Regensburg 2010 – wissenschaftliches Programm
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VA: Fachverband Vakuumphysik und Vakuumtechnik
VA 3: Vacuum generation and outgassing
VA 3.2: Vortrag
Montag, 22. März 2010, 11:40–12:00, H40
Influence of vacancies on hydrogen outgassing of stainless steel — •Manfred Leisch1 and Alfredo Juan2 — 1Institute of Solid State Physics, TU Graz, Austria — 2Departamento de Fisica, Univ. National del Sur, Bahia Blanca, Argentina
Stainless steel as one of the most used construction materials in vacuum technology contain hydrogen as impurity which is the main source for outgassing. The outgassing processes is basically described by two models: the diffusion limited model and the recombination limited model. Since recombination is strongly related to surface morphology, surface characterization has been performed by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). After vacuum firing a significant change in surface morphology can be observed. The different orientated crystallites show wide flat terraces bounded by bunched atomic steps and facets. High resolution STM micrographs show additionally stacking faults and local defects like vacancies. Theoretical studies and simulations on the interaction of hydrogen with lattice imperfections may provide a new insight in hydrogen outgassing. The energy calculations using the ASED method (Atom superposition and Electron Delocalization) result in lower energy levels in tetrahedral sites in Fe vacancies. It supports the picture that surface and subsurface defects form traps with different energetic levels. They may control the recombinative desorption process and give explanation the observed outgassing behaviour of stainless steel.