TABLE OF CONTENTS For the materials scientist one of the more important set of properties is that associated with surfaces and interfaces. This chapter treats their thermodynamic aspects. The excess free energy associated with interfaces provides a driving force for a variety of kinetic processes. These relations are developed quantitatively. Two contrasting approaches to the concept of the surface or interface, those of Gibbs and Guggenheim, are described, and applied to the phenomenon of adsorption in this chapter. Also, the various types of interfaces are investigated briefly and expressions governing their local equilibria are developed. Finally, applications are made of these concepts to some important problems in materials science.
Let us perform a thought experiment as follows. Separate a solid crystal into two halves along some plane (say plane A), parallel to a crystal plane. The separation plane A is chosen so as not to contain lattice points nor equilibrium positions of atoms. In the approximation where the cohesive energy is given by a sum over bond energies, the energy difference, energy of original solid minus energy of resulting halves, is then equal to the sum of the energies of the bonds that intersect the separation plane A in the original solid. The specific surface energy, e s, per unit area of surface, in this approximation is then one-half of the negative of the bond energy sum over the bonds intercepting unit area of the separation plane A. This follows from Gibbs definition of a specific...
