Carbon Aerogel-Based High-Temperature Thermal Insulation

Carbon aerogels, monolithic porous carbons derived via pyrolysis of porous organic precursors synthesized via the sol-gel route, are excellent materials for high-temperature thermal insulation applications both in vacuum and inert gas atmospheres. Measurements at 1773K reveal for the aerogels investigated thermal conductivities of 0.09W center dot m(-1) center dot K-1 in vacuum and 0.12W center dot m(-1) center dot K-1 in 0.1MPa argon atmosphere. Analysis of the different contributions to the overall thermal transport in the carbon aerogels shows that the heat transfer via the solid phase dominates the thermal conductivity even at high temperatures. This is due to the fact that the radiative heat transfer is strongly suppressed as a consequence of a high infrared extinction coefficient and the gaseous contribution is reduced since the average pore diameter of about 600nm is limiting the mean free path of the gas molecules in the pores at high temperatures. Based on the thermal conductivity data detected up to 1773K as well as specific extinction coefficients determined via infrared-optical measurements, the thermal conductivity can be extrapolated to 2773K yielding a value of only 0.14W center dot m(-1) center dot K-1 in vacuum.