Metal characterization techniques

For applied work, an optical characterization technique should be as simple, rapid, and informative as possible. Other valuable aspects are the ability to perform measurements in a contactless manner at (or even above) room temperature. Modulation Spectroscopy is one of the most usehil techniques for studying the optical proponents of the bulk (semiconductors or metals) and surface (semiconductors) of technologically important materials. It is relatively simple, inexpensive, compact, and easy to use. Although photoluminescence is the most widely used technique for characterizing bulk and thin-film semiconductors. Modulation Spectroscopy is gainii in popularity as new applications are found and the database is increased. There are about 100 laboratories (university, industry, and government) around the world that use Modulation Spectroscopy for semiconductor characterization. 

The STEM Is Ideally suited for the characterization of these materials, because one Is normally measuring high atomic number elements In low atomic number metal oxide matrices, thus facilitating favorable contrast effects for observation of dispersed metal crystallites due to diffraction and elastic scattering of electrons as a function of Z number. The ability to observe and measure areas 2 nm In size In real time makes analysis of many metal particles relatively rapid and convenient. As with all techniques, limitations are encountered. Information such as metal surface areas, oxidation states of elements, chemical reactivity, etc., are often desired. Consequently, additional Input from other characterization techniques should be sought to complement the STEM data. 

The metallic component of HCK catalysts provides hydrogenation, dehydrogenation, hydrogenolysis, and isomerization. The number and nature of reactive hydrogen species created by the interaction of a bifunctional catalyst with hydrogen is not well understood [103], on the other hand, neither the action of those species on the catalytic sites is understood. The main limitation in this understanding is the dynamic character of the interaction however, now that in situ characterization techniques are becoming available, research would soon defeat the limitations. 

The types of macrocycles most studied in which the active metal center is believed to be retained include Co, Fe, Ru porphyrins and related macrocycles. In these studies the optimal pyrolysis temperature is often reported to be between 400-800 °C. Above these temperatures, the active site begins to be destroyed, and activity decreases.49 An array of characterization techniques have been used to support these claims. XPS analysis has demonstrated that at the highest activity of samples, the surface composition of metal and nitrogen is also at its highest.78,96 Above the optimal treatment temperature, nitrogen and metal begin to disappear from the surface. Furthermore, Mossbauer spectroscopy and XAS have been used to... 

Transmission electron microscopy (TEM) is a powerful and mature microstructural characterization technique. The principles and applications of TEM have been described in many books [16 20]. The image formation in TEM is similar to that in optical microscopy, but the resolution of TEM is far superior to that of an optical microscope due to the enormous differences in the wavelengths of the sources used in these two microscopes. Today, most TEMs can be routinely operated at a resolution better than 0.2 nm, which provides the desired microstructural information about ultrathin layers and their interfaces in OLEDs. Electron beams can be focused to nanometer size, so nanochemical analysis of materials can be performed [21]. These unique abilities to provide structural and chemical information down to atomic-nanometer dimensions make it an indispensable technique in OLED development. However, TEM specimens need to be very thin to make them transparent to electrons. This is one of the most formidable obstacles in using TEM in this field. Current versions of OLEDs are composed of hard glass substrates, soft organic materials, and metal layers. Conventional TEM sample preparation techniques are no longer suitable for these samples [22-24], Recently, these difficulties have been overcome by using the advanced dual beam (DB) microscopy technique, which will be discussed later. 

Colloidal nanoparticles can be employed as heterogeneous catalyst precursors in the same fashion as molecular clusters. In many respects, colloidal nanoparticles offer opportunities to combine the best features of the traditional and cluster catalyst preparation routes to prepare uniform bimetallic catalysts with controlled particle properties. In general, colloidal metal ratios are reasonably variable and controllable. Further, the application of solution and surface characterization techniques may ultimately help correlate solution synthetic schemes to catalytic activity. 

The present chapter begins with a brief overview of metallic corrosion and mechanisms of corrosion control. Methods of evaluating polymer performance and electrochemical characterization techniques are discussed. Barrier and adhesion aspects of corrosion control are reviewed, and some critical issues needing further study are outlined. 

The set of results from TPR is consistent with the interpretations made so far, based on other characterization techniques used. In aU cases, the reduction in tin oxides occurs at temperatures much lower than those in the literature, where values above 900 K are reported for Sn02 [59]. The selectivity of the preparation reaction leads to a close relationship between M and Sn atoms transition metal atoms generate atomic hydrogen by dissociative adsorption, these hydrogen atoms being able to reduce tin oxides closely related to transition metals. Thus, the reduction temperature of the transition metal is the one that controls the global reduction process. As Pt is the metal that can be reduced most easily, the PtSn-BM catalyst exhibits the highest reducibiUty (lower reduction temperature) of aU the bimetalUc systems studied. 

If a correlation between the nature of the various sites and their catalytic activities and/or selectivities has to be established, methods for characterizing the different basicities will be required. Therefore, in the following sections, we discuss the methods for preparation of alkaline earth metal oxides as well as the principal characterization techniques used to evaluate their basicities. 

The mechanical properties of PLA rely on the stereochemistry of insertion of the lactide monomer into the PLA chain, and the process can be controlled by the catalyst used. Therefore, PLAs with desired microstructures (isotactic, heterotactic, and S3mdiotactic) can be derived from the rac- and W50-Iactide depending on the stereoselectivity of the metal catalysts in the course of the polymerization (Scheme 15) [66]. Fundamentally, two different polymerization mechanisms can be distinguished (1) chain-end control (depending on stereochemistry of the monomer), and (2) enantiomorphic site control (depending on chirality of the catalyst). In reality, stereocontrolled lactide polymerization can be achieved with a catalyst containing sterically encumbered active sites however, both chain-end and site control mechanisms may contribute to the overall stereocontrol [154]. Homonuclear decoupled NMR analysis is considered to be the most conclusive characterization technique to identify the PLA tacticity [155]. Homonuclear... 

All catalytic samples were submitted to a series of standard characterization techniques, summarized in Table 9.1. It should be underlined that the E-cat sample proved to be a nonpure equilibrium sample, but a blend of catalysts, as obvious from the standard characterization results. It should also be noticed that the artificial deactivated samples were prepared to contain 50% of the E-cats metals concentration. This is a compromise in order to limit the exaggeration of the metal effects on the lab-deactivated samples. Nevertheless, the undesired effects are still overestimated especially when high metal concentrations are introduced on the catalysts. As obvious from Table 3.1, the losses of the specific surface areas on the ADV-CPS samples are higher than the losses on the corresponding CPS samples. This is an indication that the deactivation is more severe when the ADV-CPS is applied. This was a rather expected observation considering the applied procedures parameters (increment of temperature in the ADV-CPS protocol). Moreover, it seems that the... 

We have briefly covered some of the important developments in structural characterization techniques. There are many other techniques such as Mossbauer spectroscopy, positron annihilation and Rutherford backscattering which have wide applications. Mossbauer spectroscopy is specially useful to investigate different oxidation states, spin-states and coordinations of metal ions, phase transitions, magnetic ordering. 

With the ability to obtain information about the concentrations of various types of metal surface sites in complex metal nanocluster catalysts, HRTEM provides new opportunities to include nanoparticle structure and dynamics into fundamental descriptions of the catalyst properties. This chapter is a survey of recent HRTEM investigations that illustrate the possibilities for characterization of catalysts in the functioning state. This chapter is not intended to be a comprehensive review of the applications of TEM to characterize catalysts in reactive atmospheres such reviews are available elsewhere (e.g., 1,8,9 )). Rather, the aim here is to demonstrate the future potential of the technique used in combination with surface science techniques, density functional theory (DFT), other characterization techniques, and catalyst testing. 

Standardized characterization techniques have been well developed for metallic catalysts and acidic-type catalysts. No such standard techniques have yet emerged for characterizing supported oxide or sulfide catalysts, with few exceptions and especially how these may relate to catalyst activity. Thus, we are not at the stage where we can discuss turnover numbers or facile versus demanding reactions for these catalysts at the present time. 

Although several metal-containing heterocyclic compounds (such as porphyrins, phthalocyanines, naphthenates) are present in oil fractions most of the bench-scale research has been based on relatively rapid Ni, V, or Ni/V deposition procedures in which experimental FCC formulations have been artificially metal contaminated with solutions of Ni and/or V naphthenate dissolved in benzene (or toluene) (24). Metal levels in these novel FCC are usually above 0.5% that is well above the concentration that today exist on equilibrium FCC, see Figure 1. High metal concentration facilitate the study and characterization of Ni and V effects by modern characterization techniques such as X-ray photoelectron spectroscopy (XPS), Laser Raman spectroscopy (LRS), X-ray diffraction (XRD), electron microscopy, secondary ion mass spectrometry (SIMS), and 51V nuclear magnetic resonance (NMR). 

Polycrystalline Ni-Sb alloys, unsupported Sb-loaded Ni powders, artificially contaminated as well as equilibrium FCC (from a heavy oil cracker) have been studied using X-ray diffraction (XRD), Auger spectroscopy and x-ray photoelectron spectroscopy (XPS) by workers at Phillips in what was one of the first examples of a multi-characterization technique approach to FCC study (39,40). XPS results have indicated that in an equilibrium FCC, 50 to 80% of the surface Sb and 30% to 50% of the surface Ni could be reduced to metal. This XPS data suggested that Ni and Sb were present on at least two different sites (that can be differentiated by their reducibility at 500°C/H2) and that reduction caused a twofold increase in the Ni/Sb ratio due to greater Ni dispersion. 

Time-Resolved Laser-Induced Incandescence (by Prof. Alfred Leipertz et al.) introduces an online characterization technique (time-resolved laser-induced incandescence, TIRE-LII) for nano-scaled particles, including measurements of particle size and size distribution, particle mass concentration and specific surface area, with emphasis on carbonaceous particles. Measurements are based on the time-resolved thermal radiation signals from nanoparticles after they have been heated by high-energetic laser pulse up to incandescence or sublimation. The technique has been applied in in situ monitoring soot formation and oxidation in combustion, diesel raw exhaust, carbon black formation, and in metal and metal oxide process control. 

The activity data indicate that the state of Pt desired in the most active alkane dehydrocyclization is not the form that is easily detected by most characterization techniques. Thus, the catalysts where crystalline Pt is easily detected, either as the metal or the alloy, are usually not the optimum catalysts from the point of view of activity. It appears that for a catalyst utilizing an acidic alumina support, alloy formation is not desirable. Likewise, a surface tin concentration that decreases acidity to a significant extent is not desirable. 

In bulk heterojunction solar cells, the metal/semiconductor interface is even more complex. Now the metal comes into contact with two semiconductors, one p-type (typically the polymer) and one n-type (typically the fullerene) semiconductor. A classical electrical characterization technique for studying the occurrence of charged states in the bulk or at the interface of a solar cell is admittance spectroscopy. If a solar cell is considered as a capacitor with capacitance C, the complex admittance Y is given by... 

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