PTFE as a viable sealing material for lightweight mass spectrometry ovens in dusty extraterrestrial environments

Abstract

Ever increasing interest in the Moon, not only for scientific but also commercial and prospecting purposes, requires a more streamlined and reproduceable approach to issues such as the sealing of sample handling ovens, in contrast to the mission-specific mechanisms which have tended to prevail in the past. A test breadboard has been designed and built in order to evaluate the leak rates of different oven sealing concepts and materials within the context of the ProSPA instrument being developed for the European Space Agency. Sealing surface geometries based on a simple 90° knife-edge, and two widely used vacuum fitting standards (VCR® and ConFlat®) have been tested using PTFE gaskets in vacuum across a temperature range of -100°C to 320°C, equivalent to a projected -100°C to 1000°C sample heating range in the ProSPA ovens. The impact of using glass- and carbon- filled PTFE has also been investigated, as has the effect of dust coverage of JSC-1A lunar simulant up to 9 per cent by area. The best combination of properties appears to be unfilled PTFE, compressed between two 90° knife-edges with a confining force of ∼ 400 N. This can produce a leak rates within the 10−7 Pa.m3.s−1 range or better regardless of the level of dust applied within the experimental constraints. A strong temperature-dependence on the leak rate is identified, meaning that careful oven design will be required to minimise the temperature at the seal interface even within the operational temperature range PTFE itself.