Interface Bond Energy

According to the BOLS correlation and the band theory, the energy value of cryst(0 equilibrium is proportional to the mean cohesive energy per bond, b . That is, the interface BE shift is proportional to the local bond energy Ei . Using Eq. (30.8), one can determine the bond energy of a constituent element at the interface as follows  

The interface bond energy is and bond length d s consist of three parts A-A, B-B, and A-B interactions. The following approach gives the mean Eis [115,116]  

The last term denotes the exchange interaction between atoms A and B. Vegard s notation derives the interface lattice constant Zis [117], 

With the derived ks and is , one is able to determine the binding energy density and atomic cohesive energy, and the interface free energy is given by 

4 Binding Energy Density and Atomic Cohesive Energy 

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The adsorption of nonelectrolytes at the solid-solution interface may be viewed in terms of two somewhat different physical pictures. In the first, the adsorption is confined to a monolayer next to the surface, with the implication that succeeding layers are virtually normal bulk solution. The picture is similar to that for the chemisorption of gases (see Chapter XVIII) and arises under the assumption that solute-solid interactions decay very rapidly with distance. Unlike the chemisorption of gases, however, the heat of adsorption from solution is usually small it is more comparable with heats of solution than with chemical bond energies. 

Figure 9-1 illustrates the energy barrier to the transfer of metallic ions across the electrode interface these energy barriers are represented by two potential energy curves, and their intersection, for surface metal ions in the metallic bond and for hydrated metal ions in aqueous solution. As described in Chaps. 3 and 4, the energy level (the real potential, a. ) of interfadal metal ions in the metallic bonding state depends upon the electrode potential whereas, the energy level (the real potential, of hydrated metal ions is independent of the electrode potential. 

The reduced hardness and improved machinability are attributed primarily to the crack deflection process. It can be seen in Fig. 13.8 that the composite showed obvious particle pullout and significant crack deflection along interphase boundaries due to the weak interface bonding. The crack deflection mechanism (absorbing fracture energy and blunting crack tip) could lead to an increase in machinability. As described above, the thermal expansion... 

X-ray photoelectron spectroscopy of atomic core levels (XPS or ESCA) is a very powerful tool for characterization of the chemical surrounding of atoms in molecules. In particular, since the method is very surface sensitive, it is possible to monitor the first stages of the interface formation, i.e., in our case the interaction between individual metal atoms and the polymer. Standard core level bonding energies are well known for common materials. However, in our case, we are studying new combinations of atoms and new types of structures for which there are no reference data available. In order to interpret the experimental chemical shifts it is useful to compare with theoretical estimates of the shifts. 

The shift of the sp states towards the interface with the acidic cluster can also explains the remarkable difference between the H in the atop position adsorbed at the PtyNa20 and at the Pt4/F20 cluster. H is tilted much more towards the interface region in the case of the acidic F20 support (Figure 2). Since the Pt 6s,p states are very important in the Pt-H bonding, the hydrogen atom tries to follow the metal sp states. Therefore, the Pt 6s,p states do not only determine the Pt-H bond energy, but also influence the geometry. 

These macroscopic quantities can be related to the bond energies eaa and bb in the bulk phases and eAB at the interface by a simple nearest neighbour interaction model. Assuming that ... 

Equation (1.12) indicates that the magnitude of Wa directly reflects the intensity of interactions between A and B atoms across the common interface. Obviously, in real systems, the relation between Wa and bond energies is more complicated than equation (1.12) suggests. However, the physical meaning of Wa remains the same. 

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