Corrosion model

Fig. 9. Corrosion model of silver development. As the haUde ion, X, is removed into solution at the etch pit, the silver ion,, travels interstitiaHy, Ag/ to the site of the latent image where it is converted to silver metal by reaction with the color developer, Dev. Dev represents oxidized developer.

Fig. 19. Oxygen evolution and corrosion model for ruthenium based electrodes. After [54].

Silver-copper (Ag-Cu) ionization systems, environmental limits on, 22 652 Silver-copper system, properties of, 22 644 Silver cyanide, 22 670-671, 674-675 in electroplating, 22 685-686 Silver cyclohexanebutyrate, 22 671 Silver development, corrosion model of, 19 245... 

Figure 15 shows the relevant results obtained with the corrosion model. 

The proposed corrosion model allows one to estimate the maximum lifetime of our hypothetical average HT material subjected to realistic conditions of corrosion. The maximum lifetime represents the time necessary to corrode the... 

Kienzler, B., Luckscheiter, B. Wilhelm, S. 2001. Waste form corrosion modeling comparison with experimental results. Waste Management, 21, 741-752. 

Bourcier, W. L. 1994. Waste glass corrosion modeling Comparison with experimental results. Materials Research Society Symposium Proceedings, 333, 69 - 82. 

Development of Corrosion Models Based on Electrochemical Measurements... 

Figure 1 attempts to define the key stages in the development of corrosion models. Irrespective of whether the key concern is safety or operating efficiency, the steps involved in model development are common up to the point where data reliability must be accounted for (stage 8). At this juncture, the approaches deviate. When public/personnel safety is the key issue, one would adopt conservative assumptions (stage 9A) to cover the uncertainties that will inevitably permeate one s model. If plant efficiency is the key issue, then at this juncture it is necessary to refine one s data input by a combination of further experimentation and the careful consideration of information from plant inspection records (stage 9B). 

Most of the examples used in this chapter emphasize assessment models that can afford to incorporate conservative assumptions. Most deal with the environmental issue of nuclear waste disposal. This emphasis should not be taken to suggest that the literature is not replete with many other examples of valuable corrosion models. It is hoped that this chapter will encourage the reader to search for them. 

A general scheme for the development of corrosion models based on electrochemical principles has been described, and a number of examples for active, passive, and localized corrosion has been given. This chapter is by no means comprehensive, and a search of the scientific and technical literature will unearth many additional examples. The value in using electrochemical methods both to develop understanding of the corrosion process and to measure the values of specific modeling parameters is obvious. However, their application alone would not provide all the elements and parameter values required for the development of corrosion models, so the use of supplementary techniques is necessary. It is necessary also to keep in mind that electrochemical techniques inevitably accelerate the corrosion process one is interested in. Consequently, the scaling of electrochemi-cally determined parameter values to the rates and time periods of interest in the corrosion process to be modeled should be undertaken carefully and with a full knowledge of the limitations involved. 

Chapter 4 describes how the electrical nature of corrosion reactions allows the interface to be modeled as an electrical circuit, as well as how this electrical circuit can be used to obtain information on corrosion rates. Chapter 5 focuses on how to characterize flow and how to include its effects in the test procedure. Chapter 6 describes the origins of the observed distributions in space and time of the reaction rate. Chapter 7 describes the applications of electrochemical measurements to predictive corrosion models, emphasizing their use in the long-term prediction of corrosion behavior of metallic packages for high-level nuclear waste. Chapter 8 outlines the electrochemical methods that have been applied to develop and test the effectiveness of surface treatments for metals and alloys. The final chapter gives experimental procedures that can be used to illustrate the principles described. 

Strategy, programs for evaluation of cracking in steels used in pipelines and refineries USL Corrosion Model, program for prediction of corrosion in gas condensate wells... 

Friedrich and Filers [113] have proposed a corrosion model of development and derived electron transfer equations based on the Butler-Volmer expression which can be simplified into three cases. Case 1 is when both the forward and reverse processes of developer oxidation are important. Case 2 is when the net rate is limited by the forward rate of developer oxidation. Case 3 corresponds to a rate which is limited by the kinetics of both developer oxidation and silver halide reduction. 

One approach to developing a corrosion model for galvanized steel based on dry deposition is to assume that the corrosion C (in moles of Zn lost per unit area) can be represented as a linear combination of the corrosion induced in a clean air environment and that associated with air pollutant x, i.e.. 

Formulation of Corrosion Model. The corrosion products formed on galvanized steel consist of insoluble compounds (Zn(0H)2, ZnC03, etc.) and soluble compounds (ZnS04, Zn(N03)2, etc.). First, the time evolution of the insoluble component will be addressed. The corrosion will be expressed in terms of change in surface thickness due to corrosion product formation. 

The proposed model represents a first step in the development of a corrosion model for galvanized steel. To validate the model, detailed testing of model predictions versus results of field exposure studies is required. Such an effort is presently being... 

The Evans diagram ( ) is a graphical presentation in semilogarithmic coordinates of the anodic and cathodic reaction rates expressed as partial currents dependent on potential. The basis for the Evans diagram is the corrosion model discussed above ... 

According to the electrochemical nature of the corrosion process and the macrocell-corrosion model (Chapter 8), a relationship may be expected between the concrete resistivity and the corrosion rate of the reinforcement after depassivation. Using a simplified approach, the corrosion rate of steel in concrete should be inversely proportional to the resistivity. This was confirmed in a general sense [24, 25], although the relationship is not universal rather it depends on the concrete composition [21]. 

Fig. 24 Principal corrosion model explaining the formation of a galvanic element in case of cathodic delamination on polymer-coated iron, (a) Cross section through a metal-polymer interface with a defect in the polymer coating (b) overview of the polarization curves at the defect (i), the intact interface fii) and the situation after galvanic coupling of the parts (c).

H.W. Song, H.J. Kim, V. Saraswathy, T.H. Kim, Micro-mechanics based corrosion model for predicting the service life of reinforced concrete structures, Int. J. Electrochem. Sci. 2 (2007) 341-354. 

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