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Electrical separation
Published in D.V. Subba Rao, Mineral Beneficiation, 2011
Conductors are materials which permit electrons to flow freely from atom to atom and molecule to molecule. An object made of a conducting material will permit charge to be transferred across the entire surface of the object. If a charge is transferred to the object at a given location, that charge is quickly distributed across the entire surface of the object. If a charged conductor is touched to another object, the conductor can even transfer its charge to that object. The transfer of charge between objects occurs more readily if the second object is made of a conducting material. Conductors allow for charge transfer through the free movement of electrons.
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.
Modeling and optimizing of anode-supported solid oxide fuel cells with gradient anode: Part I. Model description and validation by experiments
Published in Numerical Heat Transfer, Part A: Applications, 2019
Pei Fu, Xionghui Li, Jian Chen, Jian Yang, Jianbing Huang, Qiuwang Wang
Charge transfer includes electronic and ionic transfer. In the anode functional layers, both electrons and oxygen ions are served as conducting particles. In other anode regions, electrons are the only conducting particles. In the thin cathode, both electrons and oxygen ions are the conducting particles. In the electrolyte, only oxygen ions are allowed to migrate through. Conservation of the electronic and ionic transfer can be respectively formulated as where iel and iio are the local electronic and ionic current densities, respectively. According to the Ohm’s law, the current densities can be expressed as where φel and φio are the electric potential of electronic and ionic phases, respectively; and are the effective electronic and ionic conductivities, respectively, which are dependent on the microstructure characteristics of the porous electrodes [32, 33]: where Φel is the volume fraction of electronic conducting particles; σel and σio are the material electronic and ionic conductivities, respectively.