The permeation of inert gases (N2 and He) through coated SiC-based ceramic composites in the form of tubes or discs was measured. In particular, SiC–SiCf/SiC functionally graded material tubes made of SiC–SiCf with a SiC polycrystalline sealing coating and chemically vapor infiltrated SiCf/SiC composite discs were tested. The permeation tests were aimed at verifying the effectiveness of coatings obtained by chemical vapor deposition and used for closing the porosity of the composite materials and assuring their gas sealing. The measurements were carried out at room temperature, under pressures of 130 to 500kPa. The SiC–SiCf/SiC functionally graded material has shown very low permeability values. The chemically vapor infiltrated SiCf/SiC composite tested has shown rather low permeation values, although the material was not gas tight: its reduced permeance was attributed to both the high fiber percentage and the dense SiC coating.

Nitrogen and Helium Permeation Tests of SiCf/SiC Composites. S.Tosti, B.Riccardi, F.Giordano: Fusion Engineering and Design, 2007, 82[3], 317-24