Some theoretical aspects of pyrocarbon formation in the gas phase during hydrocarbon pyrolysis

Abstract Pyrocarbon deposited as a bulk coating, e.g. on nuclear fuel particles, by the pyrolysis of gaseous hydrocarbons seems to go through a pre-formation stage in the gas phase. In order to verify this assumption, experimental as well as mathematical studies on this subject have been carried out. This paper summarizes the most important results of the theoretical investigations which form the basis for the application of the model to fluidized-bed processes. The starting point for the mathematical calculations is the concept of the formation of stable nuclei of large hydrocarbon molecules which grow by condensation of hydrocarbon molecules. They finally form large agglomerates or “droplets”, which-under certain circumstances-remain deformable for a relatively long time. During the time of formation and after having reached their final size, these agglomerates obey statistical thermodynamics and migrate under the influence of the various forces controlling the motion of droplets. This process is calculated in a classical mathematical formalism, as are the temperature of the “droplets”, their hydrogen content and the process of solidification of the agglomerates during their lifetime.