AVS 61st International Symposium & Exhibition
    Vacuum Technology Tuesday Sessions
       Session VT-TuA

Paper VT-TuA3
Hydrogen Traps in the Outgassing Model of a Stainless Steel Vacuum Chamber

Tuesday, November 11, 2014, 3:00 pm, Room 303

Session: Vacuum Quality Analysis, Outgassing, and Control
Presenter: Robert Berg, National Institute of Standards and Technology (NIST)
Correspondent: Click to Email
The outgassing model 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. Nucl. Mater. 149, 180 (1987); 152, 139 (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 is illustrated by using it to predict the outgassing of a vacuum chamber made of type 304 stainless steel.