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Über dieses Buch

This brief is concerned with the fundamentals of corrosion of metallic materials and electrochemistry for better understanding of corrosion phenomena. Corrosion is related to both the environment and material properties, induced by electrochemical reactions at the interface between metallic materials and the environment as in aqueous and gaseous phases. In order to understand corrosion phenomena, knowledge of electrochemistry is thus required, and to investigate the cause of corrosion damage, appropriate electrochemical experiments must be performed. Corrosion scientists should therefore possess knowledge of both electrochemistry and its related experimental techniques. In this book, corrosion phenomena are introduced from the electrochemical aspect. Electrochemical techniques for the study of corrosion are then described with other techniques that can be combined with electrochemistry. Because this brief is characterized as starting with the fundamentals of corrosion and electrochemistry, it is accessible to undergraduate students as well as to graduate students who are beginning corrosion research.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Electrochemical Fundamentals of Corrosion and Corrosion Protection

In this chapter, we outline the corrosion process and corrosion protection, which are the basis of the more quantitative treatment presented in the following chapters. The corrosion process in aqueous solution is made up of electrochemical reactions consisting of oxidation of metallic materials and reduction of environmental substances. For the corrosion process, the local cell model has been proposed in which anodic oxidation of the metallic material and cathodic reduction of the environmental substances occur at different sites on the material and the currents of the both reactions are same as each other. The following topics are concisely described: (1) corrosion electrochemistry, (2) classification of corrosion, (3) synergistic effect of the mechanical action on corrosion, (4) corrosion protection, and (5) hydrogen entry into the metallic material and delayed rupture.

Toshiaki Ohtsuka, Atsushi Nishikata, Masatoshi Sakairi, Koji Fushimi

Chapter 2. Electrochemical Measurement of Wet Corrosion

The corrosion process consists of a combination of electrochemical oxidation and reduction reactions. Electrochemistry is founded of equilibrium and kinetic. The equilibrium phase diagram or potential-pH diagram can be drawn as a function of the solution pH and the potential from electrochemical thermodynamics, and one may predict from the diagram whether the metal in a specified environment is corroded or not. The corrosion current or rate is estimated from the electrochemical measurement of potential (E)-current (i) relationship. The corrosion current or the rate of corrosion loss can be estimated from the methods of the Tafel relation (log|i| vs. E relation) and the linear polarization (i vs. E relation). Electrochemical AC impedance or electrochemical impedance spectroscopy (EIS) was widely used for corrosion study. The electrode interface in the corrosion system is modeled from the impedance with an equivalent circuit constructed by electric elements of resistance, capacitance, inductance, and Warburg impedance. The corrosion mechanism may be discussed on the basis of the circuit.

Toshiaki Ohtsuka, Atsushi Nishikata, Masatoshi Sakairi, Koji Fushimi

Chapter 3. Identification of Passive Films and Corrosion Products

The products resulting from corrosion reactions consist of various compounds with a thickness from a few nm to several 100 μm. For in situ detection of them under the corrosion environment, optical techniques using light from ultraviolet (UV) to infrared (IR) have been applied such as reflection of ellipsometry and differential reflectance, molecular vibration of Raman spectroscopy and IR reflection absorption spectroscopy (IR-RAS), and UV photoexcitation of photocurrent and luminescence. In this chapter, the basics and application results are described. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are further introduced both of which have been used for analysis of thin passive oxide layer by many researchers.

Toshiaki Ohtsuka, Atsushi Nishikata, Masatoshi Sakairi, Koji Fushimi

Chapter 4. Electrochemical Measurement of Atmospheric Corrosion

Electrochemical measurements for studying atmospheric corrosion are written in this chapter. Firstly, typical cells employed for electrochemical studies under a thin electrolyte film are introduced. As electrochemical techniques that are suitable for atmospheric corrosion study, electrochemical impedance spectroscopy (EIS) and Kelvin methods are described. Secondly, EIS and polarization curves measured under the simulated atmospheric environments in laboratory are introduced, and then the mechanism of atmospheric corrosion and cathodic oxygen reduction under thin electrolyte films is discussed. In addition, electrochemical monitoring of pitting corrosion of stainless steel that takes place under cyclic wet–dry environments in the presence of chloride is also described. Finally, atmospheric corrosion monitoring of carbon steel and weathering steels in real atmospheric sites by continuous measurements of electrochemical impedance is demonstrated where impedance of high and low frequencies is employed.

Toshiaki Ohtsuka, Atsushi Nishikata, Masatoshi Sakairi, Koji Fushimi

Chapter 5. Hydrogen Embrittlement and Hydrogen Absorption

The focus in this chapter is on the delayed failure, hydrogen embrittlement of steels, and detection of hydrogen in the metal. Several techniques for the detection of hydrogen in the metal are also explained. The diffusible hydrogen in the metal plays an important role in the delayed failure or hydrogen embrittlement, and the electrochemical detection of permeated hydrogen by the Devanathan–Stachurski double cell is explained in detail. From the analysis of the current transient, one can evaluate the diffusion coefficient of hydrogen in the metal. From the application of micro-electrochemical cell, the permeated hydrogen can be detected local site by site. On zinc-coated steel scratched, the permeated hydrogen was found to be enhanced around the scratched area.

Toshiaki Ohtsuka, Atsushi Nishikata, Masatoshi Sakairi, Koji Fushimi

Chapter 6. Micro-electrochemical Approach for Corrosion Study

Structure of an interphase formed between a practical material and its surrounding environment is not uniform or homogeneous not only in normal direction to the interface but also in horizontal direction to the interface. This is due to heterogeneity of the material’s crystallographic structure such as crystallographic orientation of single grains, grain boundaries, and inclusions, presence of reaction product on the surface, and heterogeneous effects from the environment. Heterogeneous structure of the interphase leads to heterogeneous interfacial reaction and/or localized corrosion. For example, pitting corrosion occurs on stainless steel in aggressive anion-containing solution owing to local depassivation at the weak part of passive surface. Micro-electrochemical methods are effective to investigate heterogeneous interfacial structures and locally corroding surfaces even in corrosive environments. In this chapter, several micro-electrochemical methods developed and applied in the corrosion research field are introduced. Features of the methods in the application are described as well as the principle and experimental setup of the methods.

Toshiaki Ohtsuka, Atsushi Nishikata, Masatoshi Sakairi, Koji Fushimi
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