| Popis: |
Carbon/carbon composites made from carbon mats and propane-derived pyrolytic carbon matrices have been characterized by optical microscopy and structural parameters such as density and apparent crystallite size. It is shown that the pyrolytic carbon matrices deposited by a thermal-gradient chemical vapor deposition (CVD) technique can have wide ranges of density (1.55–2.10 g/cm 3 ) and crystallite size (23–35 A) as well as various microstructures with a strong dependence on the deposition conditions. The matrices have either a columnar, smooth laminar, isotropic, or transition structure. The isotropic structure formed in the high-temperature, low-propane-concentration region has a lower density and a smaller crystallite size than the smooth laminar and columnar structures. The transition structures are formed between the isotropic and smooth laminar region and have an intermediate character in structure. The structural changes produced by changes in the depostion condition are discussed in view of the arrangement of carbon molecules. |
