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Outgassing rate comparison of seven geometrically similar vacuum chambers of different materials and heat treatments



James A. Fedchak, Julia Scherschligt, Sefer Avdiaj, Daniel Barker, Stephen Eckel, Ben Bowers, Scott O'Connell, Perry Henderson


We have measured the water and hydrogen outgassing rates of seven vacuum chambers of identical geometry but constructed of different materials and heat treatments. Chambers of five different materials were tested: 304L, 316L, and 316LN stainless steels, titanium, and aluminum. In addition, chambers constructed of 316L and 316LN stainless steel subjected to a vacuum-fire process, where they were heated to approximately 950 °C for 24 hours while under vacuum. These latter two chambers are designated as 316L-XHV and 316LN-XHV. Because all the chambers were of identical geometry and made by the same manufacturer, a relative comparison of the outgassing rates among these chambers can be made. Water outgassing rates were measured as a function of time using the throughput technique. The results for the 304 L chamber were in accord with the results of Li and Dylla.1 The water outgassing results for the 316L, 316LN, 316L-XHV, 316LN-XHV were all similar and have a lower water outgassing rate than 304L; between a factor of 3 to 5 lower at 104 s, e.g. The water outgassing results for Ti and Al chambers were closer to that of 304L, Ti being slightly lower. Hydrogen outgassing rates were measured using the rate-of-rise method and performed after a low-temperature bake of 125 °C to 150 °C for a minimum of 72 hours. The Ti, Al, 316L-XHV, and 316LN-XHV chambers all have ultra-low specific outgassing rates below 1 × 10-11 Pa L s-1 cm-2, and are a factor of 100 or better than the 304L chamber. The 304L, 316L, and 316LN chambers with no vacuum-fire heat treatment have larger hydrogen outgassing rates than the other chambers, with determined specific outgassing rates ranging between 4.0 × 10-11 Pa L s-1 cm-2 and 8.0 × 10-11 Pa L s-1 cm-2. From this study we conclude that Ti, Al, 316L-XHV, and 316LN-XHV have hydrogen outgassing rates that make them excellent choices for ultra-high vacuum (UHV) and extreme-high vacuum (XHV) applications, the choice depending on cost and other
Journal of Vacuum Science and Technology A


outgassing, ultra-high vacuum, vacuum metrology, H2 outgassing, water outgassing


Fedchak, J. , Scherschligt, J. , Avdiaj, S. , Barker, D. , Eckel, S. , Bowers, B. , O'Connell, S. and Henderson, P. (2021), Outgassing rate comparison of seven geometrically similar vacuum chambers of different materials and heat treatments, Journal of Vacuum Science and Technology A, [online], (Accessed May 29, 2024)


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Created April 23, 2021