AVS 63rd International Symposium & Exhibition
    Vacuum Technology Tuesday Sessions
       Session VT-TuM

Paper VT-TuM4
Multi Scaled Titanium Gettered Surfaces for Enhanced Pumping of H2

Tuesday, November 8, 2016, 9:00 am, Room 104C

Session: Vacuum Pumping and Material Outgassing
Presenter: Alan Van Drie, Tri Alpha Energy
Correspondent: Click to Email

The sticking factor for any gas onto a flat surface, whether its physisorbed or chemisorbed can be enhanced by increasing the effective roughness of the flat surface. When done on multiple scale lengths, not unlike a fractal pattern, the sticking factor can approach unity. In the present case, we are interested in pumping H2 by a fresh coating of titanium, which has a sticking factor of around 3-6% at room temperature on a flat surface. The shape of the fractal pattern and number of scale lengths that can be used is limited by the feasibility of coating titanium on all the exposed surfaces. Using three distinct scale length from ~20 cm, ~2 cm to sub-micron we are able to obtain an estimated 70-80% effective sticking factor. The sub-micron scale is achieved by depositing the titanium onto a cryogenically cooled surface that changes the film’s morphology from a dense coating to a porous sub-micron needle like structure. This by itself increases the sticking factor from the normal 3-5% to 20-50%. Some deposition techniques can even create film morphologies with up to 90% sticking factor; eliminating the need for other macroscopic scale lengths. Using these techniques we can create a 2,000 m3/s pump for H2, with 10 m2 entrance area that fits within our 15 m3 vessels. The design principles and preliminary pumping speed and capacity measurements will be presented.