Specific Techniques

Good measurement practices (GMPs) describe operations specific to a technique. In general, GMPs provide instructions for maintaining, calibrating, and using the equipment and instrumentation that form the basis for a specific technique. For example, a GMP for a titration describes how to calibrate a buret (if nec-... 

The interested reader is referred to numerous other compendiums of information on this broad topic (1 5). Particularly noteworthy are the series of Fundamental Reviews on specific techniques that appear biennially in the JinalyticalChemistty. These Reviews report developments in specific fields... 

Surface Area. Overall catalyst surface area can be determined by the BET method mentioned eadier, but mote specific techniques are requited to determine a catalyst s active surface area. X-ray diffraction techniques can give data from which the average particle si2e and hence the active surface area may be calculated. Or, it may be necessary to find an appropriate gas or Hquid that will adsorb only on the active surface and to measure the extent of adsorption under controUed conditions. In some cases, it maybe possible to measure the products of reaction between a reactive adsorbent and the active site. Radioactively tagged materials are frequentiy usehil in this appHcation. Once a correlation has been estabHshed between either total or active surface area and catalyst performance (particulady activity), it may be possible to use the less costiy method for quaHty assurance purposes. 

Finally, it cannot be overemphasized that despite instmmental measurements and data manipulations, it is the perception of the eye that still is the final arbiter as to whether or to what degree two colors match. Instmmental methods do serve well for the typical industrial task of maintaining consistency under sufficiently weU-standardized conditions however, a specific technique may not serve in extreme or unusual conditions for which it was not designed. 

A multitude of analysis techniques and models have been developed to aid in performing these four steps (Figure 7). Many references exist for specific methods, and several recent publications give specific advice and how to details for the various techniques. You will not have to select specific techniques—your QRA team will do that. But you must appreciate the types of results available from each class of techniques. 

The cost of performing the hazard identification step depends on the size of the problem and the specific techniques used. Techniques such as brainstorming, what-if analyses, or checklists tend to be less expensive than other more structured methods. Hazard and operability (HAZOP) analyses and failure modes and effects analyses (FMEAs) involve many people and tend to be more expensive. But, you can have greater confidence in the exhaustiveness of HAZOP and FMEA techniques—their rigorous approach helps ensure completeness. However, no technique can guarantee that all hazards or potential accidents have been identified. Figure 8 is an example of the hazards identified in a HAZOP study. Hazard identification can require from 10% to 25% of the total effort in a QRA study. 

After XPS, AES is the next most widely used surface-analytical technique. As an accepted surface technique AES actually predates XPS by two to three years, because the potential of XPS as a surface-specific technique was not recognized immediately by the surface-science community. Pioneering work was performed by Harris [2.125] and by Weber and Peria [2.126], but the technique as it is known today is basically the same as that established by Palmberg et al. [2.127]. 

The reasons AES is a surface-specific technique have been given in Sect. 2.1.1, with reference to Fig. 2.2. The normal range of kinetic energies recorded in an AES spectrum would typically be from 20 to 1000 eV, corresponding to inelastic mean free path values of 2 to 6 monolayers. 

The book provides a comprehensive set of examples and case studies that cover a wide variety of process plant situations. Some of these are intended to illustrate the range of situations where human error has occurred in the CPI (see Appendix 1). Other examples illustrate specific techniques (for example. Chapter 4 and Chapter 5). Chapter 7 contains a number of extended case studies intended to illustrate tedmiques in detail and to show how a range of different techniques may be brought to bear on a specific problem. 

There are many other specific techniques applicable to particular situations, and these should often be investigated to select the method for developing the vapor-liquid relationships most reliable for the system. These are often expressed in calculation terms as the effective K for the components, i, of a system. Frequently used methods are Chao-Seader, Peng-Robinson, Renon, Redlich-Kwong, Soave Redlich-Kwong, Wilson. 

The capital cost for implementing a vibration-based predictive maintenance program will range from about 8,000 to more than 50,000. Your costs will depend on the specific techniques desired. 

The success of a specific technique will depend on whether, as a by-product of the technique, sizable stress levels in the plastic product may result. Guarding against potential stresses in the assembly is a very important aspect of complete product design. There are many techniques that provide assembling all kinds of products. Each have technical and/or cost advantages and limitations. Examples of a few are reviewed in this section with more information in Chapter 3, BASIC FEATURE and FEATURE INFLUENCING PERFORMANCE. 

While the measurement of the work function is losing importance in UHV studies (because other more specific techniques have been developed), such a quantity retains its role in electrochemistry because it is intimately related to the electrode potential. A major problem is thus the dichotomy between samples for which is known but not and vice versa. This is one of the major obstacles to the unambiguous interpretation of Eam0- plots. However, this point has been recently addressed in a few cases and the outcome has allowed us to clarify some debated aspects. It is now well established that within a major group of sp- and sd-metals AX (the decrease in 4> as the metal comes in contact with the solution) increases as

[Pg.190]

The dropping electrode, in partieular used with mercury and with amalgams, has been frequently employed in kinetic studies [66But3]. Data obtained with this electrode/method are labelled DME, if no specific technique is applied that is more helpful in qualifying the obtained data. 

The system used in the simulations usually consists of solid walls and lubricant molecules, but the specific arrangement of the system depends on the problem under investigation. In early studies, hard spherical molecules, interacting with each other through the Lennard-Jones (L-J) potential, were adopted to model the lubricant [27], but recently we tend to take more realistic models for describing the lubricant molecules. The alkane molecules with flexible linear chains [28,29] and bead-spring chains [7,30] are the examples for the most commonly used molecular architectures. The inter- and intra-molecular potentials, as well as the interactions between the lubricant molecule and solid wall, have to be properly defined in order to get reliable results. Readers who intend to learn more about the specific techniques of the simulations are referred to Refs. [27-29]. 

Being cut from tires, the rubber samples in this work cannot always be studied using standard test procedures. The specific techniques used to measure rubber aging have been described in detail elsewhere and are summarized below [2]. The same techniques have been used to evaluate rubber aging in both field and the laboratory oven-aging studies. For reference. Figure 34.2 shows a diagram of the internal components of a radial-ply tire. 

AES is a useful element-specific technique for quantitative determination of the elemental composition of a surface. Although some chemical information is available in principle, the technique is used largely for elemental analysis. Electron beam damage can decompose organic adsorbates and cause damage, particularly on insulating surfaces. In some cases, the beam can reduce metal oxides. 

Hyper-Raman spectroscopy is not a surface-specific technique while SFG vibrational spectroscopy can selectively probe surfaces and interfaces, although both methods are based on the second-order nonlinear process. The vibrational SFG is a combination process of IR absorption and Raman scattering and, hence, only accessible to IR/Raman-active modes, which appear only in non-centrosymmetric molecules. Conversely, the hyper-Raman process does not require such broken centrosymmetry. Energy diagrams for IR, Raman, hyper-Raman, and vibrational SFG processes are summarized in Figure 5.17. 

The availability of thermodynamically reliable quantities at liquid interfaces is advantageous as a reference in examining data obtained by other surface specific techniques. The model-independent solid information about thermodynamics of adsorption can be used as a norm in microscopic interpretation and understanding of currently available surface specific experimental techniques and theoretical approaches such as molecular dynamics simulations. This chapter will focus on the adsorption at the polarized liquid-liquid interfaces, which enable us to externally control the phase-boundary potential, providing an additional degree of freedom in studying the adsorption of electrified interfaces. A main emphasis will be on some aspects that have not been fully dealt with in previous reviews and monographs [8-21]. 

Therefore, the use of several specific techniques while implementing the method of semiconductor sensors makes it feasible to detect and analyze emission of oxygen atoms at initial stage of metal oxidation although in case of silver it should be noted that there are no phase of silver oxide formed due to its instability at such conditions [57]. Rather, the absorption of oxygen by silver would be related to dissolution and internal oxidation. 

Thereby, the application of highly sensitive sensors jointly with several specific techniques can be recommended to study complex heterogeneous and homogeneous processes where an experimentalists are faced with an option to analyze small concentrations of active particles in gaseous phase. 

This chapter will provide an introduction to each of the technologies described and the use of the specific technique for analysis of samples. It will also provide additional references for other samples and recommendations for further reading on a specific technique. 

IBA is a term that involves several specific techniques which we will consider in turn, namely ... 

Since ion beams (like electron beams) can be readily focussed and deflected on a sample so that chemical composition imaging is possible. The sputtered particles largely originate from the top one or two atom layers of a surface, so that SIMS is a surface specific technique and it provides information on a depth scale comparable with other surface spectroscopies. 

The other technique is HREELS (high resolution EELS) which utilises the inelastic scattering of low energy electrons in order to measure vibrational spectra of surface species. The use of low energy electrons ensures that it is a surface specific technique, and is often chosen for the study of most adsorbates on single crystal substrates. 

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