Electrochemical injection of organic corrosion inhibitors into concrete

Two organic bases (ethanolamine and guanidine) that are known to act as corrosion inhibitors for steel in aqueous media were introduced into saturated specimens of carbonated and non-carbonated concrete from external electrolytes under the influence of an electrical field applied between embedded steel cathodes and external anodes. The cathodic current density was galvanostatically controlled at values in the range 1-5 A/m² for periods of 3-14 days. Control experiments, in which the corrosion inhibitors were applied to similar saturated concrete surfaces from external electrolyte without current, were also conducted. After treatment, the specimens were sectioned and analysed to determine the concentration profiles of the corrosion inhibitors within the concrete. It was found that the efficiency of injection of both ethanolamine and guanidine under the applied field was far higher in carbonated concrete than in non-carbonated concrete and that, in the carbonated specimens, the inhibitors became concentrated near the embedded steel. In non-carbonated concrete, guanidine penetration was accelerated to a modest extent by the applied field but ethanolamine penetration was not significantly enhanced by the field. These findings were explicable in terms of the influence of the pH values of the pore solutions in the various specimens on the degrees of ionisation of the organic bases concerned and hence on their tendencies to migrate and neutralise cathodically-generated hydroxyl ions.     

On the penetration of corrosion products from reinforcing steel into concrete due to chloride-induced corrosion

Reinforced concretes were corroded to varying degrees by exposing to cyclic NaCl spray and 40 °C drying. The amount of corrosion products and induced damage were measured using image analysis. We found that corrosion products can accumulate at steel-concrete interface as well as penetrate cement paste and deposit within hydration products, relicts of reacted slag, and air voids. As corrosion increases, the products tend to accumulate at the steel-concrete interface, while the amount penetrating cement paste remains relatively constant. Only a small amount of corrosion is needed to induce visible cover cracking. Implications on modelling time to cover cracking are discussed.     

A theoretical study of some hydroxamic acids as corrosion inhibitors for carbon steel

The corrosion inhibition characteristics of two hydroxamic acids, i.e., oxalyl-dihydroxamic acid (C2) and pimeloyl-1,5-di-hydroxamic acid (C7), on carbon steel has been studied using density functional theory (DFT). Quantum chemical parameters such as highest occupied molecular orbital energy (E_HOMO), lowest unoccupied molecular orbital energy (E_LUMO), and energy gap (ΔE) have been calculated using B3LYP/6-31 + G∗∗ basis set. The relationship between the inhibition efficiency and quantum chemical parameters has been discussed in order to elucidate the inhibition mechanism of these compounds.     

Electrochemical methods for evaluating inhibitors of steel corrosion in concrete

Abstract

Electrochemical methods were used to evaluate sodium phosphate and sodium nitrite as inhibitors for the corrosion of steel in saturated calcium hydroxide solution containing chloride ions. The studies included immersion, potentiodynamic, potentiostatic, and galvanostatic tests. The results obtained from these methods were in good agreement. They show that sodium nitrite is an anodic inhibitor which is not effective if its concentration is lower than that of the chloride ions. Sodium phosphate acts as an anodic inhibitor if its concentration is higher than 0·6 times the chloride concentration. It is totally effective when its concentration equals the chloride concentration.     

Nitrite-benzoate inhibitors for protection against corrosion of steel reinforcement in concrete

The studies were devoted to the effect of a mixture of sodium nitrite with the salts of substituted benzoic acids on the corrosive behavior of steel in chloride-containing Ca(OH)₂ solutions. The inhibitory action of these compositions depends on the nature of the substituent and can significantly increase the protective effect of the constituent components. The inhibiting compositions of the synergetic effect, IFKhAN-80, −82, and −83, were developed for the primary protection of steel reinforcement in concrete.     

Structural effects of organic compounds as corrosion inhibitors for hydrogen entry into iron in sulphuric acid

Effects of propynol, methyl-propynyl ether, N,N-dimethylpropynylamine and trimethylpropynyl ammonium cation on hydrogen entry into iron and corrosion were investigated by weight loss tests and electrochemical measurements in de-aerated 1 N sulphuric acid. Trimethylpropynyl ammonium cation gave the best inhibition for hydrogen entry. It is proposed that the inhibition of hydrogen entry by acetylenic compounds is essential to lower the π electron density by the introduction of a strong electron attracting group adjacent to the triple bond, resulting in the enhancement of adsorption by back-donation.     

Antibacterial drugs as corrosion inhibitors for corrosion of aluminium in hydrochloric solution

The corrosion behavior of aluminium in 2 M HCl solution in the absence and presence of four compounds of antibacterial drug was investigated using hydrogen evolution, weight loss, and potentiostatic polarization techniques. It was found that, the inhibition efficiency of these compounds depends on their concentration and chemical structure. The inhibitive action of these compounds was discussed in terms of blocking the electrode surface by adsorption of the molecules through the active centers contained in their structure. The adsorption process follows Langmuir adsorption isotherm. The effect of temperature on the rate of corrosion in the absence and presence of these compounds was also, studied. Some activated thermodynamic parameters were computed.     

A study on new benzotriazole derivatives as inhibitors on copper corrosion in ground water

The corrosion inhibition properties of newly synthesized 1-(2-pyrrole carbonyl)-benzotriazole (PCBT) and 1-(2-thienyl carbonyl)-benzotriazole (TCBT) in combination with the non-ionic surfactant Triton X-100 (TX-100) on metallic copper were studied in ground water environment and the results were compared with benzotriazole (BTA). Various electrochemical studies such as open circuit potential (OCP), potentiodynamic polarization, ac impedance and cyclic voltammetric (CV) were made. Surface analytical techniques like FT-IR and XRD were also performed. The results indicated that PCBT is a better corrosion inhibitor for copper and the formulation consisting of PCBT and TX-100 offered improved inhibition efficiency (IE) in a synergistic manner.     

Experimental and theoretical investigation of organic compounds as inhibitors for mild steel corrosion in sulfuric acid medium

Three synthesized organic compounds were tested as corrosion inhibitors for mild steel in sulfuric acid medium by potentiostatic polarization, FTIR spectroscopy and SEM techniques. Quantum chemical parameters were also calculated to characterize adsorption mechanism. Acceptable correlations were obtained between inhibition efficiency and the calculated quantum chemical parameters. It was found that the investigated compounds exhibit a good inhibition effect especially at 8-10 ppm range concentration, which makes them commercially important. The adsorption of inhibitors on the surface obeys Langmuir adsorption isotherm. The values of activation energy and the thermodynamic parameters, such as K_ads, , and were calculated.     

Comparative study of bis-piperidiniummethyl-urea and mono-piperidiniummethyl-urea as volatile corrosion inhibitors for mild steel

Bis-piperidiniummethyl-urea (BPMU) and mono-piperidiniummethyl-urea (MPMU) were developed as novel volatile corrosion inhibitors (VCIs). Their vapor corrosion inhibition property was evaluated by volatile inhibiting sieve test (VIS) and vapor inhibiting ability test (VIA). Volatile weight-loss test in a closed space was used to compare their volatility. Electrochemical impedance spectroscopy of a volatile corrosion inhibitor monitor (VCIM) was applied to study the effect of BPMU and MPMU on the corrosion inhibition of mild steel in thin electrolyte layer. The results show that BPMU has the better protection effect compared with MPMU. Adsorption of BPMU and MPMU on steel surface was investigated by X-ray photoelectron spectroscopy (XPS). It was shown that one BPMU molecule has two N atoms to coordinate with one Fe atom, and that one MPMU molecule has one N atom to coordinate with one Fe atom. The quantum chemical parameters were obtained by PM3 semi-empirical method. BPMU has the smaller HOMO-LUMO energy gap and the smaller net positive charge intensities of 4N and 8N atoms in its molecule.     

Self-assembling molecules as corrosion inhibitors for 1050 aluminum

Whether it contains hexavalent chromium, chromium (VI), or simply Cr(VI), chromating has been largely used for surface preparation of aluminum aimed at corrosion protection due to its effectiveness and easy application. The most used among these processes are those that contain toxic and carcinogenic substances, which generate environmental backlash concerning the disposal of used baths with toxic elements. The high costs involved in the treatment of the disposal solutions prior to being discarded, besides the increasing restrictions concerning the environment, have encouraged research in the search for alternatives with lower toxicities than chromating processes but with high effectiveness for corrosion protection. Surface treatments with alkane diphosphonate molecules (ADM) have been investigated as potential substitutes for chromating. However, their effectiveness in the corrosion protection of aluminum alloys still needs further investigation. In the present study, the corrosion resistance of 1050 aluminum with various surface treatments was investigated by electrochemical techniques and salt spray testing. The corrosion performance of 1050 aluminum samples with a surface treatment that consisted of immersion in ADM was compared with that of the same alloy chromated by immersion in baths of Cr(III) or Cr(VI). The results showed that surface treatment with ADM was effective on samples that had been exposed to boiling water for oxide growth prior to treatment with ADM. The results also showed the superior corrosion performance for samples with the oxide-hydroxide + ADM surface treatment compared to those with both chromating treatments, either with Cr(III) or with Cr(VI). Cr(III) chromating treatment also provided better corrosion performance than chromating with Cr(VI), suggesting that both surface treatments (oxide-hydroxide + ADM and Cr(III)) are potential candidates for substitution for Cr(VI)-containing processes. However, for effective corrosion protection, the ADM treatment has to be carried out on surfaces previously exposed to treatments that favor oxide growth.     

Test protocols for migrating corrosion inhibitors (MCI®) in reinforced concrete

Corrosion induced deterioration of steel reinforcement (rebar) in concrete has increasingly become a greater world‐wide concern. This insidious dilemma focuses on the potentially dubious structural integrity of many concrete structures. The steady rise of rebar corrosion and the eventual deterioration can be directly related to several influential factors, some of which include; poor quality construction materials, the increased use of de‐icing salts, severe marine environments and increased atmospheric contaminants, such as carbon dioxide. Over the years various methods have been developed to protect either the rebar or the concrete. Today, the most recent emerging corrosion protection technology is that of Migrating Corrosion Inhibitors (MCIs). Recently, improved test methodologies have been developed which can better assess the effectiveness of corrosion inhibitors. Several of these recent electrochemical and non‐electrochemical test methods were utilized to measure the effects of migrating corrosion inhibitors. This paper includes an explanation of these test methods and presents an overview of the test results.     

Substituted phenols as corrosion inhibitors for copper in nitric acid

The dissolution of copper in nitric acid solution in the presence of resorcinol, o, p-aminophenols, catechol, o-cresol and salicylaldehyde as corrosion inhibitors has been studied by galvanostatic polarization and weight loss methods. For these compounds the two methods gave consistent results. Polarization data suggest that in the case of these inhibitors the cathode is preferentially polarized under the influence of an external current. The inhibitors appear to function through general adsorption following the Langmuir adsorption isotherm. The inhibiting effect of tested compounds is due to the destruction of the HNO₂ formed and its interference with the cathodic reaction.     

Aldehydes as corrosion inhibitors for aluminium-manganese alloys in potassium hydroxide

Some aliphatic and aromatic aldehydes have been studied as corrosion inhibitors for 3S aluminium (Al-Mn alloy) in KOH solutions. At constant alkali concentration the inhibitor efficiency increases with the concentration of the inhibitor, the order of efficiency in 0.1 M KOH + 1.0% inhibitor being: paraldehyde (13.3%) < formaldehyde ≦ propionaldehyde < crotonaldehyde < furfuraldehyde < vanillin < salicylaldehyde (74.8%); 0.5% benzaldehyde and 0.1% cinnamicaldehyde gave efficiencies of only 19.3% and 18.5%, respectively. The aldehydes appear to act by adsorption on the metal surface, preferably through the oxygen atom. The inhibitive efficiency of paraldehyde increases with the alkali concentration, the duration of immersion and the temperature; that of formaldehyde, cinnamic aldehyde, furfuraldehyde (and crotonaldehyde) increases with alkali concentration and time; that of salicylaldehyde and vanillin increases with time as well as with temperature, while the efficiency of propionaldehyde and benzaldehyde increases with alkali concentration. The activation energy for the corrosion process is generally higher in inhibited than in plain alkali in the case of formaldehyde, propionaldehyde, crotonaldehyde, benzaldehyde, cinnamicaldehyde and furfuraldehyde; with other inhibitors the E values are lower. Except vanillin and paraldehyde, all the inhibitors increase the corrosion potential of Al in 0.1 M KOH suggesting polarization of local anodes. The inhibitor efficiencies calculated from extrapolation of cathodic Tafel lines are in agreement with weight loss efficiencies.     

Benzimidazole derivatives as corrosion inhibitors for zinc in acid solution

The corrosion inhibition characteristics of 2-mercapto benzimidazole (MBI), 2-mercapto benzimidazolyl-ethyl acetate (MBEA), 2-hydroxy benzimidazole (HBI) and 2-hydroxy 5-nitro benzimidazole (HNBI) on zinc corrosion in 0.1 M hydrochloric acid were investigated by weight loss and potentiodynamic polarization techniques. The inhibition efficiency increased with increase in inhibitor concentration but decreased with increase in temperature. The adsorption of MBI and MBEA obeyed Langmuir’s adsorption isotherm but HBI and HNBI followed Temkin’s adsorption isotherm. Thethermodynamic functions for adsorption processes were evaluated. The existence of film on metal surface in presence of inhibitors was established by scanning electron microscopy (SEM) images.     

Analysis of corrosion resistance behavior of inhibitors in concrete using electrochemical techniques

Reinforced concrete is one of the most durable and cost effective construction materials. However, in high chloride environments, it can suffer from corrosion due to chloride induced breakdown of the normal passive layer protecting the reinforcing steel bars inside concrete. One means of protecting embedded steel reinforcement from chloride induced corrosion is the addition of corrosion inhibiting admixtures. In the present investigation, various inhibitors such as sodium nitrite, zinc oxide, mono ethanol amine, diethanolamine, and triethanol amine have been used in concrete in different percentages. Their effectiveness was then studied using various electrochemical techniques such as rapid chloride ion penetration test, open circuit potential measurement, electrochemical impedance measurement, potentiodynamic polarization measurement, and gravimetric weight loss measurement. The results thus obtained indicate that the addition of inhibitors enhances the corrosion resistance properties.     

Thioamidines as novel class of corrosion inhibitors

Abstract

Four nitrogen substituted thiobisformamidines – phenyl thiobisformamidines (PTBF), tolyl thiobisformamidines (TTBF), anisidyl thiobisformamidines (ATBF), and 4-chlorophenyl thiobisformamidines (CPTBF) – were synthesised and their corrosion inhibiting behaviour for mild steel in 1M, 3M, and 5M HCl was studied. The optimum concentration of these compounds for maximum inhibition efficiency was determined by weight loss methods. All the investigated thiobisformamidines gave more than 95% inhibition in the presence of 1M HCl, and CPTBF showed the best inhibition efficiency (98% in 5M HCl). Potentiodynamic polarisation studies revealed that all the tested compounds are of mixed inhibitor type. The adsorption of these compounds from the acid solution obeyed Temkin's adsorption isotherm. All the inhibitors were able to reduce hydrogen permeation through the steel surface and their performance was enhanced by the addition of iodide ions. Electron impedance spectroscopic studies were also carried out in order to understand the mechanism of inhibition. Auger electron spectroscopic analysis confirmed that the adsorption of these compounds on the surface of the mild steel occurs through nitrogen and sulphur atoms.     

Carbonyl compounds as corrosion inhibitors for mild steel in HCl solutions

The paper gives an account of the performance of a number of carbonyl compounds as corrosion inhibitors of mild steel in 1–6 N solutions of hydrochloric acid. Furfuraldehyde seems to be the best inhibitor of all the carbonyl compounds investigated. Activation energies in the presence and absence of inhibitors have been evaluated. In cathodic protection studies furfuraldehyde reduces the protective current density considerably. The difference effect is positive in the absence and presence of inhibitors. Galvanostatic polarization data indicate that all these compounds are predominantly cathodic inhibitors. These substances are more effective in preventing the corrosion of aluminium alloys in hydrochloric acid solutions than the corrosion of mild steel.     

Phenazone and aminophenazone as corrosion inhibitors for aluminum in HCl solution

The corrosion behavior of aluminum in 1 M HCl solution in the absence and presence of phenazone and aminophenazone was investigated using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results of these techniques show that, the inhibition efficiency of these compounds depends on their concentration and chemical structure. The inhibitive action of these compounds was discussed in terms of blocking the electrode surface by adsorption of the molecules through the active centers contained in their structure. The adsorption process was found to obey Temkin isotherm model. The effect of temperature on the rate of corrosion in the absence and presence of these compounds was also, studied. Some activated thermodynamic parameters were computed and discussed. Potentiodynamic polarization data indicated that these compounds act as cathodic type inhibitors. From impedance data it is found that the corrosion of aluminum is controlled by charge transfer process at all concentrations of inhibitors. Quantum chemical parameters were constructed in order to characterize the inhibition performance of the tested molecules.