Diamond chemical structure

Diamondoids show unique properties due to their exceptional atomic arrangements. Adamantane consists of cyclohexane rings in chair conformation. The name adamantine is derived from the Greek word for diamond since its chemical structure is like the three-dimensional diamond subunit, as shown in Fig. 5. 

The work on carbon nitride solids is strongly related to research on diamondlike carbon (DLC) materials [5, 6]. DLC materials are thin film amorphous metastable carbon-based solids, pure or alloyed with hydrogen, which have properties similar to that of crystalline diamond (high hardness, low friction coefficient, high resistance to wear and chemical attack). This resemblance to diamond is due to the DLC structure, which is characterized by a high fraction of highly cross-linked sp -hybridized carbon atoms. To obtain this diamond-like structure... 

Fig. 5 Chemical structure (a), absorption (a) and emission (b) spectra of POWT in different buffer solutions pH 2 (open diamond), pH 5 (open square), pH 8 (triangle) and pH 11 (x).(c) The charge of the zwitter-ionic side chain, schematic drawing of proposed backbone conformations and optical properties of POWT at different pH [9]...

The efficacy of diamond and metal-alloy electrodes for the degradation of the textile dyes Basic yellow 28 and Reactive black 5 was also followed by RP-HPLC. The chemical structures of the textile dyes under investigation are shown in Fig. 3.56. An ODS column (150 X 4.6 mm i.d. particle size 5 jttm) was employed for the RP-HPLC determination of... 

The discovery happened by accident. Lewis and Anders were frustrated by their failure to find the carrier of anomalous xenon in carbonaceous chondrites. They decided to try an extreme treatment to see if they could dissolve the carrier. They treated a sample of the colloidal fraction of an Allende residue with the harshest chemical oxidant known, hot perchloric acid. The black residue turned white, and to their surprise, when they measured it, the anomalous xenon was still there The residue consisted entirely of carbon, and when they performed electron diffraction measurements on it, they found that it consisted of tiny (nanometer sized) diamonds. After a detailed characterization that included chemical, structural, and isotopic studies, they reported the discovery of presolar diamond in early 1987 (Lewis et al., 1987). The 23-year search for the carrier of CCFXe (Xe-HL) was over, and the study of presolar grains had begun. 

Diamondlike Carbides. Silicon and boron carbides form diamondlike carbides beryllium carbide, having a high degree of hardness, can also be included. These materials have electrical resistivity in the range of semiconductors (qv), and the bonding is largely covalent. Diamond itself may be considered a carbide of carbon because of its chemical structure, although its conductivity is low. 

In the case of a polymer with a saturated chemical structure, such as polyethylene, the strength of a-bonding is such that the band gap will be comparable to that in diamond. However, for a polymer with a conjugated structure, such as polyacetylene, the chemical binding of the re-electrons is much weaker and a gap of a few eV, comparable to those in inorganic semiconductors, is anticipated. 

Carbon exists in different allotropic modifications, that is, in forms with different chemical structures. The best known are diamond and graphite, both of which are non-porous. 

Silicon is a shiny, blue-gray, high-melting, brittle metalloid. It looks like a metal, but it is chemically more like a nonmetal. It is second only to oxygen in abundance in the earth s crust, about 87% of which is composed of silica (Si02) and its derivatives, the silicate minerals. The crust is 26% Si, compared with 49.5% O. Silicon does not occur free in nature. Pure silicon crystallizes with a diamond-type structure, but the Si atoms are less closely packed than C atoms. Its density is 2.4 g/cm compared with 3.51 g/cm for diamond. 

It is well-known that diamond and graphite are totally different substances with dramatically different properties (see Fig. 4.9), but are however composed of the same particle types, of carbon particles. One has to stop from transferring the material characteristics to the smallest particles. The carbon particle cannot be simultaneously black and colorless it does not simultaneously have two different densities It was only through X-ray structural analysis of the 20th century which finally proved, that both carbon modifications can be differentiated through distinct chemical structures. The different arrangements of the carbon particles in diamond and graphite are responsible for the macroscopic characteristics (see Fig. 4.9). 

Fig. 4.9 Diamond and graphite characteristic properties and chemical structures...

Initial structure-property relationships have been studied using examples like diamond/graphite and white/red phosphorus (see Sect. 4.3), the modifications have been established from the same C atoms or P atoms respectively. However, the substances are drastically different in their chemical structure and therefore in their characteristic properties. The misconceptions could be corrected with the consideration that the individual C atom or P atom show absolutely no properties like color or density. Such characteristics can be determined only when a little crystal is visible (see Sect. 4.3). 

These facts have already been discussed in the examples of diamond/graphite and red/white phosphorus (see Sect. 4.3). The varying properties can be shown by differences in chemical structures. However, these structures are not easy to understand. Because it is possible to correctly demonstrate the arrangement of metal atoms using closest-sphere packing models, it is useful to look at metal structures with regard to the property structure relationships and try to address the above-mentioned misconceptions. 

Fig. 38 Chemical structure of Irgafos P-EPQ top) and isothermal surface potential decay (ITPD, bottom) curves of melt compounded, compression molded, and corona charged films of PEIpur additivated with 5,000 (filled diamonds), 3,200 (filledpentagons), 2,200 (filled triangles), 1,200 (filled circles), 700 (filled inverted triangles), and Oppm (filled hexagons) Irgafos P-EPQ. For comparison, the curve for commercial Ultem 1000 films (open squares) is also included [68]. Published by permission of Wiley Periodicals Inc...

In an attempt to understand further the structures of coals, the n.m.r. spectra of a series of four coals were compared with the corresponding spectra of gem quality diamonds (chemical shift 156 3 p.p.m. from CS and powdered natural graphite (chemical shift 35 p.p.m. from CSg). The spectra were rationalized in terms of increasing carbon aromaticity with increasing coal rank, leading finally to the formation of graphite-like structures. The chemical shift in diamond was found to agree well with empirical... 

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