Thermal stability and chemical erosion of the silicon doped CFC material NS31

The thermal stability of the 8-10 at.% Si doped 3D CFC material NS31 was investigated using scanning electron microscopy (SEMI) and ion beam analysis. Total erosion yields and CD4 production yields were determined by bombarding with monoenergetic deuterium ions. During heating to 1800 K SiC crystallites of a few mu m size are created on the surface. A Si depletion at the surface and an enrichment layer (20-50 at.% Si) beneath the surface of about 5-10 mu m thickness were observed. They are explained by the distribution of the crystallites of mu m size and the evaporation of Si from the surface. After heating a NS31 mock-up tile to temperatures above 2300 K in a power load test, the Si concentration in a surface layer of more than 5 mu m thickness drops below 3 at.% Si. The chemical erosion is reduced for the initial and heated samples by a factor of 2-3 compared to pure graphite. NS31 shows sputtering yields between those of graphite and silicon carbide depending on the Si concentration of the individual surface. (C) 1998 Elsevier Science B.V. All rights reserved.