Study On Carbon Nanotubes As A Novel Cryosorbent Material For CFETR

Carbon nanotube is a kind of hollow tubular carbon nanomaterial,which is widely used in medicine,chemistry,nanofabrication technology and other fields.Carbon nanotubes can be regarded as hollow cylinders with nanometer diameter made of flake graphene.Therefore,carbon nanotube inherits graphene in many physical properties,such as high thermal conductivity,electrical conductivity and large specific surface area.The specific surface area of single-walled carbon nanotubes is greatly increased by heat treatment in air atmosphere.The possibility of the application of the carbon nanotube sponge as cryosorbent on cryosorption panel in themonuclear experimental reactor has been explored,and the reasonable structure of cryosorption panel with carbon nanotube sponge as cryosorbent has been designed.China Fusion Engineering Experimental Reactor(CFETR)is in the conceptual design stage.The annular cryopump is used to balance the fuel supply and pump of the plasma exhaust which is mainly composed of hydrogen isotope,helium and impurity gases.In international thermonuclear experimental reactor(ITER),coconut shell activated carbon is used as the cryosorbent in the Torus cryopumps.However,coconut shell activated carbon contains high level of impurity and has relatively poor thermal conductivity and is easy to fall off from the cryosorption panels.Carbon nanotubes is a kind of carbon material with high purity and good thermal conductivity,which has the potential to be used as a new type of cryosorbent.After 30 years of development,the synthesis method of carbon nanotubes has been quite mature,and the corresponding cost is gradually reduced.Single-walled carbon nanotubes has large specific surface area with good physical adsorption capacity,but the specific surface area of pristine single-walled carbon nanotubes is still lower than that of coconut shell active carbon.In order to increase the inner space of single-walled carbon nanotubes and the adsorption capacity,the defects of tube wall has been formed by heat treatment of the single-walled carbon nanotubes in air atmosphere.This paper includes three aspects:1)the comparative study of single-walled carbon nanotubes and coconut shell activated carbon heat-treated in air atmosphere;2)the research on the performance of carbon nanotube sponge as a cryosorbent;3)the design of cryosorption panel using carbon nanotube sponge as cryosorbent.In the first part:The single-walled carbon nanotubes were oxidized by heat treatment in air atmosphere in the temperature range from 25? to 600? at heating rate of 1?/min.The final heat-treatment temperature of single-walled carbon nanotubes with the largest specific surface area is 500?.The morphologies of single-walled carbon nanotubes,and the carbon particles on the wall of single-walled carbon nanotubes before and after heat treatment were compared and analyzed.The Brunauer-emmette-teller(BET)specific surface areas and element contents of single-walled carbon nanotubes,pristine single-walled carbon nanotubes and coconut shell activated carbon heat-treated at different final heat-treatment temperatures were compared,which preliminarily confirmed the advantages of single-walled carbon nanotubes compared with coconut shell activated carbon in cryosorption.In the second part:A simple carbon nanotube sponge-304 stainless steel composite model was made.The thermal diffusivities,thermal conductivities and thermal resistances of carbon nanotube sponge,304 stainless steel and carbon nanotube sponge-304 stainless steel composite were measured.The results were compared with the thermal parameters measured by other scholars.The element content and BET specific surface area of carbon nanotube sponge were determined,and the results were compared with coconut shell activated carbon,and the application of carbon nanotube sponge as cryosorbent was discussed.The results confirmed that carbon nanotube sponge was suitable to be used as cryosorbent in the Torus cryopumps without inorganic adhesive.In the third part:The innovative network structure was designed for the fixation of cryosorbent on the cryosorption panel.The relative position of carbon nanotube sponge as cryosorbent on the cryosorption panel was determined.The steel wire was adopted to fix carbon nanotube sponge on the cryosorption panel,which avoided the involvement of inorganic adhesive in the cryosorption panel.