Carbon layer

The crude acetonitrile contains as impurity chiefly acetic acid, arising from the action of phosphoric acid on the acetamide. Therefore add to the nitrile about half its volume of water, and then add powdered dry potassium carbonate until the well-shaken mixture is saturated. The potassium carbonate neutralises any acetic acid present, and at the same time salts out the otherwise water-soluble nitrile as a separate upper layer. Allow to stand for 20 minutes with further occasional shaking. Now decant the mixed liquids into a separating-funnel, run off the lower carbonate layer as completely as possible, and then pour off the acetonitrile into a 25 ml, distilling-flask into which about 3-4 g. of phosphorus pentoxide have been placed immediately before. Fit a thermometer and water-condenser to the flask and distil the acetonitrile slowly, collecting the fraction of b.p. 79-82°. Yield 9 5 g. (12 ml.). 

The stmcture of activated carbon is best described as a twisted network of defective carbon layer planes, cross-linked by aHphatic bridging groups (6). X-ray diffraction patterns of activated carbon reveal that it is nongraphitic, remaining amorphous because the randomly cross-linked network inhibits reordering of the stmcture even when heated to 3000°C (7). This property of activated carbon contributes to its most unique feature, namely, the highly developed and accessible internal pore stmcture. The surface area, dimensions, and distribution of the pores depend on the precursor and on the conditions of carbonization and activation. Pore sizes are classified (8) by the International Union of Pure and AppHed Chemistry (lUPAC) as micropores (pore width <2 nm), mesopores (pore width 2—50 nm), and macropores (pore width >50 nm) (see Adsorption). 

Fig. 3. Load—deflection curve for a SiC—C—SiC composite in four-point bending. Note the extreme change in behavior fora composite fabricated with a 0.17-p.m carbon layer between the SiC fiber and the SiC matrix as compared with a composite with no interfacial layer (28).

For both forms of graphite the in-plane C-C distanee is 142 pm, i.e., intermediate between Csp Csp and CspMl sp bond lengths, 153 and 132 pm respeetively. Table 1. Consideration of the resonanee struetures between earbon atoms in the plane show that eaeh C-C bond in the earbon layer plane has about one third double bond character. Carbon layer planes (of various dimensions... 

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... 

Fig. 6. PCNTs with partially deposited carbon layers (arrow indicates the bare PCNT), (a) as-grown, (b) partially exposed nanolube and (c) 002 dark-field image showing small crystallites on the tube and wall of the tube heat treated at 2500 C.

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... 

Fig. 2. A portion of an unrolled cylinder with screw helicity. The broken line is parallel to the cylinder axis, and the cylindrical sheet has been cut along a generatrix (full line parallel to the cylinder axis), a and b are the unit vectors of the two-dimensional carbon layer in hybridization.

Fig. 4. Screw helicity the system of (P, O) coordinates used to describe Ihe orientation of the two-dimensional sp carbon layer in an unrolled cylindrical sheet whose edges are shown by the slanted unlabelled full lines. Closure of the cylinder is obtained by rolling the sheet around the direction of the cylinder axis given by the dotted line and superimposing hexagons A and B. The slanted dashed lines correspond to a continuous line of unbroken hexagons of the cylinder, and indicate the apparent angle of pitch /3.

Fig. 2. A nonclassical view of staging proposed by Herold and co-workers (JI3). From left to right are first-, second-, and third-stage compounds. (—, Carbon layer oooo, alkali-metal layer.)...

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). 

Enke, K., Some New Results on the Fabrication of and the Mechanical, Electrical and Optical Properties of I-Carbon Layers," Thin SolidFilms, Vol. 80,1981, pp. 227-234. 

In a study of dental silicate cements, Kent, Fletcher Wilson (1970) used electron probe analysis to study the fully set material. Their method of sample preparation varied slightly from the general one described above, in that they embedded their set cement in epoxy resin, polished the surface to flatness, and then coated it with a 2-nm carbon layer to provide electrical conductivity. They analysed the various areas of the cement for calcium, silicon, aluminium and phosphorus, and found that the cement comprised a matrix containing phosphorus, aluminium and calcium, but not silicon. The aluminosilicate glass was assumed to develop into a gel which was relatively depleted in calcium. 

---