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and cold rolled into -5x] 5 cm strips with nominal thicknesses of 40-75 f5 pm.
Ta foil was obtained commercially.
The foils were washed with warm soap and water, rinsed with methanol,
blown dry with nitrogen, mounted by clamping the ends of the foil strip, and
loaded into the physical vapor deposition (PVD) chamber. After evacuation,
argon was bled into the chamber to a pressure of 1.5-1 04 Torr and the ion-gun
was used to ion-mill each side of the foil for 60-90 min. The foil was visually
inspected through a window during ion-milling to ensure removal of all
remaining macroscopic contaminants. After ion-milling, the chamber was
evacuated again to 1-10- Torr and palladium was e-beam evaporated onto the
foil to the desired thickness at 3-5 A/s. A quartz crystal was used to monitor the
thickness of metal deposited. The Pd-Ag films were deposited by sputtering
from a Pdo.5oAgo.50 target. In all cases, the same metal coating was deposited
onto both sides of each foil.
Samples were handled using gloves and forceps. Discs (2 cm diameter)
were laser cut from the foil or cut by hand from larger foil samples using clean
scissors. The membrane foil was sandwiched between two Ni VCR gaskets
(12.7 mm OD) and positioned in the fixture, a stainless steel VCR fitting
adapted with an impinging flow design. A final helium pressurization test was
performed to confirm the absence of leaks.
The membrane module was placed in a heater and connected to a gas
plumbing and measurement system. Mass flow controllers metered the gas while
0-10,000 or 0-100 torr pressure transducers measured upstream and downstream
pressures, respectively. All gases used were at least 99.999% pure and used
without further purification. The membrane module was heated in the absence of
hydrogen (vacuum at the feed and permeate sides). The inlet flow was 200 sccm
of hydrogen during all tests. The feed pressure was set at 760 Torr and the
retentate pressure ranged from 700 to 750 Torr. The permeate pressure was
typically between 10 and 25 Torr. Sweep gas was not used during the
Auger Electron spectroscopy (AES) results were obtained with a PHI 5600
System. Electron energy analysis was accomplished using a CHA with an
OMNI Focus IV input lens system. AES results were obtained with a 5 keV
electron beam. Background pressure was essentially 1x10-1 Torr. Elemental
analysis should be considered to be semi-quantitative ( 20%). The built in SEM
was used for sample imaging.
3 Results and Discussion
The hydrogen flux vs. time at I atm pressure differential through 40 gm
thick Vo.95Tio0oS membranes with 30, 100, or 250 nm Pd coatings is shown in
Fig. I a. The flux through membranes coated with 30 or 100 nm of Pd were
comparable at 400 C, while the flux through the membrane with a 30 nm Pd
coating declined at a faster rate. In all cases the flux dropped much more quickly
at 450 C. In the case of the membranes coated with 250 nm of Pd, one was
tested for hydrogen flux at 320*C before testing at 450*C, while the other was
heated directly to 450 C before introducing hydrogen. The formation of hydride
at 320 C appeared to increase the hydrogen flux subsequently observed at
450 C (Fig. I a).
Hydrogen flux vs. time data for 40 pm thick Vo.95Tio.05 membranes coated
with 100 or 250 nm of Pd047Cuo.53 are shown in Fig. I b. While the fluxes were
similar to the Pd coated membranes, the flux declined more quickly at 450*C.
The flux was stable for a membrane tested at 320 C. Once again, a membrane
first exposed to hydrogen at 320 C exhibited higher initial hydrogen flux at
450 C. The flux through a 20 m thick Pdo047Cuo.53 foil was constant at 450 C.
suggesting that the flux decline was related to interaction of the V-Ti foil with
the surface coating. Coating the V-Ti foil with Pdo.5oAgo.50 resulted in higher
initial flux than for the Pd-Cu coated membranes, however, similar flux decline
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Chen, Bin; Lin, Jung-Fu; Chen, Jiuhua; Zhang, Hengzhong & Zeng, Qiaoshi. Synchrotron-based high-pressure research in materials science, article, June 1, 2016; (digital.library.unt.edu/ark:/67531/metadc935370/m1/3/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.