Contributions of Microelectrochemical Scanning Techniques for the Efficient Detection of Localized Corrosion Processes at the Cut Edges of Polymer-Coated Galvanized Steel.

Spatially resolved information on corrosion reactions operating at the cut edges of coated metals can be obtained using microelectrochemical scanning techniques using a suitable selection of operation modes and scanning probes. The scanning vibrating electrode technique (SVET) provides current density maps with a spatial resolution of the order of the dimensions of the sample, which allows the temporal evolution of the corrosion reactions to be followed over time. This leads to the identification and localization of cathodic and anodic sites, although the technique lacks chemical specificity for the unequivocal identification of the reactive species. The application of scanning electrochemical microscopy (SECM) was previously limited to image cathodic reaction sites, either due to oxygen consumption in the amperometric operation or by the alkalinisation of the electrolyte in potentiometric operation. However, it is shown that anodic sites can be effectively monitored using an ion-selective microelectrode (ISME) as a probe. The ISME probes detected differences in the local concentrations of Zn2+ and OH- ions from the cut edges of a complete coil coating system compared to the same system after the polymeric layers were removed. In this way, it has been shown that the inhibitor loading in the polymer layers effectively contributes to reducing the corrosion rates at the cut edge, thus helping to extend the useful life of the sacrificial galvanized layer bonded directly to the steel matrix. Additionally, these two probe configurations can be integrated into a multi-electrode tip for potentiometric operation to simultaneously monitor localized changes in pH values and metal ion dissolution in a single scan. Spatial and temporal distributions were further investigated using different rastering procedures, and the potential of constructing pseudomaps for 2D-imaging is described.

Evaluation of in vitro corrosion resistance and in vivo osseointegration properties of a FeMnSiCa alloy as potential degradable implant biomaterial.

In vitro electrochemical characterization and in vivo implantation in an animal model were employed to evaluate the degradation behaviour and the biological activity of FeMnSi and FeMnSiCa alloys obtained using UltraCast (Ar atmosphere) melting. Electrochemical characterization was based on open circuit potential measurement, electrochemical impedance spectroscopy and potentiodynamic polarization techniques while the alloys were immersed in Ringer's solution at 37 °C for 7 days. Higher corrosion rates were measured for the Ca-containing material, resulting from inefficient passivation of the metal surface by oxy-hydroxide products. In vivo osseointegration was investigated on a tibia implant model in rabbits by referring to a standard control (AISI 316 L) stainless steel using standard biochemical, histological and radiological methods of investigation. Changes in the biochemical parameters were related to the main stages of the bone defect repair, whereas implantation of the alloys in rabbit's tibia provided the necessary mechanical support to the injured bone area and facilitated the growth of the newly connective tissue, as well as osteoid formation and mineralization, as revealed by either histological sections or computed tomography reconstructed images and validated by the bone morphometric indices. The present study highlighted that the FeMnSiCa alloy promotes better osteoinduction and osseconduction processes when compared to the base FeMnSi alloy or with AISI 316 L, and in vivo degradation rates correlate well with corrosion resistance measurements in Ringer's solution.

Why ammonium detection is particularly challenging but insightful with ionophore-based potentiometric sensors - an overview of the progress in the last 20 years.

The monitoring of ammonium ion concentration has gained the attention of researchers from multiple fields since it is a crucial parameter with respect to environmental and biomedical applications. For example, ammonium is considered to be a quality indicator of natural waters as well as a potential biomarker of an enzymatic byproduct in key physiological reactions. Among the classical analytical methods used for the detection of ammonium ions, potentiometric ion-selective electrodes (ISEs) have attracted special attention in the scientific community because of their advantages such as cost-effectiveness, user-friendly features, and miniaturization ability, which facilitate easy portable measurements. Regarding the analytical performance, the key component of ISEs is the selective receptor, labelled as an ionophore in ISE jargon. Indeed, the preference of an ionophore for ammonium amongst other ions (i.e., selectivity) is a factor that primarily dictates the limit of detection of the electrode when performing measurements in real samples. A careful assessment of the literature for the last 20 years reveals that nonactin is by far the most employed ammonium ionophore to date. Despite the remarkable cross-interference of potassium over the ammonium response of nonactin-based ISEs, analytical applications comprising water quality assessment, clinical tests in biological fluids, and sweat monitoring during sports practice have been successfully researched. Nevertheless, there is evident difficulty in the determination of close-to-micromolar levels of ammonium in real samples with a significant potassium background level (i.e., millimolar concentration). This fact has fostered the search for a large variety of ammonium ionophores over the years, which are critically inspected herein. Overall, we provide an easily readable state of the art accompanied by a comprehensive description of other types of ammonium electrodes, including commercially available units. We conclude that newer breakthroughs are still required in the field to reach the desired analytical applications.