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Open-Circuit Metal Dissolution Processes
Published in Madhav Datta, Electrodissolution Processes, 2020
This section intends to briefly provide the essentials of thermodynamic and kinetic aspects of corrosion. Let us first define a few basic electrochemical terminologies: The OCP is the potential set up spontaneously by an electrode when immersed in an electrolyte in the absence of an external current. For a single electrode, the open-circuit potential is equal to the equilibrium potential, also known as reversible potential, Erev.When a potential is imposed on an electrode such that its potential differs from the open-circuit potential, an electric current passes through the electrode-electrolyte interface. This overpotential, η, is defined as the difference between the electrode potential, E, and the equilibrium or reversible potential of an electrode reaction: η = E − Erev.A polarization curve establishes the functional dependence between current density and potential. A polarization curve can be experimentally determined by controlling either the potential or the current. One thus obtains a potentiostatic polarization curve, i = f(E), or a galvanostatic polarization curve, E = f(i), respectively.The OCP of a mixed electrode undergoing corrosion is called the corrosion potential.Electrochemical reactions typically involve the transfer of charge across the interface. There are two types of charge transfer reactions. Ion transfer reactions involve the transfer of ions from the electrode to the electrolyte or vice versa. Electron transfer reactions involve the transfer of charge between ions in the electrolyte and typically occur heterogeneously at an electrode surface.Mass transport determines the concentration of the reactants and products at the electrode surface. The electrolyte layer close to the electrode surface, in which the concentration of the reactants or products differs from that in the bulk electrolyte, is called the diffusion layer. The thickness of the diffusion layer depends on the prevailing hydrodynamic conditions. This topic will be discussed in detail elsewhere in the book.
Ionic transport properties improvement of a new cation-exchange membrane containing functionalized CNT as a clean technology for refining of saline-liquids
Published in Environmental Technology, 2021
Farhad Heidary, Ali Reza Khodabakhshi, Davood Ghanbari
In general the ionic permeability and flux variations showed adaptability with membrane potential and surface charge density. The higher surface charge density modifies the ionic pathways and improves the uniformity of electrical field on the surface of membrane and vice versa which can improve the electrostatic interactions of the membrane surface with counter-ions and ionic permeation [23]. As an example in the case of sample 8, the flux and ionic permeability were very negligible due to inconsiderable ion-exchange capacity (or surface charge density) and also the presence of narrow channels for ionic transfer in membrane matrix.