Compressive metal

As the flexibility of the macrocycle increases, then mismatch hole-size effects are expected to be moderated. In any case, as discussed in Chapter 1, a metal ion which is too large for the cavity may be associated with folding of a flexible macrocycle thereby allowing normal metal-ligand bond distances to be achieved. However, this is not always the case, and a number of examples of unfolded macrocyclic complexes containing compressed metal-donor distances are known (Henrick, Tasker Lin-doy, 1985). 

S. Reckers et al., Leakage investigations of compressive metallic seals in SOFC stack, in Proceedings of the Fifth European Solid Oxide Fuel Cell Forum, J. Huijsmans (ed.), 1-5 July 2002, Lucerne, Switzerland, 2002, pp. 847-854. 

A possible mechanism for the conversion of a ccp structure to bcc for a metal involves compression. Metals are more compressible than solids such as salts, and metals are much more malleable and ductile than most other solids. In Figure 4.4, on the left side, we view a ccp structure parallel to the packing layers. The ccp structure is viewed from an angle so that A, B, and C positions are staggered. No attempt has been made to distinguish the distance of the atoms in each layer from the viewer. As drawn the distances from the viewer are shortest for A and longest for C (this is an arbitrary choice of sites one could choose C positions closer than either A or B). In the figure the layers are compressed so that layers are converted as follows ... 

A way to stretch or compress metal surface atoms in a controlled way is to deposit them on top of a substrate with similar crystal symmetry, yet with different atomic diameter and lattice constant. Such a single monolayer of a metal supported on another is called an overlayer. Metal overlayers strive to approach the lattice constant of their substrate without fully attaining it hence, they are strained compared to their own bulk state [24, 25]. The choice of suitable metal substrates enables tuning of the strain in the overlayer and of the chemisorption energy of adsorbates. A Pt monolayer on a Cu substrate, for instance, was shown to bind adsorbates much weaker than bulk platinum due to compressive strain induced by the lattice mismatch between Pt and Cu, with Cu being smaller [26]. 

It should be possible to use compressed metal powders as, for example, a catalytic filter, but the present authors are not aware of any industrial examples of this. Raney metals powders, however, have been employed in some liquid-based processes in shallow beds through which reactants pass. Because Raney metals are fine grained, pressure drop can be a problem so it is more common to use them in an unstructured way in slurry reactors, as, for example, formerly in the oils and fats industry [3]. Raney metals can have high surface areas when freshly prepared, but this decreases quickly in use, particularly when exposed to elevated temperatures. Pressure drop considerations are less significant for beds of metal granules, but there is less effective use of metal than with fine powders. For granules, surface areas in the region of 30-35 cm g are typical for silver used in... 

Cohen and coworkers 113] used the pseudopotential localized-orbital approach and found that this allotropic carbon structure is a low-compressibility metal because of the nearly perfect lattice match with the diamond (100) surface, they preposed that it may be possible to grow this structure epitaxially on the diamond OOO) surface. 

The whole assembly is placed in a quartz tube which is closed off on top by a special water-cooled adapter. This metallic adapter may be made either of compressed metal powder or of bronze inq>regnated with tin under vacuum. It is sealed to the quartz tube with high-vacuum silicone grease. The apparatus is connected to a high-vacuum pump by means of a flexible tombac tube. The distillation requires a vacuum of < 10 mm... 

BEARING, POROUS - Made from porous material, such as compressed metal powders, the pores acting either as reservoirs for holding or passages for supplied lubricant. 

It has been shown [193] (see Sect. 1.5.3) that compression of metals under very high pressures leads to a direct contact between their cations, and interatomic distances in the ultimate compressed metals are equal to the sums of their cation radii. For a series of MnXm crystalline compounds, calculations showed that metallization of a substance occurs at the pressure at which the energy of compression is equal to the bond dissociation energy, when the chemical bond is broken because of the shift of electrons from the metal atoms. In this state the interatomic distances are equal to the sum of the radius of a M"+ cation and the normal covalent radius of the halogen, oxygen or chalcogen [194, 195]... 

I. A. Larmour, G. C. Saunders, and S. E. J. Bell, Compressed metal powders that remain superhydrophobic after abrasion, ACS Appl. Mater. Interfaces, 2, 2703-2706, (2010). 

The inner core of the earth is made of very much compressed metallic iron and a little bit of nickel the outer core is not much different, only it is not as compressed as the inner core. These are essentially metals. However, the rest of the solid Earth is made of various minerals based on silicates. 

Figure J.5 Heterogeneous flow in uniaxially compressed metallic glasses. (Reprinted from Pampillo and Chen, 1974, with permission from Elsevier.)...

Vibrational Spectroscopy. Infrared absorption spectra may be obtained using convention IR or FTIR instrumentation the catalyst may be present as a compressed disk, allowing transmission spectroscopy. If the surface area is high, there can be enough chemisorbed species for their spectra to be recorded. This approach is widely used to follow actual catalyzed reactions see, for example. Refs. 26 (metal oxide catalysts) and 27 (zeolitic catalysts). Diffuse reflectance infrared reflection spectroscopy (DRIFT S) may be used on films [e.g.. Ref. 28—Si02 films on Mo(llO)]. Laser Raman spectroscopy (e.g.. Refs. 29, 30) and infrared emission spectroscopy may give greater detail [31]. 

Ross M 1968 Shock compression of argon and xenon. IV. Oonversion of xenon to a metal-like state Phys. Rev. 171 777... 

At potentials positive to the bulk metal deposition, a metal monolayer-or in some cases a bilayer-of one metal can be electrodeposited on another metal surface this phenomenon is referred to as underiDotential deposition (upd) in the literature. Many investigations of several different metal adsorbate/substrate systems have been published to date. In general, two different classes of surface stmetures can be classified (a) simple superstmetures with small packing densities and (b) close-packed (bulklike) or even compressed stmetures, which are observed for deposition of the heavy metal ions Tl, Hg and Pb on Ag, Au, Cu or Pt (see, e.g., [63, 64, 65, 66, 62, 68, 69 and 70]). In case (a), the metal adsorbate is very often stabilized by coadsorbed anions typical representatives of this type are Cu/Au (111) (e.g. [44, 45, 21, 22 and 25]) or Cu/Pt(l 11) (e.g. [46, 74, 75, and 26 ]) It has to be mentioned that the two dimensional ordering of the Cu adatoms is significantly affected by the presence of coadsorbed anions, for example, for the upd of Cu on Au(l 11), the onset of underiDotential deposition shifts to more positive potentials from 80"to Br and CE [72]. 

Liquid ammonia. This can be prepared by compressing ammonia gas. It has a boiling point of 240 K and is an excellent solvent for many inorganic and organic substances as well as for the alkali metals. Liquid ammonia is slightly ionised. ... 

In one extractor (FMC Inc.), the fmit is located between two cups having sharp-edged metal tubes at their base. The upper cup descends and the many fingers on each cup mesh to express the juice as the tubes cut holes in the top and bottom of the fmit. On further compression, the rag, seeds, and juice sacs are compressed into the bottom tube between the two plugs of peel. A piston moves up inside the bottom tube forcing the juice through perforations in the tube wall. A simultaneous water spray washes the peel oil expressed during extraction away from the peel as an oil—water emulsion the peel oil is recovered separately from the emulsion. 

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