Application of High Resolution Electron-Microscopy to the Study of Carbonaceous Materials

We have used high resolution electron microscopy (dark field and lattice-fringe images) to describe short range order either in natural or synthetic chars, as well as long range order occurring during graphitization process. The chars contain stacks of 2 to 3 aromatic layers 3.4 A to more than 8 A apart, with diameters from 5 to 8 A. Heat treatment leads for hard-carbons to a foam where crystallite growth is prevented by the geometry of the pore walls. On the contrary, graphitization occurs in carbons where parallel stacking is developed in large regions. In a natural environment organic matter included in sediments is progressively degraded by the combined action of pressure and temperature established during geological times. In the same way, organic matter heat-treated until 1,000°C in the laboratory is progressively degraded too. The last limit of either experimental transformations (carbonization) or natural ones (carbonification) is an almost pure carbon solid (coke) which may eventually be progressively transformed into graphite (soft carbons) when heat-treated until 3,000°C (graphitization). Any way, most of these cokes remain very far from the crystalline state (hard carbons) even when they are heat-treated until 3,000°C. At the beginning of their degradation, all these above defined natural or syntheti