Metal oxide adhesion
The strength of metal oxide adhesion effectively determines the wetting of the metal-oxide interface. The strength of this adhesion is important, for instance, in production of light bulbs and fiber-matrix composites that depend on the optimization of wetting to create metal-ceramic interfaces. The strength of adhesion also determines the extent of dispersion on catalytically active metal. Metal oxide adhesion is important for applications like complementary metal oxide semiconductor devices. These devices make possible the high packing densities of modern integrated circuits.
The majority of the entropy of metal oxidation reactions is in the O2(g) because the gaseous oxygen molecules have translation entropy which is not present in the solid phase. For this reason, the change in entropy (ΔS) for oxidation is almost always negative because this reaction generates less disorder by creating a solid oxide layer from the solid metal and gaseous oxygen. The standard state change of enthalpy is relatively independent and thus the gradient of the change in Gibbs free energy as a function of temperature is linear. This dictates that an oxide becomes less thermodynamically stable with increasing temperature.
An important distinction between equilibrium wetting and non-equilibrium wetting is that the non-equilibrium condition occurs when a chemical reaction is taking place. This non-equilibrium wetting is an irreversible thermodynamic process that accounts for the changes of the chemical potential when forming a new boundary phase, such as an oxide.
The ideal work of separation Wsep is the reversible work needed to separate the interface into two free surfaces. Important as a state function depending on the mechanical properties. It is referred to as ideal because when the two free surfaces create an interface, the concentration of the interface will only be identical to the bulk at the instant the surface is created. In order to reach chemical equilibrium, the process of diffusion will take place which will increase any measurement of the work of separation. The work of adhesion is the reversible free energy change for making free surfaces from interfaces. It is represented by the equation:
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