Technical interfaces meaning

In electrochemistry an electrode is an electronic conductor in contact with an ionic conductor. The electronic conductor can be a metal, or a semiconductor, or a mixed electronic and ionic conductor. The ionic conductor is usually an electrolyte solution however, solid electrolytes and ionic melts can be used as well. The term electrode is also used in a technical sense, meaning the electronic conductor only. If not specified otherwise, this meaning of the term electrode is the subject of the present chapter. In the simplest case the electrode is a metallic conductor immersed in an electrolyte solution. At the surface of the electrode, dissolved electroactive ions change their charges by exchanging one or more electrons with the conductor. In this electrochemical reaction both the reduced and oxidized ions remain in solution, while the conductor is chemically inert and serves only as a source and sink of electrons. The technical term electrode usually also includes all mechanical parts supporting the conductor (e.g., a rotating disk electrode or a static mercury drop electrode). Furthermore, it includes all chemical and physical modifications of the conductor, or its surface (e.g., a mercury film electrode, an enzyme electrode, and a carbon paste electrode). However, this term does not cover the electrolyte solution and the ionic part of a double layer at the electrode/solution interface. Ion-selective electrodes, which are used in potentiometry, will not be considered in this chapter. Theoretical and practical aspects of electrodes are covered in various books and reviews [1-9]. 

This approach will not be practical for some time to come. The fundamental properties of surfactants (micelle formation, enrichment at interfaces) mean that the activity of a surfactant will usually differ from its absolute concentration (1). Just as serious is the technical problem that current surfactant-selective electrodes suffer from response which varies with their past and recent history they are also sensitive to the concentration of nonsurfactant ions. The result is that quantitative applications use electrodes not in direct measurements relating potential to concentration, but as indicators of the end point of a titration. In this latter application, it is not important that the electrode potential be exactly reproducible, but only that the potential change sharply as the surfactant concentration changes. For the titration of an anionic surfactant with a cationic surfactant, the electrode used for end point detection can be chosen to respond to either surfactant. Because of the drift in electrode potential, titrations must be conducted to an inflection in the titration curve rather than to a specific millivolt value. Details of the potentiometric titration methods can be found earlier in this chapter. The electrodes have also been demonstrated as detectors for flow injection analysis. 

Why is it that insects like beetles can walk on water Why do the bristles of a brush immersed in water cling together as the brush is pulled out Phenomena such as these arise because of a special property of interfaces that separate two phases. Let us consider another example first. Everyone has had the experience of pouring more beverage into a cup or glass than that container could hold. In addition to the spills this causes, such an experience provides an opportunity to observe surface tension. Most liquids can be added to a vessel until the liquid surface bulges above the rim of the container. The liquid behaves as if it had a skin that prevents it —up to a point —from overflowing. Stated technically, a contractile force, which tends to shrink the surface, operates around the perimeter of the surface. This is what we mean when we talk about the surface tension of a liquid. All phase boundaries behave this way, not just liquid surfaces however, the evidence for this is more apparent for deformable liquid surfaces. 

In molecular beam epitaxy (MBE) [317], molecular beams are used to deposit epitaxial layers onto the surface of a heated crystalline substrate (typically at 500-600° C). Epitaxial means that the crystal structure of the grown layer matches the crystal structure of the substrate. This is possible only if the two materials are the same (homoepitaxy) or if the crystalline structure of the two materials is very similar (heteroepitaxy). In MBE, a high purity of the substrates and the ion beams must be ensured. Effusion cells are used as beam sources and fast shutters allow one to quickly disrupt the deposition process and create layers with very sharply defined interfaces. Molecular beam epitaxy is of high technical importance in the production of III-V semiconductor compounds for sophisticated electronic and optoelectronic devices. Overviews are Refs. [318,319],... 

Capillarity — (a) as a branch of science, it concerns the thermodynamics of surfaces and - interfaces. It is of utmost importance for - electrochemistry, e.g., treating the electrode solution interface (- electrode, - solution), and it extends to several other branches of physics, chemistry, and technical sciences [i]. The thermodynamic theory of capillarity goes back to the work of Gibbs, (b) In a practical sense capillarity means the rise or fall of a liquid column in a capillary caused by the interplay of gravity and -> interfacial tension and also phenomena like capillary condensation [ii]. 

Liquid-liquid interfacial tensions can in principle also be obtained by simulations, but for the time being, the technical problems are prohibitive. Benjamin studied the dynamics of the water-1,2-dichloroethane interface in connection with a study of transfer rates across the interface, but gave no interfacial tensions. In a subsequent study the interface between nonane and water was simulated by MD, with some emphasis on the dynamics. Nonane appears to orient relatively flat towards water. The same trend, but weaker, was found with respect to vapour. Water dipoles adjacent to nonane adsorb about flat, with a broad distribution the ordering is a few molecular layers deep. Fukunishi et al. studied the octane-water Interface, but with a very low number of molecules. Their approach differed somewhat from that taken in the simulations described previously they computed the potential of mean force for transferring a solute molecule to the interface. The interfacial tension was 57 11 mN m", which is in the proper range (experimental value 50.8) but of course not yet discriminative (for all hydrocarbons the interfacial tension with water is very similar). In an earlier study Linse investigated the benzene-water interface by MC Simulation S He found that the water-benzene orientation in the interface was similar to that in dilute solution of benzene in water. At the interface the water dipoles tend to assume a parallel orientation. The author did not compute a x -potential. Obviously, there is much room for further developments. 

The current research of corrosion phenomena appearing at the interface metal-natural environment showed that chemical re-combination of the metals to form ore-like compounds is a natural process, because the energy content of the metals and alloys is higher than that of their ores. It has to be emphasized that there are number of means of controlling corrosion. The choice of a means of corrosion control depends on economics, safety requirements, and a number of technical considerations. However, it is necessary to learn and recognize the forms of corrosion and the parameters that must be controlled to avoid or mitigate corrosion. 

Adsorption of the oligomer at the polymer-water interface in latex is accompanied by colloidal stabilizing action of the oligomer. Quantitative evaluation of the stabilizing tendency is made by means of a high speed stirring test, the general nature of which is well known in the latex industry and has been critically discussed in the technical literature (5). 

The interface between project planning and project execution is the conclusion of the contract. This means the signing of the contract worked out by the plant operator and the plant constructor stipulating aU commercial and technical project... 

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