Inhibition of liquid Si infiltration into carbon–carbon composites by the addition of Al to the Si slurry pre-coating: mechanism analysis

Abstract The mechanism of the inhibition of liquid Si infiltration (LSI) into a two-dimensional carbon–carbon composite (2D-C/C) by the addition of Al to the Si slurry pre-coating was investigated. It was shown by means of a vapor treatment experiment designed intentionally that the surface composition of the inner pores beneath the Si slurry pre-coating before the occurrence of LSI was pure carbon and SiC, while before the occurrence of the LSI with the Si–6 wt.%Al slurry pre-coating, the surface composition of the inner pores was Al 4 C 3 , SiC and a small amount of pure carbon. The formation of the SiC and the Al 4 C 3 was the result of the evaporation of almost all the Al additive and a little Si during the heating. For reactive infiltrations, reactions at the vapor–liquid–solid triple line are believed to affect the final infiltration depth. Faster reactions at the triple line lead to faster infiltration velocity and hence deeper reactive infiltration. The reaction at the triple line for the LSI with the Si–6 wt.%Al slurry pre-coating was mainly between liquid Si and the surface Al 4 C 3 , which was probably slower than the reaction of liquid Si with the pure carbon at the triple line corresponding to the LSI with the Si slurry pre-coating. Therefore, the extent of the penetration of liquid Si during the LSI with Si–6 wt.%Al slurry pre-coating was lower than that with the Si slurry pre-coating.