An electrochemical and analytical approach to the inhibition mechanism of an amino-alcohol-based corrosion inhibitor for reinforced concrete

Laboratory investigations were performed in order to assess the effectiveness and the inhibition mechanism of an amino alcohol-based inhibitor currently used as admixture to prevent corrosion of steel in concrete. The investigation was performed in the presence of chloride ions, using solutions simulating the concrete interstitial solution. Electrochemical measurements allowed to conclude that, an inhibitor film is formed on the surface hindering the anodic activity. Furthermore, the analytical investigation through the use of X-ray photoelectron spectroscopy (XPS) shows that the inhibitor film is able to complex with the chloride ion.     

Corrosion inhibitors for chlorides induced corrosion in reinforced concrete structures

Reinforcements corrosion is the most important cause of premature failure on reinforced concrete structures. Phenomena promoting corrosion are the ingress of chlorides and the reaction of atmospheric CO₂ with cement paste. Aim of this paper is the investigation on the effectiveness of three organic commercial inhibitors in preventing carbon steel chlorides induced corrosion in concrete, since there is not yet a clear knowledge on the real effectiveness of these products. Inhibitors were added to the concrete mixture in dosage suggested by the manufacturers. Chlorides were added in the concrete mixture or penetrated from outside by “ponding” cycles with a 3.5% sodium chloride solution. The effectiveness of the inhibitors has been evaluated by long-term rebar corrosion monitoring in reinforced concrete and by rebar visual inspection after three years tests. Also solution tests were performed in order to verify the effectiveness of inhibition. Results give information about corrosion prevention ability of analysed commercial inhibitors.     

Inhibition effect of inorganic and organic inhibitors on the corrosion of Mg–10Gd–3Y–0.5Zr alloy in an ethylene glycol solution at ambient and elevated temperatures

In this study, the corrosion performance of magnesium-based rare-earth containing alloy Mg–10Gd–3Y–0.5Zr (GW103) was evaluated in an ethylene glycol solution with a group of selected aliphatic, aromatic carboxylates and inorganic salts as inhibitors. The dependence of inhibition efficiency on the concentration ratio of sodium phosphate to sodium dodecylbenzenesulfonate (SDBS) and the total inhibitor concentration was measured by means of electrochemical techniques. It was found that the corrosion rate of GW103 decreased by addition of inorganic–organic inhibitors at both ambient and elevated temperatures. The inhibitors were more effective at the ambient temperature than at the elevated temperature. The corrosion of GW103 in the ethylene glycol solution can be effectively inhibited by 1000 ppm of the inorganic–organic inhibitor mixture. It is believed that the added phosphate can interact with SDBS, resulting in a more compact surface film on the GW103 surface. Based on these results, as well as Environmental Scanning Electron Microscope (ESEM) observations, a synergistic mechanism was proposed to explain the inhibition behavior of the sodium phosphate + SDBS combination.     

Synthesis and evaluation of the inhibitor effect of a new class of triazole compounds

In this work, a new class of triazole molecules, containing heteroatoms such as nitrogen and sulphur, is prepared. The effect of these molecules on the corrosion behaviour of iron was investigated. Electrochemical studies were performed in aerated chloride acid solution (1 M) by potentiodynamic polarisation curves. Surfaces were characterised by scanning electron microscopy.

The recorded electrochemical data showed that the corrosion resistance was greatly enhanced in the presence of inhibitor. The maximal protection efficiency exceeded 94%. The corrosion protection could be explained by the adsorption of inhibitor through the S- or N-atom and formation of a protective layer attached to the metal surface.     

Modification of 1018 carbon steel corrosion process in alkaline sour medium with a formulation of chemical corrosion inhibitors

This work is focused on researching corrosion mechanism modifications of 1018 carbon steel in alkaline sour medium (0.1 M (NH₄)₂S and 10 ppm CN⁻) using inhibitor formulation (IHF) composed of hydroxyoleic imidazoline (C₁₂H₄₂ON₂), HI, and aminoether (C₂₀H₂₈O₃N₂), AE. The accelerated formation of corrosion products was thereby carried out in the presence of the formulation alone and of each of its components separately; these films were subsequently characterized by electrochemical impedance spectroscopy and scanning electron microscopy. The study in the presence of the IHF components revealed that the films formed have different nature, because their physical and chemical properties such as thickness, porosity and (electronic and ionic) conductivity are determined by the media where they are grown. The film formed in the presence of HI has a homogeneous, non-porous topography that impairs the diffusion process of H⁰, in addition, its electronic conductivity is above that observed in the film formed with AE. Then, it was determined that the film formed with IHF presents some distinctive component characteristics which interact in a complementary way improving film passivity.     

Electrochemical study on inhibitors of rebar corrosion in carbonated concrete

Electrochemical Impedance Spectroscopy (EIS) was used to evaluate the inhibitive action of some organic compounds towards the corrosion of a carbon steel, both in a solution simulating the pore chemistry of carbonated concrete and in carbonated concrete.The synthetic solution (SS) has been made by bubbling pure CO₂ in a saturated Ca(OH)₂ solution till obtaining pH 7 and then filtering it. Concrete carbonation has been obtained by maintaining the concrete specimens in CO₂ atmosphere for 80 days, at 68% RH and room temperature.In SS, benzoate, its amino-derivatives and dicarboxylates were able to form a long-lasting passive layer on the steel surface. Their efficiency improved with time.In carbonated concrete the additives inducing a decrease in the concrete compressive strength were discarded. Some compounds were monitored for up to 400 days, but only two (the sodium salts of benzoic acid and, particularly, 2-amino benzoic acid) exhibited some inhibitive effect towards the rebar corrosion process.     

Effect of calcium nitrite-based corrosion inhibitor in preventing corrosion of embedded steel in concrete

Due to the corrosion inhibition effect and compatibility with concrete properties, calcium nitrite solution has been widely used, in North America and Asia,. However, investigation has often been restricted to tests using a macrocell corrosion monitoring or measuring corrosion rate in an aqueous condition. This study concerns the assessment of the inhibition effect of calcium nitrite-based corrosion inhibitor using a polarisation method and its influence on the chloride transport, compressive strength and setting time of concrete.The calcium nitrite-based corrosion inhibitor significantly reduced the corrosion rate of steel in chloride contaminated mortar and raised the chloride threshold level, ranging from 0.22% to 1.95% by weight of cement, while nitrite-free specimen produced the threshold level ranging from 0.18% to 0.33%. It was observed that concrete specimens containing the corrosion inhibitor produced the higher total charge passed in a rapid test for chloride ion permeability. An increase in the dosage of corrosion inhibitor resulted in a decrease in the concrete setting time. In addition, the compressive strength at early ages was increased by corrosion inhibitor, but in a long term (900 days), decreased to the level for 28 days.     

Comparing corrosion measurement methods to assess the corrosion activity of laboratory OPC and HPC concrete specimens

The corrosion of reinforcing steels in concrete is the main reason for the deterioration of bridge decks. An accurate method for measuring corrosion is a fundamental prerequisite for the detection of damaged areas and for planning an effective method for repairing bridge decks. A laboratory study was conducted to estimate the corrosion activity of a reinforcing steel embedded in two types of concrete, ordinary and high-performance, using different corrosion measurement methods. Results indicated that Tafel plot (TP), linear polarization resistance, half-cell potential (HCP), and chloride content methods would assess the same level of corrosion activity in only 24% of specimens.     

Application of the Kelvin Probe method for screening the interfacial reactivity of conducting polymer based coatings for corrosion protection

In our recent studies we could show that intrinsically conducting polymers definitely possess promising potential for application in intelligent corrosion protection coatings. One prerequisite for this was shown to be that macroscopic networks of the conducting polymers have to be avoided in the coating in order to avoid predominant and disastrously fast cation incorporation during the corrosion induced reduction of the polymer. Only then anions serving as inhibitors and safely stored in the conducting polymer will be efficiently released during a corrosive attack. This mechanism is more or less independent of the metal that has to be protected, i.e. it is a property of the composite coating derived from dispersing micro-clusters of conducting polymer in a non-conducting matrix and unspecific for the metal onto which it is to be applied. In this paper we focus on specific electrochemical reactions at the interface between the conducting polymer and the metal that were found to define further criteria for successful application. The aim should be that the conducting polymer is in electronic contact with the passive metal surface. However, the formation of an insulating interface, i.e. loss of electronic contact and hence functional inactivity of the conducting polymer, and enhanced corrosion are also possible. We will show how by application of the Kelvin Probe method a fast and easy screening between these three cases can be achieved.     

Electrodeposition of bilayered polypyrrole on 316 L stainless steel for corrosion prevention

The electropolymerization of pyrrole in aqueous solutions of salicylate leads to the formation of hollow rectangular-sectioned microtubes. With the aim to develop a coating with this morphology but with better anticorrosive properties we synthesized a bilayer system by depositing a polypyrrole underlayer electropolymerized in the presence of molybdate and nitrate and a polypyrrole film formed by the microtubes as a top layer. The corrosion performance of the coatings was monitored by following the open circuit potentials, polarization curves and electrochemical impedance spectroscopy in acid and neutral chloride solutions. The bilayers have the capacity to protect the steel against uniform as well as against pitting corrosion during long exposure times. The system with the inner layer formed in alkaline solution was the most protective coating in this study. The results are discussed in terms of the galvanic interaction between the polymer and the substrate and the role played by the dopant anions.     

电化学阻抗谱在缓蚀剂研究中的应用进展

概括了电化学交流阻抗谱的基本原理,介绍了电化学阻抗谱在缓蚀剂研究中的应用进展,并对电化学阻抗谱在腐蚀科学领域其他方面的应用进行了展望。     

Coatings based on electronic conducting polymers for corrosion protection of metals

In this work, corrosion protection of mild steel by a novel epoxy resin (EP)-based coating system containing polyaniline (PAni) as an anticorrosive agent was studied. The corrosion behavior of mild steel samples coated with an EP/PAni-EB (emeraldine base), EP/PAni-ES (emeraldine salt), EP/SPAN (PAni sulfonated), EP/PAni-fibers, EP/PhoZn (zinc phosphate), EP/ChroZn (zinc chromate) or EP/Charge was investigated in 3.5% NaCl solution. For this purpose, electrochemical impedance spectroscopy measurements were utilized. It was found that the addition of three forms of PAni—undoped, sulfonated and fibers—to the EP resin increased its corrosion protection efficiency.     

Electrochemical and quantum chemical study of purines as corrosion inhibitors for mild steel in 1 M HCl solution

The purines and its derivatives, such as, guanine, adenine, 2,6-diaminopurine, 6-thioguanine and 2,6-dithiopurine, were investigated as corrosion inhibitors for mild steel in 1 M HCl solution by weight loss measurements, electrochemical tests and quantum chemical calculations. The polarization curves of mild steel in the hydrochloric acid solutions of the purines showed that both cathodic and anodic processes of steel corrosion were suppressed. The Nyquist plots of impedance expressed mainly as a depressed capacitive loop with different compounds and concentrations. For all these purines, the inhibition efficiency increased by increasing the inhibitor concentration, and the inhibition efficiency orders are 2,6-dithiopurine > 6-thioguanine > 2,6-diaminopurine > adenine > guanine with the highest inhibiting efficiency of 88.0% for 10⁻³ M 2,6-dithiopurine.The optimized structures of purines, the Mulliken charges, molecular orbital densities and relevant parameters were calculated by quantum chemical calculations. The quantum chemical calculation results inferred that the adsorption belong to physical adsorption, which might arise from the π stacking between the π electron of the purines and the metal surface.     

含腐蚀凹坑缺陷管道的安全评定方法

对含腐蚀凹坑缺陷的压力管道进行了有限元弹塑性分析和试验研究 ,得到了含不同球形凹坑缺陷压力管道在内压和弯矩联合作用下的极限载荷 (弯矩 ) ,在此基础上提出了在役含球形凹坑缺陷管道的工程安全评定方法     

Potassium sorbate—A new aqueous copper corrosion inhibitor: Electrochemical and spectroscopic studies

This work presents the novel nature of 2,4-hexadienoic acid potassium salt (potassium sorbate (KCH₃CHCHCHCHCO₂)) as an effective copper aqueous corrosion inhibitor. The influence of pH and potassium sorbate concentration on copper corrosion in aerated sulfate and chloride solutions is reported. Degree of copper protection was found to increase with an increase in potassium sorbate concentration; an optimum concentration of this inhibitor in sulfate solutions was found to be 10 g/L. Copper is highly resistant to corrosion attacks by chloride ions in the presence of potassium sorbate. X-ray photoelectron spectroscopy (XPS) studies suggest that copper protection is achieved via the formation of a mixed layer of cuprous oxide, cupric hydroxide and copper(II)-sorbate at the metal surface.     

Effect of different corrosion inhibitors on the corrosion of cast iron in palm biodiesel

Biodiesel is currently in regular use as an alternative fuel over conventional petroleum diesel. However, corrosion of automotive materials is one of the concerns related to biodiesel compatibility issues. In addition, auto-oxidation of biodiesel can also enhance the corrosiveness of biodiesel. The present study aims to investigate inhibition effect of ethylenediamine (EDA), n-butylamine (nBA), tert-butylamine (TBA) against corrosion of cast iron. Static immersion tests in biodiesel in the presence (100 ppm) and absence of different corrosion inhibitors were carried out at room temperature for 1200 hours. At the end of the test, corrosion characteristic was investigated by weight loss measurements and changes on the exposed metal surface. Fuels were analyzed by using TAN (total acid number) analyzer and FTIR in order to investigate the acid concentration and compositional characteristics respectively. Surface morphology was examined by digital photography and scanning electron microscope (SEM). Oxide layers were investigated by X-ray diffraction. Results showed that TBA was more effective corrosion inhibitor in reducing corrosion than others.     

A thin layer cell adapted for corrosion studies in confined aqueous environments

In order to investigate the influence of the confinement on the corrosion behaviour of metallic materials, an innovative thin layer electrochemical cell was developed. The cell includes a device which allows a continuous gas supply within the electrolyte film covering the metallic specimen under study. A procedure based on high frequency impedance measurements is also proposed to control and precisely adjust the setting of the electrolyte film geometry.The experimental set-up was validated by performing measurements of the stationary limiting cathodic current on a steel disk immersed in a K₂SO₄ aerated solution for various electrolyte layer thicknesses. The results obtained demonstrate the reliability of the experimental method.     

A migrating corrosion inhibitor evaluated in concrete containing various contents of admixed chlorides

The performance of a surface-applied migrating corrosion inhibitor (MCI) based on an alkylaminoalcohol was evaluated on concrete specimens containing reinforcing steel bar (rebar) segments. Two water/cement ratios (w/c's), various chloride contents and two exposure conditions were investigated. The inhibiting efficiency was followed over a period of 1000 days by means of parameters such as corrosion potential, corrosion current and electrical resistance. Results show that when concrete is exposed to the marine environment, the inhibitor is able to reduce the corrosion rate (CR) only when the initial chloride content is below 0.16 wt.% relative to cement content. Efficiency increases as the w/c increases. There is no beneficial effect when the initial chloride content is greater than 0.43%. When concrete is immersed in a saline solution, no beneficial effect associated to the use of the inhibitor could be appreciated, regardless of w/c or initial chloride content in concrete.     

Concentration monitoring and performance of a migratory corrosion inhibitor in steel-reinforced concrete

Inhibitor concentration depth profiles for concrete samples treated with a proprietary migratory corrosion inhibitor (of the Cortec MCI range) are presented. The treated concrete was cored and these cores were then sectioned and crushed before being immersed in distilled water to extract the available inhibitor. The amine concentrations were quantified using an ammonium-sensing electrode and were then related to the inhibitor concentration present. The inhibitor examined, reported to contain a combination of volatile amines and amino carboxylate compounds, was found to readily diffuse through concrete. The inhibitor was subjected to a 5-year trial and found to be effective in suppressing corrosion of steel reinforcement in the presence of high chloride concentrations. The concentration profiles indicate that only relatively low concentrations of inhibitor were required to achieve inhibition in this case.