The study of aluminium corrosion in acidic solution with nontoxic inhibitors

The inhibitory activity of some substituted N-arylpyrroles on aluminium corrosion in hydrochloric acid was studied in relation to inhibitor concentration, using potentiodynamic and impedance spectroscopy techniques. All investigated compounds were found to act as cathodic-type inhibitors and inhibition was ascribed to the adsorption of inhibitor onto the electrode surface. The inhibiting efficiency of the additives depended on the inductive power of the groups attached to the benzene and/or pyrrole ring. The carbaldehyde group showed better inhibiting power due to additional condensation on the electrode surface. The impedance results analysed in terms of the polarization resistance showed that the EIS technique can be successfully applied in the determination of corrosion resistance in systems where the corrosion kinetics are not simple.     

4-Aminoantipyrine as an inhibitor of mild steel corrosion in HCl solution

4-aminoantipyrine (AAP) was tested as a corrosion inhibitor for mild steel in 2 M HCl solution using different techniques: weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that AAP is an inhibitor for mild steel in this medium. The inhibition was assumed to occur via adsorption of the inhibitor molecule on the metal surface. In the 20 to 60 C temperature range, the AAP adsorption follows the Flory–Huggins isotherm and/or the El-Awady et al. kinetic-thermodynamic model. The protection efficiency increases with increasing inhibitor concentration (in the range 10–310–2 M) but decreases with increasing temperature. The thermodynamic functions of dissolution and adsorption processes were calculated.     

Inhibition of acid corrosion of steel using cetylpyridinium chloride

The cationic surfactant cetylpyridinium chloride (CPC) showed high inhibition efficiency for the corrosion of low carbon steel in 1 M H₂SO₄. Electrochemical measurements were dedicated to test the performance of CPC at different concentrations and temperatures. CPC has a significant inhibiting effect on the corrosion of steel and protection efficiencies up to 97% were measured. The inhibitor shifted the corrosion potential in the cathodic direction. It was found that adsorption is consistent with the Bockris–Swinkels isotherm in the studied temperature range (30–60 °C). The negative values of the free energy of adsorption and the decrease in apparent activation energy in the presence of the inhibitor suggest chemisorption of the CPC molecule on the steel surface.     

Competent inhibitor for the corrosion of zinc in hydrochloric acid based on 2,6-bis-[1-(2-phenylhydrazono)ethyl]pyridine

A novel compound, 2,6-bis-[1-(2-phenylhydrazono)ethyl]pyridine (BPEP), was synthesized and confirmed by NMR and IR spectroscopy. BPEP was examined as an inhibitor for the corrosion of zinc electrode in 1.0 M HCl. The inhibition efficiency of BPEP was assessed through various techniques such as hydrogen evolution, galvanostatic polarization, potentiodynamic anodic polarization, and electrochemical impedance spectroscopy. The inhibiting action of BPEP was explained in terms of the formation of a stable complex between zinc ions and BPEP and then adsorbed onto the zinc surface. The formation of the complex was established by FT-IR spectroscopy. A conductometric titration indicated that the stoichiometry of Zn⁺²:BPEP (metal:ligand) is 1:1. The adsorption follows the Langmuir isotherm. The Galvanostatic polarization measurements have shown that the BPEP molecule acts as a mixed-type inhibitor. The pitting potential shifted in the noble direction, indicating that the inhibition of pitting corrosion of zinc in the presence of BPEP.The activation energy and themodyanamic parameters of the adsorption process were calculated and have been explained.     

Corrosion protection of aluminium in acidic chloride solutions with nontoxic inhibitors

Corrosion kinetics of 99.6% aluminium covered by a thin spontaneously formed oxide film in hydrochloric acid solution with and without the presence of substituted N-aryl pyrroles was studied using electrochemical impedance spectroscopy and quasi steady-state polarization. Measurements were performed on a rotating disc electrode in an argon-deaerated solution in the temperature range 20 to 50°C. The addition of inhibitor considerably increases overvoltage of the cathodic process (HER) and shifts Ecorr to negative potential values. The activation energy of the hydrogen evolution reaction was Ea=50±5kJmol–1 and was not affected by the presence of inhibitor. The inhibitory action occurs by -bonding between the adsorbed inhibitor molecules and the electrode surface. The electrode coverage follows the Langmuir adsorption isotherm with an adsorption equilibrium constant K=1.1–2.64×105dm3mol–1. The adsorption of organic compound prevents the adsorption of chloride ions and slow down the rate of corrosion.     

双咪唑啉衍生物缓蚀剂的合成与缓蚀研究

以二乙撑三胺和己二腈原料合成了双咪唑啉BM,采用了失重法和极化曲线研究了合成物质对A3钢的缓蚀性能。失重实验表明BM是一种良好的缓蚀剂,25℃,在1mol·L^-1 HCl中,缓蚀剂浓度1mmol·L^-1时,对A3钢的缓蚀率达到96.7％,在0.5mol·L^-1 H2SO4体系中,当缓蚀剂用量为2mmol·L^-1时,缓蚀率为86％。通过模型拟合表明BM符合EL-Awady吸附。极化曲线表明其是一种阴极型缓蚀剂。     

Corrosion inhibition by fatty acid triazoles for mild steel in formic acid

5-Heptadec-8-enyl-4-phenyl-4H–[1,2,4] triazole-3-thiol (HPTT), 4-phenyl-5-undecyl-4H–[1,2,4] triazole-3-thiol (PUTT), and 5-dec-9-enyl-4-phenyl-4H–[1,2,4] triazole-3-thiol (DPTT) were synthesized and their influence on the inhibition of corrosion of mild steel in 20% formic acid was investigated by weight loss and potentiodynamic polarization techniques. The inhibition efficiency of these compounds was found to vary with their nature and concentration, temperature and immersion time. The values of activation energy and free energy of adsorption of the triazoles were calculated to investigate the mechanism of corrosion inhibition. Good inhibition efficiency (>90%) was found even at lower concentration (i.e., 25 ppm) in acid solution. The adsorption on mild steel surfaces was found to obey Temkin's adsorption isotherm. Potentiodynamic polarization results revealed that the compounds studied are mixed type inhibitors. Electrochemical impedance spectroscopy was also used to investigate the mechanism of the corrosion inhibition.     

Inhibiting properties and adsorption of some thioamides on mild steel in sulphuric acid solutions

The inhibiting properties and adsorption behaviour of thioacetamide (TAA), thiobenzamide (TBA) and thiocinnamamide (TCA) on mild steel in sulphuric acid solution were studied by gravimetric, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. TBA and TCA were found to be mixed type inhibitors providing good corrosion inhibition. Different mechanisms of adsorption and corrosion inhibition were observed for the tested thioamides. In the cases of TBA and TCA, the adsorption of the compounds is chemical and the values of the activation energy (Ea) and the pre-exponential factor (A) are lower than the corresponding values observed in inhibitor free solution. The adsorption of TAA is physical and the values of Ea and А are higher than the corresponding values in sulphuric acid solution. The adsorption process of TBA and TCA on the mild steel/sulphuric acid solution interface is described by Langmuir’s isotherm. A correlation between the adsorption capability and the inhibiting efficiency of the molecules and their donor–acceptor properties (E _HOMO and E _LUMO) has been established. It is ascertained that the protection effect of TAA depends on the amount of hydrolysis products.     

Corrosion inhibition and adsorption behavior of new Schiff base surfactant on steel in acidic environment: Experimental and theoretical studies

Synthesis, adsorption and corrosion inhibiting effect of new Schiff base surfactant named 4-hydroxy-3-(3-phenyl-allylideneamino)-benzene sulphonic acid2-[2-(2-{2-[2-(2-hydroxy-ethoxy)-ethoxy]-ethoxy}-ethoxy)-ethoxy]-ethyl ether (abbreviated as PAAB) on mild steel in 1.0 M HCl were investigated using weight loss, and potentiodynamic polarization techniques. The results revealed that this compound inhibited the corrosion reaction in HCl environment. The results indicated that this inhibitor was adsorbed on the metal/solution interface. Theoretical study of the adsorption behavior of this compound was carried out in the framework of the semiempirical (SE) and molecular dynamics (MD).     

盐酸介质中吐温-60对冷轧钢的缓蚀作用机理

用失重法及电化学法研究了非离子表面活性剂吐温-60对冷轧钢在1.0～8.0 mol•L^-1盐酸溶液中的缓蚀作用. 结果表明：吐温-60对冷轧钢在1.0 mol•L^-1盐酸溶液中具有良好的缓蚀作用,且其在钢表面的吸附符合Langmuir吸附模型. 缓蚀率随缓蚀剂浓度的增加而增大,但随盐酸浓度和温度的增加而减小. 动电位极化曲线表明,吐温-60为混合抑制型缓蚀剂,但主要是抑制阴极反应. 通过吸附理论和动力学公式求出了相应的吸附热力学参数和动力学参数,并根据这些参数详细讨论了缓蚀作用机理.     

Effect of temperature on stability of adsorbed inhibitors on steel in phosphoric acid solution

Rates of steel dissolution in 35% H₃PO₄/6% butanol (test solution) in the presence of thiosemicarbazide and seven of its derivatives were determined by spectrophotometry, weight loss and potentiodynamic and impedance techniques in the temperature range 303 to 333 K. At all temperatures, the corrosion rate decreased with increasing inhibitor concentration. Increasing temperature decreased the protection efficiency particularly at concentrations less than 2.5 × 10^–4 M. At inhibitor concentrations above 2.5 × 10^–4 M, increasing the temperature did not affect efficiency. Potentiodynamic polarization measurements indicated that the inhibitors have a strong effect on the corrosion behavior of the steel and behave as mixed type inhibitors. Thermodynamic functions obtained from this study indicate that the presence of the inhibitors increase the activation energy. The negative values of G ^* indicated spontaneous adsorption on the metal surface. A kinetic-thermodynamic model was found to describe the experimental well data at different temperatures.     

Corrosion inhibition of aluminium in acid solutions by some imidazoline derivatives

2-Pentadecyl-1,3-imidazoline (PDI), 2-Undecyl-1,3-imidazoline (UDI), 2-Heptadecyl-1,3-imidazoline (HDI), 2-Nonyl-1,3-imidazoline (NI) were synthesized and characterized by FT-IR and NMR Studies. The corrosion inhibition properties of these compounds on aluminium in 1 M HCl and 0.5 M H₂SO₄ were investigated by weight loss, potentiodynamic polarization, electrochemical impedance and scanning electron microscopic techniques. The weight loss study showed that the inhibition efficiency increases with increase in the concentration of the inhibitor and was found to be inversely related to time and temperature while it shows no significant change with increase in acid concentration. The effectiveness of these inhibitors were in the order of UDI > NI > PDI > HDI .The values of activation energy, free energy of adsorption, heat of adsorption, enthalpy of activation and entropy of activation were also calculated to elaborate the mechanism of corrosion inhibition. The adsorption of these compounds on aluminium surface follows the Langmuir adsorption isotherm. The potentiodynamic polarization data show that the compounds studied are mixed type inhibitors. Electrochemical impedance was used to investigate the mechanism of corrosion inhibition. The surface characteristics of inhibited and uninhibited metal samples were investigated by scanning electron microscopy (SEM).     

INHIBITING EFFECT OF N-CYCLOHEXYL-N′-PHENYL THIOUREA ON THE CORROSION OF 304 SS IN HYDROCHLORIC ACID SOLUTION

The inhibiting action of N-cyclohexyl-N′-phenyl thiourea (CPTU) on the corrosion behavior of 304 SS in 3 M hydrochloric acid solution has been investigated using potentiodynamic polarization technique at four different temperatures. The results obtained reveal that CPTU acts as an efficient anodic inhibitor for the corrosion of 304 SS. Good inhibition efficiency (>92%) was evident in the acidic solution, and it was found to vary with temperature and concentration of the inhibitor. The adsorption of this compound on the 304 SS surface was found to obey the Temkin adsorption isotherm, and the inhibition was governed by physical adsorption mechanism. The thermodynamic parameters of adsorption deduced revealed a strong interaction and spontaneous adsorption of CPTU on the steel surface. Scanning electron microscopic study (SEM) was done to investigate the surface characterization of inhibited and uninhibited 304 SS specimens.     

盐酸中原儿茶醛在钢表面的吸附及缓蚀作用

用失重法和动电位极化曲线法研究了在1.0mol/L HCl中20~50℃原儿茶醛(3,4-二羟基苯甲醛)在冷轧钢表面上的吸附及缓蚀作用.结果表明:原儿茶醛具有中等程度的缓蚀作用,为混合抑制型缓蚀剂,缓蚀率随原儿茶醛的浓度增加而增大,但随温度的增加而减小;原儿茶醛在钢表面的吸附符合Freundlich吸附模型.通过吸附理论和动力学Arrhenius公式求出了相应的吸附热力学参数(吸附自由能ΔG°,吸附热ΔH°,吸附熵ΔS°)和动力学参数表观活化能Ea,并根据这些参数详细讨论了缓蚀作用机理.     

Effect of Schiff Bases Containing Pyridyl Group as Corrosion Inhibitors for Low Carbon Steel in 0.1 M HCl

The inhibiting effect of four newly synthesised Schiff bases containing pyridyl group was investigated on the corrosion of low carbon steel in 0.1 M hydrochloric acid solution under various conditions by potentiodynamic polarisation method and impedance measurements. The Schiff bases used were 2-((1Z)-1-aza-2-(2-pyridyl)vinyl)benzene-1-thiol, (1Z)-1-aza-1,2- di(2-pyridyl)ethene, [((1Z)-1-aza-2-(2-pyridyl)vinyl)amino]benzene-1-thione and 2-((1Z)-1-aza-2-(2-pyridyl)vinyl)benzothiazole. All the Schiff bases inhibit corrosion of low carbon steel and their inhibition efficiencies increase with decrease in temperature and increase in concentration. The difference in protection actions of the inhibitors can be attributed to the presence of substituents in the structures that increase or decrease the electron density on the azomethine (–C=N–) group. Polarisation curves indicate that the Schiff bases act as anodic inhibitors. AC impedance and potentiodynamic polarisation measurements reveal that the compounds are adsorbed on the steel surface and the adsorption obeys the Temkin isotherm. Activation parameters (E_a, ΔH*, ΔS*) for the corrosion of low carbon steel in 0.1 M HCl were calculated and showed that corrosion was much reduced in the presence of inhibitors.     

Pitting of AISI 304 stainless steel in bicarbonate and chloride solutions

Metastable and stable pitting on 304 stainless steel (SS304) in 0.1–0.5 m NaCl aqueous solution (pH ~8) has been investigated using a potentiodynamic, a potentiostatic and a weak anodic current galvanostatic techniques. The addition of bicarbonate (0.025–0.5 m) to the solution had an inhibiting effect, manifested by a shift of the pitting potentials to more positive values, a longer induction time for pitting and reduced pit nucleation. The pit nucleation frequency and growth, in the metastable and stable states, decrease as the NaHCO3/NaCl molar concentration increases and pitting is no longer observed for NaHCO3/NaCl molar ratios higher than 3 (four times larger % wt of NaHCO3). Pitting events never occurred at a potential below –0.1 V, fewer metastable events were observed at higher temperature (50°C) and none were observed in chloride free bicarbonate solutions. The inhibiting behaviour of oxyanions is discussed.     

3-Mercaptopropyltrimethoxysilane as a Cu corrosion inhibitor in KCl solution

3-mercaptopropyltrimethoxysilane (MPS) has been used as a copper corrosion inhibitor in 0.100 mol L^–1 KCl solution. The inhibition was studied as a function of the MPS pretreatment concentration in ethanol. The MPS concentration used was between 1.0 × 10^–8 mol L^–1 and 1.0 × 10^–1 mol L^–1. A freshly-cleaned Cu electrode was inserted in an ethanolic solution of MPS for 30 min for pretreatment, and was then exposed to a 0.100 mol L^–1 KCl aqueous solution for 1 h. From the polarization resistance, the inhibition efficiency improved with increase in MPS concentration during the pretreatment. The MPS adsorption on Cu followed a Langmuir adsorption behaviour. However, at MPS concentrations larger than 1.0 × 10^–4 mol L^–1 the inhibition decreased. Moreover, the inhibition efficiency decreased with increase in the exposure time of the MPS modified Cu electrode in the KCl aqueous solution. Polarization studies suggest that MPS is an anodic as well as a cathodic inhibitor, in the presence of dissolved oxygen. X-ray photoelectron spectroscopy (XPS) analysis of the Cu samples showed that the organic compound modifies the Cu surface and scanning electron microscopy (SEM) studies indicated that MPS protects the Cu surface when exposed for 350 h to laboratory environment. Polarized grazing angle Fourier transform-infrared (FTIR) microscopy analysis determined the presence of a polymer on the Cu surface.     

Electrochemical behaviour of aluminium in the presence of EDTA-containing chloride solutions

The electrochemical behaviour of pure aluminium in an EDTA-containing chloride solution was investigated using potentiodynamic and potentiostatic electrochemical techniques and electrochemical impedance spectroscopy. A pronounced EDTA-induced anodic dissolution was observed in alkaline solutions, but the presence of EDTA in solution had little activating effect on the passivation properties at pH values close to 4.0. This was attributed to the relative stability of the Al(EDTA)^– complex formed at the different pH values. This EDTA-induced activation had no deleterious effect on pitting attack, in fact, higher breakdown potentials were observed in the presence of EDTA. This was attributed to the buffering action of EDTA, which inhibited the attainment of a critical pit solution composition. But, in the presence of molybdate, EDTA had no observable effect on pitting attack. The impedance spectra recorded in the presence of EDTA showed evidence for the adsorption of EDTA species during the dissolution process, which in turn, form a large capacitive network, with capacitance values of the order of 3 mF cm^–2 in the low frequency region.     

Pyridine and its derivatives as inhibitors of aluminium corrosion in chloride solution

Pyridine and its selected derivatives (symmetric collidine and 2,5-dibrompyridine) have been studied as corrosion inhibitors for high purity aluminium in a 2m NaCl solution at 25°C and 35°C using d.c. polarization techniques. The investigations were carried out with a wide range of concentrations of the compounds examined (from 0.5×10–5m to 1×10–3m). The results show that the derivatives are adsorbed on aluminium according to the Freundlich isotherm. The values of the standard free energy of adsorption suggest that the adsorptive properties of the compounds under consideration approach the physical type. The polarization curves show that the compounds act as cathodic-type inhibitors.     

Adsorption and inhibition effect of 6-benzylaminopurine on cold rolled steel in 1.0 M HCl

The adsorption and inhibition effect of 6-benzylaminopurine (BAP) on cold rolled steel (CRS) in 1.0 M HCl at 25-50 °C was studied by weight loss and potentiodynamic polarization methods. The results showed that BAP was a good inhibitor in 1.0 M HCl, and the inhibition efficiency (IE) increased with the inhibitor concentration. The adsorption of BAP on the CRS surface obeyed the Langmuir adsorption isotherm equation. Both thermodynamic parameters (adsorption heat ΔH⁰, adsorption free energy ΔG⁰ and adsorption entropy ΔS⁰) and kinetic parameters (apparent activation energy E_a and pre-exponential factor A) were calculated and discussed. Polarization curves showed that BAP acted as a mixed-type inhibitor in hydrochloric acid. Good agreement between weight loss and polarization methods was obtained. The adsorbed film on CRS surface containing optimum dose of BAP was investigated by Fourier transform infrared spectroscopy (FTIR) and atomic force microscope (AFM). Quantum chemical calculation was applied to elucidate the adsorption mode of the inhibitor molecule onto steel surface. Depending on the results, the inhibitive mechanism was proposed from the viewpoint of adsorption theory.