Chemical Vapor Infiltration of Carbon into Graphite Block with Uniform Bore Capillary Tubes

Abstract

Chemical Vapor Infiltration with carbon was studied in uniform bore capillary tubes using CH4 as a source gasat 1300°C and 2 to 20 Torr. The relation between CVI parameters and the resultant deposition profile, rate andmicrostructure were examined.Higher CH4 flow rate produces higher deposition rate and higher degree of preferred orientation, but lessdeposition uniformity along the capillary. The contact time of 0.1 to 0.3 seconds is suggested to be a preferred numberwithin the condition studied, in terms of densification rate and uniformity.From the CVI using C2H2 and C6H6 as source gases, it is suggested that these two hydrocarbons are thedecomposition products in the early stage, and produce acetylenic and aromatic species. The aromatic species give highdeposition rate and deposit with high degree of preferred orientation. The acetylenic species give better penetration ina capillary.The CVI penetration depends on the diameter of the capillary, but in the capillarywith the diameter smaller thanmean free path of gases, deposition profile is also determined by the surface to volume ratio of the capillary.Finally, the effect of wall-block spacing was studied. Better uniformity along the flow and higher conversionrate of feed gas to deposit can be achieved by controlling the wall-block spacing.