U.S. patent application number 17/131230 was filed with the patent office on 2021-04-15 for gold nanoparticle in ceramic glaze.
This patent application is currently assigned to University of Richmond. The applicant listed for this patent is University of Richmond. Invention is credited to Ryan Coppage, Christine Lacy, Michael Leopold.
Application Number | 20210108084 17/131230 |
Document ID | / |
Family ID | 1000005303516 |
Filed Date | 2021-04-15 |
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United States Patent
Application |
20210108084 |
Kind Code |
A1 |
Coppage; Ryan ; et
al. |
April 15, 2021 |
Gold Nanoparticle in Ceramic Glaze
Abstract
A range of processes is described herein for the preparation of
a range of ceramic glazes with traditional firing methods that
represents significant efficiency and ecological advancements over
existing methods and allows for the replacement of commercial
ceramic colorant methods, while retaining the costly equipment and
firing methods already used. The process allows for ceramic surface
color while breaking standards for minimal amounts of transition
metal colorant used. The nanoparticle-based glazes described here
add new colors to the known ceramic surface palette and offers
greater consumer safety as an alternative to existing coloring
processes that use higher concentrations of toxic metal and an
increased risk of metal leaching from the final ceramic vessel into
its contents (e.g., soil, beverage, food).
Inventors: |
Coppage; Ryan; (Richmond,
VA) ; Leopold; Michael; (Glen Allen, VA) ;
Lacy; Christine; (Richmond, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Richmond |
Richmond |
VA |
US |
|
|
Assignee: |
University of Richmond
Richmond
VA
|
Family ID: |
1000005303516 |
Appl. No.: |
17/131230 |
Filed: |
December 22, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15790717 |
Oct 23, 2017 |
10913856 |
|
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17131230 |
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62412543 |
Oct 25, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 41/5022 20130101;
C04B 41/009 20130101; C04B 33/34 20130101; C04B 33/14 20130101;
C09C 1/0009 20130101; C01P 2004/51 20130101; C09C 1/62 20130101;
C04B 2111/82 20130101; C04B 41/86 20130101; C04B 33/04 20130101;
C01P 2004/04 20130101; C01P 2004/64 20130101; C04B 2111/00965
20130101 |
International
Class: |
C09C 1/00 20060101
C09C001/00; C04B 41/00 20060101 C04B041/00; C04B 41/86 20060101
C04B041/86; C04B 41/50 20060101 C04B041/50; C09C 1/62 20060101
C09C001/62; C04B 33/04 20060101 C04B033/04; C04B 33/14 20060101
C04B033/14; C04B 33/34 20060101 C04B033/34 |
Claims
1. A pre-firing ceramic glaze material consisting of: a base dry
glaze powder; and a colorant material, the colorant material
consisting of an amount of metal nanoparticles, wherein each of the
metal nanoparticles is formed of a single element type, and further
wherein the amount of metal nanoparticles is formed by loading less
than 0.1 percent by weight of an Au NP concentration to produce a
the pre-firing ceramic glaze material, wherein the Au NP
concentration consists of citrate-stabilized nanoparticles
synthesized from HAuCl.sub.4 each nanoparticle having a diameter of
less than 100 nm; and further wherein the pre-firing ceramic glaze
material produces an observable color on a ceramic item post-firing
in a kiln.
2. The pre-firing ceramic glaze material according to claim 1, the
observable color is red.
3. The pre-firing ceramic glaze material according to claim 1,
wherein the concentration of Au NPs is equal to or less than 0.015
percent by weight.
4. The pre-firing ceramic glaze material according to claim 1,
wherein the base dry glaze powder further comprises multiple
non-colorant materials include the following: G200 feldspar, Ferro
Frit 3134, Kaolin EPK, flint/silica, wollastonite, and talc.
5. The pre-firing ceramic glaze material according to claim 4,
wherein the non-colorant materials are combined by weight as
follows: 20% G200 feldspar, 20% Ferro Frit 3134, 20% Kaolin EPK,
19% flint/silica, 15% wollastonite, and 6% talc.
6. A pre-firing ceramic glaze material consisting of: a pre-firing
dry glaze powder; at least one colorant material consisting of
metal nanoparticles at a concentration of less than 0.1 percent of
a total weight of the pre-firing ceramic glaze material containing
both the pre-firing dry glaze powder and the at least one colorant
material, wherein the average diameter of the metal nanoparticles
is less than 100 nm and further wherein each metal nanoparticle is
comprised of a single element type; and further wherein the
pre-firing ceramic glaze material produces an observable color on a
ceramic item post-firing in a kiln.
7. The pre-firing ceramic glaze material according to claim 6,
wherein the at least one colorant material is selected from the
group consisting of gold nanoparticles (Au NPs) and silver
nanoparticles (Ag NPs).
8. The pre-firing ceramic glaze material according to claim 7,
wherein the observable color is selected from the group consisting
of red and green.
9. The pre-firing ceramic glaze material according to claim 7,
wherein the at least one colorant material is gold nanoparticles
(Au NPs) synthesized from HAuCl.sub.4.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a division of U.S. patent
application Ser. No. 15/790,717, directed to "GOLD NANOPARTICLE IN
CERAMIC GLAZE," filed on Oct. 23, 2017, which claims benefit of
priority to U.S. Provisional Patent Application No. 62/412,543,
directed to "GOLD NANOPARTICLE IN CERAMIC GLAZE," filed on Oct. 25,
2016, both of which are incorporated herein by reference in their
entireties.
BACKGROUND
Field of the Embodiments
[0002] The field of the embodiments is generally methods and
systems for making ceramic glaze. More particularly, the present
embodiments are in the field of producing a ceramic glaze using a
novel formulation including, gold nanoparticles, gold aggregate,
and gold and silver salts, in a novel process.
Description of the Related Art
[0003] Ceramic glazes are used to protect and color tile, pottery,
and large-scale ceramic structures. Glaze colors result from
combinations of feldspars, silicas, clays, and metal
colorants--often high amounts, e.g., anywhere from 4% to as high as
12%, of many different metals, including toxic metal colorants such
as cobalt, barium, manganese, nickel, and chromium. For example,
dark green requires a mixture of 5-10% cobalt and chromium;
Prussian Blue requires 5-10% cobalt and manganese; orange red
requires 1-4% cadmium and selenium; reds can contain 5-8% nickel--a
known carcinogen. Despite health hazards due to leaching and other
environmental concerns, these toxic materials remain standard in
pottery glazes as they produce desirable colors.
[0004] Traditionally, specific heavy metals allow for various
vibrant colors over time and under extreme conditions. These
systems are either opaque or translucent, which call for various
metal loading amounts. If a glaze is translucent, light must pass
through it, strike metal colorants in its path, hit a white clay
body, and be reflected back out, again striking more metal
colorants to produce a visible color. This allows for vibrant,
jewel-like colors. With opacifiers and thus opaque glazes, a rather
large degree of metal--upward of 8-fold the amount needed for
translucent glazes--is required at the metal surface, as light does
not penetrate and reflect off of a white clay surface. While this
will make a glaze more versatile to various clays, it also greatly
increases cost, creates greater exposure hazards, and is more
environmentally taxing with respect to opacifier and bulk metal
consumption.
[0005] It is known that the use of noble metal nanoparticles (NPs)
as stable and oxidation-resistant color sources dates back to Roman
times, where organic chromophores decompose over time and do not
survive ceramic or glass curing processes. The use of metal
nanoparticle (NP) color alternatives allows for a metal-efficient
and ecologically advantageous route to high-temperature permanent
color on glass, silica surfaces, and in feldspathic ceramic glazes.
This color is achieved through surface plasmon resonance (SPR)
emission and has been demonstrated to be dependent on NP diameter,
shape, and concentration for both intensity and wavelength of
color. SPR emission is dependent on charge-density oscillations of
individual particles and aspect ratio of non-spherical structures,
which allows for color tuning despite being trapped in a solid
glaze melt or silicate matrix. To that end, a variety of colors and
shades (intensities) can be achieved by tuning NP diameter, aspect
ratio, concentration of NP, and through controlling the methods by
which these feldspar/silicate ceramic coatings are cured.
[0006] In particular, gold nanoparticles (Au NPs) have been found
to be environmentally friendly and are considered non-toxic to
humans as an alternate metal colorant in ceramic glazes.
Additionally, the plasmon band observed with Au NP can result in
vibrant solutions by manipulating NP size, shape, and
concentration.
[0007] Previously, Au NP colorant systems have been developed for
very precise instrumentation, in lab settings and as third-firing
systems, and employed on already vitrified glossy surfaces as inks.
They have been prepared with metal oxide nucleation precursors,
with crystalline silica surfaces, and as dispersed pigments. As
inks, Au NP pigments must be applied via inkjet printing
adaptation, sintered again, such that more heat is consumed and a
larger carbon footprint is created. Accordingly, such processes are
time and cost prohibitive, and not easily adapted to bulk glaze
materials for commercial ceramics. The following references are
examples of such work with ink-based coloring systems: Blosi, M.,
Albonetti, S., Gatti, F., Baldi, G. & Dondi, M., "Au--Ag
nanoparticles as red pigment in ceramic inks for digital
decoration," Dyes Pigments 94, 355-362 (2012) and Cavalcante, P. M.
T., Dondi, M., Guarini, G., Raimondo, M. & Baldi, G., "Colour
performance of ceramic nano-pigments," Dyes Pigments 80, 226-232
(2009).
[0008] While other methods for producing ceramic surface color
through Au NPs exist, these methods of preparation require
sophisticated steps, equipment, and user controls. Further, Au NPs
have been previously reported to diminish in size during sintering
and possess significant differences in concentration with respect
to reduction and oxidation firing atmospheres.
[0009] Thus, there remains a need in the art for a formulation and
process incorporating use of noble metal NPs, e.g., Au NP, and Ag
NP in glazes that would allow for efficient and effective coloring
with low total metal loading concentrations that minimize leaching
and avoid the heavy metal toxicity of traditional glazes. Such a
formulation and process would ideally be applicable to commercial,
e.g., traditional reduction, firing and production settings.
SUMMARY OF THE EMBODIMENTS
[0010] In a first exemplary embodiment, a process for producing a
fired glaze containing gold nanoparticles (Au NPs), includes:
loading a glaze material with less than 0.1 percent of an Au NP
concentration; applying the loaded glaze to a component; and firing
the component in a kiln, wherein the fired glaze on the component
contains Au NPs after firing.
[0011] In a second exemplary embodiment, a pre-firing ceramic glaze
material includes: multiple non-colorant materials; and at least
one colorant material at a concentration of less than 0.1 percent
of a total amount of the pre-firing glaze material, wherein the
pre-firing glaze material produces an observable color on a ceramic
item post-firing in a kiln.
[0012] In a third exemplary embodiment, a process for producing a
fired glaze containing metal nanoparticles and an observable color,
includes: mixing multiple non-colorant materials; loading at least
one colorant material containing the metal nanoparticles at a
concentration of less than 0.1 percent of a total amount of a
pre-firing glaze material containing both the multiple non-colorant
materials and the at least one colorant material; applying the
pre-firing glaze to a component; and firing the component in a
kiln, wherein the fired glaze on the component contains metal
nanoparticles after firing.
BRIEF DESCRIPTION OF THE FIGURES
[0013] The following figures are intended to be part of the
description of the embodiments herein and considered when reading
the Detailed Description herein. The patent or application file
contains at least one figure executed in color. Copies of this
patent or patent application publication with color figures(s) will
be provided by the Office upon request and payment of the necessary
fee.
[0014] FIG. 1 is a photograph showing a comparison of prior art
glazed and fired tiles with tiles prepared using Au NP-red
colorants in accordance with an embodiment described herein;
[0015] FIGS. 2a and 2b show Au NP diameter and absorbance
characteristics in accordance with an embodiment described
herein;
[0016] FIGS. 3a to 3c include photographs of glazed ceramic pieces
fired in reduction and oxidation environments wherein the glaze
includes varying percentages of Au NP and diameter vs. absorbance
characteristics of same in accordance with an embodiment described
herein;
[0017] FIGS. 4a to 4c include photographs of glazed ceramic pieces
fired in reduction and oxidation environments wherein the glaze
includes varying percentages of Au NP plus opacifier and FIGS. 4a
to 4c further show diameter vs. frequency characteristics of same
in accordance with an embodiment described herein;
[0018] FIG. 5 is a photograph of a glazed ceramic mug, wherein the
glaze includes Au NP in accordance with an embodiment described
herein;
[0019] FIGS. 6a-6c are TEM images of varying Au NP glaze solutions
before firing with inset histograms of particles size distribution
of each batch in accordance with an embodiment described
herein;
[0020] FIGS. 7a to 7c include photographs of glazed ceramic pieces
fired in reduction and oxidation environments wherein the glaze
includes multiple size Au NPs in accordance with the TEM images of
FIGS. 6a-6c and FIGS. 7a to 7c further show diameter vs. frequency
characteristics of same in accordance with an embodiment described
herein;
[0021] FIGS. 8a to 8c show reflectance characteristics for glazed
ceramic pieces fired in reduction and oxidation environments
wherein the glaze includes Au NPs having different diameters in
accordance with an embodiment described herein;
[0022] FIG. 9 shows pre- and post-firing diameter characteristics
for the Au NPs in various glazes in accordance with an embodiment
described herein;
[0023] FIGS. 10a-10b are TEM images of gold nanoparticle aggregate
(Au NP Agg) (FIG. 10a) and stock silver nanoparticles (Ag NP) (FIG.
10b) used in various embodiments described herein;
[0024] FIGS. 11a to 11d include photographs of glazed ceramic
pieces fired in reduction and oxidation environments wherein the
glazes include different formulations in accordance with the TEM
images of FIGS. 10a-10b and FIGS. 11a to 11d further show diameter
vs. frequency characteristics of same in accordance with an
embodiment described herein;
[0025] FIGS. 12a to 12d show reflectance characteristics for glazed
ceramic pieces fired in reduction and oxidation environments
wherein the glaze includes varying formulations in accordance with
an embodiment described herein;
[0026] FIG. 13 shows oxidation vs. reduction firing diameter
characteristics for various glazes in accordance with an embodiment
described herein; and
[0027] FIGS. 14a-14b are photographs showing a comparison of fired
tiles with tiles prepared using glazes prepared with varying
formulations and fired in reduction (FIG. 14a) and oxidation (FIG.
14b) environments in accordance with embodiments described
herein.
DETAILED DESCRIPTION
[0028] The embodiments described herein provide for the preparation
of a red, gold nanoparticle (Au NP) glaze with traditional firing
methods that represents significant efficiency and ecological
advancements over existing methods and allows for the replacement
of commercial ceramic colorant methods, while retaining the costly
equipment and firing methods already used. These embodiments are
advantageous for and adaptable to all ceramic manufacturing
facilities, including the production of tile, pottery, and
large-scale ceramic structures. It allows for ceramic surface color
while breaking standards for minimal amounts of transition metal
colorant used. In addition to being more environmentally friendly
and cost effective compared to existing glazing procedures, the
nanoparticle-based glaze described here adds new colors to the
known ceramic surface palette and offers greater consumer safety as
an alternative to existing coloring processes that use higher
concentrations of toxic metal and an increased risk of metal
leaching from the final ceramic vessel into its contents (e.g.,
soil, beverage, food).
[0029] Initially, preparation of glazes containing Au NP were
prepared and fired onto glaze tiles and compared to prior art red
glazes using known formulations, including Panama Red, Tomato Red,
Oxidation Raspberry, and Pete's Cranberry to highlight color
comparison. FIG. 1 shows a comparison of glazed tiles prepared
using Au NP-red colorants in accordance with the embodiments
discussed herein. Table 1 below details the different traditional
formulations and one novel gold nanoparticle formulation for
comparison.
TABLE-US-00001 Panama Red (a) Tomato Red (b) Raspberry (c)
Cranberry Red (d) Au NP Red (e) Dolomite 7.76 Dolomite 10 C. Spar
31 C. Spar 73.8 G200 20 Borates 10.67 P. Spar 36 CaCO.sub.3 21
CaCO3 11.1 3134 Frit 20 SrCO.sub.3 4.17 Ball Clay 12 Borates 8
Borates 10.2 EPK 20 CaCO.sub.3 2.60 Silica 12 EPK 9 Silica 4.9
Silica 19 ZnO 2.60 Talc 9 Talc 4 Wollastonite 15 C. Spar 44.10 Bone
Ash 12 3134 Frit 9 Talc 6 3110 Frit 9.70 Iron Oxide 9 Silica 18 EPK
2.60 Silica 15.80 Colorant Colorant Colorant Colorant Colorant
SnO.sub.2 2.62 Li.sub.2CO.sub.3 2 SnO.sub.2 5 SnO.sub.2 1.5
SnO.sub.2 0-4% CuCO.sub.3 1.75 *Fe.sub.2O.sub.3* 9 CrO.sub.2 0.2
CuCO.sub.3 0.4 AuNP 0.015-0.10%
[0030] In a first embodiment, Au NPs are prepared in the lab,
concentrated, and used in small glaze batches, which are shown to
be stable for long periods--over months. Stabilized suspensions of
Au NPs are known to be highly colored with the identity of color
ranging from red to purple depending on the size of the particles.
The particles are synthesized from metal salts like HAuCl.sub.4.
(See, Musick, M. D. et al., Chem. Mater. 12, 2869-2881 (2000)). The
suspensions are surface-capped with citrates, mercaptans,
sulfur-containing and other surfactants. The color is related to
the surface plasmon resonance (SPR). SPR involves the conduction of
electrons at the interface between a negative and positive
permittivity material that is stimulated by incident light.
Additives that adhere to the surface of the particles can further
modify the color.
[0031] The Au NPs used in the first embodiment discussed below are
citrate-stabilized nanoparticles (CS-NPs) synthesized from in-house
HAuCl.sub.4 using previously developed procedures discussed in
Musick and Schmidt et al., "Nanoparticle Film Assemblies as
Platforms for Electrochemical Biosensing-Factors Affecting the
Amperometric Signal Enhancement of Hydrogen Peroxide," Langmuir 29,
4574-4583 (2013). Briefly, a 1 mM HAuCl.sub.4 aqueous solution was
placed in a flask fitted with a reflux condenser and brought to
reflux with constant stirring. Ten milliliters of a 38.8 mM (aq)
sodium citrate solution was added and promoted color transitions
from light yellow to colorless and to burgundy (wine red). After 10
min of reflux, the solution was removed from heat and allowed to
cool to room temperature with continued stirring. The product was
vacuum filtrated with a 0.8 .mu.m Gelman membrane filter and stored
protected from light. Characterization of CS-NPs by UV-Vis
spectroscopy (Agilent 8453 Photo Diode Array) and transmission
electron microscopy (TEM) showed the characteristic surface plasmon
band (SPB) at 520 nm and an average diameter of 10.3.+-.2.7 nm as
illustrated in FIGS. 2a and 2b.
[0032] For the Au NP Red in Table 1, citrate-stabilized Au NPs were
concentrated in a SORVALL RC-5B ultracentrifuge at 10,000 rpm at
5.degree. C. for 1.5 hours. The supernatant solution was poured off
and the resulting concentrated NP solution was collected as roughly
30 mL for each batch. For preparation of the AuNP-loaded glaze, a
dry glaze powder was prepared in 80 gram batches of 20% G200
feldspar, 20% Ferro Frit 3134, 20% EPK, 19% flint/silica, 15%
wollastonite, and 6% talc. The concentrated Au NP was added to each
glaze mixture in volumes allowing for 0.015%, 0.050%, and 0.100%
loading, respectively, water was added as needed, mixed, sieved,
and applied to tiles with and without the addition of 4% SnO.sub.2
for opacity and color-brightening. Accordingly, 6 different Au NP
red formulations were prepared. Each of the 6 Au NP red
formulations was tested separately in both an oxidation and
reduction atmosphere kiln.
[0033] For oxidation atmosphere samples, tiles were loaded in
electric nichrome coil kilns and fired on a medium temperature ramp
in an oxygen-rich atmosphere. It should be noted that the kilns
used were not vented via a large hood and air/fume convection, but
instead have a fan/draw system that pulls air down, through the
kiln and out a port in the base of the kiln, which contributes to
an increased oxidative atmosphere during firing. As a test, a glaze
with Cu.sub.2O red copper was prepared, fired in this atmosphere,
and was observed to turn green (oxidation state change from
Cu.sup.1+ to Cu.sup.2+) due to the oxidative nature of this
process.
[0034] For the reduction atmosphere firing samples, tiles were
loaded in a sliding door gas kiln alongside normal pottery. Pilot
lights were started immediately after loading to slowly warm the
brick kiln and the chimney, such that air draw would be initiated.
After roughly 4 hours of pilot light heat, burners were started on
a very low setting, left on overnight, and slowly heated the kiln
to roughly 800-1000 degrees by the next morning with a slightly
reductive atmosphere via CO production via natural gas combustion.
The next morning, burners were put on 2 pounds of gas pressure,
such that the kiln is put into a soft reduction climb and
monitored. Upon reaching cone 012, .about.1640.degree. F., gas
pressure is increased to 3 pounds and the chimney damper is pushed
in slightly, limiting the amount of oxygen access to the combustion
process and thus creating an aggressively reductive atmosphere in
the kiln. This change is visible by a significant difference in
flame color (red-orange), soft movement of flame inside the kiln,
and by soot production. This atmosphere is maintained up to roughly
cone 04, .about.1940.degree. F., after which a softer reduction
atmosphere is created by allowing increased chimney air flow. This
softer reductive atmosphere is maintained for the remainder of the
firing to cone 10, 2345.degree. F., after which the gas is shut
off, all ports are closed, and the kiln is allowed to cool slowly
over 36 hours to prevent cracking/crazing/dunting of the ceramic
surfaces.
[0035] In order to characterize the Au NPs post-firing, crushed
portions of the fired glaze tiles were suspended in ethanol and
deposited on copper 400-mesh TEM grids. Images of glaze tiles were
obtained for each set of samples in reduction and oxidation at
0.015%, 0.050%, and 0.100% AuNP both with and without 4% SnO.sub.2
opacifier. TEM imaging of the tiles was performed. The glaze exists
as a silicate matrix with the Au NPs locked in a solid suspension
and distributed throughout. TEM imaging analysis of the samples
showed large silicate glaze grains with Au NP initially visible at
the edge of grains. In these, imaging of the particles was
performed by focusing down, through cross-sections of grains, in
which some few Au NPs are in focus and others are blurred dependent
on the depth of focus into the grain and the depth of each
respective particle in relation to that focus. Multiple images were
taken of each sample at 80 kV, 50,000.times. magnification, such
that roughly 100 particles could be used for sizing analysis and
histogram generation.
[0036] As shown in FIGS. 3a-3c, Au NPs are observable at the lowest
gold NP loading reduction sample, 0.015%, with consistent particle
sizing analysis through the 0.050% and 0.100% Au salt tiles. For
the reduced neat tiles, Au NPs were imaged with average particle
diameters of 4.7.+-.0.7 nm, 5.5.+-.1.4 nm, and 5.0.+-.0.6 nm for
the 0.015%, 0.050%, and 0.100% Au samples, respectively. For the
oxidized neat tiles, particle sizing revealed diameters of
5.2.+-.0.7 nm, 4.2.+-.0.7 nm, and 5.2.+-.1.0 nm for the 0.015%,
0.050%, and 0.100% Au samples, respectively. Interestingly, these
diameters are statistically similar across reduction and oxidation
atmosphere firings, despite drastic differences in atmosphere and
visible color. Further, the Au NP particle diameter is reduced by
roughly half by both firing processes. The Au NP red tiles in FIGS.
3a-3c did not include SnO.sub.2 opacifier.
[0037] As shown in FIGS. 4a-4c, similar trends were observed in
particle size across oxidative and reductive firing methods for
both systems with 4% SnO.sub.2 opacifier. For the reduced tiles
with 4% SnO.sub.2, Au NPs were imaged with average particle
diameters of 5.2.+-.0.7 nm, 4.4.+-.0.7 nm, and 4.7.+-.0.3 nm for
the 0.015%, 0.050%, and 0.100% Au samples, respectively. For the
oxidized samples with 4% SnO.sub.2, particle sizing analysis
revealed diameters of 5.2.+-.0.7 nm, 4.1 .+-.0.6 nm, and 5.2.+-.0.9
nm for the 0.015%, 0.050%, and 0.100% Au samples, respectively.
Again, all particle diameters are statistically similar. The effect
of the 4% SnO.sub.2 opacifier is notable in FIG. 4c where some
slight brightening is shown in the reduction tile. For reduced
samples, color is immediately visible at 0.015% Au loading and
intensifies up to and through 0.100% Au. This is true for both the
neat and opacified samples fired in a reduction atmosphere. For the
oxidation tiles, no red color is visible at the lowest loading
(0.015%) while a faint pink color becomes visible at 0.050% AuNP
and retains a roughly consistent red intensity at 0.100%.
[0038] For the reduction atmosphere glaze samples, TEM analysis
revealed stable Au NP suspended within the glaze. In the recipe, no
other metal colorant was included; additionally, the original glaze
is a clear base. This presence of color and imaging of Au NP
supports the presence and majority contributor of color from
plasmon resonance of the Au NP. Surprisingly, the faint pink color
of the oxidation-fired samples is likely due to plasmon resonance
as well, as the particles can be imaged via TEM and are
statistically similar in size but appear to be present in less
concentrated amounts.
[0039] Referring to FIGS. 3a-3c and 4a-4c, color trends are similar
for the opacified samples as that of the neat samples between
reduction and oxidation-fired tiles. No significant brightening was
observed in the oxidation tiles, though opacity was noticeable
alongside a pink/faint red tint. Again, all samples possessed Au
NPs, imaged via TEM analysis, which possessed statistically similar
size distributions.
[0040] Additionally, the NP-doped glaze material can be both dipped
and spray-applied to ceramic surfaces, fired under traditional
reduction methods, to create functional, low metal-loading wares,
as seen in FIG. 5. At 39 mg of HAuCl.sub.4 per 100 mL batch of
colloidal AuNP, this mug contains (at most, after centrifugation)
23 mg Au metal for color. With the current market rate of gold at
1,214 $/ounce, this mug costs roughly 0.98 $ USD in gold.
[0041] Returning to FIG. 1, compared to traditional red glazes with
metal oxide colorants and coordination environment
brighteners/opacifiers ranging from 2 to 11% by weight--the use of
Au NPs for low metal loading color alternatives through plasmon
resonance allows for comparable color systems with anywhere from 20
to nearly 1000-fold less bulk metal loading. These colors and
surfaces are comparable to current systems that wastefully use bulk
metal at the glaze surface. With color appearance at 0.015% Au and
stable, hearty color present at 0.100% Au, this work presents a new
color alternative that is both ecologically and environmentally
advantageous.
[0042] The first embodiments described above are directed to a Au
NP-based glaze for use in an alternate, cost-effective, and safer
process to color ceramics. Exemplary formulations of this glaze
include 0.015%, 0.050%, and 0.100% gold nanoparticle loading
content and can be used in both traditionally reduction and
oxidation kiln atmospheres. The resulting color of the ceramic with
the use of this new nanoparticle-based glaze is achieved with 50 to
800-fold decrease in heavy metal consumption compared to
traditional, existing colored glazes. The color attained with this
new glaze utilizes the surface plasmon resonance effect known to
exist in these nanomaterials. The gold nanoparticle synthesis,
itself, is known and commonly used for a variety of applications;
however, it has not previously been adapted to being incorporated
into a glaze base or adapted to raw glaze precursors.
[0043] As discussed above, Au NP particle size is diminished and a
purple color is observed in the final product in both the oxidation
and in reduction kiln atmospheres. And though both firing
environments retained Au NPs, the reduction atmosphere firing
method demonstrated more substantial color.
[0044] Armed with the results discussed above, additional testing
was completed to better understand why, all other variables being
equal, the reduction atmosphere firing method produced more
substantial color. It was hypothesized that during the reduction
firing, the atmosphere was conducive to the spontaneous formation
of NPs. Accordingly, though the size and number of NPs was reduced
during both oxidation and reduction firing, a reductive environment
results in a larger number of remaining NPs as compared to the
oxidative environment. A higher concentration of NPs provides more
surface area for effectuating the surface plasmon resonance of the
Au NPs which relates to color reflectance.
[0045] To test this hypothesis, first glazes containing different
sizes of Au NPs were prepared. FIGS. 6a-6c are TEM images of the
varying solutions before firing with inset histograms of particles
size distribution of each batch (n=100). Batch A yielded Au NPs
with diameters of 21.0.+-.3.0 nm (n=100). Batch B yielded Au NPs
with diameters of 38.7.+-.3.4 nm (n=100). Batch C yielded Au NPs
with diameters of 57.5.+-.10.5 nm (n=100).
[0046] Next, each Au NP glaze was fired in both a reduction kiln
and an oxidation kiln. The results of firing are illustrated in
FIGS. 7a-7c. After oxidation firing, the glazes produced visibly
less intense colors, suggesting a significant decrease in NP
concentration. MS Au NP glazes produced light pink hues for all
three batches A, B and C. Samples were obtained from all tiles,
imaged via TEM, and particle sizing analysis performed on each
sample (n=100). Batch A yielded particle sizes of 5.4.+-.0.7 nm.
Batch B produced particle sizes of 15.1.+-.4.8 nm. Batch C produced
particles sizes of 24.2.+-.8.2 nm. All three batches had normal
size distribution for samples produced in the oxidation
atmosphere.
[0047] After reduction firing, all three batches resulted in
similarly distributed sizes and created similar or roughly
identical colors, with a large number of particles in the 10 nm
range. This is suggestive of renucleation and growth during firing
in a reductive atmosphere. In a gas reduction firing, lower oxygen
levels in the kiln allows for incomplete combustion within the
kiln, yielding high concentrations of carbon monoxide. The accepted
mechanism for ceramic glaze reduction is such that the carbon
monoxide strikes the surface of ceramic body, abstracting oxygen
from the surface of the glazes, forming CO.sub.2, and reducing the
glaze surface. While heat during firing allows for the degradation
of NPs, this reductive atmosphere allows for the reduction of free
Au atoms, nucleation, and finally reformation into NPs via growth.
The reformation of new nanoparticles in a reductive firing would
provide for smaller but more abundant Au NPs in the glaze, which
allows for consistently vibrant colors regardless of starting size.
The concentration of NPs in these glazes can be directly related to
color reflectance due to the surface plasmon resonance of the Au
NPs.
[0048] Referring to FIGS. 8a-8c, as the concentration of Au NPs
increase, the intensity of color increases. Samples were analyzed
using an Ocean Optics Halogen lamp (HL-2000-FHSA) and Flame
miniature spectrometer (FLAME-S-VIS-NIR-ES, 350-1000 nm) to
quantify the produced colors. Percent reflectance of the samples
was measured using the spectrometer. Percent reflectance has a
reciprocal relationship with color intensity; darker samples
demonstrate a lower reflectance profile and a somewhat more
pronounced reflectance color band, while the lighter samples have a
higher reflectance profile, as more total light is reflecting off
of the samples and individual color bands are less pronounced.
[0049] The glazed samples were also analyzed using TEM in order to
assess NP characteristics. FIG. 9 shows NP particle size trends
from batches A-C post-firing in both reduction and oxidation kilns
as compared to an original batch (O) particle size as synthesized
and characterized as shown in FIGS. 2a-b above. As discussed, the
results shown support the hypothesis that the reduction process
promotes renucleation and growth, i.e., spontaneous formation, of
NPs during firing. A reduction atmosphere causes consistent NP
degradation for all four samples. The average diameters of the
reduced MS NP samples were all statistically similar to each other.
The oxidative atmosphere, conversely, produces particles with
diameters that are more relative to their original starting size
for Batch A. As the starting particle size increases, the final
particle size after firing becomes larger. This phenomenon is
consistent with the mechanisms proposed above. As the oxidative
atmosphere does not promote significant renucleation and growth,
the reduced Au atoms nucleate and grow to shift statistical
averages down--with oxidative samples demonstrating larger particle
diameter averages. The similar color profiles of the oxidized MS NP
samples in FIGS. 8a-8b and increasing particle sizes in FIG. 9
suggest that the color is dependent on both the concentration and
diameters of the Au NPs. Although batches O and A have the smallest
particles, they appear to be in a greater abundance within the
glaze after firing. Similarly, batch C has the largest particles
but fewer NPs overall--demonstrating less intense color in FIG.
7c.
[0050] The demonstration and realization of spontaneous NP
formation during firing, may support removal of the NP synthesis
step prior to kiln sintering. Thus, skipping the expensive and
tedious steps of traditional nanoparticle synthesis, the
embodiments provide further benefits and efficiencies over the
prior art by facilitating a more direct process. Additionally, the
processes described above with respect to Au NPs are also
applicable to other materials, including silver (Ag), thus
expanding the achievable color range.
[0051] To prove out these efficiencies, HAuCl.sub.4, aggregated Au
NP waste (Au Agg) collected from previous Au NP experiments such as
those discussed herein, AgNO.sub.3, as well purchased Ag NPs were
used to prepare 4 separate glazes. More particularly, glazes
consisted of 20% Kaolin EPK, 19% silica, 6% talc, 20% frit 3134,
15% wollastinite, and 20% G-200 feldspar. 38.39 mg of HAuCl.sub.4
and 100 mg of AgNO.sub.3 were added to 160 g and 200 g glaze
batches, respectively. Aggregated Au NPs were added to a 200 g
glaze batch referenced above. Silver NP solution (10 mL) was added
to 80 g glaze batches of the glaze formulation mentioned above.
Ceramic samples were then dipped in each of the four (4) glazes and
fired in both reductive and oxidative kilns at cones 10
(1285.degree. C., 2345.degree. F.) and 6 (1200.degree. C.,
2200.degree. F.), respectively.
[0052] After firing, glazes from the fired samples were prepared
and imaged using TEM. FIG. 10a shows gold nanoparticle aggregate
(Au NP Agg). FIG. 10b shows Ag NP with particle size distribution
graph overlaid for 20 nm silver nanoparticles. Referring to FIGS.
11a-11d, the reduction-fired HAuCl.sub.4 glaze (FIG. 11a, R) is a
dark red-purple color that was comparable to that first synthesized
and imaged in FIGS. 3a-3c (R), 4a-4c (R) and 7a-7c (R), suggesting
the presence of Au NPs. The oxidized sample (FIG. 11a, O) also has
a similar color profile to FIGS. 3a-3c (O), 4a-4c (O) and 7a-7c
(O). The reduced AgNO.sub.3 glaze (FIG. 11b (R)) resulted in a
burnt laurel green glaze. The oxidized AgNO.sub.3 sample (FIG. 11b
(O)) resulted in a very light white-green color. Reduced Au Agg
(FIG. 11c (R)) produced a light red-brown color, and the oxidized
sample (FIG. 11c (O)) produced an orange glaze. Reduced Ag NP (FIG.
11d (R)) produced a light jade color, while the oxidized sample
(FIG. 11d (O)) produced almost no color. For all eight samples,
there is nanoparticle formation as seen in FIGS. 11a-11d and for
all four glazes from different metal precursors, the oxidized
samples (O) yielded nanoparticles that were significantly larger
than their respective reduced sample (R) equivalent. Both free Au
NPs and aggregated Au NPs were observed in the reduced sample of Au
agg. For the oxidized Ag NP sample, 200 NPs were measured instead
because a small percentage of particles were so large that the
standard deviation was greater than the average particle
diameter.
[0053] Reflectance spectra measurements were also taken. The color
profiles are shown in the reflectance spectra graphs in FIGS.
12a-12d, wherein FIG. 12a shows reflectance spectra for HAuCl.sub.4
glaze, FIG. 12b shows reflectance spectra for AgNO.sub.3 glaze,
FIG. 12c shows reflectance spectra for Au Agg glaze and FIG. 12d
shows reflectance spectra for Ag NP glaze. Higher percent
reflectance corresponds to more pale colors. Lower percent
reflectance corresponds to a darker, more vibrant color. And the
relationship between number of nanoparticles in the glaze with
reflectance and this color vibrance can be described as follows: as
the number of nanoparticles increases within a glaze profile, the
color becomes deeper and results in a lower percent reflectance and
as the percent reflectance increases, the glaze color becomes paler
and less vibrant.
[0054] For reference, a more complete graphing of average NP
diameters for each of the eight glazes is shown in FIG. 13.
[0055] In additional embodiments, varying colors have been achieved
using the more efficient processes described herein using Au--Ag
alloy nanoparticle-suspension ceramic glazes from metal salt
blends, including the unintentional incorporation of Al in these
alloys to supplement plasmon band color and intensity. By way of
example only, the six (6) Au--Ag alloy ratio combinations shown in
Table 2 were prepared and fired.
TABLE-US-00002 % Au HAuCl.sub.4 (mg) AgNO.sub.3 (mg) Glaze 1 100
38.39 0 Glaze 2 80 38.39 8.7 Glaze 3 60 38.39 11.5 Glaze 4 40 38.39
51.7 Glaze 5 20 38.39 137.9 Glaze 6 0 0 500
[0056] One skilled in the art recognizes that these formulations
are merely exemplary. FIGS. 14a and 14b show the colors for each
glaze post-firing in reduction (FIG. 14a) and oxidation (FIG. 14b)
kilns.
[0057] Accordingly, the embodiments herein describe
sintering-induced formation of nanoparticles within reductive and
oxidative kilns to produce a wide variety of colors. Directly
adding the metal salts HAuCl.sub.4 or AgNO.sub.3 to glazes allows
for the formation of gold and silver nanoparticles during both
reductive and oxidative firing processes. Gold aggregate is also
observed to degrade and renucleate into new Au NPs alongside
aggregated materials, resulting in color. Each of these allows for
comparable color profiles to traditional red glazes and previously
reported new Au NPs glazes by recycling nanoparticle synthesis
waste. Further methods with the use of noble metal salts may be
used in modern glaze formulations for natural nucleation and
growth, resulting in low metal loading plasmon resonance coloring.
These methods bypass preliminary nanoparticle synthesis that
require atypical acids, solvents, heat, precision, and specialized
equipment. Furthermore, the low metal levels and relative
bio-inertness of gold and silver lowers the risk of contaminating
food, drinks, or soil with toxic metals and reduces the impact of
mining on the environment.
[0058] The embodiments described herein represent a potential new
standard for low metal loading glazes, in which these systems
require significantly lower metal than the traditional 5-12% metal
loading glazes currently in use. With this decrease in colorant
consumption through nanomaterial plasmon resonance color, a new
standard for environmentally conscious ceramic surface development
is achieved. Additionally, this lower use of materials for color
formation results in lowered ecological impact via reduced energy
consumption for material mining/processing, lowered materials cost
(under 1 $ in gold per batch of glaze, which is enough to prepare
the surface of any functional ceramic), lowered ecological mining
impact, and minimized heavy metal leaching through lower surface
presence of colorants.
[0059] It is respectfully submitted that one skilled in the art
recognizes the various alternative materials, amounts, equipment
and the like which, though not explicitly described herein, are
well within their knowledge and thus are included within the scope
of the embodiments herein.
* * * * *