| AVS 61st International Symposium & Exhibition | |
| Vacuum Technology | Tuesday Sessions |
| Session VT-TuA |
| Session: | Vacuum Quality Analysis, Outgassing, and Control |
| Presenter: | Taekyun Ha, POSTECH, Republic of Korea |
| Authors: | B. Cho, Korea Research Institute of Standards and Science (KRISS), Republic of Korea S.J. Ahn, Korea Research Institute of Standards and Science (KRISS), Republic of Korea C.D. Park, POSTECH, Republic of Korea T. Ha, POSTECH, Republic of Korea |
| Correspondent: | Click to Email |
Mild steel, i.e. low carbon steel, is a soft magnetic material and widely used for shielding sensitive experimental apparatuses from stray magnetic field because of its relatively low price and high magnetic permeability. Mild steel vacuum chambers are usually nickel-plated in order to prevent corrosion and improve the vacuum. For example, electron microscopes employ nickel plated mild steel for constructing their specimen vacuum chambers in which the electron beam propagates and interacts with specimens; presence of stray magnetic field deteriorates proper propagation of the electron beam, degrading the resolution of the electron microscope.
The mild steel has not been employed, to the best of authors’ knowledge, for ultra-high vacuum (UHV) use because its outgassing rate has been known to be too high; reported values were on the order of 10-8~10-9 mbar l s-1 cm-2 or higher [1]. Ishimori et al. [2] reported that the outgassing rates of a mild steel (carbon ~0.15%), a chromium-plated mild steel and a stainless steel were 2~3×10-11 mbar l s-1 cm-2 , 7~9×10-11 mbar l s-1 cm-2 and 2~3×10-12 mbar l s-1 cm-2, respectively, after baking at 300 °C for 3 hours. The outgassing rate of UHV chambers are normally on the order of 10-12 mbar l s-1 cm-2 or less after baking at 100 ~ 200 °C.
The outgassing rates of a mild steel and a stainless steel 304 chamber were measured by using the so-called rate-of-rise (RoR) method [3]. We present that the outgassing rate of the mild steel purchasable on the market is much smaller than that of a stainless steel type 304L which is most widely used as a UHV vacuum chamber material. The ultimate pressure of a vacuum chamber made of the mild steel was 2.7x10-11 mbar, and its outgassing rate was of < 3×10-14 mbar l s-1 cm-2, which indicates the mild steel is even appropriate for extreme high vacuum use. Vacuum annealing of the mild steel at 850 °C reduced the outgassing rate further.
[1] B. B. Dayton : 6th Nat. Symp. Vac. Tech. 101 (1959).
[2] Yoshio Ishimori, Nagamitsu Yoshimura, Shuzo Hasegawa, and Hisashi Oikawa, SHINKU 14(8), 295(1971).
[3] C. D. Park, S. M. Chung, Xianghong Liu and Yulin Li, J. Vac. Sci. Technol. A 26(5), 1166(2008).