Carbon layer structure

In the 1930s Hoffman and Wilm [101] found only (hkO) graphite reflections in an x-ray diffraction study of a carbon black. The absence of graphitie (hkl) reflections led them to propose a structure consisting of graphitic carbon layer... 

The structure refinement program for disordered carbons, which was recently developed by Shi et al [14,15] is ideally suited to studies of the powder diffraction patterns of graphitic carbons. By performing a least squares fit between the measured diffraction pattern and a theoretical calculation, parameters of the model structure are optimized. For graphitic carbon, the structure is well described by the two-layer model which was carefully described in section 2.1.3. 

In Fig. 13 is shown the 002 lattice images of an as-formed very thin VGCF. The innermost core diameter (ca. 20 nm as indicated by arrows) has two layers it is rather straight and appears to be the primary nanotube. The outer carbon layers, with diameters ca. 3-4 nm, are quite uniformly stacked parallel to the central core with 0.35 nm spacing. From the difference in structure as well as the special features in the mechanical strength (as in Fig. 7) it might appear possible that the two intrinsically different types of material... 

Feitknecht has examined the corrosion products of zinc in sodium chloride solutions in detail. The compound on the inactive areas was found to be mainly zinc oxide. When the concentration of sodium chloride was greater than 0-1 M, basic zinc chlorides were found on the corroded parts. At lower concentrations a loose powdery form of a crystalline zinc hydroxide appeared. A close examination of the corroded areas revealed craters which appeared to contain alternate layers and concentric rings of basic chlorides and hydroxides. Two basic zinc chlorides were identified, namely 6Zn(OH)2 -ZnClj and 4Zn(OH)2 ZnCl. These basic salts, and the crystalline zinc hydroxides, were found to have layer structures similar in general to the layer structure attributed to the basic zinc carbonate which forms dense adherent films and appears to play such an important role in the corrosion resistance of zinc against the atmosphere. The presence of different reaction products in the actual corroded areas leads to the view that, in addition to action between the major anodic and cathodic areas as a whole, there is also a local interaction between smaller anodic and cathodic elements. 

Graphite is another solid form of carbon. In contrast to the three-dimensional lattice structure of diamond, graphite has a layered structure. Each layer is strongly bound together but only weak forces exist between adjacent layers. These weak forces make the graphite crystal easy to cleave, and explain its softness and lubricating qualities. 

This model of a carbon nanotube shows that it consists of several concentric tubes. Such layered structures are very strong. 

There are two schools of thought as to the structure of graphite oxide. Ortho or meta ether linkages have been postulated to enforce a puckering of planes (Al), whereas a keto-enol tautomerism was suggested to keep the carbon layers planar (C3). 

The carbon-based nanofillers are mainly layered graphite, nanotube, and nanofibers. Graphite is an allotrope of carbon, the stmcture of which consists of graphene layers stacked along the c-axis in a staggered array [1], Figure 4.1 shows the layered structure of graphite flakes. 

In a Japanese plasma wind tunnel, SPA specimens were tested up to 3.8 MW/m2 at 0.7 bar aerodynamic pressure (Fig. 12). After a test duration of 60 s, no obvious damage was visible. The surface temperature of about 2600°C was reduced to 100°C within 20 min. Further analysis showed a maximum charred depth of the ablator of 15 mm. The carbonization process did not change the geometric dimensions, the new heat protection system can be considered absolutely stable to deformation. The carbonized layer still has a noticeable pressure resistance and transfers the load applied by the dynamic pressure to the structure. 

High Resolution Transmission Electron Microscopy (HRTEM, Philips CM20, 200 kV) was applied to get structural and nanotextural information on the fibers, by imaging the profile of the aromatic carbon layers in the 002-lattice fringe mode. A carbon fiber coated with pyrolytic carbon was incorporated in epoxy resin and a transverse section obtained by ultramicrotomy was deposited on a holey carbon film. An in-house made image analysis procedure was used to get quantitative data on the composite. 

Carbon atoms have the ability to bond to themselves to a greater extent than those of any other element. Known as catenation, this ability gives rise to the several allotropic forms of the element. The most common form of elemental carbon is graphite, which has the layered structure shown in Figure 13.11. 

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