Design and synthesis of a novel class of inhibitors for mild steel corrosion in acidic and carbon dioxide-saturated saline media

p-(9-(2-Methylisoxazolidin-5-yl)nonyloxy)benzaldehyde I, prepared using a cycloaddition protocol, was elaborated into its cinnamaldehyde derivative II which upon quarternization with propargyl chloride afforded III bearing an interesting blend of structural traits suitable for imparting inhibition of mild steel corrosion. Novel compounds I–III showed efficient inhibition against mild steel corrosion in CO₂–0.5 M NaCl (40 °C, 1 atm; 120 °C, 10 bar), 1, 4, 7.7 M HCl, and 0.5 M H₂SO₄ at 60 °C as determined by gravimetry and electrochemical methods. The presence of carbonaceous surface and nitrogen, as revealed by XPS study, indicated the formation of a film covering the metal surface, which imparted corrosion inhibition.     

Long-term monitoring of atmospheric corrosion at weathering steel bridges by an electrochemical impedance method

Weathering steel corrosion was monitored for one to two years under natural atmosphere by an electrochemical impedance technique. Two identical comb-shape weathering steel sheets embedded in epoxy resin were used as monitoring probe electrodes at two different bridges in Japan. Impedances at 10 kHz (Z_10kHz) and 10 mHz (Z_10mHz) were automatically measured every hour. Coupons (50 × 50 × 2 mm³) prepared from the same steel sheets were exposed together to measure the corrosion mass loss. The average (Z_10mHz)⁻¹ value for half to one year exposure correlated well with the average corrosion rate determined from the corrosion mass loss.     

Electrochemical and quantum chemical studies of some azomethine compounds as corrosion inhibitors for mild steel in 1 M hydrochloric acid

The corrosion inhibition effect of new azomethine compounds: PhNNC (COCH₃)NC₆H₄Y {Y = OCH₃ (SB₁), CH₃ (SB₂), H (SB₃), Br (SB₄) and Y = Cl (SB₅)} on mild steel in 1 M HCl, was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and quantum chemistry analysis. It has been found that the inhibition efficiency increased with increasing inhibitor concentration. The polarization curves showed that these Schiff bases function as mixed inhibitors. The adsorption of studied compounds on mild steel surface was found to follow the Langmuir isotherm. Molecular modeling was used to correlate corrosion inhibition properties and calculated quantum chemical parameters.     

2-Amino-5-(4-pyridinyl)-1,3,4-thiadiazole monolayers on copper surface: Observation of the relationship between its corrosion inhibition and adsorption structure

Corrosion inhibition behavior of 2-amino-5-(4-pyridinyl)-1,3,4-thiadiazole (4-APTD) monolayers on copper surface were investigated by electrochemical impedance spectroscopy (EIS), electrochemical polarization measurement and surface-enhanced Raman scattering (SERS) experiment. The EIS mechanism of the copper surface with 4-APTD monolayers fitted to the mode of R(Q(R(QR))). The electrochemical polarization measurements indicated high inhibition efficiency of about 90.4%. SERS results suggested that 4-APTD molecules anchored at copper surface in a tilted orientation directly via N³ and N¹² atoms. The transition adsorption states of 4-APTD on the copper surface were observed as the potential applied from 0 to −1.6 V vs. SCE.     

Adsorption and inhibition effect of Ascorbyl palmitate on corrosion of carbon steel in ethanol blended gasoline containing water as a contaminant

The adsorption and inhibition effect of Ascorbyl palmitate (AP) on carbon steel in ethanol blended gasoline containing water as a contaminant (GE10 + 1%water) was studied by weight loss and electrochemical impedance spectroscopic (EIS) techniques. The results showed that the addition of ethanol and water to gasoline increase the corrosion rate of carbon steel. AP inhibits the corrosion of carbon steel in (GE10 + 1% water) solution to a remarkable extent. The adsorption of AP on the carbon steel surface was found to obey the Langmuir adsorption isotherm model. The values of activation energy (E_a) and various thermodynamic parameters were calculated and discussed.     

Inhibition effect of 2-amino-4-methylpyridine on mild steel corrosion: Experimental and theoretical investigation

The effect of 2-amino-4-methylpyridine (AMP) on the corrosion behavior of mild steel (MS) in 0.5 M HCl is investigated with electrochemical methods and theoretical calculations. The electrochemical tests show that the polarization resistance of MS increasing the presence of AMP in acid solution. Adsorption of AMP on MS surface is a physical and obeys the Langmuir isotherm. The quantum parameters signaled adsorption occurs on amine and methyl substituents of AMP. The inhibition efficiency is related to frontier orbital’s energy band gap of AMP, which are 5.357 and 6.490 eV for neutral and protonated molecules in aqueous solution, respectively.     

Ultrafine-grained copper produced by machining and its unusual electrochemical corrosion resistance in acidic chloride pickling solutions

Ultrafine-grained (UFG) copper was prepared by facile machining procedure. High resolution transmission electron microscopy images revealed that, in UFG Cu, minimum grain size of 80 nm could be formed when a small machining rake angle was applied. The electrochemical corrosion behavior of UFG Cu in 0.5 M HCl was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. Comparing with coarse-grained Cu, UFG Cu exhibited notably declined corrosion current density. Particularly, when the size of Cu grains were reduced from 500 μm to 80 nm, the charge transfer resistance of anodic dissolution step dramatically increased from 200 to 621 Ω cm².     

Electrochemical impedance spectroscopy and electrochemical noise measurements as tools to evaluate corrosion inhibition of azole compounds on stainless steel in acidic media

The corrosion inhibition function of two azole derivatives namely benzotriazole (BTR) and benzothiazole (BNS) on stainless steel in 1 M HCl was investigated using electrochemical techniques and SEM surface analysis as well. In consistency with the data obtained from EIS and polarization curves, electrochemical current noise transient analysis, noise resistance and characteristic charge from shot noise theory indicated effectiveness of the inhibitors. The corrosion damage mitigation was also confirmed through SEM in the presence of BNS. To remove the DC trend from noise data, the appropriate p value was proposed based on the correlation with polarization and EIS data.     

Schiff’s base of pyridyl substituted triazoles as new and effective corrosion inhibitors for mild steel in hydrochloric acid solution

Three Schiff’s bases namely (3-phenylallylidene) amino-5-(pyridine-4-yl)-4H-1,2,4-triazole-3-thiol (SB-1), 3-mercapto-5 (pyridine-4-yl)-4H-1,2,4-triazole-4-yl) imino) methyl) phenol (SB-2) and (4-nitrobenzylidene) amino)-5-(pyridine-4-yl)-4H-1,2,4-triazole-3-thiol (SB-3) were synthesized and investigated as corrosion inhibitors for mild steel (MS) in 1 M HCl. SB-1 exhibited best inhibition performance (96.6 η%) at 150 mg L⁻¹. The studied inhibitors follow Langmuir adsorption isotherm. Potentiodynamic polarization data suggests mixed-mode of corrosion inhibition. The effect of molecular structure on inhibition efficiency was investigated by theoretical calculations using density function theory (DFT) methods. Surface analysis supports the formation of a protective inhibitor film on the mild steel surface.     

Synergistic effect of polyaspartic acid and iodide ion on corrosion inhibition of mild steel in H2SO4

The inhibition effect of polyaspartic acid (PASP) and its synergistic effect with KI on mild steel corrosion in 0.5 M H₂SO₄ solution are studied by weight loss and electrochemical methods. The inhibition efficiency increases with the concentration of PASP and increases further with the presence of 1 mM KI. Result of the zero charge potential measurement shows that iodide ion promotes the film formation of PASP greatly. The mild steel surfaces after immersion test were analyzed using scanning electron microscopy and X-ray photoelectron spectroscopy. An adsorption model is proposed to elucidate the synergistic mechanism of synergistic effect.     

Atmospheric corrosion of field-exposed AZ31 magnesium in a tropical marine environment

Corrosion behavior of AZ31 magnesium in tropical marine atmosphere was investigated. Chloride ions deposition rate played an important role in the corrosion process, which resulted in an obvious fluctuation of the corrosion rate. The corrosion was initiated from pitting corrosion and then evolved into general corrosion as the exposure time extended. Mg₅(CO₃)₄(OH)₂·xH₂O was the dominate products during the whole exposure periods. The products on the specimens weathered for 1, 6 and 12 months slightly suppressed the corrosion process, while that generated after 24 months of exposure exhibited good protective ability against further corrosion attacks.     

Study of the correlation between pitting corrosion and the component ratio of the dual phase in duplex stainless steel welds

Three duplex stainless steel weldments were produced by changing the chromium element to study the correlation between the pitting corrosion characteristics and the component ratio of the dual phase. The pit morphologies showed that metastable pits were generated at a lower pitting resistance equivalent number (PREN) phase. The secondary austenite phases seemed to serve as a path for the corrosive environment regardless of the ferrite number (FN). There is some discrepancy between the measured values (pitting potential (E_p) through polarization test) and expected values (sequence ranked by PREN of weaker phase) in 1 mol l⁻¹ NaCl solution at 60 °C.     

Early stage oxidation of Ni–Cr binary alloy (1 1 1), (1 1 0) and (1 0 0) surfaces: A combined density functional and quantum chemical molecular dynamics study

First-principles and tight-binding quantum chemical molecular dynamics were used in this study. The chemisorption energies of O and OH on the Ni–Cr (1 1 0) surface are lower than those of other surfaces. The oxygen 2p orbitals hybridise with Ni 3d, 4s and small amounts of p orbitals for the (1 0 0) surface while Ni p orbitals have no contribution for the (1 1 0) surface, which might reduce the adsorption energy. Additionally, oxygen acquires the maximum depth into the Ni–Cr (1 1 0) surface. Applied strain increases the oxygen diffusivity. This study reveals that the Ni–Cr (1 1 0) surface is easier for oxygen diffusion accordingly oxidation accelerates.     

Oxidation of Fe–10Cr in O2 and in O2 + H2O environment at 600 °C: A microstructural investigation

Oxidation of Fe–10Cr in dry and wet O₂ was studied at 600 °C for up to 168 h. Oxide microstructure was investigated by STEM/EDX, FIB/SEM and TEM. Oxidation in dry O₂ gives a Cr-rich protective (Fe_1−xCr_x)₂O₃ scale. The same protective oxide initially forms in O₂ + H₂O environment, but after an incubation period scale breakdown is triggered by CrO₂(OH)₂ evaporation that depletes the substrate in Cr and converts (Fe_1−xCr_x)₂O₃ to FeCr spinel oxide. Internal oxidation occurs after breakaway. Alternating external and internal oxidation result in the inward-growing scale showing a characteristic banded morphology.     

Effect of titanium ions on the ion release rate and uptake at the interface of silica based xerogels with simulated body fluid

The dissolution and surface layer changes of new xTiO₂(100 − x)[4SiO₂·CaO·0.3P₂O₅] sol–gel derived xerogels (0 ⩽ x ⩽ 20 mol%) have been investigated in Kokubo’s simulated body fluid (SBF). The ionic leaching rate was analysed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). ICP-AES results showed a relatively fast dissolution of titanium free sample, with a high release of phosphorous and calcium ions in the first hour of incubation while the release of silicon ions continuously increased up to 6 h of immersion. The titanium dioxide addition up to 20 mol% differently influences the release of phosphorus, calcium and silicon ions, i.e. TiO₂ strongly stabilises the phosphorus ions, to a lesser extent the calcium ions, and has almost no effect on the silicon ions release. The structural changes were evaluated using X-ray powder diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The XRD results show that all samples remain mainly amorphous after immersion in SBF. The changes occurred in the surrounding of phosphorous and silicon ions are well reflected in FTIR spectra and they were correlated with the samples stability in SBF.     

2-Mercaptobenzimidazole as a copper corrosion inhibitor: Part I. Long-term immersion, 3D-profilometry,and electrochemistry

The high corrosion inhibition effectiveness of 2-mercaptobenzimidazole (MBIH) in 3 wt.% aqueous NaCl solution is reported using long term immersion tests, 3D-profilometry, electrochemical impedance spectroscopy, and potentiodynamic curve measurements. The high corrosion inhibition performance was proven after 180 days of immersion. The impedance spectra were characterized by two time constants relating to charge transfer and finite layer thickness or semi-infinite diffusion of copper ions through the surface layer, therefore Cu corrosion in solution containing MBIH follows kinetic-controlled and diffusion-controlled processes. Moreover, it is shown that MBIH is a mixed-type inhibitor.     

A study on the initial corrosion behavior of carbon steel exposed to outdoor wet-dry cyclic condition

The initial corrosion behavior of carbon steel subjected to outdoor wet-dry cyclic exposure and exposure under natural environments have been investigated. The weight loss results indicate a transition from corrosion acceleration to deceleration during the early stage of corrosion of carbon steel under both conditions. The corrosion kinetics under both conditions follow empirical equation D = Atⁿ. Outdoor wet-dry cyclic exposure significantly promoted the initiation but the rate of corrosion was about three times as fast. The morphology of corrosion surfaces and cross-section of rust layer have been examined using SEM and the compositions have been analyzed using XRD and EPMA.     

Electrochemical behavior of a lead-free Sn–Cu solder alloy in NaCl solution

Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization techniques and an equivalent circuit analysis are used to evaluate the electrochemical corrosion behavior of Sn–Cu alloy samples in a naturally aerated 0.5 M NaCl solution at 25 °C. It has been found that a better electrochemical corrosion resistance is provided by a coarser cellular microstructure array. It has also been found that the corrosion current density (i_corr) is of about a quarter when compared with that of the finest microstructure examined. Such behavior is attributed to both localized strains between the Sn-rich phase and intermetallic (IMC) particles and the cathode/anode area ratios. The effect of copper alloying on i_corr is also discussed.     

Effects of pH value on characteristics of oxide films on 316L stainless steel in Zn-injected borated and lithiated high temperature water

The effects of pH values from 6.9 to 7.4 on oxide films for 316L stainless steel in borated and lithiated high temperature water at 573.15 K without and with Zn injection were examined by in situ potentiodynamic polarization curves, electrochemical impedance spectra and ex situ X-ray photoelectron spectroscopy (XPS) analysis. The composition of oxide films appears slightly pH dependent: rich in chromites and ferrites at pH = 6.9 and pH = 7.4, respectively. The corrosion rate decreases significantly in the high pH value solution with Zn injection due to the formation of compact oxide films. The solubilities and structural model of oxides are proposed and discussed.