Chemical Characterization and Thermal Stressing Studies of Perfluorohexane Fluids for Space-Based Applications

Several perfluorohexane C6F14 fluids with different isomer concentrations were evaluated for use in an upcoming NASA experiment. Two commercial 'high-purity n-perfluorohexane fluids and a technical grade mixture of branched and linear isomers (FC-72 (TM)) were evaluated for exact chemical composition, impurities, and high temperature degradation (pyrolysis). Our investigation involved simulated thermal stressing under conditions likely to occur in the event of a leak within the ISS and subsequent vapor exposure to the high temperature catalyst present in its trace contaminant control subsystem. Exposure to temperatures in the temperature range of 200-450 degrees C in an inert or oxidizing atmosphere, with and without the presence of catalyst, was investigated. The most aggressive conditions studied were exposure of vapors to 450 degrees in air and in the presence of palladium catalyst. Gas chromatography/mass spectrometry and gas chromatography analyses were conducted on the samples before and after pyrolysis. The FC-72 and n-perfluorohexane samples showed no significant degradation even under the most aggressive study conditions. A potential byproduct of exposure of perfluorohexane fluids to high temperatures is the production of perfluoroisobutene, which is extremely toxic. The perfluorohexanes showed no signs of perfluoroisobutene production to an analytical detection limit of 10 parts per billion.