Importance of In Situ Studies

They have also employed an in-situ cell for carrying out these experiments. Again they studied nitrite and chromate passivated films. The results obtained in this case were significantly different from the ex-situ measurements with the spectral features for both nitrite and chromate passivated films being quite similar. This surprising similarity underscores the importance of in-situ measurements. 

In all of these studies, it is clear that scattering from water and/or electrolyte plays a crucial role, once again underscoring the importance of in-situ measurements. 

These results outline the importance of in situ techniques to study the sulfidation process. 

The most important methods used in in-situ studies of electrode surfaces are various modifications of reflection spectroscopy in the ultraviolet through infrared regions. For electrochemical applications, the specular reflection (at smooth electrode surfaces) is much more important than the diffuse reflection from matt surfaces. The reflectivity, R, of the electrode/ electrolyte interface is defined by ... 

An elegant example of the application of in situ FTIR to the study of absorbed species is provided by the work of Corrigan and Weaver (1986). As well as being extremely interesting in terms of the system under study, the work of these authors represents an important step towards the further development of in situ FTIR. If the approach is to attain its full potential, then it must be capable of providing quantitative as well as qualitative information. 

It should be apparent from the discussion above that STM possesses tremendous potential for the elucidation of processes at the electrode-electrolyte interface. Particularly promising are the prospects for in situ studies of electrode surfaces. Vibrational, electronic, and structural information is obtainable on an atomic scale for electrodes of importance to basic electrochemical studies. Although relatively few electrochemical applications have been demonstrated to date, the availability of commercial instrumentation (c.f.,95-97) ought to increase the accessibility of STM to electrochemists and widespread use of the technique is expected in the near future. 

Ideally, the site characterization study has defined the vertical and horizontal extent of the contamination. Contoured site maps showing the (three-dimensional) distribution of the contaminants allow identification of areas that require extensive restoration, or may be allowed to be monitored to closure under natural attenuation. Knowledge of how much contamination exists and its location is the important first step in the remediation process. Evaluation of these data will permit consideration of the various remediation remedies available. Where the contaminant is contained within the shallow (<6 m) unsaturated zone and is recalcitrant (not readily biodegradable), excavation for off-site treatment or disposal may be the most expeditious procedure. Alternatively, depending on the contaminant, a variety of in situ procedures, including bioremediation, air sparging, soil vapor extraction, and fixation, may be applicable. 

Table 1 lists representative examples of the application of in situ hybridization, including FISH, to studies that use chromosome preparations and interphase nuclei (4,5). FISH is superior to in situ hybridization with an enzymatic probe because it provides finer resolution and higher signal intensity. This is especially important when the localization of a gene within a specific chromosome band is to be established. 

A linear correlation is obtained between bitumen extraction with the paddle mill and the adhesion tension against water saturated pyrophyllite. That the degree of water saturation of the pyrophyllite is important in explaining the difference between the 2 extraction processes indicates that it will be necessary to study each process in terms of the relevant adhesion tensions. These results demonstrate that adhesion tension is the most important parameter found to date in determining the degree of separation in the presence of surfactants. Measurements of adhesion tension between surfactant solutions and minerals similar to those found in tar sand may be of considerable value in studies of surfactant utility in both aqueous-surfactant, solvent-aqueous-surfactant and in situ extraction processes. In addition, if appropriate model situations can be developed, measurements of adhesion tension may be useful in upgrading bitumen-water-clay emulsions obtained by a variety of in situ and heavy oil recovery processes. 

Finally, Nora McLaughlin and Marco Castaldi (Columbia University, USA) provide a review of in situ techniques to study catalytic reaction mechanisms. Because the catalyst is not static but can change during a reaction, it is important to be able to characterize the surface at reaction conditions. In addition, identification of reaction intermediates can help us understand the reaction mechanism. The authors review surface measurement techniques and recent developments in spectroscopy that can help us examine these catalytic properties. 

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