Piperazine derivatives as inhibitors of the corrosion of mild steel in 3.9 M HCl

The inhibitory action of two piperazine derivatives, 1-benzyl piperazine (P1) and bis(1-benzylpiperazine) thiuram disulfide (P2) on the corrosion of mild steel in 3.9 M HCl at different concentrations has been investigated in the temperature domain 298–333 K. Both weight loss measurements and potentiodynamic polarization methods showed that P2 was the best inhibitor and that its inhibition efficiency increased with concentration to a value >92% at 10⁻³ M. Potentiodynamic polarization studies clearly revealed that P2 acts as cathodic-type inhibitor. The activation energy for the corrosion rates was evaluated in the temperature range 298–333 K. Adsorption of P2 on the mild steel surface in 3.9 M HCl followed a Langmuir isotherm model. A physical adsorption phenomenon is proposed.     

Aluminium—thiourea inhibitors of mild steel corrosion in high specific salinity water. Compatibility with calcium,magnesium and ferrous ions at various temperatures

Aluminium—thiourea (Althi) inhibitors were found to provide good inhibition of mild steel in water of a high specific salinity (1.0% Na₂SO₄) considered characteristic for recirculating water of zero-discharge cooling systems in steam plants. As in a real cooling system this water would contain calcium, magnesium and ferrous ions, a successful application of Althi inhibitors would depend on their compatibility with these ions. In order to check this compatibility the inhibitive efficiencies of two representative Althi inhibitor formulations were measured in the presence of Ca²⁺ (as CaSO₄), Mg²⁺ (as MgSO₄) and Fe²⁺ (as FeSO₄ and FeCl₂) using the weight loss method according to NACE Standard TM 01-69 at 20–40°C. It was found that the inhibitive efficiencies of the tested formulations sharply decreased in the presence of Ca²⁺ while the action of Mg²⁺ and Fe²⁺ does not appear to have a critical influence on the inhibitive properties of the same formulations. This finding showed that the application of Althi inhibitors in zero-discharge cooling systems can be successful if a complete removal of Ca²⁺ from both makeup and recirculating water would be foreseen. Due to the high cost of this removal, in some cases the application of mild steel in conjunction with Althi inhibitors cannot be justified in zero-discharge cooling systems.     

Synergistic effect of iodide ions on inhibitive performance of 2,5-bis(4-methoxyphenyl)-1,3,4-thiadiazole during corrosion of mild steel in 0.5?M sulfuric acid solution

The synergistic effect of iodide ions on the corrosion inhibition of mild steel in 0.5 M H₂SO₄ solutions by 2,5-bis(4-methoxyphenyl)-1,3,4-thiadiazole (4-MTH) has been studied using electrochemical impedance spectroscopy (EIS) and the Tafel polarisation method. The results showed that the inhibition efficiency increased with 4-MTH concentration while the potential of desorption (E _d) remained unchanged. The addition of potassium iodide (KI) in the acid solution stabilized the adsorption of 4-MTH molecules on the metal surfaces and, therefore, enhanced the inhibition efficiency of 4-MTH and increased the value of E _d. The synergistic effect was observed between KI and 4-MTH with an optimum mass ratio of [4-MTH]/[KI] = 5/5. The calculated values of synergism parameter (S _θ) from the coverage of the surface were found to be more than unity in most cases. This clearly showed the synergistic influence of iodide ions on the corrosion inhibition of mild steel in 0.5 M H₂SO₄ by 4-MTH. The adsorption of this inhibitor alone and in combination with iodide ions followed Langmuir’s adsorption isotherm.     

Novel calixarene derivatives as inhibitors of mild C-38 steel corrosion in 1 M HCl

Calixarenes CA1–CA4 containing one to four 4-imidazolylethylamidocarbonyl groups were synthesized and tested as inhibitors for the corrosion of mild steel in 1 M HCl at 308 K. The study was made using Tafel polarisation and weight-loss methods. In contrast to CA1, calixarenes CA2–CA4 were good inhibitors, reaching inhibition efficiencies (E%) of 94 to 100% at 10⁻⁴ M. The values of the inhibition efficiency calculated by the two techniques were in acceptable agreement. E% increased with the number of 4-imidazolylethylamidocarbonyl groups attached to the calixarene. Polarisation curves showed that CA2–CA4 act as mixed-type inhibitors. Their adsorption on the steel surface followed a Langmuir isotherm. Thermodynamic parameters of adsorption were also deduced.     

The combined action of Mg2+ and Cl− ions in cement pastes

In order to study the phenomenon of seawater attack on hydrated cement components, we focused our interest on the combined action of Mg²⁺ and Cl⁻ ions on hydrated cement pastes. Thus, cement pastes were prepared from portland cement and its mixture with 30% pozzolan (Santorin Earth). These pastes were cured in baths of varied concentrations of Mg²⁺ and Cl⁻ ions and stored in 18 ± 2°C. The hydration phenomena were studied in these cement pastes, by XRD and SEM.     

Hybrid sol–gel coatings for corrosion protection of galvanized steel in simulated concrete pore solution

The aim of this experimental research was to study the electrochemical behavior of organic–inorganic hybrid (OIH) coatings for corrosion protection of hot-dip galvanized steel (HDGS) in the first instants of immersion in simulated concrete pore solution (SCPS) (pH > 12.5). The electrochemical performance of the OIH coatings was assessed by electrochemical impedance spectroscopy, potentiodynamic polarization curves, macrocell current density, and polarization resistance. The OIH coatings were prepared via the sol–gel method and were deposited on HDGS surfaces by dip-coating using one or three dip steps. The electrochemical results obtained for HDGS samples coated with OIH matrices in SCPS showed higher corrosion resistance than bare HDGS; as the molecular weight (MW) of Jeffamine^® increased the barrier protection of the coating decreased. The lowest protection efficiency was found for HDGS samples synthesized with oligopolymers with an MW of 2000. Coatings produced with an oligopolymer of 230 MW conferred the highest protection. The surface morphology of the OIH coatings deposited on HDGS surfaces was studied by atomic force microscopy. The results show that the roughness of the OIH films depends on the MW of Jeffamine^® and on the number of dip-coating steps used. Thermogravimetry results show that the Jeffamine^® MW affected the thermal properties of the prepared OIH samples. The prepared OIH materials are thermally stable within the range of 20–80°C.     

The effect of zirconia ions on corrosion performance of sol–gel coated galvanized steel

Currently, galvanized steel is treated with hexavalent chrome passivation. Sol–gel coating has been found to be a potential replacement for the hazardous hexavalent chrome passivation treatment. The aim of this work is to study the effect of zirconyl nitrate on corrosion behavior of sol–gel coating. Aminopropyl-trimethoxysilane and 3-glycidoxypropyltrimethoxysilane were employed as precursors to prepare the sol–gel-based silane coating. The sol–gel film was deposited on galvanized steel sheet by dip coating method. The chemical properties of sol–gel solution and coated films were analyzed by infrared spectroscopy. Morphology of the film was characterized by scanning electron microscope. The corrosion resistance of the coated samples was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization curve, and salt spray test. The results indicated that zirconia-doped coatings have better corrosion resistance in comparison with their undoped counterparts. The coating doped with 0.5% zirconyl nitrate provides better corrosion protection due to the inhibitive action of zirconia ion.     

Inhibition by tween-85 of the corrosion of cold rolled steel in 1.0?M hydrochloric acid solution

The inhibition effect of tween-85 on the corrosion of cold rolled steel (CRS) in 1.0 M hydrochloric acid (HCl) was studied by weight loss and potentiodynamic polarization methods. The results show that tween-85 is a good inhibitor in 1.0 M HCl and its maximum inhibition efficiency (IE) is 92% at very low concentration. Its adsorption obeys the Langmuir adsorption isotherm equation. The thermodynamic parameters of adsorption enthalpy (ΔH ⁰), adsorption free energy (ΔG ⁰) and adsorption entropy (ΔS ⁰) were calculated and discussed. Polarization curves show that tween-85 acts as a mixed-type inhibitor in hydrochloric acid. IE values obtained from weight loss and polarization are consistent. The adsorbed film on a CRS surface containing an optimum dose of tween-85 was investigated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). An inhibitive mechanism is proposed from the viewpoint of adsorption theory.     

Inhibition effect of methyl violet on the corrosion of cold rolled steel in 1.0 M sulfuric acid solution

The inhibition effect of methyl violet (MV) on the corrosion of cold rolled steel (CRS) in 1.0 M sulfuric acid (H₂SO₄) was investigated by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) methods. The results show that MV is a good inhibitor, and inhibition efficiency increases with inhibitor concentration, while decreases with the temperature. The adsorption of MV on CRS surface obeys Langmuir adsorption isotherm equation. The thermodynamic parameters of adsorption enthalpy (ΔH°), adsorption free energy (ΔG°) and adsorption entropy (ΔS°) are calculated and discussed. Potentiodynamic polarization curves show that MV acts as a mixed-type inhibitor in sulfuric acid. EIS exhibits one capacitive loop which indicates that the corrosion reaction is controlled by charge transfer process. Inhibition efficiency values obtained from weight loss, polarization and EIS are in reasonably good agreement. The adsorbed film on CRS surface containing optimum dose of MV was investigated by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Depending on the results, the inhibitive mechanism is proposed from the viewpoint of adsorption theory.     

Chitosan Schiff base as eco-friendly inhibitor for mild steel corrosion in 1 M HCl

In the present study, natural biopolymer chitosan was modified into its Schiff base derivative with salicylaldehyde by condensation method. The prepared chitosan salicylaldehyde Schiff base was characterized using ultraviolet spectroscopy, fourier transform infrared spectroscopy, scanning electron microscope and elemental analysis. Thermal analysis was also carried out to determine the thermal stability of the derivative. To explore the corrosion inhibition performance of the chitosan Schiff base, weight loss, and electrochemical techniques were conducted. The inhibitor reduces the metallic corrosion by adsorbing on to the metal surface. The adsorption of chitosan Schiff base on mild steel surface in 1 M HCl follows Temkin isotherm model. Thermodynamic parameters of adsorption and corrosion process were calculated, which revealed the chemical nature of adsorption. SEM and energy dispersive X-ray spectroscopic analysis confirmed the formation of protective chitosan derivative layer on the mild steel surface.     

Control of oxygen deficiency in Ca1−x La x MnO3−δ and its cathodic properties in alkaline solution

Ceramic samples of composition Ca_0.9La_0.1MnO_3– having various oxygen contents were prepared by a quenching method under nitrogen atmosphere. As the 3 – value decreased from 2.97 to 2.79, the sample conductivity decreased from 10² to 10^–1 S cm^–1. The porous ceramic samples showed good properties as cathode materials in alkaline solution without using conductive material such as graphite, but the discharge capacity decreased with decreasing sample conductivity. The discharge termination is explained by a simple model considering dissipation of the conductive path (high conductivity core) present in the porous sintered ceramic.     

Preparation of hybrid silica sol–gel coatings on mild steel surfaces and evaluation of their corrosion resistance

Hybrid silica sol–gel coatings were prepared on mild steel substrate by dip coating technique. The coatings were subsequently heat treated at 200 °C in order to improve their corrosion properties. The coating sols were synthesized using Glycidoxypropyltrimethoxysilane (glymo) and Aminopropylethoxysilane (ameo) as precursor materials. Potentiodynamic polarization curves were derived and Electrochemical Impedance Spectroscopy (EIS) measurements were made in NaCl solution. The surface and cross-section morphology of coated specimens were characterized by scanning electron microscopy (SEM). Fourier transformed infrared (FTIR) analysis was used to identify the presence of various functional groups in the coating solutions. A comparison of the corrosion resistance of the coated and uncoated mild steel was presented. The results indicated that the corrosion resistance of the coated mild steel was improved considerably.     

The effect of temperature and hydrodynamics on carbon steel corrosion and its inhibition in oxygenated acid–salt solution

Corrosion of carbon steel in hydrochloric acid (HCl)–sodium sulphate (Na₂SO₄) solution mixture was investigated using rotating cylinder electrode (RCE) for a range of rotation velocity, 0–2000 rpm, solution temperature of 32–52 °C, and different oxygen concentrations. The corrosion rat was determined by using both weight loss method and electrochemical polarization technique. Different acid and salt concentrations were used ranged from 0.01 to 0.2 M for salt and 0.5 to 5% for acid. The conjoint effect of increased oxygen concentration and high rotational velocity was studied based on experimental measurements of O₂ concentration. The effects of operating conditions on indole and cetyl trimethyl ammonium bromides (CTAB) inhibition efficiency were also studied and discussed. The results showed that increasing the rotational velocity leads to an increase in the corrosion rate depending on the concentration of salt and acid. Increasing the temperature and acid concentrations leads to an increase in the corrosion rate while the corrosion rate exhibited unstable trend with salt concentration leads to change of corrosion. It is found that increasing O₂ concentration leads to a considerable increase in the corrosion rates especially at high rotational velocity. Indole and CTAB inhibitors exhibited very good inhibition efficiency in most conditions investigated with the former exhibited better inhibition efficiency arriving up to 87% at low rotational velocities. The inhibition efficiency of both inhibitors was found to decrease with increasing velocity. In addition, indole inhibitor reveals excellent inhibition efficiency even at high temperatures while CTAB efficiency decreased appreciably with temperature increase.     

Nonstoichiometry in perovskite-type oxide Ca1−x Ce x MnO3−δ and its properties in alkaline solution

Nonstoichiometry in high conductivity perovskite-type oxide Ca_1-x Ce _x MnO_3- was investigated. At room temperature in air, the 3- value was determined to be 2.91 for CaMnO_3-, which meant that 82% of manganese was tetravalent. Although the 3- value increased by increasing the cerium content, i.e. by doping of higher valent cation into the calcium site, the quantity of Mn⁴⁺ in the sample oxide essentially decreased with increasingx. The oxygen contents change reversibly with temperature in air. Change of oxygen content was also observed on discharging this oxide as the cathode material of a battery in alkaline solution. Surprisingly, the sintered ceramics of this oxide worked as a cathode without mixing with a conductive powder such as graphite. Considering the discharging performance, this oxide may be a candidate for the cathode material of the alkaline battery.     

Anodic polarization behaviour of cast iron alloys in deaerated concentrated H3PO4 solutions containing Cl− and F− ions

The anodic behaviour of four cast iron alloys containing up to 16.7% Ni, in deaerated 60 wt% H₃PO₄ with and without 5 × 10^–3 M F^–, Cl^– ions and 1:1 Cl^–/F^– mixture was studied by the potentiostatic technique. Values of E _corr of the alloys are markedly influenced by their composition. The anodic behaviour in the active region is controlled by Fe in the alloys and the dissolution reaction is characterized by Tafel slopes, b _a, between 64 and 88 mV (decade)^–1. A two-electron transfer mechanism for the anodic dissolution is proposed. Passivation of the alloys is due to the formation of oxide layers including Fe₂O₃ and/or Fe₃O₄. Both critical and passive c.d. (I _cc and I _P) are markedly increased in the presence of Cl^– ions, but the presence of F^– ions inhibit the active dissolution of the alloys. The Tafel slope for oxygen evolution reaction (o.e.r.) in the transpassive region, is 240 ± 25 mV. In the proposed mechanism for the o.e.r., the rate determining step is an electron transfer reaction and possible interpretation of the high Tafel slopes is given based on the dual barrier model.     

The role of chloride ions and pH in the corrosion and pitting of Al–Si alloys

The role of chloride ions in the pitting corrosion of some Al–Si alloys was investigated by chemical, polarization and EIS measurements, as well as SEM studies. Differences in corrosion rates of pure aluminium and the alloys are discussed. The capacitive behaviour of the oxide covered surface is replaced by resistive behaviour as immersion time increases in HCl solutions. At neutral pH corrosion currents increase then decrease with chloride ion concentrations. Pitting by chloride ions initiates more readily in acidic media.     

Evaluation of the corrosion protection performance of epoxy coatings containing Mg nanoparticle on carbon steel in 0.1 M NaCl solution by SECM and EIS techniques

The effect of corrosion protection performance of epoxy coatings containing magnesium (Mg) nanoparticles on carbon steel was analyzed using scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). Localized measurements such as oxygen consumption and iron dissolution were observed using SECM in 0.1 M NaCl in the epoxy-coated sample. Line profile and topographic image analysis were measured by applying ?0.70 and +0.60 V vs the Ag/AgCl/saturated KCl reference electrode as the tip potential for the cathodic and anodic reactions, respectively. The tip current at ?0.70 V for the epoxy-coated sample with Mg nanoparticles decreased rapidly, which is due to cathodic reduction in dissolved oxygen. The EIS measurements were conducted in 0.1 M NaCl after wet and dry cyclic corrosion test. The increase in the film resistance (R _f) and charge transfer resistance (R _ct) values was confirmed by the addition of Mg nanoparticles in the epoxy coating. Scanning electron microscope/energy-dispersive X-ray spectroscope analysis showed that Mg was enriched in corrosion products at a scratched area of the coated steel after corrosion testing. Focused ion beam–transmission electron microscope analysis confirmed the presence of the nanoscale oxide layer of Mg in the rust of the steel, which had a beneficial effect on the corrosion resistance of coated steel by forming protective corrosion products in the wet/dry cyclic test.     

A corrosion mechanism of titanium diboride in KF−AlF3−Al2O3 melt

TiB₂ samples were exposed to molten KF?AlF₃?Al₂O₃: 54.8-42.1-3.1 mol% salt, at 680 °C for 50, 100 and 200 h. The corroded samples of TiB₂ were investigated by SEM-EDX, EBSD, XRD, FT-IR and MAS NMR analysis. Corrosion was noted to occur predominantly as pitting attacks on the surface of the investigated materials. An inter-crystal and trans-crystal corrosion were identified on the cross-sections of the samples. A perturbation of TiB bonds was detected (SEM-EDX and NMR analysis), at which a formation of orthorhombic TiO₂ was also identified (EBSD analysis). The subsequent NMR, XRD and FT-IR analysis of the behaviour of TiB₂ powder in molten KF?AlF₃?Al₂O₃ supports the statement about the formation of orthorhombic TiO₂ and mullite type of aluminium borates.     

Inhibiting effect of cerium ions on corrosion of 3003 aluminum alloy in ethylene glycol–water solutions

In this study, the inhibiting effect of cerium ions (Ce³⁺) on corrosion of 3003 aluminum alloy (AA3003) in ethylene glycol–water solutions was investigated using a rotating cylinder electrode, simulating the hydrodynamic condition of the automotive cooling system. Electrochemical measurements and surface characterization were conducted to study the inhibiting mechanism of Ce³⁺ on the Al alloy corrosion. It is found that Ce³⁺ serves as a cathodic inhibitor, and inhibits effectively corrosion of AA3003 in the flowing ethylene glycol–water solutions. The inhibiting effect of Ce³⁺ is resulted from the formation and deposit of Ce oxide and/or Ce hydroxide on the electrode surface. With the immersion time, the Ce deposit layer increases its thickness to cover the second phase particles, eliminating the galvanic coupling effect between the second phase particles and Al alloy substrate.