Chapter 17: Corrosion and Degradation of Materials

For metals, corrosion is fundamentally electrochemical, driven by coupled oxidation and reduction reactions occurring at distinct anodic and cathodic sites. The chapter establishes key frameworks for predicting corrosion behavior: standard electrode potentials and the emf series rank metals by inherent reactivity, while the galvanic series accounts for environmental effects, revealing how dissimilar metals in contact form galvanic couples where less noble metals preferentially corrode. Corrosion rates are quantified through corrosion penetration rate and current density measurements, with activation polarization and concentration polarization identified as primary rate-limiting factors. Passivity—the formation of protective oxide films that dramatically suppress corrosion—is explained through polarization curves and demonstrated in stainless steels and aluminum alloys. The chapter systematically presents eight major forms of metallic corrosion: uniform attack across surfaces, galvanic corrosion between dissimilar metals in electrolytes, crevice corrosion from localized oxygen depletion, pitting corrosion as insidious localized attack especially in stainless steels, intergranular corrosion and weld decay in sensitized microstructures, selective leaching such as dezincification in brass alloys, erosion-corrosion combining mechanical wear with chemical attack in flowing systems, and stress corrosion cracking where tensile stress and specific environments cause brittle failure. Hydrogen embrittlement is analyzed as a separate failure mode where atomic hydrogen penetration reduces ductility catastrophically in high-strength steels. Ceramic corrosion is less common since ceramics are already oxidized compounds, but extreme environments cause dissolution through molten salt or slag attack on refractories. Polymer degradation replaces corrosion concerns and encompasses swelling and dissolution from solvent penetration, bond scission from thermal, UV, or radiation exposure, and weathering from sunlight and moisture. The chapter concludes with comprehensive prevention strategies including material selection, design optimization, chemical inhibitors, protective coatings, and cathodic protection using sacrificial anodes or impressed currents. Oxidation in dry environments is addressed through the Pilling-Bedworth ratio and oxide growth rate laws describing parabolic, linear, and logarithmic kinetics.