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Hydrogen traps in the outgassing model of a stainless steel vacuum chamber



Robert F. Berg


This article describes a model for hydrogen outgassing into a stainless steel vacuum chamber. It accounts for the geometry of the chamber components, the hydrogen dissolved in those components, and the processes of diffusion, recombination, and trapping. Strongly bound or “trapped” hydrogen, which occurs at heterogeneities such as dislocations and grain boundaries, can hold most of the dissolved hydrogen even though those locations comprise fewer than 0.1 % of all lattice sites. Four simplifications allowed practical use of the model: 1. Each component was described as a one-dimensional object. 2. The hydrogen initially dissolved in each component was described as a uniform concentration. 3. Accurate, consistent values were used to describe diffusion and recombination in stainless steel types 304 and 316 [Grant et al., J. Nuclear Materials 149, 180-191 (1987); 152, 139-145 (1988)]. 4. Only one type of hydrogen trap was considered, and trapping was ignored in components made from vacuum remelted stainless steel. The simple model was developed and validated by comparing it to outgassing measurements. Traps were required to describe the outgassing from a component made of drawn stainless steel 304. The initial hydrogen concentration in that component was comparable to concentrations found elsewhere by thermal desorption and almost 100 times larger than in the components made of vacuum remelted 316 stainless steel. The model’s usefulness was illustrated by using it to predict the outgassing of a vacuum chamber made of type 304 stainless steel.
Journal of Vacuum Science and Technology A


AISI type 304, AISI type 316, austenitic stainless steel, diffusion, hydrogen outgassing, hydrogen traps, recombination, AISI type 304, AISI type 316, vacuum chamber


Berg, R. (2014), Hydrogen traps in the outgassing model of a stainless steel vacuum chamber, Journal of Vacuum Science and Technology A, [online], (Accessed May 22, 2024)


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Created March 31, 2014, Updated November 10, 2018