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Novel Wide Area Hydrogen Sensing Technology. W. Hoagland D. K. Benson R. D. Smith. Outline. New developmental hydrogen gas indicators Technologies Response kinetics Possible applications. What are Chemochromic H2 Detectors?. - PowerPoint PPT Presentation
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Novel Wide Area Hydrogen Sensing Technology
W. Hoagland
D. K. Benson
R. D. Smith
Outline
New developmental hydrogen gas indicators
Technologies Response kinetics Possible applications
What are Chemochromic H2 Detectors?
Chemochromic hydrogen detectors change color when exposed to gaseous hydrogen. This color change is caused by a chemical reaction between hydrogen and the active material. It may be reversible or non-reversible.
Reversible partial reductionof tungsten trioxide
Coloration
1. H2 + 2(Pd) 2(Pd.H)
2. 2(Pd.H) + 2(WO3) 2(W+5O2.OH) + 2(Pd)
Bleaching
3. 2(W+5O2.OH) + 1/2O2 2WO3 + H2O
ChemochromicChemical Reactions
Optical absorption by electrons localized at oxide vacancies
Electrons are localized in the vicinity of W5+ ions as small polarons
hv + W5+(A) + W6+(B) W6+(A) + W5+(B)
Technology addresses a recognized need
“Although safety-by-design and passive mitigation systems are preferred, it will still be necessary to develop technologies to detect hydrogen releases or other system failures.For example, coatings that change color upon exposure to hydrogen can provide immediate visual evidence of a leak.”
U.S. DOE Multi-year Plan 2003-2010
Critical Research Topic
“The overall goal is to develop low-cost sensor technologies that are not based on conventional practices, that can be directly integrated with hydrogen systems, and that are resistant to contamination.”
…Goal #3: Develop a sensing technology for a wide-area determination of hydrogen presence prior to any combustion or local temperature rise.”
U.S. DOE - February 2004
Advantages of Chemochromic Hydrogen Indicators
Reversible color change Inherently safe – no ignition source Convenient indication from a distance No instrumentation needed Applicable in various forms
Paints, inks, coatings Tape/Stretch Films Conformable Wrap Decals
Very low cost
Typical structures of chemochromic indicator material
Substrate polymer sheet
Tungsten oxide 500 nm
Palladium 3 nm
PTFE 100 nm Vacuum depositedmulti-layerthin film
Nano-powderTungsten oxide (~50 nm)
PlatinizedChemically (~5%)
Chemically synthesizednano-particles
Thin film indicator responds quickly and reversibly
Thin Film Indicator
Could be used for lettering on safety decals
No hydrogen present
Hydrogen present
Flexible Plastic Indicating Tape
Could be used to wrap around pipe fittings
Shrink wrap indicator appliedto a low pressure cylinder with an intentional 50 micron hole
Nano-particles could be used in “smart paints” or printing inks
• Epoxy (100% solids)
• Polyurethane
• Acrylic (Solvent based)
• Acrylic (Water Based)
Paint formulations shown to work include:
Indicators turn dark blue when exposed to hydrogen
Optical Absorption
0
20
40
60
80
500 600 700 800 900 1000
Wavelength (nm)
Ab
so
rpti
on
(%
)
Transmittance at 830 nm
0
50
100
0 100 200 300
Time (s)
T (
%)
Response of Chemochromicindicator is exponential
– thin film
Switch to air
H2
Response mechanism
Double exponential decay in transmittance is characteristic of two parallel first-order chemical reactions.
Speculation: The reactions occur at different kinds of catalytic sites -
At the catalyst metal/tungsten oxide interface At catalyst metal/tungsten oxide/gas interface
Response of Chemochromic– nano-particles
Nano-Particles
0
20
40
60
80
100
0 50 100
Time (s)
Re
lati
ve
Tra
ns
mit
tan
ce
(%
)
Response of a Chemochromic– PVA water-base
“Smart Paint”
40
50
60
70
80
90
100
0 200 400 600 800
Time (s)
Rel
ativ
e T
ran
smit
tan
ce (
%)
tau1= 97 s; 100%
Thin film indication threshold in air is less than 400 ppm H2
0
0.005
0.01
0 500 1000 1500
Hydrogen Conc. (ppm)
Init
ial
Slo
pe
of
res
po
ns
e,
(-%
/s)
Chemochromic indicators respond more quickly at higher temperatures
1
10
100
1000
10000
-50 -30 -10 10 30
Temperature (C)
Tim
e c
on
sta
nt
tau
1 (
s)
A protective coating reduces the effect of humidity
02468
0 20 40 60 80 100
Relative Humidity (%)
Tim
e c
on
sta
nt
(s)
PTFE coating
No coating
Indicator response slows over time
05
10152025303540
0 20 40 60
Exposure (days)
tau
1 (
s)
Different film structures reduce the rate of response slowing
0102030
0 20 40 60 80
Exposure (days)
tau
1 (
s)
NASA/KSC Project
H2 Dispensing Station
H2 Dispensing Station
H2 Dispensing Station
RFID H2 Sensor Network
RFID Hydrogen Sensors
RFID Response
On-going R&D Activities
Optimize nano-particle pigment Catalyst choice Pd, Pt, or mixed Catalyst concentration Possible protective coatings
Select suitable paint vehicles Optimize paint formulations for various applications Field test prototype indicators in realistic
environments Optimize thin film coating for polymer substrates
Optimize film component proportions Improve protective coatings to stabilize response
over longer time
Range of Products
Conclusions
Present indicators are promising for leak detection in many applications
New designs are being developed with slower rates of degradation
Performance parameters can be modified for specific applications and requirements
Partnerships
Actively seeking industry partnersStrategicTestingManufacturing
Thank you!
www.elem1.com