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The effect of chlorides on corrosion of reinforcing steel is well documented in the literature. However, few studies have focused attention on the effect of sulphates on the corrosion of low carbon steel in alkaline media. This paper aims to address this issue.

This paper describes the results of the investigation into the corrosion behaviour of low carbon steel (typically used as reinforcing steel), exposed to alkaline media at a pH of 9 and 12 with varying concentrations of sulphate and chloride ions, as well as, in sulphate only solutions. An attempt was made to inhibit corrosion of steel exposed to the corrosive media using laser surface treatment of the steel specimens. Mass loss tests and electrochemical tests were conducted to evaluate the effect of sulphate only and the combined effect of sulphate and chloride ions in an alkaline media on steel.

It was found that sulphate ions could cause corrosion of steel in alkaline media. The severity of the attack increased with increasing sulphate ion concentrations, as well as with combinations of sulphate and chloride ions. The pH 12 conditions seem to show much more critical attack with evidence of pitting corrosion as compared to uniform corrosion for test conditions at a pH of 9. The attempt to inhibit the observed corrosion of steel exposed to the corrosive high alkaline media containing sulphate ions on their own and in combination of chloride ions by laser surface treatment proved to be successful.

The research undertaken here adds to the body of knowledge relating to the effect of sulphate ions on reinforcing steel corrosion in highly alkaline media. Most literature points out that sulphate ions on their own do not have a corrosive effect, but rather, a passivating effect!

‘Cebelcor’ (Centre Beige d'Etude de la Corrosion) is a non‐profit‐making association founded for the purpose of fighting corrosion by scientific, technical and educational means. It pursues this objective in collaboration with similar bodies in Belgium and abroad. A description of the organisation and workings of this corrosion research centre is given in this article, the sixth in our series describing corrosion research laboratories.

The purpose of this study is to develop a method of thermodynamic and kinetic evaluation of corrosion properties of alloys.

Method of estimation of corrosion-electrochemical behaviour of multicomponent alloys is proposed. The method takes into account both thermodynamic and kinetic data and is based on mutual construction of equilibrium and polarization potential – pH diagrams. The usage of the proposed method is illustrated in the example of the structural steel 20KT.

Passivation of steel 20KT is determined by formation of oxide film based on magnetite (Fe₃O₄); silicon, manganese and copper oxides as well as manganese sulphides can be locally included into the inner side of the passivation layer. An experimental potential – pH diagram of steel 20KT is constructed. Interpreting the results of polarization measurements revealed good agreement between equilibrium and polarization potential – pH diagrams.

It is shown in the example of structural steel 20KT that for interpretation of experimental potential – pH diagrams, one should compare them with corresponding equilibrium diagrams for multicomponent alloys rather than with Pourbaix diagrams for pure metals. The corrosion properties of steel 20KT are estimated using equilibrium and polarization potential – pH diagrams.

The purpose of this work is to study the corrosion rate of X52 pipeline steel exposed to three types of soils collected in Campeche State in México. The electrochemical evaluation for X52 steel exposed to soils ranging from saturated soil until dry conditions was carried out for a period of 21 days. Owing to its versatility to study the steel corrosion process exposed to different types of soils, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and cyclic voltammetry tests were performed. Additionally, optical and electronic microscopy observations of the steel surface were carried out.

Electrochemical cell arrangement was described elsewhere (Quej-Ake et al., 2014). Owing to soil being an electrolytic system with high resistivity and impedance, all electrodes were placed as close as possible, and iR-drop compensation was taken into account using two rods of graphite as an auxiliary electrode. In addition, the conductivity of the soil (R_s) obtained from EIS was used to correct the potential of the working electrode according to iR-drop, and an analysis of ohmic drop from the polarization curves was carried out.

Saturated conditions of the three soils were initially considered as the most corrosive conditions for X52 steel surface. Finally, 21 days of immersion time was taken into account as the more drastic condition. So, according to results, X52 steel exposed to beach sand was more susceptible to the corrosion process (0.092 mm/year). iR corrected was negligible at low over-potentials region in saturated soils, which is inside the linear region of Tafel or the activation region. In addition, high cathodic peak potential value obtained from cyclic voltammetry for X52 steel exposed to saturated soil may be attributed to hydrogen evolution reaction and neutral pH.

The paper has implications for research. It bridges the gap between theory and practice.

Cyclic voltammetry is a really important tool for the electrochemical analysis of the pipeline steel surface exposed to saturated soils, but is not adequate for analysis of steel exposed to dried soils. In addition, the physicochemical results show that fissures, voids and extra-oxygen presence could also affect the electrochemical responses obtained for X52 steel exposed to soils.

The following two articles report the outcome, in practical anti‐corrosion terms, of two subjects discussed at the recent international corrosion conference organised in Brussels by ‘Cebelcor’ (June 8–12, 1965). This conference was attended by representatives from 28 nations and the 80 papers read were for the most part in French or English. Of the five days of the proceedings, two, in which half the papers were read, were concerned with practical and technological aspects of the subject; the remaining three days being devoted to a scientific colloquium in which the behaviour of metals, alloys and systems of protection were discussed and techniques of investigation described. The proceedings took place under the supervision of Professor M. Pourbaix, the renowned Belgian authority on the corrosion behaviour of metals

The purpose of this paper was to characterize the surface of steel reinforcement of concrete under cathodic protection (CP), submerged in seawater, to understand the surface changes due to the application of CP and their consequences on cathodic current requirements.

Reinforced concrete specimens with applied CP were immersed in natural seawater. The experimental methodology included monitoring of corrosion potential (E_corr); measurement of galvanic current (Igalv), protection potential (E_protection) and the depolarization potential of steel during the time of exposure; and electrochemical impedance spectroscopy (EIS). The chemical composition of the steel surface was assessed using X-ray diffraction (XRD).

The application of CP leads to the formation of a deposit on the steel surface that according to XRD results, Pourbaix diagram and physical characteristics, is a protective oxide: magnetite (Fe₃O₄). This oxide causes a decrease in the corrosion rate and requires application of the protection current. It was found that the surface remained protected even after eight days when the CP system was interrupted.

It is necessary to carry out analysis of the chemical composition of deposits formed on the steel surface, perhaps using X-ray photoelectron spectroscopy, Mössbauer, to verify the presence of the magnetite.

Determination of the main cause of the decrease in current required for protection and deposit formation conditions will enable the design of a CP system to be optimized and economized. At present, the CP design considers only a constant current value for the duration of the protection time.

CP is a technique that has proven effective for the protection of metal structures. However, little attention has been devoted to the surface changes that occur under applied CP and their impact on the electrochemical behavior of the system. This paper describes the phenomena produced at the metal surface and determines kinetic parameters and their consequences on the CP behavior.

Until recently, chlorine used to be an important chemical in bleaching process in paper industry, but as a result of environmental concerns, it is being replaced by chlorine dioxide. However, chlorine dioxide is more corrosive in certain conditions. Plant personnel, therefore need to better understand the reactions taking place in the changed media and search for more resistant materials. It is with this in mind that the present work was undertaken. The paper reports the electrochemical polarisation measurements performed on stainless steels 316L, 317L, 2205 and 254SMO in chlorine dioxide solutions to observe localised corrosion. The results have been analysed with reference to Pourbaix diagrams, taking into account the various chemical species present in the bleach solutions. Conclusions drawn from electrochemical tests have been compared with those from long‐term laboratory and plant tests. Materials options are proposed on the optimal choice of materials for bleach plants, in a context of probable corrosion performance, capital cost and mechanical strength.

The purpose of this paper is to study the use of titanium as a protecting element for aluminum in alkaline conditions.

Aluminum coatings containing up to 20 weight per cent Ti6Al4V were produced using laser cladding and were investigated using light optical microscope, scanning electron microscope – energy-dispersive X-ray spectroscopy and X-Ray Diffraction, together with alkaline exposure tests and potentiodynamic measurements at pH 13.5.

Cladding resulted in a heterogeneous solidification microstructure containing an aluminum matrix with supersaturated titanium (<1 weight per cent), Al₃Ti intermetallics and large partially undissolved Ti6Al4V particles. Heat treatment lowered the titanium concentration in the aluminum matrix, changed the shape of the Al₃Ti precipitates and increased the degree of dissolution of the Ti6Al4V particles. Corrosion testing showed significant localized dissolution of the aluminum matrix.

Increased titanium concentration and heat treatment gave improved alkaline corrosion properties. At pH 13.5, the Al₃Ti phases were protected, while the aluminum matrix corroded.

For alkaline corrosion-protection of aluminum in the automobile industry, titanium might be useful at pH values below 13.5 or by using other coating techniques.

This is the first study testing the use of titanium as a protective element of aluminum in stringent alkaline conditions.

A brief review of a technical report compiled by Cebelcor, the Belgian Centre for Corrosion Study.

The behaviour of iron electrodes immersed in pH 8.9‐11.0 Na₂HPO₄ solutions was studied by potentiodynamic measurements (cyclic voltammetry) and scanning electron microscopy (SEM). The influence of proton and phosphate content, scan rate, anodic switching potential and other devised potential/time perturbation regimes were evaluated in order to obtain an understanding of the reactions involved during the passivation process. The oxidation‐reduction peaks were analysed using a thermodynamic approach. It was possible to reveal the most important reactions coming about on the electrode surface, which comprise, initially, the formation of Fe₃(PO₄)₂ and Fe(OH)₂ at ca. −0.8 V/SCE. Subsequently, these ferrous species are further oxidized to γ‐FeOOH at ca. −0.36 V/SCE, the latter being transformed into Fe₂O₃ in the passive region. Depending on the pH value (11.0) and scan rate (slow), Fe₃O₄ is clearly present as an intermediate oxide structure between the ferrous and ferric species mentioned earlier. In addition, scan rate was discovered to play a remarkable influence on the surface morphology observed during the SEM examinations.