科研之友
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摘要
An ultrahigh vacuum (UHV) chamber is generally supposed to have a constant base background outgassing rate q(0) over very long periods of time. In experiments with ionized or molecular hydrogen, this level might be increased by absorption of a small fraction of hydrogen. In this work, absorption of molecular hydrogen is monitored in a small austenitic stainless steel UHV chamber during 3 h exposures at initial pressures from 0.01 to 1 mbar at room temperature. An absorbed dose of similar to 10(13)-10(14) atom H cm(-2) was recorded. After gas removal, desorption period in the closed vacuum system lasted for 20 h, wherein most of the absorbed hydrogen was released. The initial desorption rate was 10-100 times higher than the previous q(0). Calculations based on well accepted models for hydrogen-metal interactions confirm that the observed absorption-desorption processes are related mainly to the native oxide layer. Its reported thickness is between 1 and 3 nm and our results express its high solubility, which at 1 nm ranges from K-sox(294 K) = 2.0 x 10(22) to 3.8 x 10(22) atom Hcm(-3) bar(-0.5). The recombination rate coefficient ranges from K-Lox(294 K) = 8.9 x 10(-19) to 6.45 x 10(-18) cm 4 s(-1). The bulk metal was not involved noticeably in 24 h cycles as the oxide layer-bulk metal interactions proceed substantially slower.
- 出版日期2017-3
