Note: Descriptions are shown in the official language in which they were submitted.
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[1] AEROGEL AND METHOD OF MANUFACTURING SAME
[2] FIELD OF THE INVENTION
[3] The present invention relates to an efficient method for rapidly producing
silica aerogel by rapid solvent exchange, inside wet gels, with little water,
alcohol
and acetone produced as the reaction byproducts. Preferably, dynamic
frequencies are induced throughout the gel mass/continuum, during the aging
and washing processes, in order to enhance, and thus accelerate, diffusion
throughout the nanoporous gel structure.
[4] BACKGROUND OF THE INVENTION
[5] The formation of aerogels, in general, involves two major steps, the first
is the formation of a sol-gel like material, and the second is drying of the
sol-gel
like material to form the aerogel. In the past, the sol-gel like materials
were
made by an aqueous condensation of sodium silicate, or a similar material.
While this process works relatively well, the reaction forms salts within the
gel
that need to be removed by an expensive ion exchange technology, and
repetitive washing, thereby rendering this process time consuming, expensive,
and laborious -With the -recent development of-sol-gel-chemistry -over the
last -
few decades, a vast majority of silica aerogels prepared today utilize silicon
alkoxide precursors. The most common of these are tetramethyl orthosilicate
(tetramethoxysilane (TMOS) Si(OCH3)4), and tetraethyl orthosilicate
(tetraethoxysilane (TEOS) Si(OCH2CH3)4). However, many other alkoxides,
containing various organic functional groups, can be used to impart different
properties to the gel. Alkoxide-based sol-gel chemistry avoids the formation
of
undesirable salt byproducts and allows a much greater degree of control over
the final product. The balanced chemical equation for the formation of a
silica
gel from TEOS, by a standard method is:
[6] Si(OCH2CH3)4 (1)+ 2H20 (I) - Si02 (s)+ 4HOCH2CH3 (I)
[7] SUMMARY OF THE INVENTION
[8] The present invention is directed to an improved silica aerogel product
and an improved method for preparing the silica aerogel product. The improved
silica aerogel product can be one of a granule, a coating, a hybrid composite,
or
a monolith, in which the byproduct of reaction is almost always alcohol--with
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negligible amounts of water--and in which the time required to perform solvent
extraction and drying typically ranges from 2-16 hours per batch, as opposed
to
the standard ambient process time of about 120-200 hours per batch, for
example.
[9] Aerogels are chemically inert, highly porous ceramic materials. Generally,
these materials are produced by forming a gel which contains a solvent. Once
the solvent is removed, a porous solid component is formed. Removal of the
solvent, while still preserving the porous solid structure, can be a difficult
process
because the gel often shrinks upon removal of the solvent and this causes the
porous solid structure to collapse, thereby leaving an optically transparent
material with a relatively small surface area and low pore volume, referred to
as
"Zeolite." This obstacle is overcome by utilizing a solvent which promotes
hydrolysis of the alkoxides in the presence of a catalyst, specifically a base
catalyst and more specifically a silane-based catalyst (namely, gamma-APTES)
gamma-aminopropyl triethoxysilane, and generates alcohol as the primary
reaction byproduct. In so doing, the duration of the washing process is
significantly reduced while, at the same time, the structural integrity of the
alcogel is significantly enhanced. Concurrently therewith, silation (-OH
capping)
-- of-the alcogel- may-be carried out almost immediately after the-initial or
first gel
point is attained (within 10-50 minutes or so) or while gelation is attained,
but
while self-assembly is in progress.
[10] Recent advances in this technology have produced--currently only in
laboratories,--aerogels that are the product of a sol-gel process, whose final
stage involves extracting the pore-filling solventwith an organic liquid, at
ambient
pressure. The end product is a very low density solid (e.g., having a density
of
between 0.003-0.25 grams/cm3), with the same volume as the original hydrogel
and a chemical composition substantially identical to that of glass.
[11] A sol-gel technique has been developed by Keller Companies,
Incorporated, and this technique is used to prepare wet gels in ethanol, more
specifically in diacetone alcohol, inside a jacketed glass-lined reactor or a
stainless steel vessel, that are suitable for aging and subsequent silation,
washing and drying. The process generally takes between 2-16 hours to
produce a final product, however, depending on specific characteristics of the
aerogel, the process may be completed in about 3-4 hours or so.
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[12] The length of drying time of the aerogel is dependent upon the pore size,
the particle size distribution, the tortuosity of the pores and the thickness
of the
aerogel sample being prepared, since it is the thickness, i.e., the largest
dimension of the aerogel sample being prepared, that determines the distance
required for heat and mass diffusion during the drying process. The time
required for solvent exchange varies approximately proportionally to the
square
of the sample thickness.
[13] The present invention focuses on reducing the overall processing time for
preparing a high quality silica aerogel. The present invention focuses on
specific
reactants and their byproducts. Specifically, the use of a diacetone alcohol
solvent eliminates the need for water as the hydrolyzing media for the
alkoxide
precursors which, in turn, reduces the processing time.
[14] It is an object of the present invention to substantially reduce the
synthesis time required for ambient pressure drying of wet gels to form the
silica
aerogel product.
[15] It is a further object to produce aerogel products in a minimum amount of
time while reducing the solvent-particle contact angle, and thereby avoiding
particle collapse.
[16] --It-is-a- still further object to-produce an aerogel product while-
maintaining
the temperature within the wet gels sufficiently spatially uniform in order to
avoid
thermal stress damage within the skeletal structure of the gel.
[17] It is a further object to produce an aerogel product while maintaining
the
fluid surrounding the wet gels at substantially the same temperature and
pressure as the fluid within the wet gels.
[18] This invention further relates to an aerogel synthesis process with a
significant reduction in the synthesis time.
[19] Yet another object of the invention is to maintain narrow temperature and
pH ranges for the mixed reactants to optimize the particle size distribution,
the
optical clarity, the light scattering coefficient, and/or the density of the
aerogel
product, depending upon the particular application for the end product.
[20] Additionally, the present invention relates to the use of a diacetone
alcohol (DAA) solvent, and the elimination of water as a hydrolyzing media for
the synthesis process.
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[21] The present invention further relates to the use of ethanol solvent in
combination with ammonium hydroxide to form a catalyst solution, where the
catalyst solution is reacted with the precursor solution, which is a
combination
of ethanol solvent and an alkoxide, and more specifically tetraethyl
orthosilicate
(TEOS).
[22] Also, the present invention relates to the use of carbamaidehyde
(formamide) solvent in combination with ammonium hydroxide to form the
catalyst solution, where the catalyst solution is reacted with the precursor
solution, which is a combination of carbamaldehyde (formamide) solvent and an
alkoxide, and more specifically tetraethyl orthosilicate (TEOS).
[23] Also, the present invention relates to the use of carbamaldehyde
(formamide) solvent in combination with gamma-APTES to form the catalyst
solution, where the catalyst solution is reacted with the precursor solution,
which
is a combination of carbamaldehyde (formamide) solvent and an alkoxide, and
more specifically tetraethyl orthosilicate (TEOS).
[24] Also, the present invention is directed at using (dynamic) frequencies
throughout the gel continuum as a mechanism for enhancing diffusion of the
solvent and thus reduce the processing time. Diffusion is enhanced as a result
of-an increase in-the effective-mass and heat-diffusion rate at-the-solvent-
(e.g.;
hexane, heptane, etc.)-fluid (e.g., alcohol, water) interface.
[25] The present invention is further directed at the use of carbamaldehyde as
an evaporation controlling agent, which acts as a morphology stabilizer for
the
lattice structure of the silica nanogel, thereby reducing the external thermal
stress which prevents, or minimize at the very least, collapse of the nano-
structure of the porous silica aerogel.
[26] Additionally, the present invention relates to the use of more efficient
and
compatible catalysts such as ammonium hydroxide, and gamma-aminopropyl
triethoxy silane (gamma-APTES). Ammonium hydroxide is an efficient catalyst
which, upon reaction, leaves no ionic species and thus leads to the formation
of
a high translucency hydrogel. Gamma-aminopropyl triethoxy silane is a high
performance silane-based catalyst and a coupling agent, referred to as gamma-
APTES. This catalyst is added to the solvent solution (H20/EtOH) in an amount
of about 0.01 % to 5% by weight of the precursor (e.g., alkoxide). The
catalyst
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gamma-aminopropyl triethoxysilane has the formula (NH2)(CH2)3 Si(OC2H5)3
while ammonium hydroxide has the formula NH4OH
[27] The present invention also relates to a method of manufacturing a silica
aerogel, the method comprising the steps of: a) preparing a precursor solution
chilled to a temperature of between 20 -60 F (-6.7 -15.5 C); b) preparing a
catalyst solution chilled to a temperature of between 20 -60 F (-6.7 -15.5 C);
c)
mixing the chilled catalyst solution with the chilled precursor solution to
form a
mixed solution with the mixed solution having a pH of between 9.5 and 12.2; d)
aging the mixed solution for a time of between 1 and 120 minutes, to form a
gel
and control a particle size distribution of the gel while maintaining the
mixed
solution at a temperature of between 34 -55 F (1.1 -12.8 C); e) immediately
upon the mixed solution reaching a gel point, silating the gel for a time
period of
between 1 and 120 minutes; and f) drying the gel at a temperature of at least
122 F (50 C) to form the aerogel
[28] The present invention finally relates to an aerogel manufacture by: a)
preparing a precursor solution chilled to a temperature of between 20 -60 F (-
6.7 -15.5 C); b) preparing a catalyst solution chilled to a temperature of
between
20 -60 F (-6.7 -15.5 C); c) mixing the chilled catalyst solution with the
chilled
precursor- solutionto-for-m-a mixed solution with the-mixed solution-having a-
pH---
of between 9.5 and 12.2; d) maintaining the mixed solution at a temperature
range of between 34 -55 F (1.1 -12.8 C) and aging the mixed solution for a
time
of between 1-120 minutes to form a gel and control a particle size
distribution of
the gel; e) silating the gel for a time period of between 1-120 minutes; f)
washing
the gel in wash fluid; and g) drying the gel to form the aerogel, with the
aerogel
having a density in the range of about 1.87-15.61 lb/ft3 (0.03-0.250 g/cc), an
R
value of at least 20 and light transmission of at least 25%.
[29] BRIEF DESCRIPTION OF THE DRAWINGS
[30] The invention will now be described, by way of examples, with reference
to the accompanying drawings in which:
[31] Fig. 1A diagrammatically illustrates a process for manufacturing the
inventive areogel via a vapor phase reaction;
[32] Fig. 1 B diagrammatically illustrates describes an ambient pressure
process for manufacture of the inventive areogel;
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[33] Fig. 2A illustrates a condensed acoustic trace for the inventive areogel
manufactured by the inventive method;
[34] Fig. 2B illustrates the expanded acoustic trace of Figure 2A for the
inventive areogel manufactured by the inventive method;
[35] Figs. 3A, 3B, 3C, and 3D are photographs illustrating the quality of
first-
generation of the inventive areogel;
[36] Figs. 4A, 4B, 4C, 4D, 4E, and 4F illustrate the quality of second-
generation of the inventive areogel as manufactured using a rapid drying
method, but having only DAA and the precursor (condensed TEOS, and pre-
condensed silbond series) as the primary reactants;
[37] Figs. 5A and 5B illustrate hybrid type insulation doped with the
inventive
areogel and an untreated insulation (control), respectively;
[38] Fig. 6 is a transmission curve comparing a Cabot Aerogel, a NASA
Aerogel, an India Aerogel, and the areogel according to the present invention;
[39] Fig. 7 is a table I which lists test results for Kalgel aerogel vs.
competitive
aerogel products;
[40] Fig. 8 is an experimental set up for testing a modulus of elasticity of
the
Kalgel aerogel;
[41]- --- - -- Fig. 9- is an- illustration showing -the -displacement -of
residual-water with
acetone and alcohol;
[42] Fig. 10 is an illustration of the silation process and OH capping used to
cap the free hydroxyl groups; and
[43] Fig. 11 is a diagrammatic representation showing use of the aerogel as
an insulating material within an insulating panel.
[44] DETAILED DESCRIPTION OF THE INVENTION
[45] The present invention is directed to an improved process and novel
chemistry for the manufacture of a variety of types of aerogel product,
including
granules, films, monoliths, and hybrid composites.
[46] As used herein, an "aerogel" includes structures that are microporous or
have a nanoporous lattice from which a solvent has been removed, such as a
xerogel, silica gel, and water glass.
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[47] The term "granules" refers to aerogel bodies of a generally organized
dimensional geometry for specific applications that were optimized for an
efficient end use.
[48] The term "particle" refers to micro-granule.
[49] The term "monolith" refers to a single aerogel body having a minimum
dimension, i.e., a thickness, with the other two dimensions being larger than
the
thickness, orto a cylindrical object having a diameter. The thickness or
diameter
is typically in the range of millimeters to tens of centimeters.
[50] The term "hybrid" refers to an aerogel that has been formed with another
substance, e.g., glass fibers dispersed in the gels or glass fibers doped with
the
aerogel raw materials (precursor-solvent-catalyst), or a new chemistry which
involves a modified silica backbone.
[51] The term "solvent" refers to the liquid dispersion medium used to form
the
gels which is later removed to form the aerogel in accordance with the
invention.
It is a non-supercritical fluid at the pressure and temperature of interest.
[52] The term "dynamic frequency" refers to dynamic signals induced within
the continuum for creating continuous micro vibrations generally in a
pulsating
form. The pulse (or wave) preferably has a sinusoidal waveform, but other
types
--- - ofwavefor-ms, e-:g~,- saw-tooth;-squarej -gaussian;-or harmonics of-any
of these,-- -
may also be utilized.
[53] The term "gel point" as used herein refers to the stage at which the sol
begins to exhibit pseudoelastic properties and the viscosity of the sol has
increased and is generally in the range of between about 5500-10000 cps
(centipose) or more preferably in the range of between at about 7500-8000 cps
which thereby indicates gelling of the sol.
[54] With reference to Fig. 1A, a schematic drawing of a proposed aerogel
manufacturing process is shown. This process focuses on the production of a
transparent type aerogel which is clear and has super weathering coatings and,
in particular, this vapor phase process focuses on the ability of efficiently
and
effectively doping Kalwall insulation (RAH reinforced angel hair and DRAH
dense
reinforced angel hair) thus providing a unique and inexpensive insulation with
high a R-value, e.g., an R-value = 8-40, and more preferably an R-value of at
least 12. According to a first step, a precursor solution and a catalyst
solution--
each solution is described below in further detail--are both introduced into a
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controlled flow-mixing chamber 2. The mixing chamber 2 is preferably
maintained under vacuum, e.g., at a negative pressure of between about 28-
29.4 inches (71.12-74.68 cm) of Hg, for example, and typically at a
temperature
of between about 120 -200 F (48.9 -93.3 C). As the precursor solution and the
catalyst solution are introduced into the mixing chamber 2 via metering pumps
(not shown), they combine and mix with one another and react quickly, e.g., on
the order of a few milliseconds, and create a dry gel (hydrophilic granular
aerogel) byproduct. The temperature within the reaction chamber is maintained
at a minimum of 120 F (48.9 C) and at a maximum of 200 F (93.3 C) and, as
a result of this, the kinetics of the reaction are quite rapid. The formed gel
is
either treated with HMDZ vapors in the reaction chamber, thus rendered
hydrophobic, or it is collected and discharged into a chamber, at a
temperature
of 43 -120 F (6.1 -50.0 C), where the chamber contains a 10% hexamethyl
disilazane (HMDZ) solution in hexane, heptane or a higher alkane. The HMDZ
solution is the silation agent. Mixing of the reaction byproducts in the
HMDZ/hexane solution, at a temperature of about 122 F (50.0 C), continues for
about 2-4 hours, most preferably for about 3 hours or so, while ultrasonic
sawtooth vibrations are simultaneously introduced to the chamber. Next, the
--- - -solvent is discharged~-and the resulting residual-alcogel-is-placed in-
a-convection
oven or on a fluid bed drier to dry the alcogel, as described below in further
detail.
[55] The embodiment of the inventive process as seen in the schematic
drawing of Fig. 1 B is an alternative process which focuses on liquid/liquid
phase
reactions and produces translucent silica aerogel which is suitable for use as
an
insulating media, e.g., within an insulating panel (Fig. 11). The process
includes
the steps of combining the catalyst solution 20 and the precursor solution 22
in
a reaction/aging chamber 24 and initiate the reaction, thus forming the
alcogel.
The gel, e.g., an alcogel, is then washed and introduced into a HDMZ reactor
30
and silated using 10% HMDZ solution in hexane, heptane or a higher alkane for
about 2-6 hours, most preferably for about 3-4 hours, while ultrasonic
vibrations
are introduced. The HMDZ solution is next discharged, and the gel, e.g., an
alcogel, is further washed in a wash reactor 32 with hexane, heptane or a
higher
alkane, while the gel, e.g., the alcogel, is continuously agitated. Finally,
the gel,
e.g., the alcogel, is collected and dehydrated or dried in a convection oven
or a
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fluid bed dryer only generally shown as dehydration 34, for example, as
described below in further detail.
[56] Aerogels are open pore materials having about 80% or more porosity by
volume and a pore size ranging from about 1-50 nm, preferably the pore size
range from about 5-30 nm, and most preferably the pore size range from about
20-25 nm. Aerogels may be prepared from any gel-forming material(s) from
which the solvent used for gelation can be removed by a drying process without
destroying, significantly shrinking and/or collapsing the pore structure.
Drying,
for example, can be accomplished by supercritical extraction, atmospheric
drying, freeze-drying, vacuum drying, orthe like. In the relevant art,
aerogels are
typically produced by an ambient pressure drying/extraction of the solvent (or
any liquid replacement for the solvent) that was used to prepare the starting
gels.
[57] According to the method of the present invention, the inventive areogel
(e.g., Kalgel) is initially dried by an ambient pressure drying process,
typically at
a temperature of about 122 F 9 F (50.0 C + 5 C). This involves the evolution
of inorganic networks through the formation of a sol and gelation of the sol
to
form a continuous phase.
[58] The precursors for synthesizing these colloids consist of metal
alkoxides.
The- -most -widely- used ----alkoxides are- - -the -alkoxysilanes, - such---
as
tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS).
[59] At the functional group level, three reactions are generally used to
describe the sol-gel process: (1) re-esterification/hydrolysis, (2) water
condensation, and (3) alcohol condensation (alcoholysis). The general reaction
schemes for each are illustrated below.
,-...:Zi- OR. + H'-f3H Nuclpaphili+w S6.--OH + P,rJC-1 -r R r R, i
i Nucleopl-iiie Sukrstituiwic,n
10tssoc.ia'tiorr
~ Hydrrrly~is ~ ~
~ Si-i3H ,~ - Si-OH = = - S i- 'a' -- Si- + H.jQH (2)
!
~i-~.7R: Si.-- cr':-.~i- + ROF i
I 1 ~.
Sol-GiI Re-actiors Prleclvahism
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[60] A consecutive reaction is the dehydration of DAA which results in
formation of mesityl oxide (MO) as illustrated in equation (4) below:
)L)H
+ H2 (4)
DAA N10
or in the formation of two molecules of acetone, as illustrated in equation
(5)
below:
0 OH ~H ol
CH,-Q-CH~-C~CH } ~ 2~H -~ ~H~ (5)
the MO formation is reversible, but the equilibrium is very much toward the
side
of MO formation. At the low concentrations of water and/or MO, the reverse
reaction (MO + H20 = DAA) can be negligible. Both DAA and MO can undergo
aldol condensation with acetone, with DAA or MO forming heavier products,
such as isophorone and isoxylitone.
[61 ]--- ----- - - - The-formation-of DAA from AC is--second order- in AC, the
formation-of AC
from DAA is first order in DAA, and the formation of MO from DAA is also first
order in DAA. All three reactions are base catalyzed (e.g., a NH4OH catalyst).
For nano-particles, the intra-particle diffusion is important. It is to be
appreciated
that diffusion limitations promote the formation of MO.
[62] In equation (5), the rate of decomposition is first-order with respect to
the
concentrations of both diacetone alcohol and the hydroxide ion (generated from
the catalyst). However, since the hydroxide ion is a catalyst, its
concentration
remains constant during the reaction and the overall reaction appears first-
order.
[63] Since the overall reaction is first-order, the kinetics of the reaction
can be
determined by measuring any property of the system that had undergone a
change, which is proportional to the extent of the reaction. In such case, the
property is the volume of the reaction solution.
[64] It is worth noting that the effective volume of one molecule of diacetone
alcohol is not the same as the effective volume of two molecules of acetone
and,
as a result of this, the total volume of the reaction solution changes as the
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reaction proceeds. In this case, the solution expands although in some
reactions
it may contract. This characteristic becomes critical when, for example,
synthesizing a Kalgel aerogel in a fixed volume reaction vessel. As the
gelling
occurs, the stress exerted on the skeletal structure becomes a concern and
must
be relieved in order to maintain the high mechanical integrity for the final
gel.
[65] The temperature, the pH, the induced (sonic) energy, and the ratio of
carbamaldehyde, alcohol, or DAA-to-the ratio of the precursor are among the
most critical parameters which determine the characteristics of the resulting
aerogel, e.g., the Kalgel aerogel. Those parameters control OH dissociation,
hydrolysis, and polycondensation, and thus they can control the final
characteristics of the resulting aerogel product.
[66] By controlling the pH of the catalyst during formation of the gel to a pH
of
between 9.5-12.5, more preferably a pH of between 10.0-11.0, and most
preferably at a pH of about 10.2, the optical clarity, the light scattering
coefficient, and the mechanical properties of the resulting aerogel product
are
optimized. The Kalgel aerogel, for example, has a measured optical clarity C =
0.0037 (zero is optimal) and a Light Scattering Coefficient A = 0.7883 (one is
optimal). The C and A values were determined using optical transmittance
curves-measured for--the Kalgel aerogel-samples; using a-Keller-Companies'-
sphectroradiometer. Optical transmittance T versus wave length between 400
and 700 nanometers were then plugged into Hunt's Equation, i.e., T(,\) = A e
(ct/Aexp4) are optimum. As for mechanical properties, acoustic measurements of
the Kalgel aerogel were measured and a Bulk Modulus of elasticity for the
Kalgel
aerogel was determined to be in the range of 0.60-0.70 Gpa. The density for
Kalgel aerogel was measured to be in the range of 0.070-0.035 g/cc and have
a Light Transmission = 28% (Artificial Light) and 16% (Blue Sky). To assist
with
controlling the pH of the precursor/catalyst mixture, ammonium hydroxide
NH4OH, for example, can be added to the solution mixture if the pH is below
12.0, for example, (less basic/more acidic) while an acid such as acetic acid
CH3COOH can be added to the solution mixture if the pH is above 10 (less
acidic/more basic), for example. Optimization of the end product is achieved
when all the raw materials (RM) are chilled to a temperature range of between
20 -60 F (-6.7 -15.5 C), more preferably chilled to a temperature range of
between 33 F to 55 F (0.5 -12.8 C) and most preferably chilled to a
temperature
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of between 35 F to 55 F (1.5 -12.8 C) during formation of the gel from the raw
materials.
[67] If reaction temperature is closely maintained at a temperature of from
about 34 F to 43 F (1.1 -6.1 C), for example, a crystal clear (sol) gel is
produced, as illustrated in Figs. 4A, 4B, and 4D. This behavior is critical
and is
mainly attributed to the ability to control particle growth while the
particles self-
assemble. By maintaining a narrow temperature range, the particle growth
slowly but steadily undergoes a self assembly mode with a stable
interpenetrating lattice structure. This steady self assembly process provides
important properties which are reflected in the reduced light scattering, the
improved optical clarity and light transmission, as well as the improved
thermal
stability and resistance to color degradation of the particles.
[68] In the case of second generation Kalgel, the inventor found that a molar
ratio (rM) of diacetone alcohol to TEOS of 4:1, more preferably a molar ratio
of
diacetone alcohol to TEOS of 3.7:2.5, and most preferably a molar ratio of
diacetone alcohol to TEOS of about 3:2, and at a chilled temperature of about
40 F 3 F ( 4.4 1.7 C) for all raw materials (including the catalyst) yields
a
crystal clear (sol) gel with extremely narrow particle size distribution of
about 5-
30 nm,- preferably a particie- size-distribution of -about 10-20- nm,- -and--
most- -
preferably a particle size distribution of about 15-20 nm.
[69] Thus, by controlling these factors, it is possible to vary the structure
and
properties of the (sol) gel-derived inorganic network over wide ranges. This
is
shown during the hydrolysis under basic conditions (NH4OH conditions), with R-
values ranging from 2.5-40 where monodisperse spherical particles were
produced.
[70] In the case of the second generation Kalgel, the inventor introduced a
novel aldehyde, with properties that leads to the elimination of the washing
process. In particular, when this aldehyde, referred to as carbamaldehyde
(also
referred to as formamide) and more preferably de-ionized carbamaldehyde, is
utilized, a critical reduction occurs in the forces (i.e., thermal stresses)
which act
to prevent collapse of the nano structure of aerogel. Thus, when the gel
(e.g.,
hydrogel) is placed in an oven for drying, the water can be removed without an
adverse impact on the final aerogel product, i.e., the final product is at
least
translucent or preferably approaching the transparency of glass. This aidehyde
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must be used in a ratio equal to about 0.3 - 3.0 times the weight of the
precursor,
more preferably about 0.5 - 2.0 times the weight of the precursor, and most
preferabiy about 0.75 - 1.5 times the weight of the precursor.
[71] Generally speaking, the (sol) gel reaction mechanism clearly illustrates
how a hydrolysis reaction replaces alkoxide groups (OR) with hydroxyl groups
(OH). Subsequent condensation reactions involving silanol groups (Si-OH)
produce siloxane bonds (Si-O-Si) plus byproducts such as a very little water
and
alcohol as well as acetone. Under most conditions, condensation commences
before hydrolysis is complete. However, as mentioned earlier, conditions such
as pH, the DAA/Si molar ratio, and the catalyst can induce completion of
hydrolysis before condensation begins.
[72] As the number of siloxane bonds increases, the individual molecules are
bridged and aggregate in the sol. When the sol particles aggregate, or inter-
knit
into a network, the gel is formed. Upon drying, the trapped volatile
components
(such as water, alcohol, etc.) are driven off and the network shrinks as
further
condensation occurs. It should be emphasized, however, that the addition of
solvents and certain reaction conditions might promote esterification and
depolymerization reactions.
-[73] ----While- a- single -alkoxide-alcohol (DAA)- solution is generally
used, a
combination of two or more alkoxide-alcohol solutions may be used to fabricate
mixed oxide aerogels. After formation of the alkoxide-alcohol solution,
dissociation of DAA in a base-catalyzed environment yields water and acetone
as the byproducts, where the water causes hydrolysis so that a hydroxide in a
"soP' state is present. When using TEOS, the hydrolysis reaction is:
Si(OCZHJ4+CH3COCH3+4H20 - Si(OH)4+4(C2H5OH)+CH3COCH3 (6)
[74] As the sol state alkoxide solution is aged, an aerogel monolith begins to
show its nanocrystaline form. According to the invention, aging generally
occurs
over a period of preferably about 20-120 minutes, where condensation reaction
reaches full maturity, as illustrated in equation (7) below:
Si(OH)4 - Si02 +2H20 (7)
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[75] The silation process and OH capping is the method used to cap free
hydroxyl groups, at which point the gel is rendered hydrophobic. The preferred
silating agent is HMDZ (hexamethyl disilazane). Use of a silating agent is not
novel. That is, the silating agent is used in generally in the same manner it
has
always been used in the relevant art. However, the novelty according to the
present invention, is two-fold:
[76] (a) HMDZ which utilized by the present process is technical or
commercial grade (i.e., not high purity), yet the results obtained are still
as good as those obtained using high purity HMDZ; and
[77] (b) The point at which the HMDZ is added is critical in capping OH and
when using commercial grade HMDZ. The process is illustrated in Fig.
10.
[78] A 10% chilled (at a temperature of between 34 F to 43 F (1.1 -6.1 C))
solution of HMDZ, in hexane, heptane, or pentane, for example, is added to the
sol mass (sol gel), just at the moment when formation of the initial or first
gel
occurs and is complete, as opposed to the current state of the art where HMDZ
is added after the washing step. The above percent is based on the amount of
alkoxide added in the_for_mutation.. Silationtakes.effect as-aging_continues
over
a period of about 20-120 minutes, for example. After this time period, an
ambient pressure drying process commences.
[79] An ambient pressure drying of the wet gel (i.e., alcogel) generally
commences at the end of the aging and wash cycles. Prior to drying, the gel
mass (e.g., the hydrogel-alcogel mass) is immersed twice in hexane, pentane,
or most preferably heptane. The heptane is typically chilled to a temperature
of
34 F to 43 F (1.1 -6.1 C), and added to the chilled gel mass. This gel mass is
then subjected to a sawtooth type or sine wave type vibration. Such vibration
enhances the diffusion of the solvent throughout the skeletal structure of the
nanogel. In order to induce thermal shock propagation in the gel mass and
cause displacement of residual water (i.e., a byproduct) with acetone and
alcohol
(i.e., byproducts of the synthesis process), as seen in Fig. 9, the wash
solvent
can be heated to a temperature of 140 F (60 C), for example, and such a
drastic
temperature difference, between the chilled gel, at 43 F ( 6.1 C) for example
and
the heated wash solvent, induces thermal shock propagation in the gel mass.
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[80] A first heptane wash cycle typically occurs for a period of about 2 hours
or so. Generally, a second wash occurs immediately thereafter, for a period of
about 2-4 hours or so. Both of the solvent washes each occur at a temperature
of about 122 F (50 C). During the solvent wash process, dynamic waves are
transmitted throughout the gel mass to assist with diffusion.
[81 ] According to the present invention, the efficiency of the solvent
exchange
process is enhanced by increasing the solvent effective mass diffusivity. More
particularly, improved solvent exchange efficiency was achieved by inducing
ultrasonic waves through the solvent medium. This was accomplished using
high frequency low amplitude vibration (pulsating) waves-e.g., at a frequency
about 200-3500 Hz and an amplitude below 0.002 inches (0.005 cm).
[82] The mechanism of diffusion enhancement using ultrasonic high frequency
vibrations at the interface region of the solvent (liquid alcohol) and the
alkane
wash fluid phase is due to the differential wave propagation coupled with
acoustic impedance within the solvent systems. The vibrations travel through
the wash fluid (e.g., alkane) through the porous gel, and again into the
solvent-
solvent interface. Due to the impedance discontinuity, the wave phenomenon
may be assumed to be two-fold and out of phase. This causes molecules within
the wash fluid to-pr-opagate--at di .fferent-velocities. - This creates micro-
signais
within the interface and nano signals within the porous media, leading to
enhanced diffusion within the solvent continuum.
[83] As the enhanced diffusion process continues, the interface region moves
in the direction of the remaining solvent liquid region of the gel until that
region
completely disappears and the entire gel structure contains an alkane phase.
Once this occurs, the entire gel structure participates in a mass transport
enhanced mostly by slower pulses that generate a longer distance pumping
effect. The pumping action of the vibratory signals tends to rapidly lower
solvent
concentration inside the gel at a rate much faster than that of a simple
diffusion
process relying merely on a concentration gradient.
[84] As can be seen in Fig. 2A, a condensed acoustic trace illustrate the high
internal mechanical characteristics of the aerogel. As seen in the Fig. 8, a
high-
density polyethylene (HDPE) tube is filled with granular Kalgel aerogel. A
high
frequency sound signal is introduced at one end of the tube, and a sound
detector is placed at the other opposite end of the tube. The sound detector
is
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connected to a data acquisition system (DAS), where data is collected and
evaluated using ProTools Software. Figs. 2A and 2B are condensed acoustic
trace and the detailed acoustic trace obtained by the ProTools Software.
[85] In Fig. 5A, Reinforced Angel Hair (RAH) is doped with the inventive
areogel and processed at ambient temperature. The final insulation is referred
to as a hybrid insulation.
[86] Fig, 6 is a graphical representation of a number of transmission curves
comparing a CabotTM Aerogel, a NASATM Aerogel, an IndiaTM Aerogel, and the
inventive areogel according to the present invention. It is a measure of the
percent transmittance versus wavelength (nm). The graph indicates the superior
light transmission properties of the inventive areogel according to the
present
invention in the visible light region, with a solid cut-off region in the UV
range of
the spectrum.
[87] Typically, an acid or a base catalyzed TEOS-based gels are often
classified as "single-step" gels, referring to the "one-pot" nature of this
reaction.
A recently developed approach (i.e., the Kalgel approach) uses pre-polymerized
TEOS as the silica source.
[88] Pre-polymerized TEOS is prepared by heating an ethanol solution of
-TEOS with a-sub-stoichiometric amount of water and an acid catalyst, such as
hydrochloric acid. The solvent is removed by distillation, leaving a viscous
fluid
containing higher molecular weight silicon alkoxides. This material is re-
dissolved in ethanol and reacted with additional water under basic conditions
until gelation occurs. Gels prepared in this way are known as "two-step" acid-
base catalyzed gels. Pre-polymerized TEOS is available commercially in the
United States from Silbond Corp. (i.e., Silbond H-5, H-30, H40, etc.), for
example.
[89] These slightly different processing conditions impart subtle, but
important
changes to the final aerogel product. Single-step base catalyzed aerogels are
typically mechanically stronger, but more brittle, than two-step aerogels.
While
two-step aerogels have a smaller and narrower pore size distribution, they are
often optically clearer than single-step aerogels.
[90] Two wet gel samples were prepared essentially from tetra-ethoxysilane
(TEOS) as described in Example 1 below. The aerogel had a density of approx.
0.045 g/cc. The gel time was approximately 10-115 minutes, depending on
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temperature (in this instance, the inventor used chilled raw materials).
[91] Example 1
[92] A. PREPARATION OF PRECURSOR SOLUTION
[93] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) alkoxide= 440.4 grams
[94] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) absolute EtOH = 400
grams
[95] B. PREPARATION OF CATALYST SOLUTION
[96] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) absolute EtOH = 240
grams
[97] Wt. of chilled (i.e., 34 F to 43 F (1.1 -6.1 C)) de-ionized water= 333
grams
[98] Wt. of ammonium hydroxide (i.e., 20 F to 43 F (-6.7 - 6.1 C)) = 1.79
grams (for a final pH of 12.20 or gamma-APTES = (1.20 grams) with the catalyst
solution having a temperature of between 34 F to 43 F (1.1 -6.1 C) so as to
prevent crystallization or freezing of the water within the solution. The
final
aerogel properties are C = 0.0045 um4/cm; Light Scattering Coefficient A =
0.884; Light Transmission (% LT) of 41 % for Artificial Light and 25-27% for
Blue
S-ky~ -and--for- a --Kalwall --- Panel- incorporating -the_ inventive-
aerogel, a_ Light
Transmission (% LT) of 25-27% for Artificial Light passing therethrough and 19-
20% for Blue Sky Day passing therethrough; a density of 0.044-0.091 g/cc; a
Bulk Modulus of Elasticity = 0.33 Gpa; and a Durometer Hardness (Type A)
32-35.
[99] Slowly, the catalyst solution is added to the precursor solution while
the
precursor solution is being constantly mixed. Mixing of the solutions with one
another to form a mixed solution and continue mixing the mixed solution while
the pH is periodically checked in order to maintain the pH between 9.5-12.2
and
thereby control the particle size distribution of the resulting aerogel. It is
to be
appreciated that the pH of the mixture will generally be reduced slightly as
the
catalyst solution is mixed with the precursor solution. As noted above, either
an
acid or ammonium hydroxide can be added to maintain the pH within the desired
range. Once the pH for the mixture is between 9.5-12.2, preferably between
10.0-10.5, and most preferably at 10.2, and the viscosity of the mixture is at
about 5500-10000 cps (centipose) or more preferably between about 7500-8000
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cps, a 10% solution of hexamethyl disilazane (HMDZ) in hexane (99% assay) is
added thereto at ambient temperature, e.g., 72+5 F (22.2 +2.8 C). It is
important to ensure that the weight of the HMDZ is 10% of the initial weight
of
the precursor solution. The combined mixture is continued to be mixed for
about
20 4 minutes and then aged for a period of 8-12 hours, after which, the HMDZ
solution in hexane is discharged and then a second wash takes place by adding
the hexane to the washed aerogel. The second wash takes a period of 8-24
hours at ambient temperature, e.g., 72+5 F (22.2 +2.8 C). The hexane wash
solution is then discharged. The washed gel (e.g., alcogel) is then dried at a
temperature of about 150 F (65.6 C) for about 6 hours, followed by drying at a
temperature of about 220 F (104.4 C) for 6 hours, followed by drying (e.g.,
annealing of the aerogel) at a temperature of about 392 F (200 C) for up to 6
hours, e.g., typically between about 0.5-2 hours. The dried product is
collected
and screened, per the specific requirements, to obtain the final nanogel.
[100] Example 2
[101] A. PREPARATION OF PRECURSOR SOLUTION
[102] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) alkoxide = 900 grams
[103] Wt: -of chilled-(i.e:; 2-0 F to 43 F (-6.7 - 61 C))_-absolute EtOH = 800
grams
[104] B. PREPARATION OF CATALYST SOLUTION
[105] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) absolute EtOH = 560
grams
[106] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) ammonium hydroxide =
2.27 grams (for a final pH = 12.20 or gamma-APTES = 1.83 grams) with the
catalyst solution having a temperature of between (i.e., 20 F to 43 F (-6.7 -
6.1 C)). The final aerogel properties are C = 0.0065 ,um4/cm; Light
Scattering
Coefficient A = 0.780; Light transmission (% LT) of 41 % for Artificial Light,
25-
27% for Blue Sky, 25-27% for Artificial Light passing through a Kalwall Panel
incorporating the inventive aerogel, and 19-20% for Blue Sky Day passing
through a Kalwall Panel incorporating the inventive aerogel; Density of 0.044-
0.091 g/cc; a Bulk Modulus of Elasticity = 0.33 Gpa; and a Durometer Hardness
(Type A) = 32-35.
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[107] Slowly, the catalyst solution is added to the precursor solution while
the
precursor solution is being constantly mixed. Mixing of the solutions with one
another to form a mixed solution and continue mixing the mixed solution while
the pH is periodically checked in orderto maintain the pH between 9.5-12.2 and
thereby control the particle size distribution of the resulting aerogel. It is
to be
appreciated that the pH of the mixture will generally be reduced slightly as
the
catalyst solution is mixed with the precursor solution. As noted above, either
an
acid or ammonium hydroxide can be added to maintain the pH within the desired
range. Once the pH for the mixture is between 9.5-12.2, preferably between
10.0-10.5, and most preferably at 10.2, and the viscosity of the mixture is at
about 5500-10000 cps (centipose) or more preferably at about 7500-8000 cps,
a 10% solution of hexamethyl disilazane (HMDZ) in hexane (99% assay) is
added thereto at ambient temperature, e.g., 72+5 F (22.2 +2.8 C). It is
important to ensure that the weight of the HMDZ is 10% of the initial weight
of
the precursor solution. The combined mixture is continued to be mixed for
about
20 4 minutes and then aged for a period of 8-12 hours, after which, the HMDZ
solution in hexane is discharged and then a second wash takes place by adding
the hexane to the washed aerogel. The second wash takes a period of 8-12
hours at ambient temperature, e.g., 72 5 F (22.2 2.8 C). The hexane wash
solution is then discharged. The washed gel (e.g., alcogel) is then dried at a
temperature of about 150 F (65.6 C) for about 6 hours, followed by drying at a
temperature of about 220 F (104.4 C) for 6 hours, followed by drying (e.g.,
annealing of the aerogel) at a temperature of about 392 F (200 C) for up to 6
hours, e.g., typically between about 0.5-2 hours. The dried product is
collected
and screened, per the specific requirements, to obtain the final nanogel.
[108] Example 3
[109] A. PREPARATION OF PRECURSOR SOLUTION
[110] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) alkoxide = 225.0
grams
[111] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) DAA = 200.0 grams
[112] B. PREPARATION OF CATALYST SOLUTION
[113] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) DAA = 240 grams
[114] Wt. of chilled 34 F to 43 F (1.1 -6.1 C) de-ionized'water = 333 grams
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[115] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) ammonium hydroxide =
2.45 grams (for a final pH = 12.20 or gamma-APTES = 2.11 grams) with the
catalyst solution having a temperature of between 34 F to 43 F (1.1 -6.1 C)
so
as to prevent crystallization or freezing of the water within the solution.
The final
aerogel properties are C = 0.0031 ,um4/cm; Light Scattering Coefficient A =
0.872; Light transmission (% LT) of 41% forArtificial Light, 25-27% for Blue
Sky,
25-27% for Artificial Light passing through a Kalwall Panel incorporating the
inventive aerogel, and 19-20% for Blue Sky Day passing through a Kalwall Panel
incorporating the inventive aerogel; Density of 0.044-0.110 g/cc; a Bulk
Modulus
of Elasticity = 0.53 Gpa; and a Durometer Hardness (Type A) = 39-42.
[116] Slowly, the catalyst solution is added to the precursor solution while
the
precursor solution is being constantly mixed. Mixing of the solutions with one
another to form a mixed solution and continue mixing the mixed solution while
the pH is periodically checked in order to maintain the pH between 9.5-12.2
and
thereby control the particle size distribution of the resulting aerogel. It is
to be
appreciated that the pH of the mixture will generally be reduced slightly as
the
catalyst solution is mixed with the precursor solution. As noted above, either
an
acid or ammonium hydroxide can be added to maintain the pH within the desired
-range.- - Once the pH -for the mixture -is-between- 9.5-12.2, -pr.eferably_
between__
10.0-10.5, and most preferably at 10.2, and the viscosity of the mixture is at
about 5500-10000 cps (centipose) or more preferably at about 7500-8000 cps,
a 10% solution of hexamethyl disilazane (HMDZ) in hexane (99% assay) is
added thereto at ambient temperature, e.g., 72 5 F (22.2 +2.8 C). It is
important to ensure that the weight of the HMDZ is 10% of the initial weight
of
the precursor solution. The combined mixture is continued to be mixed for
about
20 4 minutes and then aged for a period of 8-12 hours, after which, the HMDZ
solution in hexane is discharged and then a second wash takes place by adding
the hexane to the washed aerogel. The second wash takes a period of 8-12
hours at ambient temperature, e.g., 72f5 F (22.2 2.8 C) . The hexane wash
solution is then discharged. The washed gel (e.g., alcogel) is then dried at a
temperature of about 150 F (65.6 C) for about 6 hours, followed by drying at a
temperature of about 220 F (104.4 C) for 6 hours, followed by drying (e.g.,
annealing of the aerogel) at a temperature of about 392 F (200 C) for up to
six
(6) hours, e.g., typically between about 0.5-2 hours. The dried product is
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collected and screened, per the specific requirements, to obtain the final
nanogel.
[117] Example 4
[118] A. PREPARATION OF PRECURSOR SOLUTION
[119] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) alkoxide = 100 grams
[120] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) absolute EtOH = 80
grams
[121] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) carbamaldehyde = 100
grams
[122] B. PREPARATION OF CATALYST SOLUTION
[123] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) absolute EtOH = 56
grams
[124] Wt. of chilled 34 F to 43 F (1.1 -6.1 C) de-ionized water = 150 grams
[125] Wt. chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) of ammonium hydroxide =
1.79 grams (for a final pH = 12.20 or gamma-APTES = 1.20 grams) with the
catalyst solution having a temperature of between 34 F to 43 F (1.1 -6.1 C)
so
as to prevent crystallization or freezing of the water within the solution.
The final
aerogel properties are C = 0.0035,um4/cm; Light Scattering CoefficientA =
0.833
Light transmission (% LT) of 41 % for Artificial Light, 25-27% for Blue Sky,
25-
. 27% _for Artificial_ Light_ passing through a Kalwall Panel incorporating
the
inventive aerogel, and 19-20% for Blue Sky Day passing through a Ka(wall Panel
incorporating the inventive aerogel; Density of 0.044-0.061 g/cc; a Bulk
Modulus
of Elasticity = 0.53 Gpa; and a Durometer Hardness (Type A) = 39-45.
[126] Slowly, the catalyst solution is added to the precursor solution while
the
precursor solution is being constantly mixed. Mixing of the solutions with one
another to form a mixed solution and continue mixing the mixed solution while
the pH is periodically checked in order to maintain the pH between 9.5-12.2
and
thereby control the particle size distribution of the resulting aerogel. It is
to be
appreciated that the pH of the mixture will generally be reduced slightly as
the
catalyst solution is mixed with the precursor solution. As noted above, either
an
acid or ammonium hydroxide can be added to maintain the pH within the desired
range. Once the pH for the mixture is between 9.5-12.2, preferably between
10.0-10.5, and most preferably at 10.2, and the viscosity of the mixture is at
about 5500-10000 cps (centipose) or more preferably at about 7500-8000 cps,
a 10% solution of hexamethyl disilazane (HMDZ) in hexane (99% assay) is
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added thereto at ambient temperature, e.g., 72+5 F (22.2 +2.8 C). It is
important to ensure that the weight of the HMDZ is 10% of the initial weight
of
the precursor solution. The combined mixture is continued to be mixed for
about
15 minutes and then aged for a period of 8-12 hours, after which, the solution
is
discharged. The washed gel (e.g., alcogel) is then dried at a temperature of
about 150 F (65.6 C) for about 6 hours, followed by drying at a temperature of
about 220 F (104.4 C) for 6 hours, followed by drying (e.g., annealing of the
aerogel) at a temperature of about 392 F (200 C) for up to 6 hours, e.g.,
typically
between about 0.5-2 hours. The dried product is collected and screened, per
the specific requirements, to obtain the final nanogel.
[127] Example 5
[128] A. PREPARATION OF PRECURSOR SOLUTION
[129] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) alkoxide = 100 grams
[130] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) carbamaldehyde = 100
grams
[131] B. PREPARATION OF CATALYST SOLUTION
[132] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) absolute EtOH = 56
grams
[133] Wt. of chilled (34 F to 43 F (1.1 -6.1 C)) de-ionized water = 150
grams
[134] Wt. chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) of ammonium hydroxide =
1.79 grams (for a final pH = 12.20 or gamma-APTES = 1.20 grams) with the
catalyst solution having a temperature of between 34 F to 43 F (1.1 -6.1 C)
so
as to prevent crystallization or freezing of the water within the solution.
The final
aerogel properties are C = 0.0035 ,um4/cm; Light Scattering Coefficient A =
0.833; Light transmission (% LT) of 41 % for Artificial Light, 25-27% for Blue
Sky,
25-27% for Artificial Light passing through a Kalwall Panel incorporating the
inventive aerogel, and 19-20% for Blue Sky Day passing through a Kalwall Panel
incorporating the inventive aerogel; Density of 0.044-0.061 g/cc; a Bulk
Modulus
of Elasticity = 0.53 Gpa; and a Durometer Hardness (Type A) = 39-45.
[135] Slowly, the catalyst solution is added to the precursor solution while
the
precursor solution is being constantly mixed. Mixing of the solutions with one
another to form a mixed solution and continue mixing the mixed solution while
the pH is periodically checked in order to maintain the pH between 9.5-12.2
and
thereby control the particle size distribution of the resulting aerogel. It is
to be
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appreciated that the pH of the mixture will generally be reduced slightly as
the
catalyst solution is mixed with the precursor solution. As noted above, either
an
acid or ammonium hydroxide can be added to maintain the pH within the desired
range. Once the pH for the mixture is between 9.5-12.2, preferably between
10.0-10.5, and most preferably at 10.2, and the viscosity of the mixture is at
about 5500-10000 cps (centipose) or more preferably at about 7500-8000 cps,
a 10% solution of hexamethyl disilazane (HMDZ) in hexane (99% assay) is
added thereto at ambient temperature, e.g., 72+5 F (22.2 +2.8 C). It is
important to ensure that the weight of the HMDZ is 10% of the initial weight
of
the precursor solution. The combined mixture is continued to be mixed for
about
15 minutes, after which, the solution is discharged. The washed gel (e.g.,
alcogel) is then dried at a temperature of about 150 F (65.6 C) for about 6
hours, followed by drying at a temperature of about 220 F (104.4 C) for 6
hours,
followed by drying (e.g., annealing of the aerogel) at a temperature of about
392 F (200 C) for up to 6 hours, e.g., typically between about 0.5-2 hours.
The
dried product is collected and screened, per the specific requirements, to
obtain
the final nanogel.
-[136]---- --Example_6
[137] A. PREPARATION OF PRECURSOR SOLUTION
[138] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) alkoxide = 100 grams
[139] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) DAA = 80 grams
[140] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) carbamaidehyde = 100
grams
[141] B. PREPARATION OF CATALYST SOLUTION
[142] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) DAA = 56 grams
[143] Wt. of chilled (32 F to 43 F (0 -6.1 C)) de-ionized water = 150 grams
[144] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) ammonium hydroxide =
2.23 grams (for a final pH = 12.20 or gamma-APTES = 1.77 grams) with the
catalyst solution having a temperature of between 34 F to 43 F (1.1 -6.1 C)
so
as to prevent crystallization or freezing of the water within the solution.
The final
aerogel properties are C = 0.0035 ,um4/cm; Light Scattering Coefficient A =
0.833; Light transmission (% LT) of 41 % for Artificial Light, 25-27% for Blue
Sky,
25-27% for Artificial Light passing through a Kalwall Panel incorporating the
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inventive aerogel, and 19-20% for Blue Sky Day passing through a Kalwall Panel
incorporating the inventive aerogel; Density of 0.044-0.061 g/cc; a Bulk
Modulus
of Elasticity = 0.53 Gpa; and a Durometer Hardness (Type A) = 39-45.
[145] Slowly, the catalyst solution is added to the precursor solution while
the
precursor solution is being constantly mixed. Mixing of the solutions with one
another to form a mixed solution and continue mixing the mixed solution while
the pH is periodically checked in order to maintain the pH between 9.5-12.2
and
thereby control the particle size distribution of the resulting aerogel. It is
to be
appreciated that the pH of the mixture will generally be reduced slightly as
the
catalyst solution is mixed with the precursor solution. As noted above, either
an
acid or ammonium hydroxide can be added to maintain the pH within the desired
range. Once the pH for the mixture is between 9.5-12.2, preferably between
10.0-10.5, and most preferabiy at 10.2, and the viscosity of the mixture is at
about 5500-10000 cps (centipose) or more preferably at about 7500-8000 cps,
a 10% solution of hexamethyl disilazane (HMDZ) in hexane (99% assay) is
added thereto at ambient temperature, e.g., 72+5 F (22.2 +2.8 C). It is
important to ensure that the weight of the HMDZ is 10% of the initial weight
of
the precursor solution. The combined mixture is continued to be mixed for
about
_15_ minutes, _after which, _thesolution is discharged. The washed gel (e.g.,
alcogel) is then dried at a temperature of about 150 F (65.6 C) for about 6
hours, followed by drying at a temperature of about 220 F (104.4 C) for 6
hours,
followed by drying (e.g., annealing of the aerogel) at a temperature of about
392 F (200 C) for up to 6 hours, e.g., typically between about 0.5-2 hours.
The
dried product is collected and screened, per the specific requirements, to
obtain
the final nanogel.
[146] Example 7
[147] A. PREPARATION OF PRECURSOR SOLUTION
[148] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) alkoxide = 47 grams
[149] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) EtOH = 243 grams
[150] B. PREPARATION OF CATALYST SOLUTION
[151] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) EtOH = 400 grams
[152] Wt. of chilled 32 F to 43 F (0 -6.1 C) de-ionized water = 32.9 grams
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[153] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) ammonium hydroxide =
8.64 grams (for final pH = 10.9-11.9) with the catalyst solution having a
temperature of between 34 F to 43 F (1.1 -6.1 C) so as to prevent
crystallization
or freezing of the water within the solution. The final aerogel properties are
C =
0.0035,um4/cm; LightScattering CoefficientA= 0.833; Light transmission (% LT)
of 41% for Artificial Light, 25-27% for Blue Sky, 25-27% for Artificial Light
passing through a Kalwall Panel incorporating the inventive aerogel, and 19-
20%
for Blue Sky Day passing through a Kalwall Panel incorporating the inventive
aerogel; Density of 0.044-0.061 g/cc; a Bulk Modulus of Elasticity = 0.53 Gpa;
and a Durometer Hardness (Type A) = 39-45.
[154] Slowly, the catalyst solution is added to the precursor solution while
the
precursor solution is being constantly mixed. Mixing of the solutions with one
another to form a mixed solution and continue mixing the mixed solution while
the pH is periodically checked in order to maintain the pH between 9.5-12.2
and
thereby control the particle size distribution of the resulting aerogel. It is
to be
appreciated that the pH of the mixture will generally be reduced slightiy as
the
catalyst solution is mixed with the precursor solution. As noted above, either
an
acid or ammonium hydroxide can be added to maintain the pH within the desired
range. _Once the_pH for the mixture is between 10.9-11.9 and the viscosity of
the
mixture is at about 5500-10000 cps (centipose) or more preferably at about
7500-8000 cps, a 10% solution of hexamethyl disilazane (HMDZ) in hexane
(99% assay) is added thereto at ambient temperature, e.g., 72 5 F
(22.2 2.8 C). It is important to ensure that the weight of the HMDZ is 10% of
the initial weight of the precursor solution. The combined mixture is aged for
a
period of 8-12 hour, after which, the HMDZ solution is discharged. The washed
gel (e.g., alcogel) is then dried at a temperature of about 150 F (65.6 C) for
about 6 hours, followed by drying at a temperature of about 220 F (104.4 C)
for
1-6 hours, followed by drying (e.g., annealing of the aerogel) at a
temperature
of about 300 F (148.9 C) for one 1-6 hours. The dried product is collected and
screened, per the specific requirements, to obtain the final nanogel.
[155] Example 8
[156] A. PREPARATION OF PRECURSOR SOLUTION
[157] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) alkoxide = 47 grams
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[158] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) EtOH = 243 grams
[159] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) carbamaidehyde = 47
grams
[160] B. PREPARATION OF CATALYST SOLUTION
[161] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) EtOH = 400 grams
[162] Wt. of chilled (i.e., 32 F to 43 F (0 -6.1 C) de-ionized water = 32.9
grams
[163] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) ammonium hydroxide -
8.64 grams (for a final pH - 11.2) with the catalyst solution having a
temperature
of between 34 F to 43 F (1.1 -6.1 C) so as to prevent crystallization or
freezing
of the water within the solution. The final aerogel properties are C = 0.0035
m4/cm; Light Scattering Coefficient A = 0.833; Light transmission (% LT) of 41
%
for Artificial Light, 25-27% for Blue Sky, 25-27% for Artificial Light passing
through a Kalwall Panel incorporating the inventive aerogel, and 19-20% for
Blue
Sky Day passing through a Kaiwall Panel incorporating the inventive aerogel;
Density of 0.044-0.061 g/cc; a Bulk Modulus of Elasticity = 0.53 Gpa; and a
Durometer Hardness (Type A) = 39-45.
[164] Slowly, the catalyst solution is added to the precursor solution while
the
precursor solution is being constantiy mixed. Mixing of the solutions with one
___another_to form_a mixed_solution_and_continue mixing the mixed solution
while
the pH is periodically checked in order to maintain the pH between 9.5-12.2
and
thereby control the particle size distribution of the resulting aerogel. It is
to be
appreciated that the pH of the mixture will generally be reduced slightly as
the
catalyst solution is mixed with the precursor solution. As noted above, either
an
acid or ammonium hydroxide can be added to maintain the pH within the desired
range. Once the pH for the mixture is between 9.5-11.2 and the viscosity of
the
mixture is at about 5500-10000 cps (centipose) or more preferably at about
7500-8000 cps, a 10% solution of hexamethyl disilazane (HMDZ) in
carbamaldehyde (99% assay) is added thereto at ambient temperature, e.g.,
72 5 F (22.2 +2.8 C). It is important to ensure that the weight of the HMDZ is
10% of the initial weight of the precursor solution. The combined mixture is
aged
for a period of 8-12 hours, after which, the HMDZ solution is discharged. The
washed gel (e.g., alcogel) is then dried at a temperature of about 150 F (65.6
C)
for about 1-6 hours, followed by drying at a temperature of about 220 F
(104.4 C) for one1-6 hours, followed by drying (e.g., annealing of the
aerogel)
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at a temperature of about 300 F (148.9 C) for 2-8 hours. The dried product is
collected and screened, per the specific requirements, to obtain the final
nanogel.
[165] Example 9
[166] A. PREPARATION OF PRECURSOR SOLUTION
[167] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) alkoxide = 47 grams
[168] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) carbamaldehyde = 47
grams
[169] B. PREPARATION OF CATALYST SOLUTION
[170] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) carbamaldehyde = 53
grams
[171] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) de-ionized water =
32.9
grams
[172] Wt. of chilled (i.e., 20 F to 43 F (-6.7 - 6.1 C)) ammonium hydroxide =
8.64 grams (for final pH = 10.5-12.20) with the catalyst solution having a
temperature of between 34 F to 43 F (1.1 -6.1 C) so as to prevent
crystallization
or freezing of the water within the solution. The final aerogel properties are
C=
0.0035-,urn4/cm-; Light-Scattering CoefficientA= 0.83.3;_Lighttrar+smission (%
LT)
of 41 % for Artificial Light, 25-27% for Blue Sky, 25-27% for Artificial Light
passing through a Kalwall Panel incorporating the inventive aerogel, and 19-
20%
for Blue Sky Day passing through a Kalwall Panel incorporating the inventive
aerogel; Density of 0.044-0.061 g/cc; a Bulk Modulus of Elasticity = 0.53 Gpa;
and a Durometer Hardness (Type A) = 39-45.
[173] Slowly, the catalyst solution is added to the precursor solution while
the
precursor solution is being constantly mixed. Mixing of the solutions with one
another to form a mixed solution and continue mixing the mixed solution while
the pH is periodically checked in order to maintain the pH between 9.5-12.2
and
thereby control the particle size distribution of the resulting aerogel. It is
to be
appreciated that the pH of the mixture will generally be reduced slightly as
the
catalyst solution is mixed with the precursor solution. As noted above, either
an
acid or ammonium hydroxide can be added to maintain the pH within the desired
range. Once the pH for the mixture is between 10.5-12.2 and the viscosity of
the
mixture is at about 5500-10000 cps (centipose) or more preferably at about
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7500-8000 cps, a 10% solution of hexamethyl disilazane (HMDZ) in
carbamaidehyde (99% assay) is added thereto at ambient temperature, e.g.,
72+5 F (22.2 +2.8 C). It is important to ensure that the weight of the HMDZ is
10% of the initial weight of the precursor solution. The combined mixture is
aged
for a period of 8-12 hours, after which the HMDZ solution is discharged. The
washed gel (e.g., alcogel) is then dried at a temperature of about 150 F (65.6
C)
for about 1-8 hours, followed by drying at a temperature of about 220 F
(104.4 C) for two 2-8 hours, followed by drying (e.g., annealing of the
aerogel)
at a temperature of about 300 F (148.9 C) for 2-8 hours. The dried product is
collected and screened, per the specific requirements, to obtain the final
nanogel.
[174] With reference now to Fig. 11, one appiication of the aerogel product,
according to the present invention, will now be discussed. As can be seen in
this
Figure, the aerogel is used as an insulating material to form an insulating
panel.
The insulating panel 50 generally comprises a perimeter top and bottom walls
52, 54 interconnected with one another by a pair of opposed side walls 56, 58
which are typically is manufactured from a material which has relatively low
thermal conductivity and so as to be a desirable insulating material. The top,
-bottom and--side walls 52,54, 56,-5-8 support-and space_apart-a pair of
opposed
transparent or translucent panels 60, 62, e.g., a plastic panel or some other
transparent panel. The pair of opposed glass panels 60, 62, together with the
top, bottom and side walls 52, 54, 56, 58, form an enclosed internal chamber
64
which has an interior volume which accommodates a suitable quantity of aerogel
68 material to provide a desire insulating R value which still remaining
relatively
transparent/translucent following filling of the internal volume with the
aerogel .
Typically, one of the top, bottom and side walls 52, 54, 56, 58 is provided
with
an opening to facilitate filling of the internal volume of the insulating
panel 50
with the aerogel and this opening is covered by a cover 66, after sufficient
filling
with the aerogel, to seal the aerogel therein.
[175] The aerogel is located between the spaced apart panels 60, 62 and is
typically in granular form. Due to the relatively high R-value of the aerogel,
e.g.,
an R-value of at least 21, for example, it is suitable for use as an
insulating
material and minimizes the heat transfer from the first panel 60 to the second
opposed panel 62 while still allowing a light to pass readily through both
panels
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60, 62 into a room or structure incorporating such an insulating panel 50 as a
barrier to the exterior environment.
[176] The inventor believes that the most important factors in obtaining a
desired areogel, having superior light transmission characteristics, low
density
and a high insulating R value, are to utilize raw materials which are
relatively
pure, e.g., the catalyst has to at least be an industrial grade and the
precursor
must only contain a very small amount of impurities, i.e., a few parts per
million,
because any trace amounts of sodium within either solution has a tendency to
oxidize or otherwise react in any undesired fashion during manufacture of the
aerogel. It is also important to maintain the pH of the reacting raw materials
generally in the range of about 9.5-12.2. The temperature at which the raw
materials react as well as the time period during which the material react are
also very important. The vibration process is also important in helping remove
any water from the pore structure and replacing the water with a solvent which
can be subsequently removed during the drying process without any significant
damage or shrinkage occurring to the pore structure.
[177] The washing process, according to the present invention, is directed at
displacing the water contained within the pore structure with a solvent, such
as
pentane-or-heptane,_which is insoluble in water andhas a low surface energy.
Such solvent is useful in drawing and/or removing the water out of the pores
by
a conventional diffusion process. The solvent is relatively easily removed
subsequently, during the drying process, without causing significant collapse
or
damage to the pore structure. To increase the efficiency of the washing
process, the aerogel is preferably broken into smaller particles and these
smaller
aerogel particles are vibrated at an ultrasonic high frequency, during the
washing
process, to enhance the diffusion process.
[178] The drying process typically employs a vacuum dryer, which removes the
low surface tension solvent from the nanopores of the aerogel. The walls of
the
nanoporous silica gel are typically elastic and flexible and therefore when
the
solvent evaporates, i.e., exits or leaving the pores, the solvent molecules
have
a tendency to leave a void which otherwise (if a low surface tension solvent
is
not utilized) may lead to the collapse of the pores. The drying process
generally
occurs at a temperature of about 120 -250 F (48.9 -121.1 C).
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[179] Once substantially all of the solvent is removed from the nanopores,
while
minimizing collapse of the nanopores, the structure is then annealed by
heating
the pores structure at an elevated temperature in the range of 250 -392 F
(121.1 -200 C), where the structure of the pores become hard and rigid.
[180] The aerogel product, according to the present invention, has a
relatively
high R value, e.g., an R value in the range of 21-31 and more preferably an R
value of about 25-30, a relatively high light transmission characteristics in
the
range of 24-26% and also has a relatively high density of around 0.0085 to
0.0112 g/cc). In addition, the aerogel product is inert and will not react
with any
element, compound or water and will typically not degrade when exposed to
light, high temperature, etc. That is, the aerogel product will not
deteriorate, fall
apart or have any significant reduction in the optical clarity of the areogel.
[181] The inventor has discovered that use of cold or chilled raw materials
enhances the self-assembly of the nanogel. This self-assembly takes place in
almost all nanogels at a variety of different temperatures. However, self-
assembly, associated with a controlled pore size for both the primary and the
secondary nanoparticles, is achieved more effectively at a lower temperature
34 F to 43 F (1.1 -6.1 C). By controlling the particle size, e.g.,
controlling the
nanoparticle-size.distr_ibution.to,be_in the range of about 5 to about 30 nm,
more
preferably within the range of about 15+5 nm, and by controlling the above
noted
characteristics, a unique product, e.g., a Kalgel aerogel, is obtained which
has
a low density (around 0.0035 g/cc), high R value (in the range of 35-40) and
high
optical clarity (in the range of 0.001-0.003).
[182] Similarly, precise control of the pH as results in an improved areogel
product. The inventor discovered that by controlling the pH of the reacting
raw
materials, within a very tight pH range of from 9.5-12.2, in turn leads to a
controlled self-assembly for both the primary and the secondary nanoparticles
of the gel (e.g., sol gel). Precise and careful control of the pH results in a
final
aerogel which higher structural integrity, higher optical clarity (thermal
stress
during heating is easily endured and thus collapse of the pore structure is
avoided). The inventor determined that if the pH is too high, e.g., over 12.2,
the
gel process and self-assembly occurs too slowly and the particle size
distribution
is not precisely controlled. Conversely, if the pH is too low, e.g., below
9.5, the
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gel process and self-assembly occurs too quickly and the particle size
distribution is again not precisely controlled
[183] The acoustical and optical vibration techniques, are utilized during the
final stages of the self-assembly of the (sol) gel. The final stages of the
self-
assembly of the gel (e.g., sol gel) is important because it leads to a silica
nanogel with high mechanical integrity, low friability, very low density and
thus
very high R value. Such high R vaiue is very useful in employing the aerogel
as
an insulting material for a variety of different applications.
[184] Preferably the catalyst solution comprises a solution of one or more of
an
acetyl acetonate-based catalyst, gamma-aminopropyl triethoxy silane, de-
ionized water, ethanol (absolute), diacetone alcohol (DAA), carbamaldehyde, de-
ionized carbamaldehyde and ammonium hydroxide and mixtures thereof; the
precursor solution comprising a solution of one or more of alkoxide, ethanol
(absolute), diacetone alcohol (DAA), carbamaldehyde, de-ionized
carbamaidehyde and mixtures thereof
[185] Since certain changes may be made in the above described improved
aerogel, without departing from the spirit and scope of the invention herein
involved, it is intended that all of the subject matter of the above
description or
shown in the-accompanying drawings_shall be interpreted- merely as examples _
illustrating the inventive concept herein and shall not be construed as
limiting the
invention.
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