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 o f a hydrocarbon gas and a subsequent graphitization treatment. Its mic rostructure is still, however, a matter of controversy. Several sample s of different quality were extensively studied by x-ray diffraction t opography. The contrast obtained on 00l reflections is mainly explaine d in terms of 'primary extinction' acid orientation contrast. This imp lies that the interlayer spacing of the graphite lattice planes remain s constant over distances of several tens of micrometres. Graphitizati on mechanisms are discussed in the light of this interpretation. A mic rostructural model, closely related to that of as-deposited pyrolytic carbon, is proposed.