Anderson Dahlen Vacuum Research Published in Leading Journal

We’re pleased to announce that our research, “Outgassing rate comparison of seven geometrically similar vacuum chambers of different materials and heat treatments,” was recently published in the Journal of Vacuum Science & Technology (JVST) newsletter, “Beneath the AVS Surface.” JVST is devoted to publishing reports of original research, letters, and review articles on microelectronics and nanotechnology. 

Research Objective

The research objective was to test a series of vacuum chambers with identical geometries, constructed from different materials and material treatments. The results would help research entities better determine the ideal material they would need for their high and extreme vacuum research equipment.

Research Summary

Water and hydrogen outgassing rates were measured in 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 (ASTM grade 2); and 6061 aluminum.

Chambers constructed of 316L and 316LN stainless steel were subjected to a vacuum-fire process – heated to approximately 950 °C for 24 h 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 Anderson Dahlen, a relative comparison of the outgassing rates among these chambers can be made.

Research Results

After extensive testing, we concluded that, depending on cost and other material properties, TI and AL as well as 316L, and 316LN stainless steel are by far the best materials for ultrahigh vacuum and extreme-high vacuum applications. For the experts out there, are the numbers:

• Water outgassing rates were measured as a function of time using the throughput technique. The water outgassing results for 316L, 316LN, 316L-XHV, and 316LN-XHV were all similar but lower than those for 304L by a factor of 3–5 lower at 104 s.
• Water outgassing results for the 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 125–150 °C for a minimum of 72 h.
• The Ti, Al, 316L-XHV, and 316LN-XHV chambers all have ultralow 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 determining a specific outgassing rate ranging between 4.0 and 8.0 × 10−11 Pa l s−1 cm−2. 

Research Origins – A Collaboration Between Anderson Dahlen Vacuum and NIST

Our research into the different outgassing from various metals and heat treatments was the result of extensive collaboration efforts between the Applied Vacuum Division of Anderson Dahlen and the National Institute of Standards and Technology (NIST). Both groups completed a Cooperative Research and Development Agreement (CRADA) to study the effectiveness of various material and pre-fabrication processing techniques for achieving extremely low hydrogen outgassing rates in vacuum chambers.

The results from our testing different metals and heat treatments can be highly useful for anyone needing the ideal material for their research equipment. 

Customer Considerations of Research

With these findings in mind, customers can now consider the following before specifying a material for their project:

• Most manufacturing companies are tooled to machine 316L, which is easily acquired in all sizes of sheet metal, plate and bar. From a pricing standpoint, 316L is on par with aluminum and less expensive compared with titanium. 
• Given the large heat zone during welding, aluminum is difficult to weld for ultra-high vacuum (UHV)/XHV applications. Aluminum also requires the use of bimetal flanges (i.e., explosion-bonded aluminum to stainless-steel or titanium), largely because aluminum knife-edges are soft and will deform or fail to seal properly as users open and close the vacuum chamber. Yet, because aluminum is a magnetically inert material, it is a critical feature for some big-science experiments. 
• Titanium is significantly more expensive when compared with 316L and aluminum and also more difficult to machine and acquire in the same group of material sizes. Additional complications associated with titanium include potential sealing issues when instruments are attached to the vacuum chamber with stainless steel flanges, which occurs when the chamber is baked during operation. 

Please note that, regardless of which material is selected for an XHV application, the Applied Vacuum Division of Anderson Dahlen can produce any chamber required.

Help Us Take Our Research and Development to New Heights
We need more help taking our research and development, like the study referenced above, to new heights with more highly skilled talent. Please get in touch with our vacuum systems team if you’re considering a role in vacuum technology and want to work with the leading manufacturer of XHV systems. Together we can continue developing industry-leading systems and technology.