Ex-situ techniques

A variety of other techniques have been used to investigate ion transport in conducting polymers. The concentrations of ions in the polymer or the solution phase have been monitored by a variety of in situ and ex situ techniques,8 such as radiotracer studies,188 X-ray photoelectron spectroscopy (XPS),189 potentiometry,154 and Rutherford backscatter-ing.190 The probe-beam deflection method, in which changes in the density of the solution close to the polymer surface are monitored, provides valuable data on transient ion transport.191 Rotating-disk voltammetry, using an electroactive probe ion, provides very direct and reliable data, but its utility is very limited.156,19 193 Scanning electrochemical microscopy has also been used.194... 

STM, X-ray reflectivity, and AFM are excellent in situ techniques for studying surface topography and morphology. Scanning electron microscopy is a useful ex situ technique. 

Currently, most remediation projects are carried out using ex situ technologies, both in the U.S. and in Europe. However, there is an increasing trend toward the application of in situ technologies because of their considerable advantages over ex situ techniques, such as less disturbance of the site, lower treatment costs, and so on. 

The various examples discussed above and several others, not mentioned in this necessarily incomplete chapter, demonstrate that XPS and also UPS assist and improve our understanding of the electrode/electrolyte interface and of electrochemical reactions. XPS, UPS and other ex situ techniques will continue to play a key role in providing information about the structure and composition of the electrochemical interface on a microscopic scale. 

In order to put the various ex situ techniques on a safer basis, the effects of electrode emersion and transfer deserve further clarification. Preferably those techniques which can be applied in both environments, in situ as well ex situ, will serve this purpose. 

It is evident from the above discussion that the study of complex electrochemical mechanisms involving homogeneous processes has reached a level at which a reasonably complete analysis can be carried out. By contrast, complex processes taking place purely through surface adsorbed intermediates have proved far less easy to explore by the type of study referred to above and understanding such processes in detail has led to the development of the large array of in situ and ex situ techniques discussed in this book. 

These ex situ techniques require ultra high vacuum (U H V) to operate since ... 

The growth mechanisms of two typical materials, ZnS and PbS, have been studied by AFM by both in situ and ex situ techniques.91013-17 An AFM liquid cell was used for the in situ studies for comparison with films grown with the SILAR equipment. 

A large variety of tools, utilizing both chemical and physical methods, are available to the experimentalist for rate measurements. Some can be classified as ex-situ techniques, requiring the removal and analysis of an aliquot of the reacting mixture. Other, in-situ, methods rely on instantaneous measurements of the state of the reacting system without disturbance by sample collection. 

As an ex situ technique for structural information on surfaces, STM is an excellent complement to the standard electron and ion diffraction probes of surface order. The STM method can identify both short range order and long range periodicity, as well as disordered surface layers (e.g., images of sorbic acid on Highly Ordered Pyrolitic Graphite (HOPG), vida infra). In contrast,... 

There are a wide range of bioremediation technologies either in use or proposed for use on oil/gasoline-contaminated land [301, 319], and these can be divided into two broad groups. In situ techniques treat the contamination at the site of the pollution event, whereas ex situ techniques remove the contamination from the ground and transfer it to another location for treatment. The use of in situ treatment is often preferable in terms of financial considerations, due to the cost of moving large quantities of soil [20]. Some novel approaches to the problem of hydrocarbon contamination of contaminated aqueous-solid phase environments is the use of (1) gas-liquid foams to enhance in situ bioremediation, and (2) biostimulation, as follows. 

After the tests, Djilali s group used mathematical assumptions and equations to correlate the intensity of the dye in the image with the depth in the gas diffusion layer. With this method they were able to study the effect of compression on diffusion layers and how fhaf affects water transport. Water removal in a flow charmel has also been probed with this technique and it was observed that, with a dry DL slug, formation and flooding in the FF channels followed the appearance and detachment of water droplets from the DL. Even though this is an ex situ technique, it provides important insight into water transport mechanisms with different DLs and locations. 

The early indications and correlations of catalyst surface impacts on performance were obtained via ex situ techniques in which the catalyst is removed from the actual operating system. The catalysts studied were either... 

During a full-scale remediation of 10,000 tons of contaminated soil and sludge at a Louisiana petroleum refining facility, costs were estimated at 40 per ton. The cleanup involved of both in situ and ex situ techniques (D10103H, pp. 23-15). 

Erdey-Gruz, 1048, 1306 1474 Erschler, 1133, 1134, 1425 Ethylene oxidation, anodic, 1052 1258 Exchange current density, 1049, 1066 correction of, 1069 definition, 1053 electrocatalysis and, 1278 impedance and, 1136 interfacial reaction, 1047 and partly polarizable interface, 1056 Excited states, lifetime, 1478 Exothermic reaction, 1041 Ex situ techniques, 785, 788, 1146... 

The techniques used in studying interfaces can be classified in two categories in situ techniques and ex situ techniques. In situ methods are those where a surface is probed by one or several techniques while immersed in solution and under potential control. In contrast, in ex situ methods, an electrochemical experiment is first carried out. Then the electrode is removed from solution and examined by one or several spectroscopic techniques, which generally require ultrahigh vacuum (UHV) conditions. Figures 6.10 and 6.11 show some of the most common ex situ and in situ techniques applicable to the study of the metal/solution interface. 

Two of the most common UHV-spectroscopic methods used in electrochemistry are briefly described next, and Fig. 6.10 lists other ex situ techniques, which can be reviewed in the literature by the inquisitive student. 

Define the following terms used in Section 6.2 (a) single crystal, (b) polycrystalline solid, (c) in situ technique, (d) ex situ technique, (e) diffraction pattern, (f) infrared radiation, (g) s-polarized and p-polarized light, and (h) radioactive isotope. (Gamboa-Aldeco)... 

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