Electrochemical evidence of caffeine adsorption on zinc surface in ethanol

Several electrochemical methods were employed to confirm the ability of caffeine (1,3,7-trimethylxanthine) to adsorb on zinc surface in aerated ethanol solutions. The interaction between the organic compound and the electrode surface was dependent on the electrode potential. Adsorption on the electrode surface was confirmed by comparing the voltammograms, Tafel plots and EIS curves of a zinc electrode in the absence and presence of dissolved caffeine. The calculated standard free energy of adsorption confirms a spontaneous chemical adsorption step.     

Chlorhexidine digluconate as corrosion inhibitor for carbon steel dissolution in emulsified diesel fuel

Nitrogen oxide (NO_x) and particulate matter (PM) emissions from diesel engines are reduced by mixing water in the diesel fuel in the form of water-in-diesel emulsion. The results of experiment showed that blend of span 80 and tween 80 at HLB 6 was found to be the most suitable emulsifier for water/diesel emulsion. The effect of chlorhexidine digluconate on the corrosion of carbon steel electrode in aerated stagnant water/diesel emulsion solution has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency was found to increase with increasing inhibitor concentration. The inhibition is attributed to adsorption of the inhibitor on the carbon steel surface. The adsorption behavior of chlorhexidine digluconate on the carbon steel surface follows Temkin-type isotherm. The standard free energies of adsorption are lower than 40 kJ mol⁻¹ confirming the physical adsorption of chlorhexidine digluconate on the electrode surface. Chlorhexidine digluconate has a significant inhibiting effect on the growth of micro-organisms in the liquid fuel and protection efficiencies up to 99.9% were measured.     

Disbonding of underwater-cured epoxy coating caused by cathodic protection current

Cathodic disbonding of the underwater-applied, ultra-thick, solvent free epoxy coating subjected to various levels of cathodic protection was investigated during the period of the coating cure. The results indicate that the partially cured coating was of low resistivity, between 10³ and 10⁵ Ω cm² for the cathodic polarization of on-potentials between −0.98 and −1.4 V_Ag/AgCl/sw. The coating was shown to be capable of withstanding normal levels of cathodic protection between off-potentials of −0.8 and −1.1 V_Ag/AgCl/sw while the IR drop, introduced by the coating in the same potential range, increased from 0.06 to 0.1 V and has to be taken into account at the design stage of the cathodic protection system. Beneficial influence of calcareous deposit formation on the cathodic protection current was confirmed, particularly for the failed coating. The initial period (1 week) of coating cure was shown as the most critical for disbonding processes caused by the excessive cathodic polarization.     

Inhibition of brass corrosion in sodium chloride solutions by self-assembled silane films

Self-assembled monolayers (SAMs) of 3-mercaptopropyltrimethoxysilane (PropS-SH), dodecyltrimethoxysilane (DTMS), 3-aminopropyl(trimethoxy)silane (APS), and chloropropyl(trimethoxy)silane (CPTMS) were investigated to evaluate the influence of the silane molecule structure towards brass corrosion protection. The results indicated that SAMs of PropS-SH, CPTMS and DTMS inhibited the corrosion of brass in 0.2 M NaCl showing a mixed type behavior, while APS was not a good inhibitor. The inhibitive action of the PropS-SH and DTMS can be explained by chemisorption which obeys the Langmuir adsorption isotherm. The thiolate bond allows a better anchorage of the silane layer to the brass surface than the oxane bond.     

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.     

Effect of cationic surfactant and inorganic anions on the electrochemical behavior of carbon steel in formation water

Corrosion behavior of carbon steel in formation water associated crude oil from Egyptian western desert was studied at various concentrations of dodecyl dimethyl ammonium chloride (CS) as a cationic surfactant. Polarization curves indicate that CS has a good inhibition efficiency for carbon steel in formation water and behaves as cathodic inhibitor. The inhibition efficiency was found to increase with increase in CS concentration until reaches a maximum constant value corresponding to the critical micelle concentration of CS and decrease with increase in solution temperature. The adsorption of CS follows the kinetic thermodynamic model and Flory-Huggins isotherm. Thermodynamic parameters obtained indicate that that the presence of the CS increases the activation energy. Polarization and Impedance measurements indicate that the addition of KI has a significant synergistic effect with CS and results in increase the inhibition efficiency of CS in formation water.     

Effects of alternating current on corrosion of a coated pipeline steel in a chloride-containing carbonate/bicarbonate solution

In this work, the alternating current (AC)-induced corrosion of a coated pipeline steel was studied in a chloride-containing, concentrated carbonate/bicarbonate solution, which simulated the trapped high pH electrolyte under coating, by potentiodynamic polarization measurements, immersion tests and surface characterization technique. It was found that an application of AC resulted in a negative shift of corrosion potential of the steel, caused an oscillation of anodic current density, and degraded the steel passivity developed in the solution. With the increase of AC current density, the corrosion rate of the steel increased. At a low AC current density, a uniform corrosion occurred, while at a high AC current density, pitting corrosion occurred extensively on the steel electrode surface. At individual applied AC, there was a higher electrochemical dissolution activity of the coated steel electrode containing a 1 mm defect than that of the electrode containing a 10 mm defect.     

EIS study of the corrosion behaviour of zinc-based coatings on steel in quiescent 3% NaCl solution. Part 2: coatings covered with an inhibitor-containing lacquer

An EIS study has been made of the behaviour of several lacquered and inhibited zinc-based coatings on steel exposed to a 3% NaCl solution in quiescent conditions. Under the hypothesis that the HF-LF arc supplied the R_t value of the corrosion reaction, the possibility of obtaining quantitative information about the effect of the lacquer film and the inhibitor on the progress of attack has been demonstrated. Different values of the constant B in the Stern-Geary equation must be used depending on the specific metallic coating tested. The relatively high interfacial capacitance values of the lacquered coating suggest a highly defective lacquer film which leave a considerable fraction of the surface of the metallic substrate exposed to the corrosive medium.     

Evaluation of the corrosion of UNS G10200 steel in aerated brines under hydrodynamic conditions

The influence of the flow velocity and the temperature on the corrosion of UNS G10200 in aerated brines had been evaluated by means of electrochemical techniques at the RCE. Increasing the flow velocity and the temperature enhances the corrosion kinetic of the system and changes the corrosion mechanism. This behaviour was adduced to the presence of a mixed control on the corrosion process related with the formation and stabilization of corrosion product layers on the electrode surface. The correlations of Wranglen and Silverman for the mass transfer and the wall shear stresses respectively were validated at the RCE for this system.     

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.     

Tryptamine as a corrosion inhibitor of mild steel in hydrochloric acid solution

The inhibitor effect of tryptamine on the corrosion of mild steel in 0.5 M hydrochloric acid at 30 °C was investigated using linear polarization, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency increases with an increase in concentration of tryptamine. At 500 ppm tryptamine the inhibition efficiency calculated by these techniques is around 97%. Cathodic and anodic polarization curves of mild steel in the presence of different concentrations of tryptamine at 30 °C reveal that it is a mixed type inhibitor. Tryptamine follows Langmuir adsorption with adsorption free energy of −35.07 kJ mol⁻¹.     

Effect of cobalt on the corrosion resistance of low alloy steel in sulfuric acid solution

This study examines the effect of cobalt addition on the corrosion resistance of low alloy steel in a 10 wt.% sulfuric acid solution at room temperature. All specimens show passive behaviors over the potential range, 0.5–1.55 V_SCE, and the passive current density decreased with increasing Co addition. The Co-containing steels also show higher polarization resistance and lower corrosion rate. The beneficial effect of Co is attributed to the formation of a uniform and continuous rust layer due to an interaction between Co and other elements such as Fe, O and S.     

Investigation on some Schiff bases as corrosion inhibitors for mild steel

In the present work, the effect of some newly synthesized Schiff bases containing sulphur nitrogen as heteroatom was investigated on mild steel corrosion in acidic media. Electrochemical studies of the mild steel samples were performed in an aerated solution of 0.1 M HCl + dimethyl sulphoxide (DMS) as co-solvent. DMS is also behaving as a corrosion inhibitor for mild steel. At low inhibitor concentration and short immersion time one can see only the inhibitive effect of DMS as anodic inhibitor for mild steel. At high concentration and long immersion time inhibition efficiencies are increased and cathodic inhibition is observed.     

Studies on enhancement of surface durability for steel surface by camphor oil modified epoxy polyamide coating

Epoxy polyamide coatings are generally used to protect mild steel structures from corrosive atmosphere due to their better adhesion over under prepared surface and effective barrier protection. But the coating has the ability to disintegrate due to UV radiation and high humidity condition. To improve the weatherability and chemical resistance performance of epoxy polyamide, there is a need to modify it with suitable cross linking agent. In this work, it has been found that camphor oil at 5 wt.% as the optimum level to protect the mild steel structures from corrosive electrolyte. Further the impedance study has shown that the resistance exerted by the Camphor oil incorporated coating in 0.5 M NaCl solution after 60 days is 3 × 10⁷ Ω cm² where as the resistance of the coating without this modifier is 3 × 10⁶ Ω cm². The FTIR spectral study indicates that the formation of ether linkages in the dried film and also the other functional groups present in the epoxy polyamide polymer is completely disappeared in the modified coating. Similarly the TG and DTA analysis showed that considerable shift in the degradation temperature has been noticed for the polymer coating with modifier.     

Effect of citrate ions on the electrochemical behaviour of low-carbon steel in borate buffer solutions

The electrochemical behaviour of cold-rolled low carbon steel was studied on both active and passive potential regions in borate buffer solutions with and without the addition of sodium citrate (NaCit). In the active region anodic charges increased significantly and R_CT values decreased with citrate, due to the formation of soluble complexes. In the passive potential region the film formed at +0.4 V in borate buffer solution with and without 0.010 M NaCit is probably enriched by Fe₃O₄ oxide, while films formed at +0.8 V are probably enriched by γ-Fe₂O₃. The equivalent circuit [R_s(R_CTQ)] fitted all experimental impedance data.     

Corrosion studies of stainless steel protected by a TiO2 thin film deposited on a sulfonate-functionalized self-assembled monolayer

Thioacetate hexadecyltrimethoxysilane was deposited on SiO₂-coated stainless steel to form a thioacetate-functionalized monolayer. In situ oxidation of the thioacetate yielded a sulfonate-functionalized monolayer. Solution deposition of TiO₂ on this monolayer covered the stainless steel with a thin layer of the metal oxide (5-10 nm). Cyclic voltammetry (CV) and potentiostatic current transient demonstrated the efficiency of the corrosion protection in sodium chloride media, including protection against pitting corrosion.     

Effect of niobium on the corrosion behaviour of low alloy steel in sulfuric acid solution

This study examines the effect of niobium (Nb) addition on the electrochemical properties of low alloy steel using electrochemical techniques in a 10 wt.% sulfuric acid solution as well as surface analysis techniques. The potentiodynamic test reveals the passive behaviour of all specimens and a decrease in the passive currents with increasing Nb content. Electrochemical impedance spectroscopy (EIS) shows that the Nb-containing steels have higher passive and charge transfer resistance than the control samples. These results suggest that the interaction of elements improves the corrosion resistance of low alloy steel due to the formation of Nb, C, S, P, and Fe products on the surface.     

Effect of temperature and fluid velocity on corrosion mechanism of low carbon steel in presence of 2-hydrazino-4,7-dimethylbenzothiazole in industrial water medium

The corrosion inhibition of 2-hydrazino-4,7-dimethylbenzothiazole on low carbon steel in industrial water has been investigated at different temperatures and fluid velocities at different concentrations of the inhibitor using mass loss, potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The results showed that corrosion resistance increased by increasing the inhibitor concentration. Optimization of the three variables has been made and correlating the results obtained using Box–Wilson statistical method. The adsorption process on low carbon steel surface obeys Flory–Huggins isotherm. The values of ΔG_ads obtained suggest that, the adsorption process of 2-HMBT on low carbon steel is chemisorption. The activation energy increased with increasing the concentration of inhibitors leading to decrease of the pre-exponential factor, and the entropy of activation increased negatively in the presence of inhibitor. SEM was used to identify the film formed on the metal surface.     

Influence of flow on the corrosion inhibition of St52-3 type steel by potassium hydrogen-phosphate

Influence of hydrodynamic conditions on the corrosion of St52-3 type steel rotating disc electrode, RDE, in 3.5% NaCl and its corrosion inhibition using K₂HPO₄ have been studied. Results showed that by rotating the electrode in blank and inhibited solutions, corrosion current density, i_corr, increased, corrosion potential, E_corr, shifted toward more positive values and charge transfer resistance, R_ct, decreased. The inhibition efficiencies increased with electrode rotation rate. This increase was attributed to the enhanced mass transport of inhibitor molecules toward the metal surface and formation of more protective films. Little decrease of efficiencies at higher rotation speeds was probably because of the separation of protective films due to high shear stresses.