No abstract

This paper presents a new outgassing test facility based on the difference method, which is a rarely used modified throughput technique. Furthermore, the experimental approach presented is validated based on new measurement data for three relevant materials. The facility allows to measure at a good resolution thermal outgassing rates at variable temperatures between room temperature and 300 °C. The measurement approach is discussed, the facility is described, and the measurement uncertainty is evaluated. Three materials were measured to demonstrate the new experimental approach and to compare the results obtained for stainless steel 316L and two polymers, Viton® and Vespel®. For stainless steel 316L, the influence of different pretreatments was analyzed. It was found that by baking in vacuum as well as in air (400 °C, 100 h), the outgassing rate can be reduced by almost a factor of ten, in line with predictions based on outgassing theory. The polymers were investigated, as they represent materials with quite large outgassing rates. This was confirmed, especially when they were measured as received, without baking. In general, the difference method for measuring thermal outgassing was found to work well in a wide range of outgassing rates.

In vacuum applications, polymers often need to be used in spite of their relatively high outgassing rates, e.g., as sealing or spacer material. For some polymers—like Viton®, which is used for O-rings—data on outgassing rates can be found in literature, while for others, in particular, the most relevant ones that can be used at higher temperatures, only few results are available. Therefore, different high-temperature resistant polymers were measured at the Outgassing Measurement Apparatus, which uses the difference method. These polymers were polyimides like Kapton®, Vespel®, and Meldin®, as well as a polyetheretherketone and a polybenzimidazole. In order to investigate the temperature behavior of the outgassing of the polymers, the measurements were performed at room temperature, 100 °C, and 200 °C. The outgassing species were determined by a mass spectrometer. In addition, the dependence of the outgassing on the material thickness was analyzed. The paper shows that the outgassing rates of the examined polymers are higher than 10−4 (Pa m3)/(s m2) after 10 h at room temperature, except for the thin Kapton samples. Thus, further treatment of the materials will be necessary depending on the application. It is shown that a vacuum bake-out at not less than 200 °C is favorable. The main outgassing species is water, as expected, but also different hydrocarbons with higher mass can be seen for the polyimides. Concerning different thicknesses, the outgassing rate of a thin sample generally decreases more steeply than the outgassing rate of the thicker sample. Nevertheless, the steepest decrease was found for the thickest Kapton sample, with a difference of nearly factor 500 between 10 and 100 h at room temperature.

No abstract

No abstract