Mitsuo Nakagawa

New composite composed of boron carbide and carbon fiber with high thermal conductivity for first wall

Abstract A new composite was created from B 4 C powder and carbon fiber by hot-pressing at 1700°C or more. The composite sintered at 1700°C with 20–35 vol% B 4 C shows a thermal conductivity of 250 W/m·K at 25°C which is slightly lower than the felt type C/C, but its value becomes higher than the C/C at temperatures above 400°C. The composite with 40 at% B shows more controllable recycling properties than B 4 C. The erosion yield for the composite is about half the yield for graphite at 800 K. After electron beam irradiation in order to test heat resistance no cracks were detected up to 22–23 MW/m 2 leading to a surface temperature of 2500°C.

Thermal conductivity and retention characteristics of composites made of boron carbide and carbon fibers with extremely high thermal conductivity for first wall armour

Abstract The thermal conductivity of the composite hot-pressed at 2100°C including B 4 C and carbon fibers with a thermal conductivity of 1100 W / m · K was nearly the same as that of the composite including carbon fibers with a thermal conductivity of 600 W / m · K . This resulted from the higher amount of B diffused into the carbon fibers through the larger interface. The B 4 C content in the composite can be reduced from 35 to 20 vol% which resulted from the more uniform distribution of B 4 C by stacking the flat cloth woven of carbon fibers (carbon fiber plain fabrics) than in the composite with 35 vol% B 4 C including curled carbon fiber plain fabrics. The decrease in the B 4 C content does not result in the degradation of D (deuterium)-retention characteristics or D-recycling property, but will bring about the decreased amount of the surface layer to be melted under the bombardment of high energy hydrogen ions such as disruptions because of higher thermal conduction of the composite.

Effect of Particle Size Distribution Shape in Bimodal Packing

Effects of the shape of particle size distributions of fine and coarse particles on composite packing density in bimodal mixtures are investigated. Conventional view for bimodal mixtures has it that particle packing density can be increased by increasing individual fines or coarse packing density. It is shown in the present study that for practically sized bimodal particle mixtures, highest relative composite packing density is not determined by individual component packing density, but is determined by the matching of appropriate coarse and fines size distributions. Maximum packing is achieved by minimizing formation of extra pore volume through appropriate design of the mixtures particle size distribution and minimization of midsized particles.