|
International Hydrolytics Ltd. |
|
United States Patent |
5,244,726 |
|
Laney , et al. |
September 14, 1993 |
Advanced geopolymer composites
Abstract
A self-hardened, high
temperature-resistant, foamed composite is described. An alkali metal
silicate-based matrix devoid of chemical water has dispersed therein inorganic
particulates, organic particulates, or a mixture of inorganic and organic
particulates, and is produced at ambient temperature by activating the
silicates of an aqueous, air-entrained gel containing matrix-forming silicate,
particulates, flyash, surfactant, and a pH-lowering and buffering agent.
|
Inventors: |
Laney; Bill E. (Albuquerque, NM); Williams;
F. Truman (Albuquerque, NM); Rutherford;
Ronald L. (Albuquerque, NM); Bailey;
David T. (Albuquerque, NM) |
|
Assignee: |
The HERA Corporation (Albuquerque, NM) |
|
Appl. No.: |
939548 |
|
Filed: |
August 31, 1992 |
|
Current U.S. Class: |
428/312.6; 106/601; 106/602; 106/605; 106/610; 106/632;
428/312.4; 428/703 |
|
Intern'l Class: |
C04B 012/04; C04B 018/08; C04B 020/00; C04B 032/00 |
|
Field of Search: |
106/601,602,605 428/312.4,312.6 |
References Cited [Referenced By]
U.S. Patent Documents
|
1944008 |
Jan., 1934 |
Hobart |
106/601. |
|
2170102 |
Aug., 1939 |
Thompson et al. |
106/601. |
|
2481390 |
Sep., 1949 |
Campbell |
106/605. |
|
2921357 |
Jan., 1960 |
Fujii et al. |
106/601. |
|
3203813 |
Aug., 1965 |
Gyardo et al. |
106/602. |
|
3466221 |
Sep., 1969 |
Sams et al. |
106/601. |
|
3508936 |
Apr., 1970 |
Lyass et al. |
106/610. |
|
3741898 |
Jun., 1973 |
Mallow et al. |
106/601. |
|
3856539 |
Dec., 1974 |
Mallow et al. |
106/601. |
|
3951834 |
Apr., 1976 |
Gillilan |
106/601. |
|
4230765 |
Oct., 1980 |
Takahashi et al. |
428/283. |
|
4263048 |
Apr., 1981 |
Hacker |
428/453. |
|
4647499 |
Mar., 1987 |
Takahashi et al. |
428/312. |
Primary Examiner: Cannon; James C.
Attorney, Agent or Firm: Freund;
Samuel M.
Parent
Case Text
This is a continuation of copending application Ser. No. 159,345 filed on Feb.
23, 1988, now abandoned.
Claims
What is claimed:
1. A self-hardened, high temperature-resistant, foamed composite comprising (1)
an alkali metal silicate-based matrix devoid of chemical water having dispersed
therein, (2) inorganic particulates, organic particulates, or mixed inorganic
and organic particulates, produced at ambient temperature by activating the
silicates of an aqueous, air-entrained gel containing matrix-forming silicate,
particulates, flyash, surfactant, and a pH-lowering and buffering agent.
2. The foamed composite as described in claim 1, wherein said organic
particulates include expanded polystyrene beads.
3. The foamed composite as described in claim 1, wherein said matrix-forming
silicate is selected from the group consisting of sodium silicate, potassium
silicate, and lithium silicate.
4. The foamed composite as described in claim 1, further comprising a
strengthening agent.
5. The foamed composite as described in claim 1, wherein said strengthening
agent includes wollastonite.
6. The foamed composite as described in claim 1, wherein said surfactant
includes anionic surfactants.
7. The foamed composite as described in claim 6, wherein said anionic
surfactant has hydrophylic and hydrophobic segments.
8. The foamed composite as described in claim 6, wherein said anionic surfactant
includes sodium laurel sulfate.
9. The foamed composite as described in claim 1, wherein said silicates of said
aqueous, air-entrained gel are activated using sodium fluorosilicate.
10. The foamed composite as described in claim 1, further comprising the
wollastonite form of calcium metasilicate.
11. The foamed composite as described in claim 1, wherein said inorganic
particulates, organic particulates, or mixed inorganic and organic particulates
are present in amounts between 30 and 40 volume percent.
12. The foamed composite as described in claim 1, wherein said inorganic
particulates, organic particulates, or mixed inorganic and organic particulates
are selected from the group consisting of expanded polystyrene beads and
polyethylene terephthalate polyester chopped fibers.
13. The foamed composite as described in claim 1, further comprising added
water.
14. The foamed composite as described in claim 13, wherein said added water is
present in about 15 volume percent.
15. The foamed composite as described in claim 1, wherein said pH-lowering and
buffering agent includes at least one alkaline earth metal chloride.
16. The foamed composite as described in claim 15, wherein said alkaline earth
metal chloride is selected from the group consisting of calcium chloride and
magnesium chloride.
Description
BACKGROUND OF THE INVENTION
This invention relates to a broad class of high temperature composite materials
that consist, essentially, of two distinct phases--a ceramic-like matrix which
can be one of many different silicate-based geopolymers and a homogeneous
dispersion of organic/inorganic additives of various shapes and dimensions.
Individually, these two phases are generally unsuitable for high temperature
applications, however, they combine in the composite form to produce a wide
spectrum of refractory materials. More particularly, this invention relates to
ambient cured, controlled density, advanced geopolymer composites whose
macroscopic physical properties can be tailored for specific applications, over
significant temperature ranges, by judicious specifications of dispersed phase
components and selective chemical modifications to pre-gelled geopolymer
resins. The invention also relates to process-dependent methods for fabricating
such advanced geopolymer composites.
Particulate additives or "fillers" are sometimes added to high
temperature materials to impart certain characteristics such as strength,
flexibility or insulation. These fillers often include mineral glasses or
fibrous reinforcers. Many naturally occurring mineral glasses, i.e., amorphous
silica, contain sufficient chemically bound water to facilitate steam
production upon melting. This causes the glass to expand into a very low
density cellular aggregate, in a sense, an inorganic foamed material. Perlite
is a popular volcanic glass which expands to very low density particles and is
often used in the expanded form as a composite additive/filler in conjunction
with sodium silicate binders, gypsum plasters, and Portland cements. These
inorganic composites form low density, low thermal conductivity, insulating
materials.
Fiber reinforcement of Portland cements, gypsum plasters, and sodium silicate
binders is one method of enhancing the strength of inorganic materials. Fiberglass,
mineral wool, and certain new ceramic refractory fibers have also been
employed; however, the strong alkaline nature of these cements often produces
considerable damage to the fibers. Alkaline resistant fiberglass has been
developed and marked; however, many of these fibers are not easily bonded with
inorganic cements. Water soluble foaming agents have also been added to various
inorganic materials to enhance air entrainment and further reduce density.
Over the past several decades, industry has shown a preference for low cost
petrochemical and thermoplastic hydrocarbon substitutes over inorganic
materials. Typical examples include: foam plastic insulation substitutes for
fiberglass and mineral wool; latex/acrylic modified cements and stuccoes; and
synthetic substitutes for gypsum products. Some of these substitutions produce
very desirable properties and advantages, however, in most cases, the
substituted products increase fire and smoke hazards due to the combustibility
of substituted ingredients.
In general, although organic materials have certain advantageous features which
commend themselves to specific applications, these uses are usually attended by
increased fire risk and smoke production when compared to their traditional
inorganic counterparts. Therefore, it would be desirable to provide a class of
material composites which incorporates significant proportions of both organics
and inorganics. It would further be desirable to limit the combustibility of
these composites to a level generally associated with inorganics while taking
advantage of the desired physical properties of the organic constituents. In
this manner, product designers can benefit from the advantages of organic
fibers, foam fillers, etc., while enjoying the assurance of limited
combustibility, non-toxicity, and energy conservation.
SUMMARY OF THE INVENTION
This invention is drawn to a class of advanced geopolymer composition, useful
for a myriad of commercial applications, and methods for making the composites.
In a broad aspect, advanced geopolymer composites include both organic and
inorganic dispersed phases within a high temperature geopolymer matrix
material.
In a more specific aspect, the invention is drawn to geopolymer resins which
set and cure at ambient temperature and pressure to form a stable composite
material whose process-dependent macroscopic physical properties may include
selected features of the geopolymer matrix material as well as the particles,
i.e., fibers, fillers, and extenders.
During mixing or other formulation stages, advanced geopolymer composites may
comprise a foamable liquid geopolymer resin, an activator, and active filler
particle ingredients. Upon activation and curing, the ingredients combine to
form a high temperature geopolymer matrix material having filler particles
interspersed therein. Depending on specified high temperature performance
requirements, the preferred filler particles may include a wide variety of
organic or inorganic materials in various shapes and sizes.
Upon curing, the geopolymer resin hardens to encase the filler particles. Thus,
even when an interior organic filler material melts or decomposes due to
intense heat conduction from external high temperature surfaces, the geopolymer
matrix material retains its structural qualities.
In a preferred embodiment of the invention, a substantial volume proportion of
organic or inorganic particles, e.g., at least about 30-40 percent, is added to
a geopolymer resin which is foamed by air entrainment to achieve any desired density.
The additive particles are mixed with the geopolymer resin in a manner that
provides substantial or at least effective wetting of the particles. An
activator is then added to initiate a gel, set, and cure cycle, and process
water is released during the curing cycle. The geopolymer matrix material
typically hardens in the absence of externally applied heat or pressure, e.g.,
under ambient conditions.
In an especially preferred embodiment of the invention, the geopolymer resin
includes kaolin, flyash, or wollastonite suspended in an aqueous solutions of
sodium silicate, magnesium chloride, and anion surfactant. The activator
preferably comprises a dry powder formulation of a pH-lowering, slowly
dissolving buffer, such as sodium silicofluoride and a high density, slowly
dissolving, long term strengthening agent such as the wollastonite form of
calcium metasilicate.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawing, which is incorporated in and forms a part of the
specification, illustrates an embodiment of the present invention and, together
with the description, serves to explain the principles of the invention. The FIGURE illustrates aged and
fresh-mixed foamed geopolymer adhesive product densities as a function of
mixing time.
DETAILED DESCRIPTION OF THE INVENTION AND A PREFERRED EMBODIMENT
In a general aspect, the invention is directed to a composition comprising a
foamable geopolymer resin, activator, and a particulate additive. Broadly, the
foamable geopolymer resin may include a major portion of a soluble alkali metal
silicate, preferably sodium silicate. It also may include: effective amounts of
an alkali earth metal chloride, such as calcium chloride or magnesium chloride;
a variety of inorganic thickeners; and a surfactant that is capable of wetting
plastics and other organics, preferably an anionic surfactant.
The foamable geopolymer resin is of a type that, upon the addition of an
activator which comprises a pH lowering buffer agent and may include a
strengthening agent, converts to a self-hardening geopolymer matrix material.
Before the reacting geopolymer resin reaches the gel stage, it may be
air-entrained to the desired density, i.e., foamed and intermixed with an
effective amount of organic or inorganic particulate filler, or "filler
particles".
The geopolymer resin material is an essential part of the invention, and it
must be present in sufficient amounts to coat and support the filler particles.
This is particularly true when organic filler particles are used in the
fabrication of advanced geopolymer composites. Without being limited by theory,
it is believed that the geopolymer matrix material surrounds the filler
particles and, even when internal organic particles melt or decompose due to
intense heat conduction from external high temperature surfaces, the geopolymer
matrix material retains its structural integrity and other performance
qualities. Accordingly, even when the advanced geopolymer composite includes
such flammable organic particles as expanded polystyrene (EPS) beads, overall
fire resistance is improved. In this manner, the inorganic geopolymer matrix
material, when bonded to organic fiber particles in accordance with the present
invention, prevents excessive surface burning, flame spread, and smoke
generation while maintaining adequate dimensional stability.
An especially preferred ingredient of the geopolymer resin material is a
water-soluble alkali metal silicate. Sodium, potassium, and lithium silicates
have been prepared commercially, and any one of these may be employed in solid,
hydrated, or anhydrous forms.
A specific preferred embodiment of the present invention comprises a
commercially available soluble sodium silicate. In that embodiment, although
water is added during the formulation of the geopolymer resin, the final cured
matrix material will have lost all available process water. Commercially
available solutions of sodium silicate have a density of approximately
41.degree. Baume (1.4 gram/cc), and the silica:alkali weight ratio for such a
material is about 3.22. From an economic standpoint, the higher silica ratios
are preferred. Any ratio throughout the available range of 1.6 to 4.5 may be
used, however, modest accommodations in gelation time, buffering, etc, must be
made for the more alkaline silicates.
The ingredients of geopolymer resin materials are therefore primarily
inorganic. Minor amounts of organic surfactant present in the foamable
geopolymer resin wet the filler particles prior to gelation.
Another important ingredient of the geopolymer resin is the thickener or
thickening agent. Thickeners as used herein are so-called "nucleation
site" materials. In accordance with the present invention, three types of
materials have been identified as thickeners, each of which imparts slightly
different properties to the final, cured, geopolymer matrix material. A
preferred embodiment of the invention comprises one type of thickener from the
hydrous aluminum silicate clay mineral group commonly referred to as kaolin,
china clay, or porcelain clay. The lamella plates of the kaolin with their
associated edge electrical charge are exemplary as nucleation sites for
silicate growth.
Other aluminum silicate clays, which may be any of the non-intercalating,
non-expanding, clays such as halloyaite, illite, and attapulgite may be
employed. Water absorbing clays such as bentonite and montmorillonite may also
be employed in modest amounts to promote rapid gelation, however, they usually
produce geopolymer matrix materials with undesired physical properties.
A third type of thickener which often gives superior results is flyash. The
high aluminum oxide and silicon dioxide content of coal-fired power plant
flyash in conjunction with its large specific surface area and ability to
collect residual electrical charge make this material a good substitute for
kaolin. Experimental data indicate that flyash produces a geopolymer matrix
material with higher melting point than does the kaolin. An even higher melting
geopolymer matrix material can be produced by substituting wollastonite for
kaolin; however, the density of the cured geopolymer matrix tends to be greater
with wollastonite than matrix materials which employ kaolin or flyash.
The amount of thickener necessary to prevent the geopolymer resin, once foamed,
from collapsing is an important aspect of the invention. A specific embodiment
of the invention, for example, may comprise as much as 28% by weight of
thickener.
In a specific embodiment of the invention which includes kaolinite thickening
and wollastonite strengthening agents, respectively, crystallographic
investigations indicate the existence of kaolinite lamella uniformly
distributed in a matrix bonded by silicate stock. Although the resolution was
insufficient to show the distribution of wollastonite (a long-term
strengthening agent), wollastonite is generally insoluble in sodium silicate
and readily forms fusion bonds to glass. Therefore, it may be inferred that long-term
strength is developed in the geopolymer matrix by additional
fusion/polymerization of the wollastonite. Some soluble salts may be present in
the interstitial pores of the matrix, and, presumably, the surfactant remains
at the surface of spherical interstitial foam voids where it is deposited as a
result of water evaporation.
The geopolymer resin of this invention differs from other inorganic cements and
adhesives in that it sets and cures at ambient temperature and pressure through
a complicated series of chemical reactions to form an insoluble geopolymer
matrix material which is devoid of chemical water. Any water retention is the
result of the matrix porosity and not that of a chemical bond or water of
hydration. The reactions are considered irreversible although they proceed with
a negligible release of energy, i.e., low exotherm reactions. Advanced
geopolymer composites are rigid within an hour of mixing, and, subject to
hygroscopicity of the additives and wet density, they cure overnight to within
10% of final density. High density composite materials lose water more slowly,
and hygroscopic additives may never release their water content. The reaction
does not depend on dry air or elevated temperature for the development of
solidity and strength, and gelation and solidification processes continue even
when geopolymer resins are submerged in water.
Another important feature of the invention is the surfactant. In accordance
with the present invention, the surfactant may be used to promote foaming,
however, if a high density geopolymer composite is desired, foaming may not be
necessary. Regardless of whether foaming is desired, the surfactant is an
essential ingredient which promotes bonding by wetting organic filler
particles. The surfactant should be present in amounts designed to provide for
interfacial wetting of interfaces between the geopolymer resin and the plastic
foam or fiber material, i.e., the "filler particles". A proper
surfactant is one which "wets" organics well, and anionic surfactants
having hydrophilic and hydrophobic segments are within the scope of this
invention provided they promote bonding. A preferred surfactant is sodium
lauryl sulfate.
Activation of the geopolymer resin is a necessary step for achieving an
advanced geopolymer in accordance with this invention. The activation process
should include an activator that is chemically compatible with the geopolymer
resin. When the geopolymer resin includes a silicate binder, a preferred
activator is a pH-lowering, slowly dissolving, buffer agent such as sodium
fluorosilicate. Other additives, e.g., the wollastonite form of
calcium-metasilicate, should also be included to control shrinkage and promote
long term strength of the geopolymer matrix material.
The filler particles which are added to the geopolymer resin provide different
macroscopic physical and thermal properties to the advanced geopolymer
composites. Organic particles, for example, generally provide different
"effective" thermal and physical properties than inorganic particles.
A specific embodiment of the invention comprises EPS beads, which may be added
to the geopolymer resin to provide a low density thermal insulating composite.
When the composition is cast into boards or panels of appropriate thicknesses,
such a material can serve as its own fire safe thermal barrier. Fire test
investigations have shown that, in the presence of intense surface
temperatures, although certain amounts of the EPS may slowly burn, vaporize, or
melt within the geopolymer matrix of this invention, the remaining material
resists the fire exposure in a manner that allows the hardened matrix structure
to act as its own fire-thermal barrier. Because there is little or no melting,
running, flowing, and subsequent concentration of the EPS in hot molten pools,
the material avoids the normal fire hazards associated with large boards and
exterior sealed panels.
Another organic particle useful in the invention is polyethylene terephthalate
(PET) polyester chopped staple fibers. Because PET has a heat of combustion of
about 9,600 btu/lb. it is possible to employ over 1/3 pound of PET per pound of
cured geopolymer matrix material and still meet one of the criteria for limited
combustibility. The National Fire Protection Association Standard 220 defines
combustibility in semi-quantitative terms. For example, a "limited
combustible" material has a potential heat of combustion which is less
than 3500 btu/lb. of material and demonstrates a flame spread rating of less
than 25 when tested in accordance with ASTM E-84 "Surface Burning
Characteristics of Building Materials". Smoke generated ratings are not
directly specified; however, a rating of less than 25 places the material in
the same class as incombustible inorganics, e.g., calcium silicate board. Compositions
of the present invention which incorporate PET filler particles in the form of
short fibers or laminated blankets have achieved all three criteria for limited
combustibility. Although advanced geopolymer composites which employ EPS
materials have not been tested in accordance with ASTM E-84; qualitatively,
they have been observed to perform in a manner similar to the PET compositions,
and, accordingly, they are expected to achieve similar quantitative ratings.
The term "particles" is intended to encompass particles of various
dimensions and shapes, including for example, beads, fibers, and blankets. The
dimensions of the particles may be relevant for optimizing the strength,
thermal conductivity, acoustic absorptivity, etc. of the final advanced
geopolymer composite. In addition, particle size can impact dispersion
throughout the foamed geopolymer resin, and total surface area of the particles
is important in relation to the amount of foamed geopolymer resin material.
Generally, sufficient geopolymer resin should be present to bond, support, and
provide fire resistance to the particles. Accordingly, different amounts of
geopolymer resin may be used, depending on particle size and the desired
macroscopic thermophysical properties of the cured matrix material.
In certain aspects of the invention, an important part of the preparation of
geopolymer resin is the amount of water added. In some cases, for example,
additional water should be added to increase mobilities of other ingredients
and reduce viscosities to promote foaming and air entrainment. The addition of
too much water, however, may promote either immediate gelation/-precipitation
of the silicates or dilution to the point of decomposition of the alkali
silicate. Accordingly, a specific embodiment of the invention includes a
suspension wherein about 15% of the foamable geopolymer resin is added water.
An important ingredient of the geopolymer resin of this invention is an
alkaline earth metal chloride, or some other buffer agent, that lowers the pH
of the suspension and provides for gelation. Without being limited by theory,
the binding mechanism of the soluble silicates during gelation is believed to
be heavily influenced by the pH of the geopolymer resin. Accordingly, since
relatively minor changes in pH can have a large effect, in accordance with the
invention, an effective amount of either magnesium chloride or calcium chloride
or a mixture of the two is added to the water to buffer the solution and
prevent decomposition. An alkali metal salt such as sodium chloride may promote
immediate gelation, and is normally to be avoided.
The range of proportions of the foamed geopolymer resin ingredients, prior to
gelation, may be important for achieving the desired properties in the cured
matrix material. For final cured densities in the 10-40 pcf range, the
following wet weight percentages of foamed geopolymer resin prior to gelation
are indicative of the operative ranges: sodium silicate--from 15% to 66%;
wollastonite strengthener--from 6.4% to 58%; sodium silicofluoride
activator--from 2.8% to 12.9%; sodium lauryl sulfate surfactant--from 0.12% to
2.0%; magnesium chloride buffer--up to 0.43%; water--up to 15%; and kaolin
thickener--up to 28%.
A first mixture may be made by dissolving into water an alkaline earth metal
chloride and an anionic surfactant. A sufficient amount of surfactant is added
to provide for surface wetting of the filler particles by the geopolymer resin.
A second mixture is made by suspending a thickener such as kaolin, wollastonite,
or flyash in a sodium silicate solution. The mixture and suspension are then
combined and mixed to form a foamable geopolymer resin. At this point, the
geopolymer resin may be air entrained to the desired density prior to the
addition of additive filler particles. After all ingredients are properly
mixed, i.e., dispersed, the geopolymer resin is activated to initiate gelation
and curing which will produce the matrix material. In effect, the procedures
for making advanced geopolymer composites include activating the silicates in
the geopolymer resin to form a self-hardening composition wherein the
geopolymer matrix material encases and supports the filler particles. A
preferred activator is sodium silicofluoride.
It has been found that slight modifications to the above procedures produce
cured geopolymer matrix materials with considerably higher melting points. For
example, substitution of flyash for kaolin in the foamed geopolymer resin
produces foamed matrix materials having densities of about 20 pcf and melting
points greater than 2050.degree. F.
In a broad aspect, this invention is directed to methods for producing fire
resistant composites, however, fire resistance is only one of the numerous
significant characteristics of the present invention. A broad spectrum of other
macroscopic properties may be obtained, depending generally on the type and
amount of added filler materials. For example, fibers may be added for strength
or acoustic attenuation properties; carbon or graphite may be added for
alteration of dielectric properties; synthetic fabrics may be laminated for
structural rigidity, tensile strength, and projectile penetration resistance;
and foam plastic beads may be added to lower effective thermal conductivities.
In particular, by combining different types of organic/inorganic filler
particles, the invention provides a broad avenue for additional synergisms
within the area of advanced geopolymer composites.
Although low density advanced geopolymer composites are usually preferred, it
is not necessary to achieve low density in every instance. The overall density
of the composition is merely a design criterion which may be related to the
binder/particle weight ratio. For example, the cured composition of limited
combustible materials should have a weight fraction of organics in the cured
geopolymer matrix which is less than 3,500 btu's divided by the organic
material's heat of combustion in btu/lb.
This invention is defined by the claims. Without limiting the scope of the
invention, and in order to promote a clearer understanding of the invention,
the following examples describe various process-dependent aspects of the
invention.
EXAMPLE 1
Geopolymer Resin Formulations
In this example, geopolymer resin formulations are prepared using a Hobart
Model L-800 mixer fitted with an 80 quart mixing bowl and a wire beater paddle.
Basic features of this mixer include: a planetary gear drive; and a four
position gear shift speed adjustment (Speed 1 through Speed 4). A typical
mixing session follows:
In step 1, 7-13 lb. of English kaolin is added to 20-40 lbs. of sodium silicate
solution, SiO.sub.2 :Na.sub.2 O weight ratio of 3.22, and mixed Speed 1 for
approximately 1 minute. Once the kaolin is wetted, the mixer speed is increased
to Speed 2 for about 3 minutes, and, after 7 minutes of mixing at Speed 3, the
initial blending process is complete.
Step 2 begins by dissolving 90-160 grams of flake MgCl.sub.2. 6H.sub.2 O in
7-13 lb. of tap water at ambient temperature. Additionally, 60-100 grams sodium
lauryl sulfate, CH.sub.3 (CH.sub.2).sub.11 OSO.sub.3 Na, in dry form, is
stirred into the solution. Five minutes of dissolution time, with occasional
stirring, are adequate to dissolve the magnesium chloride and produce a foam
froth.
The surfactant/salt solution from Step 2 is added to the sodium silicate and
kaolin suspension of step 1 to form a foamable geopolymer resin. The
entrainment of air during mixing creates a froth whose density decreases as a
function of time and mixing parameters. After mixing for 45 minutes at Hobart
Speed 3, foamed geopolymer resin densities are approximately 0.8 gram/cc.
Foamed geopolymer resins are relatively stable for a period of hours, however,
overnight storage may result in some separation of large surface froth bubbles
with a remainder of the foamed suspension maintaining a density of about 0.9
gram/cc. It is further noted that, after about 3 days, the foamed geopolymer
will collapse to a nominal density of about 1.42 gram/cc. and separation will
begin to occur.
EXAMPLE 2
Geopolymer Resin Aging
This example demonstrates
the importance of aging geopolymer resins. The FIGURE is a comparison of foamed
densities for freshly prepared and aged geopolymer adhesive product as a
function of mixing time. It can be seen that aging promotes a better behaved
quantitative foaming relationship with mixing time and speed parameters. The
values in the FIGURE were taken with equal quantities of foamable geopolymer
resin at the same mixing speeds.
EXAMPLE 3
Geopolymer Resin Mixing Parameters
This example demonstrates the importance of mixing parameters. From routine
observations, it is highly desirable to begin agitation of geopolymer resins at
speed settings 3 and 4. In addition, although very low density foamed
geopolymer resins cannot be produced with the mixer set on Speed 4, optimum low
density foamed geopolymer resins can be achieved with a mixer speed of 3. In
general, it has been established that beater tip speeds in excess of 1000 feet
per minute tend to break up the foam cell structure.
Thus, high shear mixing conditions generally break down the foam bubble cell
structure. This means that, following the addition of coarse aggregates, mixing
should be carried out in very short time periods at very low mixing speeds.
Composites characterized by high surface area fine powder dispersions cannot be
completely wetted under low speed mixing and blending restraints; therefore,
the fine powder component should be added at the beginning of the foaming
period and mixed accordingly.
EXAMPLE 4
Geopolymer Resin Gelation And Ambient Cure
This example describes the activation and gelation of foamable geopolymer
resins. Geopolymer resins prepared in accordance with this invention exhibit
the following characteristics: an unfoamed density of 1.4 gram/cc.; viscosity
at normal ambient temperature of about 100 centipoise; and pH of approximately
11.3.
Sodium silicofluoride activator slowly dissolves in the geopolymer resin and lowers
its pH. As the pH reaches a value of about 11.1 to 11.2, the generally
electro-negative repulsive field within the geopolymer resin collapses
sufficiently to allow gelation of the colloidal silicate suspension. Within 30
to 45 minutes after addition of the activator, geopolymer resin ceases to
behave as a liquid. At that point, mature gelation has taken place, and the
geopolymer matrix material exhibits a jelly-like or rubbery quality for another
30 to 45 minutes until solidification occurs, as evidenced by process water
leaving the material. The reaction proceeds with a negligible exotherm, i.e.,
no detectable release of heat, and cures by loss of water until bulk densities
of about 0.9 gram/cc. are achieved. The overall cycle produces very little shrinkage,
and curing to no significant change in weight shows that all original water has
left the geopolymer matrix material. Loss of process water is represented in
the final geopolymer material as porosity.
EXAMPLE 5
Geopolymer Resin Modifications
This example demonstrates how the geopolymer resins of Example 1 can be
chemically modified to produce advanced geopolymer composites with a variety of
macroscopic physical properties. For example, when powdered relay steel or
ferrite particles are dispersed in geopolymer resins to produce castable, high
magnetic permeability, refractory materials, the simple addition of 2% by
weight of calcium chromate to the solution of Step 2 inhibits long-term
corrosion of the dispersed phase components. Similarly, the electrical
conductivity of geopolymer resins can be altered by adding 1%-5% by weight of
acetylene black to the suspension of Step 1, and these modified geopolymer
resins, in combination with "spherical close packed" dispersions of
EPS beads or other non-conducting "spacer" particles, provide a high
temperature material which is electromagnetically equivalent to low temperature
"reticulated foam" microwave absorbers. Fundamentally, these types of
chemical modifications are possible due to the large fraction of water
contained in either the Step 1 suspension or the Step 2 solution of Example 1.
EXAMPLE 6
Dispersed Phase Raw Materials
This example identifies an extensive collection of raw materials which are
chemically compatible with the geopolymer resins of Example 1 and, therefore,
qualify as acceptable candidates for dispersed phase components of advanced
geopolymer composites. These raw materials, by category, include: waste
materials --flyash, sludges, slags, confetti, rice husks, bagasse, saw dust, etc;
volcanic aggregates --expanded perlite, pumice, scoria, and obsidian; mineral
forms --expanded mica (vermiculite), borosilicates, clays, metal oxides, etc.;
plant and animal remains --distomaceous earth, sea shells, coral, excreta, hemp
fibers, etc.; and manufactured fillers --silica microspheres, mineral fibers
and mats, chopped/woven fiberglass, metal wools, turnings, or shavings, and
synthetic microspheres, fibers, or mats. Advanced geopolymer composites
fabricated from these raw materials typically exhibit the following
characteristics: low combustibility; high melting points (similar to ceramics
and refractories); low thermal and electrical conductivity; high acoustic
absorptivity; low toxicity; low solubility in water; moderate acid/base resistance;
mildew-, rot-, and vermin-proof; and insensitivity to infrared, ultraviolet,
neutron, and charged particle radiation.
EXAMPLE 7
Manufacturing Processes
This example illustrates the adaptability of geopolymer resins and associated
raw material additives to a variety of processes in the manufacture of advanced
geopolymer composites. In general, high temperature performance specifications
for final cured products will dictate uncured densities, viscosities, etc.
These parameters, in turn, define the following manufacturing process
classifications: wetted powders/fibers--compression molding with platen
presses, rollers, etc.; pastas --sculpture, injection, or compression; and
liquid slurries --pour-cast or spray-on. Therefore, depending on required production
rates, potential manufacturing scenarios for advanced geopolymer composites
span the full range from single unit hand-mixing and pour-casting by unskilled
labor to fully automated production lines with continuous mixers, belts, etc,
* * * * *
[ Home ]
[ AHC Products ] [ AHC Applications ] [ AHC Markets] [ AHC
Technology ] [ SolGel Chemistry ]
[ Materials Testing ] [ Materials
Comparison ] [ Company Profile ]
[ Marketing ] [ Franchise opportunities ] [ Exclusive Licensing ] [ Marketing Representatives ] [ University Consortia ] [ Literature and Reference ]
[ Contact Us ]