Metal particle dispersion

The geometrical factor, like the filling factor, shifts the position of the resonance peak. When = 0 we have the case of an infinite cylinder (see Table 1). An infinite cylinder connects one side of the crystal to the other. Therefore, the electrons travel freely through the crystal. Actually, this is not the situation of metallic particles dispersed in an insulator any more. The situation corresponds... 

The ionic polymerisation of styrene is as dangerous. Interlaminar compounds of sodium or potassium with graphite catalyse the polymerisation of styrene. This method can usually be controlled. Nevertheless, it gives rise to detonations. It was assumed that in these cases the lamellar structure of graphite is destroyed and the metallic particles dispersed. 

The structure of the metal particles dispersed on a silica powder support ( Aerosil 380, 70 A average silica particle diameter) has been studied by Avery and Sanders (47) using electron microscopy in both bright and dark field, to determine the extent to which the metal particles were multiply twinned or of ideal structure. Platinum, palladium, and gold were examined. These catalysts were prepared by impregnation using an aqueous solution of metal halide derivatives, were dried at 100°-150°C, and were hydrogen... 

HREM methods are powerful in the study of nanometre-sized metal particles dispersed on ceramic oxides or any other suitable substrate. In many catalytic processes employing supported metallic catalysts, it has been established that the catalytic properties of some structure-sensitive catalysts are enhanced with a decrease in particle size. For example, the rate of CO decomposition on Pd/mica is shown to increase five-fold when the Pd particle sizes are reduced from 5 to 2 nm. A similar size dependence has been observed for Ni/mica. It is, therefore, necessary to observe the particles at very high resolution, coupled with a small-probe high-precision micro- or nanocomposition analysis and micro- or nanodiffraction where possible. Advanced FE-(S)TEM instruments are particularly effective for composition analysis and diffraction on the nanoscale. ED patterns from particles of diameter of 1 nm or less are now possible. 

Identification of metal particles dispersed in pictorial or decorative layers in works of art is often difficult for microscopy techniques because of (i) their presence as highly diluted components and concentrated in microparticles that, in turn, are included in binding media and attached to priming and protective layers (ii) the coexistence of metals with priming, ground or pigmenting layers in the samples and (iii) the presence of products resulting from the alteration of metals. 

The catalyst is called bifunctional both the carrier and the metallic particles dispersed over the carrier exhibit different catalytic functions. The carrier contains chlorine ions and, as a consequence, it has acid properties and exhibits isomerization and cyclization activities. The metal particles consist of alloys of, for example, Pt/Re which exhibit hydrogenation/dehydrogenation activity. 

These observations confirm that a treatment in O2 at 773 K is severe enough to destroy the intermetallic but does not regenerate the situation corresponding to a Pt/Ce02 catalyst directly reduced at 773 K or lower temperatures, i.e. a system consisting of small metal particles dispersed on the support. To summarise, the... 

Figures 4.30(c) and 4.31(c) show HREM images representative of the catalysts reduced at 1173 K and further oxidised in pure O2 at 1173 K. The structure of both catalysts is clearly different from that observed after re-oxidation at 773 K. Notice that in this case both materials seem to be formed by small, crystalline, metal particles dispersed over the ceria surface. Fringe analysis confirms that these crystallites consist of metallic rhodium and platinum, respectively. Thus, the DDPs of the larger particles observed in the image of the Pt catalyst show 0.8 nm Moire-type fringes aligned with the (111 )-Ce02 reflections. These spots arise from double diffraction in the (lll)-Pt and (Ill)-Ce02 planes under a parallel orientation relationship. Therefore this result, in addition to confirm the presence of metallic Pt particles in the sample oxidised at 1173 K, suggest that these particles are epitaxially grown on the support. A detailed inspection also reveals that the exposed surfaces of these particles are clean, i.e. free from support overlayers.

The size and size distribution of metallic particles (dispersion less than 30%). 

Because the HRS intensity from metallic particles may be enhanced through SP resonances, wavelength dependence measurements were also performed. Tliese experiments allow for a direct confrontation of the theoretical developments with the experimental data. The first wavelength dependence of the HRS intensity for metallic particles dispersed in a homogeneous environment has been reported for... 

The thin layer of transition metal macrocycles attached to carbon generally lack long-term stability in concentrated acid and alkaline solutions. This drawback can be overcome by thermal treatment at 450-900°C for cobalt tetramethoxy phenyl porphyrin (Co-TMPP) [65]. Under these conditions, the Co-TMPP is substantially degraded to cobaltous oxide. Pyrolyzed layers involve high-area carbonaceous materials with a significant surface nitrogen and the transition metals as small oxide and metallic particles dispersed on the high-area substrate. These layers catalyze peroxide elimination in alkahne solutions. 

Small metallic particles dispersed in glasses scatter light and can create striking colors. This phenomenon is essentially a scattering effect and is discussed in greater detail in the next section. 

The blank catalysts imderwent the same preparation procedure as the bimetallic catalysts but using Ge-free n-heptane solutions. By this way, it was possible to investigate the influence of the preparation procedure (i.e. the effect of used conditions) on metallic particles dispersion and on the structure of the parent monometallic catalysts. 

Many heterogeneously catalyzed reactions are performed using metal particles dispersed on oxide supports, commonly on alumina or silica but also many others, including transition metal and rare earth metal oxides. Metal clusters have interesting reactions with or at the surfaces of such oxide materials. It has recently been shown that the oxide surface is actually a good medium for the synthesis of... 

The full reduction of the metal oxide enables one to prepare composite materials consisting of nanometer-sized metallic particles dispersed in a Li20 matrix. The nanodimensional size of the metal particles is instrumental in making the reactions highly reversible. Conversion reactions are not limited to metal oxides, as it is now clear that there are a number of other systems that can be used, including sulfides, nitrides, phosphides, and fluorides. For a binary metal compound (MX ), with X = F, O, S, N, these reactions proceed as follows ... 

Yes, through a pseudocapacitive process such as is the case for V2O5, or through conversion reactions where the metal oxide is converted into nanometer-sized metallic particles dispersed in a Li20 matrix. 

Fig. 18.4 Ratio of tin fixed/surface metal atoms as a function of metallic particles dispersion.

Electrically conductive adhesives perform two primary functions. Like other types of adhesives, these materials provide a physical bond between two surfaces. In addition, an electrical interconnection between the two bonded surfaces is formed. This dual functionality is usually achieved by composite materials composed of metallic particles dispersed in an adhesive matrix. The electrical resistivity of conductive adhesives is compared to values of pure metals and polymers in Table 1. 

J.C. Moutet, Y. Ouennoughi, A. Oruari, and S. Hamar-Thibault, Electrocatalytic hydrogenation on noble metal particles dispersed in polymer films. Enhanced catalytic activity induced by the incorporation of bimetallic catalysts, Electrochim. Acta, 40, 1827-1833 (1995). 

Effective medium theories characterize the frequency-dependent transport in systems with large-scale inhomogeneities such as metal particles dispersed in an insulating matrix [118,119]. An IMT in the effective medium model represents a percolation problem where a finite a c as T 0 is not achieved until metallic grains in contact span the sample. To understand the frequency dependence of the macroscopic material, an effective medium is built up from a composite of volume fraction /of metallic grains and volume fraction 1 — / of insulator grains. The effective dielectric function semaCw) and conductivity function (Tema(w) are solved self-consistently. 

Amalgam butter—a commonly used term in mercury cell operations—is a multiphase material, which has not been characterized thoroughly. The butter formed with Fe, Ni, and C consists of finely divided metal particles dispersed in mercury, whereas graphite butter is shiny and foamy. Ca butter is hard and compact, while Fe butter is blackish. 

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