Organic substances as inhibitors for chloride‐induced corrosion in reinforced concrete

Corrosion inhibitors are used to prevent chloride‐induced corrosion in reinforced concrete structures. Since performance of commercial organic inhibitors is only partially satisfactory, a 7‐year long research has been carried out in order to set‐up a new organic inhibitive mixture, able to prevent chlorides‐induced corrosion. A first screening, by means of potentiodynamic polarisation test in alkaline synthetic pore solution, was performed on 80 organic compounds, mainly primary and tertiary amines, aminoalcohols, carboxylates compounds and aminoacids, in order to select the best inhibiting substances. The nine best inhibitive organic substances were selected for long‐term tests: 2 amines (dimethylethanolamine and triethylentetramine), 4 aminoacids (aspartate, asparagine, glutamate and glutamine) and 3 carboxylates compounds (tartrate, benzoate and EDTA). Potentiostatic polarisation and free corrosion tests in synthetic pore solution were performed, as well as tests in concrete exposed to accelerated chlorides penetration. Five years of tests allow estimating the efficiency of the substances in preventing chlorides‐induced corrosion, in term of influence on chlorides penetration and on critical chlorides threshold.     

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.     

Experimental and theoretical evaluation of semicarbazones and thiosemicarbazones as organic corrosion inhibitors

The inhibition ability of four thiosemicarbazones (1A–D) and two semicarbazones (2A–B) towards carbon steel corrosion in 1.0 M HCl was evaluated by molecular modeling, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) at different inhibitor concentrations. Polarization curves showed that all of the evaluated compounds acted as mixed inhibitors. EIS plots indicated that the presence of the inhibitors increases the charge transfer resistance of the corrosion process, increasing the inhibition efficiency. The adsorption of the evaluated inhibitors obeys the Langmuir adsorption isotherm. The theoretical results were corroborated by experimental data, with both the experimental and theoretical data showing that the thiosemicarbazones are better corrosion inhibitors than the semicarbazones.     

Experimental and theoretical study of organic corrosion inhibitors on iron in acidic medium

The corrosion inhibition on metallic iron surfaces by organic molecules has been investigated both experimentally and theoretically. The inhibition efficiency of thiophenol, phenol and aniline have been compared through gravimetric and electrochemical experiments. From EH–MO and EH-tight-binding calculations, it has been possible to compare the strength of the bonding interaction between the inhibitors and the metal, with and without the presence of adsorbed protons on the metal surface, and to provide a rationalization of their different efficiencies.     

Monitoring of chloride-induced corrosion in steel rebars

Chloride-induced corrosion is very serious for steel rebar, because chloride-induced corrosion causes local disruption in the passive layer of the steel, forming surface pits. This paper proposes a novel corrosion monitoring method for steel rebars on the basis of the stress concentration in the plane stress condition caused by chloride-induced corrosion. The fundamentals of corrosion monitoring and the design concept of the proposed sensor are illustrated. The influence factors for corrosion monitoring are simulated to improve the sensitivity. Potentiostatic accelerated corrosion tests are conducted to evaluate the efficacy. The studies indicate that this indirect method for monitoring changes of physical properties caused by corrosion is effective. Influence factors in chloride-induced corrosion can be neglected, as compared with electrochemical techniques. The proposed corrosion monitoring method can provide useful information to evaluate the risk of corrosion initiation and propagation for steel rebars.     

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.     

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.     

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.     

拜耳法氧化铝生产流程溶液中有机物积累研究

拜耳法生产氧化铝过程中,有机物在铝土矿预热、溶出、赤泥沉降等工序进入铝酸钠溶液中,随着铝酸钠溶液的循环,有机物经过积累达到一定浓度后会严重影响拜耳法生产.本文研究了在铝土矿预热、溶出、赤泥沉降等过程中有机物的行为,进入铝酸钠溶液中有机物的量以及变化规律.试验研究发现:在预热和溶出过程中,铝土矿中20％～30％的有机碳进入溶液,占矿石质量的0.04％ ～0.07％,铝酸钠溶液中的有机物主要来源于矿石,少量来源于赤泥沉降过程使用的添加剂,其他过程带入溶液中的有机物极少.