Synthesis and evaluation of new long alkyl side chain acetamide, isoxazolidine and isoxazoline derivatives as corrosion inhibitors

2-(Alkylsulfanyl)-N-(pyridin-2-yl) acetamide derivatives were synthesized via amidation reaction of acyl chlorides bearing S atom in the long chain with 2-aminopyridine. Derivatives of isoxazolidine and isoxazoline were synthesized through 1,3-dipolar cycloaddition reactions with three different long chain alkenes containing O or S as hetero atoms and C,N-diphenyl nitrone or benzonitrile-N-oxide, respectively. Synthesized compounds were characterized with their FT-IR, ¹H NMR spectra and then their physical properties and corrosion prevention efficiencies were investigated. All compounds were tested with steel coupons in acidic medium by gravimetric method, and also some of them were tested with steel stripe in paraffin based mineral oil medium via standard method. Acidic test was done with a medium concentration of 2 M HCl for 20 h at room temperature. Mineral oil was used and the test in this medium was done at 60 °C constant temperature but varying time from 42 to 63 h. The best inhibition was generally obtained at 50 ppm inhibitor concentration in the acidic medium. All tested inhibitors except two of them in oil medium also showed promising inhibition efficiencies.     

Theoretical elucidation on corrosion inhibition efficiency of 11-cyano undecanoic acid phenylamide derivatives: DFT study

The inhibition effects of 11-cyano undecanoic acid phenylamide derivatives against corrosion are studied by means of density functional approach B3LYP/6-311G(d,p) calculations. The efficiencies of corrosion inhibitors and the molecular structure relate to some parameters, such as E _HOMO, E _LUMO, the energy gap between E _LUMO and E _HOMO (ΔE = E _LUMO ? E _HOMO), dipole moments (μ), and other parameters, including electronegativity (χ), global hardness (η), softness (ρ), chemical potential (μ_c) and the fraction of electrons transferred from the inhibitor molecule to metallic atom (ΔN). The computed quantum chemical properties indicate good correlation with experimental corrosion inhibition efficiencies of 11-cyano undecanoic acid phenylamide derivatives. A good correlation between the substituent type and inhibition efficiency of inhibitors through the application of Hammett relationship is obtained. The linear correlation is also found between the Hammett parameters and calculated molecular orbital energies.     

Molecular dynamics and density functional theory study on relationship between structure of imidazoline derivatives and inhibition performance

The inhibition performance of two imidazoline derivatives, 3-ethylamino-2-undecyl imidazoline (EUI) and chloride-3-ethylamino-3-(2,3-two hydroxyl) propyl-2-undecyl imidazoline sodium phosphate(CEPIP), for Q235 steel in CO₂ saturated solution at 298 K have been tested by weight loss experiment and electrochemical techniques. The adsorption behavior of the two inhibitors on Fe surface has been studied using molecular dynamics (MD) method and density functional theory. The results indicated that the two imidazoline derivatives could both adsorb on the Fe surface firmly through the imidazoline ring and heteroatoms, the two inhibitors both have excellent corrosion inhibition performance.     

Theoretical study of corrosion inhibition of amides and thiosemicarbazones

An examination of quantum chemical and corrosion inhibition studies were carried out to investigate whether any clear links exist between the results of quantum chemical calculations and the experimental efficiencies of urea (U), thiourea (TU), acetamide (A), thioacetamide (TA), semicarbazide (SC), thiosemicarbazide (TSC), methoxybenzaldehydethiosemicarbazone (MBTSC), 2-acetylpyridine-(4phenyl) thiosemicarbazone (2AP4PTSC), 2-acetylpyridine-(4-methyl) thiosemicarbazone (2AP4MTSC), benzointhiosemicarbazone (BZOTSC) and benzilthiosemicarbazone (BZITSC) being corrosion inhibitors. The quantum chemical calculations have been performed by using DFT, ab-initio molecular orbital and semi-empirical methods for some amides and thiosemicarbozone derivatives being corrosion inhibitors. The highest occupied molecular orbital energy (E_HOMO), lowest unoccupied molecular orbital energy (E_LUMO), the energy gap between E_HOMO and E_LUMO (ΔE_HOMO-LUMO), dipole moments (μ), charges on the C, O, N, S atoms, the total energies of the molecules and the polarizabilities 〈α〉, the coefficients of the development of the MO over the atomic orbital (AO) corresponding to the between atoms which a new bond is established have been calculated.The results of quantum chemical calculations and experimental efficiencies of inhibitors were subjected to correlation analysis. We have reached the conclusion that the synthesis of better corrosion inhibitors can be achieved by controlling all electronic properties and parameters of a selected group of molecules.     

Influence of the alkyl chain length of 2 amino 5 alkyl 1,3,4 thiadiazole compounds on the corrosion inhibition of steel immersed in sulfuric acid solutions

The corrosion inhibition efficiency of 2 amino 5 alkyl 1,3,4 thiadiazole compounds with different alkyl chain lengths, namely: 2 ethyl, 3 n propyl, 5 n penthyl, 7 hepthyl, 11 undecyl and 13 tridecyl, was evaluated in the system steel/1 M H₂SO₄. These compounds were synthesized, characterized by FT-IR and NMR spectroscopy analysis and evaluated using electrochemical impedance spectroscopy and SEM analysis. The results showed that the inhibition mechanism involves blockage of the steel surface by the inhibitor molecules by a Langmuir-type adsorption process and that the alkyl chain length plays an important role in the inhibition efficiency of the synthesized inhibitors.     

Theoretical investigation of corrosion inhibition effect of imidazole and its derivatives on mild steel using cluster model

Interaction energies of imidazole and its seven derivatives on the surface of mild steel were calculated via a cluster model by using quantum chemical calculations at density functional theory level. The mild steel surface and its adsorption sites were considered as some clusters taken from two-layered (0 0 1) planes and the quantum chemical calculations which were carried out consist of adsorption of the inhibitor molecules on the surface of these clusters. It is shown that 90% of inhibition variations of the imidazole derivatives are described by considering perpendicular interaction of the inhibitors by iron atom in the mild steel unit cell.     

Theoretical considerations on the supposed linear relationship between concrete resistivity and corrosion rate of steel reinforcement

Traditionally, the assessment of service life of steel reinforced concrete structures has been focused on the prediction of the time required to achieve a transition from passive to active corrosion rather than to accurately estimate the subsequent corrosion rates. However, the propagation period, i.e. the time during which the reinforcing steel is actively corroding, may add significantly to the service life. Consequently, ignoring the propagation period may prove to be a conservative approach. On the other hand the prediction of the corrosion rate may result in a very complex task in view of the electrochemical nature of corrosion and the numerous parameters involved. In order to account for the various influences an essentially empirical model has been introduced in which the electrolytic resistivity of the concrete environment serves as the major parameter. This model will be discussed for carbonation‐induced corrosion based on the commonly accepted theory of aqueous corrosion. An alternative model for microcell corrosion is proposed which is based on the commonly accepted view that anodic and cathodic sites are microscopic and their locations change randomly with time. In line with this view electrolytic resistivity can be incorporated and thus may play a significant role in the kinetics of the corrosion process. For a wide range of corrosion current densities the relationship between corrosion current density, log(i_corr), and concrete resistance, log(R_con), can then be approximated by an almost ideal linear relationship. Assuming a fixed geometrical arrangement of anodic and cathodic sites on the steel surface, this linear relationship is also valid for concrete resistivity, ρ_con. However, from the theoretical treatment of the electrochemical processes underlying reinforcement corrosion it becomes evident that a linear relationship between corrosion current density and concrete resistivity does not necessarily imply that concrete resistance is dominating the overall corrosion cell resistance. In most cases a significant portion of the driving voltage of the corrosion cell will be consumed by the transfer of electrical charge involved in cathodic reactions, i.e. cathodic activation control will dominate.     

Theoretical study of benzimidazole and its derivatives and their potential activity as corrosion inhibitors

A theoretical study of benzimidazole (BI) and two of its derivatives namely 2-methylbenzimidazole (2-CH₃BI) and 2-mercaptobenzimidazole (2-SHBI) recently used as corrosion inhibitors for mild steel in 1 M HCl was undertaken by considering Density Functional Theory (DFT) at the B3LYP/6-311G++(d,p) level. The properties most relevant to their potential action as corrosion inhibitors has been calculated in the neutral and protonated form: E_HOMO, E_LUMO, energy gap (ΔE), dipole moment (μ), electronegativity (χ), global hardness (η) and the fraction of electrons transferred from the inhibitor molecule to the metallic atom (ΔN). The theoretical results are in agreement with the experimental data.     

A study of the inhibition of iron corrosion by imidazole and its derivatives self-assembled films

The self-assembled (SA) films of imidazole and its derivatives were prepared on the iron surface. The protection abilities of these films against iron corrosion in 0.5 M H₂SO₄ solution were investigated using electrochemical impedance spectroscopy (EIS) and polarization techniques. The results of EIS and polarization curves demonstrated that films of the imidazole and its derivatives were able to protect iron from corrosion effectively. XPS was also used for the surface analysis, the results from XPS confirmed the adsorption of imidazole derivatives on the iron surface by monitoring the functional group peaks of the compounds.     

On the relationship between corrosion inhibiting effect and molecular structure of 2,5-bis(n-pyridyl)-1,3,4-thiadiazole derivatives in acidic media: Ac impedance and DFT studies

The inhibition properties of 2,5-bis(n-pyridyl)-1,3,4-thiadiazoles (n-PTH) on corrosion of mild steel in different acidic media (1 M HCl, 0.5 M H₂SO₄ and 1 M HClO₄) were analyzed by electrochemical impedance spectroscopy (EIS). The n-PTH derivatives exhibit good inhibition properties in different acidic solutions and the calculated values of revealed that the adsorption mechanism of n-PTH on steel surface is mainly due to chemisorption. While in 1 M HClO₄, both 2-PTH and 4-PTH isomers stimulate the corrosion process especially at low concentrations. Quantum chemical calculations using the density functional theory (DFT) were performed on n-PTH derivatives to determine the relationship between molecular structure and their inhibition efficiencies. The results of the quantum chemical calculations and experimental inhibition efficiency were subjected to correlation analysis and indicate that the inhibition effects of n-PTH may be explained in terms of electronic properties.     

Free and Wilson correlation between the molecular structure of some imidazolines and their corrosion inhibiting properties

In deaerated media containing hydrogen sulfide, the inhibition of the corrosion of N 80 steel by a homologous series of imidazolines was measured potentiokinetically. The data obtained were correlated to the structure of these molecules by means of Free and Wilson relationships. These correlations, allowed the behaviour of some derivatives to be predicted successfully.     

Impact of gamma-ray-pre-irradiation on the efficiency of corrosion inhibition of some novel polymeric surfactants

The effect of gamma-ray-pre-irradiation on the efficiency of two types of polymeric surfactants, (I and II) as corrosion inhibitors for 304 stainless steel in 2 M hydrochloric acid solution was examined. The inhibition efficiency of the undertaken additives was evaluated using both chemical and electrochemical techniques. The chemical structure of the two polymeric surfactants is illustrated as follows: where MA=maleic anhydride; BP=block polymer of polyoxy ethylene-polyoxy propylene (M.Wt=5000 g mol⁻¹).The obtained corrosion data, indicated that the corrosion inhibition efficiency of the inhibitor (II) was obviously not affected by gamma-ray-irradiation, meanwhile the efficiency of the inhibitor (I) demonstrated a remarkable decrease. Scanning electron microscope (SEM) was used to examine the surface morphology of stainless steel samples after immersion in 2 M HCl solution in absence and presence of the inhibitors at concentration of 400 ppm before and after exposure to gamma-ray-radiation up to a total does of 100 kGy.     

2,5-Bis(n-methoxyphenyl)-1,3,4-oxadiazoles used as corrosion inhibitors in acidic media: correlation between inhibition efficiency and chemical structure

The efficiency of 2,5-bis(n-methoxyphenyl)-1,3,4-oxadiazoles (n-MOX), as corrosion inhibitors for mild steel in 1 M HCl and 0.5 M H₂SO₄ have been determined by weight loss measurements and electrochemical studies. The results showed that these inhibitors revealed a good corrosion inhibition even at very low concentrations. Comparison of results among those obtained by the studied oxadiazoles showed that 2-MOX was the best inhibitor. It is found to behave better in 1 M HCl than in 0.5 M H₂SO₄. Polarisation curves indicate that 2-MOX is a mixed inhibitor in 1 M HCl, but in 0.5 M H₂SO₄, the inhibition mode of 2-MOX depends on the electrode potential and acts essentially as a cathodic inhibitor. The inhibition efficiency slightly increases with temperature in the range from 25 to 60 °C, the associated activation energy have been determined. The addition of 2-MOX leads to decrease this activation energy. The adsorption of 2-MOX on the mild steel surface in both acidic media follows a Langmuir isotherm model. Significant correlations are obtained between inhibition efficiency with the calculated chemical indexes, indicating that variation of inhibition with structure of the inhibitors may be explained in terms of electronic properties.     

Theoretical study on the second-order nonlinear optical properties of gold (III) alkyl complexes

The equilibrium geometries of gold (III) alkyl complexes are optimized by DFT/B3LYP method. On the basis of the optimized structures, the electronic structures and second-order nonlinear optical properties are calculated by using time-dependent density-functional theory (TDDFT) combined with the sum-over-states (SOS) method. The results show that these complexes possess remarkably larger molecular second-order polarizabilities compared with the typical organometallic and organic complexes. The analysis suggests that charge transfer from the z-axis directions plays a key role in the second-order nonlinear optical response. Moreover, different ancillary ligands can substantially adjust the second-order nonlinear optical response. Thus, it can be concluded that these complexes will be hopeful candidates for the second-order nonlinear optical materials from the standpoint of high transparency, relatively large β values and small dispersion behaviors.     

Electrochemical and theoretical investigation on the corrosion inhibition of mild steel by thiosalicylaldehyde derivatives in hydrochloric acid solution

Inhibitory effect of three Schiff bases 2-{[(2-sulfanylphenyl)imino]methyl}]phenol (A), 2-{[(2)-1-(4-methylphenyl)methylidene]amino}-1-benznethiol (B), and 2-[(2-sulfanylphen-yl)ethanimidoyl)]phenol (C) on corrosion of mild steel in 15% HCl solution has been studied using weight loss measurements, polarization and electrochemical impedance spectroscopy (EIS) methods. The results of the investigation show that the compounds A and B with mean efficiency of 99% at 200 mg/L additive concentration have fairly good inhibiting properties for mild steel corrosion in hydrochloric acid, and they are as mixed inhibitor. All measurements show that inhibition efficiencies increase with increase in inhibitor concentration. This reveals that inhibitive actions of inhibitors were mainly due to adsorption on mild steel surface. Adsorption of these inhibitors follows the Langmuir adsorption isotherm. Thermodynamic adsorption parameters (K_ads, ΔG_ads) of studied Schiff bases were calculated using the Langmuir adsorption isotherm. Activation parameters of the corrosion process such as activation energies, E_a, activation enthalpies, ΔH^∗, and activation entropies, ΔS^∗, were calculated by the obtained corrosion currents at different temperatures. Obvious correlation was found between the corrosion inhibition efficiency and the calculated parameters. The obtained theoretical results have been adapted with the experimental data.     

Protection of reinforcements using mixed corrosion inhibitors. Dependence of inhibition mechanism on interaction between rebar and corrosion inhibitor

Abstract

The level of efficiency and protection against corrosion of an inhibitor depends on its interaction with the reinforcement. Taking into account this assumption, in present paper, the corrosion inhibition efficiency of Ferrogard 903 has been studied following two procedures: immersion of the rebar in the commercialised solution containing the corrosion inhibitor blend, before being introduced in the aggressive media; and addition of the corrosion inhibitor directly to the media with or without a previous presence of oxides on the reinforcement’s surface. The study has been developed in systems simplifying the aqueous phase of the concrete pores: alkaline solutions polluted with chlorides and neutral solutions. The inhibition mechanism seems to be related with the mixed composition of the corrosion inhibitor whose behaviour depends on the exposure environment, on the inhibitor’s method of application and on the surface state of the rebar.     

Experimental and theoretical study on the inhibition performance of triazole compounds for mild steel corrosion

A relationship between quantum chemical parameters for three triazole compounds and their inhibition ability was studied using electrochemical measurements (potentiodynamic polarization and EIS), molecular dynamic method and quantum chemical calculations. Electrochemical measurements results revealed that the inhibition efficiencies increased with the concentration of inhibitors. The molecular dynamic method results showed that the higher interaction potential between the inhibitor and metal surface, the higher the inhibition efficiency. The quantum chemical calculation results showed that the triazole ring is the active site in these inhibitors and they can absorb on Fe surface by donating electrons to Fe d-orbital.     

Electrochemical and theoretical investigation of triazole derivatives on corrosion inhibition behavior of copper in hydrochloric acid medium

The inhibition effect of three triazole derivatives namely 4-amino-4H-1,2,4-triazole-3thiol (ATT), 4-amino-5-methyl-4H-1,2,4-triazole-3thiol (AMTT) and 4-amino-5-ethyl-4H-1,2,4-triazole-3thiol (AETT) have been investigated against the corrosion of copper in 0.5 M HCl solution. The investigations were analyzed using potentiodynamic polarization, electrochemical impedance, weight loss methods and quantum chemical studies. Potentiodynamic polarization measurements indicate that all three examined compounds are cathodic type inhibitors. Among the studied compounds, 4-amino-5-ethyl-4H-1,2,4-triazole-3thiol exhibited the best inhibition efficiency 96.09% at 2.58 mM. The adsorption of these compounds obeyed the Langmuir adsorption isotherm. The electronic properties obtained using quantum chemical approach, were correlated with the experimental results.     

The relationship between the corrosion resistance and impurity content of aluminium oxide layers

In the last few years there has been an increased production and application of aluminium foil of under 20 μm thickness all over the world. Household foil is often stored in a wet environment, where the surface is only protected against corrosion by an aluminium oxide layer produced during manufacturing. In this study it has been shown that the aluminium-water vapour reaction is greatly affected by the composition and structure of the amorphous oxide layer on the surface and this depends on the composition of base metal and on the annealing of the foil. The incubation period of aluminium hydroxide nucleation is shortened and its growth rate accelerated by alkali and alkaline earth metal cations incorporated in the oxide layer. In particular the corrosion resistance is decreased by the presence of alkali (Li) and alkaline earth metal (Mg) cations in the oxide layers.