Resistance to oxidation of graphite silicided by reactive infiltration

In order to improve the oxidation resistance of graphite at high temperatures, graphite surfaces are modified by two silicidation processes involving reactive infiltration of molten silicon or, alternatively, of gaseous silicon monoxide. The resistance to oxidation of silicided graphite is studied by cyclic oxidation tests performed under a dry air flux at temperatures in the range 1550-1600 degrees C. During oxidation three successive regimes are evidenced: (i) initial growth of a passive silica layer on the continuous SiC superficial layer responsible for the remarkable oxidation resistance at 1550 degrees C; (ii) then, slow mass consumption in the intermediate composite SiC C region; (iii) and finally, rapid local consumption of the underlying non-infiltrated porous graphite. The temporal stability of the silicided layer in air is analyzed and the reactions affecting this stability are identified. The analysis interprets the experimental findings in a satisfactory manner, especially the dramatical variation with temperature of silicided graphite lifetime observed in this temperature range. (C) 2011 Elsevier Ltd. All rights reserved.