Diagnostics of Anodic Stripping Mechanisms under Square-Wave Voltammetry Conditions Using Bismuth Film Substrates

A mechanistic study to provide diagnostics of anodic stripping electrode processes at bismuth-film electrodes is presented from both theoretical and experimental points of view. Theoretical models for three types of electrode mechanisms are developed under conditions of square-wave voltammetry, combining rigorous modeling based on integral equations and the step function method, resulting in derivation of a single numerical recurrent formula to predict the outcome of the voltammetric experiment. In the course of the deposition step, it has been assumed that a uniform film of the metal analyte is formed on the bismuth substrate, in situ deposited onto a glassy carbon electrode surface, without considering mass transfer within either the bismuth or the metal analyte film. Theoretical data are analyzed in terms of dimensionless critical parameters related with electrode kinetics, mass transfer, adsorption equilibria, and possible lateral interactions within the deposited metal particles. Theoretical analysis enables definition of simple criteria for differentiation and characterization of electrode processes. Comparing theoretical and experimental data, anodic stripping processes of zinc(II), cadmium(II), and lead(II) are successfully characterized, revealing significant differences in their reaction pathways. The proposed easy-to-perform diagnostic route is considered to be of a general use while the bismuth film exploited in this study served as a convenient nonmercury model substrate surface

Characterisation of NiTi Orthodontic Archwires Surface after the Simulation of Mechanical Loading in CACO2-2 Cell Culture

Nickel-titanium (NiTi) orthodontic archwires are crucial in the initial stages of orthodontic therapy when the movement of teeth and deflection of the archwire are the largest. Their great mechanical properties come with their main disadvantage-the leakage of nickel. Various in vitro studies measured nickel leakage from archwires that were only immersed in the medium with little or minimal simulation of all stress and deflection forces that affect them. This study aims to overcome that by simulating deflection forces that those archwires are exposed to inside the mouth of a patient. NiTi orthodontic archwires were immersed in CACO2-2 cell culture medium and then immediately loaded while using a simulator of multiaxial stress for 24 h. After the experiment, the surface of the NiTi orthodontic archwires were analysed while using scanning electron microscopy (SEM) and auger electron spectroscopy (AES). The observations showed significant microstructural and compositional changes within the first 51 nm thickness of the archwire surface. Furthermore, the released nickel and titanium concentrations in the CACO2-2 cell culture medium were measured while using Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). It was found out that the level of released nickel ions was 1.310 mu g/L, which can be assigned as statistically significant results. These data represent the first mention of the already detectable release of Ni ions after 24 h during the simulation of mechanical loading in the CACO2-2 cell culture medium, which is important for clinical orthodontic praxis

Studies on Electrode Processes in Stripping Analysis Using Square-Wave Voltammetry: Theory and Application

This paper presents mechanistic studies on electrode processes in stripping trace and ultratrace analysis under square-wave voltammetry conditions from both theoretical and experimental points of view. Besides adsorptive stripping and cathodic stripping mechanisms [1], a special attention is given to the anodic stripping processes at bismuth-film electrodes [2]. Several electrode mechanisms are analyzed, including those coupled with adsorption equilibria and lateral interactions of selected metal analytes within the deposited electroactive film. An attempt is made to identify a critical set of voltammetric properties upon which diagnostic criteria can be established for differentiation between particular electrode mechanisms. Theoretical data are analyzed in terms of dimensionless critical voltammetric parameters related to electrode kinetics, mass transfer, adsorption equilibria, and possible lateral interactions. Several strategies for electrode kinetic measurements are presented. The study mainly focuses on the role of the height of the potential pulses used in square-wave voltammetry that enables kinetic measurements at a constant scan rate. Theoretical considerations outlined are illustrated using experimental data collected at bismuth-film electrodes

Electrochemical Dissolution of Iridium and Iridium Oxide Par-ticles in Acidic Media: Transmission Electron Microscopy, Electrochemical Flow Cell Coupled to Inductively Coupled Plasma Mass Spectrometry and X-ray Absorption Spectros-copy Study

Iridium based particles as the most promising proton exchange membrane electrolyser electrocatalysts were investigatedby transmission electron microscopy (TEM), and by coupling of electrochemical flow cell (EFC) with online inductivelycoupled plasma mass spectrometer (ICP-MS). Additionally, a thin-film rotating disc electrode (RDE), an identical location transmissionand scanning electron microscopy (IL-TEM and IL-SEM) as well as an X-ray absorption spectroscopy (XAS) studies havebeen performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that iridiumparticles dissolved already well below oxygen evolution reaction (OER) potentials, presumably induced by iridium surface oxidationand reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile type IrO2 particles (T-IrO2)are substantially more stable and less active in comparison to as prepared metallic (A-Ir) and electrochemically pretreated (E-Ir)analogues. Interestingly, under OER relevant conditions E-Ir particles exhibit superior stability and activity owing to the alteredcorrosion mechanism where the formation of unstable Ir(>IV) species is hindered. Due to the enhanced and lasting OER performance,electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low temperatureelectrochemical hydrogen production device, namely a proton exchange membrane electrolyser