Oxidation usually dominates high-temperature corrosion reactions, but under certain conditions, some alloys may be affected by nitridation as well. This chapter explains why nitridation occurs and how it attacks various metals, in some cases, penetrating deeper than oxidation. It provides images and data describing the nitridation process and its effects on metals and alloys in high-temperature air as well as NH3-H2O, NH3 and H2-N2-NH3, and N2 environments. It also includes test data showing that nitridation is more severe in a nitrogen atmosphere than an ammonia environment at 1090 °C (2000 °F).

This chapter discusses the conditions under which carburization and metal dusting occur. It describes the chemical reactions and thermodynamic relationships that drive carburization and metal dusting attack and the factors that determine the amount of damage that metals and alloys are likely to sustain. The chapter also explains how carburization affects creep strength and fracture toughness, and how surface conditions and finish and the presence of sulfur affect metal dusting behaviors.

This chapter provides a thorough introduction to the electrochemical thermodynamics that govern electrode reactions associated with corrosion. It begins with a review of the thermodynamic criteria for the stability of chemical reactions based on Gibbs free energy and explains how energies of formation are determined using the oxidation of iron as an example. It then considers how iron reacts with hydrochloric acid, explaining how it can be expressed as two half reactions modeled as electrodes in an electrochemical cell. It goes on to describe the chemical reactions occurring at each electrode, accounting for different variables, mechanisms, and electrochemical effects. The chapter concludes with an in-depth review of Pourbaix diagrams, explaining what they reveal about the stability of metal-water systems and the formation of corrosion products.