Effect of heat treatments and coatings on the outgassing rate of stainless steel chambers

Abstract

The outgassing rates of three nominally identical 304L stainless steel vacuum chambers were measured to determine the effect of chamber coatings and heat treatments. One chamber was coated with titanium nitride (TiN) and one with amorphous silicon (a-Si) immediately following fabrication. The last chamber was first tested without any coating, and then coated with a-Si following a series of heat treatments. The outgassing rate of each chamber was measured at room temperatures between 15 and 30 °C following bakes at temperatures between 90 and 400 °C. Measurements for bare steel showed a significant reduction in the outgassing rate by nearly a factor of 20 after a 400 °C heat treatment-12 Torr L s -1 cm -2 prior to heat treatment, reduced to 1.7×10 -13 Torr L s -1 cm -2 following heat treatment). The chambers that were coated with a-Si showed minimal change in outgassing rates with heat treatment, though an outgassing rate reduced by heat treatments prior to a-Si coating was successfully preserved throughout a series of bakes.The TiN coated chamber exhibited remarkably low outgassing rates, up to four orders of magnitude lower than the uncoated stainless steel, but the uncertainty in these rates is 2 large due to the sensitivity limitations of the spinning rotor gauge accumulation measurement and the possibility of a small pump speed due to inhomogeneity in the TiN coating. The outgassing results are discussed in terms of diffusion-limited versus recombination-limited processes.3

Compact −300 kV dc inverted insulator photogun with biased anode and alkali-antimonide photocathode

“…The photogun vacuum chamber is made of 304L stainless steel 0.5 cm thick. Prior to assembly, the empty chamber was vacuum baked at 400°C for 100 hours to reduce outgassing from the chamber walls [27]. The resulting outgassing rate was ∼2 × 10 −13 Torr l=s=cm 2 measured using a spinning rotor gauge.…”

Investigations of medium-temperature heat treatments to achieve low outgassing rates in stainless steel ultrahigh vacuum chambers

“…16 to calculate the Fourier number. The Fourier number is very sensitive to E D , and it is worth noting that choosing E D = 0.65 eV from Mamun et al ., 12 for example, decreases the Fourier numbers in Table II by more than a factor of two. We use the flange thickness for d .…”

Vacuum furnace for degassing stainless-steel vacuum components

“…We provide an overview of such treatments below; for more detail, the reader is encouraged to consult various texts on the subject 6—8 . For untreated 300 series stainless steel, the atomic hydrogen concentration is on the order of 2 ×10 19 cm −3 , corresponding to an H 2 equivalent pressure of roughly 4.1 ×10 4 Pa at 23 °C (approximately 4/10 of an atmosphere) 9 . In discussing gas evolution from materials, one often distinguishes outgassing due to gas dissolved within the material (absorbed gas) from desorption of gas adsorbed on the material surface.…”