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Voltage, Capacitors, and Batteries
Published in Juan Bisquert, The Physics of Solar Energy Conversion, 2020
the electrode potential is given by the Nernst equation Vredox=Vredox0+kBTzqlncoxcred
Introduction to Corrosion
Published in S.K. Dhawan, Hema Bhandari, Gazala Ruhi, Brij Mohan Singh Bisht, Pradeep Sambyal, Corrosion Preventive Materials and Corrosion Testing, 2020
S.K. Dhawan, Hema Bhandari, Gazala Ruhi, Brij Mohan Singh Bisht, Pradeep Sambyal
The magnitude of the change in free energy (ΔG) of a particular corrosion reaction is the measure of the spontaneity of the reaction. It gives an idea about the extent to which a reaction will proceed before the attainment of equilibrium. The negative value of ΔG (ΔG << 0) shows the tendency of a metal to react readily with the species in the solution, but whether the reaction proceeds to any extent will depend on the kinetic factors. On the other hand, if the value of ΔG is positive (ΔG > 0) then the metal shows its stability in the environment. If the value of ΔG = 0, then the system will not proceed in any direction (equilibrium state). The value of free energy change (ΔG) and equilibrium constant (K) of corrosion reaction are calculated by using standard electrode potential (E0) or the standard chemical potentials. The value of electrode potential is calculated from the Nernst equation. ()E=E°−RT/nFln[reduced]/[oxidized]
Removal of Corrosive Substances
Published in Samuel D. Faust, Osman M. Aly, Chemistry of Water Treatment, 2018
This is the left to right corrosion reaction, which will proceed until the metal reaches an equilibrium state with its ion in solution. An anodic current results from this oxidation reaction. In the right to left reaction, metal ions are reduced by acceptance of the electrons, which results in a cathodic current. When these two currents are equal, the forward reaction proceeds at the same rate as the reverse reaction. Consequently, no net corrosion occurs in this state of equilibrium. It can be shown that the electric current, which is equal to the velocity of the reaction, depends on the electrode potential.6 The net current is zero when the rate of reduction is equal to the rate of oxidation, whereupon the system reaches a state of equilibrium.
Plant wastes as alternative sources of sustainable and green corrosion inhibitors in different environments
Published in Corrosion Engineering, Science and Technology, 2023
Nnabuk Okon Eddy, Anduang O. Odiongenyi, Eno E. Ebenso, Rajni Garg, Rishav Garg
From the above, it follows that any process that can alter the electrode potential of a corrosion cell would certainly alter the rate of corrosion. One such factor is the application of an inhibitor. A corrosion inhibitor is any substance, that retards the rate of corrosion when added in minute concentration to the corrosion medium [15]. Factors that can affect the efficiency of corrosion inhibitors include temperature, the concentration of the inhibitor, the chemical composition of the inhibitor, the type of metal and the aggressive medium [16,17]. Effective corrosion inhibitors can alter the direction of the corrosion reaction (hence electrode potential) through the operation of charge transfer from the charged inhibitor to the charge vacant metal surface (physical adsorption) or electron transfer from the inhibitor to the metal surface (chemical adsorption) [18]. Such alteration can alter the surface of the meta through one or more of the following processes: Decrease in the tendency towards oxidationLocking of the corrosion active sitesRetardation of the rate of the anodic or cathodic reactionAlteration in current in the flow of current.
Redox potential measurement during pressure oxidation (POX) of a refractory gold ore
Published in Canadian Metallurgical Quarterly, 2018
Igor Guzman, Steven J. Thorpe, Vladimiros G. Papangelakis
Figure 7(a) shows that the electrode potential is not influenced by variations of temperature within ±0.2°C. It also shows the initial offset from the target temperature to compensate for the heat generated by the sulphur oxidation. The target temperature is reached in 1 min from the time of oxygen injection. It is worth note that by 90 min the electrode potential has plateaued; in Figure 2(a), it was only shown up to 60 min.