Typical Examples

Products derived from the carbon element are found in most facets of everyday life, from the grimy soot in the chimney to the diamonds in the jewelry box. They have an extraordinary broad range of applications, illustrated by the following examples current in 1993. 

The assessments for the Si-Al, Si-As, Si-B, Si-C, Si-Fe, Si-N, Si-O, Si-P, Si-S and Si-Sb systems will briefly be introduced in this section. Typical examples of the database calculation results are presented as diagrams. 

The Si-As system has been reassessed based on the phase equilibrium data reported by Klemm and Pirscher [15], Ugay and Miroshnichenko [16], and Ugay et al. [17]. Arsenic solubility data measured by Trumbore [18], Sandhu and Reuter [19], Fair and Weber [20], Ohkawa et al. [21], Fair and Tsai [22], Miyamoto et al. [23] and the activity data given by Reuter [19], Ohkawa 

The new assessment for the Si-C system was primarily based on experimental SiC solubility data in liquid solution given by Scace and Slack [34], Hall [35], Iguchi [36], Kleykamp and Schumacher [37], Oden and McCune [38], and Ottem [14], Solid solubility data given by Nozaki et al. [39], Bean [40], and Newman [41] were used to determine the properties of solid solution. The eutectic composition reported by Nozaki et al. [39] and Hall [35] and peritec-tic transformation temperature determined by Scace [34] and Kleykamp [37] were also used in the thermodynamic optimization. Thermodynamic description of the SiC compound was taken from an early assessment [42]. The 

Thermodynamic properties of the Si3N4 compound were also reassessed based on the JANAF thermochemical tables [61]. 

The recent assessment for the Si-0 system by Schnurre et al. [62] was accepted in the present database. The stable phase equilibria in the Si-O system, together with the experimental data [58,63-68], is shown in Fig. 13.8. 

Catalytic activity is closely dependent on the method of preparation, so considerable attention has been focused upon new preparation methods to improve the performance of carbon-supported platinum alloy catalysts in DMFC applications. The simultaneous reduction of metal salts [86-88], microwave-assisted reactions [89, 90], micro-emulsion-based synthesis [91-93], and the reduction of single-source molecular precursors [94-99] have been used to various extents. 

Platinum electrocatalysts are dispersed as small particles on high surface area conductive supports for effective use of costly Pt. The size of platinum particles, therefore, plays an important role in the oxygen reduction kinetics for fuel cell applications, in terms of both electrocatalytic activity and practical application of catalysts. Carbon-supported platinum shows a large surface area and increased catalytic activity. Alloy catalysts with various transition metals have been employed to increase the catalytic activity and reduce the cost. Various Pt-based alloy catalysts (binary, ternary, and quaternary alloy) have been tested over the last two decades. Many researchers have reported that Pt-based alloy catalysts show not only higher activity than Pt alone, but also exhibit good performance in the ORRs in PEFCs and DMFCs [100-108]. 

Supported PtRu alloys are so far considered the best anodic materials for DMFC [109, 110], It is well known that the oxidation of methanol on platinum catalysts generates CO as an intermediate, which is a poison that adsorbs on the active sites of the catalyst. Ru forms oxygenated species at lower potentials than Pt and its presence in the catalyst promotes the oxidation of CO to CO2, through the so-called bifunctional mechanism [111, 112], 

In addition, Xin et al. [115] prepared multiwalled carbon nanotube-supported Pt (Pt/MWCNT) nanocomposites by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of a Pt ion salt in ethylene glycol solution (EG). For comparison, a Pt/XC72 nanocomposite was also prepared by the EG method. The Pt/MWCNT catalyst prepared by the EG method has a high and homogeneous dispersion of spherical Pt metal particles with a narrow particle-size distribution. 

Carbon nanotubes (CNTs) are a subject of great interest given their unique structure and excellent properties. They offer potential applications in electronic devices, catalysts, sensors, field-emission devices, and hydrogen-storage media [117-125]. The size and morphology of CNTs enable them to be a suitable catalyst support in which active metal partieles may disperse on the external walls or be 

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The nitration, sulphonation and Friedel-Crafts acylation of aromatic compounds (e.g. benzene) are typical examples of electrophilic aromatic substitution. 

The winter period corresponds, of course, to the moment in the year where the diesel fuel and home-heating oil characteristics are noticeably different. Table 5.18 gives a typical example of tbe recorded differences heating oil appears more dense and viscous than diesel fuel, while its initial and final boiling points are higher. 

Table 10.21 gives a typical example of hydrotreating a straight run (SR) gas oil. 

Figure 2 shows a typical example of the row data measured by this method The data exhibit a classic curves, namely velocity, contact force and depth of the indenter intrusion, obtained on polyvinyl chloride sample. 

With contracts of duration typically varying from 3 to 5 years, it is in most cases impossible at the outset to determine performance factors which can reflect the probably changing asset need with time but typical examples are ... 

The parameters a and b are characteristic of the substance, and represent corrections to the ideal gas law dne to the attractive (dispersion) interactions between the atoms and the volnme they occupy dne to their repulsive cores. We will discnss van der Waals equation in some detail as a typical example of a mean-field theory. 

Figure Bl.17.5 shows typical examples of the CTF for weak phase, weak amplitude or combined samples.

A fiirther theme is the development of teclmiques to bridge the length and time scales between truly molecular-scale simulations and more coarse-grained descriptions. Typical examples are dissipative particle dynamics [226] and the lattice-Boltzmaim method [227]. Part of the motivation for this is the recognition that... 

Pitting occurs witli many metals in halide containing solutions. Typical examples of metallic materials prone to pitting corrosion are Fe, stainless steels and Al. The process is autocatalytic, i.e., by initial dissolution, conditions are established which furtlier stimulate dissolution inside tire pit tire metal (Fe in tire example of figure C2.8.6 dissolves. 

Therefore, this type of coating is not sensitive to defects, pinlroles or mechanical damage during service. A typical example is galvanized steel (Zn layer on steel). 

Typical examples of hierarchical database systems arc the file system of personal computers or the organization of parts (e.g., a construction plan). In the case of car parts, the objects (e.g. B = rear suspension, E = right wheel, J = rim, K = screw) are... 

Further prerequisites depend on the chemical problem to be solved. Some chemical effects have an undesired influence on the structure descriptor if the experimental data to be processed do not account for them. A typical example is the conformational flexibility of a molecule, which has a profound influence on a 3D descriptor based on Cartesian coordinates. In particular, for the application of structure descriptors with structure-spectrum correlation problems in... 

The trained and validated network of Figure 10.3 -4b can now be used for the prediction of the correct isomer in novel pyrazole syntheses. As a typical example, the reaction shown in Figure 10.3-5 was chosen. 

The second type of system is characterised by decreasing mutual solubility with rise of temperature. As the temperature is lowered the mutual solubilities increase and below a certain critical temperature the two liquids become miscible in all proportions. A typical example is triethylamine and water. The behaviour of this system with respect to... 

By treatment of the alcohol with a mixture of constant boiling point hydrobromic acid and concentrated sulphuric acid the presence of sulphuric acid results, as a rule, in more rapid reaction and improved 3delds. A typical example is ... 

In order to obtain practice in the preparation of the above derivatives, experimental details for a few typical examples will be given. 

Choosing a standard GTO basis set means that the wave function is being described by a finite number of functions. This introduces an approximation into the calculation since an infinite number of GTO functions would be needed to describe the wave function exactly. Dilferences in results due to the quality of one basis set versus another are referred to as basis set effects. In order to avoid the problem of basis set effects, some high-accuracy work is done with numeric basis sets. These basis sets describe the electron distribution without using functions with a predefined shape. A typical example of such a basis set might... 

The early Escherunoser-Stork results indicated, that stereoselective cyclizations may be achieved, if monocyclic olefins with 1,5-polyene side chains are used as substrates in acid treatment. This assumption has now been justified by many syntheses of polycyclic systems. A typical example synthesis is given with the last reaction. The cyclization of a trideca-3,7-dien-11-ynyl cyclopentenol leads in 70% yield to a 17-acetyl A-norsteroid with correct stereochemistry at all ring junctions. Ozonolysis of ring A and aldol condensation gave dl-progesterone (M.B. Gravestock, 1978 see p. 279f.). 

Table 1 gives a broad summary of the reactions of the corrunon classes of reducing agents, In the following sections some typical examples of synthetically useful reductions (in the educt order given on the table) together with some more sophisticated methods of stereoselective hydrogenations will be discussed. 

A few typical examples indicate the large variety of five-membered heterocycles, which can be synthesized efficiently by [2 + 3]-cycloadditions. [2 + 2]-Cycloadditions are useful in the synthesis of certain four-membered heterocycles (H. Ulrich, 1967), e.g. of 8-lactams (J.R. 

Migration of a hydride ligand from Pd to a coordinated alkene (insertion of alkene) to form an alkyl ligand (alkylpalladium complex) (12) is a typical example of the a, /(-insertion of alkenes. In addition, many other un.saturated bonds such as in conjugated dienes, alkynes, CO2, and carbonyl groups, undergo the q, /(-insertion to Pd-X cr-bonds. The insertion of an internal alkyne to the Pd—C bond to form 13 can be understood as the c -carbopa-lladation of the alkyne. The insertion of butadiene into a Ph—Pd bond leads to the rr-allylpalladium complex 14. The insertion is usually highly stereospecific. 

Organic compounds M—R and hydrides M—H of main group metals such as Mg, Zn, B, Al, Sn, SI, and Hg react with A—Pd—X complexes formed by oxidative addition, and an organic group or hydride is transferred to Pd by exchange reaction of X with R or H. In other words, the alkylation of Pd takes place (eq. 9). A driving force of the reaction, which is called transmetallation, is ascribed to the difference in the electronegativities of two metals. A typical example is the phenylation of phenylpalladium iodide with phenyltributyltin to form diphenylpalladium (16). 

As a typical example, the catalytic reaction of iodobenzene with methyl acrylate to afford methyl cinnamate (18) is explained by the sequences illustrated for the oxidative addition, insertion, and /3-elimination reactions. 

The Pd—C cr-bond can be prepared from simple, unoxidized alkenes and aromatic compounds by the reaction of Pd(II) compounds. The following are typical examples. The first step of the reaction of a simple alkene with Pd(ll) and a nucleophile X or Y to form 19 is called palladation. Depending on the nucleophile, it is called oxypalladation, aminopalladation, carbopalladation, etc. The subsequent elimination of b-hydrogen produces the nucleophilic substitution product 20. The displacement of Pd with another nucleophile (X) affords the nucleophilic addition product 21 (see Chapter 3, Section 2). As an example, the oxypalladation of 4-pentenol with PdXi to afford furan 22 or 23 is shown. 

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