U.S. patent application number 12/521142 was filed with the patent office on 2010-02-18 for zirconia body and methods.
Invention is credited to Peter Bissinger, Ruediger Franke, Martin Goetzinger, Holger Hauptmann, Jacqueline C. Rolf.
Application Number | 20100041542 12/521142 |
Document ID | / |
Family ID | 39589214 |
Filed Date | 2010-02-18 |
United States Patent
Application |
20100041542 |
Kind Code |
A1 |
Rolf; Jacqueline C. ; et
al. |
February 18, 2010 |
ZIRCONIA BODY AND METHODS
Abstract
A translucent zirconia sintered body, a dental article
comprising a shaped, translucent zirconia body, a zirconia green
body, and methods of making a translucent zirconia sintered body,
methods of making a dental article comprising a shaped, translucent
zirconia body, and methods of making a zirconia green body are
described.
Inventors: |
Rolf; Jacqueline C.; (River
Falls, WI) ; Goetzinger; Martin; (Eching a. Ammersee,
DE) ; Hauptmann; Holger; (Sindelsdorf, DE) ;
Bissinger; Peter; (Diessen, DE) ; Franke;
Ruediger; (Seefeld, DE) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Family ID: |
39589214 |
Appl. No.: |
12/521142 |
Filed: |
December 28, 2007 |
PCT Filed: |
December 28, 2007 |
PCT NO: |
PCT/US07/89057 |
371 Date: |
June 25, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60882714 |
Dec 29, 2006 |
|
|
|
Current U.S.
Class: |
501/104 ; 264/16;
501/103; 501/105 |
Current CPC
Class: |
C01P 2004/64 20130101;
C04B 35/6264 20130101; C04B 2235/77 20130101; C01P 2006/16
20130101; C04B 2235/5454 20130101; C04B 2235/6027 20130101; C04B
35/6263 20130101; C04B 2235/656 20130101; A61K 6/17 20200101; C04B
2235/612 20130101; C04B 2235/3225 20130101; C04B 2235/3251
20130101; C01G 25/00 20130101; C04B 2235/608 20130101; C04B
2235/765 20130101; C04B 2235/96 20130101; C01P 2002/72 20130101;
C04B 2235/9653 20130101; C01P 2004/03 20130101; C04B 2235/5296
20130101; C04B 2235/781 20130101; A61C 8/0012 20130101; A61K 6/818
20200101; B82Y 30/00 20130101; C04B 2235/6562 20130101; C04B 35/64
20130101; C04B 2235/3208 20130101; C04B 2235/3217 20130101; C04B
35/486 20130101; C04B 2235/449 20130101 |
Class at
Publication: |
501/104 ;
501/103; 501/105; 264/16 |
International
Class: |
C04B 35/48 20060101
C04B035/48; A61C 13/20 20060101 A61C013/20 |
Claims
1. A translucent zirconia sintered body comprised of primary
particles and having a density of at least 99 percent of full
density, the primary particles having: a major phase which is
tetragonal zirconium oxide, and a size no greater than 100 nm; and
wherein the diameter of any pores which are present in the zirconia
sintered body is not more than about 25 nm.
2. The translucent zirconia sintered body of claim 1 wherein the
primary particle size is no greater than 50 nm.
3. (canceled)
4. The translucent zirconia sintered body of claim 1 wherein the
percent light transmittance through a 1 mm thickness of the
zirconia sintered body is at least 60% at 350-700 nm.
5-6. (canceled)
7. The translucent zirconia sintered body of claim 1 wherein the
major phase which is tetragonal zirconium oxide comprises at least
70 percent of the zirconium oxide in the primary particles.
8. (canceled)
9. A dental article comprising a shaped, translucent zirconia
sintered body comprised of primary particles and having a density
of at least 99 percent of full density, the primary particles
having: a major phase which is tetragonal zirconium oxide, and a
size no greater than 100 nm; and wherein the diameter of any pores
which are present in the translucent zirconia sintered body is not
more than about 25 nm.
10. The dental article of claim 9 wherein the primary particle size
is no greater than 50 nm.
11-14. (canceled)
15. The dental article of claim 9 wherein the major phase which is
tetragonal zirconium oxide comprises at least 70 percent of the
zirconium oxide in the primary particles.
16-21. (canceled)
22. A method of making a translucent zirconia sintered body
comprising: providing a zirconia green body comprised of primary
particles and having a density of at least 50 percent of full
density, the primary particles having: a major phase which is
tetragonal zirconium oxide, and a size no greater than 50 nm; and
wherein the diameter of any pores which are present in the green
body is not more than about 30 nm; and sintering the zirconia green
body at a temperature no greater than 1200.degree. C. to provide a
translucent zirconia sintered body comprised of primary particles
and having a density of at least 99 percent of full density, the
primary particles having: a major phase which is tetragonal
zirconium oxide, and a size no greater than 100 nm; and wherein the
diameter of any pores which are present in the translucent zirconia
sintered body is not more than about 25 nm.
23. The method of claim 22 further comprising: providing a zirconia
sol comprising zirconia particles having an average primary
particle size no greater than 50 nm; and drying the zirconia sol to
provide the zirconia green body.
24-27. (canceled)
28. The method of claim 23 wherein the zirconia particles have a
dispersion index of 1 to 3, a ratio of intensity-average particle
size to volume-average particle size no greater than 3.0, and a
crystal structure that is at least 70 percent tetragonal.
29. (canceled)
30. The method of claim 23 further including a sintering additive
with the zirconia sol, wherein the sintering additive is selected
from the group consisting of aluminum, niobium, calcium, and oxides
thereof.
31. (canceled)
32. The method of claim 23 wherein drying the zirconia sol is
carried out in a mold.
33-35. (canceled)
36. The method of claim 23 wherein drying the zirconia sol is
carried out by spray drying to form a powder, and compacting the
powder at an elevated temperature to form the green body.
37-39. (canceled)
40. The method of claim 22, wherein a temperature no greater than
1000.degree. C. is used during sintering.
41-47. (canceled)
48. A method of making a dental article comprising: providing a
translucent zirconia sintered body comprised of primary particles
and having a density of at least 99 percent of full density, the
primary particles having: a major phase which is tetragonal
zirconium oxide, and a size no greater than 100 nm; and wherein the
diameter of any pores which are present is not more than about 25
nm; and shaping the translucent zirconia sintered body to provide a
dental article.
49-53. (canceled)
54. The method of claim 48 wherein the major phase which is
tetragonal zirconium oxide comprises at least 70 percent of the
zirconium oxide in the primary particles.
55. (canceled)
56. The method of claim 48 wherein shaping the translucent zirconia
sintered body is carried out by milling.
57-58. (canceled)
59. A method of making a dental article comprising: providing a
zirconia green body comprised of primary particles and having a
density of at least 50 percent of full density, the primary
particles having: a major phase which is tetragonal zirconium
oxide, and a size no greater than 50 nm; and wherein the diameter
of any pores which are present in the zirconia green body is not
more than about 30 nm; sintering the zirconia green body at a
temperature no greater than 1200.degree. C. and for a time
sufficient to form a partially sintered zirconia green body;
shaping the partially sintered zirconia green body; and sintering
the shaped, partially-sintered zirconia green body to provide a
dental article comprising a shaped, translucent zirconia sintered
body comprised of primary particles and having a density of at
least 99 percent of full density, the primary particles having: a
major phase which is tetragonal zirconium oxide, and a size no
greater than 100 nm; and wherein the diameter of any pores which
are present in the shaped, translucent zirconia sintered body is
not more than about 25 nm.
60-62. (canceled)
63. The method of claim 59 wherein sintering the zirconia green
body is carried out at a temperature no greater than 1000.degree.
C. and for a time sufficient to form a partially-sintered zirconia
green body;
64-71. (canceled)
72. The method of claim 59 wherein the major phase which is
tetragonal zirconium oxide comprises at least 70 percent of the
zirconium oxide in the primary particles of the translucent
zirconia sintered body.
73-74. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present invention claims priority to U.S. Provisional
Application Ser. No. 60/882,714, filed Dec. 29, 2006, which is
incorporated herein by reference.
BACKGROUND
[0002] Ceramic bodies made from metal oxide powders have been used
for some time in making dental articles, because of good
biocompatibility and stability under load. These ceramic bodies
have been typically processed by machining, for example, a green
compact or a sintered body using a milling cutter. Green compacts
have been made by compacting the metal oxide powder using cold
isostatic or uniaxial pressing methods. After machining, the green
compact must be sintered to achieve final properties. Sintered
bodies have been made by hot isostatic processing whereby the
starting metal oxide powder is simultaneously compacted and
sintered.
[0003] Aluminum oxide has been particularly important, although
zirconia has been considered, because it has greater mechanical
strength than aluminum oxide. Tetragonal zirconia has exceptional
mechanical strength due to a phase transformation mechanism that is
triggered when a crack propagates into the material, causing the
crack to be arrested. However, tetragonal zirconia is presently
found to be opaque, thus limiting this material from applications
requiring higher translucency, such as dental applications.
Translucent cubic zirconia is known, but it has relatively low
mechanical strength. Therefore, there is a continuing need for
ceramic bodies that have both high strength and translucency.
SUMMARY
[0004] A translucent tetragonal zirconia body has now been
developed. In one aspect, therefore, the present invention provides
a translucent zirconia sintered body useful in dental articles. In
one embodiment, there is provided a translucent zirconia sintered
body comprised of primary particles and having a density of at
least 99 percent of full density, the primary particles having:
[0005] a major phase which is tetragonal zirconium oxide, and
[0006] a size no greater than 100 nm; and
wherein the diameter of any pores which are present in the zirconia
sintered body is not more than about 25 nm.
[0007] In another embodiment, there is provided a dental article
comprising a shaped, translucent zirconia sintered body comprised
of primary particles and having a density of at least 99 percent of
full density, the primary particles having:
[0008] a major phase which is tetragonal zirconium oxide, and
[0009] a size no greater than 100 nm; and
wherein the diameter of any pores which are present in the
translucent zirconia sintered body is not more than about 25
nm.
[0010] In another aspect, the present invention provides a zirconia
green body useful for making translucent zirconia sintered bodies
and dental articles. In one embodiment, there is provided a
zirconia green body comprised of primary particles and having a
density of at least 50 percent of full density, the primary
particles having:
[0011] a major phase which is tetragonal zirconium oxide, and
[0012] a size no greater than 50 nm; and
wherein the diameter of any pores which are present in the green
body is not more than about 30 nm.
[0013] In another aspect, the present invention provides methods of
making translucent zirconia sintered bodies, zirconia green bodies,
and dental articles.
[0014] In one embodiment, there is provided a method of making a
translucent zirconia sintered body comprising:
[0015] providing a zirconia green body comprised of primary
particles and having a density of at least 50 percent of full
density, the primary particles having: [0016] a major phase which
is tetragonal zirconium oxide, and [0017] a size no greater than 50
nm; and wherein the diameter of any pores which are present in the
green body is not more than about 30 nm; and
[0018] sintering the zirconia green body at a temperature no
greater than 1200.degree. C. to provide a translucent zirconia
sintered body comprised of primary particles and having a density
of at least 99 percent of full density, the primary particles
having: [0019] a major phase which is tetragonal zirconium oxide,
and [0020] a size no greater than 100 nm; and wherein the diameter
of any pores which are present in the translucent zirconia sintered
body is not more than about 25 nm.
[0021] In another embodiment, there is provided a method of making
a zirconia green body comprising:
[0022] providing a zirconia sol comprising zirconia particles
having an average primary particle size no greater than 50 nm;
[0023] drying the zirconia sol to form a zirconia green body
comprised of primary particles and having a density of at least 50
percent of full density, the primary particles having:
[0024] a major phase which is tetragonal zirconium oxide, and
[0025] a size no greater than 50 nm; and
wherein the diameter of any pores which are present in the green
body is not more than about 30 nm.
[0026] In another embodiment, there is provided a method of making
a dental article comprising:
[0027] providing a translucent zirconia sintered body comprised of
primary particles and having a density of at least 99 percent of
full density, the primary particles having:
[0028] a major phase which is tetragonal zirconium oxide, and
[0029] a size no greater than 100 nm; and
wherein the diameter of any pores which are present is not more
than about 25 nm; and
[0030] shaping the translucent zirconia sintered body to provide a
dental article.
[0031] In another embodiment, there is provided a method of making
a dental article comprising:
[0032] providing a zirconia green body comprised of primary
particles and having a density of at least 50 percent of full
density, the primary particles having:
[0033] a major phase which is tetragonal zirconium oxide, and
[0034] a size no greater than 50 nm; and
[0035] wherein the diameter of any pores which are present in the
zirconia green body is not more than about 30 nm;
[0036] sintering the zirconia green body at a temperature no
greater than 1200.degree. C. and for a time sufficient to form a
partially sintered zirconia green body;
[0037] shaping the partially sintered zirconia green body; and
[0038] sintering the shaped, partially-sintered zirconia green body
to provide a dental article comprising a shaped, translucent
zirconia sintered body comprised of primary particles and having a
density of at least 99 percent of full density, the primary
particles having:
[0039] a major phase which is tetragonal zirconium oxide, and
[0040] a size no greater than 100 nm; and
[0041] wherein the diameter of any pores which are present in the
shaped, translucent zirconia sintered body is not more than about
25 nm.
DEFINITIONS
[0042] As used herein, the term "translucent" refers to a percent
light transmittance of at least 50% for wavelengths 350-700 nm
through a 1 mm thickness of a ceramic body.
[0043] As used herein, the terms "sintered" and "sintering" refer
to a reduction in size and/or number or the elimination of
interparticle pores in a granular structure comprised of particles
by heating without melting.
[0044] As used herein, the term "body" or variations thereof refers
to a three-dimensional structure.
[0045] As used herein, the term "zirconia green body" refers to a
three-dimensional granular structure comprised of zirconium oxide
particles, which is not sintered or is partially sintered.
[0046] As used herein, the term "full density" refers to the
density of a pore-free body.
[0047] As used herein, the term "major phase" refers to a crystal
phase that is present in the primary particles in an amount such
that this phase comprises more than 50% of the zirconium oxide in
the primary particles.
[0048] As used herein, the term "primary particle size" refers to
the size of a non-associated single crystal zirconia particle.
X-ray Diffraction (XRD) can be used to measure the primary particle
size.
[0049] As used herein, the term "sol" refers to a dispersion or
suspension of colloidal particles in a liquid phase (e.g., aqueous
medium). The particles in the sol are typically not agglomerated or
aggregated.
[0050] As used herein, the term "zirconia" refers to various
stoichiometries for zirconium oxides, most typically ZrO.sub.2, and
may also be known as zirconium oxide or zirconium dioxide. The
zirconia may contain up to 30 weight percent of oxides of other
chemical elements such as, for example, oxides of yttrium (e.g.,
Y.sub.2O.sub.3).
[0051] As used herein, the term "associated" refers to a grouping
of two or more primary particles that are aggregated and/or
agglomerated. Similarly, the term "non-associated" refers to
groupings of two or more primary particles that are free from
aggregation and/or agglomeration.
[0052] As used herein, the term "aggregation" refers to a strong
association between primary particles. For example, the primary
particles may be chemically bound to one another. The breakdown of
aggregates into smaller particles (e.g., primary particles) is
generally difficult to achieve.
[0053] As used herein, the term "agglomeration" refers to a weak
association of primary particles. For example, the primary
particles may be held together by charge or polarity. The breakdown
of agglomerates into smaller particles (e.g., primary particles) is
less difficult than the breakdown of aggregates into smaller
particles.
[0054] As used herein, the term "hydrodynamic particle size" refers
to the volume-average particle size of the zirconia particles in a
liquid phase as measured by Photon Correlation Spectroscopy (PCS)
using the method described herein.
[0055] As used herein, the term "hydrothermal" refers to a method
of heating an aqueous medium, in a closed vessel, to a temperature
above the normal boiling point of the aqueous medium at a pressure
that is equal to or greater than the pressure required to prevent
boiling of the aqueous medium.
[0056] The term "comprising" and variations thereof (e.g., having,
comprises, etc.) do not have a limiting meaning where these terms
appear in the description and claims.
[0057] Also herein, the recitations of numerical ranges by
endpoints include all numbers subsumed within that range (e.g., at
least 50 percent includes 50, 50.5, 55, 60, 67.5, 70, 73.8,
etc.).
[0058] The above summary of the present invention is not intended
to describe each disclosed embodiment or every implementation of
the present invention. The description that follows more
particularly exemplifies illustrative embodiments. In several
places throughout the application, guidance is provided through
lists of examples, which examples can be used individually and in
various combinations. In each instance, the recited list serves
only as a representative group and should not be interpreted as an
exclusive list.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] FIG. 1 is a representative x-ray diffraction pattern for an
exemplary translucent zirconia sintered body having tetragonal
zirconia as the major phase.
[0060] FIG. 2 is a scanning electron microscopy (SEM) image of an
exemplary translucent sintered zirconia body.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE
INVENTION
[0061] Until now, tetragonal zirconia bodies were obtainable only
as an opaque material or a translucent material having a percent
light transmittance of less than 40%. The opacity of previous
tetragonal zirconia is attributed to light scattering caused by
various lattice parameters of the crystal structure, as well as
large particle and pore sizes in these bodies. However, a
translucent zirconia sintered body comprising tetragonal zirconia
can now be provided, at least in part, by making the size of the
primary particles of the sintered body no greater than 100 nm. In
one embodiment, therefore, the present invention provides a
translucent zirconia sintered body comprised of primary particles
and having a density of at least 99 percent of full density, the
primary particles having:
[0062] a major phase which is tetragonal zirconium oxide, and
[0063] a size no greater than 100 nm; and
wherein the diameter of any pores which are present in the zirconia
sintered body is not more than about 25 nm.
[0064] As the primary particle size is reduced relative to the
wavelength of light being transmitted, light scattering caused by
the primary particles can be minimized or even eliminated. For
certain embodiments of the translucent zirconia sintered body, the
primary particle size is preferably no greater than 50 nm. For
certain of these embodiments, the primary particle size is no
greater than 25 nm.
[0065] For certain embodiments, including any one of the above
embodiments of the translucent zirconia sintered body, the percent
light transmittance through a 1 mm thickness of the zirconia
sintered body is at least 60% at 350-700 nm. For certain of these
embodiments, the percent light transmittance is at least 70%.
[0066] The translucent zirconia sintered body can provide high
flexural or bending strength because of the presence of tetragonal
zirconia as the major crystal phase of the primary particles
comprising the sintered body. For certain embodiments, including
any one of the above embodiments of the translucent zirconia
sintered body, the flexural strength of the zirconia sintered body
is at least 600 MPa. For certain of these embodiments, the flexural
strength of the zirconia sintered body is at least 800 MPa. For
certain of these embodiments, the flexural strength of the zirconia
sintered body is at least 1000 MPa. Flexural strength can be
measured via a 3-point bend test per ASTM standard C1161.
Dimensions of the test fixture and test specimen can be altered to
accommodate other sizes of samples as long as the equations to
calculate the strength values are corrected accordingly.
[0067] For certain embodiments, including any one of the above
embodiments of the translucent zirconia sintered body, the major
phase which is tetragonal zirconium oxide comprises at least 70
percent of the zirconium oxide in the primary particles. For
certain of these embodiments, the major phase which is tetragonal
zirconium oxide comprises at least 80 percent, at least 90 percent,
at least 95 percent, or at least 99 percent of the zirconium oxide
in the primary particles.
[0068] The amount of the zirconium oxide in the primary particles
that is tetragonal zirconium oxide was determined using x-ray
diffraction pattern analysis whereby the levels of tetragonal and
cubic zirconia can be most easily distinguished by an examination
of the positions of the tetragonal (220), tetragonal (400), and
cubic (400) peaks that occur in the 71 to 76 degree (two-theta)
scattering angle range. The tetragonal (220) and (400) peak
positions provide direct evaluation of the tetragonal (a) and (c)
lattice parameters, respectively, and the cubic (400) maximum
provides direct evaluation of the cubic (a.sub.0) lattice
parameter. The lattice parameters are calculated from peak
positions corrected by use of a silicon internal standard. By this
analysis, the major zirconia phase present in the translucent
zirconia sintered bodies appeared to be solely the tetragonal form
as shown in the representative x-ray diffraction pattern of FIG. 1.
There was no direct evidence for the presence of the cubic form of
zirconia in the translucent zirconia sintered bodies, although with
this analysis a small amount of cubic zirconia could be
present.
[0069] The translucent zirconia sintered body has a low pore size,
which is established during deposition of zirconia nanoparticles
and is maintained through sintering. Light scattering resulting
from the presence of large pores is, therefore, avoided in the
present zirconia sintered body. For certain embodiments, the
diameter of any pores which are present in the translucent zirconia
sintered body is not more than about 20 nm. For certain
embodiments, the diameter of any pores which are present in the
translucent zirconia sintered body is not more than about 10 nm.
For certain embodiments, the diameter of any pores which are
present in the translucent zirconia sintered body is not more than
about 5 nm.
[0070] The translucent zirconia sintered body can be shaped by
conventional machining methods to provide a dental article.
Accordingly, in another embodiment, there is provided a dental
article comprising a shaped, translucent zirconia sintered body
comprised of primary particles and having a density of at least 99
percent of full density, the primary particles having:
[0071] a major phase which is tetragonal zirconium oxide, and
[0072] a size no greater than 100 nm; and
wherein the diameter of any pores which are present in the
translucent zirconia sintered body is not more than about 25
nm.
[0073] For certain embodiments of the dental article, the primary
particle size of the shaped, translucent zirconia sintered body is
no greater than 50 nm. For certain of these embodiments, the
primary particle size is no greater than 25 nm.
[0074] For certain embodiments, including any one of the above
embodiments of the dental article, the percent light transmittance
through a 1 mm thickness of the translucent zirconia sintered body
is at least 60% at 350-700 nm. For certain of these embodiments,
the percent light transmittance is at least 70%.
[0075] For certain embodiments, including any one of the above
embodiments of the dental article, the flexural strength of the
translucent zirconia sintered body is at least 600 MPa. For certain
of these embodiments, the flexural strength of the translucent
zirconia sintered body is at least 800 MPa. For certain of these
embodiments, the flexural strength of the zirconia sintered body is
at least 1000 MPa.
[0076] For certain embodiments, including any one of the above
embodiments of the dental article, the major phase which is
tetragonal zirconium oxide comprises at least 70 percent of the
zirconium oxide in the primary particles. For certain of these
embodiments, the major phase which is tetragonal zirconium oxide
comprises at least 80 percent, at least 90 percent, at least 95
percent, or at least 99 percent of the zirconium oxide in the
primary particles.
[0077] For certain embodiments, including any one of the above
embodiments of the dental article, the diameter of any pores which
are present in the translucent zirconia sintered body is not more
than about 20 nm. For certain of these embodiments, the diameter of
any pores which are present in the translucent zirconia sintered
body is not more than about 10 nm. For certain of these
embodiments, the diameter of any pores which are present in the
translucent zirconia sintered body is not more than about 5 nm.
[0078] The dental article in the above embodiments includes any
format of a product for placement in the oral environment, wherein
high flexural strength and translucency in the product are
advantageous. For certain embodiments, the dental article is
selected from the group consisting of a crown, a bridge, a
framework, an abutment, an inlay, an onlay, an implant, and an
orthodontic bracket. A framework includes a substructure, or part
for a crown or bridge, for example, a coping for a crown.
Additional material or structure, for example, a veneer, may be
optionally applied to a framework prior to placement in the oral
environment. For certain of these embodiments, the dental article
is a crown, a bridge, or an abutment.
[0079] In another aspect, a new zirconia green body is provided,
which is useful for making translucent zirconia sintered bodies and
dental articles comprising the translucent zirconia sintered
bodies. The new zirconia green body has a microstructure, including
a low pore size and low primary particle size, that can ultimately
serve as the basis for the translucency and strength properties of
the above described translucent zirconia sintered body.
Accordingly, in one embodiment, there is provided a zirconia green
body comprised of primary particles and having a density of at
least 50 percent of full density, the primary particles having:
[0080] a major phase which is tetragonal zirconium oxide, and
[0081] a size no greater than 50 nm; and
wherein the diameter of any pores which are present in the green
body is not more than about 30 nm.
[0082] The low pore size contributes to a higher density. For
certain embodiments, the zirconia green body has a density which is
at least 65 percent of full density. For certain of these
embodiments, the density is at least 75 percent of full
density.
[0083] For certain embodiments, including any one of the above
embodiments of the zirconia green body, the primary particle size
is no greater than 25 nm.
[0084] For certain embodiments, including any one of the above
embodiments of the zirconia green body, the diameter of any pores
which are present in the green body is not more than about 25 nm.
For certain of these embodiments, the diameter of any pores which
are present in the green body is not more than about 20 nm.
[0085] For certain embodiments, including any one of the above
embodiments of the zirconia green body, the major phase which is
tetragonal zirconium oxide comprises at least 70 percent of the
zirconium oxide in the primary particles of the zirconia green
body. For certain of these embodiments, the major phase which is
tetragonal zirconium oxide comprises at least 80 percent, at least
90 percent, at least 95 percent, or at least 99 percent of the
zirconium oxide in the primary particles.
[0086] In another aspect, the present invention provides methods of
making translucent zirconia sintered bodies, zirconia green bodies,
and dental articles. Accordingly, in one embodiment, there is
provided a method of making a translucent zirconia sintered body
comprising:
[0087] providing a zirconia green body comprised of primary
particles and having a density of at least 50 percent of full
density, the primary particles having: [0088] a major phase which
is tetragonal zirconium oxide, and [0089] a size no greater than 50
nm; and wherein the diameter of any pores which are present in the
green body is not more than about 30 nm; and
[0090] sintering the zirconia green body at a temperature no
greater than 1200.degree. C. to provide a translucent zirconia
sintered body comprised of primary particles and having a density
of at least 99 percent of full density, the primary particles
having: [0091] a major phase which is tetragonal zirconium oxide,
and [0092] a size no greater than 100 nm; and wherein the diameter
of any pores which are present in the translucent zirconia sintered
body is not more than about 25 nm. For certain of these
embodiments, the zirconia green body is provided by providing a
zirconia sol comprising zirconia particles having an average
primary particle size no greater than 50 nm; and drying the
zirconia sol to provide the zirconia green body.
[0093] In another embodiment, there is provided a method of making
a zirconia green body comprising:
[0094] providing a zirconia sol comprising zirconia particles
having an average primary particle size no greater than 50 nm;
[0095] drying the zirconia sol to form a zirconia green body
comprised of primary particles and having a density of at least 50
percent of full density, the primary particles having:
[0096] a major phase which is tetragonal zirconium oxide, and
[0097] a size no greater than 50 nm; and
wherein the diameter of any pores which are present in the green
body is not more than about 30 nm.
[0098] The zirconia sol comprising zirconia particles can be made
as described in U.S. Patent Application Publication Nos.
2006/0148950 and 2006/0204745. Preparation of the zirconia sol is
also described below.
[0099] For certain embodiments, the zirconia sol is provided
containing zirconia particles dispersed in an aqueous medium that
includes a carboxylic acid. The carboxylic acid contains no greater
than four carbon atoms and is substantially free of a polyether
carboxylic acid. For certain of these embodiments, the carboxylic
acid is acetic acid.
[0100] For certain embodiments, including any one of the above
embodiments where a zirconia sol containing zirconia particles is
provided, the zirconia particles contain 0.1 to 8 weight percent
yttrium based on the weight of the inorganic oxides in the zirconia
particles.
[0101] For certain embodiments, including any one of the above
embodiments where a zirconia sol containing zirconia particles is
provided, the zirconia particles have an average primary particle
size no greater than 40 nanometers. For certain of these
embodiments, the average primary particle size is no greater than
30 nanometer. For certain of these embodiments, the average primary
particle size is no greater than 25 nanometers. For certain of
these embodiments, the average primary particle size is no greater
than 20 nanometers. For certain of these embodiments, the average
primary particle size is no greater than 10 nanometers. For certain
of these embodiments, the average primary particle size is no
greater than 5 nanometers. The primary particle size, which refers
to the non-associated particle size of the zirconia particles, can
be determined by x-ray diffraction
[0102] For certain embodiments, including any one of the above
embodiments where a zirconia sol containing zirconia particles is
provided, the zirconia particles have a dispersion index of 1 to 5,
a ratio of intensity-average particle size to volume-average
particle size no greater than 3.0, and a crystal structure that is
more than 50 percent tetragonal. For certain of these embodiments,
the zirconia particles have a dispersion index of 1 to 3, a ratio
of intensity-average particle size to volume-average particle size
no greater than 3.0, and a crystal structure that is at least 70
percent tetragonal.
[0103] The particles of zirconia tend to exist in a substantially
non-associated (i.e., non-aggregated and non-agglomerated) form in
the sol. The extent of association between the primary particles
can be determined from the hydrodynamic particle size. The
hydrodynamic particle size is measured using Photon Correlation
Spectroscopy and is described in more detail in the Examples
section. The term "hydrodynamic particle size" and "volume-average
particle size" are used interchangeably herein. If the particles of
zirconia are associated, the hydrodynamic particle size provides a
measure of the size of the aggregates and/or agglomerates of
primary particles in the zirconia sol. If the particles of zirconia
are non-associated, the hydrodynamic particle size provides a
measure of the size of the primary particles.
[0104] A quantitative measure of the degree of association between
the primary particles in the zirconia sol is the dispersion index.
As used herein the "dispersion index" is defined as the
hydrodynamic particle size divided by the primary particle size.
The primary particle size (e.g., the weighted average crystallite
size) is determined using x-ray diffraction techniques and the
hydrodynamic particle size (e.g., the volume-average particle size)
is determined using Photon Correlation Spectroscopy. As the
association between primary particles in the sol decreases, the
dispersion index approaches a value of 1. The zirconia particles
typically have a dispersion index of 1 to 5, 1 to 4, 1 to 3, 1 to
2.5, or 1 to 2.
[0105] Photon Correlation Spectroscopy can be used to further
characterize the zirconia particles in the sol. For example, the
intensity of the light scattered by particles is proportion to the
sixth power of the particle diameter. Consequently, the
light-intensity distribution tends to be more sensitive to larger
particles than smaller ones. The intensity-average size (e.g.,
measured in nanometers) is, in effect, the size of a particle that
corresponds to the mean value of the light intensity distribution
measured by the instrument. The zirconia particles tend to have an
intensity-average size that is no greater than 70 nanometers, no
greater than 60 nanometers, no greater than 50 nanometers, no
greater than 40 nanometers, no greater than 35 nanometers, or no
greater than 30 nanometers.
[0106] The light-intensity distribution obtained during analysis
using Photon Correlation Spectroscopy can be combined with the
refractive indices of the particles and the refractive index of the
suspending medium to calculate a volume distribution for spherical
particles. The volume distribution gives the percentage of the
total volume of particles corresponding to particles of a given
size range. The volume-average size is the size of a particle that
corresponds to the mean of the volume distribution. Since the
volume of a particle is proportional to the third power of the
diameter, this distribution is less sensitive to larger particles
than the intensity-average size. That is, the volume-average size
will typically be a smaller value than the intensity-average size.
The zirconia sols typically have a volume-average size that is no
greater than 50 nanometers, no greater than 40 nanometers, no
greater than 30 nanometers, no greater than 25 nanometers, no
greater than 20 nanometers, or no greater than 15 nanometers. The
volume-average size is used in the calculation of the dispersion
index.
[0107] For a sample that has particles of only one size, the
intensity-average size and volume-average size will be the same.
Therefore, the ratio of the intensity-average size to the
volume-average size gives a measure of the spread of sizes in the
particles. Larger ratios correspond to broader particle size
distributions. The zirconia particles typically have a ratio of
intensity-average size (i.e., measured in nanometers) to
volume-average size (i.e., measured in nanometers) that is no
greater than 3.0, 2.5, 2.0, 1.8, 1.7, or 1.6.
[0108] The zirconia sols often have a high light transmittance due
to the small size and non-associated form of the primary zirconia
particles in the sol. High light transmittance of the sol can be
desirable in the preparation of transparent or translucent
materials such as ceramic bodies. As used herein, "light
transmittance" refers to the amount of light that passes through a
sample (e.g., a zirconia sol) divided by the total amount of light
incident upon the sample and may be calculated as a percent using
the following equation:
Percent Transmittance=100(I/I.sub.0)
where I is the light intensity passing though the sample and
I.sub.0 is the light intensity incident on the sample. The light
transmittance of the zirconia sol may be determined using an
ultraviolet/visible spectrophotometer set at a wavelength of 600
nanometers with a 1 cm path length.
[0109] The light transmittance is a function of the amount of
zirconia in a sol. For zirconia sols having about 1 weight percent
zirconia, the light transmittance is typically at least 70, 80, or
90 percent. For zirconia sols having about 10 weight percent
zirconia, the light transmittance is typically at least 20, 50, or
70 percent.
[0110] Sintering additives can be used to act on and control the
primary particle size during sintering. The sintering additive
should be uniformly distributed throughout the zirconia green body.
In one embodiment, a sintering additive is included with the
zirconia sol. The sintering additive can be included, for example,
during the preparation of the zirconia sol or added to the zirconia
sol after the sol is prepared. For certain of these embodiments, a
sintering additive is included with the zirconia sol, wherein the
difference between the refractive index of the sintering additive
and the refractive index of zirconia is less than 0.1.
Alternatively, for certain of these embodiments, a sintering
additive is included with the zirconia sol, wherein the sintering
additive is selected from the group consisting of aluminum,
niobium, calcium, and oxides thereof. For certain of these
embodiments, the sintering additive is niobium or an oxide
thereof.
[0111] The zirconia green body can be provided by drying the
zirconia sol comprising zirconia particles. To obtain a crack-free
body with a low pore size, the drying can be carried out slowly, at
a low temperature, and/or at a high humidity, for example, at
20.degree. C. and 80-90 percent relative humidity. For certain
embodiments, including any one of the above embodiments which
include drying the zirconia sol, drying the zirconia sol is carried
out in a mold. The mold can be constructed from any of a variety of
materials which are rigid or flexible, capable of containing the
zirconia sol, and, preferably, which are essentially inert with
respect to the zirconia sol. The mold can define the shape of the
resulting green body. A wide range of shapes can be employed. For
example the shape can be a three dimensional structure, such as a
block, suitable for machining into a desired product shape.
Alternatively, the shape can be such that, after sintering, a
desired product shape is provided. For certain of these
embodiments, for example, when a green body of about 5 mm by 5 mm
by 5 mm or greater is desired, the mold has a diameter to height
ratio of less than 2.
[0112] For certain embodiments, including any one of the above
embodiments which include drying the zirconia sol in a mold, the
mold is a flexible mold capable of accommodating the shrinkage of
the zirconia sol during drying. As the volume of the drying
zirconia sol is reduced, the volume of the mold is commensurately
reduced, thereby minimizing or eliminating crack formation in the
resulting green body. The mold may also apply a pressure greater
than atmospheric pressure on the zirconia sol. Examples of flexible
mold material include flexible membranes, which can be non-porous
or nano-porous.
[0113] For certain embodiments, including any one of the above
embodiments which include drying the zirconia sol in a mold, the
mold is a nano-porous mold capable of wicking water out of the
zirconia sol. The nano-porous mold can be rigid or flexible.
Examples of nano-porous mold material include plaster of paris and
nano-porous membranes with pore sizes less than the zirconia
particle size.
[0114] To minimize crack formation and maximize the density of the
zirconia green body, pressure can be applied during drying. This
can be done as described above using a flexible mold.
Alternatively, uniaxial pressure can be applied to the zirconia sol
by opposing nano-porous punches within a nano-porous mold. The rate
of water removal from the mold can be increased by placing the mold
in warm circulating air or the like. In another alternative, the
zirconia sol or a partially dried zirconia sol can be enveloped in
a water permeable membrane to which isostatic pressure is applied
by a hygroscopic fluid, such as glycerine, dimethylsulfoxide, or
the like. The hygroscopic fluid can be heated to increase the rate
of water removal from the sol. When using this water permeable
membrane method, the sol is preferably partially dried (e.g., 1 to
10% water) prior to being placed within the water permeable
membrane.
[0115] Electrophoretic deposition methods can also be used to
produce zirconia green bodies with low pore size (and, therefore,
high density). A membrane can be place in the zirconia sol with the
major surfaces of the membrane facing opposing electrodes in the
sol, and a potential difference (e.g., 5 to 30 V) can be applied
across the membrane. The zirconia particles collect and build into
a green body on the membrane. Use of the membrane avoids cracks and
flaws caused by electrolysis of water that could occur during
particle build at an electrode. In another alternative, the
zirconia sol can be placed in a membrane reservoir (i.e., a
reservoir defined by membrane walls), which in turn is placed in an
electrolyte between two electrodes. Application of a potential
difference (e.g., 3-70 V) causes zirconia particles to collect and
build on the membrane surface, which is not in contact with the
electrolyte.
[0116] Alternatively, for certain embodiments, drying the zirconia
sol is carried out by spray drying to form a powder, and compacting
the powder at an elevated temperature to form the green body. The
zirconia sol can be atomized in a flame or in a hot wall reactor.
Because of the elevated temperatures used (e.g., 600-1000.degree.
C.), bound acetic acid (or other carboxylic acids) is removed. The
resulting dried powder is then compacted using suitable hot
pressing method to form the zirconia green body.
[0117] For certain embodiments, including any one of the above
embodiments which provides a green body, the density of the green
body is at least 75 percent of full density.
[0118] For certain embodiments, including any one of the above
embodiments which provides a green body, the primary particle size
of the green body is no greater than 25 nm.
[0119] For certain embodiments, including any one of the above
embodiments which provides a green body, the diameter of any pores
which are present in the green body is not more than about 25 nm.
For certain of these embodiments, the diameter of any pores which
are present in the green body is not more than about 20 nm.
[0120] For certain embodiments, including any one of the above
embodiments which provides a green body, the major phase which is
tetragonal zirconium oxide comprises at least 70 percent of the
zirconium oxide in the primary particles of the zirconia green
body. For certain of these embodiments, the major phase which is
tetragonal zirconium oxide comprises at least 80 percent, at least
90 percent, at least 95 percent, or at least 99 percent of the
zirconium oxide in the primary particles.
[0121] The zirconia green body is sintered to provide the
translucent zirconia sintered body. The primary particle size and
growth of pores are limited during sintering, at least in part, by
controlling the temperature and keeping the temperature from
exceeding 1200.degree. C. For certain embodiments, including any
one of the above embodiments which provides a translucent zirconia
sintered body, a temperature no greater than 1000.degree. C. is
used during sintering. For certain of these embodiments, a
temperature no greater than 900.degree. C. is used during
sintering.
[0122] Several additional techniques can be considered for limiting
the primary particle size and growth of pores during sintering.
These include two-step sintering (e.g., using a higher temperature
range for a shorter period of time and then a lower temperature
range for a longer period of time), vacuum sintering, reactive gas
sintering, electric field enhanced sintering (e.g., spark plasma
sintering), hot uniaxial pressing, or hot isostatic pressing.
[0123] For certain embodiments, including any one of the above
embodiments which provides a translucent zirconia sintered body,
the primary particle size of the translucent zirconia sintered body
is no greater than 50 nm. For certain of these embodiments, the
primary particle size of the translucent zirconia sintered body is
no greater than 25 nm.
[0124] For certain embodiments, including any one of the above
embodiments which provides a translucent zirconia sintered body,
the diameter of any pores which are present in the translucent
zirconia sintered body is not more than about 20 nm. For certain of
these embodiments, the diameter of any pores which are present in
the translucent zirconia sintered body is not more than about 10
nm.
[0125] For certain embodiments, including any one of the above
embodiments which provides a translucent zirconia sintered body,
the percent light transmittance through a 1 mm thickness of the
translucent zirconia sintered body is at least 60% at 350-700
nm.
[0126] For certain embodiments, including any one of the above
embodiments which provides a translucent zirconia sintered body,
the flexural strength of the translucent zirconia sintered body is
at least 600 MPa. For certain of these embodiments, the flexural
strength of the translucent zirconia sintered body is at least 800
MPa.
[0127] For certain embodiments, including any one of the above
embodiments which provides a translucent zirconia sintered body,
the major phase which is tetragonal zirconium oxide comprises at
least 70 percent of the zirconium oxide in the primary particles of
the translucent zirconia sintered body.
[0128] In another embodiment, the present invention provides a
method of making a dental article comprising:
[0129] providing a translucent zirconia sintered body comprised of
primary particles and having a density of at least 99 percent of
full density, the primary particles having:
[0130] a major phase which is tetragonal zirconium oxide, and
[0131] a size no greater than 100 nm; and
wherein the diameter of any pores which are present is not more
than about 25 nm; and
[0132] shaping the translucent zirconia sintered body to provide a
dental article. For certain embodiments, the primary particle size
is no greater than 50 nm. For certain of these embodiments, the
primary particle size is no greater than 25 nm.
[0133] For certain embodiments, including any one of the above
embodiments which provides a dental article, percent light
transmittance through a 1 mm thickness of the translucent zirconia
sintered body is at least 60% at 350-700 nm.
[0134] For certain embodiments, including any one of the above
embodiments which provides a dental article, the flexural strength
of the translucent zirconia sintered body is at least 600 MPa. For
certain of these embodiments, the flexural strength of the
translucent zirconia sintered body is at least 800 MPa.
[0135] For certain embodiments, including any one of the above
embodiments which provides a dental article, the major phase which
is tetragonal zirconium oxide comprises at least 70 percent of the
zirconium oxide in the primary particles of the translucent
sintered body.
[0136] For certain embodiments, including any one of the above
embodiments which provides a dental article, the diameter of any
pores which are present in the translucent zirconia sintered body
is not more than about 20 nm. For certain of these embodiments, the
diameter of any pores which are present in the translucent zirconia
sintered body is not more than about 10 nm.
[0137] The translucent zirconia sintered body can be shaped using
known methods of machining. For certain embodiments, including any
one of the above embodiments which provides a dental article,
shaping the translucent zirconia sintered body is carried out by
milling. For certain of these embodiments, shaping the translucent
zirconia sintered body is carried out by milling to a shape
obtained by digital imaging.
[0138] For certain embodiments, including any one of the above
embodiments which provides a dental article, the dental article is
selected from the group consisting of a crown, a bridge, a
framework, an abutment, an inlay, an onlay, an implant, and an
orthodontic bracket.
[0139] In another embodiment, the present invention provides a
method of making a dental article comprising:
[0140] providing a zirconia green body comprised of primary
particles and having a density of at least 50 percent of full
density, the primary particles having:
[0141] a major phase which is tetragonal zirconium oxide, and
[0142] a size no greater than 50 nm; and
[0143] wherein the diameter of any pores which are present in the
zirconia green body is not more than about 30 nm;
[0144] sintering the zirconia green body at a temperature no
greater than 1200.degree. C. and for a time sufficient to form a
partially sintered zirconia green body;
[0145] shaping the partially sintered zirconia green body; and
[0146] sintering the shaped, partially-sintered zirconia green body
to provide a dental article comprising a shaped, translucent
zirconia sintered body comprised of primary particles and having a
density of at least 99 percent of full density, the primary
particles having:
[0147] a major phase which is tetragonal zirconium oxide, and
[0148] a size no greater than 100 nm; and
wherein the diameter of any pores which are present in the shaped,
translucent zirconia sintered body is not more than about 25 nm.
For certain embodiments, the density of the green body is at least
65 percent of full density. For certain of these embodiments, the
density of the green body is at least 75 percent of full
density
[0149] For certain embodiments, including any one of the above
embodiments which includes partially sintering the zirconia green
body, the primary particle size of the green body is no greater
than 25 nm.
[0150] For certain embodiments, including any one of the above
embodiments which includes partially sintering the zirconia green
body, the diameter of any pores which are present in the green body
is not more than about 25 nm. For certain of these embodiments, the
diameter of any pores which are present in the green body is not
more than about 20 nm.
[0151] For certain embodiments, including any one of the above
embodiments which includes partially sintering the zirconia green
body, sintering the zirconia green body is carried out at a
temperature no greater than 1000.degree. C. and for a time
sufficient to form a partially-sintered zirconia green body. For
certain of these embodiments, sintering the zirconia green body is
carried out at a temperature no greater than 900.degree. C. and for
a time sufficient to form a partially-sintered zirconia green body.
For certain of these embodiments, sintering the zirconia green body
is carried out at a temperature no greater than 600.degree. C. and
for a time sufficient to form a partially-sintered zirconia green
body.
[0152] For certain embodiments, including any one of the above
embodiments which includes partially sintering the zirconia green
body, the density of the partially-sintered zirconia green body is
at least 75 percent of full density and less than 99 percent of
full density.
[0153] For certain embodiments, including any one of the above
embodiments which includes shaping the partially sintering the
zirconia green body, shaping the partially-sintered zirconia green
body is carried out by milling.
[0154] For certain embodiments, including any one of the above
embodiments which includes shaping the partially sintering the
zirconia green body, shaping the partially-sintered zirconia green
body is carried out by milling to a shape obtained by digital
imaging.
[0155] For certain embodiments, including any one of the above
embodiments which includes sintering the shaped, partially-sintered
zirconia green body to provide a dental article comprising a
shaped, translucent zirconia sintered body, the primary particle
size of the translucent zirconia sintered body is no greater than
50 nm. For certain of these embodiments, the primary particle size
of the translucent zirconia sintered body is no greater than 25
nm.
[0156] For certain embodiments, including any one of the above
embodiments which includes sintering the shaped, partially-sintered
zirconia green body to provide a dental article comprising a
shaped, translucent zirconia sintered body, the percent light
transmittance through a 1 mm thickness of the translucent zirconia
sintered body is at least 60% at 350-700 nm.
[0157] For certain embodiments, including any one of the above
embodiments which includes sintering the shaped, partially-sintered
zirconia green body to provide a dental article comprising a
shaped, translucent zirconia sintered body, the flexural strength
of the translucent zirconia sintered body is at least 600 MPa. For
certain of these embodiments, the flexural strength of the
translucent zirconia sintered body is at least 800 MPa.
[0158] For certain embodiments, including any one of the above
embodiments which includes sintering the shaped, partially-sintered
zirconia green body to provide a dental article comprising a
shaped, translucent zirconia sintered body, the major phase which
is tetragonal zirconium oxide comprises at least 70 percent of the
zirconium oxide in the primary particles of the translucent
zirconia sintered body.
[0159] For certain embodiments, including any one of the above
embodiments which includes sintering the shaped, partially-sintered
zirconia green body to provide a dental article comprising a
shaped, translucent zirconia sintered body, the diameter of any
pores which are present in the translucent zirconia sintered body
is not more than about 20 nm. For certain of these embodiments, the
diameter of any pores which are present in the translucent zirconia
sintered body is not more than about 10 nm.
[0160] For certain embodiments, including any one of the above
embodiments which includes sintering the shaped, partially-sintered
zirconia green body to provide a dental article comprising a
shaped, translucent zirconia sintered body, the dental article is
selected from the group consisting of a crown, a bridge, a
framework, an abutment, an inlay, an onlay, an implant, and an
orthodontic bracket.
Preparation of the Zirconia Sol
[0161] The zirconia sol comprising zirconia particles can be made
by preparing a first feedstock that contains a zirconium salt and
subjecting the first feedstock to a first hydrothermal treatment to
form a zirconium-containing intermediate. A second feedstock is
then formed by removing at least a portion of any byproduct formed
in the first hydrothermal treatment and subjecting the second
feedstock to a second hydrothermal treatment to form a zirconia sol
that contains the zirconia particles.
[0162] The first feedstock is prepared by forming an aqueous
precursor solution that contains a zirconium salt. The anion of the
zirconium salt is usually chosen so that it can be removed during
subsequent steps in the process for preparing the zirconia sol.
Additionally, the anion is often chosen to be non-corrosive,
allowing greater flexibility in the type of material chosen for the
processing equipment such as the hydrothermal reactors.
[0163] The anion of the zirconium salt is usually a carboxylate. At
least 50 mole percent of the carboxylate anions have no greater
than four carbon atoms. For example, in some precursor solutions,
at least 60, 70, 80, 90, 95, 98, or 99 mole percent of the
carboxylate anions have no greater than four carbon atoms.
[0164] Suitable carboxylates having no greater than four carbon
atoms include formate, acetate, propionate, butyrate, or a
combination thereof. These carboxylate anions can often be removed
during the process by conversion to the corresponding volatile
acid.
[0165] In some precursor solutions, the anion is a mixture of a
carboxylate having no greater than four carbon atoms and a
polyether carboxylate anion. Suitable polyether carboxylate anions
are the corresponding weak bases of water-soluble monocarboxylic
acids (i.e., one carboxylic acid group per molecule) having a
polyether tail. The polyether tail contains repeating difunctional
ether radicals having the general formula --O--R-- where R is an
alkylene group such as, for example, methylene, ethylene and
propylene (including n-propylene and iso-propylene) or a
combination thereof. Suitable polyether carboxylates have more than
four carbon atoms and include, but are not limited to, those formed
from polyether carboxylic acids such as
2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA) and
2-(2-methoxyethoxy)acetic acid (MEAA). The polyether carboxylate,
if included in the precursor solution, is typically present in an
amount no greater than 50 mole percent based on the moles of
carboxylate anions in the precursor solution. For example, the
amount of polyether carboxylate can be no greater than 40, 30, 20,
10, 5, 2, or 1 mole percent of the carboxylate anions in the
precursor solution.
[0166] Some precursor solutions are substantially free of polyether
carboxylates, substantially free of carboxylates that have more
than four carbon atoms, or a combination thereof. As used herein,
the term "substantially free of polyether carboxylates" means that
less than 1 mole percent of the carboxylate in the precursor
solution are polyether carboxylates or the corresponding polyether
carboxylic acid. For example, less than 0.5, 0.2, or 0.1 mole
percent of the carboxylates in the precursor solution are polyether
carboxylates or the corresponding polyether carboxylic acid. As
used herein, the term "substantially free of carboxylates that have
more than four carbon atoms" means that less than 1 mole percent of
the carboxylates or the corresponding carboxylic acids in the
precursor solution have greater than four carbon atoms. For
example, less than 0.5, 0.2, or 0.1 mole percent of the
carboxylates or corresponding carboxylic acids have greater than
four carbon atoms.
[0167] Some precursor solutions are substantially free of halides
such as chlorides. As used herein, the term "substantially free of
halides" means that the precursor solution has less than 10.sup.-2,
10.sup.-3, 10.sup.-4, or 10.sup.-5 moles/liter halide.
[0168] The zirconium salt is often zirconium acetate. Zirconium
acetate can be represented by a formula such as
ZrO.sub.((4-n)/2).sup.n+(CH.sub.3COO.sup.-).sub.n where n is in the
range of 1 to 2. The zirconium ion may be present in a variety of
structures depending, for example, on the pH of the precursor
solution. Methods of making zirconium acetate are described, for
example, in W. B. Blumenthal, "The Chemical Behavior of Zirconium,"
pp. 311-338, D. Van Nostrand Company, Princeton, N.J. (1958).
Suitable aqueous solutions of zirconium acetate are commercially
available, for example, from Magnesium Elektron, Inc. (Flemington,
N.J.) that contain up to 17 weight percent zirconium, up to 18
weight percent zirconium, up to 20 weight percent zirconium, or up
to 22 weight percent zirconium.
[0169] Some precursor solutions contain a yttrium salt in addition
to a zirconium salt. As with the zirconium salt, the anion of the
yttrium salt is typically chosen to be removable during subsequent
processing steps and to be non-corrosive. The anion of the yttrium
salt is often a carboxylate having no more than four carbon atoms.
For example, the anion can be acetate. The yttrium salt is often
present in an amount up to 0.12, 0.10, 0.08, 0.06, or 0.04 grams
yttrium per gram of zirconium.
[0170] The liquid phase of the precursor solution is typically
predominately water. However, other miscible co-solvents can be
included in the liquid phase in amounts up 20 weight percent based
on the weight of the liquid phase. Suitable co-solvents include,
but are not limited to, 1-methoxy-2-propanol, ethanol, isopropanol,
ethylene glycol, N,N-dimethylacetamide, and
N-methylpyrrolidone.
[0171] In some embodiments, the first feedstock is prepared by
forming an aqueous precursor solution that includes a zirconium
salt and an optional yttrium salt and then removing at least a
portion of the anions in the precursor solution. Any suitable
method known in the art for removing a portion of the anions can be
used. Removal methods include, but are not limited to,
vaporization, dialysis, ion exchange, precipitation, filtration,
and the like. In some removal methods, the anion is removed as an
acid. Although not wanting to be bound be theory, the partial
removal of the anion in the precursor solution may reduce the
formation of agglomerates and aggregates during one or more of the
subsequent hydrothermal treatment steps.
[0172] In one method of at least partially removing the anions in
the precursor solution, the precursor solution can be heated to
vaporize an acidic form of the anion. For example, a carboxylate
anion having no more than four carbon atoms can be removed as the
corresponding carboxylic acid. More specifically, an acetate anion
can be removed as acetic acid. The heating also can at least
partially remove the liquid phase (e.g., aqueous medium) of the
precursor solution in addition to the carboxylic acid. The partial
removal of the liquid phase results in the formation of a
concentrated precursor. In some methods, the solids can be
increased up to 25, 50, 75, or 100 weight percent. The concentrated
precursor often contains at least 10, 15, 20, 25, 30, 35, or 40
weight percent zirconium. For example, the concentrated precursor
can contain 11 to 43 weight percent zirconium or 21 to 43 weight
percent zirconium.
[0173] All or a portion of the liquid phase removed to form the
concentrated precursor can be replaced prior to the first
hydrothermal treatment. The concentrated precursor can be diluted
with water (e.g., deionized water) to provide the first feedstock.
The first feedstock can have a solid content that is lower than the
solid content of the precursor solution, equal to the solid content
of the precursor solution, or greater than the solid content of the
precursor solution.
[0174] The first feedstock typically has solids in the range of 0.5
to 20 weight percent or 2 to 15 weight percent. The first feedstock
often contains at least 0.2, 0.5, 1, or 2 weight percent zirconium.
In some embodiments, the first feedstock contains up to 6, 8, or 9
weight percent zirconium. For example, the first feedstock often
contains 0.2 to 9 weight percent zirconium or 1 to 6 weight percent
zirconium.
[0175] The pH of the first feedstock is typically in the acidic
range. For example, the pH is usually less than 6, 5, 4, or 3.
[0176] The first feedstock is subjected to a first hydrothermal
treatment. The zirconium species in the first feedstock undergoes
partial hydrolysis to form a zirconium-containing intermediate and
a byproduct. Likewise, any optional yttrium salt present in the
first feedstock can undergo partial hydrolysis. The hydrolysis
reaction is often accompanied by the release of an acidic byproduct
when the anion is a carboxylate. For example, if the anion is
formate, acetate, propionate, or butyrate, the corresponding acid
(i.e., formic acid, acetic acid, propionic acid, or butyric acid
respectively) can be released during the hydrolysis reaction.
[0177] The hydrothermal treatments can be in a batch reactor or a
continuous reactor. The residence times are typically shorter and
the temperatures are typically higher in a continuous reactor
compared to a batch reactor. The time of the hydrothermal
treatments can be varied depending on the temperature of the
reactor and the concentration of the feedstock. The pressure in the
reactor can be autogeneous (i.e., the vapor pressure of water at
the temperature of the reactor), can be hydraulic (i.e., the
pressure caused by the pumping of a fluid against a restriction),
or can result from the addition of an inert gas such as nitrogen or
argon. Suitable batch hydrothermal reactors are available, for
example, from Parr Instruments Co. (Moline, Ill.). Suitable
continuous hydrothermal reactors are described, for example, in
U.S. Pat. Nos. 5,453,262 (Dawson et al.) and 5,652,192 (Matson et
al.); Adschiri et al., J. Am. Ceram. Soc., 75, 1019-1022 (1992);
and Dawson, Ceramic Bulletin, 67 (10), 1673-1678 (1988).
[0178] In some methods, at least one of the hydrothermal treatments
is in a continuous reactor. For example, the first hydrothermal
treatment can be in a continuous reactor while the second
hydrothermal treatment is in a batch reactor. In another example,
the first hydrothermal treatment can be in a batch reactor while
the second hydrothermal treatment is in a continuous reactor. In
still another example, both the first and second hydrothermal
treatments are in a continuous reactor.
[0179] The first hydrothermal treatment can be in a batch reactor
at a temperature in the range of 150.degree. C. to 300.degree. C.,
in the range of 155.degree. C. to 250.degree. C., or in the range
of 160.degree. C. to 200.degree. C. In some first hydrothermal
treatments in a batch reactor, the reactor is heated to the desired
temperature and then cooled immediately. It may take, for example,
about 1 hour to reach the desired temperature. In other first
hydrothermal treatments in a batch reactor, the reaction
temperature is held for at least 0.5, 0.75, 1, or 2 hours. The time
at the reaction temperature can be up to 3, 3.5, 4, 5, 6, or 8
hours in a batch reactor. For example, the time the reaction
temperature is held can be 0.25 to 8 hours, 0.5 to 6 hours, or 0.75
to 3.5 hours.
[0180] Alternatively, the first hydrothermal treatment can be in a
continuous reactor at a temperature in the range of 150.degree. C.
to 300.degree. C., in the range of 160.degree. C. to 250.degree.
C., in the range of 170.degree. C. to 220.degree. C., or in the
range of 180.degree. C. to 215.degree. C. for a period of at least
1 minute. In some continuous reactors, the residence time is at
least 2, 3, 3, 5, or 4 minutes. The residence time can be up to 8,
10, 12, 15, or 20 minutes in a continuous reactor. For example, the
residence time in a continuous reactor can be 1 to 20 minutes, 2 to
15 minutes, or 3 to 10 minutes.
[0181] The zirconium salts and optional yttrium salts in the first
feedstock undergo only partial hydrolysis during the first
hydrothermal treatment. The product of the first hydrothermal
treatment includes a zirconium-containing intermediate plus various
byproducts in a liquid phase. If an optional yttrium salt is
included in the first feedstock, the zirconium-containing
intermediate also contains yttrium. The zirconium-containing
intermediate is only partially hydrolyzed and is not crystalline
zirconia. The zirconium-containing intermediate is essentially
amorphous based on x-ray diffraction analysis. That is, the x-ray
diffraction pattern for the zirconium-containing intermediate tends
to have broad peaks rather than the relatively narrow peaks
indicative of crystalline material.
[0182] The percent conversion (i.e., the extent of hydrolysis) can
be calculated, for example, using Thermal Gravimetric Analysis
(TGA). This method of calculating the percent conversion is
particularly suitable when the carboxylate anions in the first
feedstock are free of polyether carboxylates, free of carboxylates
having more than four carbon atoms, or combinations thereof. The
percent conversion of the zirconium-containing intermediate can be
given by the following equation
% Conversion=100(A-B)/(A-C)
where A is the percent weight loss of the first feedstock, B is the
percent weight loss of the zirconium-containing intermediate, and C
is the percent weight loss of the zirconia sol. The percent weight
loss for the first feedstock, the intermediate, and the zirconia
sol is determined by drying each sample at 120.degree. C. for 30
minutes before analysis. After equilibration at 85.degree. C. in
the thermal gravimetric analyzer, each sample is heated at a rate
of 20.degree. C./minute to 200.degree. C. The temperature is held
at 200.degree. C. for 20 minutes, increased at a rate of 20.degree.
C./minute to 900.degree. C., and held at 900.degree. C. for 20
minutes. The percent weight loss can be calculated from the
following equation
% weight
loss=100(weight.sub.200C-weight.sub.900C)/weight.sub.900C
for the first feedstock, the zirconium-containing intermediate, and
the zirconia sol. The percent weight loss corresponds to what is
not an inorganic oxide in each of the dried samples.
[0183] The percent conversion of the zirconium-containing
intermediate is typically 40 to 75 percent. In some methods, the
percent conversion of the zirconium-containing intermediate is 45
to 70 percent, 50 to 70 percent, 55 to 70 percent, or 55 to 65
percent. The percent conversion can be used to select suitable
conditions for the first hydrothermal treatment.
[0184] If the hydrolysis reaction during the first hydrothermal
treatment is allowed to proceed to produce a zirconium-containing
intermediate with a percent conversion greater than about 75
percent, the final zirconia sol tends to contain associated (e.g.,
aggregated and/or agglomerated) rather than non-associated primary
particles of zirconia. Although not wanting to be bound by theory,
it is advantageous to remove at least a portion of the byproducts
of the hydrolysis reaction during the course of the reaction. Thus,
it is advantageous to subject the first feedstock to a first
hydrothermal treatment and remove a portion of the byproduct prior
to the second hydrothermal treatment.
[0185] The second feedstock, the material that is subjected to the
second hydrothermal treatment, is prepared from the product of the
first hydrothermal treatment. The preparation of the second
feedstock usually involves removing at least some of the byproducts
that are produced during the first hydrothermal treatment. An acid,
which can be formed from the anion of the zirconium salt and the
optional yttrium salt, is often one of the byproducts of the first
hydrothermal treatment. When the acidic byproduct is a carboxylic
acid having no more than four carbon atoms, the acid can be removed
by a variety of methods such as vaporization, dialysis, ion
exchange, precipitation, filtration, and the like.
[0186] The removal of at least some of the byproducts of the first
hydrothermal treatment also can result in the removal of at least
some of the liquid phase (e.g., aqueous medium). That is, an
intermediate concentrate can be formed. In some embodiments, only a
portion of the liquid phase is removed (i.e., the intermediate
concentrate has a liquid phase). For example, some products of the
first hydrothermal treatment contain a solid phase that can be
separated from part of the liquid phase (e.g., the solid phase can
settle out of the liquid phase). At least a portion of the liquid
phase can be removed by methods such as by siphoning, decantation,
or centrifugation. In other embodiments, the product of the first
hydrothermal treatment is dried to form a residue (i.e., the
intermediate concentrate has little or no liquid phase). The solids
of the intermediate concentrate are often in the range of 10 to 100
weight percent.
[0187] The intermediate concentrate typically contains at least 5,
8, 10, 20, or 30 weight percent zirconium. The intermediate
concentrate can contain up to 30, 40, 50, or 52 weight percent
zirconium. For example, the intermediate concentrate can contain 5
to 52 weight percent zirconium or 8 to 52 weight percent
zirconium.
[0188] The intermediate concentrate, if the solids are no greater
than 50 weight percent, can be used as the second feedstock.
Alternatively, the intermediate concentrate can be diluted with
water (e.g., deionized water) to form the second feedstock. The
second feedstock often contains 0.5 to 50 weight percent solids or
3 to 40 weight percent solids when the second hydrothermal reactor
is a batch reactor. The second feedstock often contains 0.5 to 25
weight percent solids or 7 to 22 weight percent solids when the
second hydrothermal reactor is a continuous reactor.
[0189] The second feedstock typically contains at least 0.3 weight
percent zirconium. When the second reactor is a batch reactor, the
second feedstock often contains at least 0.5, 1, or 2 weight
percent zirconium. The second feedstock for a batch reactor can
contain up to 15, 20, 21, 25, or 26 weight percent zirconium. For
example, the second feedstock for a batch reactor can contain 0.3
to 26 weight percent zirconium or 2 to 21 weight percent zirconium.
When the second reactor is a continuous reactor, the second
feedstock often contains at least 1, 2, 4, or 8 weight percent
zirconium. The second feedstock for a continuous reactor often
contains up to 11, 12, or 13 weight percent zirconium. For example,
the second feedstock for a continuous reactor can contain 0.3 to 13
weight percent zirconium or 8 to 11 weight percent zirconium.
[0190] The pH of the second feedstock is typically less than 7. For
example, the second feedstock can have a pH that is no greater than
6 or no greater than 5.
[0191] The second feedstock is subjected to a second hydrothermal
treatment to form a zirconia sol. If a batch reactor is used for
the second hydrothermal treatment, the reaction temperature is
often in the range of 150.degree. C. to 300.degree. C., in the
range of 160.degree. C. to 250.degree. C., or in the range of
175.degree. C. to 200.degree. C. for a period of at least 30
minutes. In some batch reactors, the residence time is at least 1
hour, 2, or 4 hours. The residence time can be up to 8, 10, 12, 14,
16, 18, or 24 hours in a batch reactor. For example, the residence
time in a batch reactor can be 0.5 to 24 hours, 1 to 18 hours, or 1
to 14 hours. Alternatively, the second hydrothermal treatment can
be in a continuous reactor at a temperature in the range of
150.degree. C. to 300.degree. C., in the range of 160.degree. C. to
250.degree. C., in the range of 180.degree. C. to 220.degree. C.,
or in the range of 200.degree. C. to 215.degree. C. for a period of
at least 1 minute. In some continuous reactors, the residence time
is at least 1, 2, 5, or 10 minutes. The residence time can be up to
60, 80, 90, 100, or 120 minutes in a continuous reactor. For
example, the residence time in a continuous reactor can be 1 to 120
minutes, 5 to 100 minutes, or 10 to 90 minutes.
[0192] During the second hydrothermal treatment, the
zirconium-containing intermediate undergoes further hydrolysis. The
product of the second hydrothermal treatment is a zirconia sol that
contains crystalline zirconia particles. The zirconia sol can be
dried at a temperature of 120.degree. C. to provide zirconia
particles that typically contains 75 to 95 weight percent inorganic
oxides. The zirconia particles can contain yttrium oxide (i.e.,
Y.sub.2O.sub.3) in addition to zirconia (i.e., ZrO.sub.2). The
zirconia particles can also contain some organic material, for
example, by surface treating the zirconia particles.
[0193] In some embodiments, the zirconia sol is further treated to
at least partially remove the byproducts formed during the second
hydrothermal treatment. The byproducts are often acids formed from
the anion of the zirconium salt or the optional yttrium salt. It is
often desirable to remove the acidic byproduct if the zirconia
particles in the zirconia sol will be combined with an organic
matrix to form a composite material. For example, the acidic
byproduct can be a carboxylic acid that can be removed by
vaporization, ion exchange, precipitation, or dialysis. The
zirconia sol often contains 0.5 to 55 weight percent solids or 2 to
51 weight percent solids.
[0194] The zirconia sol typically contains at least 0.3 weight
percent zirconium. For example, the zirconia sol can contain at
least 1, 2, 5, or 10 weight percent zirconium. The zirconia sol
often contains up to 34, 35, or 37 weight percent zirconium. For
example, the zirconia sol can contain 0.3 to 37 weight percent
zirconia, 0.5 to 35 weight percent zirconium, or 1 to 34 weight
percent zirconium.
[0195] The zirconia sol is prepared using at least two hydrothermal
treatments. In some embodiments, more than two hydrothermal
treatments are used. Between each hydrothermal treatment, at least
some of the acidic byproducts formed in the preceding hydrothermal
treatment can be removed.
[0196] Objects and advantages of this invention are further
illustrated by the following examples, but the particular materials
and amounts thereof recited in these examples, as well as other
conditions and details, should not be construed to unduly limit
this invention.
EXAMPLES
[0197] All parts, percentages, ratios, etc. in the examples and the
rest of the specification are by weight, unless noted otherwise.
Solvents and other reagents used were obtained from Sigma-Aldrich
Chemical Company; Milwaukee, Wis. unless otherwise noted.
Test Methods
Photon Correlation Spectroscopy (PCS)
[0198] The volume-average particle size was determined by Photon
Correlation Spectroscopy (PCS) using a Malvern Series 4700 particle
size analyzer (available from Malvern Instruments Inc.,
Southborough, Mass.). Dilute zirconia sol samples were filtered
through a 0.2 .mu.m filter using syringe-applied pressure into a
glass cuvette that was then covered. Prior to starting data
acquisition the temperature of the sample chamber was allowed to
equilibrate at 25.degree. C. The supplied software was used to do a
CONTIN analysis with an angle of 90 degrees. CONTIN is a widely
used mathematical method for analyzing general inverse
transformation problems that is further described in S. W.
Provencher, Comput. Phys. Commun., 27, 229 (1982). The analysis was
performed using 24 data bins. The following values were used in the
calculations: refractive index of water equal to 1.333, viscosity
of water equal to 0.890 centipoise, and refractive index of the
zirconia particles equal to 1.9.
[0199] Two particle size measurements were calculated based on the
PCS data. The intensity-average particle size, reported in
nanometers, was equal to the size of a particle corresponding to
the mean value of the scattered light intensity distribution. The
scattered light intensity was proportional to the sixth power of
the particle diameter. The volume-average particle size, also
reported in nanometers, was derived from a volume distribution that
was calculated from the scattered light intensity distribution
taking into account both the refractive index of the zirconia
particles and the refractive index of the dispersing medium (i.e.,
water). The volume-average particle size was equal to the particle
size corresponding to the mean of the volume distribution.
[0200] The intensity-average particle size was divided by the
volume-average particle size to provide a ratio that is indicative
of the particle size distribution.
Crystalline Structure and Size (XRD Analysis) of Zirconia Particles
in Zirconia Sol
[0201] The particle size of a dried zirconia sample was reduced by
hand grinding using an agate mortar and pestle. A liberal amount of
the sample was applied by spatula to a glass microscope slide on
which a section of double coated tape had been adhered. The sample
was pressed into the adhesive on the tape by forcing the sample
against the tape with the spatula blade. Excess sample was removed
by scraping the sample area with the edge of the spatula blade,
leaving a thin layer of particles adhered to the adhesive. Loosely
adhered materials remaining after the scraping were remove by
forcefully tapping the microscope slide against a hard surface. In
a similar manner, corundum (Linde 1.0 .mu.m alumina polishing
powder, Lot Number C062, Union Carbide, Indianapolis, Ind.) was
prepared and used to calibrate the diffractometer for instrumental
broadening.
[0202] X-ray diffraction scans were obtained using a Philips
vertical diffractometer having a reflection geometry, copper
K.sub..alpha. radiation, and proportional detector registry of the
scattered radiation. The diffractometer was fitted with variable
incident beam slits, fixed diffracted beam slits, and graphite
diffracted beam monochromator. The survey scan was conducted from
25 to 55 degrees (2.theta.) using a 0.04 degree step size and 8
second dwell time. X-ray generator settings of 45 kV and 35 mA were
employed. Data collections for the corundum standard were conducted
on three separate areas of several individual corundum mounts. Data
was collected on three separate areas of the thin layer sample
mount.
[0203] The observed diffraction peaks were identified by comparison
to the reference diffraction patterns contained within the
International Center for Diffraction Data (ICDD) powder diffraction
database (sets 1-47, ICDD, Newton Square, Pa.) and attributed to
either cubic/tetragonal (C/T) or monoclinic (M) forms of zirconia.
The (111) peak for the cubic phase and (101) peak for the
tetragonal phase were reported together. The amounts of each
zirconia form were evaluated on a relative basis and the form of
zirconia having the most intense diffraction peak was assigned the
relative intensity value of 100. The strongest line of the
remaining crystalline zirconia form was scaled relative to the most
intense line and given a value between 1 and 100.
[0204] Peak widths for the observed diffraction maxima due to
corundum were measured by profile fitting. The relationship between
mean corundum peak widths and corundum peak position (2.theta.) was
determined by fitting a polynomial to these data to produce a
continuous function used to evaluate the instrumental breadth at
any peak position within the corundum testing range. Peak widths
for the observed diffraction maxima due to zirconia were measured
by profile fitting observed diffraction peaks. The following peak
widths were evaluated depending on the zirconia phase found to be
present: [0205] Cubic/Tetragonal (C/T): (1 1 1) [0206] Monoclinic
(M): (-1 1 1), and (1 1 1) A Pearson VII peak shape model with
K.sub..alpha.1 and K.sub..alpha.2 wavelength components accounted
for, and linear background model were employed in all cases. Widths
were found as the peak full width at half maximum (FWHM) having
units of degrees. The profile fitting was accomplished by use of
the capabilities of the JADE diffraction software suite. Sample
peak widths were evaluated for the three separate data collections
obtained for the same thin layer sample mount.
[0207] Sample peaks were corrected for instrumental broadening by
interpolation of instrumental breadth values from corundum
instrument calibration and corrected peak widths converted to units
of radians. The Scherrer equation was used to calculate the primary
crystal size.
Crystallite Size (D)=K.lamda./.beta.(cos .theta.)
In the Scherrer equation, [0208] K=form factor (here 0.9); [0209]
.lamda.=wavelength (1.540598 .ANG.); [0210] .beta.=calculated peak
width after correction for instrumental broadening (in
radians)=[calculated peak FWHM-instrumental breadth] (converted to
radians) where FWHM is full width at half maximum; and [0211]
.theta.=1/2 the peak position (scattering angle). The
cubic/tetragonal crystallite size was measured as the average of
three measurements using (1 1 1) peak.
[0211] Cubic/Tetragonal Mean Crystallite Size=[D(1 1 1).sub.area
1+D(1 1 1).sub.area 2+D(1 1 1).sub.area 3]/3
The monoclinic crystallite size was measured as the average of
three measurement using the (-1 1 1) peak and three measurements
using the (1 1 1) peak.
Monoclinic Mean Crystallite Size=[D(-1 1 1).sub.area 1+D(-1 1
1).sub.area 2+D(-1 1 1).sub.area 3+D(1 1 1).sub.area 1+D(1 1
1).sub.area 2+D(1 1 1).sub.area 3]/6
The weighted average of the cubic/tetragonal (C/T) and monoclininc
phases (M) were calculated.
Weighted average=[(% C/T)(C/T size)+(% M)(M size)]/100
In this equation, [0212] % C/T=the percent crystallinity
contributed by the cubic and tetragonal crystallite content of the
ZrO.sub.2 particles; [0213] C/T size=the size of the cubic and
tetragonal crystallites; [0214] % M=the percent crystallinity
contributed by the monoclinic crystallite content of the ZrO.sub.2
particles; and [0215] M size=the size of the monoclinic
crystallites.
X-Ray Diffraction Pattern Analysis for Sintered Bodies
Sample Preparation
[0216] Samples were placed on a zero background specimen holder
composed of single crystal quartz. Samples were mixed with a
silicon internal standard and applied to the specimen holder as a
MEK slurry.
Data Collection
[0217] Reflection geometry data were collected in the form of a
survey scan by use of a Philips vertical diffractometer, copper K,
radiation, and proportional detector registry of the scattered
radiation. The diffractometer is fitted with variable incident beam
slits, fixed diffracted beam slits, and graphite diffracted beam
monochromator. The survey scan was conducted from 68 to 78 degrees
(two theta) using a 0.02 degree step size and 90 second dwell time.
X-ray generator settings of 45 kV and 35 mA were employed.
Resulting data were subjected to profile fitting using a Pearson
VII peak shape model to determine silicon and zirconia peak
positions. Zirconia peak positions were corrected for sample
transparency and displacement using the positions of the silicon
(400) and (331) maxima. For calculation of zirconia lattice
parameters, cubic phase (400) peak, tetragonal (220), and
tetragonal (400) peaks were employed, as appropriate.
Dispersion Index
[0218] The Dispersion Index is equal to the volume-average size
measured by PCS divided by the weighted average crystallite size
measured by XRD.
Weight Percent Solids
[0219] The weight percent solids were determined by drying a sample
weighing 3 to 6 grams at 120.degree. C. for 30 minutes. The percent
solids can be calculated from the weight of the wet sample (i.e.,
weight before drying, weight.sub.wet) and the weight of the dry
sample (i.e., weight after drying, weight.sub.dry) using the
following equation.
wt-% solids=100(weight.sub.dry)/weight.sub.wet
Thermal Gravimetric Analysis (TGA)
[0220] The percent conversion of the zirconium-containing
intermediate and the weight percent inorganic oxides were
determined by thermal gravimetric analysis using a Model 2950 TGA
from TA Instruments (New Castle, Del.).
[0221] To determine the percent conversion of the zirconium
containing intermediate, a sample (e.g., 3 to 6 grams) was
initially heated at 120.degree. C. in an oven for 30 minutes to
dry. The dried sample (e.g., 30 to 60 mg) was equilibrated at
85.degree. C. in the TGA. The temperature was then increased at a
rate of 20.degree. C./minute to 200.degree. C., held at 200.degree.
C. for 20 minutes, increased at 20.degree. C./minute to 900.degree.
C., and held at 900.degree. C. for 20 minutes. The organic material
was volatilized between 200.degree. C. and 900.degree. C. leaving
only the inorganic oxides such as ZrO.sub.2 and Y.sub.2O.sub.3. The
percent weight loss was calculated using the following
equation.
% weight
loss=100(%-weight.sub.200C-%-weight.sub.900C)/%-weight.sub.900C
The %-weight.sub.200C was calculated from the weight of the sample
at 200.degree. C. (weight.sub.200C) and from the weight of the
dried sample (weight.sub.dry) used for the analysis (e.g., sample
dried at 120.degree. C. before analysis).
%-weight.sub.200C=100(weight.sub.200C)/weight.sub.dry
The %-weight.sub.900C is calculated from the weight of the sample
at 900.degree. C. (weight.sub.900C) and from the weight of the
dried sample (weight.sub.dry) used for the analysis (e.g., sample
dried at 120.degree. C. before analysis.
%-weight.sub.900C=100(weight.sub.900C)/weight.sub.dry
[0222] The percent conversion of the zirconium-containing
intermediate is given by the following equation
% Conversion=100(A-B)/(A-C)
where A is the percent weight loss of the first feedstock, B is the
percent weight loss of the zirconium-containing intermediate, and C
is the percent weight loss of the zirconia sol.
[0223] The weight percent inorganic oxide was calculated from the
weight percent solids and the weight percent oxide at 900.degree.
C. That is, the weight percent inorganic oxide can be calculated
using the following equation.
wt-% inorganic oxides=(wt-% solids)(%-weight.sub.900C)/100
Index of Refraction
[0224] The refractive index was measured using an Abbe
refractometer commercially available from Milton Roy Co. (Ivyland,
Pa.).
Example 1
Preparation of a Zirconia Body in a Flexible Mold
[0225] The open top of a beaker was covered with flexible
thermoplastic film (available under the trade designation PARAFILM
M). A depression was formed in the film and this depression was
filled with a zirconia sol prepared essentially as described in
U.S. Patent Application Publication No. 2006/0148950. The zirconia
sol was allowed to dry by evaporation at room temperature to afford
a zirconia green body. The zirconia green body was then sintered by
heating it in a furnace. The temperature of the furnace was
increased at a rate of 5.degree. C. per minute to a temperature of
900.degree. C. The furnace temperature was held at 900.degree. C.
for ten minutes, and then the furnace heater was turned off and the
furnace was allowed to cool to room temperature. Analysis of the
sintered zirconia body by XRD analysis, as described above,
indicated that tetragonal zirconia was the predominate phase in the
body. The sintered zirconia was observed to be translucent.
Example 2
Preparation of a Zirconia Body in a Rigid Mold
[0226] A mold of a cylinder, the cylinder having a diameter of 3.8
centimeters (1.5 inches) and a length of approximately 10
centimeters (approximately 4 inches) with a 1.3 centimeter (0.5
inch) diameter hole in it, was prepared using dental plaster. After
the plaster was set, the mold was dried at room temperature for one
day. The mold was then filled with a zirconia sol prepared
essentially as described in U.S. Patent Application Publication No.
2006/0148950. The zirconia sol was allowed to dry by evaporation at
room temperature, and was continually replenished as it dried, to
afford a zirconia green body having the cylindrical shape of the
mold cavity and a length of approximately 1.3 centimeters (0.5
inch). The mold was broken into several pieces to remove the
zirconia green body from it. The zirconia green body broke into
several pieces during this removal step. The pieces of the zirconia
green body were then sintered essentially as described in Example
1. Analysis of the sintered zirconia body pieces by XRD analysis,
as described above, indicated that tetragonal zirconia was the
predominate phase. The sintered zirconia was observed to be
translucent.
Example 3
Preparation of a Zirconia Body in Sheet Form
[0227] A zirconia sol prepared essentially as described in U.S.
Patent Application Publication No. 2006/0148950 was poured into a
Petri dish in an amount sufficient to cover the bottom of the dish.
The Petri dish was placed in a convection oven at 80.degree. C.,
and the zirconia sol was dried to a sheet, which cracked into small
flakes during drying. The flakes were then transferred to a
crucible and sintered in a muffle furnace by heating to 900.degree.
C. at a rate of 10.degree. C./minute. After cooling to room
temperature, the flakes were imaged by SEM as shown in FIG. 2. The
SEM image showed that the flakes were sintered bodies in which the
nano-particle size was maintained.
[0228] The complete disclosures of the patents, patent documents
and publications cited herein are incorporated by reference in
their entirety as if each were individually incorporated. In case
of conflict, the present specification, including definitions,
shall control. Various modifications and alterations to this
invention will become apparent to those skilled in the art without
departing from the scope and spirit of this invention. Illustrative
embodiments and examples are provided as examples only and are not
intended to limit the scope of the present invention. The scope of
the invention is limited only by the claims set forth as
follows.
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