Fine metal particle

Vapor-grown carbon fibers have been prepared by catalyzed carbonization of aromatic carbon species using ultra-fine metal particles, such as iron. The particles, with diameters less than 10 nm may be dispersed on a substrate (substrate method), or allowed to float in the reaction chamber (fluidized method). Both... 

Cathodic disintegration can occur with lead, observable as a grey cloud of fine metal particles. Hydrogen evolved on the surface of the lead can be absorbed if the current density is sufficiently high . Above this level, avalanche penetration can occur, feadipg to the formation of lead hydride, which leads to disintegration in the manner described . Electrochemical implantation pf alkali metals Can also lead to disintegration, ... 

High color carbon blacks, 4 798t High contrast films, fine metal particles in, 19 368-369... 

Bonnemann, H. et al., Preparation, characterization, and application of fine metal particles and metal colloids using hydrotriorganoborates, J. Mol. Catal., 86, 129,1994. 

It is with the understanding of the above that one can give some insight to what establishes the pyrophoricity of small metal particles. The term pyrophoricity should pertain to the instantaneous combustibility of fine metal particles that have no oxide coat. This coating prevention is achieved by keeping the particles formed and stored in an inert atmosphere such as argon. Nitrogen is not used because nitrides can be formed. When exposed to air, the fine metal particle cloud instantaneously bursts into a flame. Thus it has been proposed... 

Certain apparently solid—solid reactions with a solid product are, in reality, solid—gas reactions. Thus, the reduction of a metal oxide by solid carbon is really a two stage process, the oxidation of carbon by gaseous carbon dioxide to form carbon monoxide, followed by the reduction of the metal oxide by the carbon monoxide to form metal plus carbon dioxide. Often, the carbon oxidation is the rate-controlling reacion and the rate of this reaction can be catalysed by the addition of small amounts of alkali and also by fine metal particles produced as a result of the reduction reaction [7]. 

Amorphous carbon is one of the most important and economical materials in catalysis and is generally used as a support for metallic catalysts. Normally, fine metallic particle catalysts are dispersed on such carbon supports. In the following section we briefly review such carbons, its uses and carbon deposits resulting... 

Fine metal particles have received much attention in recent years from the viewpoints of chemical, physical, and biological interests (1-4). They are one of the most promising advanced materials. Compared with metal oxide or metal salts, metals have the highest electric and thermal conductivity, considerably higher weight and melting point, and usually excellent catalytic properties. These properties of metals cannot be replaced by other materials. Thus, even after the rapid growth of plastic, bulk metals keep their important position as one of the most common raw materials. 

When we consider the metals of nanoscopic size, fine metal particles from micrometer to nanometer size can be synthesized by both physical and chemical methods. The former method provides the fine metal particles by decreasing the size by addition of energy to the bulk metal, while in the latter methods, fine particles can be produced by increasing the size from metal atoms obtained by reduction of metal ions in solution. Since chemical reactions usually take place in homogeneous solution in any case, this chapter includes most of the cases of synthesis and growth of fine metal particles. However, the polyol process, reaction in microemulsions, and formation in the gas phase are omitted, since they are described in later chapters by specialists in those fields. 

Synthesis of Fine Metal Particles in Homogeneous Solution... 

Colloidal dispersions of fine metal particles can usually be prepared by reduction of metal ions. The first scientific report to synthesize colloidal dispersion of metals was presented by Faraday, who prepared metal colloids without stabilizers (5). In his case counteranions may have played the role of the stabilizer. In most recent cases, however, stabilizers are usually added to the system to stabilize the colloidal dispersions. 

In this section, the general concept and practical procedures to synthesize the colloidal dispersions of fine metal particles in homogeneous solution are described. 

Stabilizers are usually used during the reduction of metal ions to stabilize the colloidal dispersions of fine metal particles. The coordination interaction is the main factor to stabilize the metal particles. Thus, polymers with coordinating groups are good stabilizers. The choice of coordinating groups should depend on the kind of metal. 

Here, the detailed synthetic methods and procedures of colloidal dispersions of bimetallic nanoparticles in a homogenous solution are described because the bimetallic system is one of the recent greatest topics of the fine metal particles (2). 

Colloidal dispersions of fine metal particles have a long history. Metal nanoparticles are now in the spotlight because of recent developments in nanometer-scale science and technology. Especially the precise structure of the monodispersed bimetallic nanoparticles has become clear quite recently, thanks to the development of EXAFS technology. The mechanism of formation, growth, and structure control is not completely clear yet. In some parts, especially in Section 9.1.4, the discussion may be speculative but is based on the experience of the present author for over 20 years. 

The various methods of preparation employed to prepare nanoscale clusters include evaporation in inert-gas atmosphere, laser pyrolysis, sputtering techniques, mechanical grinding, plasma techniques and chemical methods (Hadjipanyas Siegel, 1994). In Table 3.5, we list typical materials prepared by inert-gas evaporation, sputtering and chemical methods. Nanoparticles of oxide materials can be prepared by the oxidation of fine metal particles, by spray techniques, by precipitation methods (involving the adjustment of reaction conditions, pH etc) or by the sol-gel method. Nanomaterials based on carbon nanotubes (see Chapter 1) have been prepared. For example, nanorods of metal carbides can be made by the reaction of volatile oxides or halides with the nanotubes (Dai et al., 1995). 

The liquid phase is added to the mix vessel before solids addition to minimize the formation of solid agglomerates. Various methods of adding the fine metal particles have been used varying from hand-scoop to elaborate hopper facilities. In many cases, these additions must be accomplished in an inert atmosphere to avoid deterioration of the resultant slurry. 

Given fine metallic particles averaging 0.01, 0.1, and 1 mm in diameter, t> = 0.4 and p = 5.0. Determine the percentages of each which will give a mixture of maximum density. 

Oxidation is the most common factor in the fretting process. In oxidizing systems, fine metal particles removed by adhesive wear are oxidized and trapped between the fretting surfaces. The oxides act like an abrasive (such as lapping red) and increase the rate of... 

Since hydrogen-containing samples have strong absorption bands in the NIR range, they may behave as gray or even black emitters, according to the combination of Planck s with Kirchhoff s law (Eq. 3.3-8). Samples which contain black particles like soot or fine metal particles behave like black bodies. The particles are heated in the laser beam and emit Planck radiation, which at somewhat elevated temperatures is as strong as that of weak Raman lines. 

A previous study (12) on the interaction of fine metal particles on graphite surfaces demonstrated that particles can catalyze surface reactions and lead to the generation of elongated pores of the type shown in Figure 4. The similarities of the pore geometry and the presence of mineral particulates led to the speculation that the pores observed in the exinite were the consequence of a reaction catalyzed by the mineral particles. The source of the particles is believed to be the mineral-rich granular inertinite that typically surrounds the spore exine. However, further studies revealed that all particles analyzed to date contain only calcium as the heavy atom, which leads one to question the absence of... 

Preparation of MejC by Adsorption of Metal Hydroxide Ammoniates This method requires an excess of ion-exchange groups compared to the number of the supported metal ions and thus relies on the utilization of oxidized carbon materials. Reduction of adsorbed precursors in H2 at 100-300 °C results in the generation of very fine metal particles, their size being 1.5-2.5nm for... 

Kawabata, A., Kubo, R. Electronic properties of fine metallic particles. 11 Plasma resonance absorption. J. Phys. Soc. Jpn. 21, 1765-1772 (1966)... 

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