Graphite cohesion

Because the cohesive energy of the fullerene Cyo is —7.29 eV/atom and that of the graphite sheet is —7.44 eV/atom, the toroidal forms (except torus C192) are energetically stable (see Fig. 5). Finite temperature molecular-dynamics simulations show that all tori (except torus Cm2) are thermodynamically stable. 

The value 125 kcal/mol represents an upper bound to the cohesive energy per carbon atom in graphite, since the interaction between iayers in the buik has not been accounted for. Given the reiativeiy large distance and the physicai properties of graphite, the interiayer interaction energy is estimated to be < 5 kcai/mol. 

This leaves us with a computed resuit in iess than satisfactory agreement with the experimental value of about 170 kcal/mol(57). The neglect of electron correlation and the limited basis set used are the most important sources of the discrepancy. In a previous study on monolayer graphite(56), basis set effects were found to lead to a significant underestimation of the cohesive energy. 

The cohesive energy per carbon atom in a poly-yne ring is only 99.1 kcal/mol, clearly lower than the value in Cc. Anticipating a long and complicated route of formation when starting from graphite, in does not seem likely that any of the larger clusters observed experimentally would have a linear or cyclic chain structure. 

In cases where the solid reduction products of the solvent molecules form highly cohesive and adhesive surface films, the surface reactions are quickly blocked before further massive reduction of solution species (which also form the gas molecules) takes place. When passivation of the graphite is not reached quickly enough (as in the case of PC solutions), intensive surface reactions build up the internal pressure that cracks the particles and leads to their deactivation. 

From the above discussion, it is clear that the stabilization or failure of graphite electrodes depends on a delicate balance between passivation phenomena (due to the formation of highly cohesive and adhesive surface films) and a buildup of internal pressure due to the reduction of solution species inside crevices in the graphite particles. This delicate balance can be attenuated by both solution composition (EC-DMC vs. EC-PC or PC, etc.) and the morphology of the graphite particles (i.e. the structure of the edge planes and the presence of crevices). 

Phenyl (Cohesive Technologies), the polymer-based Oasis HLB (Waters), the Cyclone (Cohesive Technologies), and the porous graphitized carbon-based Hypercarb (ThermoHypersil, Cheshire, UK) Cohesive s 2300 system was the HTLC component. Merck s monolithic reversed-phased Chromolith Speed ROD (RP-C18 (50 x 4.6 mm) served as the analytical column. The Oasis HLB, Cyclone TFC, and Hypercarb yielded the best retention capacity and good elution efficiency and volume. Recovery was 42 to 94% with a sample volume of 10 mL. Run time was 14 min. LODs were 0.4 to 13 ng/L for most compounds. 

Coating smokeless proplnts with graphite usually achieve the following purposes a)aids in removal of static electricity b)acts as burning deterrant c)acts as a lubricant and d)prevents caking or cohesion of the proplnt grains... 

On the other hand, the role of both, binders for stabilizing structure and the graphite for increasing porosity was analysed. A literature search [18] showed that the most common binders for these reactions were the bentonite and natural silicates (2-4% w/w) with 1,5-3 Kg/mm in order to provide some cohesion and increase the mechanical strength to the zinc titanite and zinc ferrite particles. In the second step, several supported sorbents (10% of active phase) have been prepared and characterised. 

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