Corrosion Engineering,Science and Technology: The International Journal of Corrosion Processes and Corrosion Control

A wire beam electrode (WBE) method for investigating the crevice corrosion has been demonstrated by mapping non-uniform corrosion processes occurring on copper and copper alloys including the pure copper UNS No. C11000 (Cu), brass UNS No. C28000 (Cu–Zn alloy) and tin bronze UNS No. C51900 (Cu–Sn alloy) in mass 0.6% NaCl solution with the crevice spacings of d=103 μm and 206 μm. It was found that the sequence of three copper alloys in susceptibility for the crevice corrosion was that Cu–Zn alloy > Cu–Sn alloy > pure Cu. The average galvanic current of the Cu–Sn alloy in the covered region was changed from cathode to anode when the crevice spacing was increased to 206 μm. To sum up, it is feasible to study the behaviours of crevice corrosion within the different crevice spacings with the WBE method.

Development of countermeasure for corrosion and hydrogen embrittlement of Ni-Ti superelastic alloy in an acidulated phosphate fluoride (APF) solution has been attempted by adding NaHCO₃ and H₂O₂ to the solution. Upon addition of only 0.001 M NaHCO₃ to a 0.2% APF solution, almost no changes in corrosion current density and corrosion potential are observed. With an increasing NaHCO₃ concentration up to 0.01 M, the corrosion current density substantially decreases and the corrosion potential slightly shifts in the noble direction. The corrosion loss significantly decreases and hydrogen absorption is slightly inhibited. Upon the combined addition of 0.01 M NaHCO₃ and 0.001 M H₂O₂, the corrosion current density is lowest and the corrosion potential shifts in the noble direction. The corrosion and hydrogen absorption are substantially inhibited. The present study clearly indicates that the combined addition is exceptionally effective as a simultaneous countermeasure for corrosion and hydrogen embrittlement of the alloy.

To develop a biomedical magnesium alloy with desirable mechanical properties and corrosion resistance, Mg–6Zn–8.16Y–2.02Mn and Mg–6Zn–8.16Y–2.02Mn–0.3Mo alloy were prepared. Then the alloys were solution-treated at 500°C for 40 h and cooled in the furnace. The results showed that partly 18R-long-period stacking ordered (LPSO) phase transformed to 14H-LPSO phase during solid-solution treatment. The hollowed-out W phase vanished and spherical W phase was formed. And the volume fraction of 18R-LPSO and the average size of the spherical W phase particles were reduced. Corrosion behaviour of the alloy in Hank's solution under each condition was studied by immersion test and electrochemical test. The solution-treated Mg–6Zn–8.16Y–2.02Mn–0.3Mo alloy exhibited the best mechanical property (ultimate tensile strength, UTS 270 MPa and elongation, EL 23%) and corrosion resistance (P_W 1.03 mm/year and I _corr 0.20 mm/year) due to fine and homogeneous microstructure.

Bacterial biofilm that formed when the Ti6Al4 V alloy was exposed to Escherichia coli, was monitored over 48 h by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PP) to estimate the rate of corrosion and the influence of the bacteria on this process. High-resolution scanning electron microscopy was used to examine bacterial growth, colonisation and the process of biofilm formation. Our results highlighted several critical points regarding the impact of E. coli and its use as a model for monitoring biofilm formation and the biocorrosion of this alloy. Impedance spectra revealed the formation of a compact passive film after 48-hour exposure to an aging culture of E. coli in chloride media. The formation of the biofilm influenced the resistance to corrosion. Biofilm impedance parameters that emerged over time corresponded directly to the properties of a typical exponential bacterial growth curve determined by ultraviolet-visible light spectroscopy.

Corrosion-induced degradation in marine steel structures is highly dependent on the surrounding environmental conditions and sea water compositions that varies significantly around global sea water bodies. This research investigates the corrosion behaviour of ship-grade steels exposed under different sea water compositions and environmental conditions typical of the Arabian Sea. More, environmental conditions spanning those anticipated for the shipping structures operating in the highly saline and warmest regions in the Arabian Sea have been simulated in laboratory-based experiments by using heated and aerated artificial sea water. Following their exposures, the corrosion performance of coupons has been investigated using the standard weight loss and a new dimensional metrology-based approach. Besides, the corrosion products formed on the steel surfaces have been characterised using various analytical techniques. Considerably higher corrosion losses and maximum corrosion depths were observed in the nutrient-rich polluted sea waters than those recorded in the natural sea waters, as well as in the simulated artificial sea water conditions.

Electrochemical techniques such as Polarisation and Galvanic tests as well as immersion test were used to analyse both the effects of different Bi contents and the length scale of dendritic spacings on Zn–8 wt-%Al–(1.5, 2.3 and 3 wt-%Bi) alloys on their corrosion behaviour. The results revealed that no significant differences in the corrosion kinetics were observed with the scale of the dendritic and lamellar spacings. Conversely, the corrosion behaviour was shown to be dependent on the alloy Bi content. Despite the cathodic character of Bi, its addition to the Zn–8%Al alloy was shown to reduce the corrosion rate as compared with that of the binary alloy.

Carbonation-induced corrosion limits the durability of reinforced concrete structures exposed in urban environments. In these exposure conditions, the propagation phase of corrosion can be an important part of the service life and, hence the knowledge of the corrosion rate is essential for the design. However, data regarding the corrosion rate in carbonated concrete are scarce and mainly refer to Portland cement concrete. This paper reports the corrosion rate and corrosion potential of steel bars embedded in concretes with different binders and water/binder ratios, exposed both outdoor in unsheltered conditions and in laboratory conditions characterised by different temperatures and relative humidities. Concrete resistivity at different depths is also reported and correlations among these parameters are discussed. Corrosion potential, corrosion rate and concrete resistivity were strongly influenced by the relative humidity, while temperature played an important role only at high relative humidity. Steel in Portland cement concrete showed the lowest corrosion rate.

The present study compares corrosion behaviour of three austenitic stainless steels 316L, 317L and 904L (base materials and welds) in wet-process phosphoric acid (WPA) and reagent grade phosphoric acid with impurities, e.g., Cl-, F- and SO₄ ^2-. The corrosion study was done by performing electrochemical polarisations at 50°C followed by Tafel extrapolation. Welds always had higher corrosion rates than their respective base materials. The corrosion rates of stainless steels in plant WPA were much less compared to that in reagent grade phosphoric acid with almost similar levels of Cl⁻, F⁻ and . This is due to the presence of a variety of dissolved metallic ions in WPA that reduces its corrosiveness. Among the three metallic cations (Fe³⁺, Mg²⁺ and Al³⁺) examined in this study, the inhibiting action increased in the order Fe³⁺ < Mg²⁺ < Al³⁺. SS 904L was the most corrosion-resistant alloy in WPA followed by SS 317L and 316L.