親水性ナノ粒子断熱材の熱伝導率におよぼす水分の影響

Hydrophilic nanoporous materials have extremely low thermal conductivities ranging from 0.02 to 0.05 W/(m·K) in the temperature range from room temperature to 800°C. However, the effect of water absorbed in the specimen on the thermal conductivity has not almost been investigated under 100°C. Therefore, we have made an new apparatus, and have measured thermal conductivities of the nanoporous materials, which were made of fumed silica, in the temperature range from about 30°C to 80°C. The result of the measurements has proved that a cusp wave profile, which appears as the peak value at about 100°C for the relationship between the thermal conductivity and the mean temperature of the specimen, was observed due to the evaporation of water around 100°C. Furthermore, it was suggested that the water absorbed in the material lowered the efficiency of scattering on the thermal radiation.