Abstract
As a plasma facing material of nuclear fusion reactors, B4C-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°C 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 0.90atom%, as the hot-pressing temperature was increased from 1600 to 2100°C. The reciprocal phonon mean free path in the CF's of the composite, 1/lL, was estimated from sound velocity in graphite in the in-plane directions divided by thermal diffusivity in the fiber axis direction of the composite, vL/α. Thus, the phonon scattering probability due to structural defects, including substitutional B solution into CF's of B4C-CF's of different sintering temperatures, was estimated from vertical axis intersection in 1/lL-T plot. The mean substitutional B density was found to change proportionally to the vertical axis intersection in the 1/lL-T plot. The decrease in thermal conductivity due to substitutional B solution into the CF's was found to be remarkable only below 400°C, but the decrease was insignificant above 400°C. Thus, hot-pressing at 2100°C is recommendable from total material designing aspects.
