核融合炉用プラズマ対向材料としての炭化ホウ素-炭素繊維複合セラミックスの開発(第2報) : 熱伝導特性に対する炭素繊維中へのボロン固溶の影響

概要

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As a plasma facing material of nuclear fusion reactors, B_4C-high thermal conductivity carbon fiber (CF) composite ceramics have been fabricated through hot-pressing. Effect of sintering temperature on the thermal conductivity of the composites was investigated in a 1600-2100℃ range. The mean density of substitutional solute B in the CF, estimated from shifts in (110) Bragg diffraction angle, was found to increase from 0.26 to 0.90 atom%, as the hot-pressing temperature was increased from 1600 to 2100℃. The reciprocal phonon mean free path in the CF's of the composite, 1/l_L, was estimated from sound velocity in graphite in the in-plane directions divided by thermal diffusivity in the fiber axis direction of the composite, v_L/α. Thus, the phonon scattering probability due to structural defects, including substitutional B solution into CF's of B_4C-CF's of different sintering temperatures, was estimated from vertical axis intersection in 1/l_L-T plot. The mean substitutional B density was found to change proportionally to the vertical axis intersection in the 1/l_L-T plot. The decrease in thermal conductivity due to substitutional B solution into the CF's was found to be remarkable only below 400℃, but the decrease was insignificant above 400℃. Thus, hot-pressing at 2100'℃ is recommendable from total material designing aspects.
社団法人日本セラミックス協会の論文
1997-11-01