Effective atomic size

Trace elements added to copper exert a significant influence on electrical conductivity. Effects on conductivity vary because of inherent differences ia effective atomic size and valency. The decrease ia conductivity produced by those elements appearing commonly ia copper, at a fixed atomic concentration, rank as follows Zn (least detrimental), Ag, Mg, Al, Ni, Si, Sn, P, Fe (most). Table 12 summarizes these effects. In the absence of chemical or physical interactions, the increase in electrical resistivity is linear with amounts of each element, and the effect of multiatom additions is additive. 

The catalyst manufacturers control PSD of the fresh catalyst, mainly through the spray-drying cycle. In the spray dryer, the catalyst slurry must be effectively atomized to achieve proper distribution. As illustrated in Figure 3-10, the PSD does not have a normal distribution shape. The average particle size (APS) is not actually the average of the catalyst particles, but rather the median value. 

Calculate the ratio of the number of electrons in a neutral xenon atom to the number in a neutral neon atom. Compare this number to the ratio of the atomic volumes of these two elements. On the basis of these two ratios, discuss the effects of electron-electron repulsions and electron-nuclear attractions on atomic size. 

Qualitative predictions about atomic size can be made on the basis of electron configurations and the effects of Z and it on size. 

The structure of a vapor-quenched alloy may be either crystalline, in which the periodicity of the unit cell is repeated within the crystallites, or amorphous, in which there is no translational periodicity even over a distance of several lattice spacings. Mader (64) has given the following criteria for the formation of an amorphous structure the equilibrium diagram must show limited terminal solubilities of the two components, and a size difference of greater than 10% should exist between the component atoms. A ball model simulation experiment has been used to illustrate the effects of size difference and rate of deposition on the structure of quench-cooled alloy films (68). Concentrated alloys of Cu-Ag (35-65%... 

The first problem was resolved when it was shown that the Es values for symmetric groups are a linear function of van der Waals radii42. The latter have long been held to be an effective measure of atomic size. The second and third problems were solved by... 

The first problem was resolved when it was shown that the Es values for symmetric groups are a linear function of van der Waals radii41. The latter have long been held to be an effective measure of atomic size. The second and third problems were solved by Charton, who proposed the use of the van der Waals radius as a steric parameter42 and developed a method for the calculation of group van der Waals radii for tetracoordinate symmetric top substituents MZ3 such as the methyl and trifluoromethyl groups43. In later work the hydrogen atom was chosen as the reference substituent and the steric parameter v was defined as ... 

Pressure effects The diffusion through liquids is governed by the number of defects or atomic-sized holes in the liquid. A high external pressme can reduce the concentration of holes and slow diffusion. Therefore, in a liquid, a diffusion-controlled rate constant also depends on the pressure. 

The sensitivity of Z contrast for the detection of small clusters depends not only on the signal Z dependence, but also depends on the microscope resolution, which is governed by the probe size 6. A small cluster containing N atoms of atomic number Zi, supported on a film of effective atomic number Z2 of thickness t, will have a contrast in the annular detector signal given by... 

Fig. 1 The effect of size on metals. Whereas bulk metal and metal nanoparticles have a continuous band of energy levels, the limited number of atoms in metal clusters results in discrete energy levels, allowing interaction with light by electronic transitions between energy levels. Metal clusters bridge the gap between single atoms and nanoparticles. Even though in the figure the energy levels are denoted as singlets, we must remark that the spin state of the silver clusters is not yet firmly established...

A clear, commonly accepted terminology to describe few-atom subnanoscale metals exhibiting quantized energy levels is lacking. The lack of a coherent terminology leads to confusion and may hamper development. In this chapter, we restrict the term metal cluster to describe few-atom metals with discrete energy levels, and use metal nanoparticle, for particles that have surface plasmon resonance effects (approximate size range between 1 and 100 nm). 

The sample is converted into an aerosol in an atomizer. It then passes through an expansion chamber to allow a fall in the gas pressure and the larger droplets to settle out before passing to the burner, where the solvent evaporates instantly, the atoms remaining as a finely distributed gas. Atoms in the sample that are bound in molecules should be decomposed at the flame temperature so rapidly that the same effect is achieved. In practice only a small proportion of the sample (approximately 5%) is effectively atomized because the drop size of the remaining 95% is so large that the water is never effectively stripped away. In low temperature flames, for instance, only one sodium atom in about 60000 is excited but despite this apparently low efficiency the technique is very sensitive. 

First rule Effect of the size factor. If the atomic sizes of the two components differ more than 15%, extended solid solution formation is not expected. 

For a discussion on the effective coordination number , its relation to atomic size, bond strength, Madelung constant, etc., see also Simon (1983). For a computation of the heats of formation based on the so-called effective coordination, see a formula by Kubaschewski and Evans (1958), and for a discussion on its application and limits, see Borzone etal. (1993). 

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