Outgassing rate measurements of stainless steel and polymers using the difference method

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.