Outgassing Behavior of Carbon-Bonded Carbon-Fiber Thermal Insulation

摘要

A carbon-bonded carbon-fiber (CBCF3) thermal insulation has been developed and has demonstrated acceptable strength, thermal conductivity, and outgassing properties for the Selenide Isotope Generator. Primary outgassing at 1350 exp 0 C and 0.1 mPa (10 exp -6 torr) for 70 h seems satisfactory because reabsorption during exposure to argon or air is minimal and the total weight loss during secondary outgassing is also very small. The total outgassing of CBCF3 insulation during generator start-up and operation is equivalent to the weight loss during secondary outgassing, (i.e., 0.08 mg per gram of CBCF3 insulation). The dominating gaseous species of secondary outgassing are CO and CO sub 2 . Primary outgassing (1350 exp 0 C at 0.1 mPa (10 exp -6 torr) for 70 h) causes no increases in the thermal conductivity of CBCF3 insulation. Specimen size affects the first few hours of primary outgassing and thus the fraction of total amount of volatile species being driven off at the end of primary outgassing. However, the time required to outgas a large specimen does not vary with the square of specimen size because diffusion in each fiber or bond is the rate-determining step of primary outgassing. (ERA citation 05:001501)