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The formation of calcareous deposits on thermally sprayed aluminum (TSA)-coated surfaces immersed in natural seawater and connected to a cathodic protection system is a recurring issue. There is at present limited knowledge on the calcareous deposits’ formation kinetics on TSA in natural seawater following prolonged exposure at different temperatures. In this study, bare 25Cr super-duplex stainless steel (SDSS) and TSA-coated SDSS tube coupons (with and without a silicone-based sealer) were exposed to natural seawater under potentiostatic cathodic protection (CP) and open-circuit potential (OCP) conditions at different temperatures (i.e., 20°C, 35°C, 60°C, and 80°C) for 1.5 y. The coupons were extracted at various intervals to construct growth kinetics curves under various test conditions. The deposits were subsequently examined using scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. For all of the specimens, the deposits on the exposed surfaces increased with exposure time. Fewer deposits were seen under CP conditions than OCP at low temperatures (20°C and 35°C), whereas more deposits were observed with CP than those at OCP at high temperatures (60°C and 80°C). Last, a recommended protection potential of −0.90 VSSC (VAg/AgCl) and cathodic current density values of −8 mA/m2 and −15 mA/m2 were obtained based on the findings of this study.

In this work, a galvanostatic method based on the one-dimensional pit electrode technique was developed to identify the critical pit stability product of 316 L stainless steel (SS). The critical pit stability product of 316 L SS in 0.6 M NaCl at 25 °C was between 0.8 and 0.9 A m−1, which was confirmed by mass transport modelling and potentiodynamic polarization results in pit-like solutions. The critical concentration of metal cations at the pit base was between 70 and 82% of the saturation concentration. The implications of these findings are discussed in detail.

Tribo-electrochemical behavior of a high chromium white cast iron (high-Cr WCI) used in, e.g., slurry pumps in mining and mineral processing applications, was investigated using a combination of electrochemical techniques, including zero resistance amperometry as well as potentiostatic and potentiodynamic polarisation. The effects of third body particles angularity on the localised tribocorrosion response of the cast alloy was studied during and post abrasion-corrosion by round ceramic beads and semi-angular silica sand particles. Advanced characterization methods such as electron backscatter diffraction and focused-ion beam cross-sectioning of affected areas were also employed to understand the wear and corrosion interactive actions. It was found that in chloride-free solutions, the behavior of high-Cr WCI resembled that of the austenitic 316 SS studied before. In contrast, in chloride-containing electrolytes, the semi-angular silica sand particles increased interfacial (carbide/matrix) localised corrosion susceptibility during and post-abrasion as indicated by the stark increase in anodic current and the morphology of the attack. Semi-angular silica sand abrasives had a greater adverse impact on post-abrasion interfacial corrosion vulnerability, compared to round ceramic beads. The complex behavior observed indicates that any material developed for tribocorrosive conditions must account for the particles angularity and their subsequent effects on localised corrosion.

A comprehensive mathematical model, including electrode kinetics, hydrolysis and complexation reactions, salt film precipitation and pit interface movement, was developed to investigate pit growth of 316L stainless steel under a salt film. The new mathematical framework incorporates activity coefficients into the hydrolysis and complexation reaction calculations for the first time, using experimental results to parametrize the electrode kinetics in a saturated pit solution. The model was validated by 1D pit experiments and results documented in the literature. It can successfully estimate the transition potentials, salt film thickness, pit stability product, saturated pit concentration, and the pH at the pit base during pit propagation under the presence of a salt film. Moreover, the model can predict the Cr enrichment and Fe depletion in the saturated solution at the pit base, attributed to the higher diffusion coefficient of Fe and the lower Cr diffusivity.

Today, there is a large number of accepted tests to study crevice corrosion phenomena. The different methodologies can be used for comparing and ranking alloys, quality control, assessing the effects of changes in manufacturing routes and alloy composition on crevice corrosion resistance, as well as in evaluations to determine critical temperatures and potentials and induction times.The goal of the chapter is to describe the various standard test methods available to the corrosion specialist as well as adaptations to study specific crevice corrosion parameters. The focus is on test methods developed by the ASTM Committee G-1 on corrosion of metals, but other procedures are also included. While the test principles have been applied to many alloy systems, the scope of the chapter is on stainless steels and nickel-based alloys.

In this work, the methods used for the pre-dissolving step in one-dimensional (1D) pit experiments have been investigated in combination with a “sandwich” like 1D pit electrode, which enabled the in situ and ex situ visualization of pit depth. The proposed methodology avoided lacy cover formation during the pre-dissolving step for a Type 316L stainless steel 1D electrode placed upright. In contrast, it was challenging to avoid lacy cover formation with the proposed method when the 1D pit electrode was placed facing down, plausibly caused by accelerated convection effects inside the pits.

This study investigates the effects of particle angularity on the tribo-electrochemical behaviour of 316L stainless steel under low-stress three-body abrasion–corrosion conditions. Different angularity particles were delivered to the interface between the samples and a rotating rubber counterface, while changes in current with time were potentiostatically monitored. Based on a linear relationship existed between tribological factors (load and speed) and the average current evolved, an empirical correlation is proposed and possible underlying mechanisms are discussed. The effects of particle angularity on the surface and sub-surface damage are also demonstrated. It was found that increasing particle angularity improved their depassivation efficiency.

Tribo-electrochemical behaviour of 316L stainless steel was studied using three contact configurations: two-body ceramic counterface (2B-CC), three-body rubber counterface (3B-RC) and three-body ceramic counterface (3B-CC). Electrochemical methods were employed to investigate the effects of tangential speed and wear mechanism on the tribo-electrochemical characteristics of the 316L samples at each contact configuration. In both 2B-CC and 3B-RC contacts increasing the tangential speed resulted in higher current measured while in the 3B-CC contact the current was an increasing function of time even at a constant rotational speed. After the abrasion-corrosion tests different repassivation kinetics was found for each contact configuration.

The discrete depth characteristics of thin passive oxide films were investigated using high-resolution electron microprobe and nanoscale secondary ion mass spectrometry (NanoSIMS). A novel NanoSIMS method involving a Cs layer deposition before Cs + sputtering was employed for the first time to determine the elemental distribution at different sub-layers of a passive film. The film was formed in air on the surface of a multi-phase microstructure of high-chromium cast iron (HCCI). It was found that the film composition and thickness varied according to the underlying microstructure phase. Based on the microprobe and NanoSIMS results, the influence of the HCCI passive film thickness and composition on the localized passivity breakdown has been proposed.

Electrical conductivities and densities of acidic zinc, cadmium and manganese sulphate solutions were measured. Empirical equations have been derived to represent the measured values with high accuracy. Electrical conductivity of solutions has been shown to be expressed as a logarithmic function of temperature, a second order polynomial function of sulphuric acid concentration and a linear function of metal ion concentration. It can be deduced that the density of solution can be described as a linear function of metal ion concentration, temperature and sulphuric acid concentration. These equations could be used to improve the electrowinning or electrorefining process conditions.

High-Cr white cast irons (WCIs) are multiphase alloys commonly used in aqueous industrial environments in applications that require both high abrasion and high corrosion resistance. Various electrochemical techniques can be useful in elucidating tribocorrosion characteristics of metallic materials undergoing wear in a corrosive environment. This study is focused on the interpretation of electrochemical measurements applied to three-body abrasion corrosion contacts of high-Cr WCIs. Particular attention has been paid to determine whether tribo-electrochemical data can pick up any effects that the multiphase microstructure of WCIs may have on the tribocorrosion characteristics, especially in environments containing chloride ions. Since both wear and corrosion of multiphase alloys are usually not uniform, their tribocorrosion behaviour is difficult to study and is still poorly understood. The experimental results are discussed in terms of benefits and limitations of tribo-electrochemical techniques such as polarization (potentiostatic, potentiodynamic) and electrochemical noise (galvanic coupling, potentiostatic) in studying abrasion corrosion behaviour of high-Cr WCIs. The application of high-resolution surface analysis techniques (microprobe, NanoSIMS, C-AFM and SKPFM), used in support of the electrochemical data interpretation, is also demonstrated.