|Title of Invention||
HOLLOW GLASS MICROSPHERES FOR HYDROGEN STORAGE
|Abstract||A hollow glass microsphere is provided having a diameter range of between 1 to 140 microns, a density of between 0.05 to 0.50 gm/cc, a porouswall structure having wall openings defining an average pore size of between 10 to 1000 angstroms, and which contains therein a hydrogen storage material. The porous-wall structure facilitates the introduction of a hydrogen storage material into the interior of the hollow glass microsphere. Thereafter, a barrier coating may be applied and/or the microspheres are processed to alter or reduce the effective pore size. In this manner, the hollow glass microsphere can provide a membrane for the selective transport of hydrogen through the porous walls of the microsphere, the small pore size preventing gaseous or liquid contaminants from entering the interior of the hollow glass microsphere.|
|Full Text||FIELD OF THE INVENTION
This invention is directed towards hollow glass microspheres and a process of using the microspheres as part of a hydrogen storage system. The hollow glass microsphere wall defines a series of pores. The pores facilitate the placement of a hydrogen storage material within the interior of the hollow glass microsphere. The porosity of the hollow glass microspheres can thereafter be modified by either altering or reducing the overall pore size or by coating the individual hollow glass microspheres so as to maintain the hydrogen storage material within a sealed interior of the hollow giass microsphere. The coating and/or the controlled pore size enables the selective absorption of hydrogen gas through the walls of the hollow giass microsphere while isolating the hydrogen storage material encapsulated therein from other external gases and fluids.
The hollow glass microspheres can thereafter be subjected to variations in temperature, pressure, or other release stimulus triggers to bring about the release of hydrogen gas. Once dehydrided, the hollow glass
microspheres and hydrogen storage material can be reused so as to once
again selectively absorb hydrogen gas.
BACKGROUND OF THE INVENTION
The formation of hollow glass microspheres (HGMs) is well known in
the art. The production of hollow glass microspheres has been described in
U.S. Pat. Nos. 3,365,315 (Beck); 4,661,137 (Gamier); and 5,256,180
(Gamier), and which are incorporated herein by reference.
It is also known in the art to produce large macrospheres having hollow
glass walls which provide a semipemneable liquid separation medium for
containing absorbents. The production of macrosphere structures can be
seen in reference to U.S. Pat. Nos. 5,397,759 and 5,225,123 to Torobin and
which are incorporated herein by reference. The Torobin references disclose
hollow glass macrospheres comprising multiple particle glass walls. The
reference teaches the use of the macrospheres for gas/liquid separation and
for use with absorbents but does not discuss any features or characteristics
which would make the microspheres suitable as a hydrogen storage medium.
U.S. Pat. No. 4,842,620 (PPG Industries) is directed to non-crystalline
silica fibers having porous walls which are used in gas separation. The fibers
described in this application have different physical characteristics than
microspheres and which makes fibers less desirable with respect to hydrogen
separation and storage capabilities.
U.S. Pat. No. 6, 358, 532 (CaP Biotechnology, Inc.) uses porous-wall
hollow glass microspheres for cell clustering and biomedical uses. The
porous-wall structures are designed to readily release microsphere contents
when present within a biotic system. Alternatively, the microspheres are used
to provide a substrate to support cell growth within the porous-wall structure.
While the above references disclose a variety of glass microspheres
and porous-wall structures having various uses in material separation or drug
delivery capabilities, there remains room for improvement and variation within
SUMMARY OF THE INVENTION
It is at least one aspect of at least one embodiment of the present
invention to provide for a hollow glass microsphere (HGM) having a diameter
range of between about 1.0 micron to about 140 microns, a density of about
0.05 gm/cc to about 0.50 gm/cc, and having a porous-wall structure having
wall openings with an average pore size of between about 10 angstroms to
about 1000 angstroms, which contains within an interior of the hollow glass
microsphere a hydrogen storage material.
It is another aspect of at least one embodiment of the present invention
to provide for a hollow glass microsphere containing therein an effective
amount of the hydrogen storage material palladium, the hollow glass
microsphere having a pore size which prevents the loss of palladium fines
from the interior of the hollow glass microsphere.
It is at least one aspect of at least one embodiment of the present
invention to provide for a hollow glass microsphere (HGM) having a diameter
range of between about 1.0 to about 140 microns , a density of about 0.05
gm/cc to about 0.50 gm/cc, and having a porous-wall structure having wall
openings with an average pore size which may range from about 10 to about
1000 angstroms, and which contains within an interior of the hollow glass
microsphere a hydrogen storage material, the exterior wall of the hollow glass
microsphere containing a barrier coating sufficient to prevent gaseous or
liquid contaminants from entering an interior of the HGM while permitting the
passage of hydrogen gas through the exterior wall.
These and other features, aspects, and advantages of the present
invention will become better understood with reference to the following
description and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
A fully enabling disclosure of the present invention, including the best
mode thereof to one of ordinary skill in the art, is set forth more particularly in
the remainder of the specification, including reference to the accompanying
Figure 1 is a cross sectional view of a hollow glass porous-wall
microsphere containing a hydrogen storage material within the interior of the
Figure 2 is a cross sectional view similar to Figure 1 showing a
microsphere having an exterior coating.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference will now be made in detail to the embodiments of the
invention, one or more examples of which are set forth below. Each example
is provided by way of explanation of the invention, not limitation of the
invention. In fact, it will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention without
departing from the scope or spirit of the invention. For instance, features
illustrated or described as part of one embodiment can be used on another
embodiment to yield a still further embodiment. Thus, it is intended that the
present invention cover such modifications and variations as come within the
scope of the appended claims and their equivalents. Other objects, features,
and aspects of the present invention are disclosed in the following detailed
description, It is to be understood by one of ordinary skill in the art that the
present discussion is a description of exemplary embodiments only and is not
intended as limiting the broader aspects of the present invention, which
broader aspects are embodied in the exemplary constructions.
The hollow glass microspheres of the present invention are prepared
using a special glass composition which after appropriate heat treatment
separates into two continuous glass phases. In the examples provided
herein, one of the phases is rich in silica, while the other is an extractable
phase. The extractable phase is preferably present in an amount of at least
about 30 weight percent of the total glass composition. However, other
porous glass compositions may be used.
The extractable phase of the glass composition preferably includes
boron-containing materials such as borosilicates or alkali-metal borosilicates.
Suitable borosilicates and alkali-metal silicates may be found in reference to
the teachings of U.S. Pat. No. 4,842,620 directed to teachable glass fiber
compositions and which is incorporated herein by reference.
The extractable and non-extractable glass components are mixed,
melted, quenched, and crushed to a fine glass powder consisting of individual
glass particles having a particle size of about 5 to 50 microns. The individual
glass particles are then reheated using a gas/oxidizer flame. The glass is
raised to a temperature where a latent blowing agent within the glass, such as
alkali sulfate along with various hydrates, carbonates, and halides, the
selection and use of .which are well known in the art, causes a single bubble
to nucleate within each particle of glass. As the glass particle temperature
increases by exposure to the flame, the glass particle reaches a viscosity
where the particle transforms to a sphere due to the surface tension forces.
As the temperature increases, the pressure within the bubble exceeds the
surface tension/viscous forces value and the bubble expands to form a hollow
glass microsphere. The hollow glass microsphere is then rapidly quenched to
Preferably, the resulting hollow glass microspheres have densities in
the range of about 0.05 gm/cc to about 0.5 gm/cc and diameters may range
between about 1 to about 140 microns. Once formed, the hollow glass
microspheres may be separated on the basis of density so as to select and
segregate the hollow glass microspheres according to desired densities.
Additionally, it is possible to separate the HGMs according to the microsphere
The resulting hollow glass microspheres have a glass wall composition
in which the glass is essentially homogeneous. The hollow glass
microspheres may be heat treated to enhance the glass-in-glass phase
separation by mixing the hollow glass microspheres with carbonaceous
materials and heating in the absence of oxygen to the desired temperature
region. After heat treating the hollow glass microspheres, the homogeneous
glass separates into two continuous glass phases: one extractable and the
other rich in silica. The extractable phase is readily leachable using strong
mineral acids which results in the formation of wall pores within the remaining
silica-rich phase. Suitable mineral acids and methods for leaching the glass
may be seen in reference to U.S. Pat. No. 4,842,620 which is incorporated
herein by reference.
The resulting hollow glass microspheres exhibit a high degree of cell
wall porosity. As used herein, the term "porosity" means a series of pores and
similar openings which either directly or indirectly define a series of
passageways which provide communication between the interior and the
exterior of the hollow glass microsphere. An average cell wall porosity of
about 10 angstroms to about 1000 angstroms can be achieved using this
technology. The cell wall porosity is dependent upon the percentage of
extractable components formulated into the special glass composition used in
the formation of the HGM and the degree of heat treatment employed. The
duration and severity of the extraction process also can have some influence
on the characteristics of the resulting cell wall pores including size and density
of pores formed.
As seen in reference to Figure 1, a cross section through a hollow
glass microsphere 10 is provided. Microsphere 10 comprises a glass wall
having an exterior surface 12 and an interior surface 14. The microsphere 10
further defines a hollow cavity 16 within the interior of the microsphere. As
best seen in reference to the figure, a plurality of pores 20 are defined within
the glass wall of the microsphere. As illustrated in Figure 1, a number of the
pores 20 provide for communication between an exterior of the hollow glass
microsphere and the interior cavity 16 of the hollow glass microsphere.
Present within the hollow cavity 16 is a hydrogen absorption material 30. The
placement of the hydrogen storage material within the cavity 16 is provided in
greater detail below.
Once formed, the porous-wall hollow glass microspheres can be filled
with a hydrogen absorbent such as palladium. To successfully introduce
palladium into the interior of the HGM, palladium chloride can be forced
through the porous glass walls using pressure. Following the introduction of
palladium chloride, hydrogen is then introduced under pressure to reduce the
palladium chloride to palladium metal. Subsequent heat and vacuum drying
may be used to remove any residual hydrochloric acid or water. This process
can be repeated through several cycles to increase the amount of palladium
ultimately encapsulated within the hollow glass microsphere.
Once a desired amount of palladium is present within the hollow glass
microsphere, the porosity of the hollow glass microsphere wall can be altered
or reduced by additional heat treatment. Alternatively, the pores can be
effectively sealed by applying a coating material 40 such as tetraethyl
orthosilicate solution and as illustrated in Figure 2. The coating material can
be formulated to permit the diffusion of hydrogen while excluding other gases.
HGMs were formed from a silicate glass composition containing boron
oxide and alkali as seen in Table 1 set forth below. The constituents of the
glass composition were prepared and heat treated at a temperature of about
600° C for at least 10 hours. It is believed that the 10 hour time interval is
sufficient to allow the glass and the HGM walls to separate into two
continuous glass phases by the known process of spinodal decomposition. In
so doing, two interconnected glass phases are formed within the walls of the
HGMs. A first glass phase consists of a high percentage of silica while the
second glass phase contains a greater percentage of the alkali and borate
material. The alkali borate phase has a greater solubility in a heated acid
solution (80-85° C) of 2-3 N HCL solution. During the leaching process it was
observed that the HGMs began sinking in the solution indicating that leaching
of soluble components believed to be the alkali borate phase was occurring.
Following the leaching process, it is believed that the HGM cell wall
contains small interconnected pores predominantly in the range of about 10 to
about 1000 Angstroms and which pass completely through the HGM wall.
It was further observed that following the leaching process, HGMs
exhibited a weight loss of approximately 33% which is again indicative of the
formation of pores through the selective removal of the alkali borate phase.
Further, using a gas pycnometer, the HGM density of the HGMs change from
about 0.35 g/cc (unleached) to a density of about 1.62 g/cc for the leached
HGMs. The increase in density is further indicative that the alkali borate
material has been selectively removed and that openings exist for the gas to
enter the interior of the HGM. If is noteSd that the density of fused silica is
about 2.2 g/cc. It is believed that the HGM density following extraction
approaches the value of fused silica, but the lower density is indicative that a
small percentage of HGMs are not porous or that during the drying process a
gel film may have formed over some of the pores and/or not all of the alkali
borate phase was extracted during the heated acid treatment.
The porous wall HGMs made according to Example 1 above were
compared to commercially obtained non-porous HGMs for determination of
total surface area. Using gas absorption techniques, it was demonstrated that
the surface area of the non-porous commercial samples was approximately 1
square meter/gram. The surface area of the HGM made according to the
present invention was 29.11 square meter/gram. The increased surface area
of the porous walls of the HGMs indicates a significant increase in surface
area reflective of the formation of pores. It is noted that if the HGMs simply
had holes present within the walls, the surface area would merely include the
interior and exterior surfaces for an expected value of approximately 2 square
meters/gram. Additional analysis of the porous HGMs using gas
absorption/deabsorption indicated an average pore size of about 553
The efficacy of using the porous wall HGMs for hydrogen absorption
was also demonstrated by introducing a palladium solution into the porous
wall HGMs using a vacuum introduction process. Following introduction into
the interior of the HGMs of a palladium tetra amine solution, the palladium
salts were precipitated and later reduced by exposure to heated hydrogen
For certain applications, it is noted that by additional heating of the
porous HGMs to a temperature of about 1000° C, the porosity can be
removed and/or selectively reduced by controlling the temperature and
treatment time intervals. It is believed advantageous for some hydrogen
storage materials to subsequently remove the porosity once the hydrogen
storage material is inserted into the interior of the HGM. Hydrogen can still be
cycled into and out of the hydrogen storage material by using sufficient
pressure and at temperature combinations as are well known in the art.
However, by removing the pores and/or substantially reducing the size of the
pores, the hydrogen storage material is protected from gaseous poisons that
could render the hydrogen storage material inactive.
The resulting hollow glass microsphere containing a hydrogen
absorbent offers numerous advantages for use with hydrogen absorbing
technologies. For instance, when palladium metal and other metal hydrides
are used in a hydrogen absorption/desorption process, the hydrogen storage
material tends to fracture into smaller particles or "fines." The resulting fines
can clog filters, limiting gas flow through the filtration bed in hydrogen
separation devices, and/or blocking gas flow in hydrogen storage devices
resulting in an overall loss of efficiency of the hydrogen absorption/desorption
system. However, when encapsulated within the hollow glass microsphere,
the resulting fines are contained within the hollow glass microsphere and
continue to function in an absorption/desorption capacity.
Additionally, it is possible to select HGMs having a sufficiently small
pore size such that gaseous poisons which may interfere with the hydrogen
absorbing material are physically excluded from entry into the interior of the
HGM. As a result, the HGM functions as a selective membrane which permits
the flow of hydrogen gas into and out of the hollow glass microsphere while
preventing the entry of larger gaseous or liquid molecules.
While it is possible to force hydrogen into and out of solid-walled
microspheres, the use of a porous-wall hollow glass microsphere structure
allows hydrogen gas to enter and exit the microsphere at much lower
pressures and temperatures. Consequently, less strenuous
rehydriding/dehydriding conditions can be employed using the porous-wall
structure as a conduit to enable the passage of hydrogen gas through the wall
of the glass microsphere.
Where the pore size of the resulting hollow glass microsphere is
sufficiently large that gaseous poisons or other materials could enter, it is
possible to provide barrier coatings to the exterior of the HGM. The various
barrier coatings may be selected for special properties so as to provide for
selective membrane properties. One such coating material is a sol gel
material having a sufficiently defined pore structure that provides for a barrier
against gaseous poisons while permitting the flow of hydrogen gas
therethrough. One such sol gel material may be found in reference to the
commonly assigned U.S. Pat. No. 5,965,482, and which is incorporated
herein by reference.
The hollow glass microspheres, containing therein a hydrogen storage
material, offer additional advantages within the hydrogen storage technology
field. The hollow glass microspheres used in accordance with the present
invention may have diameters of between about 1 micron to about 140
microns. Given the size and selectable particle densities, the resulting hollow
glass microspheres have fluid-like properties which make the hollow glass
microspheres suitable for easier transport and bulk storage. For instance,
transportation of large quantities of the filled hollow glass microspheres may
be made utilizing existing pipelines used to convey the supplies of petroleum
products and/or natural gas.
Though the collective volume of hydrogen storage material may
contain enormous quantities of stored hydrogen gas, the transport is much
safer in that the hydrogen is stored within a plurality of discrete hollow glass
microsphere vessels. As a result, the dangers associated with the storage of
a comparable volume of hydrogen gas is greatly lessened since the volume is
now distributed within a large number of individual hollow glass microsphere
vessels. The individual hollow glass microspheres provide an enhanced level
of safety against explosion and fire in that there are no exposed large
volumes of hydrogen gas. For example, a leak or release of HGMs containing
releasable hydrogen has a much reduced threat of explosion or fire since no
free hydrogen is available. Even if released into flame or high temperature
conditions, the insulating properties of the hollow glass microspheres are such
that the net result is a series of very small releases of hydrogen gas as
opposed to a release of a single large volume of hydrogen gas.
While palladium represents one hydrogen storage material which may
be incorporated into the interior of the hollow glass microspheres, it should be
noted that a variety of other hydrogen storage materials are also suitable for
use within the interior of a porous-wall hollow glass microsphere. Such
materials include sodium aluminum hydride, lithium aluminum hydride,
titanium aluminum hydride, complex hydrides, and various fused or hybrid
hydrogen storage materials such as those described in commonly assigned
PCT application PCT/US03/34980 which is incorporated herein by reference,
and various catalyzed borohydrtdes as described in commonly owned U.S.
provisional application entitled "Catalyzed Borohydrides For Hydrogen
Storage having Attorney Docket No. WSR-78-P filed on August 27, 2004, by
Express Mail EV504784466US and which is incorporated herein by reference,
and combinations of these hydrogen storage materials. Additionally, the
hollow glass microspheres can be utilized to provide a "protective
environment" for reactive hydrides or other hydrogen storage materials which
occupy the hollow interior of the porous hollow glass microsphere.
It is within the scope of the present invention to provide for a number of
different hydrogen storage materials which may be contained within the
interior of a suitable HGM. Doing so would allow a plurality of different
hydrogen storage media to be utilized within a given application. For
instance, within a given volume of hollow glass microspheres, there could be
two or more different hydrogen storage materials present within discrete
populations of microspheres having different hydrogen release properties. In
this way, the volume of evolved hydrogen gas may be controlled or regulated
by the appropriate environmental conditions or stimuli needed to release the
In addition, the use of the hollow glass microspheres greatly simplifies
commercial recharging of the spent hydrogen storage material. For instance,
where the hollow glass microspheres containing the hydrogen storage
material are used to power a device, the spent HGM may be removed during
a refueling operation and subsequently recharged. By allowing a separate
recharging or hydrogen absorption process, the HGMs having a hydrogen
storage material can be utilized in various environments such as a hydrogenpowered
motor vehicle. To the extent the vehicle only needs to provide for a
hydrogen release mechanism, the mechanics and operation of the vehicle
may be greatly simplified. Upon refueling with a fresh supply of HGMs
(containing hydrided hydrogen storage material) the spent HGMs are simply
removed for subsequent rehydriding.
It is also envisioned that the formation of a hollow glass microsphere
may be simplified by selection of an appropriate hydrogen storage material to
serve as the source of the nucleating gas. In other words, a hydrogen storage
material which, when heated, may release hydrogen or other inert gas that
may be used as the blowing agSnt for the resulting microsphere. As a result,
it may be possible to use a hydrogen storage or precursor material which
evolves a nucleating agent when heated. As a result, it may be possible to
form the hollow glass microsphere directly around a hydrogen storage
Although preferred embodiments of the invention have been described
using specific terms, devices, and methods, such description is for illustrative
purposes only. The words used are words of description rather than of
limitation. It is to be understood that changes and variations may be made by
those of ordinary skill in the art without departing from the spirit or the scope
of the present invention which is set forth in the following claims. In addition,
it should be understood that aspects of the various embodiments may be
interchanged, both in whole, or in part. Therefore, the spirit and scope of the
appended claims should not be limited to the description of the preferred
versions contained therein.
1. A hydrogen storage apparatus comprising:
a hollow glass microsphere (10) having a wall (12) surrounding an internal volume (16), said wall further defining a series of structural defined pores (20) within the wall having a pore size of at least 10 angstroms and which provide communication between said interior volume (16) and an exterior of said hollow glass microsphere, said pores (20) having a pore size which restricts the entry of gaseous poisons; and,
a hydrogen storage material (30) selected from the group consisting of palladium, alanates, chemical hydrides, and combinations thereof, positioned within said volume (16) of said hollow glass microsphere (10).
2. The hydrogen storage apparatus as claimed in claim 1 wherein said hollow glass microsphere (10) has a density of between about 0.05 gm/cc to about 0.50 gm/cc.
3. The hydrogen storage apparatus as claimed in claim 1 wherein said hollow glass microsphere (10) has a diameter ranging from about 1.0 micron to about 140 microns.
4. The hydrogen storage apparatus as claimed in claim 1 wherein said series of pores (20) have an average pore diameter of between about 10 angstroms to about 1000 angstroms.
5. The hydrogen storage apparatus as claimed in claim 1 wherein said hollow glass microsphere additionally contains a porous coating on an exterior surface of said microsphere, said porous coating further defining a semipermeable membrane.
6. A hydrogen storage apparatus as claimed in claim 1:
wherein said hollow glass microsphere (10) having said pores (20) allows the passage of hydrogen gas through the exterior wall under conditions which require less pressure and lower temperatures in comparison to a hollow glass microsphere having no structural defined pores.
7. The process of making a hydrogen storage apparatus comprising the
forming a hollow glass microsphere (10) having an extractable phase;
removing said extractable phase, thereby providing a plurality of structural pores (20) within a glass wall (12) of said microsphere (10), said structural pores (20) permitting communication between an interior (16 ) and an exterior of the hollow glass microsphere (10), said porous wall hollow glass microsphere (10) having a pore size which restricts the entry of gaseous poisons; and,
introducing into an interior (16) of said hollow glass microsphere (10), a hydrogen storage material (30) wherein said hydrogen storage apparatus can reversibly release and store hydrogen in the presence of gaseous poisons.
8. The process as claimed in claim 7 comprising the additional step of
providing a selectively permeable coating (40) on an exterior surface of said
9. A process of providing a hydrogen storage apparatus comprising:
forming a hollow glass microsphere (10) having a plurality of structural
pores (20) defined within the wall (12);
introducing through said pores (20) a hydrogen storage material (30) into an interior (16) of said hollow glass microsphere (10); and,
thereafter treating said hollow glass microsphere (10) so as to reduce the pore size of said porous hollow glass microspheres (10) to exclude the entry of gaseous poisons to the interior of said hollow glass microsphere.
10. The process as claimed in claim 9 wherein said step of treating said pores (20) of said hollow glass microspheres (10) comprises a method selected from the group of methods consisting of providing a semi-permeable coating, providing a sol gel coating, heat treating said hollow glass microspheres (10), and combinations thereof.
|Indian Patent Application Number||1863/DELNP/2007|
|PG Journal Number||16/2012|
|Date of Filing||09-Mar-2007|
|Name of Patentee||SAVANNAH RIVER NUCLER SOLUTIONS,LLC|
|Applicant Address||SAVANNAH RIVER SITE,AIKEN, SOUTH CAROLINA 29808,USA|
|PCT International Classification Number||C01B 3/00|
|PCT International Application Number||PCT/US2005/033677|
|PCT International Filing date||2005-09-21|