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SRNL Develops New Permeable Microspheres; Potential for Hydrogen Storage
6 June 2008
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| SRNL researchers removed the top of a glass microsphere to show how palladium has easily passed through the sphere’s pores and assembled itself into a new nanostructure. Click to enlarge. Credit: Savannah River National Lab, American Ceramic Society |
Researchers at the Savannah River National Laboratory (SRNL) have developed a novel material called Porous Wall-Hollow Glass Microspheres (PW-HGM)—tiny glass microballoons 2-100 microns in diameter. The distinguishing characteristic of the microspheres is the interconnected porosity of their thin outer walls that can be produced and varied on a scale of 100 Å to 3,000 Å.
SRNL Researchers G.G. Wicks, L.K. Heung, and R.F. Schumacher have been able to use these open channels to fill the microballoons with gas absorbents and other materials. Hydrogen or other reactive gases can then enter the microspheres through the pores, creating a relatively safe, contained, solid-state storage system. As part of a program with Toyota, SRNL is investigating filling these microspheres with other special hydrogen absorbents to develop safe hydrogen-gas storage systems for vehicles.
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| Schematic representation of microsphere wall porosity. Click to enlarge. Credit: Savannah River National Lab, American Ceramics Society |
Photographs of these glass-absorbent composites also reveal that the wall porosity generates entirely new nano-structures.
The microspheres are fabricated by heating ~20 µm to 40 µm glass powders in a hot zone formed by a controlled gas-air flame. As the glass particles pass through the zone, the flame softens the glass and forms a spherical particle. The glass contains a latent blowing agent that becomes unstable as the glass is heated and forms a gas nucleus or bubble. The bubble expands as the glass is heated and forms the HGMs.
The conversion of the HGMs into PW-HGMs occurs when the microspheres are heat-treated and acid leached with 3.0M hydrochloric acid. To induce the special porosity, the researchers first produce phase separation in the glasses.
The importance of this process is that it actually produces two different glass phases: one rich in silica and the other rich in sodium borate. The sodium borate phase is an interconnected wormlike morphology. When it is removed by a leaching process, similar to the making of commercial Vycor glass, it produces interconnected pores or channels that, in this case, extend from the outside of the microsphere shell to its inside... These channels can later be used to fill the microspheres.
Wicks, Heung and Schumacher have shown that the PW-HGM’s permeable walls can be used for non-composite purposes, too. For example, the porosity can be altered and controlled in various ways that allow the spheres to filter mixed gas streams within a system.
Another feature of the microballoons is that their mechanical properties can be altered so they can be made to flow like a liquid. This suggests that an existing infrastructure that currently transports, stores and distributes liquids such as the existing gasoline distribution and retail network can be used. This property and their relative strength also make the PW-HGMs suitable for reuse and recycling.
The SRNL team is involved in more than a half dozen programs and collaborations involving the PW-HGMs in addition to the hydrogen storage work with Toyota, targeting applications such as gas purification and separations, and even very diverse applications including abatement of global warming effects, improving lead-acid battery performance and nuclear non-proliferation.
As a byproduct of the Toyota collaboration, researchers discovered that effective and reactive absorbents could be incorporated inside the PW-HGMs and, interestingly, these absorbant materials assembled themselves into unfamiliar nanostructures...From chemical analyses of these structures, they do not appear to be any of the anticipated phases. This suggests that along with new nanostructures produced by the porosity of the microsphere walls, new phases also may result. Further work is needed to clarify and characterize in more detail these interesting findings.
A paper describing their work is published in the June issue of The Bulletin, the monthly magazine of The American Ceramic Society.
Resources
G.G. Wicks, L.K. Heung and R.F. Schumacher (2008) Microspheres and Microworlds, American Ceramic Society Bulletin, Vol. 87, No. 6
June 6, 2008 in Hydrogen Storage, Materials | Permalink | Comments (2) | TrackBack (0)
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Comments
So this is yet another effort to use the princple of adhesion to store gases at low pressure for use in a vehicle. What I always trip over with these approaches is that the ultimate goal is to safely store much fuel in a lightweight compact form, and yet these matrix materials all have mass and volume, thus reducing the space and weight allowance remaining for fuel.
I guess it's a question of optimization, but it seems like there is probably a mathematical limit to how good these matrix storage schemes can be. Does anyone have any sense of that limit, and how it compares to high pressure storage or cryogenic liquid storage?
Posted by: | Jun 6, 2008 3:55:20 PM
--use these open channels to fill the microballoons with gas absorbents and other materials--
gas absorbents --> palladium --> forget it!
Posted by: Head Case | Jun 6, 2008 6:26:43 PM
