Development of iron-base composite materials with high thermal conductivity for DEMO
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Development of iron-base composite materials with high thermal conductivity for DEMO H. Homma1, N. Hashimoto1, S. Ohnuki1 1 Graduate School of Engineering, Hokkaido University, N-13, W-8, Sapporo 060-8278, Japan ABSTRACT One of the critical issues for development of the nuclear fusion demonstration reactor (DEMO) is the high heat flux on heat-resistant equipments, especially the blanket and divertor. Materials of such equipments require relatively high thermal conductivities. In this study, we developed iron-based composite materials with carbon nanotube (CNT) and copper, which have high thermal diffusivities, by means of Hot Pressing (HP) and Spark Plasma Sintering (SPS). The thermal diffusivity in the iron/CNT composites was not high enough compared with that of pure iron, while iron/copper composite showed a relatively high thermal diffusivity in the joining conditions. One of the reasons not to be improved thermal diffusivity could be nonmono-dispersion of CNT by the formation of carbides in the matrix. INTRODUCTION Reduced activation ferritic/martensitic (RAFM) steels, e.g. the Japanese candidate structure material, F82H, developed by Japan Atomic Energy Agency (JAEA) [1-3], are one of candidate structure materials for blanket and divertor in DEMO. blanket and divertor will be exposed to the high heat flux from plasma. In particular, divertor in DEMO could receive more than 10 MW/m2 as well as the divertor in ITER [4]. From this viewpoint, adequate thermal conductivity is requested to structural materials of diverter. However, the thermal conductivity of RAFM does not meet the demanded performance. In this study, we focused on increasing the thermal conductivity of the complicated joint structure in the heat-resistant equipments. With using a high thermal conductivity material such as CNT [5] or copper [6], we have developed iron-based composite materials with a better thermal diffusivity than that of steels. EXPERIMENT Diffusion bonding The base material used in this study was stainless steel (SCM440). As the high thermal conductivity materials, 99.96% pure copper (plate with 1.0 mm thick, The Nilako, Co. LTD.) and Multi-walled nanotubes (MWNTs, 150 nm diameter, specific surface area 13 g/cm2, Showa Denko K.K.) were used. The steels were cut in the form of cuboids with dimensions of 18 mm×10 mm×11 mm. The sample surfaces were prepared by a conventional grinding technique. Final grinding was performed with a sandpaper of #1500. The copper plates were ground in the same manner. Adhered contaminants on the sample surface were removed in an acetone bath, followed by dried in air. Guoliang Ding et al. reported [7] that arrangement of CNT direction was required to get a high thermal conductivity of CNT. Therefore, the ditched (1.0 μm in width) surface sample was prepared by using a sandpaper of #1000, and then the surface was covered with the MWNTs in order to accomplish the well-aligned MWCNT on the ditched surface. In the case of HP (Fuji Electronic Industrial Co., Ltd.), the graphite punches in contact with the
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