Chemical potential of a material surface

The concept of chemical potential as an indicator of the tendency for mass transfer to occur in a system has been generalized to a range of physical phenomena. The issue is not so much the transfer itself, but is rather the energetics of forming or breaking chemical bonds, and the local state of the material as bonds are established or severed. In this section, several such 

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Chemical potential of a material surface it is readily calculated in terms of system parameters to be... 

The chemical potential of a curved surface is extremely critical in ceramic processing. It detemiines reactivity, tlie solubility of a solid in a liquid, tire rate of liquid evaporation from solid surfaces, and material transport during sintering. 

The term 7 7 ln p/p° is clearly the chemical potential of a surface of radius r with respect to a flat surface of the same material as standard state. It follows that the difference in chemical potential between two surfaces, where... 

As discussed above, a thermodynamically unstable surface will reduce its total surface energy by forming facets. From the point of view of kinetics, gradients in the chemical potential on a nonequilibrium surface will drive the movement of surface materials toward equilibrium. The transport mechanisms are the same as those that can operate during sintering (47) (a) surface diffusion, (b) bulk diffusion, (c) evaporation-condensation, and (d) plastic or viscous flow. 

The chemical potential of a homogeneous material (a phase) is a function of two intensive variables, usually chosen as temperature and pressure. We say that such a material has two degrees of freedom (i.e., we are free to set two intensive variables). (Note that only intensive variables count as degrees of freedom.) In addition to being able to specify a number of intensive variables equal to the number of degrees of freedom of a system, we are also at liberty to specify the size of the phase with one extensive variable. The chemical potential can be represented as a surface on a plot of p versus P and T. The condition for equilibrium between phase a and phase p is, according to Eq. (24),... 

Potentiation is appHed to a condition where one material, of relatively low toxicity, enhances the expression of toxicity by another chemical. The result may be a larger response or more severe injury than that produced by the toxic chemical alone. A particular example is an enhancement of the absorption of a material of known toxicity by a surface-active material. 

In conclusion, nanorods are a potentially interesting material, but present results still do not allow understanding of whether the nanostructure leads to an improvement of the intrinsic photocatalytic behaviour, or whether other factors (accessible surface area, enhanced adsorption, etc) are responsible for the observed differences. In ZnO nanorods have been shown quite recently by surface photovoltage spectroscopy that the built-in electrical field is the main driving force for the separation of the photogenerated electron-hole pairs.191 This indicates that the nano-order influences the photophysical surface processes after photogeneration of the electron-hole pairs. A similar effect could be expected for Titania nanorods. However, present data do not support this suggestion, mainly due to the absence of adequate photo-physical and -chemical characterization of the materials and surface processes. 

The extent to which ions, etc. adsorb or experience an electrostatic ( coulombic ) attraction with the surface of an electrode is determined by the material from which the electrode is made (the substrate), the chemical nature of the materials adsorbed (the adsorbate) and the potential of the electrode to which they adhere. Adsorption is not a static process, but is dynamic, and so ions etc. stick to the electrode (adsorb) and leave its surface (desorb) all the time. At equilibrium, the rate of adsorption is the same as the rate of desorption, thus ensuring that the fraction of the electrode surface covered with adsorbed material is constant. The double-layer is important because faradaic charge - the useful component of the overall charge - represents the passage of electrons through the double-layer to effect redox changes to the material in solution. 

Encapsulation of other material into carbon nanotubes would also open up a possibility for the applications to electrodevices. By applying the template method, perfect encapsulation of other material into carbon nanotubes became possible. No foreign material was observed on the outer surface of carbon nanotubes. The metal-filled uniform carbon nanotubes thus prepared can be regarded as a novel onedimensional composite, which could have a variety of potential applications (e.g novel catalyst for Pt metal-filled nanotubes, and magnetic nanodevice for Fe304-filled nanotubes). Furthermore, the template method enables selective chemical modification of the inner surface of carbon nanotubes. With this technique, carbon... 

The XPS mechanism, which can be used for quantitative and qualitative chemical analysis of surfaces, is based on the photoelectric effect. A monochromatic soft Mg or Al anode X-ray source is used to irradiate the surface. The absorbed X-rays ionize die core shell, and in response, the atom creates a photoelectron that is transported to the surface and escapes. The ionization potential of a photoelectron that must be overcome to escape into vacuum is the binding energy (BE) plus the work function of the material. The emitted photoelectrons have a remaining kinetic energy (KE), which is measured by using an electron analyzer. Individual elements can be identified on the basis of their BE. The resulting XP spectrum is a characteristic set of peaks for a specific element, with BE as the abscissa and counts per unit time as... 

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