Metal polycrystalline

A summary of physical and chemical constants for beryUium is compUed ia Table 1 (3—7). One of the more important characteristics of beryUium is its pronounced anisotropy resulting from the close-packed hexagonal crystal stmcture. This factor must be considered for any property that is known or suspected to be stmcture sensitive. As an example, the thermal expansion coefficient at 273 K of siagle-crystal beryUium was measured (8) as 10.6 x 10 paraUel to the i -axis and 7.7 x 10 paraUel to the i -axis. The actual expansion of polycrystalline metal then becomes a function of the degree of preferred orientation present and the direction of measurement ia wrought beryUium. 

Meyers, M.A., A Model for Elastic Precursor Waves in the Shock Loading of Polycrystalline Metals, Mater. Sci. Engrg. 30, 99-111 (1977). 

Slides Microstructures showing precipitates electron micrographs of dislocation tangles micrographs of polycrystalline metals. 

Single-crystal samples of conductors best other solid samples are suitable, including polycrystalline metals, polymeric materials, semiconductors, and insulators, ultrahigh vacuum compatible typically > 5 mm diameter, 1-3 mm thick... 

The lack of a well-defined specular direction for polycrystalline metal samples decreases the signal levels by 10 —10, and restricts the symmetry information on adsorbates, but many studies using these substrates have proven useful for identifying adsorbates. Charging, beam broadening, and the high probability for excitation of phonon modes of the substrate relative to modes of the adsorbate make it more difficult to carry out adsorption studies on nonmetallic materials. But, this has been done previously for a number of metal oxides and compounds, and also semicon-... 

Polycrystalline electrodes are still used in many electrochemical experiments. For this reason, polycrystalline metals are still included in compilations of pzc as in this chapter, although the physical significance of such a quantity is ambiguous (see Section I). 

Figure 14. Plot of the potential of zero charge, Ea=0 (from Table 26), against the work function,

Relative and Absolute Interfacial Parameter for Polycrystalline Metals in Contact with Water... 

The quantities jXe, pe >

bulk properties of the metal. The quantities O, and of course F, are surface properties which can vary on a metal surface from one crystallographic plane to the other. Such variations are typically on the order of 0.1 eV but can be as high as 0.5 V. The measured work function , of a polycrystalline metal is an average of the d> values on different crystallographic planes. 

Clean, polycrystalline metals expose mostly their most densely packed surface, because, to create this surface, the minimum number of bonds have to be broken (see Fig. 5.3). 

Epitaxial effects are not limited to single-crystalline substrates. The possibility for substrate-induced epitaxial development in the difficult case of ZnSe (cf. conventional electrodeposition) has been established also by using strongly textured, albeit polycrystalline, zinc blende (111) CdSe electrolytic films to sustain monolithic growth of ZnSe in typical acidic selenite baths [16]. Investigation of the structural relations in this all-electrodeposited ZnSe/CdSe bilayer revealed that more than 30-fold intensification of the (111) ZnSe XRD orientation can be obtained on the textured (111) CdSe films, compared to polycrystalline metal substrates (Fig. 4.2). The inherent problems of deposition from the Se(IV) bath, i.e., formation of... 

Compared to the corresponding polycrystalline metal chalcogenides, chalcogenide glasses exhibit better chemical stability in acidic and redox media and often... 

S. F. Pugh, Relations between the Elastic Moduli and the Plastic Properties of Polycrystalline Metals, Phil. Mag., 43, 823 (1954). 

Figure 4.10 Correlation between the upd shift 4>Upd and the work function difference for polycrystalline metals A/B denotes the upd of A on B.

Most of the work in our laboratory has been done using specially designed cells that are incorporated in a rather simple cooling device. In working with polycrystalline metal foils, a cell design as pictured in Fig.l has been used. Metal... 

Tammann48 pointed out that (polycrystalline) metals contain internal boundaries and that their energy should be considered when calculating the area A which is being extended by the load W. At present, this idea is used above all to estimate the energies of grain boundaries49. ... 

According to a proposed definition, the electron work function

Fermi level of the metal across a surface carrying no net charge, and to transfer it to infinity in a vacuum. The work function for polycrystalline metals cannot be precisely determined because it depends on the surface structure it is different for smooth and rough surfaces, and for different... 

Electrodes modified by underpotential deposition of metal were subjected as electrocatalysts to reduction of oxygen,oxidation of formic acid, and other processes in which polycrystalline metal substrates were used (see review in Ref. 151). Electrocatalysis of single-crystal electrodes modified by underpotential deposition was also investigated, as reviewed by Ad2iC. ... 

This reported pzc is for polycrystalline Au. Electrochemists may debate the precise meaning of the pzc for a polycrystalline metal surface. However, for our purposes here it is the potential at which there is no net excess charge on the polycrys-taUine metal surface. 

Both the copper and nickel surfaces are efficient for the electrochemical reduction of nitrobenzene to aniline. With time however, the properties of this surface are transformed to those of the polycrystalline metal and azoxybenzene becomes as major reduction product [49]. 

This paper is a report on stable and reproducible current-controlled bistable electrical switching and memory phenomena observed in polycrystalline metal-organic semiconducting films. 

Tables I-VI summarize the more reliable results for the adsorption of alkali metals and gases on polycrystalline metal surfaces. Many of the older...

Sayers, C. M. (1985). Angular dependence of the Rayleigh wave velocity in polycrystalline metals with small anisotropy. Proc. R. Soc. Lond. A400,175-82. [245]... 

Window glass, 2) A polycrystalline metal, 3) Sandstone, 4) Concrete, 5) A brick wall, 6) The surface crust of the Earth, with folds and intrusions. 

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