| 摘要 |
A carbon body with low permeability to fission products is made by steps which comprise impregnating pores of said carbon body with a liquid impregnant comprising a carbonaceous polymerizable substance which, upon application of heat, will undergo polymerization and then carbonization to deposit a carbon residue equal to at least 45% by weight of the liquid, clearing said impregnant from a proportion of the impregnant filled pores, whereby gases evolved from the said impregnant during subsequent curing and carbonizing can readily pass from the carbon body without cracking said body, curing said impregnant to cause polymerization of said carbonaceous polymerizable substance, and carbonizing said impregnant in said pores to deposit a substantial carbon residue therein, whereby an improved crack-free carbon body having lowered permeability to fission products is provided. The impregnating, pore clearing, curing and carbonizing steps are preferably repeated also preferably with an impregnant of progressively reduced viscosity. The clearing operation may be carried out by subjecting the carbon body to a pressure differential across the impregnating pores. The preferred impregnant comprises a mixture of maleic anhydride and furfuryl alcohol and the impregnation may be carried out by first degassing the body and subsequently immersing in the impregnant and then subjecting the body to a series of changes in pressure between super atmospheric and sub-atmospheric whereby the impregnant is driven into the pores. An optional modification of the process dispenses with the pore clearing step in the third and subsequent impregnation, pore-clearing, curing and carbonization cycles. A detailed example of rendering a graphite tube impermeable which entails six impregnating cycles is included and uses furfuryl alcohol and maleic anhydride as the impregnant. Reference has been directed by the Comptroller to Specification 874,592. |
