Microstructure and properties of fine-grained isotropic graphite based on mixed fillers for application in molten salt breeder reactor

Abstract

Fine-grained isotropic graphite (FG) derived from mixed fillers with different weight ratio of natural graphite flake (NG) and calcined coke was prepared by cold isostatic pressing method. The average diameters of NG and coke were both 10 μm. The structure and properties of FG were investigated and compared with IG-110 graphite from Toyo Tanso Co., Ltd. The structure and properties of FG changed regularly when the weight percentage of NG in filler varied from 0 to 100%. The average pore diameter and porosity respectively minimized from 1.05 to 0.183 μm and 17.1 ± 0.1% to 11.8 ± 0.1%. Nevertheless, thermal conductivity at 298 K and density respectively increased from 93 ± 2 to 130 ± 2 W/m·K and 1.74 ± 0.02 to 1.85 ± 0.02 g/cm3. Result of molten salt infiltration experiment indicated that FG exhibited much better molten salt barrier property than IG-110 once the NG in filler excess 50 wt%. Especially, only 0.085 wt% fluoride salt could be detected for the graphite derived from 100% NG even up to 10 atm, which implied it could nearly totally inhibit the molten fluoride salt permeation and NG might be used as filler to fabricate moderator or reflector graphite materials for molten salt breeder reactor.