Shaping of Metals

Fig. 4. Shapes of metal powder particles (a) spherical (b) rounded (c) angular (d) acicular (e) dendritic (f) kregular (g) porous and (h) fragmented. Density. The density of a metal powder particle is not necessarily identical to the density of the material from which it is produced because of...

Mol ding sands, composed essentially of sand and clay, are used extensively ia the metallurgical iadustry for the shaping of metal by the castiag process (see Metallurgy). Using a pattern, a cavity of the desired shape is formed ia the sand iato which molten metal is poured and then allowed to cool. 

Figure 7-25 Shapes of Metal versus Composite Stiffeners...

Besides electronic effects, structure sensitivity phenomena can be understood on the basis of geometric effects. The shape of (metal) nanoparticles is determined by the minimization of the particles free surface energy. According to Wulffs law, this requirement is met if (on condition of thermodynamic equilibrium) for all surfaces that delimit the (crystalline) particle, the ratio between their corresponding energies cr, and their distance to the particle center hi is constant [153]. In (non-model) catalysts, the particles real structure however is furthermore determined by the interaction with the support [154] and by the formation of defects for which Figure 14 shows an example. 

Figure 1.2 shows the different sizes and shapes of metal NPs prepared in ILs using several types of reducing agents. 

There have been three primary motives behind the study of metal carbonyl photochemistry in the gas phase first, to discover the shapes of metal carbonyl fragments in the absence of perturbing solvents or matrices second, to probe the effect of uv photolysis wavelength on product distribution and third, to measure the reaction kinetics of carbonyl fragments. All three areas have already proved fruitful. The photochemistry of two molecules, Fe(CO)5 and Cr(CO)6, has been studied in detail. 

Focused X-ray beam (at Beam Line 15A) was used for this study. In order to improve the resolution, the focused beam (about 1 x 1.5 mm) was cut into 0.9-0.5 mm O by apertures which were set just in front of the cell. Modulation frequency was 10 Hz. Scanning X-Y stage which was originally developed for the laser microscopy was set perpendicular to the surface of the iron-base table and scanning and data acquisition were controlled by PC-9801 VM2 microcomputer (NEC Co. Ltd.) with the original program Various size and shape of metal foils were glued on the paper to have a model patterned sample. 

Cold Extrusion of Metals. See under Cold Working or Shaping of Metals... 

However, the shape of metal granules does not strongly differ from spherical one for significantly large number of metal-insulator granular... 

Shao X, Prada S, Giordano L, Pacchioni G, Nilius N, Freund H-J. Tailoring the shape of metal ad-particles by doping the oxide support. Angew Chem Int Ed. 2011 50 11525-7. 

A considerable collection of data exists that describe the state of catalysts under reaction conditions. The cases presented here show that typical processes observed under reaction conditions include changes of the oxidation states (of transition metals), changes of particle size and shape (of metal clusters), or formation of coke. However, without the corresponding catalytic performance, relevant and spectator species cannot be distinguished. 

The peak shapes of metal chelating analytes are often poor because metal impurities in the stationary phase behave as active sites characterized by slowo desorption kinetics and higher interaction energies compared to reversed phase ligand sites. This phaiomaion is typical of silica-based stationary phases [31] ultrapure silicas were made commercially available to reduce it. However, styrene-divinylbenzene-based chromatogripliic packings suffer from the same problem and it was hypothesized that metals may be present in the matrix at trace conditions because they were used as additives in the polymerization process they may have been c tured via Lewis acid-base interactions between the aromatic ring n electrons and impurities in the mobile phase [32]. 

Westcott SL, Jackson JB, Radloff C, Halas NJ (2002) Relative contributions to the plasmon line shape of metal nanoshells. Phys Rev B 66 155431... 

The shape of metal particles affects field enhancement magnitude in a manner that depends on both the identity of the metal and the wavelengths of both the laser and the Raman-shifted light. For example, spherical and elliptical particles have different radii of curvature for... 

Volume and shape of metal pool in ESR is one of the most important characteristics, which define the quality of metal of ingot being melted. With increase in volume and depth of metal pool the length of zone of two-phase state is increased which is the source of all defects of a liquation origin. Therefore, to produce quality ingots, it is necessary to approach shallow shape of the metal pool. 

Figure 3. Shape of metal pool during melting in longitudinal field a - B=0 T b - B=0,06 T c - B=0,1 T.

For optimal use of Pt, a preferred size of Pt crystal can be predicted. For catalytic activity of exposed atoms (STY), this would take place around point C (Fig. 6.7 d). The opposite trends of dispersion and catalytic activity (related to metal character of atom in the dispersion) give the resulting curve C for overall catalysis observed as function of cluster size. Catalysts prepared by different methods will, generally, yield different crystallite size distribution and shape of metal crystals. This will result in dissimilarities in sorptive and catalytic behavior, even if allowance is made for the difference in active surface area285. ... 

Researchers in the area of heterogeneous catalysis have recently focussed considerable attention to the relationships among catalytic activity, product selectivity and the size and shape of metal particles for reactions catalyzed by metals (15). Reactions that are influenced by the size and shape of metal particles or electronic interactions of the metal particles with the support are known as structure sensitive reactions. Theoretical calculations of various crystallographic structures (16) have shown that the number of specific type of surface atoms (face, corner, edge) change as a function of particle size. For example, for a face centered cubic system, the number of face atoms decreases as particle size decreases. If, therefore, a reaction is catalyzed on a face and there are a substantial number of face atoms necessary for catalysis to occur, then as particle size decreases catalytic activity will decrease. This idea often runs counter to principles discussed in general science texts (17). 

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