Inhibitive and adsorption behaviour of carboxymethyl cellulose on mild steel corrosion in sulphuric acid solution

Chemical methods were used to assess the inhibitive and adsorption behaviour of carboxymethyl cellulose (CMC) for mild steel in H₂SO₄ solution at 30-60 °C. Results obtained show that CMC act as inhibitor for mild steel in H₂SO₄. The inhibition efficiency was found to increase with increase in CMC concentration but decreased with rise in temperature, which is suggestive of physical adsorption mechanism. The adsorption of the CMC onto the mild steel surface was found to follow Langmuir and Dubinin-Radushkevich adsorption isotherm models. The inhibition mechanism was further corroborated by the values of activation parameters obtained from the experimental data.     

The influence of the polarization time on the passivation of iron in sulphuric acid

The aim of the investigations was to define the time necessary to completely cover an iron surface with a passivating solid layer of FeSO₄.7H₂O resp. with FeSO₄.1H₂O. This was determined by anodic passivation of Armco iron in a wide range of concentrations of sulphuric acid and also by varying the time of the polarization. A log/log relationship between the passivation time (t) and acid concentration (N) was found. This indicated that the film was formed from the nuclei of FeSO₄ which precede the crystallization of the appropriate form of hydrated FeSO₄.     

Effect of methanol on the corrosion behaviour of Al-Cu Alloys in sulphuric acid

The effect of Cu additions (1, 3 and 5?at.-%) on the corrosion behaviour of Al in 0.5?M H₂SO_4?+?2?ppm hydrofluoric acid?+?methanol at 50°C, environment found in a direct methanol fuel cell, has been evaluated using electrochemical techniques. Electrochemical techniques included potentiodynamic polarisation curves, electrochemical impedance spectroscopy and electrochemical noise measurements measurements. Methanol concentrations included 1, 5, 10 and 20?M. Results have shown that corrosion resistance increases with increasing the methanol concentration. The addition of Cu to Al increases the corrosion rate of the former by the formation of micro galvanic cells, inducing localised typo of corrosion also.     

The influence of light on corrosion phenomena: the behaviour of mild steel in citric acid solution

Experiments using photopotential, galvanic current, a.c. impedance and harmonic analysis techniques were carried out to observe the effect of visible light on mild steel in a citric acid solution. The photopotential and galvanic current techniques show that the steady state potential and current after illumination of one of the electrodes is negative with respect to the electrode in darkness. Both the impedance and harmonic analysis techniques indicate an increase in the corrosion rate of the illuminated electrode. On coating the mild steel with a vinyl lacquer, the effect of illumination is eliminated.     

The effect of cysteine on the corrosion of 304L stainless steel in sulphuric acid

The effect of cysteine on the corrosion of 304L stainless steel in 1 mol l⁻¹ H₂SO₄ was studied using open-circuit potential measurements, anodic polarization curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). All the electrochemical measurements obtained in the presence of low cysteine concentration (10⁻⁶-10⁻⁵ mol l⁻¹) presented the same behaviour as those obtained in the absence of cysteine, a passivated steel surface. However, for higher cysteine concentrations (10⁻⁴-10⁻² mol l⁻¹), a different behaviour was observed: the corrosion potential stabilized at a more negative value; an active region was observed in the anodic polarization curves and the electrochemical impedance diagrams showed an inductive loop at lower frequencies and a much lower polarization resistance. These results show that the presence of cysteine at high concentration turns the surface of 304L stainless steel electrochemically active, probably dissolving the passivation layer and promoting the stainless steel anodic dissolution. SEM experiments performed after immersion experiments at corrosion potential were in good agreement with the electrochemical results.     

Synergistic inhibition between o-phenanthroline and chloride ion for steel corrosion in sulphuric acid

The corrosion inhibition of cold rolled steel in 0.5 M sulphuric acid in the presence of o-phenanthroline and sodium chloride (NaCl) has been investigated by using weight loss and electrochemical techniques. The experimental data suggest that the inhibition efficiency increases with increasing NaCl concentration in the presence of 0.0002 M o-phenanthroline, but decreases with increasing temperature. A synergistic effect is observed when o-phenanthroline and chloride ions are used together to prevent cold rolled steel corrosion in 0.5 M sulphuric acid. The polarization curves showed that the complex of o-phenanthroline and NaCl acts as a mixed type inhibitor. The experimental results suggested that the presence of chloride ions in the solution stabilized the adsorption of o-phenanthroline molecules on the metal surface and improved the inhibition efficiency of o-phenanthroline. The adsorption of the complex accords with the Langmuir adsorption isotherm. Some thermodynamic parameters such as adsorption heat, adsorption entropy and adsorption free energy have been calculated by employing thermodynamic equations. Kinetic parameters such as apparent activation energy and pre-exponential factor have been calculated and discussed.     

The influence of various major and minor alloying elements on the corrosion of an Fe-40 %Cr Superferritic stainless steel in sulphuric acid

The corrosion resistance of an Fe-40%Cr superferritic alloy containing various major and minor alloying additions, e. g. nickel, molybdenum, aluminium, zirconium, nitrogen, niobium, titanium and ruthenium, as well as various combinations of them, was investigated in dilute sulphuric acid. Although small nickel and molybdenum additions alone cannot cause spontaneous passivation of the Fe-40%Cr alloy to which they are added, a combination of these two alloying elements result in an Fc-40%-Cr superferritic stainless steel which can passivated spontaneously in dilute sulphuric acid. Further additions of minor alloying elements like Ti, Nb, Ru and N have an influence on the time required to achieve spontaneous passivation and the final open-circuit potential eventually reached. Further additions of Al and Zr to the Fe-40%Cr-2%Ni-2%Mo alloy did not have much of an effect on the final open-circuit potential reached, and only affected the time required before this potential was reached in each case.     

Effect of Chloride Ions on the corrosion behaviour of iron-nickel alloys in sulphuric acid solutions

The effect of chloride ions on the corrosion behaviour of binary iron-nickel alloys in sulphuric acid solutions has been investigated using polarization resistance and potentiodynamic polarization measurements. A moderate inhibition effect of the chloride ions on the corrosion of these alloys has been found, which depends on the pH of the medium, as well as on the composition and the structure of the alloys investigated. It has been shown that the action of the chloride ions on the partial corrosion reactions is reflected by an inhibition of the cathodic hydrogen evolution reaction and by an activation of the anodic metal dissolution reaction, the first effect being stronger. Using atomic absorption analysis it has been established that no preferentional dissolution of the alloy components in the presence and in the absence of chloride ions occurs during the corrosion of the iron-nickel alloys.     

Effect of hydrogen sulphide on The corrosion behaviour of titanium

In this paper the effect of hydrogen sulphide on the electrochemical and corrosion behaviour of VT 1–0 commercial titanium has been studied in acidic solutions containing polarization and analytical methods. Neither in the presence of sulphate nor chloride ions hydrogen sulphide affected electrochemical corrosion parameters in less acidic solutions but in 1 M sulphuric and hydrochloric acid where the increase of the corrosion rate can be attributed first of all to the decrease of the hydrogen overvoltage. The interpretation of the results is based on considerations including the role of titanium hydrides formed during the processes.     

Effect of yttrium on the corrosion behaviour of 09CrCuSb alloy in concentrated sulphuric acid

The effect of yttrium on the corrosion behaviour of 09CrCuSb alloy (ND steel) in concentrated sulphuric acid at 383 K has been investigated. The results demonstrate that addition of 0.15 wt.% Y effectively improves the corrosion resistance of such alloy. By observing the surface morphology and cross-section of the scale, it is found that Y addition refines the corrosion product, and improves the adhesion ability between the scale and the matrix. The electrochemical test exhibits a decrease passive currents as well as a higher passive and charge transfer resistance of the Y-modified alloy.     

Inhibition of mild steel corrosion in 1N sulphuric acid through indole

The corrosion inhibition of mild steel in 1N sulphuric acid containing various concentrations of indole was studied in the temperature range of 25–70°C through the use of potentiodynamic polarization curves. The indole was found to shift the corrosion potentials to positive values and to decrease the dissolution of mild steel and hydrogen evolution reaction. The effect, however, was more pronounced on the anodic rather then the cathodic process. Indole did not generally affect the corrosion reaction mechanism (blocking effect). The reported activation energy (E_a) values indicate that the inhibiting effect increased with the indole concentration. At temperatures of 25, 40, 55 and 70°C the adsorption behaviour of the indole follows Temkin's isotherm with a standard free energy of adsorption of ?54.49, ?39.41, ?43.49 and ?55.25 kJ/mol, respectively.     

Effect of sulphide on the corrosion behaviour of AISI 316L stainless steel and its constituent elements in simulated Kraft digester conditions

The electrochemical behaviour of AISI 316L steel and its constituent metals in simulated Kraft digester white liquor at 170 °C has been studied by registering slow scan rate voltammograms and impedance spectra at the corrosion potential. Interpretation of the results in terms of two approaches - the Mixed-Conduction Model for passive films and a two-step dissolution reaction - allowed for the estimation of corrosion currents and polarisation resistances as depending on the material and electrolyte medium. Tentative conclusions on the effect of sulphur-containing species in the white liquor on the corrosion mechanism of the studied materials are drawn.     

Effect of carbon on corrosion behaviour of Fe3Al intermetallics in 0.5 N sulphuric acid

Electrochemical corrosion behaviour of iron aluminides, produced by electroslag remelting technique, having the compositions (1) Fe-15.6Al-0.05C, (2) Fe-15.6Al-0.14C, (3) Fe-15.6Al-0.5C and (4) Fe-15.6Al-1C were investigated in 0.5 N H₂SO₄ media. Corrosion rates of these alloys were found to increase with carbon content. This was attributed to the preferential attack of the carbide phases. These alloys exhibited typical active-passive-transpassive behaviour. In addition, they displayed a secondary anodic current maxima during polarization. The resistance of aluminides to breakdown of passivity was assessed by varying addition of chloride ions in the same media.     

Influence of Ru additions on the corrosion behaviour of WC-Co cemented carbide alloys in sulphuric acid

The aim of the study is to investigate the influence of ruthenium (Ru) additions on the corrosion behaviour of WC-Co cemented carbides when exposed in a reducing acid medium. The study involved the characterization of the microstructures, morphologies and phases present by using the optical microscopy, SEM, XRD and Raman spectroscopy before and after corrosion. The corrosion behaviour was investigated using the electrochemical polarization tests and chronoamperometry. Ruthenium affects the cathodic Tafel constant (β_c) in 1 M H₂SO₄, which indicates that it influences the cathodic part of the corrosion reaction. It also appears that Ru is more effective in improving corrosion resistance than a small vanadium carbide addition. Therefore, ruthenium additions of up to 3 wt.% Ru increased the corrosion resistance of the WC-Co alloys.     

The influence of ion implantation on the corrosion behaviour of iron in acid solution

The influence of ion implantation on the aqueous corrosion of pure iron in IN H₂SO₄ was studied. The iron was bombarded with 5 × 10¹⁵–10¹⁷ ions.cm^?2 of Ne, Ar, Cu, Pb and Au. The current density-potential curves of the implanted samples were measured and compared with that of untreated pure iron. Ne⁺ and Cu⁺ bombardments lead to a slightly higher corrosion rate in comparison with untreated iron. Pb⁺ depressed the corrosion rate by orders of magnitude, Au⁺ enhanced it by a factor of more than ten. The effect is attributed to a reduction or an increase of the activity of the electrode surface with respect to the cathodic hydrogen evolution reaction, i.e. the ion implantation influences strongly the exchange current density of the hydrogen evolution reaction. A marked influence of the implantation on the anodic behaviour of the corroding metal could also be observed.     

Producing micro-droplet of dilute sulphuric acid on pure iron surface and observing its corrosion behaviour by atomic force microscopy

A simple method was presented to produce a micro-droplet of sulphuric acid on a pre-selected micro-zone on a pure iron surface with the tip of an AFM cantilever. The three-dimensional shape of the droplet was imaged with the AC non-contact mode of the AFM, and the liquid/solid interface was observed in situ during corrosion using the contact mode. The substrate surface beneath the droplet was lowered by approximately 19 nm after 3.6 ks of adhesion. This method has important implications for experimental studies of micro-zone corrosion or lubrication.     

The anoxic corrosion behaviour of copper in the presence of chloride and sulphide

The Canadian used fuel container for the long-term containment of spent nuclear fuel in a deep geological repository comprises a 3-mm copper corrosion barrier applied directly to a strong carbon steel container. Although a final site for the Canadian deep geological repository has not yet been chosen, the site selection process has narrowed down to two candidate locations with unique groundwater chemistry, particularly with respect to salinity. Therefore, to ensure the long-term integrity of the used fuel container, the effect of a range of groundwater chemistries on copper corrosion must be understood. The primary variables of interest are the influence of chloride concentration and the consequences of the interaction of hydrogen sulphide, naturally present in the groundwaters in very low concentrations, with the copper cladding. An additional aspect that has been investigated is the behaviour of copper in pure water. The anoxic corrosion of copper can be inferred by the very slow release of hydrogen gas. In this paper, new data are presented, which demonstrate an extremely sensitive approach to quantify the very limited hydrogen release at 75°C. Initially, corrosion rates under conditions approximating an anticipated Canadian deep geological repository were significantly less than 0.5 nm/year and they invariably declined over the course of several months/years. The presence of chloride or hydrogen sulphide was found, under specific conditions, to stimulate short-term corrosion behaviour, which was consistent with anion-assisted surface rearrangement, not bulk corrosion.     

Effects of dithionite ion on corrosion of type 304 stainless steel in sulphuric acid solution

Corrosion behaviour of type 304 stainless steel was investigated, with particular attention to additive effects of hydrosulphite (Na₂S₂O₄) on corrosion in 0.1 mol/l H₂SO₄ solution with various amounts of Na₂S₂O₄ up to 60 mmol/l.Corrosion of SUS304 occurred below pH 3.0 at 30 °C in a 0.1 mol/l H₂SO₄ solution in which Na₂S₂O₄ was added to 0.1-20 mmol/l. The maximum corrosion rate at 30 °C was measured as 7.2 g/m² h (7.9 mm/y) in 0.1 mol/l H₂SO₄-10 mmol/l Na₂S₂O₄ at pH 1.2. Microscopic surface observation revealed that active dissolution was accompanied by intergranular corrosion at the metal surface.The SUS304 was easily passivated in 0.1 mol/l H₂SO₄ solution with more than 30 mmol/l Na₂S₂O₄. NiS was detected in the passivated film.     

2,3-Diphenylbenzoquinoxaline: A new corrosion inhibitor for mild steel in sulphuric acid

2,3-diphenylbenzoquinoxaline (2,3DPQ) has been synthesized and its inhibiting action on the corrosion of mild steel in 0.5 M H₂SO₄ has been assessed by weight loss method at 30 °C. The results of the investigation show that this compound has excellent inhibiting properties for steel corrosion in sulphuric acid. Inhibition efficiency increases with increase in the concentration of the inhibitor. The adsorption of 2,3DPQ onto the mild steel surface followed the Langmuir adsorption model with the free energy of adsorption of −11.4 kJ mol⁻¹. Quantum chemical calculations were employed to give further insight into the mechanism of inhibition action of 2,3DPQ.