Thad M. Adams, Marie Kane, & Paul S. Korinko Materials Science ...

3.00E-01
2.50E-01
2.00E-01
1.50E-01
1.00E-01
5.00E-02
0.00E+00
MetGlas Permeation Test
0 1000 2000 3000 4000 5000 6000 7000 8000
Time (s)
Leak 400C
Perm 400 T 400C
Sat 400T 400C
Perm 700T 400C
Sat 700T 400C
Alternative Materials to Pd Membranes for Hydrogen Purification
Pressure (Torr)
Thad M. Adams, Marie Kane, & Paul S. Korinko
Materials Science and Technology
Savannah River National Laboratory
Prepared for the U.S. Department of Energy under Contract DE-AC09-96SR1850
WSRC-STI-2007-00379

Background
• DOE interested in developing low cost membrane
purification technology to replace Pd based
membranes
• Target application is forecourt purification for
distributed hydrogen production
• Purity target 99.99% H2, ideally to meet SAE/ISO
requirements to be defined by 2010

Membrane Properties and Technologies
Membrane Properties
• High flux
• Low pressure drop
• High contaminant tolerance
– S, CO, solids, etc.
• Low cost
• Moderate operating
temperature
– 250 – 600 o C
Membrane Separation
Technologies
• Molecular
• Atomic
• Ionic

Molecular Membranes
• Porous media
– Physical size separation
• Φ H2 = 2.89 Å
– Small pore ceramics, metals, etc. Ф Holes = 10 Å
• Zeolites, SiC, SiO 2 , Al 2 O 3 , metals
– Mean free path dependant
– Flux α P H2
– 99% purity achievable
Oak Ridge National Laboratory

Proton Transport
• Protons and electrons transported separately
– Single or dual phase materials
– Mixed conductor materials
• Ceramic oxides
• High temp (>800 o C)
• Flux currently lower than desired
– Cermet
• Ceramic and metal composite
• Higher electron flow and proton flow
• May use separate membranes
• Flux α fn(e - & p + conductivities)
• Flux αln (P H2 , T)

Atomic Membranes
• Dense metallic membrane
– Thin metal sheets / tubes
• Active surfaces
– Dissociates H 2
– H diffuses
– H recombines to H 2+
• May need supports
– Porous metals
– May be poisoned
• CO, S, etc
– Not thermally stable
• High temp phase change
• Low temp hydriding
• No long range order
possible
– Flux α√P H2
– High purity possible > 99.99%

Metallic Membrane Hydrogen Purification
H-H
H-H
High Pressure
H-H
H-H
C-O
H-H
O-C-O
H-H
H
|
H -C- H
|
H
Absorption
N-N
H-
H-
Dissolution
and
Diffusion
H
H
H
H
H
Desorption
-H
-H
Membrane
Low Pressure
H-H
H-H
H-H

Why Dense Metallic Membranes?
• Simple to operate
• Reliable—No moving parts
• High purity hydrogen product—99.95% or better
• Small size
• Flexible designs
• Cost effective—more so with non-noble metal
membranes

Approach
• Investigate non-precious metal membrane materials
– High H 2 solubility (S)
– High H 2 diffusivity (D)
• High Permeability (Φ = D*S)
• Bulk amorphous metals
– Bulk metallic glasses (BMG)
• Commercially available
– Low cost
– Dense metallic membranes
• Aqueous and gaseous permeation testing

Materials of Interest
• Pd / Pd alloys
– Good solubility and diffusion
characteristics
– Well accepted in use
– Susceptible to poisoning and
embrittlement
– High raw material costs
• Alternatives to Pd based membranes
– Pd-Coated Porous Ceramics
• Pin-holes/holidays create short
circuit pathways
– Others investigating V and V-alloys
and V-Al and V-Ni alloys
• V has high solubility and
diffusivity but suffers severely
from embrittlement
• Attempts at alloying V have not
made significant decrease in
embrittlement susceptibility
– Group 5A-Ti-Ni Alloys
• Ni-Ti alloys have been researched
for decades due to their shape
memory properties
• NI-Ti Alloys are susceptible to H2
Embrittlment and do not possess
high permeability
• Additions of Group 5A Metals (
Nb, V, and Ta)
• Nb additions have produced high
permeation and good resistance
to embrittlement
• Duplex structure—Ni4Ti13Nb83
and eutectic
– Bulk Metallic Glasses
• Commercially available Fe and Co
based foil materials
• Zr-Cu-Ni-Al-Y Bulk Metallic Glass

Ni-Ti-Group 5A Alloys
Composite Membranes?
Nb
Zr
V
Ta
H
2
Undesired
contaminants or
poison gases
leakage through
the ceramic.
Pd
Ceramic
Pt
Pinholes
Dense Metallic
Steward, LLNL, 1983
Non-alloyed membranes highly susceptible to embrittlement

Previous Work
Previous Work by Hashi, Ishikawa, Matsuda, and Aoki—Kitami Institute of Technology--Japan
•
Duplex Ni 30 Ti 31 Nb 39
Ternary Eutectic Ni 41 Ti 42 Nb 17
Permeability of Ni 30
Ti 31
Nb 39

Sample Preparation
•Raw Materials:
•99.95% Ti
•99.6% Nb
•99.7% V
•99.99 Ni
•Vacuum and Backfill with Ar
•UHP Ar:

Microstructure Results
Scanning Electron Microscopy
Nb51-Ti28-Ni21
Nb48-Ti28-Ni24
Nb54-Ti28-Ni18
V51-Ti28-Ni21

Microchemical Results
X-ray Mapping of Nb48-Ni24-Ti28 Alloy
x
Element
Weight%
Atomic%
Ti K
Ni K
Nb L
13.4
1.76
84.84
22.87
2.45
74.68
Totals
100

Microchemical Results
X-ray Mapping of V51-Ni21-Ti28 Alloy
x
Element
Weight%
Atomic%
Ti K
V K
Ni K
19.46
72.21
8.33
15.54
65.28
6.53
Totals
100

Devanathan Permeation Cell
Sample
SCE
Gas Bubbler
Pt Counter Electrode
ASTM G148-97

Experimental Parameters
• ASTM G-148-97
• Devanathan permeation cell
• 0.1 M sodium hydroxide solution
• 22 and 50 °C
• Nitrogen deaerated solution
• Anode side: -0.125 V, SCE
• Cathode side: 0.1, 0.5, 1.0 mA
• Background stabilization, 2-24 hours

Sample Preparation
• EDM from cast buttons
• Size: 12.5 mm (0.5 in) diameter,
0.64 mm (0.025 in) thick
• Surface ground with 600 grit SiC paper
• Plasma coated with Pd on either anode side or both
• Contact wires spot welded on edge

Permeation Results
• Platinum efficiencies 85-90% (40 °C) and 80% (22°)
• Permeation currents increased with Nb concentration
• V alloy showed better permeation than Nb alloys
• Alloys appear to have a saturation level
• No alloys failed during testing

Ni-Ti-X Permeation Curves
3.0E-05
2.5E-05
2.0E-05
Current (A)
1.5E-05
1.0E-05
21Ni-28Ti-48Nb
24Ni-28Ti-51Nb
21Ni-28-Ti-54Nb
24Ni-28Ti-51V
5.0E-06
0.0E+00
0.0E+00 5.0E+03 1.0E+04 1.5E+04 2.0E+04 2.5E+04 3.0E+04
Time (Sec)

Permeation Rates
Material Permeation Rate (mol H2/m s)
Palladium 3.26-4.25 x 10 -10
Nb48 Alloy 6.58 x 10 -11 - 1.65 x 10 -10
Nb51 Alloy 2.96 x 10 -10 - 6.0 x 10 -9
Nb54 Alloy 3.25 x 10 -10
V51 Alloy 1.0- 3.7 x 10 -9

• Tested at 250°, 300°, &
400°C
• Gaseous Hydrogen @ 400 &
700Torr
• Two Alloy Compositions
Tested:
– V48-Ti28-Ni24
– V51-Ti28-Ni21
• Lower Temp Membrane
Failure
• Membrane Robustness Test
– 400°C @ 10Torr H2
Gaseous Permeation Testing

Results—V48-Ti28-Ni24 Alloy
Test Conditions
•Temperature: 400°C
•H2 Pressure: 700T
•Thickness: 0.089cm (0.035in)
2.00E+00
1.80E+00
1.60E+00
V48-Ti28-Ni24 Permeation Test
1.40E+00
•SA:≅ 5 cm 2 1.20E+00
1.00E+00
8.00E-01
Determine Permeability at Steady-State
Pressure (torr)
6.00E-01
4.00E-01
2.00E-01
0.00E+00
0 2 4 6 8 10 12 14
Time (hr)
•Slope of Saturation Data= Torr/hr—convert to mols H 2
/min
•Flux (J)= K/l (P feed
1/2
)
•Flux (J)= (Sat Slope (mols H 2
/min)/Area Permeating (m 2 )) = mols H 2
/min m 2
•l=m and P feed
=Pascals and Solve for K=Permeability (mols H 2
/m s Pa 1/2 )
•For V48-Ti28-Ni24 Permeability = 1.0 x 10 -9 mols H 2
/m s Pa 1/2

Bulk Metallic Glass Raw Permeation Data
Sample #1
1.20E-01
1.00E-01
Pressure (Torr)
8.00E-02
6.00E-02
4.00E-02
350C Lk
350c 400T
350C 400T S
350C 700T
350C 700T S
400C Lk
400C 400T
400C 400T S
400C 700T
400C 700T S
2.00E-02
0.00E+00
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Time (s)

Initial Gaseous Hydrogen Results for Both
V alloys and BMG Materials
Compare Favorably to Palladium
Results--Comparison

Results--Comparison

XRD Results—V48-Ti28-Ni24 Alloy
5000
[metalground.xrdml] metal ground Adams
04-003-5868> Ti 0.5V 0.5 - Titanium Vanadium
04-007-8828> VH 2 - Vanadium Hydride
04-003-2228> Ti 0.8V 0.2 - Titanium Vanadium
04-005-6101> Ti 0.11V 0.82 O - Titanium Vanadium Oxide
4000
Intensity(Counts)
3000
2000
Vanadium Hydride Formation @250°C @700T
1000
0
20 30 40 50 60
Two-Theta (deg)

Summary
• Dense metallic membranes are an attractive means for
purification of hydrogen isotopes streams
• Group 5A-Ti-Ni alloys offer the potential for a lower
cost alternative to Pd-based membranes
• Initial results for Nb- and V- alloys are favorable

Summary
• Gaseous hydrogen testing has demonstrated permeabilities
similar to Pd-alloy systems
– Further understanding of robustness of these membrane materials is
required
• Longer term exposure to hydrogen
• Some preliminary evidence at lower temps (250°C) indicate potential
issue with embrittlment
– Alloys could be optimized to further enhance permeability
• Gaseous hydrogen testing for BMG demonstrated permeabilities
like Pd-alloys
– Further testing is needed,
• Scaling to larger size is needed
– Thermal cycling under hydrogen to demonstrate embrittlement
resistance