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Testing was conducted to determine and compare the sensitivities of two oxygen test methods for detecting the presence of hydrocarbon oil contamination on polytetrafluorethylene tape. Ambient pressure mechanical impact tests were conducted, using ASTM Test Method for Compatibility of Materials with Liquid Oxygen (Impact Sensitivity Threshold and Pass-Fail Techniques) (ASTM D 2512); the tests determined the effect of contaminant concentration on the minimum impact energy for ignition. In the other test method, developed at the NASA Johnson Space Center White Sands Test Facility, the contaminated tape was heated using a pyrolysis furnace in flowing, gaseous oxygen. The presence of hydrocarbons in the gaseous oxygen stream was detected by fourier transform infrared spectroscopy (FTIR). This test method also determined the autoignition temperature of the contaminated tape. The test results showed that FTIR of the gases from the pyrolysis furnace is significantly more sensitive than liquid oxygen mechanical impact tests for detecting the presence of contamination. However, the autoignition temperature determined in the pyrolysis furnace is far less sensitive to the presence of hydrocarbon oil contaminants than liquid oxygen mechanical impact tests. Additional testing was conducted using a modified pneumatic impact test system (ASTM Test Method for Ignition Sensitivity to Materials to Gaseous Fluid Impact [ASTM G 74]), to study the effect of hydrocarbon contamination on the ignition process.
polytetrafluoroethylene, tape, hydrocarbon contaminant, mechanical impact test, pneumatic impact test, fourier transform, infrared spectroscopy pyrolysis furnace, ignition, combustion, autoignition temperature
Senior Scientist, Lockheed-ESC, NASA Johnson Space Center White Sands Test Facility, Las Cruces, NM
Principal Scientist, Lockheed-ESC, Houston, TX
Section Head of Nonmetallic Materials, NASA Johnson Space Center, Houston, TX