Transmission electron microscopy of isotropic pyrocarbon deposited on spherical particles for high temperature reactor

Thin films of isotropic pyrocarbons deposited onto nuclear fuel kernels in a fluidized bed were studied by transmission electron micrography. The pyrocarbons were found to be made of stacked growth units exhibiting a more or less spherical shape. The existence of two distinct structural arrangements of carbon atoms could be evidenced by electron diffraction: one, identical with the structure of turbostratic graphite, and the other, poorly organized, similar to vacuum evaporated 'amorphous' carbon. Micrographs of the material clearly showed the distribution of the two pyrocarbon varieties. It is concluded from all these observations that there is a close relationship between the microstructure of the spherical growth units and that of carbon blacks. (author)