U.S. patent application number 17/549128 was filed with the patent office on 2022-03-31 for aqueous gelcasting formulation for ceramic products.
The applicant listed for this patent is Delta Faucet Company. Invention is credited to Paul A.V. Bridgett, Nathanael W. Dennis, Joseph A. Elmer, Kurt J. Thomas, Michael J. Veros.
Application Number | 20220098112 17/549128 |
Document ID | / |
Family ID | 1000006024041 |
Filed Date | 2022-03-31 |
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United States Patent
Application |
20220098112 |
Kind Code |
A1 |
Thomas; Kurt J. ; et
al. |
March 31, 2022 |
AQUEOUS GELCASTING FORMULATION FOR CERAMIC PRODUCTS
Abstract
The present disclosure relates to the manufacture of ceramic
products by aqueous gelcasting. Exemplary ceramic products include
sanitary ware, such as toilets and sinks. The process includes a
slurrying step, a mixing step, a molding step involving aqueous
gelcasting, a drying step, a glazing step, and a firing step.
Inventors: |
Thomas; Kurt J.;
(Indianapolis, IN) ; Bridgett; Paul A.V.; (Carmel,
IN) ; Veros; Michael J.; (Carmel, IN) ; Elmer;
Joseph A.; (Zionsville, IN) ; Dennis; Nathanael
W.; (Greensburg, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Delta Faucet Company |
Indianapolis |
IN |
US |
|
|
Family ID: |
1000006024041 |
Appl. No.: |
17/549128 |
Filed: |
December 13, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16651032 |
Mar 26, 2020 |
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PCT/US2018/052621 |
Sep 25, 2018 |
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17549128 |
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62563345 |
Sep 26, 2017 |
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62563350 |
Sep 26, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 33/28 20130101;
C04B 33/34 20130101; C04B 35/19 20130101; C04B 33/04 20130101; C04B
2235/349 20130101; C04B 2235/6027 20130101; B28B 1/26 20130101;
C04B 33/131 20130101; C04B 2235/6023 20130101; C04B 33/30 20130101;
C04B 2235/3472 20130101; C04B 2235/3418 20130101; B28B 7/46
20130101; B28B 11/243 20130101; B28B 7/42 20130101 |
International
Class: |
C04B 35/19 20060101
C04B035/19; B28B 1/26 20060101 B28B001/26; B28B 7/42 20060101
B28B007/42; B28B 7/46 20060101 B28B007/46; B28B 11/24 20060101
B28B011/24; C04B 33/04 20060101 C04B033/04; C04B 33/13 20060101
C04B033/13; C04B 33/28 20060101 C04B033/28; C04B 33/30 20060101
C04B033/30; C04B 33/34 20060101 C04B033/34 |
Claims
1. A ceramic product having a formulation comprising: at least one
mineral oxide; at least one alkali aluminosilicate mineral
configured to serve as a fluxing agent to reduce the melting point
of the formulation; and colloidal silica.
2. The ceramic product of claim 1, wherein the at least one mineral
oxide of the formulation includes silica and alumina.
3. The ceramic product of claim 1, wherein the at least one alkali
aluminosilicate mineral of the formulation includes Feldspar or
Nepheline Syenite.
4. The ceramic product of claim 1, wherein the formulation is a
slurry comprising water.
5. The ceramic product of claim 4, wherein the at least one mineral
oxide of the formulation constitutes about 10 wt. % to about 88 wt.
% of the slurry.
6. A formulation having a solid portion, the formulation
comprising: silica, wherein at least a portion of the silica
comprises colloidal silica; alumina, wherein the alumina
constitutes at least 15 wt. % of the solid portion; and at least
one fluxing agent.
7. The formulation of claim 6, wherein the at least one fluxing
agent is sourced from an alkali aluminosilicate mineral.
8. The formulation of claim 7, wherein the alkali aluminosilicate
mineral is Feldspar.
9. The formulation of claim 7, wherein a portion of the silica and
a portion of the alumina is sourced from the alkali aluminosilicate
mineral.
10. The formulation of claim 6, wherein the formulation is a slurry
further comprising a liquid portion.
11. A ceramic product having the formulation of claim 6.
12. A formulation comprising: a majority of silica and alumina,
wherein at least a portion of the silica comprises colloidal
silica; and a minority of at least one fluxing agent.
13. The formulation of claim 12, wherein silica is a primary
component and alumina is a secondary component.
14. The formulation of claim 12, wherein the at least one fluxing
agent comprises sodium oxide, potassium oxide, and calcium
oxide.
15. The formulation of claim 12, wherein the formulation consists
essentially of the silica, the alumina, and the at least one
fluxing agent.
16. A ceramic product having the formulation of claim 12.
17. A molded formulation comprising: at least one mineral oxide
constituting about 10 wt. % to about 88 wt. % of the formulation;
at least one alkali aluminosilicate mineral, separate from the at
least one mineral oxide, configured to serve as a fluxing agent to
reduce the melting point of the formulation; colloidal silica; and
water, wherein the molded formulation is gelled in a mold and
configured to maintain a solid shape in the mold.
18. The molded formulation of claim 17, wherein the formulation is
chemically gelled or freeze gelled.
19. A molded object formed from the molded formulation of claim 17,
wherein the molded object is removed from the mold and dried to
remove at least a portion of the water from the molded formulation.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/651,032, filed Mar. 26, 2020, which is a
371 U.S. National Phase of International Application No.
PCT/US2018/052621, filed Sep. 25, 2018, which claims priority to
U.S. Provisional Patent Application Ser. Nos. 62/563,345 and
62/563,350, filed Sep. 26, 2017, the disclosures of which are
hereby expressly incorporated by reference herein in their
entirety.
BACKGROUND AND SUMMARY OF THE DISCLOSURE
[0002] The present invention relates generally to ceramic products.
More specifically, the present invention relates to ceramic
products made by aqueous gelcasting.
[0003] Traditional ceramic products are made with clay as the
primary ingredient. Clay is a highly variable material that is
structured as a series of flat plates and contains a significant
amount of chemically-bound water. Initially, the clay must be mixed
with water and other ingredients to produce a moldable formulation.
Later, the clay must be dried and fired to remove the added water,
as well as the chemically-bound water that exists naturally in the
clay. Clay's plate-like structure causes the initial water
absorption and the subsequent water release to be very long, slow,
and expensive processes. Clay also exhibits significant shrinkage
as the added water and chemically-bound water are released. Based
on all of these factors, manufacturing a traditional ceramic
product can take several days or weeks, is labor intensive, is
expensive, and is variable.
[0004] It is desired to provide a more efficient, cost effective,
robust, and/or predictable solution for manufacturing ceramic
products, especially sanitary ware.
[0005] According to an illustrative embodiment of the present
disclosure, a formulation is provided including at least one
mineral oxide, at least one alkali aluminosilicate mineral
configured to serve as a fluxing agent to reduce the melting point
of the formulation, and colloidal silica.
[0006] In certain embodiments, the at least one mineral oxide
includes silica and alumina.
[0007] In certain embodiments, the at least one alkali
aluminosilicate mineral includes Feldspar or Nepheline Syenite.
[0008] In certain embodiments, the formulation is a slurry
comprising water. The at least one mineral oxide may constitute
about 10 wt. % to about 88 wt. % of the slurry, or about 25 wt. %
to about 45 wt. % of the slurry. The at least one alkali
aluminosilicate mineral may constitute about 10 wt. % to about 85
wt. % of the slurry, or about 50 wt. % to about 70 wt. % of the
slurry. The at least one alkali aluminosilicate mineral may
constitute a majority of the slurry. The colloidal silica may have
a solid content of about 10 wt. % to about 50 wt. % and may
constitute about 2 wt. % to about 40 wt. % of the slurry. The
formulation may further include at least one additive of clay or
clay minerals constituting about 10 wt. % or less of the slurry.
The formulation may further include at least one additive of an
organic gum constituting about 2 wt. % of less of the slurry. A
solid content of the slurry may be about 70 wt. % or more.
[0009] In one particular embodiment, the formulation may include
17.8 wt. % silica, 17.4 wt. % alumina, 56.0 wt. % of the at least
one alkali aluminosilicate mineral, and 8.8 wt. % of the colloidal
silica, and the colloidal silica may comprise 30 wt. % silica and
70 wt. % water.
[0010] In one particular embodiment, the formulation may include
12.9 wt. % silica, 17.4 wt. % alumina, 56.0 wt. % of the at least
one alkali aluminosilicate mineral, and 13.7 wt. % of the colloidal
silica, and the colloidal silica may comprise 40 wt. % silica and
60 wt. % water.
[0011] In certain embodiments, the formulation is a ceramic
product.
[0012] According to another illustrative embodiment of the present
disclosure, a formulation is provided having a solid portion, the
formulation including silica, wherein at least a portion of the
silica comprises colloidal silica, alumina, wherein the alumina
constitutes at least 15 wt. % of the solid portion, and at least
one fluxing agent.
[0013] In certain embodiments, the at least one fluxing agent is
sourced from an alkali aluminosilicate mineral.
[0014] In certain embodiments, the alkali aluminosilicate mineral
is Feldspar.
[0015] In certain embodiments, a portion of the silica and a
portion of the alumina is sourced from the alkali aluminosilicate
mineral.
[0016] In certain embodiments, the formulation is a slurry further
comprising a liquid portion.
[0017] In certain embodiments, the formulation is a ceramic
product.
[0018] According to yet another illustrative embodiment of the
present disclosure, a formulation is provided including a majority
of silica and alumina, wherein at least a portion of the silica
comprises colloidal silica, and a minority of at least one fluxing
agent.
[0019] In certain embodiments, silica is a primary component and
alumina is a secondary component.
[0020] In certain embodiments, the at least one fluxing agent
comprises sodium oxide, potassium oxide, and calcium oxide.
[0021] In certain embodiments, the formulation consists essentially
of the silica, the alumina, and the at least one fluxing agent.
[0022] In certain embodiments, the formulation is a ceramic
product.
BRIEF DESCRIPTION OF DRAWINGS
[0023] A detailed description of the drawings particularly refers
to the accompanying figures in which:
[0024] FIG. 1 is a flow chart of an exemplary method of the present
disclosure including a slurrying step, a mixing step, a molding
step, a drying step, a glazing step, and a firing step;
[0025] FIG. 2 is a block diagram of an exemplary slurry formulation
of the present disclosure;
[0026] FIGS. 3A-3D are schematic views of the molding step of the
present disclosure, where FIG. 3A shows introducing a mixture into
a mold, FIG. 3B shows solidifying the mixture in the mold to form a
solid article, FIG. 3C shows ejecting the solid article from the
mold, and FIG. 3D shows the molded article; and
[0027] FIG. 4 is a flow chart of an exemplary drying step of the
present disclosure.
DETAILED DESCRIPTION OF THE DRAWINGS
[0028] The embodiments of the invention described herein are not
intended to be exhaustive or to limit the invention to the precise
forms disclosed. Rather, the embodiments selected for description
have been chosen to enable one skilled in the art to practice the
invention.
[0029] The present disclosure relates to the manufacture of ceramic
products by aqueous gelcasting. Exemplary ceramic products include
consumer products like sanitary ware (e.g., toilets, sinks) and
dinner ware. Other ceramic products may be used in electrical,
automotive, aerospace, and other industries.
[0030] Referring initially to FIG. 1, an exemplary method 100 is
disclosed for manufacturing a ceramic product. The illustrative
method 100 includes a slurrying step 102, a mixing step 104, a
molding step 106, a drying step 108, a glazing step 110, and a
firing step 112. Each step of method 100 is described further
below.
[0031] The slurrying step 102 of method 100 involves producing a
slurry formulation.
[0032] As shown in FIG. 2, an illustrative slurry formulation 200
includes one or more refined mineral oxides 202, one or more
fluxing agents 204, and one or more bonding agents, such as
colloidal silica 206. The slurry formulation 200 may also contain
one or more optional additives 208. Each of these ingredients is
described further below.
[0033] The refined mineral oxides 202 in the slurry formulation 200
are used to produce a crystalline or non-crystalline (e.g., glass)
network structure in the resulting ceramic product having a desired
stiffness and porosity. With respect to porosity, for example, the
ceramic product may exhibit less than 0.5% water absorption to
qualify as a vitreous product according to ASME A112.19.2 or less
than 15% water absorption to qualify as a non-vitreous product
according to ASME A112.19.2, but other water absorption levels are
also contemplated. Exemplary mineral oxides 202 for use in the
slurry formulation 200 include silica (SiO2), which is relatively
inexpensive, and/or alumina (Al.sub.2O.sub.3), which is relatively
expensive but enhances durability of the resulting product. The
mineral oxides 202 may be provided in granular or powder form to
facilitate mixing, such as fumed silica. The concentration of
mineral oxides 202 in the slurry formulation 200 may be as low as
about 10 wt. %, about 20 wt. %, about 30 wt. %, or about 40 wt. %,
and as high as about 50 wt. %, about 60 wt. %, about 70 wt. %,
about 80 wt. %, or about 88 wt. %. For example, in certain
embodiments, the concentration of mineral oxides 202 in the slurry
formulation 200 may be between about 25 wt. % and about 45 wt. %.
Lower concentrations of mineral oxides 202 may lead to lower
strength products, lower stiffness resulting in more deflection,
lower bulk density, higher porosity, longer processing times for
removing water, higher potential shrinkage during processing, and
lower material costs, while higher concentrations of mineral oxides
202 may lead to higher strength products, higher bulk density,
lower porosity, shorter processing times for removing water, lower
potential shrinkage during processing, and higher material
costs.
[0034] The fluxing agents 204 are used to decrease the melting
point of the resulting slurry formulation 200, specifically the
network-forming silica in the slurry formulation 200. Exemplary
fluxing agents 204 include oxides of potassium (K), sodium (Na),
and calcium (Ca). The fluxing agents 204 may be provided in
granular or powder form to facilitate mixing.
[0035] Rather than using pure forms of potassium oxide (K2O),
sodium oxide (Na2O), and calcium oxide (CaO), for example, the
fluxing agents 204 of the present disclosure may be sourced from
one or more refined alkali aluminosilicate minerals of Formula I
below:
M.sub.wAl.sub.xSi.sub.yO.sub.z (I)
[0036] wherein:
[0037] M is an alkali metal (e.g., K, Na) or an alkaline earth
metal (e.g., Ca).
[0038] Exemplary alkali aluminosilicate minerals include Feldspar
(KAlSi.sub.3O.sub.8--NaAlSi.sub.3O.sub.8--CaAl.sub.2Si.sub.2O.sub.8)
and Nepheline Syenite ((Na,K)AlSiO.sub.4), for example.
Advantageously, such alkali aluminosilicate minerals are more
readily available and less expensive than pure fluxing oxides.
Also, in addition to providing the desired fluxing oxides, the
alkali aluminosilicate minerals may also contribute additional
quantities of the elements found in the above-described mineral
oxides 202 (e.g., silicon, aluminum). The concentration of alkali
aluminosilicate minerals as fluxing agents 204 in the slurry
formulation 200 may be as low as about 10 wt. %, about 20 wt. %,
about 30 wt. %, or about 40 wt. %, and as high as about 50 wt. %,
about 60 wt. %, about 70 wt. %, about 80 wt. %, or about 85 wt. %.
For example, in certain embodiments, the concentration of alkali
aluminosilicate minerals in the slurry formulation 200 may be about
50 wt. % to about 70 wt. %, which constitutes a majority of the
slurry formulation 200 and makes the fluxing agents 204 the primary
ingredient (i.e., the ingredient present in the largest amount) in
the slurry formulation 200. Lower concentrations of fluxing agents
204 may lead to higher material costs and higher firing
temperatures in the subsequent firing step 112 (FIG. 1), while
higher concentrations of fluxing agents 204 may lead to lower
material costs and lower firing temperatures in the subsequent
firing step 112 (FIG. 1).
[0039] The colloidal silica (i.e., sol-gel synthesized silica) 206
in the slurry formulation 200 comprises nanoparticles of silica
(SiO2) suspended in water. The solid content of the colloidal
silica 206 may vary. For example, the solid content of the
colloidal silica 206 may be about 10 wt. %, about 20 wt. %, about
30 wt. %, about 40 wt. %, or about 50 wt. %, with water making up
the balance. The colloidal silica 206 may serve as a bonding agent
throughout method 100 (FIG. 1). During both the initial forming
step 102 and the mixing step 104 (FIG. 1), which is described
further below, the colloidal silica 206 may be used to hold the
other granular ingredients in suspension. During the subsequent
molding step 106 (FIG. 1), which is also described further below,
the colloidal silica 206 may be used to bind the other ingredients
together by forming a gel network or scaffold that remains even
after the water is removed. The colloidal silica 206 is typically a
basic solution (i.e., pH>7), but neutral solutions (pH=7) and
acidic solutions (i.e., pH<7) are also available. The
concentration of colloidal silica 206 in the slurry formulation 200
may be as low as about 2 wt. %, about 5 wt. %, about 10 wt. %,
about 15 wt. %, or about 20 wt. %, and as high as about 25 wt. %,
about 30 wt. %, about 35 wt. %, or about 40 wt. %, for example.
Lower concentrations of colloidal silica 206 may lead to lower
material costs and lower green strength before the firing step 112
(FIG. 1), while higher concentrations of colloidal silica 206 may
lead to higher material costs and higher green strength before the
firing step 112 (FIG. 1).
[0040] One optional additive 208 for use in the slurry formulation
200 includes clay or clay minerals (e.g., kaolinite, bentonite).
Rather than relying on clay as a primary ingredient and bonding
agent like traditional ceramic products, small amounts of clay or
clay minerals may be used as a suspension agent in the slurry
formulation 200. The concentration of clay or clay mineral
additives 208 in the slurry formulation 200 may be as low as about
0 wt. %, about 2 wt. %, or about 4 wt. %, and as high as about 6
wt. %, about 8 wt. %, or about 10 wt. %, for example. Compared to
traditional ceramic products, the slurry formulation 200 of the
present disclosure may be considered entirely or substantially
clay-free.
[0041] Other optional additives 208 include mixing agents,
suspension agents, and/or dispensing agents. One such additive 208
is organic gum, such as carboxymethyl cellulose (CMC) gum, xanthan
gum, guar gum, acacia gum, or methylcellulose. The concentration of
organic gum additives 208 in the slurry formulation 200 may be
about 0 wt. %, about 1 wt. %, or about 2 wt. %, for example.
[0042] Still other optional additives 208 include organic
de-foamers and surfactants such as polyvinyl alcohol or polyvinyl
pyrrolidone. Such additives 208 may promote bubble formation to
remove air from the slurry formulation 200.
[0043] Still other optional additives 208 include dispersants,
including anionic dispersants such as polyacryline acid, cationic
dispersants such as poly(ethyleneimine), and/or comb polymers such
as poly(ethylene oxide)-poly(ethyleneimine).
[0044] The solid particles in the slurry formulation 200 may
include the mineral oxides 202, the fluxing agents 204, the silica
from the colloidal silica 206, and any solid additives 208. The
liquid in the slurry formulation 200 may include added water and/or
the water from the colloidal silica 206 and any other
liquid-containing ingredients. The solid content of the slurry
formulation 200 may be about 70 wt. %, about 80 wt. %, about 90 wt.
%, or more. The solid content of the slurry formulation 200 may be
optimized between a maximum solid content, in which the
corresponding liquid content would be too low and the slurry
formulation 200 would be too thick for injection into a mold during
the subsequent molding step 108, and a minimum solid content, in
which the corresponding liquid content would be too high and cause
undesirable shrinkage and/or deformation when the liquid is removed
during the subsequent drying step 108 and firing step 112.
[0045] Exemplary slurry formulations 200 are set forth in Table 1
below, but these slurry formulations 200 may vary based on the
trends described above to achieve a final ceramic product having
desired properties.
TABLE-US-00001 TABLE 1 Sample Sample Concentration Concentration
Concentration Range A B Slurry Ingredients (wt. %) (wt. %) (wt. %)
Mineral Oxides 202 Silica Balance 17.8 12.9 Alumina 10-70 17.4 17.4
Fluxing agent 204 Alkali 10-85 56.0 56.0 aluminosilicate minerals
(e.g., Feldspar) Colloidal silica 206 2-40 8.8 13.7 (30 wt. %
SiO.sub.2/ (40 wt. % SiO.sub.2/ 70 wt. % water) 60 wt. % water)
Additives 208 0-12 -- -- Total 100 100.0 100.0
[0046] The solid ingredients in Table 1 above may include: the
silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) mineral oxides
202, the Feldspar
(KAlSi.sub.3O.sub.8--NaAlSi.sub.3O.sub.8--CaAl.sub.2Si.sub.2O.su-
b.8) fluxing agent 204, and the additional silica (SiO.sub.2) from
the colloidal silica 206. The composition of these solid
ingredients, taken together, is set forth in Table 2 below. In
certain embodiments of slurry formulation 200, the mineral oxides
(e.g., silica and alumina) are the majority solid components, and
the fluxing oxides (e.g., sodium oxide, potassium oxide, and
calcium oxide) are the minority solid components. In the "Sample
Concentration" embodiment of Table 2, in particular, silica is the
primary solid component, alumina is the secondary solid component,
and the fluxing oxides are the tertiary solid component.
TABLE-US-00002 TABLE 2 Concentration Sample Range Concentration
Composition (wt. %) (wt. %) Silica Balance 65.0 Alumina 15-75 27.8
Sodium Oxide 1-9 3.6 Potassium Oxide 1-5 2.3 Calcium Oxide 0.25-2
0.8 Total 100 100.0
[0047] Slurry formulation 200 may consist of or consist essentially
of the ingredients listed in Table 1 and Table 2 above and may lack
certain ingredients found in other ceramic materials. For example,
slurry formulation 200 may lack lithium oxide, barium oxide,
zirconium oxide, cerium oxide or cerium fluoride, iron oxide,
and/or magnesium oxide.
[0048] Returning to FIG. 1, the slurry formulation from step 102 is
mixed during the mixing step 104 of method 100. With respect to the
slurry formulation 200 of FIG. 2, for example, the mixing step 104
may involve evenly distributing the solid particles in the slurry
formulation 200--namely the mineral oxides 202, the fluxing agents
204, the silica from the colloidal silica 206, and any solid
additives 208--throughout the liquid in the slurry formulation
200--namely, any added water and/or the water from the colloidal
silica 206 and any other liquid-containing ingredients. Care should
be taken to minimize air entrainment in the slurry formulation 200
during the mixing step 104. A double planetary, low shear mixer has
been shown to minimize such air entrainment. The mixing step 104
may be terminated when adequate mixing is achieved, which may be
measured using a Hegman gauge, for example. A well-dispersed and
deagglomerated mixture typically has a value of 6 or better using a
Hegman gauge. The mixing step 104 of the present disclosure may be
terminated after less than an hour and in some cases after several
minutes. Traditional clay ceramics, by contrast, are usually mixed
for several days.
[0049] Next, the mixture from step 104 is molded into a desired
shape during the molding step 106 of method 100. The molding step
106 may involve: introducing the mixture 300 into a mold 310, as
shown in FIG. 3A; solidifying the mixture 300 in the mold 310 to
form a solid article 320, as shown in FIG. 3B; and ejecting the
solid article 320 from the mold 310, as shown in FIG. 3C, to form a
molded article 325, as shown in FIG. 3D.
[0050] As shown in FIG. 3A, the introducing process may involve
injecting the mixture 300 into the mold 310 under pressure (e.g.,
1-2 psi), such as using a manual or hydraulic piston 302. Other
methods for introducing the mixture 300 into the mold 310 may also
be used, such as pouring the mixture 300 into the mold 310. Because
the mixture 300 may have a low viscosity and may be capable of
flowing easily into the mold 310, any seams 312 in the mold 310
should be adequately sealed to prevent leakage. Care should be
taken to minimize air entrapment in the mold 310, especially in any
blind pockets of the mold 310. One or more air vents 314 may be
provided in the mold 310 to allow air to escape from the mold
310.
[0051] As shown next in FIG. 3B, the solidifying process may
involve destabilizing the colloidal silica in the mixture 300 to
form a gel network or scaffold of siloxane bonds that maintain the
shape of the solid article 320. Thus, the solidifying process may
also be referred to herein as a gelcasting or gelling process.
[0052] An exemplary method for destabilizing the colloidal silica
is freeze gelling. Freeze gelling involves freezing the water in
the mixture 300 and forming ice crystals, which may expand and
physically force the silica particles together to form the gel
network. Advantageously, the freezing may occur directly in the
mold 310 by placing the entire mold 310 in a freezer 330, which is
considered a vessel configured to expose its contents, directly
and/or indirectly, to a low-temperature cooling agent 332 capable
of freezing the contents. In certain embodiments, the cooling agent
332 is directed across the mold 310, as shown in FIG. 3B. In a
traditional freezer 330, for example, the cooling agent 332 may
include low-temperature air that is blown across a refrigerant
(e.g., norflurane, freon) in an evaporator coil. However, as
discussed further below, other freezer 330 arrangements and
low-temperature or cryogenic cooling agents 332 are also
contemplated, such as dry ice or liquid nitrogen.
[0053] According to an exemplary embodiment of the present
disclosure, the freezing process occurs at a fast rate, especially
as the geometric complexity of the mold 310 increases. When the
freezing occurs at a fast rate, the resulting ice crystals will be
smaller and more homogeneous, and the resulting gel network will
also be more homogeneous. If the freezing occurred at a slow rate,
by contrast, the resulting ice crystals would be larger (e.g.,
snowflake type structures), and the resulting gel network may be
variegated with large grain boundaries and cracks. The freezing
rate may be increased by subjecting the mold 310 to very low
temperatures in the freezer 330. For example, the freezing rate may
be increased by introducing a cryogenic cooling agent 332, such as
dry ice or liquid nitrogen, across the mold 310 in the freezer 330,
as shown in FIG. 3B. The freezing rate may also be increased by
increasing the thermal conductivity of the mold 310, such as by
constructing the mold 310 with thin and/or highly thermally
conductive walls, such as metallic (e.g., aluminum, copper alloy)
walls, rather than thick and/or thermally insulating walls, such as
plastic walls. In certain embodiments, the freezing process is
performed in 30 minutes, 20 minutes, 10 minutes, 5 minutes, or
less.
[0054] According to another exemplary embodiment of the present
disclosure, the freezing process occurs in a predetermined
direction toward the air vent 314 in the mold 310. This controlled
freezing direction may be achieved by directing the cooling agent
332 toward a surface of the mold 310 that opposes the air vent 314
in the mold 310. In the illustrated embodiment of FIG. 3B, for
example, the cooling agent 332 is directed toward a lower surface
316 of the mold 310 opposing the air vent 314, across the mold 318,
and toward the upper surface 318 of the mold 310 including the air
vent 314 such that the article 320 freezes in a predetermined
direction from the lower surface 316 toward the air vent 314 in the
upper surface 318. Because the water in the article 320 expands in
volume as it freezes, air and any excess mixture 300 in the mold
310 may be displaced toward the air vent 314 and allowed to escape
through the air vent 314 during the freezing process. Allowing such
materials to escape from the mold 310 rather than being trapped in
the mold 310 may minimize internal stresses in the article 320,
thereby minimizing stress cracks in the article 320. Also, allowing
such materials to escape from the mold 310 may provide a visual
indication that the freezing process is completed. The cooling
agent 332 may be exhausted from the freezer 330 or recirculated
through the freezer 330, as shown in FIG. 3B.
[0055] Another available method for destabilizing the colloidal
silica is chemical gelling. Chemical gelling involves adding a
gelling agent to the mixture 300 to change the pH and reduce
surface charges of the mixture 300 in a manner that discourages
chemical repulsion of the silica particles and encourages gelling
of the silica particles. Suitable gelling agents include
hydrochloric acid (HCl), citric acid (C.sub.6H.sub.8O.sub.7),
magnesium carbonate (MgCO.sub.3), and sodium chloride (NaCl) salts,
for example. Care should be taken to adequately blend the gelling
agent into the mixture 300 without breaking the gel network as it
forms.
[0056] Yet another available method for destabilizing the colloidal
silica is drying. Drying involves heating the mixture 300 and
evaporating the water from the mixture 300 to physically force the
remaining silica particles together to form the gel network.
Advantageously, the drying may occur directly in the mold 310 by
placing the entire mold 310 in a heater (not shown). The mold 310
may require several openings to allow the evaporating water to
escape.
[0057] Still other available methods for destabilizing the
colloidal silica include: traditional gelcasting by adding a
monomer and an initiator into the mixture 300 and heating the
mixture 300 to polymerize and cross-link the gel network; chemical
gelcasting by adding ionic polymers or particles to bridge the
charged silica particles into the gel network; and slip-casting by
removing water from the mixture 300, such as using a plaster mold,
to form the gel network.
[0058] As shown next in FIG. 3C, the solid article 320 is ejected
from the mold 310. If the solid article 320 was formed by freeze
gelling, the solid article 320 may remain frozen during the
ejection process. The ejection process may involve opening the mold
310 and applying an ejection force F to push the solid article 320
out of the mold 310. The ejection force F may be achieved by
directing ejector pins and/or compressed air against the solid
article 320, for example.
[0059] As shown next in FIG. 3D, the solid article 320 is removed
from the mold 310 as a molded article 325. The illustrative molded
article 325 is in the shape of a sink basin having a bowl 326 and a
rim 328, but it is understood that the molded article 325 may have
any desired shape or purpose, such a toilet, another sanitary ware
product, a dinner ware product, or any other product. The molded
article 325 may be coupled to one or more other solid articles to
form a larger and/or more complex product. The mixture 300 that was
used to form the molded article 325 may also be used as an adhesive
to couple the various solid articles together. The smooth finish of
the mold 310 (FIG. 3B) may produce a similarly smooth molded
article 325, so the molded article 325 may require minimal
secondary finishing after being removed from the mold 310. In
certain embodiments, the secondary finishing may be limited to
parting lines on the molded article 325 imparted by the seams 312
of the mold 310 (FIG. 3A).
[0060] Referring to FIGS. 1 and 4, the molded article 325 from the
molding step 106 is dried during the drying step 108 of method 100
to remove water from the molded article 325. It is within the scope
of the present disclosure for the drying step 108 to at least
partially overlap the molding step 106. For example, the drying
step 108 may be at least partially performed with the solid article
320 remaining inside the mold 310 (FIG. 3B). The drying step 108
should be controlled to minimize shrinking and cracking as the
water is removed from the molded article 325. If the molded article
325 from the molding step 106 was formed by freeze gelling, the
drying step 108 may be a multi-stage process as shown in FIG. 4,
which illustratively includes a pre-thawing normalizing stage 400,
a thawing stage 402, and an evaporating stage 404. Each stage 400,
402, 404 of the drying step 108 is described further below.
[0061] The pre-thawing normalizing stage 400 of the drying step 108
involves placing the still-frozen molded article 325 in a
temperature-controlled, optionally high-airflow environment to
bring the molded article 325 to a substantially uniform frozen
state having a substantially uniform temperature near a
thawing/freezing point of water (e.g., near about 32.degree. F.).
The molded article 325 may enter the normalizing stage 400 in a
non-uniform frozen state having a non-uniform temperature. In one
embodiment, the molded article 325 enters the normalizing stage 400
from the freezing process of FIG. 3B with a temperature gradient
caused by the directional nature of the freezing process. For
example, the area of the molded article 325 that was positioned
close to the cooling agent 332 in FIG. 3B (e.g., the rim 328 of
FIG. 3D) may be colder than the area of the molded article 325 that
was positioned away from the cooling agent 332 and close to the
vent 314 in FIG. 3B (e.g., the bowl 326 of FIG. 3D). In another
embodiment, thinner areas of the molded article 325 may be colder
than thicker areas of the molded article 325, regardless of whether
the freezing process was directional in nature. The temperature of
the normalizing stage 400 may be just below the thawing/freezing
point of water, such as about 20.degree. F. to about 30.degree. F.,
more specifically about 25.degree. F. to about 30.degree. F., more
specifically about 28.degree. F. The duration of the normalizing
stage 400 may be sufficient to minimize any temperature differences
and achieve the substantially uniform temperature throughout the
molded article 325, such as about 15 minutes to about 60 minutes,
more specifically about 30 minutes. Of course, the temperature and
duration of the normalizing stage 400 may vary based on the size
and shape of the molded article 325, the design of the mold 310,
and the freezing process conditions. It is also within the scope of
the present disclosure to eliminate the normalizing stage 400
altogether if the molded article 325 already has a sufficiently
uniform temperature.
[0062] The thawing stage 402 of the drying step 108 involves
heating the molded article 325 in a temperature-controlled,
optionally high-airflow environment from a substantially uniform
frozen state near the thawing point to a thawed state. The
temperature of the thawing stage 402 may be above the
thawing/freezing point of water, such as about 40.degree. F., about
50.degree. F., about 60.degree. F., about 70.degree. F., or more.
During the thawing stage 402, the water in the molded article 325
decreases in volume. Without the prior normalizing stage 400, the
molded article 325 could transition from the freezing process to
the thawing stage 402 in a non-uniform manner (e.g., with a
temperature gradient caused by directional freezing, with different
temperatures in areas of different thickness, with different
temperatures caused by inconsistent warming after freezing),
causing the thawing process and its related dimensional changes to
occur inconsistently. Such inconsistent thawing could create
internal stresses in the molded article 325, which lead to stress
cracks in the molded article 325. However, by subjecting the molded
article 325 to the prior normalizing stage 400, the molded article
325 enters the thawing stage 402 with a substantially uniform
temperature already near the thawing point of water, allowing the
thawing process and its related dimensional changes to occur
quickly and uniformly. In one example, the molded article 325 is
thawed quickly and uniformly in the thawing stage 402 from the
normalized temperature of about 28.degree. F. to the thawing point
of about 32.degree. F. Such uniform thawing minimizes internal
stresses in the molded article 325 and reduces the formation of
stress cracks in the molded article 325.
[0063] The evaporating stage 404 of the drying step 108 involves
further heating the molded article 325 in a temperature-controlled,
optionally high-airflow environment from the thawed state to a
heated state sufficient to evaporate water. Water may be more
easily and evenly liberated from the gel-based articles of the
present disclosure than from traditional ceramic articles.
Therefore, the evaporating stage 404 of the drying step 108 may be
performed at higher temperatures and higher speeds than traditional
drying processes, including temperatures above the boiling point of
water. For example, the evaporating stage 404 of the drying step
108 may be performed at temperatures of about 200.degree. F. to
about 500.degree. F., whereas traditional drying processes are
typically performed at temperatures below 150.degree. F. It is also
within the scope of the present disclosure to perform the
evaporating stage 404 over an extended period of time and at a
lower temperature (e.g., less than about 200.degree. F., less than
about 150.degree. F., less than about 100.degree. F., or about
70.degree. F.).
[0064] According to an exemplary embodiment of the present
disclosure, the normalizing stage 400, the thawing stage 402,
and/or the evaporating stage 404 of the drying step 108 may be
performed in a controlled, low-humidity environment. In one
embodiment, at least the thawing stage 402, if applicable, is
performed in the low-humidity environment. The low-humidity
environment may be a vacuum having 0% humidity.
[0065] The dried product from the drying step 108 may be very
strong. In certain embodiments, the dried product may be capable of
withstanding machining and robust handling, even before the final
firing step 112.
[0066] In step 110 of method 100, the dried product from step 108
is glazed. The glazing step 110 of the present disclosure may be
similar to a traditional glazing process. The glaze formulation may
include one or more glass-formers such as silica, one or more
fluxing agents, and one or more optional additives. Advantageously,
the dried product from step 108 may be an attractive white color,
so the need for adding colorants to an otherwise clear glaze
formulation may be reduced or eliminated. In certain embodiments,
the glaze formulation may be applied to the dried product in
aqueous form, such as by dipping the product into the glaze,
brushing the glaze onto the product, spraying the glaze onto the
product, or pouring the glaze onto the product. In other
embodiments, the glaze formulation may be applied to the dried
product in dry or powder form.
[0067] In step 112 of method 100, the glazed product from step 110
is fired. The firing step 112 of the present disclosure may be
similar to a traditional firing process. However, the firing step
112 of the present disclosure may be performed at a faster rate
than a traditional firing process and with less regard to
outgassing, because the ceramic products of the present disclosure
lack significant amounts of chemically-bound water and organics
that are associated with traditional clay ceramic products. The
firing step 112 may convert the applied glaze to an impervious,
vitreous coating that is fused to the underlying ceramic product,
similar to traditional Vitreous china (VC) products.
[0068] The final ceramic product may have substantially the same
composition as the initial slurry formulation 200, except the final
ceramic product lacks the water present in the initial slurry
formulation 200. For example, the composition of the final ceramic
product may be set forth in Table 1 (not including water) or Table
2 above. In certain embodiments of the final ceramic product, the
mineral oxides (e.g., silica and alumina) are majority components,
and the fluxing oxides (e.g., sodium oxide, potassium oxide, and
calcium oxide) are minority solid components.
[0069] Although the invention has been described in detail with
reference to certain preferred embodiments, variations and
modifications exist within the spirt and scope of the invention as
described and defined in the following claims.
* * * * *