Basic Structural Units BSUs

The HRTEM observation of the cross section of a coated fiber showed that the core is constituted of aromatic layers highly misoriented, whereas they are preferentially oriented in parallel for the thin coating pairs of stacked layers form mainly Basic Structural Units (BSUs) in which the average interlayer distance is smaller than between the aromatic layers in the bulk of the fiber. Since the nanotexture is more dense for the pyrolytic carbon than for the fiber itself, it acts as a barrier which prevents the diffusion of the large solvated lithium ions to the core of the fiber, allowing the passivation layer to be less developed after this treatment. Hence, the major amount of lithium inserted is involved in the reversible contribution therefore this composite material is extremely interesting for the in-situ 7Li NMR study of the reversible insertion. 

Figure 2.16 Schematic model of the aUgnment of aromatic layers in carbon spherules with radial point orientation of basic structural units (BSUs). Several types of sections and the corresponding cross-sections of the spherules are also indicated. (Reprinted from Ref. [82] with permission from Elsevier.)...

BASIC STRUCTURAL UNITS (BSUs) AS ELEMENTAL BRICKS OF DISORDERED CARBONS... 

FIGURE 1.33 (a) Disclinations in mesophase (b) aromatic molecular distribution (basic structural units [BSUs]). (Adapted from a sketch in Ref. 99.)... 

Softening suspension of aromatic molecules at random As concentration increases —> basic structural units (BSUs) piled up face to face by two to three Local molecular orientation (LMO) occurrence Solidification Maximum spins Polygonization ... 

In the majority of polymer systems designed for an SiC synthesis, the atom ratio C/Si is significantly >1. Therefore, in the crystallization model described by Monthioux and Delverdier [147] the excess carbon is considered to play a very important role. By means of HRTEM it was observed that more or less in all the systems investigated the formation of the so-called Basic Structure Units (BSU) of the free carbon - i.e. the formation of small stacks of only a few polyaromatic layers - seems to be the first step for the following nucleation mechanism of SiC. Such BSUs (graphenes) have lateral extensions in the order of 1 nm, are laterally saturated by hydrogen atoms and piled up in a... 

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