document: The vapour phase consists of a number of different gases with silicon exhibiting a far higher partial pressure than all carbon containing species over the full temperature range. As an immediate result the vapour contains a higher amount of silicon leaving the solid phase with excess carbon. This carbon is likely to precipitate on the surface of the SiC grains, a process that becomes very rapid as the temperature approaches 2100K [24]. Within the TRISO particle the SiC layer is sandwiched between two coatings of dense carbon. The partial pressure in thermodynamic equilibrium of gaseous carbon forming above graphite was calculated using data taken from JANAF tables and added to Fig. 1 [25], which showed that in the whole temperature range relevant for this study the vapour pressure of carbon is several magnitudes smaller than that of the dominant gas phases above SiC.
extractive_keyphrases: carbon data taken from janaf tables gas graphite number of different gases partial pressure precipitate on the surface of the sic grains sic silicon solid phase triso particle vapour
abstractive_keyphrases: gaseous carbon sic grains vapour phase vapour pressure of carbon