Structure of SiC coatings from polycarbosilane on graphite for fuel element matrix of high temperature gas-cooled reactor

The structures of the SiC coatings fabricated from polycarbosilane (PCS) on graphite for fuel element matrix of high temperature gas-cooled reactor were studied. It was shown that uniform dense SiC coatings could be obtained by this method when the PCS concentration of impregnation solution was in the range of 10-30 wt.%. The graded transition layers at the interface between coatings and graphite substrates were obtained for the content of SiC in pores transformed from PCS became smaller with the increase of depth due to the gradually changing impregnation resistance of PCS/xylene in the pores. The SiC coatings became denser and thicker with increase of PCS concentration. The largest thickness of SiC coatings by one impregnation was 1-2 mu m. The SiC coatings mainly contained beta-SiC, but free carbon, which was detected by Raman spectrum, still existed in the coatings. (c) 2005 Elsevier B.V. All rights reserved.