efficiency for a long time (about 190 h) and it was also able to provide a certain anodic protection. After 240 h of immersion time in corrosive test solution, the protection efficiency value was determined to be 98.9%.     

The inhibiting effect of quaternary phosphine on Ni–P alloys in 1 M H2SO4

Polarization curves, electrochemical impedance measurements and SEM analysis were used to study the dissolution and the inhibition of nickel–phosphorous alloys in 1 M H₂SO₄. The alloy specimen was obtained by electroless plating on copper substrates. The inhibiting effect of triphenyl-alkyl (C₆)-phosphonium (P₃AP) was examined. The shape of the polarization curves remained essentially unchanged by addition of the inhibitor, but the current density values decreased significantly in both the anodic and the cathodic domains. The impedance spectra at open circuit potential obtained for various immersion times showed that the dissolution of this alloy was characterized by three capacitive loops. The loops were barely distinguishable at short immersion times, but, in contrast, they appeared clearly when the specimens were left in aggressive medium for one day. Tafel extrapolation in the cathodic region gave a corrosion inhibition efficiency of 90%. In the anodic domain, the current plateau decreased approximately 100 fold as a result of inhibitor addition. The phenomenon leading to the formation of this plateau is more likely related to a film growth process than to a diffusion limitation.     

Anticorrosive properties of polypyrrole films modified with zinc onto SAE 4140 steel

Polypyrrole (PPy) films modified with zinc were electrosynthesized onto SAE 4140 steel in presence of bis(2-ethylhexyl) sulfosuccinate (AOT). The Zn and PPy electrodeposition was realized by using cyclic voltammetry at different temperatures. The corrosion protection properties of the films were examined in chloride solution by open circuit measurements, linear polarization and electrochemical impedance spectroscopy (EIS). The obtained results indicate that the presence of Zn in the polymer matrix improves the anticorrosive performance of PPy films. The best anticorrosion efficiency was obtained for the coatings modified at 20 °C which provided anodic protection to the steel substrate for a long period of immersion in chloride solution. Cathodic protection was observed when the electrodeposition temperature was increased. Adherence and anticorrosive properties declined sharply for the coatings electrosynthesized at 5 °C.     

植酸对镁-锂合金阳极氧化膜的影响

利用无铬阳极氧化技术在镁-锂合金表面生成了阳极氧化膜,通过扫描电镜、X射线衍射、极化曲线和电化学阻抗谱等测试技术对氧化膜进行了表面形貌、晶相组成和耐蚀性能的研究。讨论了在基本电解液里添加植酸对氧化膜性能的影响。研究结果表明:基本电解液中加入植酸后获得的氧化膜表面形貌没有得到很大改善,仍然存在孔洞;当植酸的质量浓度达到10.0 g/L时,可得到表面光滑亮白、耐蚀性最好的阳极氧化膜。     

硫脲衍生物缓蚀剂的合成及其缓蚀性能初探

合成了月桂酰基硫脲缓蚀剂,并通过传统的静态失重法结合现代的电化学测试方法初步考察了其抗CO2腐蚀的缓蚀性能。结果表明,该缓蚀剂在CO2腐蚀介质中,当投加量为0.10 g/L时,缓蚀剂的缓蚀效率达91.49%。通过极化曲线分析可知,该缓蚀剂一种抑制阳极过程为主的阳极型缓蚀剂。电化学阻抗谱测试表明,该缓蚀剂通过负催化效应而起到缓蚀效果。     

NH4Cl溶液浓度对Incoloy 825合金腐蚀行为的影响

通过电化学阻抗技术、极化曲线和浸泡腐蚀实验对Incoloy 825合金在不同浓度NH₄Cl溶液中的腐蚀行为进行了研究。研究结果表明：开路电位随着浓度的升高而负移,腐蚀倾向增大;采用等效电路R_S（Q₁R₁）（Q_dlR_t）对电化学阻抗谱进行拟合,电荷转移电阻R_t随浓度增加而减小,Incoloy 825合金的维钝电流密度和腐蚀速率随浓度的增加而增大;825合金的腐蚀形貌主要为局部腐蚀,点蚀的密集度和大小随浓度的增加而增大;EDS结果表明Cl^-参与了电化学反应过程。     

Investigation of the inhibitive effect of ortho-substituted anilines on corrosion of iron in 1 M HCl solutions

The inhibitory activity of some o-substituted anilines on iron corrosion in hydrochloric acid (HCl) was studied in relation to inhibitor concentration using potentiodynamic and electrochemical impedance spectroscopy (EIS) measurements. O-substituted anilines were found to act as mixed type inhibitors. The results showed that o-substituted anilines suppressed both cathodic and anodic processes of iron corrosion in 1 M HCl by its adsorption on the iron surface according to Langmuir adsorption isotherm. Potentiodynamic and EIS measurements reveal that these compounds inhibit the iron corrosion in 1 M HCl and that the efficiency increases with increasing of the inhibitor concentration. Data obtained from EIS are analyzed to model the corrosion inhibition process through equivalent circuit.     

Electrochemical corrosion behavior of composite coatings of sealed MAO film on magnesium alloy AZ91D

Protective composite coatings were prepared on magnesium alloy AZ91D by micro-arc oxidation (MAO) treatment plus a top coating with sealing agent using multi-immersion technique under low-pressure conditions. The corrosion resistance of AZ91D alloy with composite coatings was superior evidently to that with merely MAO film. SEM observations revealed that the sealing agent was integrated with MAO film by physically interlocking; therewith covered uniformly the surface as well as penetrated into pores and micro-cracks of MAO film. The anti-corrosion properties in 3.5% NaCl solution of the composite coatings were evaluated by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. Based on the results of chronopotentiometric (E ∼ t) and EIS measurements for long time immersion in 3.5% NaCl solution, appropriate equivalent circuits for the composite coatings system were proposed. It follows that due to the blocking effect of the sealing agent in pores and cracks in MAO film, the composite coatings can suppress the corrosion process by holding back the transfer or diffusion of electrolyte and corrosion products between the composite coatings and solution during immersion.     

Acetyl thiourea chitosan as an eco-friendly inhibitor for mild steel in sulphuric acid medium

Acetyl thiourea chitosan polymer (ATUCS) has been synthesized and evaluated as corrosion inhibitor. The electrochemical behavior of mild steel in naturally aerated 0.5 M H₂SO₄ acid containing different concentrations of ATUCS has been studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements and surface examination via scanning electron microscope (SEM) technique. The results of EIS showed that the resistance (R_t) increases slightly with increasing immersion time indicating a slight decrease in corrosion rate of the steel with time. Also, the corrosion rate increases with either increasing temperature or decreasing the polymer concentration as observed by polarization technique. Electrochemical impedance spectroscopy measurements under open-circuit conditions confirmed well polarization results. ATUCS has shown very good inhibition efficiency (IE) in 0.5 M sulphuric acid solution reaches to 94.5% for 0.76 mM concentration. IE of this compound has been found to vary with the concentration of the polymer solution, immersion time and temperature.     

Experimental and theoretical studies of anti-ulcer drugs with benzimidazole rings as corrosion inhibitor for copper in 1 M nitric acid medium

The adsorption effect of esomeprazole (ESP) and lansoprazole (LP) on corrosion behavior of copper in 1 M HNO₃ solution was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurements. The experimental results indicate that both ESP and LP inhibited the corrosion of copper in nitric acid solution and the inhibition efficiency increased as the concentration of the compounds increased. EIS measurements confirmed that the charge transfer resistance increases on increasing the inhibitor concentration. Polarization measurements showed that the inhibitors are of mixed type. From the weight loss measurements, the inhibition efficiency of the inhibitors was found to vary with concentration, immersion time, and temperature. The adsorption of inhibitors on the copper surface follows Langmuir isotherm. The surface morphology was examined by scanning electron microscope and atomic force microscope. Further, the computational calculations are performed to find a relation between their electronic and structural properties.     

BIOMASS EXTRACTS FOR MATERIALS PROTECTION: CORROSION INHIBITION OF MILD STEEL IN ACIDIC MEDIA BY Terminalia chebula EXTRACTS

The inhibiting action of the fruit extract of Terminalia chebula (TC) on mild steel corrosion in 1 M HCl solution was studied using gravimetric, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The experimental results showed that TC functioned as an inhibitor in the acidic corrodent and that corrosion inhibition efficiency increased with extract concentration. Cathodic and anodic polarization curves show that TC functioned as a mixed-type inhibitor, while impedance results show that the extract organic matter was adsorbed at the metal/corrodent interphase. A computational study of the adsorption behavior of some of the organic constituents of the extracts was carried out using density functional theory (DFT). The computations were used to theoretically ascertain the individual contributions of the constituents to the observed corrosion-inhibiting effect of the extract.     

Effect of Zn and Pb contents on the electrochemical behavior of brass alloys in chloride-free neutral sulfate solutions

Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of brass alloys with various Zn contents (5.5–38.0 mass%) and Cu–38.0Zn–Pb alloy with different Pb contents (1.0–3.4 mass%) in neutral sodium sulfate solutions. The influence of working conditions, e.g., immersion time, sulfate ions concentration and temperature on the electrochemical behavior of the different alloys was also studied. It was found that the initial corrosion rate is relatively high for alloys with the higher zinc content due to dezincification. The dezincification process initiates by selective dissolution of zinc and continues by a simultaneous dissolution of copper and zinc followed by re-deposition of copper. An increase in the lead content and immersion time in the sodium sulfate solution increases the corrosion resistance of the alloy and improves its stability. The stability of the leaded brass was considered to be due to the formation of an insoluble film of lead sulfate on its surface. The impedance data were fitted to theoretical data obtained according to an equivalent circuit model describing the electrode/electrolyte interface. The mechanism of the alloy dissolution was discussed in view of the obtained results.     

Influence of Various Albumin Concentrations on the Corrosion Resistance of Zr-2.5%Nb Alloy

The Zr-2.5% Nb alloy corrosion resistance in four saline solutions with and without albumin was tested through electrochemical measurements of electrochemical impedance spectroscopy (EIS), linear polarization, and cyclic voltammetry at human body temperature.

The EIS measurements were performed at open circuit potential. The impedance spectra were recorded and the equivalent electric circuits were elaborated. From the linear polarization the Tafel slopes were recorded and the corrosion parameters were calculated. From the potentiodynamic polarization curves, the breakdown potential, the protection potential, and the protection domain were observed.

The amount of ions released from the material was quantified using the ICPMS technique and the results concerning the corrosion resistance were compared with those obtained from linear and cyclic polarization.

Before and after potentiodynamic polarization the topographic measurements were performed; the roughness at the samples surface was observed using AFM. The roughness was co-related to the contact angle measurements.     

紫铜海水管焊接部位在人工海水中的腐蚀行为

通过阳极极化曲线、交流阻抗测试、扫描电镜研究了紫铜海水管焊接部位在人工海水中的腐蚀行为.结果表明：紫铜、白铜焊缝和黄铜焊缝在人工海水中的阳极过程类似,相同电位下,白铜焊缝的电流密度最小,耐蚀性最佳,与阻抗测试结果一致.黄铜焊缝在电位-0.012 V时出现电流峰,腐蚀产物膜多孔、疏松,随后电极进入钝化区,钝化膜由Cu₂O、CuCl和ZnO组成;随电位升高,钝化膜溶解,发生铜锌置换反应,沉积的Cu导致活性电对的形成,增加了合金的腐蚀速度;当电位为＋0.87 V时,电极表面富集了针状锡和锡的氧化物.随后,电极表面积累的锡和锡的氧化物及腐蚀产物层对脱锌腐蚀有一定的阻碍作用,电流密度有所下降,最后腐蚀达到一种动态平衡,腐蚀机制为溶解-再沉积机理.     

The inhibition of benzimidazole derivatives on corrosion of iron in 1 M HCl solutions

The inhibitive action of some benzimidazole derivatives namely 2-aminobenzimidazole (AB), 2-(2-pyridyl)benzimidazole (PB), 2-aminomethylbenzimidazole (MB), 2-hydroxybenzimidazole (HB) and benzimidazole (B), against the corrosion of iron (99.9999%) in solutions of hydrochloric acid has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). At inhibitor concentration range (10⁻³-10⁻² M) in 1 M acid, the results showed that these compounds suppressed both cathodic and anodic processes of iron corrosion in 1 M HCl by adsorption on the iron surface according to Langmuir adsorption isotherm. The efficiency of these inhibitors increases in the order AB>PB>MB>HB>B. Both potentiodynamic and EIS measurements reveal that these compounds inhibit the iron corrosion in 1 M HCl and that the efficiency increases with increasing of the inhibitor concentration. Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit. A correlation between the highest occupied molecular orbital E_HOMO and inhibition efficiencies was sought.