Comparison of PEEK and VESPEL ®SP1 characteristics as vacuum seals for fusion applications

Abstract

In this paper, the results of a detailed comparison of PEEK and VESPEL ®SP1 properties as vacuum seals are reported. These synthetic materials have good insulating and mechanical characteristics at relatively high temperatures, which make them very good candidates for UHV applications. Since PEEK has never been used as a vacuum gasket, the main purpose of the paper is to assess its performances, particularly in comparison to VESPEL, which is the reference material for fusion applications. The bench tests include the analysis of the materials behavior at various temperatures up to 250°C. In addition to tightness and permeation tests, thermal desorption and gas chromatographic-mass spectrometer (GC/MS) analysis have been performed, to assess PEEK outgassing with respect to VESPEL ®SP1 in UHV environment. The results obtained indicate that in general PEEK performances are comparable to those of VESPEL ®SP1 in the investigated operating ranges. VESPEL ®SP1 outgassing results in a factor about five times higher than that of PEEK; moreover, the He permeation of PEEK is almost an order of magnitude lower than VESPEL ®SP1.