Introduction to the High-Temperature Oxidation of Metals – Second Edition
Published by Cambridge University Press, 2006, pp350, £65, ISBN 0521480426.
This book deals with the thermodynamics and chemical kinetics of oxidation, hot corrosion and erosion-corrosion of metals and alloys at temperatures above 500ºC in single as well as mixed oxidants. A combined knowledge of reaction kinetics and morphologies of the oxide film provides an understanding of the physical process. Application and degradation of protective coatings against oxidation are also described.
The feasibility of high temperature reactions is assessed from the relations of Gibbs free energy with enthalpy and entropy of the system. The methodology of construction and use of 2D isothermal stability diagrams is discussed for the Ni-O-S system (one metal reacting with two oxidants) using the logarithmic values of the partial pressures of the two gases. Complication arises from the added variable of the composition of metals when the oxidation of a binary alloy (two metals) is considered in a single oxidant, the Fe-Cr-O system at 1,300ºC. The situation worsens when dealing with a 3D stability diagram for the oxidation of a binary alloy in mixed oxidants, namely a Ni-Cr-S-O system, due to the lack of sufficient experimental data.
The mechanism of oxidation via transport of ions and electrons through a growing oxide film is discussed for both p- and n-type semiconducting oxides. Results are based on the variation of oxidation rate with temperature and oxygen pressure. Wagner's theory of lattice diffusion for the parabolic rate of oxidation, as well as short-circuit diffusion along grain boundaries, are highlighted for an understanding of the overall growth of oxide films. The oxidation of metals is described in terms of the nature of oxides - namely Ni, Zn and Al forming a single layer of oxide, Fe and Co forming multiple oxides, Cr, Mo, W, Pt, Pd and Si forming volatile oxides, Ti with a high degree of oxygen solubility and Nb forming cracks in the oxide scale.
The largest section of the book is justifiably dedicated to a discussion of the oxidation theories of alloys that, unlike metals, have more practical importance. Alloys are uniquely grouped as either noble parent (Au, Ag, Pt etc) with base alloying elements (Cu, Ni, Fe, Co, Cr, Al, Ti etc), or the more common type with both parent and alloying elements as base metals. The difference in oxidation behaviour of alloys from metals is discussed in terms of various free energies of formation of the oxides, diffusivities of metals in the alloy, dissolution of oxygen in the alloy (internal oxidation) and solid solubility between oxides.
The oxidation behaviour of alloys in single as well as mixed gases is reviewed, including oxygen, air, and gases from sulphur, carbon, halogens and nitrogen.
Besides mixed gases, oxidation in complex environments of liquid deposits (hot corrosion) and erosive conditions is also considered.
The authors have written an excellent book reflecting their expertise and enthusiasm. Throughout the text, they diligently present examples of various aspects of high temperature oxidation of metals and alloys, and provided references to reviews for interested readers. A good balance is maintained between comprehensive and informative content. There are some minor criticisms. About 80% of the references are more than a decade old and ought to be updated. The unit of temperature is always expressed in Celsius, except for Figures 2.8, 4.14 and 4.15 where it is in Kelvin. Strictly speaking, the title of the book should include alloys and not just metals.