Transmission Electron Microscopy of Pyrocarbon Coatings

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Abstract
Transmission electron microscopy reveals that the pyrolytic carbons deposited in a fluidized bed of particles are made up of growth features, the shapes of which vary with the deposition conditions. Three different microstructures, also varying with deposition conditions, are observed within the growth features. The microstructures are: a “mosaic” structure composed of tightly packed small carbon crystallites arranged with the (002) planes nearly parallel to the surface of the growth feature; a “tangled fiber” structure with carbon crystallites arranged with the (002) planes parallel to the axes of long, bent, or twisted ribbons or fibers; and a “layered” structure composed of large crystallites only slightly misoriented from one another over fairly long distances. The microstructural changes that occur during high-temperature annealing and during irradiation help explain the behavior of these carbons during these treatments.