Outgassing Characteristics of Stainless Steel and Aluminum with Different Surface Treatments

Abstract

The outgassing characteristics of 304 stainless steel with different surface treatments have been measured. The surface treatments investigated were: (1) glass-bead shot blasting; (2) electropolishing with a surface roughness of 20–25 μ in.; (3) electropolishing with a surface roughness of 4–6 μ in.; (4) one of the above treatments plus oxidation by baking in air at 250 ° or 450 °C; (5) treatment (2) above plus 450 °C bake under vacuum. The outgassing characteristics of type-1100 aluminum, which had been cleaned with detergent and rinsed with acetone, were also determined. Results obtained indicate the outgassing rates for stainless steel cleaned by glass-bead shot blasting or electropolishing after a 250 °C bake for 15–30 h are approximately the same and equal to 2×10−12 Torr liter/sec cm2. These results are in agreement with the results reported by Calder and Lewin. Oxidized stainless steel produced a lower outgassing rate between 3 and 5×10−13 Torr liter/sec cm2. Also, a 450 °C bake for 17 h of stainless steel with the inner surface exposed to vacuum exhibited an outgassing rate of 4×10−13 Torr liter/sec cm2. Aluminum baked at 250 °C for 15 h provided an outgassing rate of 4×10−13 Torr liter/sec cm2. These results are explainable on the basis of H2 depletion from the samples due to high temperature baking for long periods of time and also the lower H2 permeation through oxide films.