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Two environmentally friendly inhibitors of imidazolium-based ionic liquids namely 3-benzyl-1-hexadecyl-1H-imidazol-3-ium chloride (IL-H), and 3-(4-chlorobenzyl)-1-hexadecyl-1H-imidazol-3-ium chloride (IL-Cl) were manufactured and their chemical structures were confirmed by spectra tools (FT-IR, and 1H NMR). The utilizing of these two new ionic liquids as green corrosion inhibitors for low carbon steel (LCS) in 1.0 M HCl under altered experimental conditions. Mass loss (ML), potentiodynamic polarization (PP), AC impedance spectroscopy (EIS) and surface morphology are take place in this study. The protection performance found to increase with increasing ionic liquid dose and temperature, reaching 92.9% and 95.1% for IL-H and IL-Cl at 120 ppm, respectively. Based on the PP records, the investigated ionic liquids behave as mixed-type inhibitors, influencing both anodic and cathodic responses. The inhibitory activity from these explored ionic liquids was stimulated by their adsorption on the effective surfaces of the steel surface in accordance with the Langmuir adsorption isotherm. The Density Functional Theory (DFT) method is used to analyze the relationship between quantum chemical calculations and the protection efficiency of ionic liquids.

Two azo derivatives, 4-((4-hydroxy-3-((4-oxo-2-thioxothiazolidin-5-ylidene)methyl)phenyl) diazinyl) benzenesulfonic acid (TODB) and 4-((3-((4,4-dimethyl-2,6-dioxocyclohexylidene) methyl)-4-hydroxyphenyl)diazinyl) benzenesulfonic acid (DODB) were synthesized and characterized using Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (

Two new organic based corrosion compounds were prepared from Acryloyl chloride are namely: N,N-bis(2-hydroxyethyl) acrylamide (DEA) and N-(2-hydroxyethyl) acrylamide (MEA). The prepared compounds were studied as corrosion inhibitors for carbon steel (CS) in 1 M hydrochloric acid solution while the efficiency of the prepared compounds were studied through different chemical (weight loss, WL) and electrochemical techniques [potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS)] in addition to, the theoretical techniques as Quantum chemical calculations, Monte Carlo simulation and the surface morphology study using atomic force microscopy (AFM). The obtained results showed that the investigated compounds are working as good corrosion inhibitors, the inhibition efficacy (%IE) increases with the increase of the compound concentrations. However, the %IE decreases with the rise in the temperature proving that the adsorption of the inhibitor molecules on the CS surface is physisorption, while the polarization data revealed that these compounds are classified as mixed kind inhibitors, that inhibits both anodic and cathodic reactions. Results reveal that DEA and MEA exhibit an excellent %IE of 89.2 and 71.6% at 60 ppm for DEA and MEA, respectively. The adsorption of the inhibitor molecules on CS surface following Langmuir adsorption isotherm. There is a strong matching between results obtained from experimental and theoretical studies. The order of the investigated inhibitors based on the %IE is DEA > MEA.

The inhibiting impact of two 5-arylidene barbituric acid derivatives on the corrosion of carbon steel has been examined via the weight loss method, potentiodynamic polarization, electrochemical impedance spectroscopy, and electrochemical frequency modulation tests.

Three novel p-phenylenediamine and benzidine coumarin derivatives were synthetized (PhODB), (BODB) and (DODB), these compounds showed excellent anti corrosion effect for steel in 1.0 M HCl and significant SRB resistance.

This study describes the adsorption behavior of three arylthiophene derivatives namely: 2-(4-Amidino-3-fluorophenyl)-5-[4-methoxy phenyl] thiophene dihydrochloride salt (MA-1217), 2-(4-Amidinophenyl)-5-[4-chlorophenyl] thiophene dihydrochloride salt (MA-1316) and 2-(4-amidino-3-fluorophenyl)-5-[4-chlorophenyl]thiophene dihydrochloride salt (MA-1312) at C-steel in 1.0 mol·L−1 HCl interface using experimental and theoretical studies. Electrochemical and mass loss measurements showed that the inhibition efficiency (IE) of the arylthiophene derivatives increases with increasing concentrations and exhibited maximum efficiency 89% at 21×10−6 mol·L−1 (MA-1217) by mass loss method. The investigated arylthiophene derivatives obey the Langmuir adsorption isotherm. From polarization studies the arylthiophene derivatives act as mixed-type inhibitors. Surface analysis were carried out and discussed. The mode of orientation and adsorption of inhibitor molecules on C-steel surface was studied using molecular dynamics (MD) simulations. Quantum chemical parameters as well as the radial distribution function indices and binding energies confirm the experimental results.

The inhibition efficiency and adsorption affinity were investigated for two novel compounds, namely: 6-methoxy-2-naphthyl-[2, 2’-bithiophene]-5-carboxamidine hydrochloride salt (MA-1440) and 5'-(4-chlorophenyl)-2, 2’-bifuran-5-carboxamidine hydrochloride salt (MA-1456). The inhibition study was conducted on carbon steel surface in 1.0 M HCl with different inhibitor doses and different temperature levels, to investigate the optimum dose and preferable temperature. The performed investigation included chemical, electrochemical, instrumental, and quantum computation techniques. A chemical technique was accomplished by using weight-loss measurements. Different factors were studied using weight-loss measurements in order to reach the maximum inhibition efficiency. The adsorption study revealed that the examined inhibitors obey the Langmuir adsorption isotherm and are chemically adsorbed on the steel surface. The electrochemical measurements were accomplished through the electrochemical impedance (EIS) and potentiodynamic polarization (PDP) techniques. Based on the electrochemical measurements, the examined compounds were categorized as mixed inhibitors. The instrumental examination using different techniques namely: scanning electron microscope (SEM), energy dispersive X-ray (EDX), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) confirmed that the considered inhibitors are excellently adsorbed over the carbon steel surface. The extent of the adsorption affinity of these compounds on the carbon steel surface was studied theoretically using quantum computations and Monte Carlo simulation. The theoretical investigation results of quantum chemistry were validated with those obtained by chemical and electrochemical methodologies. All investigations prove that, the tested compounds were adsorbed chemically on the steel surface and achieved maximum inhibition efficiency of, 94.69% and 90.85% for M-1440 and MA-1456, respectively, at the optimum concentration 3010-6 mol. L-1 and temperature 328 K.

The corrosion behavior of Al in 1 M HCl solution with and without thiophene derivatives is studied utilizing altered chemical and electrochemical methods. Thiophene derivatives have been prepared and characterized by infrared (IR), proton nuclear magnetic resonance (1H NMR) and mass spectral studies. The corrosion data were obtained using weight reduction and electrochemical techniques. The outcome data revealed that the efficiency rises with improving the dose of thiophene derivatives in aggressive solution, while it lowered with the rise of temperature. The adsorption of the studied thiophene derivatives on the surface of Al follows Langmuir isotherm. The thermodynamic parameters such as adsorption constant Kads and free energy of adsorption ( $$\Delta G_{{{\text{ads}}}}^{^\circ }$$ ) are calculated and discussed. Polarization curves indicated that the thiophene derivatives are mixed-kind inhibitors. The quantum calculation such as EHOMO, ELUMO and ΔE were obtained and related to the experimental data. The biological effect of these derivatives also discussed.

Aizoon extract is used as an eco-friendly anti-corrosive material for stainless steel 430 (SS430) in a 2 M hydrochloric acid solution. Many strategies were utilized to estimate the mitigation efficacy such as mass reduction (MR), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP). The inhibition percentage (%

Sargassum latifolium extract was used as new extract for the protection of Al dissolution using chemical and electrochemical methods. It was extracted, tested, and its high inhibition quality with addition of 1 × 10–2 M KI at 298 K for 300 ppm in 1M hydrochloric acid was recorded. The adsorption mechanism agreed with the Temkin isotherm from the weight loss procedure. From Tafel extrapolations showed that the used extract acts as mixed inhibitor. The thermodynamic parameters were organized and clarified. The attenuated total reflectance-Fourier transform infrared spectroscopy and atomic forced microscopy were performed for the Al surface analyses and a good decrease in the surface roughness was reached. The used extract has also demonstrated a satisfying biological activity against bacterial growth.

Expired Famotidine was tested as a corrosion protection for α-brass in 1 M HCl using modified methods: weight loss (WL), Tafel polarization (TP), AC impedance spectra (EIS) and electrochemical frequency modulation (EFM). The polarization resistance (Rp) data increased with increasing famotidine dose. The inhibition efficiency (IE) improved with raising famotidine concentration. The maximum IE of 90% has been achieved at 300 ppm. On the other hand, the efficiency lowered with temperature increased. The outcome data obtained revealed that famotidine performed excellently as a corrosion inhibitor for α‑brass in this medium at dissimilar temperatures. The surface of α-brass was tested utilizing scanning electron microscope (SEM), energy dispersion spectroscopy X-ray spectra (EDX), Fourier transform infrared spectroscopy (FT–IR), and atomic force microscopy (AFM analysis).

The influence of corrosion inhibition of some thiazole derivatives, namely: 2-(3,5-dimethyl-4-(p-tolyldiazenyl)-1H-pyrazole-1-yl)thiazol-5(4H)-one, 2-(3,5-dimethyl-4(phenyldiazenyl)-1H-pyrazole-1-yl)thiazol-5(4H)-one, and 2-(4-((4-chlorophenyl)diazenyl)-3,5-dimethyl-1H-pyrazole-1-yl)thiazol-5(4H)-one on Zn in 1.0 M HCl solution was studied by utilizing electrochemical and non-electrochemical tests. The obtained data without and with these derivatives were utilized to measure the protection efficiency (η %) which rises with the rise in the concentration of these derivatives. The phenomenon of physical adsorption was proposed and inhibitors adsorption was established to adapt Langmuir adsorption isotherm. Polarization data clearly indicated that these derivatives behaved as mixed inhibitors.

The corrosion inhibition of C-steel in 1 M HCl was assessed using three newly synthesized hydrazide derivatives (H1, H2 and H3) using weight loss (WL), potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques. Also, the adsorption of these compounds was confirmed using several techniques such as atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). High inhibition efficiencies were obtained resulting from the constitution of the protective layer on the C-steel surface, which increased with increasing concentration and temperature and reached 91.7 to 96.5% as obtained from the chemical method at 20 × 10

The inhibiting effect of the expired meloxicam on the corrosion of mild steel (MS) in 1 M HCl was tested by the weight loss, electrochemical frequency modulation, potentiodynamic polarization (PP) and electrochemical impedance spectroscopy techniques. The PP curves showed that this drug acts as mixed type inhibitor. This drug was adsorbed chemically on the MS surface following the Temkin adsorption isotherm. Some thermodynamic parameters were computed and discussed. The results indicated that the protection efficiency increases by raising both the doses of the inhibitor and the temperature of the medium. The morphology of the MS surface was analyzed by scanning electron microscopy, atomic force microscopy, and Fourier transform infrared spectroscopy. All of the obtained results from different techniques are similar.

Herein, An examination into the corrosion inhibition of mild steel (MS) in 1.0 M HCl by the Chicoriumintybus extract as a green inhibitor had been achieved via chemical, electrochemical and morphological measurements. The effect of KI additives on corrosion inhibition efficiency was carried out using a weight loss method. The results reveal that the Chicoriumintybus extract inhibited the corrosion reaction by adsorption onto the metal/solution interface. Inhibition efficiency, increased with the Chicoriumintybus concentration and synergistically increased with the presence of KI. The addition of iodide ions to the Chicoriumintybus extract raises inhibition efficiency of 74 to 99%. Polarization data suggest that the Chicoriumintybus extract acts as a mixed inhibition-mechanism. This observation was further corroborated by the fit of experimental adsorption data to the Temkin isotherm. The results were confirmed by AFM, SEM images and ATR-IR for the surface morphology.

The corrosion inhibition action of three newly synthesized furanylnicotinamidine derivatives namely: 6-[5-{4(dimethylamino)phenyl}furan-2-yl]nicotinamidine (MA-1256), 6-[5-(4-chlorophenyl)furan-2-yl]nicotinamidine (MA-1266), and 6-[5-{4-(dimethylamino)phenyl}furan-2-yl]nicotinonitrile (MA-1250) on carbon steel (C-steel) was investigated in 1.0 mol⋅L−1 HCl solution by weight loss (WL), potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM) techniques. Morphological analysis was performed on the uninhibited and inhibited C-steel using atomic force microscope (AFM) and Infrared Spectroscopy (ATR-IR) methods. The effect of temperature was studied and discussed. Inspection of experimental results revealed that the inhibition efficiency (IE) increases with the incremental addition of inhibitors and with elevating the temperature of the acid media. The adsorption of furanylnicotinamidine derivatives on C-steel follows Temkin's isotherm. PP studies indicated that the investigated compounds act as mixed-type inhibitors and showed that p-dimethylaminophenyl furanylnicotinamidine derivative (MA-1256) was the most efficient inhibitor among the other studied derivatives with IE reached (95%) at 21 × 10−6 mol⋅L−1. MA-1266 is highly soluble in aqueous solution and has non-toxicity profile with LC50 > 37 mg·L−1. Thus, MA-1266 can be a promising green corrosion inhibitor candidate with IE > 91% at 21 × 10−6 mol⋅L−1. The experiments were coupled with computational chemical theories such as quantum chemical and molecular dynamic methods. The experimental results were in good agreement with the computational outputs.

The proton pump inhibitor lansoprazole (PPIL) drug is examined as corrosion inhibitor for high carbon steel (HCS) dipped in 1.0M HCl. The study was conducted utilizing ac impedance spectroscopy (EIS), Mass loss (Ml), polarization tests, and surface checks were utilized to illustrate the importance of this PPIL extract to the prevent corrosion process for HCS. The influence of temperature and concentration of PPIL on the efficiency of inhibition were tested. The corrosion mechanism occurs, when the PPIL extract molecules block the active center in the electrode surface. The inhibition efficiency (%IF) of HCS occurs by the adsorption procedure and HCS is subject to the adsorption of Langmuir. Polarization curves showed that PPIL drug is a mixed- type inhibitor that retards the dissolution of HCS. IF % was deliberated with altering in the concentration of PPIL various temperature of the medium. From the outcome data we get that the good agreement in the all methods.

The present work aims to study 6-amino-4-aryl-2-oxo-1-phenyl-1,2-dihydropyridine-3,5-dicarbonitrile derivatives namely: 6-Amino-2-oxo-1,4-diphenyl-1,2-dihydropyridine-3,5-dicarbonitrile (PdC-H), 6-Amino-2-oxo-1-phenyl-4-(p-tolyl)-1,2-dihydropyridine-3,5-dicarbonitrile (PdC-Me) and 6-Amino-4-(4-hydroxyphenyl)-2-oxo-1-phenyl-1,2-dihydropyridine-3,5-dicarbonitrile (PdC-OH) as corrosion inhibitors to provide protection for carbon steel in a molar hydrochloric acid medium. Chemical measurements such as (weight loss) and electrochemical techniques such as (Potentiodynamic polarization, electrochemical impedance spectroscopy, and Electron frequency modulation) were applied to characterize the inhibitory properties of the synthesized derivatives. The adsorption of these derivatives on the carbon steel surface was confirmed by Attenuated Total Refraction Infrared (ATR-IR), Atomic Force Microscope (AFM), and X-ray Photoelectron Spectroscopy (XPS). Our findings revealed that the tested derivatives have corrosion inhibition power, which increased significantly from 75.7 to 91.67% on the addition of KI (PdC-OH:KI = 1:1) to inhibited test solution with PdC-OH derivative at 25 °C. The adsorption process on the metal surface follows the Langmuir adsorption model. XPS analysis showed that the inhibitor layer consists of an iron oxide/hydroxide mixture in which the inhibitor molecules are incorporated. Computational chemical theories such as DFT calculations and Mont Carlo simulation have been performed to correlate the molecular properties of the investigated inhibitors with experimental efficiency. The theoretical speculation by Dmol3 corroborates with the results from the experimental findings.

Aizoon extract used as anti-corrosion for stainless steel430 (SS430) in 2M hydrochloric acid solution. The mass reduction, electrochemical impedance, and potentiodynamic polarization were carried out to demonstrate the performance of Aizoon extract as corrosion resistance for SS430. Polarization revealed that the Aizoon extract is mixed type inhibitor with superiority to inhibiting the cathodic reaction. The inhibition percentage reaches 93% at 300 ppm extract. Adsorption of the extract on SS430 surface is regular with Langmuir adsorption model. Thermodynamic factors for adsorption and activation processes for SS430 dissolution were estimated and discussed. Furthermore, the SS430 surface is characterized using different techniques. The surface morphology of SS430 was tested utilizing several techniques. The experimental data were supported by the theoretical data.

The efficiency of Ferula hermonis plant extract, as inhibitor for zinc (Zn) corrosion in a 1 M HCl solution, has been tested by mass loss (ML), electrochemical measurements (potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) procedures), in addition to surface examination analysis. The outcomes indicated that F. hermonis extract showed good efficiency to Zn corrosion, and displayed high inhibition efficiencies. The maximum inhibition efficiency approached 90.6% at 300 ppm extract. The adsorption isotherm of extract on the Zn surface was found to follow Langmuir adsorption isotherm. Thermodynamic parameters were determined and discussed. Also, the inhibition efficiency (%IE) was found to increase as the concentration of extract increases, and depressed as the temperature rises. The morphology of the surface of uninhibited and inhibited Zn was examined by Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersion spectroscopy (EDX) and ultraviolet–visible spectroscopic (UV). Biological effect of the extract was studied. The results indicated that there is a protective film formed by extract on the Zn surface that protects it from dissolution in the acid media. The outcomes of the applied chemical and electrochemical techniques are in good agreement.

Novel anionic 4-tert-Octylphenol Ethoxylated Phosphate Dipotassium salt (ethoxylated with 5 moles of ethylene oxide) surfactant was prepared and designated as OP-5-EO-K2PO, was characterized for its structure using spectroscopic measurements, in addition, its surface properties were investigated. The results indicated that OP-5-EO-K2PO exhibits excellent surface activity. Evaluation of the prepared surfactant as a corrosion inhibitor was carried out. The inhibition effect of OP-5-EO-K2PO surfactant, on the corrosion of C-steel in 0.5 M HCl was studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. It was found that the novel anionic surfactant acts as effective inhibitor and its inhibition efficiency was significantly increased with increasing concentration. Polarization curves revealed that the novel prepared anionic surfactant represents mixed-type inhibitors. Adsorption of the investigated surfactant led to a reduction in the double layer capacitance and an increase in the charge transfer resistance.

PurposeThe purpose of this paper is to investigate three Arylfuranylnicotinamidine derivatives against corrosion of carbon steel (C-steel) in 1.0 M HCl by chemical and electrochemical means. The inhibition efficiency (%IE) increases with increasing the dose of inhibitors. The tested compounds exhibited improved performance at elevated temperature, with %IEreaching 93 percent at 21 µM. Tafel polarization method revealed that the tested compounds act as mixed-type inhibitors. The inhibition action was rationalized due to chemical adsorption of inhibition molecules on C-steel surface following Temkin’s isotherm. Surface examination was carried out by AFM and FTIR techniques. Further, theoretical chemical approaches were used to corroborate the experimental findings.Design/methodology/approachExperimental and computational methods were applied to investigate the efficiency of these new compounds. These studies are complemented with spectral studies and surface morphological scan by AFM. The theoretical results indicate good correlation with experimental findings.FindingsThe tested derivatives are promising corrosion inhibitors for C-steel in the acid environment. The molecular scaffold of this class of compounds can be used to design new highly efficient inhibitors by screening its activity by modeling studies.Originality/valueThe studied compounds are safe inhibitors and greatly adsorbed on Fe surface. The action of compounds is enhanced with temperature, which means these compounds can be used in higher temperature systems. The new compounds are effective at very low concentration.

In this study, the inhibition effect of Tamarix Boveana (TB) extract on Cu corrosion in 1 mol L–1 (HNO3 + H3PO4) mixture was studied. Electrochemical techniques such as (potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM)) and non-electrochemical technique such as mass loss were used. Results showed that TB extract has good inhibition efficiency (IE), follows Langmuir adsorption isotherm and all of the methods are in good agreement. The IE increased by increasing the concentration of the extract and decreased by increasing the temperature so, the extract adsorbed on Cu surface physically. The IE depends on the concentration of the extract and reaches 73.5% at 300 ppm of the extract. PP results revealed that the (TB) extract doings as mixed type one. Surface analysis revealed that the extract components are adsorbed on Cu surface forming a film.

The effect of Olive leaf as a corrosion inhibitor for C-steel in 10% Sulfamic acid (NH2SO3H) solution was tested utilizing different techniques. The effect of temperature (298–328 K) was determined and activation and adsorption thermodynamic parameters were counted and discussed. The surface morphology was analyzed utilizing a scanning electron microscope (SEM). Potentiodynamic polarization procedures evidenced that Olive leaf acts as mixed-type inhibitor for corrosion of C-steel in 10% NH2SO3H solution. The addition of Olive leaf produces an increase in the charge transfer resistance (Rct) and reduction in capacitance of the double layer (Cdl). The inhibition mechanism involves physisorption. The adsorption of this extract on C-steel surface follows Langmuir isotherm. All the studied techniques gave similar results.

The new compound 4-(2-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)hydrazono)-3-methyl-5-oxo-4,5-dihydro-1H-pyrazole-1-carbothioamide (PY) was synthesized. Its anti-corrosion properties for C-steel in acid solution (1.0 M HCl) were evaluated utilize electrochemical tools. The synthesized compound was described using FT-IR and 1H-NMR analyses. The purity of PY was affirmed by thin-layer chromatography (TLC). The outcome data proved that PY possess adequate anti-corrosion features for C-steel in corrosive solution. The polarization parameters mentioned that the PY is a mixed inhibitor. Inhibition performance obtained by polarization measurements (i.e. 91.5%) are consistent with the one obtained by EIS (i.e. 88.6%). Quantum chemical parameters for PY were studied to supply assist knowledge into the anti-corrosion properties of the new compound.

The inhibiting effect of an Alfalfa extract in a corrosive medium (3.5% NaCl + 16 ppm Na2S) on the corrosion of carbon steel was studied by the mass loss measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy. The results showed that the inhibition efficiency, increases with an increase in the extract dose but decreases at higher temperatures. The obtained results indicated that the investigated extract is physically adsorbed on the carbon steel surface and follows the Temkin adsorption isotherm. The polarization data revealed that this extract acts as mixed type inhibitor. The surface morphology was tested using atomic force microscope. The results obtained from different techniques are in good agreement.

The inhibition effect of expired Simvastan drug on Cu corrosion in 1 M HNO3 at 25°C was investigated using potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS) and electrical frequency modulation (EFM) as well as weight loss (WL) measurements. Electrochemical studies data support that examined expired drug is an efficient inhibitor for mild steel corrosion. The adsorption of the examined drug obeys Langmuir’s adsorption isotherm. Polarization studies indicate that this inhibitor acts as a mixed type inhibition. The effect of temperature on corrosion inhibition has been studied and the thermodynamic activation and adsorption parameters were calculated and discussed. The protective film formed on the surface was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The results collected from the studied techniques are in good agreement to confirm the ability of using expired Simvastan drug as corrosion inhibitor for Cu in acid media. The relationships between the inhibition efficiency (%IE) and some quantum chemical parameters have been discussed.

Herein, the corrosion inhibition performance of mild steel (MS) in an acidic environment (1.0 M HCl) by the valerian extract has been studied via weight loss method (WL), potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. The results illustrated that the inhibition efficiency, raised by the rise of the extract concentrations. The inhibitory mechanism depended on the creation of a stable plant extract-complex on the mild steel surface. Polarization studies confirmed that the extract behaved as a mixed type inhibitor. The corrosion inhibition was supposed to exist via adsorption of the main components of the valerian extract. Attenuated total reflection-infrared spectroscopy (ATR-IR), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied to investigate the change in the surface morphology and confirmed the corrosion inhibition mechanism. The complete study confirmed that the efficiency of the valerian extract as a safe, eco-friendly and exchange corrosion inhibition for mild steel in an acidic environment.

The inhibiting action of three derivatives of azole compounds has been investigated for the corrosion of two aluminum-silicon alloys in 0.5 M HCl solution using some electrochemical measurements such as potentiodynamic polarization, electrochemical impedance, and electrochemical frequency modulation. The morphology of the surface was examined by the scanning electron microscopy. It was found that the inhibition efficiency increases with the increase in the concentration of azole compounds. Those compounds acted as mixed inhibitors and their inhibiting effect was revealed through the formation of an adsorbed film, which blocked the active site present on the alloys. The adsorption process follows the Freundlich isotherm. The addition of Si to Al electrode increases in the corrosion protection of the alloys in the following sequence: Alloy II > Alloy I. The inhibition efficiencies obtained via different techniques are consistent with each other.