Electrochemical model, corrosion

A. Anderko. Simulation of FeC03/FeS scale formation using thermodynamic and electrochemical models. Nace Int Corrosion Conf (Corrosion 2000) (Orlando, FL, 3/26-3/31), 2000. 

An electrochemical model for the process of electroless metal deposition was suggested by Paunovic (10) and Saito (8) on the basis of the Wagner-Traud (1) mixed-potential theory of corrosion processes. According to the mixed-potential theory of electroless deposition, the overall reaction given by Eq. (8.2) can be decomposed into one reduction reaction, the cathodic partial reaction. 

If the data collected do not fit the simplest equivalent-circuit model (Fig. 6.18), more complex models are analyzed. A number of equivalent circuits have been developed to model corrosion processes involving diffusion control, porous films or coatings, pseudoinductive mechanisms, simultaneous electrochemical and chemical reactions, and pitting corrosion (Ref 14-18). 

Nesic S, Postlethwaite J, Olsen S. An electrochemical model for prediction of corrosion of mild steel in aqueous carbon dioxide solutions. Corrosion/95, Paper No 131, NACE, Houston, Texas, 1995. 

For RBP, a logarithmic current density range of 2.5 to 6 mA/cm was used, as shown in Figure 7.13. Treated samples at 60,100, and 120 N are shown, whereas the other samples are not shown because of crowdedness in the figure. Potentiostatic polarization measurements were carried out using a Radiometer Analytical model PGZ 100 potentiostat/galvanostat with VoltaLab software. The electrochemical parameters—corrosion potential corrosion current... 

Although there is little evidence for auto-catalysis in dechlorination by Fe , it is still possible that localized corrosion contributes to the remediation of contaminants in environmental applications. Various investigators have postulated that localized corrosion contributes through increased surface area (44) and creation of corrosion cell domains (49-51). The corrosion cell model works on the same principle as the electrochemical model described above (Figure 3), but invokes additional effects such as the reduction of protons as the major cathodic reaction, and the creation of an electrical double layer between the anode and cathode that permits transport due to electrical migration as well as diffusion. Although many aspects of these models are plausible, there are not yet any data that specifically support them, and a study that systematically addresses the role of localized corrosion in remediation applications of Fe remains to be done. 

F is the Faraday constant, and n is the number of electrons transferred in the redox reaction. F, named after Michael Faraday, has a value of 96,485 J mol or 96,485 C moLh (Remember that 1 J = 1 C V.) Equation 13.3 bears a resemblance to Equation 12.7, which we used to derive the relationship between AG° and the equilibrium constant. We can apply the Nernst equation to estimate the potential of the electrochemical system in the corrosion of steel at more realistic concentrations. Example Problem 13.2 explores the use of the Nernst equation in an electrochemical cell that models corrosion. 

The electrochemical model for corrosion breaks the process down into anodic and cathodic half-cell reactions, each having their own equations, which may include ... 

Modeling CO2 Corrosion A CO2 corrosion "worst case" model baised on an ANN approach was developed and the model validated against a large experimental database [28], An experimental databaise was used to train and test the ANN. It consisted initially of six elemental descriptors (temperature, partial CO2 pressure, ferrous and bicarbonate ion concentrations, pH, and flow velocity) and one output, i.e., the corrosion rate. The system demonstrated superior interpolation performance compared to two other well known semi-empirical models. The ANN model also demonstrated extrapolation capabilities comparable to a purely mechanistic electrochemical CO2 corrosion model. 

The explanations based on the crystal structure model of Kossel and Stranski of Fig. 1-35 still require detailed investigations. The development of scanning tunneling microscopy provides a valuable in situ tool to follow the structural details of electrochemical alloy corrosion. Although mechanistic studies of this kind require complicated investigations and a careful preparation technique for single crystal surfaces the application of these methods promises progress in the near future. 

Roberge PR. Analyzing electrochemical impedance corrosion measurements by the systematic permutation of data points. In Muim RS. ed. Computer Modeling in Corrosion [STP 1154]. Philadelphia, Pa. American Society for Testing and Materials, 1992 197-211. 

In maldug electrochemical impedance measurements, one vec tor is examined, using the others as the frame of reference. The voltage vector is divided by the current vec tor, as in Ohm s law. Electrochemical impedance measures the impedance of an electrochemical system and then mathematically models the response using simple circuit elements such as resistors, capacitors, and inductors. In some cases, the circuit elements are used to yield information about the kinetics of the corrosion process. 

In recent years the mechanism of crevice has been mathematically modelled and a more thorough understanding of the corrosion processes has been evolved . From such mathematical modelling it is feasible to predict critical crevice dimensions to avoid crevice corrosion determined with relatively simple electrochemical measurements on any particular stainless steel. 

Corrosion of. power-station condenser tubes by polluted, waters has been particularly troubles ome in Japan anil efforts have been made to,study the problem by, electrochemical methods and by exposing model condensers at a variety of bower station sites ., Improved results have been reported, using tin. brasses , or special, tin bronzes. . Pretreatment with sodium dimethyldithiOcarbamate is reported to give protective films that will withstand the action of polluted waters , though the method would be economic only in special circurtistapcies., , , . ... 

The implication of the foregoing equations, that stress-corrosion cracking will occur if a mechanism exists for concentrating the electrochemical energy release rate at the crack tip or if the environment in some way serves to embrittle the metal, is a convenient introduction to a consideration of the mechanistic models of stress corrosion. In so far as the occurrence of stress corrosion in a susceptible material requires the conjoint action of a tensile stress and a dissolution process, it follows that the boundary conditions within which stress corrosion occurs will be those defined by failure... 

Most metals (other than the alkali and alkaline-earth metals) are corrosion resistant when cathodically polarized to the potentials of hydrogen evolution, so that this reaction can be realized at many of them. It has thus been the subject of innumerable studies, and became the fundamental model in the development of current kinetic concepts for electrochemical reactions. Many of the principles... 

The impedance spectroscopy of steel corrosion in concentrated HC1, with and without inhibitors, exhibit relatively straightforward electrochemical phenomenology and can be represented by simple equivalent circuits involving primarily passive electrical elements. Analysis of these circuits for steel corroding in HC1 per se reveals that the heterogeneity of the surface is established rapidly and can be simulated with a simple electrical circuit model. 

Paunovic [23] and Saito [24] first advanced the notion that an electroless deposition process could be modeled using a simple electrochemical approach. They reasoned that the potential of a surface undergoing electroless deposition could be regarded as a mixed potential intermediate in value between the potentials of its constituent anodic and cathodic partial reactions. These authors employed the mixed potential concept of corrosion reactions first outlined in a systematic manner by Wagner and... 

Electrochemical impedance spectroscopy was used to determine the effect of isomers of 2,5-bis( -pyridyl)-l,3,4-thiadiazole 36 (n 2 or 3) on the corrosion of mild steel in perchloric acid solution <2002MI197>. The inhibition efficiency was structure dependent and the 3-pyridyl gave better inhibition than the 2-pyridyl. X-ray photoelectron spectroscopy helped establish the 3-pyridyl thiadiazoles mode of action toward corrosion. Adsorption of the 3-pyridyl on the mild steel surface in 1M HCIO4 follows the Langmuir adsorption isotherm model and the surface analysis showed corrosion inhibition by the 3-pyridyl derivative is due to the formation of chemisorbed film on the steel surface. 

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