AN X-RAY-DIFFRACTION TOPOGRAPHIC STUDY OF HIGHLY ORIENTED PYROLYTIC-GRAPHITE

Highly oriented pyrolytic graphite is a very efficient and well-known x-ray and neutron monochromator that is obtained by thermal cracking of a hydrocarbon gas and a subsequent graphitization treatment. Its microstructure is still, however, a matter of controversy. Several samples of different quality were extensively studied by x-ray diffraction topography. The contrast obtained on 00l reflections is mainly explained in terms of 'primary extinction' acid orientation contrast. This implies that the interlayer spacing of the graphite lattice planes remains constant over distances of several tens of micrometres. Graphitization mechanisms are discussed in the light of this interpretation. A microstructural model, closely related to that of as-deposited pyrolytic carbon, is proposed.