Epoxy ester resins as corrosion inhibitors for aluminium and zinc pigments

The hydrogen evolution of aluminium and zinc pigments in aqueous media at pH 10 is inhibited by several epoxy ester resins. One certain epoxy ester resin (EPE b) is an excellent corrosion inhibitor both for aluminium and zinc pigment. An increase of resin addition effects a decreasing hydrogen evolution, i.e., an increase of corrosion inhibition. Moreover, corrosion inhibition of aluminium and zinc pigments by the epoxy ester EPE b is not significantly affected by other added paint resins. Furthermore, the mobility of resins dissolved in a liquid medium seems to be a requirement for corrosion inhibition.     

Corrosion inhibition of aluminium and zinc pigments by saccharides

Both aluminium and zinc pigments react in aqueous alkaline media (e.g., water-borne paints) with the evolution of hydrogen which can be measured gas volumetrically. The hydrogen corrosion of aluminium pigment can be inhibited with addition of the reducing saccharides fructose and mannose as well as with addition of the reducing ascorbic acid whereas the non-reducing saccharose did not inhibit this corrosion reaction. With increasing addition of fructose or ascorbic acid the hydrogen volumes evolved increase; this observation leads to the assumption that reaction products of aluminium and fructose or ascorbic are the actual corrosion inhibitors.The hydrogen corrosion of zinc pigment is inhibited by ascorbic acid only. So, the most efficient of the examined natural corrosion inhibitors both for aluminium and zinc pigment is ascorbic acid. But corrosion inhibition of ascorbic acid on zinc pigment is much less effective when compared to aluminium.     

Citric acid as corrosion inhibitor for aluminium pigment

Aluminium pigments corrode in aqueous alkaline media (e.g., water-borne paints) with the evolution of hydrogen.The hydrogen corrosion of aluminium pigment can be inhibited by the chelating agent citric acid, which is a renewable raw material and absolutely non-toxic. At pH 8 more hydrogen is evolved as at pH 10 which can be explained with the isoelectric point of aluminium oxide (pH 9) and a chemical reaction of citrate with aluminium. The product of this reaction should be an aluminium(III)-citric acid-chelate which is assumed to be the actual corrosion inhibitor. This assumption can be corroborated by tests with aluminium(III)-citric acid-chelates. With increasing addition of citric acid the hydrogen volumes evolved increase, which could also be explained with a chemical reaction of citrate with aluminium.Agaric acid (α-hexadecyl-citric acid) can be considered as a surfactant with the chelating agent citric acid as hydrophilic group and inhibits the corrosion reaction of aluminium pigment better when compared to citric acid.     

The inhibition activity of ascorbic acid towards corrosion of steel in alkaline media containing chloride ions

The activity of ascorbic acid towards steel corrosion in saturated Ca(OH)₂ solution containing chloride ions was investigated in this study. Concentration and time dependence of the protective properties of the passive film were acquired by electrochemical impedance spectroscopy. The best inhibitive performance, i.e. the longest pitting initiation time was obtained in the presence of 10⁻³ M ascorbic acid, while both lower and higher concentrations showed shortening of the pitting-free period. The overall behaviour of ascorbic acid was attributed to its ability to form chelates of various solubility having various metal/ligand ratios and oxidation states of the chelated iron. The assumption of ascorbic acid assisted reductive dissolution of the passive layer at higher inhibitor concentrations was confirmed by cyclic voltammetry and ATR FTIR spectroscopy. It is proposed that the overall inhibitive effect at lower concentrations is due to the formation of insoluble surface chelates and the effective blocking of the Cl⁻ adsorption at the surface of passive film. A pronounced inhibitive effect observed after the pitting had initiated was ascribed to the formation of a resistive film at the pitted area.     

Inhibitive effect of sodium eperuate on zinc corrosion in alkaline solutions

The effect of sodium eperuate prepared from Wallaba (Eperua falcata Aubl) extract on zinc corrosion was investigated in alkaline solutions with chloride ions (i.e., simulated concrete pore solutions) by using electrochemical techniques. Sodium eperuate inhibits the corrosion of zinc in 0.1 M NaCl solutions with pH 9.6. As its concentration increases to 1 g/L, the inhibition efficiency reaches approximately 92%. In alkaline solutions with pH 12.6, sodium eperuate has no adverse effect on passivity of zinc, and retards the chloride attack. These suggest that sodium eperuate is an effective inhibitor for the protection of zinc in alkaline environments.     

Measurements of pitting corrosion currents of zinc in near neutral media

Using a simple model cell the susceptibility of the zinc electrode to pitting corrosion by SO₄²⁻, SO₃²⁻, S₂O₃²⁻ and S²⁻ anions were examined in naturally aerated carbonate solutions. It was found that, pitting started after an induction period, τ, which depended on the type and concentration of the aggressive and passivating anions. The pitting corrosion current increased with time until steady state values were attained. These values depended on both the type and the concentration of the passivating and pitting anions. For the same concentration of the passivating anions, the corrosion current varied with the concentration of the aggressive anion according to the relation: logi_pit.=a₁+b₁logC_agg. At a constant concentration of the aggressive anion, the corrosion current varied with the concentration of the passivating anions according to: logi_pit.=a₂−b₂logC_pass. The constants a₁ (a₂) and b₁ (b₂) were determined for all the systems studied. From the values of a₁ the corrosivity of the sulphur-containing anions is found to decrease in the order SO₄²⁻>SO₃²⁻>S₂O₃²⁻>S²⁻.     

Modelling of phosphate inhibition of copper corrosion in aqueous chloride and sulphate media

Mathematical models were built to predict sodium phosphate inhibition of copper corrosion in aqueous chloride and sulphate media. SEM-EDXS and AFM were used to characterize material surfaces without and with inorganic salt addition. Inhibitor efficiency was compared with that exhibited by benzotriazole.     

Contribution of the electrochemical impedance measurement technique to zinc corrosion inhibition studies in acid media

Electrochemical impedance measurements have been applied to zinc corrosion inhibition by phosphonium salts in acid media. The results described in this work point out that this method is not always suitable to provide valid information about the corrosion rate: zinc corrosion in acid medium which appears to be too fast a system.     

Long-term atmospheric corrosion of zinc

A great deal of information is available on the short- and mid-term atmospheric corrosion of zinc: corrosion rate data as a function of atmosphere type, corrosion mechanisms, effect of environmental variables, effect of surface orientation, damage functions, etc. However, very little information has been published on the atmospheric corrosion of zinc over long time periods (10-20 years), despite its great usefulness. On the other hand, many studies have analyzed the nature of corrosion products formed on zinc in a wide range of atmospheric environments, using different experimental techniques, but few have focused on the morphology of corrosion product layers. This paper reports the characteristics—mainly composition and morphology—of corrosion products formed on zinc panels after long-term exposure (13-16 years) in various types of atmospheres in Spain: rural, urban, industrial, mild marine and severe marine.     

Corrosion domain analysis of copper corrosion in aqueous media

Abstract

The technology that is being developed in Sweden for the disposal of high level nuclear waste calls for storage of the waste in copper canisters, which are encapsulated in a bentonite buffer contained in drill holes in the floors of drifts (tunnels) in a granitic rock repository. A controversial issue has arisen during the development of this technology: that copper, when in contact with pure water under anoxic conditions corrodes and hence is not immune as previously believed. This issue is resolved in the present paper by deriving corrosion domain diagrams as a means of presenting the thermodynamics of the system in the clearest form possible, when assessing the immunity and activation of copper.     

Synergistic inhibition of zinc corrosion in 0.5 M NaCl by combination of cerium(III) chloride and sodium silicate

The synergistic inhibition effects of cerium(III) chloride, CeCl₃ and sodium silicate, Na₂Si₂O₅ (water glass) on corrosion of zinc in an aerated 0.5 M NaCl solution at 30°C were examined by polarization measurements. Equimolar mixtures of these inhibitors were markedly effective, indicating that the inhibition efficiencies of the mixture at 1×10⁻⁴ of each inhibitor were 95.9 and 93.6 after immersion of a zinc electrode in the solution for 3 and 120 h, respectively. X-ray photoelectron spectra revealed that a protective layer composed of hydroxylated or hydrated cerium-rich oxide and small amounts of zinc hydroxide and silicate formed on the zinc surface. A high inhibition efficiency of 1×10⁻³ M Na₂Si₂O₅, 97.7% was obtained for corrosion of a zinc electrode which was previously treated in the NaCl solution of 1×10⁻³ M CeCl₃ at 30°C for 30 min.     

The inhibition of the corrosion of iron in alkaline solutions

Abstract

The inhibition of the corrosion of iron in alkaline solutions is due to the anodic formation of a film of a ferrous compound, which is usually ferrous hydroxide, but in the presence of anions yielding less soluble ferrous salts, e.g. carbonate, the composition may be mixed. The ferrous compounds are subsequently oxidised to anhydrous cubic oxide; consequentty the film thickens until it prevents the passage of ferrous ions into solution.     

The effect of synthetic zinc corrosion products on corrosion of electrogalvanized steel. II. Zinc reactivity and galvanic coupling zinc/steel in presence of zinc corrosion products

The reactivity of zinc under synthetic zinc patinas and the galvanic coupling in steel/patina/Zn are studied. Zn₅(OH)₆(CO₃)₂ and Na₂Zn₃(CO₃)₄⋅3H₂O inhibit zinc anodic dissolution in NaCl, while Zn₅(OH)₈Cl₂ H₂O and Zn₄(OH)₆SO₄ nH₂O do not. The galvanic current in steel/patina/NaCl/Zn is smaller as compared to steel/NaCl/Zn. The inhibiting effect decreases with time for Na₂Zn₃(CO₃)₄⋅3H₂O or Zn₄(OH)₆SO₄ nH₂O due to the transformation into Zn(OH)₂. In NaHCO₃, the polarity between zinc and steel can reverse. The effect of confinement on the cathodic current is stronger than the initial effect of patina which is explained by the instability of the patinas under rapid pH-increase.     

Corrosion inhibition of an aluminium-silicon-magnesium alloy in alkaline media

The inhibition of corrosion has been studied for an AlSiMg alloy in a 0.1N NaOH solution at 60°C. The best results are obtained cheaply with sodium “silicate” + aluminate mixture, the latter ions being necessary for a total and almost instantaneous inhibition. The 100% inhibition efficiency of a tartrate + calcium ions mixture decreases after a few hours.     

Ethoxylated fatty alcohols as corrosion inhibitors for dissolution of zinc in hydrochloric acid

The effect of some ethoxylated fatty alcohols, with different numbers of ethylene oxide units, on the corrosion of zinc in 0.5 M HCl has been studied using weight loss and polarization measurements. The inhibition efficiency was found to increase with increasing concentration, number of ethylene oxide units per molecule and with decreasing the temperature. Inhibition was explained on the basis of adsorption of ethoxylated fatty alcohols molecules on the metal surface through their ethoxy groups. The degree of surface coverage varied linearly with logarithm of inhibitor concentration fitting Temkin isotherm. The thermodynamic parameters were calculated for the tested system from the data obtained at different temperatures.     

Contact corrosion of metals in aqueous media. Part I

The corrosion behavior of aluminum, steel, and cast iron in aqueous solutions is studied both for individual metal specimens and short-circuited systems (aluminum-steel, aluminum-cast iron, steel-cast iron, and aluminum-steel-cast iron). It is shown that aluminum behaves as a cathode with respect to steel and cast iron. The high corrosion rates of ferrous metals are caused by the specificity of iron surface state in aqueous solutions of electrolytes. Original Russian Text ? V.N. Esenin, L.I. Denisovich, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 4, pp. 390–395.     

An electrode array study of electrochemical inhomogeneity of zinc in zinc/steel couple during galvanic corrosion

The local electrochemical properties of anodic metal within a zinc/steel couple immersed in seawater was studied via an electrode array composed of zinc and mild steel wire sensors. It showed that the potential and current density distribution of zinc wires were inhomogeneous, and the main anodic area moved from the zinc wires adjacent to the steel wires and even further away. Also, some zinc wires behaved as secondary cathodes. The observed electrochemical inhomogeneity was attributed to the variation of distances between the zinc and mild steel wire sensors over the electrode array as well as their surface electrochemical status.     

The initiation mechanism of corrosion of zinc by sodium chloride particle deposition

This study details the mechanism of attack by sodium chloride particles on zinc. The dissolution and subsequent reaction of a single micro-particle of salt on zinc has shown explicitly the mechanism by which attack occurs. Following the initial formation of a hemispherical droplet when the particle wets in humid air, a secondary spreading effect occurs. The rate and potential associated with this spreading process has been measured using a Kelvin probe, and the chemistry of the compounds formed as a result of the corrosion mechanism have been determined using spectrographic techniques.     

Atmospheric corrosion of zinc induced by runoff

Atmospheric corrosion and runoff of zinc were investigated during two years in humid tropical climate on hot dip galvanized steel and zinc samples. The high zinc mass loss (14.70 g m⁻²) is induced by the intensive zinc release (12.40 g m⁻²). No corrosion phase containing chloride was detected on the zinc surface, while a variety of sulfates not dissolved by rains reveals the sensitivity of zinc to SO₂ pollutant. However, two chloride-containing corrosion products were detected on the galvanized steel. Exponential equation is proposed that fits well the experimental data for zinc mass loss induced by runoff process as a function of the time of wetness. The formula gives possibility to predict the mass loss even before a steady state in the corrosion process has been reached. This equation can converge to a Benarie lineal function (C = At_w), when the coefficient b = 1 for the corrosion which is accelerated with the partial removal of the corrosion layer during the runoff phenomena.     

Synthesis and evaluation of corrosion resistance of molybdate-based conversion coatings on electroplated zinc

Three molybdate-based conversion coatings on electroplated zinc have been prepared and the composition, morphology, and structure of these coatings are measured by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. It was found that these coatings with ‘meshwork’ surface were complex coatings composed of multiple compounds. Molybdenum species were present in the conversion coating as Mo (VI) and Mo (IV) compounds. The results of neutral salt spray test showed that molybdate-based conversion coatings with the addition of H₃PO₄, SiO₂ and TiOSO₄ in the passivation baths possess higher corrosion resistance compared with chromate conversion coatings, which was due to the compactness and anti-corrosion essence of the conversion coating.