Ultra high vacuum properties of some engineering polymers

Engineering Polymers are very good candidates for applications requiring mechanical properties comparable with metals, chemical inertia, high insulation capability, high temperature operation and ultra high vacuum (UHV) compatibility. The results of a systematic test series, aimed at qualifying the engineering resins VESPEL® SP1, PEEK and CELAZOLE® PBI as UHV seals, are reported. The study of the materials behavior has been carried out over a wide temperature interval, ranging from 20 to 400°C. In addition to the tightness and permeation tests, thermal desorption and gas chromatographic-mass spectrometer (GC/MS) analysis have also been performed. The results obtained indicate that CELAZOLE®PBI provides the best performance, since it can be operated safely up to 375°C, without giving any sign of leak or other drawbacks. PEEK, on the contrary, does not stand temperatures higher than 275°C but, below this limit, it remains a very cost effective and reliable alternative. VESPEL® SP1, in its turn, can be operated safely up to 325°C but above this temperature its properties start to degrade even if not in an abrupt manner as is the case for the other two resins. The possible applications of some of these polymers in the field of nuclear fusion research are also briefly described.