Graphite model structure

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. 

Molecular orientational order in adsorbed monolayers can be inferred indirectly from elastic neutron diffraction experiments if it results in a structural phase transition which alters the translational symmetry of the 2D lattice. In such cases, Bragg reflections appear which are not present in the orientationally disordered state. Experiments of this type have inferred orientational order in monolayers of oxygen (41) and nitrogen (42) adsorbed on graphite. However, these experiments have not observed a sufficient number of Bragg reflections to determine the molecular orientation by comparing relative Bragg peak intensities with a model structure factor. 

Unfortunately, the structure of GO cannot be determined unequivocally by x-ray or by electron diffraction because only hkO and 001 but no hkl reflections are observed. The interplanar distance of vacuum-dried GO is in the range 590-670 pm , and the C—C distance in the carbon planes is only slightly higher than in graphite. Thus, structural models for GO are based mainly on its reactivity and physical properties. 

Fig. 24 Top from left to right chemical structure of CUP TCDB drawing of a TCDB dimer. Bottom from left to right model of the TCDB/CUP host-guest architecture STM image (11.8 nmxll.8 nm) of the TDCB/COR host-guest architecture deposited from toluene on graphite model of the TDCB/COR host-guest architectiue. (Reproduced with permission from [68])...

The literature which attempts to model structure in activated carbon and its consequential porosity is somewhat in disarray and is contradictory. The purpose of this chapter is an attempt to create a rational of this subject area. The concept of crystallites, microcrystallites, graphitic or otherwise, cannot be looked upon favorably and the use of this concept may not have been to the advantage of a realistic understanding of structure in activated carbon. In fact, it may have led to serious misunderstandings of structure in activated carbon. The complex nature of activated carbon is such that it requires the assessment and contrasting of many models, available in the one text, to assist in gaining an understanding, perhaps incomplete, of structure of porosity in carbons. The use of such words as... 

Promising strategies regarding this issue were followed recently. Eastwood et al. and Lin et al. have made use of the phase contrast to successfully image a graphite electrode with sub-pm resolution [14] or to understand the dissolution and re-deposition of poly sulfides in lithium sulfur cells [15]. Another approach followed by Zielke et al. was to model structures corresponding to low atomic number elements in combination with FFTXM tomography reconstmctions [55]. 

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