Some Fundamental Aspects of Interface Thermodynamics

By changing 6, the surface planes (hm) may become strained or even reconstruct. We conclude that, given P and T, the boundary composition Nb depends on a) the chemical potential of the components in the adjacent phases and b) the orientation o. In equilibrium, 8G = 8Gb = 0 which determines, at any given P, T, and /xh the set 6 (equ). In other words, we can formally express the equilibrium interface state (i.e., structure, strain, composition) as 

As has already been mentioned in Chapter 3, we may discuss the interface thermodynamics and in particular the degrees of freedom of the interface from a purely phenomenological point of view. We then introduce instead of the Miller indices in addition to the three microscopic degrees of freedom related to the vector rap two 

Let us extend these relations to the equally important case of coherent interfaces, lb do so, it is necessary to include the strain energy of the a and p phases. To this end, we formulate the thermodynamic relations in terms of SE s (A , V) [W.C. Johnson, H. Schmalzried (1992)]. Under the condition of coherency, the number of lattice sites is conserved. Instead of Eqn. (10.7), we obtain 

We note that fik is sometimes called the diffusion potential of component k in the metal physics literature. 

In order to determine the equilibrium state of systems including coherent interfaces, the conditions of thermal, chemical, and mechanical equilibrium have to be met, that is, for the first two 

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The aqueous corrosion and passivation of metal surfaces involve electrochemical processes at the electrode-electrolyte interface. Like for all chemical reactions, the two aspects of equilibrium and kinetics have to be treated. Thermodynamic data give an important first insight into layer formation. They have been used to compose potential-plT diagrams for all elements and thus for all metals [26,27]. In Chapter 1 of this book on the fundamentals of corrosion, passivity of iron has been mentioned and the calculation of some of the lines based on thermodynamic data has been described. Here a more detailed description of foe potential-pH diagrams of iron and copper are presented. 

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