Particulates from PTFE degradation in terrestrial and microgravity.

It has recently been discovered that the ultrafine particles generated during polymer thermodegradation are a major health hazard, owing to their unique pathway of processing in the lung. This hazard in manned spacecraft is poorly understood because the particulate products of polymer thermodegradation are generated under low gravity conditions. Particulates generated from the degradation of polytetrafluoroethylene (PTFE), insulation coating for 20 AWG copper wire (representative of spacecraft application) under intense current overload, were studied in terrestrial gravity and microgravity. Microgravity tests were done in a 1.2-s drop tower at the Colorado School of Mines. Thermophoretic sampling was used for particulate collection. Transmission electron microscopy (TEM) was used to examine the smoke particulates. The pigmentation of PTFE insulation seems to have an overwhelming effect on size, shape and morphology of the particulate. Nanometer-sized particles were found in all cases, but their extent of aggregation and size distribution were dependent on both PTFE pigmentation and gravity; higher aggregation occurred in low gravity. Four different color insulations (viz. white, black, red and yellow) were studied.

Inhalation risk in low-gravity spacecraft.

Inhalation risks on long-duration manned spaced flight include gasses chronically released by outgassing of materials, gasses released during spills, thermodegradation events (including fires) with their attendant particulates, and fire extinguishment. As an example, an event in which electronic insulation consisting of polytetrafluoroethylene undergoes thermodegradation on the Space Station Freedom was modeled experimentally and theoretically from the initial chemistry and convective transport through pulmonary deposition in humans. The low-gravity environment was found to impact various stages of event simulation. Critical unknowns were identified, and these include the extent of production of ultrafine particles and polymeric products at the source in low gravity, the transport of ultrafine particles in the spacecraft air quality control system, and the biological response of the lung, including alveolar macrophages, to this inhalation risk in low gravity.

Fullerenes C60 and C70 in flames.

The fullerenes C60 and C70 were first identified in carbon vapour produced by laser irradiation of graphite, and have recently been produced in macroscopic quantities by vaporization of graphite with resistive heating. It has also been suggested that fullerenes might be formed in sooting flames, and indeed all-carbon ions with mass/charge ratios suggestive of fullerenes have been detected in flames. These species were assumed to have the cage structures of fullerenes, but the mass spectroscopic evidence could not establish this conclusively. We have now collected samples of condensible compounds and soot from hydrocarbon combustion under a range of conditions, and analysed these using conventional techniques in an effort to detect fullerenes. Spectroscopic studies reveal the presence of C60 and C70 in yields and ratios that depend on temperature, pressure, carbon/oxygen ratio and residence time in the flame. Control of these conditions allows optimal yields of 3 g of fullerenes per kilogram of fuel carbon burned, and variation of the C70/C60 ratio over the range 0.26-5.7.