Protection of reinforcements using mixed corrosion inhibitors. Dependence of inhibition mechanism on interaction between rebar and corrosion inhibitor

Abstract

The level of efficiency and protection against corrosion of an inhibitor depends on its interaction with the reinforcement. Taking into account this assumption, in present paper, the corrosion inhibition efficiency of Ferrogard 903 has been studied following two procedures: immersion of the rebar in the commercialised solution containing the corrosion inhibitor blend, before being introduced in the aggressive media; and addition of the corrosion inhibitor directly to the media with or without a previous presence of oxides on the reinforcement’s surface. The study has been developed in systems simplifying the aqueous phase of the concrete pores: alkaline solutions polluted with chlorides and neutral solutions. The inhibition mechanism seems to be related with the mixed composition of the corrosion inhibitor whose behaviour depends on the exposure environment, on the inhibitor’s method of application and on the surface state of the rebar.     

Study of corrosion behaviour of A106 carbon steel absorber for CO2 removal in amine promoted hot potassium carbonate solution (Benfield solution)

The CO₂ absorber is one of the largest pressure vessels in ammonia plants, which are suffering from severe corrosion problems worldwide. The aim of the present study is to examine the corrosion behaviour of A106 carbon steel absorber for CO₂ removal in amine promoted hot potassium carbonate solution (Benfield solution). This study simulates CO₂ removal unit in ammonia production process at Abu Qir Fertilizers and Chemical Industries Company (Alexandria, Egypt) and many other plants all over the world. A typical Benfield solution contains hot potassium carbonate K₂CO₃, potassium bicarbonate KHCO₃, diethanol amine (DEA) as a promoter and potassium metavanadate KVO₃ as corrosion inhibitor. The rate of galvanic corrosion of carbon steel absorber/stainless steel pall packings couple in Benfield solution was measured without adding the corrosion inhibitor KVO₃ in order to measure the influence of corrosive solution. The corrosion rate was measured by weight loss technique in relation to different operating parameters such as solution velocity, solution temperature, %K₂CO₃, CO₂ loading, %DEA and the effect of the presence of solution contaminants. In general, increasing solution velocity, solution temperature, %K₂CO₃, CO₂ loading and the presence of solution contaminations increase the corrosion rate. However, the increase in %DEA in solution decreases the corrosion rate. The strong dependence of corrosion rate on both solution and gas velocities indicates the diffusion controlled nature of the corrosion process. In addition, estimation of activation energy revealed a value of 4·8 kcal mol^?1. Surface morphology study depicted the presence of a porous solid film of corrosion products on carbon steel surface. It has been found that the liquid phase diffusion of bicarbonate to the steel solution interface is the rate determining step.     

Role of complexes in inhibition of mild steel by zinc–1-hydroxyethylidene-1, 1-diphosphonic acid mixtures

Abstract

The action of 1-hydrox yethylidene-1, 1-diphosphonic acid (HEDP) in combination with zinc ions as a corrosion inhibitor for mild steel in oxygen containing aqueous solutions has been investigated in relation to the presence of different zinc levels, the presence of aggressive anions, and different pH values. The highest inhibition effect was obtained at a 2·7:1 zinc/HEDP molar ratio, corresponding to 60 ppm zinc, and was associated with a significant anodic effect. In the absence of chloride and with no free forms of the inhibitor components, the zinc-HEDP mixture exhibited good protection over a wide range of pH (6·5-9·5). However, in a weakly acidic medium, protection could not be achieved. Calculations based on the dissociation constants of the HEDP and the stability constants of the possible zinc-HEDP complexes showed that this inhibition can be attributed to the presence of the 2:1 zinc-HEDP complex (Zn₂H_-1L^-) at a sufficient level. It is found that this anionic complex can behave as an anodic, passivating, inhibitor at a concentration as low as 0·00015M (20 ppm zinc-32 ppm HEDP mix ture). This passivity is prevented by the presence of sufficient chloride. The critical chloride concentration in these studies is approximately ten times higher than the complex concentration, in molar terms. It is also found that free phosphonate is aggressive and can prevent passivity due to the preferential formation of soluble iron-HEDP complex. The tolerance of the 2:1 complex to free phosphonate is substantially less than to chloride, approx imately equimolar.     

Reports of Meetings

Abstract

The corrosion resistance of a number of stainless steels and nickel alloys in solutions of pure phosphoric acid boiling under reflux and in similar solutions under conditions of heat transfer has been investigated. The effect of phosphoric acid concentrationand alloy composition on the corrosion rates obtained has been evaluated. The effect of additions of impurities such as fluoride, chloride, silicate and ferric ions on the corrosion behaviour of a number of the alloys in concentrated phosphoric acid under conditions of heat transfer has also been determined; such impurities are often present in wet-process plant phosphoric acid at the evaporator stage. The work has demonstrated that the alloys of highest nickel content generally exhibit the best corrosion resistance in such environments. It has also been shown that whilst chloride ion additions considerably increase the aggressive nature of the environment, fluoride additions in general have very little effect.     

Molecular modeling of corrosion processes: development and engineering applications

Abstract

The effect of two polyacrylate based polyelectrolytes, one cationic, the other anionic, on the corrosion of mild steel in aqueous solutions has been examined. It is shown that under conditions where they accelerate corrosion the effect arises from different properties of the compounds in each case. The cationic polymer is a mild oxidising agent and, in alkaline solution, is aggressive to passive films producing localised attack. The anionic compound acts as an anodic stimulator in neutral and alkaline solutions possibly by virtue of its ability to form a complex ion with the emerging cation. Both compounds therefore accelerate corrosion in neutral and alkaline solutions. By contrast, the anionic polyelectrolyte is a mild mixed inhibitor in acid solutions. It is suggested that not all soluble polymers will adversely affect the corrosion of mild steel and that by redesign of the molecule it might be possible for polyectrolytes generally to act as both water treatment chemicals and corrosion inhibitors.     

Corrosion behaviour of Fe80-xCoxB10Si10 metallic glasses in sulphate and chloride media

The corrosion behaviour of a series of glassy alloys, Fe_80-xCo_xB₁₀Si₁₀ (x = 0, 15, 30, 55, 70, 80), well known for their magnetic properties, has been investigated in sulphate- and chloride-containing solutions of different pH, employing weight loss measurements. In order to point out preferential dissolution reactions of metallic glasses constituent elements, analyses of the solutions were performed after corrosion tests by means of plasma source mass spectrometry and optical emission spectroscopy. A higher aggressivity of the sulphate containing solutions has been observed. The amorphous alloys exhibit an increased corrosion resistance with the increase of cobalt content. Increasing the pH of the aggressive media from 1.5 to 5.6 a decrease of two orders of magnitude in the corrosion rates has been observed. The corrosion products have been investigated by means of X-ray diffraction and scanning electron microscopy. Hydrated iron oxide Fe₂O₃ · H₂O was the major constituent of the film formed on iron-rich amorphous alloys immersed in sulphate-containing media.     

Pitting Corrosion Currents on Steel in Relation to the Concentration of the Inhibitive and Corrosive Anions under Natural Corrosion Conditions

Abstract

The changes with time in the pitting corrosion current density on a steel electrode with the concentration of both the inhibitive anions (CrO₄^2?, HPO₄^2? and WO₄^2?) and aggressive anions (Cl^?, Br^? and I^?) was followed using a simple electrolytic cell. In chromate solutions the pitting corrosion currents started to flow after an induction period, τ, which varied, in one and the same inhibitor solution, with the concentration of the aggressive anion, according to the expression: log τ =a?b log C_agg.

The pitting corrosion currents finally reached steady-state values which depended on the type and concentration of both the inhibitive and corrosive anions. At a constant inhibitor concentration,the corrosion current varied with the concentration of the aggressive anion according to: log i_corr = a_l + b₁ log C_agg, and with constant aggressive ion concentration according to: log i_corr =a₂ - b₂ log C_inh Comparison was made between the experimentally obtained values of a_l (a₂ and b₁ (b₂), and the corresponding computed values. The a₂ values show that the corrosivity of the three aggressive anions decreases in the order: Cl^? > Br^? > I^?; on the other hand the inhibitive efficiency of the inhibiting anions decreases in the order: CrO₄^2? > HPO₄^2? > WO₄^2?.     

Behaviour of stainless steel in simulated concrete pore solution

Abstract

The localised corrosion behaviour of austenitic, martensitic, and duplex stainless steels has been studied in several solutions simulating the liquid present in the pores of both alkaline and carbonated concrete in the presence of chloride ions. The work aimed to evaluate the suitability of these types of stainless steel as rebars in reinforced concrete structures exposed to very aggressive environments. Electrochemical tests have been performed in solutions with pH values in the range 7·6-13·9, chloride concentration in the range 0-10%, and temperatures of 20 and 40°C. The adverse effect of a decrese in pH on the critical chloride content is discussed, as a function of stainless steel composition and temperature, and the inhibitive effect of high carbonate/bicarbonate concentrations is also shown.     

A study of 4-carboxyphenylboronic acid as a corrosion inhibitor for steel in carbon dioxide containing environments

4-Carboxyphenylboronic acid (CPBA) has been found to be an efficient carbon dioxide (CO₂) corrosion inhibitor for steel in aqueous media. The results indicate that the addition of CPBA to CO₂ containing sodium chloride solutions at a low concentration is able to retard corrosion anodic reactions, reduce corrosion current densities, increase charge transfer and total resistances, resulting in more uniform and smoother steel surfaces. These effects are attributed to the formation of a barrier layer on steel surface, which provides metal surface protection. The inhibitor was also found to mitigate corrosion by promoting random distribution of minor anodes.     

Environmental factors affecting the corrosion behavior of reinforcing steel. IV. Variation in the pitting corrosion current in relation to the concentration of the aggressive and the inhibitive anions

The pitting corrosion current of reinforcing steel is measured under natural corrosion conditions in Ca(OH)₂ solutions in presence of Cl⁻ as aggressive ions and as inhibiting anions. The corrosion current starts to flow after an induction period which depends on solution composition (concentration, pH and presence or absence of the aggressive and the inhibiting anions). The limiting corrosion currents increase with increasing the Cl⁻ ion concentration and decrease with increasing the pH and inhibiting ions concentration. The inhibition efficiency of the studied inhibiting ions increases in the following order: , and depends on the way by which the inhibitor is added to the solution. Injection of the inhibiting anions in solution causes repassivation of the pre-formed pits through competition with Cl⁻ ions for adsorption sites on metal oxide surface. The adsorbability constant and the free energy of repassivation of the inhibiting anions are calculated.     

Estimate of contributions of polysulfide film and inhibitor to the protection of steel from hydrogen-sulfide corrosion

A method for estimating the contributions of film formed on a corrosive surface in aggressive medium favoring its formation and INKORGAS-T30 inhibitor at the inhibition of corrosion in steel has been proposed. Experimental results obtained by studying the behavior of the St3 carbon steel in mineralized chloride medium (5 wt % NaCl) containing 50–400 mg/l H₂S and the addition of an inhibitor have been presented. Using the polarization resistance method, the protective efficacy of oxide and polysulfide surface films and an inhibitor has been estimated as a function of the duration of the action of the aggressive medium, hydrogen sulfide concentration, and the corrosion inhibitor.     

Preparation and Properties of Electroless Ni-Cu-B Alloy Deposits

Two series of Ni-Cu-B deposits were prepared by electroless plating. The effects of the [Cu²⁺]/[Ni²⁺] molar ratio and concentration of KBH₄ in solution on the deposition rate, surface appearance, structure, composition, hardness, corrosion resistance and wettability have been studied. The high-B content deposits are amorphous and their structural change with annealing at different temperature results in changes of hardness of the deposits. For low-B content deposits, structures range from Ni-rich solid solution to Cu-rich solid solution with increasing (Cu²⁺]/[Ni²⁺] molar ratio; an intermediate solid solution is obtained near 0.024 (Cu²⁺]/[Ni²⁺] molar ratio. The corrosion resistance of the deposits is much better in basic media than acid, and their wettability is worse than Ni-B deposit and silver or gold wire.     

Rapid evaluation of corrosion inhibitors in acidic solution using the coulostatic method

Abstract

A monitoring method for the corrosion rate of metal based on the coulostatic principle and a new mathematical model for the evaluation of Tafel coefficients from coulostatic experimental data are presented in this paper. Different kinds of equivalent circuit models involving R(CR(RL)) and R(RC) have been applied to examine the characteristics of the response curves to coulostatic and AC perturbations. In addition, weight loss and electrochemical impedance spectroscopy (EIS) experiments on Q235 mild steel in 0.5 M H₂SO₄ solutions with and without thiourea as inhibitor have been used to verify the results from the coulostatic method. It was found that the coulostatic technique can not only determine values of R_p and C_d quickly, but also the Tafel coefficients in the acidic solution with and without inhibitor. Moreover, since coulostatic measurements can always assume R_p equal to R_t in this system, the corrosion rate calculated by the coulostatic method is free of confusion between R_p and R_t . This facilitates the rapid calculation of corrosion current density based on the Geary–Stern equation, and provides a simple procedure for the evaluation of corrosion and corrosion inhibitors.     

Contribution to the Study of Localised Corrosion of Aluminium and its Alloys: I. Critical potential,ER, with respect to pitting

Abstract

The corrosion behaviour of Al and some Al-Si and Al-Zn alloys in solutions of 0·5 M NaCl at pH 2 and pH 6 has been studied. It was found possible to determine a potential value, E_R, which correlates directly with the onset of pitting corrosion of the metal.

This potential, E_R, has the advantage of being simply and easily determined, with good reproducibility. It is independent of the cell geometry and of the condition of the surface of the specimen, but is closely correlated with the composition and structure of the metallic material and with the composition and temperature of the solution.     

Comparative Study of Factors Influencing the Action of Corrosion Inhmitors for Mild Steel in Neutral Solution: II. Potassium Chromate

Abstract

The action of potassium chromate as a corrosion inhibitor for mild steel in neutral aqueous solution has been studied in relation to the surface preparation of the steel, the presence of aggressive salts in the solution, and temperature.

Surface preparation of mild steel has little effect on the minimum concentration of chromate required for protection in distilled water. In solutions containing aggressive anions a linear relation exists between the logarithm of the chromate concentration and the logarithm of the maximum concentration of aggressive anion that will permit inhibition. In solutions of low chromate concentration, up to 10^?1M, the order of aggressiveness of anions is chloride > sulphate > nitrate; the order changes at chromate concentration above 10^?1M to chloride > nitrate > sulphate. Corrosion in non-inhibiting chromate/aggressive anion solutions is always of a localised nature but is usually stifled, thus not leading to ‘dangerous’ attack. A 5-fold increase in chromate requirement for inhibition of abraded mild steel in distilled water is found between 5° and 60°, with a further large, rather indeterminate, increase above 60°.     

Study of the inhibition of the acid corrosion of steel by auger electron spectroscopy

The Auger spectra for mild steel specimens immersed in deoxygenated uninhibited and inhibited acid solutions gave clear peaks for iron, oxygen and carbon. A comparison between the height of the oxygen and carbon peaks in an acid medium and in an acid medium containing 1-phenyl thio-semicarbazide indicated that the height of the oxygen peak becomes less in the presence of the inhibitor while the carbon peak becomes larger: this behaviour was attributed to the adsorbed molecules of the inhibitor.From the Auger sputtering depth profile for mild steel immersed in H₂SO₄ solutions in the absence and presence of the inhibitor, the thicknesses of the oxide film formed were found to be similar in both cases, i.e. the inhibitor does not appear to change the composition of the corrosion product film.     

ATR characterisation of synergistic corrosion inhibition of mild steel surfaces by cerium salicylate

The nature of deposits on mild steel surfaces formed by exposure to corrosive and inhibiting solutions has been examined by attenuated total reflectance spectroscopy. For cerium-based inhibitors, e.g. CeCl₃ the formation of cerium-containing coatings was detected whilst the cerium carboxylate Ce(sal)₃ (sal=salicylate), which combines the Ce³⁺ with the known organic inhibitor sal⁻, was shown to involve substantial deposition of both cerium and a salicylate species. These results, combined with corrosion inhibition data for the respective inhibitor compounds clearly indicate a synergistic corrosion mechanism for Ce(sal)₃ which underpins the improved performance of this corrosion inhibitor in comparison to the individual components (i.e. Na(sal) or CeCl₃).     

Inhibitive Effect of Tannic Acid on the Corrosion of Copper in Acid Solutions

Abstract

The behaviour of copper has been studied in lM solutions of HCl, HNO₃ and an HCl–HNO₃ mixture, containing various amounts of tannic acid (0 · 25, 0·5 and 1·0%). As tannic acid is a mixture of galloylglucoses, the same acids containing gallic acid (0·1, 0·2 and 0·5%) or glucose (0·1, 0·5 and 1·0%) have also been studied.

Glucose inhibits the corrosion of copper in HNO₃ solution to a very slight extent and has no effect in other solutions. Gallic and tannic acids have no effect in HCl but, at the highest concentrations tested, show an inhibitive efficiency of 80% and 70%, respectively, in HNO₃ and about 65–70% in HCl–HNO₃ mixtures.

Gallic acid may be considered to be a cathodic inhibitor that does not interfere directly with the cathodic process but modifies the corrosive environment. Tannic acid behaves both as a cathodic inhibitor and also as an anodic inhibitor due to the formation of an oxidation compound that is adsorbed on the copper surface.     

Corrosion and erosion-corrosion of electrodeposited Ni–P/B4 C composites

Abstract

The present paper reports on electrodeposition, characterisation, corrosion, and erosion–corrosion of Ni–P and Ni–P/B₄ C layers on a brass substrate. Alloys with 5%P and 8 vol.-% micrometric B₄ C were prepared from a lactate bath at pH 4 containing H₃ PO₃ . The following deposit properties were measured and related to corrosion behaviour: composition (EDS, XPS), crystalline structure (XRD), morphology (inplane and cross-sectional SEM), and mechanical properties. The immersion and anodic behaviour of pure matrix and composite samples was studied in slightly acidic, aerated chloride solutions. The presence of B₄ C particles is correlated with higher crystallinity of the matrix at a given P content. Anodic linear sweep voltammograms show more noble breakdown potentials and lower plateau current densities for the composites. The pit-arresting effect of particle addition was assessed. More noble corrosion potentials and much lower mass losses, pitting, and crevice formation were observed under erosion–corrosion conditions with normal impact of a sand containing slurry.     

Comparative Study of Factors Influencing the Action of Corrosion Inhibitors for Mild Steel in Neutral Solution: III. Sodium Nitrite

Abstract

The action of sodium nitrite as a corrosion inhibitor for mild steel in neutral aqueous solution has been studied in relation to the surface preparation of the steel, the presence of aggressive salts in the solution, and temperature.

Surface preparation of mild steel has little effect on the minimum concentration of nitrite required for protection in distilled water. In solutions containing aggressive anions a linear relation exists between the logarithm of the nitrite concentration and the logarithm of the maximum concentration of aggressive anion that will permit inhibition. In solutions of low nitrite concentration the order of aggressiveness of anions is sulphate > chloride > nitrate; the order changes with increase in nitrite concentration. Corrosion in non-inhibiting nitrite/aggressive anion solutions is frequently of a severely localised form. A 5-fold increase in nitrite requirement for inhibition of abraded mild steel in distilled water is found between 5° and 70°, with a further large, rather indeterminate, increase above 70°.

Of the three inhibitors studied in Parts I-III, chromate and nitrite are slightly moreeffective than benzoate for the protection of an abraded surface, and considerably more so for a grit-blasted surface. In general, nitrite is the most tolerant towards the presence of chloride, but it is the most dangerous if excess chloride is present. The increase in inhibitor requirement with increase in temperature from 5° to 70° is very approximately the same for all three inhibitors, that is, about 5– to 10–fold,with all inhibitors needing much higher concentrations at about 90°.