ISSN 2305-6894

2018, Vol. 7, Issue 4 (pp. 460-717)

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Nitrogen-containing six-membered heterocyclic compounds as corrosion inhibitors for metals in solutions of mineral acids – A review

  • Ya.G. Avdeev
A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 119071 Russian Federation

Abstract: The current state of studies on metal protection from corrosion in mineral acid solutions by six-membered N-containing heterocyclic compounds is reviewed. Literature data on the protection of various metals in acid solutions by these compounds are summarized. The specific features of their protective action mechanism are discussed. The feasibility of metal protection by formulations containing these compounds, even in high-temperature corrosion, is noted. N-Containing six-membered heterocyclic compounds are prone to adsorption on metal surfaces from mineral acid solutions. Based on the free adsorption energy values of these corrosion inhibitors (CIs) on metal surfaces, it can be deemed with high probability that they are mostly bound to a metal by physical forces, but upon adsorption on its surface they slow down the cathodic and anodic reactions, and eventually inhibit its corrosion. Compounds containing S atoms or bulky substituents are most interesting. These compounds are adsorbed on metals more strongly and behave as more efficient CIs. It often happens that such CIs hinder metal corrosion in HCl solutions but do it much more weakly in H2SO4, HClO4, and H3PO4. A known method for improving the protective effect of N-containing six-membered heterocyclic CIs in these media involves combining them with anionic additives, e.g., halide or rhodanide anions. The heterocycles discussed behave as CIs in “cold” solutions but lose these properties at higher temperatures. Examples of the use of six-membered N-containing heterocycles as CIs of various steels and non-ferrous metals (Al, Cu, Sn, Zn and their alloys) are available in literature. The industrial application of individual six-membered N-containing heterocycles and their derivatives for metal protection in acid media is of little promise and is unjustified. It is more appropriate to use these compounds as components of inhibitor mixtures. Mixed CIs containing these compounds can hinder corrosion even in such corrosive media as high-temperature HCl solutions or hot H3PO4 solutions. The base for creating prospective mixed corrosion inhibitors for metals in acids should be searched for among six-membered heterocyclic compounds containing two or more nitrogen atoms or compounds obtained from natural raw materials. The bibliography includes 150 references.

Int. J. Corros. Scale Inhib., , 4, 460-497 PDF (1 205 K)
doi: 10.17675/2305-6894-2018-7-4-1

Quantum chemical studies on inhibition activities of 2,3-dihydroxypropyl-sulfanyl derivative on carbon steel in acidic media

  • and
1 Department of Pure and Applied Chemistry, Ladoke Akintola University of Technology, P.M.B. 4000, Ogbomoso, Oyo State, Nigeria
2 Department of Chemistry, University of Ibadan, P.M.B. 5116, Ibadan, Oyo State, Nigeria

Abstract: The inhibiting activity of 3 sets of organic compounds ([2-[(2,3-dihydroxypropyl)sulfanyl]-N-octylacetamide (DSO), 2-[(2,3-dihydroxypropyl)sulfanyl]-N-decylacetamide (DSD) and 2-[(2,3-dihydroxypropyl)sulfanyl]-N-dodecylacetamide (DSDD)) were studied. The studied anti-corrosion compounds i.e. 2,3-dihydroxypropyl-sulfanyl derivatives were calculated using quantum chemical calculation and several descriptors (highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO) and chemical reactivity indices (global electrophilicity index (ω), chemical hardness (η), electronegativity (χ), local reactivity index, electron affinity and ionization potential) which described the anti-corrosion properties of the studied compounds were obtained. Fukui Indices for nucleophilic and electrophilic Attacks for inhibitors i.e. [2-[(2,3-dihydroxypropyl)sulfanyl]-N-octylacetamide (DSO), 2-[(2,3-dihydroxypropyl)sulfanyl]-N-decylacetamide (DSD) and 2-[(2,3-dihydroxypropyl)¬sulfanyl]-N-dodecylacetamide (DSDD) were observed and sites for nucleophilic and electrophilic attacks for DSO were C6 (0.047) and O3 (0.170); for DSD, the utmost value for fk+ was found on C6 (0.047), and the highest value for fk- was located on C5 with 0.099 while the greatest value for fk+ was situated on C6 with 0.047 and the highest value for fk- is found on C3 and C4 with 0.053 each for the DSDD molecule. The molecules used in this study was calculated using quantum chemical calculation and it was achieved using Spartan 14. More so, the QSAR study using multiple linear regression method was executed using Gretl 1.9.8. The selected descriptors among the entire calculated descriptors were used in the development of quantitative structural activity relationship (QSAR) model and the developed model replicated the observed %IE. The correlation coefficient (R2) was calculated to be 0.926, cross validation (CV.R2) was 0.963 and adjusted R2 was 0.852. Also, ELUMO was the predominating parameter in the corrosion inhibition property of the studied compounds.

Int. J. Corros. Scale Inhib., , 4, 498-508 PDF (1 044 K)
doi: 10.17675/2305-6894-2018-7-4-2

Experimental, quantum chemical studies of oxazole derivatives as corrosion inhibitors on mild steel in molar hydrochloric acid medium

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1 Laboratory of Engineering, Electrochemistry, Modeling and Environment (LIEME), Faculty of Sciences, University Sidi Mohamed Ben Abdellah, Fez, Morocco
2 Laboratory of organical Chemistry (LOC), Faculty of sciences, University Sidi Mohamed Ben Abdellah, Fez, Morocco
3 Laboratory of Applied Analytical Chemistry Materials and Environment (LC2AME), Faculty of sciences, University of Mohammed Premier, Oujda, Morocco

Abstract: The corrosion inhibition performances of (4-ethyl-2-phenyl-4,5-dihydro-1,3-oxazol-4-yl)-methanol (C1); 4-{[(4-ethyl-2-phenyl-4,5-dihydro-1,3-oxazol-4-yl)methoxy]methyl}-benzene-1-sulfonate (C2) and 4-[(azidoxy)methyl]-4-ethyl-2-phenyl-4,5-dihydro-1,3-oxazole (C3) mild steel in molar hydrochloric solution have been evaluated by using gravimetric, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques as well as quantum chemical calculations. Results obtained reveal that these compounds reduce significantly the corrosion rate of mild steel, their inhibition efficiencies increased with inhibitor concentration. This behavior means that the inhibitive effect of the studied oxazole derivatives occur through the adsorption of inhibitor molecules on the metal surface. Polarization curves reveal that both compounds C1 and C3 act essentially as mixed type inhibitors with cathodic predominance effect, while the compound C2 can be classified as cathodic type inhibitor. EIS spectra obtained show a typical Nyquist plot with single semicircles shifted along the real impedance of x-axis. Impedance data are analyzed in term of the simple modified Randles equivalent circuit with one relaxation time constant. Indeed, a Constant phase element, CPE, is introduced in the circuit instead of a pure double layer capacitor in order to take into account the electrode surface heterogeneity. Adsorption of these inhibitors on the mild steel surface was found to obey the Langmuir adsorption isotherm. Some thermodynamic parameters were calculated and discussed. The correlation between inhibition efficiency and molecular structure of oxazole derivatives was theoretically studied via quantum chemical calculations using density functional theory (DFT) at B3LYP/6-31G (d,p). Results showed a general correlation between the computed descriptors and the experimental data.

Int. J. Corros. Scale Inhib., , 4, 509-527 PDF (1 213 K)
doi: 10.17675/2305-6894-2018-7-4-3

Influence of the acidity of the medium and the activity of chloride ions on kinetics of partial electrode reactions on steel with a superhydrophobic surface in chloride media

  • , , and
1 Tambov State Technical University, ul. Sovetskaya, 106, Tambov, 392000, Russian Federation
2 All-Russian Scientific Research Institute of Use of Machinery and Oil Products, Novo-Rubezhnyi per., 28, Tambov, 392022, Russian Federation
3 Derzhavin State University, ul. Internatsyonalnaya, 33, Tambov, 392000, Russian Federation
4 Angara GmbH, In der Steele 2, D-40599, Düsseldorf, Germany

Abstract: The electrochemical behavior of carbon steel with a superhydrophobic surface in weakly acid solutions with a constant ionic strength equal to 1 and a complex composition of the electrolyte x M HCl + (1–x) M NaCl with x = 0.0005–0.01 mol/L has been studied. The effect of the concentration (activity) of Cl anions was evaluated in NaCl solutions with variable concentrations in the range 0.0005–0.01 mol/L of the salt. To obtain a superhydrophobic coating, the metal surface was textured by IR laser radiation of nanosecond duration followed by chemisorption of MAF (methoxy-{3- [2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl)oxy]propyl}silane from a solution of n-decane. The thickness of the superhydrophobic coating, including the textured metal layer and the adsorbed nanosize layer of the superhydrophobization agent (2–3 nm), was of the order of 100 μm. The wetting angle is 168.8±1.5°. The kinetic parameters of the hydrogen evolution reaction, accompanied by cathodic reduction of dissolved oxygen, and anodic ionization of the metal as a function of the acidity of the medium were obtained. With increasing duration of exposure, corrosion potential (Ecor) shifts to the region of more negative potentials and the most negative Ecor is observed at minimal HCl concentration. The steady state is achieved only after 120 hours and the corrosion potentials of the steel that corrodes in the active state assumes very negative values (–0.550 to –0.580 V) due to inhibition of the cathodic reaction. In media containing 0.0005–0.01 mol/L sodium chloride, the relationship between the kinetic parameters of the same electrode reactions and the activity of chloride ions (aCl-) has been studied. The anodic reaction is accelerated and the corrosion rate of the steel increases with an increase in the activity of chloride ions (1.0≤d lg ia/d lg aCl-≤2, 1.0≤d lg icor/d lg aCl-≤1.3). This may be a consequence of the participation of halogen anions in the anodic process.

Int. J. Corros. Scale Inhib., , 4, 528-541 PDF (827 K)
doi: 10.17675/2305-6894-2018-7-4-4

Inhibitory performance of some pyrazole derivatives against corrosion of mild steel in 1.0 M HCl: Electrochemical, MEB and theoretical studies

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1 Laboratoire d’Ingénierie d’Electrochimie de Modélisation et d’Environnement (LIEME) FSDM Fès, Morocco
2 Laboratoire National de Contrôle des Médicaments, D M P, Ministère de la Santé, Madinat Al Irnane, BP 6206, Rabat, Morocco

Abstract: In this study, we discussed the inhibition properties of three new Pyrazole derivatives (DPA, DPM and DPF) against the corrosion of mild steel in 1.0 M HCl, using the weight loss technique, the stationary method and the transitional method. The experimental results show that the inhibition properties increase with the concentration and can reach a limit value of 97% for the inhibitor DPA at 10–3 M. The curves of polarization show that the Pyrazole derivatives were a mixed inhibitor. The data obtained by electrochemical impedance spectroscopy were analyzed to be modeled by appropriate equivalent circuit models. The evolution of the temperature leads to a decrease in the inhibition efficiency of the Pyrazole compounds. Several adsorption isotherms have been modeled such as Langmuir, Temkin, Frumkin, Flory–Huggins, Freundlich and the kinetic thermodynamic model of El-Awady, in order to provide additional information on the inhibitory properties of the compounds studied. The coefficient of determination values of all the isotherms are very high, from the two models of Flory–Huggins and El-Awady we find that the adsorption of molecules on the surface of the steel moves more than a single molecule of water which is at odds with the Langmuir isotherm. Whereas the isotherms of Temkin and Frumkin suggest the existence of the lateral interactions between the adsorbed species. Scanning electron microscopy (SEM) and EDX analyzes were used to characterize the chemical composition of the film formed on the surface of the steel. Surface studies have shown that the inhibitory layer consists of an iron oxide/hydroxide mixture in which the N, F atoms are incorporated. The DFT studies have also been carried out for protonated form of the inhibitor molecules by considering that in acidic medium the heteroatoms of organic inhibitors easily undergo protonation. The experimental and density functional theory (DFT) studies were in good agreement.

Int. J. Corros. Scale Inhib., , 4, 542-569 PDF (1 608 K)
doi: 10.17675/2305-6894-2018-7-4-5

Influence of water-soluble monomers on the corrosion protection ability of chromium coatings obtained from Cr(III)-based solutions

  • and
1 Dmitry Mendeleev University of Chemical Technology of Russia, Miusskaya sq., 9, Moscow, 125047 Russian Federation
2 A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskii pr., 31, Moscow, 119071 Russian Federation

Abstract: The effect of water-soluble electropolymerizable monomer additives in Cr(III) sulfate–oxalate electrolytes on the corrosion–electrochemical behavior of chromium coatings and their ability to protect the steel support is studied. The additives into the Cr(III) sulfate–oxalate electrolytes were caprolactam, aniline, and acrylamide. The XPS technique showed that both the surface and bulk layers of chromium coatings obtained from electrolytes with additives contain products of chemical or electrochemical conversions of caprolactam, aniline, and acrylamide, including their polystructures. It is found that caprolactam and aniline produce a positive effect on the protective ability of chromium coatings, while the protective ability of chromium coatings in the presence of acrylamide decreases. These properties are determined primarily by a decrease in the number of defects in chromium coatings in case of caprolactam and aniline and an increase in the number of cracks in the deposits in case of acrylamide. According to the earlier studies, the corrosion–electrochemical behavior of chromium coatings from Cr(III) sulfate–oxalate electrolytes in 0.5 M H2SO4 is determined primarily by the presence of the chromium carbide phase acting as a cathodic agent. The effect of additives on the anodic polarization curve in 0.5 M H2SO4 is most probably determined not only by an increase or decrease in the porosity of chromium deposits, but also by incorporation of the additives and products of their electrochemical conversion that, according to the literature, can act as corrosion inhibitors.

Int. J. Corros. Scale Inhib., , 4, 570-581 PDF (1 139 K)
doi: 10.17675/2305-6894-2018-7-4-6

Peculiarities of the effect of secondary amines with cyclic substituents on microbial steel corrosion

  • , , , , and
1 T.H. Shevchenko National University “Chernihiv Colehium”, 53 Hetmana Polubotka str., Chernihiv, 14013, Ukraine
2 National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, 37 Peremohy Ave, Kyiv, 03056 Ukraine
3 Ukrainian State University of Chemical Technology, ave. Gagarin, 8, 49005, Dnipro, Ukraine

Abstract: The effect of secondary amines with cyclic substituents (triazoloazepine, unsubstituted phenyl or substituted phenyl ones) on the microbial corrosion of low-carbon steel induced by sulfate-reducing bacteria isolated from various technogenic media was studied. The compounds were obtained by reactions of 7-methoxy-3,4,5,6-tetrahydro-2H-azepine with hydrazides of substituted N-arylaminoacetic acids. It was found by gravimetric and electrochemical methods that secondary amines with p-methoxyphenyl and p-chlorophenyl substituents hinder steel corrosion in the neutral Postgate “B” water-salt medium, both in the presence of enrichment bacterial culture and the Desulfovibrio sp. M.4.1 strain. The highest inhibitive effect (a 2.13-fold corrosion rate decrease) is shown by the compound with the p-chlorophenyl substituent. It has been shown that the effect of concentration within 0.5–2.0 g/l on the efficiency of biocorrosion inhibition is insignificant. The results obtained were explained by the antimicrobial action of secondary amines on sulfate-reducing bacteria and their satellites (iron-reducing and denitrifying bacteria). Using energy dispersive spectroscopy, it has been shown that secondary amines studied can be adsorbed adsorb on mild steel surface under conditions of microbial corrosion in a water-salt medium with bacterial sulfate reduction. The surface layers were found to contain nitrogen contained in the elementary composition of the compounds, as well as chlorine in the case of the secondary amine with the p-chlorophenyl substituent. It has been found that the biofilm (a polymeric matrix consisting of bacterial excrements and corrosion products) is formed atop the film of adsorbed compounds. The inhibition effect is ensured only upon adsorption of compounds with antimicrobial properties toward sulfate-reducing bacteria. If secondary amines have no antimicrobial properties toward sulfate-reducing bacteria, iron sulfides are formed on the metal surface and microbial corrosion is accelerated.

Int. J. Corros. Scale Inhib., , 4, 582-592 PDF (1 036 K)
doi: 10.17675/2305-6894-2018-7-4-7

Dendrimers as novel class of polymeric corrosion inhibitors: A review

  • , and
1 Department of Chemistry, School of Chemical and Physical Sciences, Faculty of Natural and Agricultural Sciences, North-West University, Private BagX2046, Mmabatho 2735, South Africa
2 Material Science Innovation &Modelling (MaSIM) Research Focus Area, Faculty of Natural and Agricultural Sciences, North-West University, Private Bag X2046, Mmabatho 2735, South Africa
3 Department of Chemistry, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, India
4 Center of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia

Abstract: Dendrimers are a new class of highly branched, nano-sized, monodisperse macromolecules that have several fascinating physical and chemical characteristics. They are highly soluble in the polar solvents, contain several surface functionality and high surface area which makes them suitable reagents for industrial and biological applications. Recently, several dendrimers have been investigated as effective corrosion and scale inhibitors for metallic and silica corrosion using experimental and theoretical methods. Generally, dendrimers become effective by forming insoluble metal-dendrimer or silica-dendrimer composite on the surface. Their inhibition performance of dendrimers have been measured using several experimental such as weight loss, electrochemical (EIS and PDP) and surface (EDX, SEM and AFM) as well as computation techniques such as molecular dynamics simulation and DFT based quantum chemical calculations. The interactions between metal surface and dendrimers can be explain through some common parameters such as EHOMO, ELUMO, ∆E, electronegativity (χ), hardness (η), softness (σ), dipole moment (µ) and fraction of electron transfer (∆N). Present book chapter deals with detail description on the corrosion inhibition and anti-scaling behaviours of dendrimers for metals and silica in several electrolytic media.

Int. J. Corros. Scale Inhib., , 4, 593-608 PDF (977 K)
doi: 10.17675/2305-6894-2018-7-4-8

Inhibitor effect of new azomethine derivative containing an 8-hydroxyquinoline moiety on corrosion behavior of mild carbon steel in acidic media

  • , , , , , , , , and
1 Laboratoire Interface Matériaux Environnement, Faculté des Sciences, Université Hassan II Casablanca, B.P 5366 Maârif Casablanca, Morocco
2 Laboratory of Agricultural Resources, Polymer and Process Engineering, Department of Chemistry, Faculty of Sciences, Ibn Tofail University, Kenitra, Morocco
3 Laboratory of Separation Procedures, Faculty of Sciences, Ibn Tofail University, Kenitra, Box 133, Kenitra, Morocco
4 LC2AME, Faculty of Sciences, Mohammed First University, PO Box 717, 60 000 Oujda, Morocco
5 Laboratory of Materials, Nanotechnology and Environment, Faculty of Sciences, Mohammed V University, Av. IbnBattouta, Box 1014 Agdal-Rabat, Morocco

Abstract: A new Azomethine derivative namely 5-(((4-hydroxybenzylidene) amino)methyl)quinolin-8-ol (HBHQ) was synthesized and identified by different spectroscopic methods. The product was assessed in the inhibition of corrosion of carbon steel (CS) in 1 M HCl using Tafel polarization, weight loss and electrochemical impedance spectroscopy. Their property anticorrosion is relative in concentrations and achieved 92% at the optimum concentration of 10–3 M. Polarization studies showed that that the newly synthesized inhibitor was of mixed type in nature. The EIS data bring that, the development of a protective layer of azomethine derivative increase the charge transfer resistance and decreases in the double layer capacitance of carbon steel in acid medium. The adsorption process at interface of carbon steel in hydrochloric acid by HBHQ was studied at different temperatures (298–338 K) by means of Tafel polarisation measurements. The adsorption of azomethine derivative on the carbon steel (CS) surface followed Langmuir adsorption isotherm and in order to discover the mode of adsorption process, various thermodynamic and activation parameters were evaluated. Quantum chemical calculations were performed using methods based on density functional theory (DFT/B3LYP) and Monte Carlo simulations (MCs). Indeed, the results obtained by this computation reflect a good agreement with the practical part.

Int. J. Corros. Scale Inhib., , 4, 609-632 PDF (1 629 K)
doi: 10.17675/2305-6894-2018-7-4-9

A combined experimental and theoretical study of (E)-ethyl 3-(4-methoxyphenyl)acrylate as corrosion inhibitor of iron in 1 M HCl solutions

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1 Chemistry Education Division, Faculty of Science Education, University of Mataram, Jalan Majapahit no 62 Mataram, 83125, Indonesia
2 Department of Chemistry, Faculty of Mathematics and Natural Science, University of Jalan Majapahit no 62 Mataram. Mataram, 83125, Indonesia
3 Department of Chemistry, Universitas GadjahMada, Sekip Utara, Yogyakarta 55281, Indonesia
4 Department of Chemistry, Faculty of Mathematics and Natural Science, Institut Teknologi Bandung. Jalan Ganesha No 10 Bandung, 40132, Indonesia

Abstract: The study aimed to isolate, characterize and measure the corrosion inhibition efficiency of (E)-ethyl 3-(4-methoxyphenyl)acrylate (EPE) from Kaempferia galanga extract of iron in 1 M HCl solution. The experimental study was conducted with weight loss and electrochemical impedance measurements followed by theoretical study using density functional theory (DFT) method at the B3LYP level of theory. EPE has been successfully isolated and confirmed by spectroscopic techniques. Thermodynamic parameters: activation energy Ea, adsorption enthalpy ΔH, entropy ΔS, and Gibbs-free energy of adsorption ΔG0ads indicate physisorption mechanism. The adsorption of EPE on the iron surface follows Temkin’s isothermal. It was revealed that the efficiency of corrosion inhibitor of EPE at the maximum tested concentration was 76.22%. Density functional theory (DFT) calculation of EPE was applied to compare the effect of electron donating and withdrawing groups on the efficiency of corrosion inhibitors, as an approach for designing high-efficiency new corrosion inhibitors. The corrosion inhibition performance of the EPE and its derivatives was evaluated using quantum chemical parameters such as frontier orbital energies (EHOMO, ELUMO), ionization potential (I), electron affinity (A), absolute electronegativity (χ), the fraction of electrons transferred (ΔN), corrosion inhibition efficiency (IE%), and binding energy (ΔE). The study shows that the corrosion inhibition efficiency of EPE increases with the addition of the NH2 function group whereas the NO2 group gives the opposite result.

Int. J. Corros. Scale Inhib., , 4, 633-647 PDF (1 124 K)
doi: 10.17675/2305-6894-2018-7-4-10

Adsorbtion of sodium tridecanoate on copper from aqueous solutions and copper protection from atmospheric corrosion

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A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, Moscow, 119071 Russian Federation

Abstract: The adsorption and protective effect of sodium tridecanoate CH3(CH2)11COONa (NaC13) on copper and the possibility of increasing the effectiveness of protection by joint use with a trialkoxysilane (TAS) were investigated. A set of electrochemical, ellipsometric and corrosion tests was carried out on samples of M1 copper (copper content > 99.9%). From an analysis of the anodic polarization curves of copper from solutions containing NaC13, it follows that when the inhibitor concentration is >0.07 mmol/l, the current density of copper active dissolution decreases and spontaneous passivation of the electrode occurs with a shift in the value of the pitting potential Epit in the positive direction. With an increase in the concentration of the inhibitor, the value of Epit increases while the anodic current density decreases. When the concentration of the inhibitor in the solution is 1.6 mmol/l or more, the value of Epit shifts to the oxygen evolution region. Studies of NaC13 using the ellipsometric method showed that the adsorption of the inhibitor starts at very low concentrations, viz., 0.01 nmol/l. Adsorption is described by the Temkin equation with an adsorption free energy of 67 kJ/mol. In comparison with sodium oleyl sarcosinate СН3(СН2)7СН=СН(СН2)7СОN(CH3)СН2СООNa (SOS) and sodium laurate CH3(CH2)10COONa (NaC12), adsorption begins at lower concentrations. Sodium tridecanoate adsorption on copper is polymolecular. Accelerated corrosion tests with daily moisture condensation on copper pretreated with an inhibitor solution at 60°C for 5 minutes were carried out. It was shown a protective mixture of NaC13 and TAS significantly increased the time until the appearance of the first corrosion site.

Int. J. Corros. Scale Inhib., , 4, 648-656 PDF (922 K)
doi: 10.17675/2305-6894-2018-7-4-11

Triazole derivatives as chamber inhibitors of copper corrosion

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A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, Moscow, 119071 Russian Federation

Abstract: A set of physicochemical (ellipsometry, wetting angle measurement), electrochemical (electrochemical impedance spectroscopy, electrochemical polarization measurements) and corrosion methods (recurrent moisture condensation conditions, salt fog) was used to study the properties of adsorption films formed on copper by the chamber method from benzotriazole (BTA), 1,2,4-1H-triazole (TZ), tolyltriazole (TTA), 5-chloro-1,2,3-benzotriazole (Cl-BTA), 3-amino-1H-1,2,4-triazole and 4-amino-1H-1,2,4-triazole vapors at 100°C. It was shown that upon one-hour treatment of copper with vapors of these compounds, nanosized hydrophobic adsorption films were formed on it, which hindered the thermal oxide growth but stabilized the passive state of the metal and improved its corrosion resistance. Of various triazole derivatives studied as chamber corrosion inhibitors, BTA and its derivatives can be distinguished. After one-hour chamber treatment of copper, the protective after-effect of their adsorption films grows symbatically with the saturated vapor pressure at the CT temperature, i.e., in the series BTA > TTA > Cl-BTA. This may indicate that at 100°C, there is not enough time for the formation of equilibrium adsorption films on the metal. There are reasons to believe that upon prolonged copper treatment with vapors of substituted benzotriazoles (24 hours or more), equilibrium adsorption films of inhibitors are formed thereon. In this case, the character of the effect of the properties of chamber inhibitors on their protective after-effect changes. Under these conditions, the best metal protection is provided by Cl-BTA, i.e., the least volatile and most hydrophobic of the substituted benzotriazoles studied.

Int. J. Corros. Scale Inhib., , 4, 657-672 PDF (718 K)
doi: 10.17675/2305-6894-2018-7-4-12

The structure and protective properties of IFHANAL conversion coatings on aluminum alloys

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, Moscow, 119071 Russian Federation

Abstract: The chemical oxidation in a chromate-free IFHANAL converting solution leads to the formation of conversion coatings with different thicknesses on aluminum (1010) and its alloys (5154, 6063, 2024, 7075). According to the data of polarization measurements in chloride solutions, the thickness of the coatings under study is not a determining factor in their protective ability. A significant increase in the protective properties of the coatings obtained is observed upon filling of the coatings in a solution of IFKhAN-25 corrosion inhibitor. This effect of coating filling is associated with changes in their structure during the hydration of surface oxides. According to X-ray phase analysis data, the conversion coating on 1010 aluminum alloy in its initial state consists of amorphous aluminum oxide phases. Filling of the coating in distilled water and in a solution of corrosion inhibitor equally changes the phase state of the surface oxide. The level of oxide crystallization increases in both cases, but the effect of the inhibitor on the process of oxide hydration is not observed. Perhaps, the crystallization of the oxide promotes adsorption of the inhibitor and increases the protective properties of the filled coating. Filling of conversion coatings on the Al–Mg alloys studied also modifies the phase state of surface oxides, making them less amorphous. The corrosion inhibitor in filling solutions is directly involved in the process of oxide hydration in conversion coatings on Al–Mg alloys, contributing to the strengthening of their protective properties. During the filling of more complex hetero-oxide structures in Al–Mg–Cu(Zn) alloys, the corrosion inhibitor adsorption makes a prevalent contribution to the increase in protective properties.

Int. J. Corros. Scale Inhib., , 4, 673-682 PDF (991 K)
doi: 10.17675/2305-6894-2018-7-4-13

Localized dissolution of carbon steel used for pipelines under constant cathodic polarization conditions. Initial stages of defect formation

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A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: This work is aimed at studying the possibility of initiation and growth of local (pit-like) defects under cathodic polarization, both in neutral and alkaline solutions, as well as the effect of hydrogen on the local dissolution of tube carbon steel and on the defect formation under permanent cathodic polarization conditions. A combination of optical and electrochemical methods of research allowed us to study the kinetics of the initial stages of localized cathodic dissolution of steel in detail. In fact, the initiation of pit-like defects under cathodic polarization of carbon steel in the presence of chloride ions in the electrolyte was observed experimentally. The incubation period of defect formation under various conditions was determined with high accuracy, and the factors affecting the incubation period of defect initiation were determined. It has been shown that the dependence of the density of appearing corrosion defects on the potential passes through a maximum, while the time until the appearance of the first defect decreases as the potential is shifted towards negative values. It has also been shown that the dependence of the density of corrosion defects on the time of the test passes through a maximum, i.e., some of the appearing defects are metastable and stop functioning after a few dozen hours. It has also been found that the increased rate of hydrogen penetration into the metal caused by addition of a metal hydrogen absorption promoter (thiourea) stimulates both the initiation and development of local defects at cathodic potentials. An increase in thiourea concentration, rate of hydrogen penetration into the metal and the amount of hydrogen absorbed by steel results in a shortening of the incubation period, on the one hand, and in an increase in the number of pit-like defects, on the other hand.

Int. J. Corros. Scale Inhib., , 4, 683-696 PDF (1 014 K)
doi: 10.17675/2305-6894-2018-7-4-14

Electrochemical impedance spectroscopy (EIS) of composite polymer coatings on metal substrates

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A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: The electrochemical properties of multilayer composite polymer coatings consisting of a Zn-filled inhibited primer layer and an external insulating polymer coating are investigated by the EIS method. During long-term exposure in aggressive media, the kinetics of the properties of coatings obtained on corrosion-inert (Pt) and corrosion-active (mild steel St3) substrates were compared. It is shown that the impedance spectrum in the studied systems is determined by the imposition of two relaxation processes: high-frequency (HF), due to the processes of electrolyte transfer, and low-frequency (LF) associated with the Faraday process of under-coating corrosion of Zn powder in the primer layer or substrate corrosion. The frequencies of the HF process for all investigated composite coatings, including those applied to different substrates, are close, while the frequency of the LF process depends on the coating structure and the substrate type. It is shown that frequencies of LF processes at high exposure times in composite coatings with Zn-protective primer on different substrates (mild steel St3 or Pt) are identical (9.3 Hz). This fact is the base for the conclusion that the Faraday process in both cases is the same and deals with corrosion of Zn powder. The coating structure is a factor determining the frequency of the LF process for coatings on a steel substrate. In composite systems with Zn-rich primer, the Faraday low-frequency process is observed at significantly lower frequencies (9.3 Hz) than in the case of applying only the insulating coating (250 Hz), not only at the initial stage, but also at high exposure times in 3% NaCl. This can be seen as evidence of prolonged protective action of the Zn powder in composite coatings. So the nature of the under-coating corrosion process can be determined by its EIS characteristic frequency.

Int. J. Corros. Scale Inhib., , 4, 697-709 PDF (1 521 K)
doi: 10.17675/2305-6894-2018-7-4-15

A quantum chemical insight into corrosion inhibition effects of moxifloxacin and betamethasone drugs

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1 Bursa Tecnical University Department of Chemistry Faculty of Engineering and Natural Sciences,16310 Yildirim Bursa, Turkey
2 Ankara University Faculty of Science, Department of Physical Chemistry, 06100 Beşevler Ankara, Turkey

Abstract: The corrosion protection properties of several drugs attract too much attention in recent years due to the structural closeness they share with effective corrosion inhibitors. It is obvious that the mainstay for the choice of drugs as corrosion inhibitors is mostly due to their environmentally friendly nature. In parallel, interest in the use of expired drugs has also seen a resurgence in corrosion research community. However, there still exists much skepticism about the value such usage can add to corrosion inhibition of metals. In this regard, in a previous study, two expired drugs, i.e., moxifloxacin and betamethasone (betnesol), which are widely used for the systemic treatment of bacterial infections and inflammation respectively, have been experimentally investigated as effective corrosion inhibitors for aluminum in sulfuric acid solution. According to the experimental findings, an increase in inhibitor concentration resulted in an increase of the inhibition efficiency of the inhibitors and transfer resistance. The anodic type nature of moxifloxacin and betamethasone has also been illustrated by polarization curve, and from a thermodynamical aspect, both chemisorption and physisorption of these drugs on aluminum metal surface have been proposed. However, very little is known about the relation between molecular structure/electronic properties and inhibition efficiencies of these compounds at the atomic level. For this purpose, the structures and the ground-state energies of moxifloxacin and betamethasone have been analyzed employing density functional theory (DFT) calculations. The reported optimized geometries, molecular properties such as highest occupied molecular orbital energy (EHOMO), the lowest unoccupied molecular orbital energy (ELUMO) and the energy gap (ΔE) as well as essential global reactivity parameters have also been used to reveal the inhibition efficiency of moxifloxacin and betamethasone. The experimental data which suggest better inhibition by betamethasone have been theoretically acknowledged.

Int. J. Corros. Scale Inhib., , 4, 710-717 PDF (723 K)
doi: 10.17675/2305-6894-2018-7-4-16

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