Particles inert metallic

The typical solid catalyst used in technology consists of small catalytically active species, such as particles of metal, metal oxide, or metal sulfide, dispersed on a low-cost, high-area, nearly inert porous support such as a metal oxide or zeolite. The catalytic species are typically difficult to characterize in-... 

Small metal particles can also be obtained by vacuum evaporation in low pressure inert gases (16). Magnetic particles of metals such as iron, cobalt, nickel, and alloys of these metals can be prepared by this method. Though the amounts of particles obtainable by this method are limited, the particles are clean as compared with particles precipitated from solutions. They are mainly used for studies of physical properties of fine particles. 

The booster-and-attenuator system is selected to provide about the desired shock pressure in the sample wedge. In all but a few of the experiments on which data are presented here, the booster-and-attenuator systems consisted of a plane-wave lens, a booster expl, and an inert metal or plastic shock attenuator. In some instances, the attenuator is composed of several materials, The pressure and particle velocity are assumed to be the same on both sides of the attenuator-and-sample interface. However, because initiation is not a steady state, this boundary condition is not precisely correct. The free-surface velocity of the attenuator is measured, and the particle velocity is assumed to be about half that. The shock Hugoniot of the attenuator can be evaluated using the free-surface velocity measurement. Then, the pressure (P) and particle velocity (Up) in the expl sample are found by determining graphically the intersection of the attenuator rarefaction locus and the explosives-state locus given by the conservation-of-mom-entum relation for the expl, P = p0UpUs where Us = shock velocity and p0 = initial density. The attenuator rarefaction locus is approximated... 

The chrome yellow pigments [4344-37-2], C.I. Pigment Yellow 34 77600 and 77603, are pure lead chromate or mixed-phase pigments with the general formula Pb(Cr,S)04 [3.131] (refractive index 2.3-2.65, density ca. 6 g/cm3). Chrome yellow is insoluble in water. Solubility in acids and alkalis and discoloration by hydrogen sulfide and sulfur dioxide can be reduced to a minimum by precipitating inert metal oxides on the pigment particles. 

The details of the sample preparation and studies of the nature of the supported-metal samples have been described in a paper dealing with the effect of surface coverage on the spectra of carbon monoxide chemisorbed on platinum, nickel, and palladium (1). The samples consist of small particles of metal dispersed on a nonporous silica which is produced commercially under the names Cabosil or Aerosil.f This type of silica is suitable as a support because it is relatively inert and has a small particle size (150-200 A.). The small particle size is important because it reduces the amount of radiation which is lost by scattering. A nonporous small particle form of gamma-alumina, known as Alon-C, is also available. This material is not so inert as the silica and will react with gases such as CO and CO2 at elevated temperatures. 

Platinum metal catalysts have been employed either in the form of unsupported fine particles of metal, usually referred to as blacks, or in the state supported on an inert... 

Experiments by Bezemer et al. (10) demonstrated a strong decrease in activity of cobalt catalysts when the cobalt particles became smaller than 4 mn in diameter. The authors excluded support effects by using an inert support. They also concluded that the cobalt particles remained metallic. These results agree with earlier reports of a structure dependence of the Fischer-Tropsch reaction (11,12). 

Chrome yellow is insoluble in water. Solubility in acids and alkalis and discoloration by hydrogen sulfide and sulfur dioxide can be reduced to a minimum by precipitating inert metal oxides on the pigment particles. 

It appeared finally that the support can no longer be considered as a pure inert stabilizing partner. Actually, the support acts as a supramolecular ligand and has been claimed to promote specific electronic properties and/or geometrical features of the nano-sized supported metal particles. Any metal-support interaction (MSI) does occur in any case when small particles are deposited on a carrier. However, the extent of their interaction depends on the nature of the metal, but much more on the size of the particles and the nature of the support. 

In the particle synthesis, metal atoms produced by the heating collide with the inert gas atoms to decrease the diffusion rate of the atoms fi-om the source region. The collisions also cool the atoms to induce the formation of small clusters of fairly homogeneous size. The clusters grow mainly by cluster-cluster condensation to give nanoparticles with a broader size distribution. A convective flow of the inert gas between the warm region near the vapour source and the cold surface carries the nanoparticles to the cooled finger, where they are let to deposit. The inert gas pressure, the evaporation rate, and the gas composition can control the characteristics... 

The first observation from these results is that Au catalysts are able to work under reductive as well as oxidative atmosphere. The second is that the high activity of supported Au catalysts in CO oxidation depends mainly on Au particle size and the presence of suitable metal oxides. The synergy in the metal-support interaction is not well understood, but we may underline that an inert metal can be catalytically active if its size is small enough, around 2-3 nm. At this point is also underlined the very important aspect of the preparation of the catalyst, and in this field much work has to be done [69-71]. 

As is well known, gold is the most chemically inert metal, and as such the most noble metal. However, when it is present as particles of nanosize (<5 nm), it becomes reactive. This may be due to the increasing fraction of low coordination surface sites as particle size decreases, on which, for instance, CO molecules can adsorb, and H2 can dissociate. This may be due also to changes in the electronic properties exemplified, for instance, by the contraction of the Au—Au bond when the gold particles are smaller than 2 nm [1-3]. 

C, the metal—nitrogen chelate bonds are known to decompose and a reduction in ORR activity was commonly observed. Various reports have attributed this decrease in ORR activity to either (1) formation and growth of relatively inert metallic or metal oxide/carbide particles at these excessive temperatures, or (2) a decrease in the surface nitrogen content of the pyrolyzed M—Nx/C catalysts. 

Finally, hychogen evolution becomes crucial factor determining the shape of powder particles of the group of the inert metals, and the concept of effective overpotential is applicable to explain the formation of these powder particles. Due to vigorous hychogen evolution, dendritic growth is almost completely inhibited. Analysis of the polarization curves for Co and Ni [12, 26, 30] showed that their... 

The pathway of induction means that electric energy is applied to create a magnetic field in the fluidization chamber the magnetic field, in turn, creates an electric current in large and inert metallic particles, which are co-fluidized with the product. The energy of this electric current is immediately dissipated as heat Such heat is transferred to the fluidization gas and then from the gas to the particles of the product to be dried alternatively, it may be transmitted directly to the product particles by contact (by collisions between inert and product particles). In order for this process to function, the inert metallic particles and wet product particles must fluidize in a rather homogeneous fashion - that is, their fluidization properties must match. The Archimedes number (see Eq. 4.3) shows that fluidization behavior depends on both the diameter and density of particles consequenfly, compact metallic particles will never have the same fluidization behavior as would, for example, food particles, unless they are much smaller. However, as it is... 

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