Thermodynamics of Metals and Alloys

In Chapter 1, the assertion was made that Elements are materials, too We will use this fact to begin our description of equilibrium transformation processes in materials. Not all elements are metals, of course, but most of the elements that are of interest from a materials application standpoint are. 

1 Gibbs Phase Rule. The goal of this section section is to predict what wiU happen to our element when it is subjected to changes in those variables that we can manipulate, usually temperature and pressure. For example, what happens when we heat a sample of pure sulfur It will probably melt at some point. What happens when we subject carbon to very high pressures We predict that diamond will form. We seek quantitative explanations of these phenomena and an ability to predict under what conditions they will occur. 

Consider a single component, A. A component is a chemical constituent (element or compound) that has a specified composition. For simplicity, we will assume that component A is an element, but we will see in subsequent sections that it can be anything that does not undergo a chemical change, including compounds. But for now, we have an element. A, that can exist in two phases, which we will designate a and p. A phase is defined as a homogeneous portion of a system that has uniform physical and 

Phase a and phase are in equilibrium with one another. What does this mean First of aU, it means that although there is probably an exchange of atoms between the two phases (i.e., some of the sohd phase a is melting to form and some of the liquid phase /i is solidifying to form a) these processes are occurring at essentially equal rates such that the relative amounts of each phase are unchanged. This is known as a dynamic equilibrium. In terms of intensive variables, equilibrium means that 

for a one-component system containing two phases in equilibrium, we have three thermodynamic conditions of equilibrium [Eqs. (2.14)-(2.16)] and four unknown parameters, Ta, Pa, Pp, and Pp. If we arbitrarily assign a value to one of the parameters, we can solve for the other three (three equations, three unknowns). 

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Specific Features of the Thermodynamics of Metal and Alloy Phase Formation and Degradation... 

Selected Values, Thermodynamic Properties of Metals and Alloys, Minerals Research Laboratory, University of California, Berkeley. 

Corrosion is the deterioration of a material by reaction with its enviromnent. Although the term is used primarily in conjunction with the deterioration of metals, the broader definition allows it to be used in conjunction with all types of materials. We will limit the description to corrosion of metals and alloys for the moment and will save the degradation of other types of materials, such as polymers, for a later section. In this section, we will see how corrosion is perhaps the clearest example of the battle between thermodynamics and kinetics for determining the likelihood of a given reaction occurring within a specified time period. We will also see how important this process is from an industrial standpoint. For example, a 1995 study showed that metallic corrosion costs the U.S. economy about 300 billion each year and that 30% of this cost could be prevented by using modem corrosion control techniques [9], It is important to understand the mechanisms of corrosion before we can attempt to control it. 

Hultgren et al, "Selected Values of Thermodynamic Properties of Metals and Alloys , J. Wiley Sons, NY (1963), Supplements available from the Univ of California, Berkeley (1972)... 

Hultgren, R. H., Orr, R., Anderson, P., and Kelley, K. K. (1963). Selected Values for the Thermodynamic Properties of Metals and Alloys. New York John Wiley-Books Demand UMI. 

R. Hultgren, R. L. Orr, and K. K. Kelley, "Supplement to Selected Values of Thermodynamic Properties of Metals and Alloys, C-Ta table, December, 1965. 

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