Chicken wire’ structures

Benzo(a)pyrene (Figure 1.14) is the most studied of the polycyclic aromatic hydrocarbons (PAHs), which are characterized by condensed ring systems ( chicken wire structures). These compounds are formed by the incomplete combustion of other hydrocarbons, a process that consumes hydrogen in preference to carbon. The carbon residue is left in the thermodynamically favored condensed aromatic ring system of the PAH compounds. 

Different theories exist about the thickening mechanism of fumed silicas. One of the first was the so-caUed chicken wire structure. That means the silica particles interact with each other via their silanol groups and form a three dimensional structure, which reduces the mobility of the hquid molecules. Under mechanical impact like shearing or shaking the structure is destroyed and the viscosity of the system decreases. After the end of the mechanical impact, the three dimensional network re-establishes itself and the viscosity increases again as a function of time. This mechanism may be valid in simple nonpolar liquids. In liquid mixtures or polymer solutions it is much more complicated and the adsorption pattern on the fumed silica surface seems to play an important role [76]. 

Figure 1 Open network arrangements of trimesic acid on graphite under UHV at low temperature, (a) and (c) The chicken wire structure and (b) and (d) the flower arrangement. (Reproduced from Ref. 18. Wiley-VCH, 2002.)...

The "tubones" existing at the top -three in number-, are composed of an aggregate of nodules with reniform morphology, suiTounded by a thin layer, more or less abundant, of dark-gray dolomitic marls. At times this layer is weak and remember the chicken-wire structure. 

Alabastrines (Figure 6J) Compact, sometimes translucent masses formed by microcrystals with "saccharoid" texture (Ogniben, 1957). Their colour is usually white, salmon or black, and they are commonly arranged foiming nodules with "chicken-wire" structure. This morphology of gypsum could come from former anhydrite. 

The tubes were found to have a bonding structure similar to that of graphite. A nanotube can be thought of as a narrow sheer of a million or more carbon atoms linked together in six-membered benzenelike rings resembling chicken wire and rolled into a very long cylinder only 1-3 nm in diameter. 

The hardest of the transition-metal borides are the diborides. Their characteristic crystal structure (Figure 10.6) consists of plane layers of close-packed metal atoms separated by plane openly-patterned layers of boron atoms ( chicken-wire pattern). If the metal atoms in the hexagonal close-packed layer have a spacing, d, then the boron atoms have a spacing of d/V3. 

In graphite, three ordinary electron-pair bonds link each C to its neighbors in a quasi-infinite tessellated hexagonal or chicken wire pattern, and the remaining valence electrons, one from each C, are delocalized in a n-orbital system extending across the entire chicken wire sheet, above and below. The three-dimensional structure consists of stacks of these sheets. The structure of the sheets is, in effect, one huge collection of fused benzene... 

Traditionally, the principal forms of carbon have (1) diamond, with its tetrahedral arrangement of atoms (2) graphite, whose structure resembles layers of chicken wire and sometimes (3) amorphous, a poorly defined... 

Figure 8.43 (a) Chicken wire and (b) ladder motifs for saturated hydrogen bonded structures. The... 

Historically, the chemistry of layered intercalates began in 1840 with the report that graphite was able to intercalate sulfuric acid between successive layers of its chicken wire mesh. It was not until after the 1960s that serious interest was aroused by intercalates, following the realisation that guest intercalation may significantly alter the host s chemical, catalytic, electronic and optical properties. This is especially true when the host properties are dependent on its layered structure. In the case of graphite, for example, its use as a dry , low-temperature lubricant has come about because of the ease... 

Fig. 2 a The linear tape structure of terephthalic acid, b The zigzag tape structure of isophthalic acid, c The chicken wire sheet structure of trimesic acid [29]... 

From the reaction of Au with alkali metal polysulfide liquids, LiAuS and NaAuS were discovered. Both compounds contain infinite one-dimensional (AuS) chains, featuring alternating sulfide anions and linear coordinated Au centers. In LiAu8, the chains are zigzag and fully extended and they pack in mutually perpendicular sets. In NaAuS, the same chains coil in an unusual fashion so that they become interwoven to form layers reminiscent of chicken-wire (Figure 17). This novel coiling mode allows Au Au contacts to form, which help to stabilize the structure. 

Figure 8.43 (a) Chicken wire and (b) ladder motifs for saturated hydrogen bonded structures. The a, b and c designations are assigned in order of increasing hydrogen bond length. (Reprinted with permission from lUCr). 

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