U.S. patent application number 14/933980 was filed with the patent office on 2016-03-03 for method and apparatus for sintering flat ceramics.
The applicant listed for this patent is NITTO DENKO CORPORATION. Invention is credited to Hironaka Fujii, Hiroaki Miyagawa, Amane Mochizuki, Toshitaka Nakamura, Guang Pan, Bin Zhang.
Application Number | 20160060178 14/933980 |
Document ID | / |
Family ID | 49379243 |
Filed Date | 2016-03-03 |
United States Patent
Application |
20160060178 |
Kind Code |
A1 |
Miyagawa; Hiroaki ; et
al. |
March 3, 2016 |
Method and Apparatus for Sintering Flat Ceramics
Abstract
A method and apparatus for sintering flat ceramics using a mesh
or lattice is described herein.
Inventors: |
Miyagawa; Hiroaki;
(Oceanside, CA) ; Pan; Guang; (Carlsbad, CA)
; Fujii; Hironaka; (Osaka, JP) ; Zhang; Bin;
(San Diego, CA) ; Mochizuki; Amane; (Osaka,
JP) ; Nakamura; Toshitaka; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NITTO DENKO CORPORATION |
Osaka |
|
JP |
|
|
Family ID: |
49379243 |
Appl. No.: |
14/933980 |
Filed: |
November 5, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13865950 |
Apr 18, 2013 |
9206086 |
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14933980 |
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13842878 |
Mar 15, 2013 |
9205571 |
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13865950 |
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61635129 |
Apr 18, 2012 |
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Current U.S.
Class: |
252/301.36 ;
264/607 |
Current CPC
Class: |
C04B 35/64 20130101;
C04B 2235/3224 20130101; C04B 2235/6581 20130101; C04B 35/6342
20130101; C04B 35/597 20130101; C04B 2235/3225 20130101; C04B
2235/9638 20130101; C04B 35/58 20130101; C04B 38/067 20130101; C04B
2237/562 20130101; C04B 35/6261 20130101; C04B 2235/9653 20130101;
C04B 2235/5409 20130101; C04B 2235/3418 20130101; C04B 35/44
20130101; C04B 38/067 20130101; C04B 2237/343 20130101; C04B
2237/567 20130101; C04B 35/14 20130101; B32B 18/00 20130101; C04B
38/0038 20130101; C04B 35/505 20130101; C04B 35/50 20130101; C04B
2235/9646 20130101; C04B 2235/963 20130101; C04B 35/632 20130101;
C04B 2235/6025 20130101; C04B 2235/612 20130101; C04B 2235/6562
20130101; C04B 2235/6565 20130101; C04B 2237/704 20130101; C04B
2235/763 20130101; C04B 35/63488 20130101; C04B 2235/441 20130101;
C04B 35/6263 20130101; C04B 35/44 20130101 |
International
Class: |
C04B 38/00 20060101
C04B038/00; C04B 35/50 20060101 C04B035/50; C04B 35/505 20060101
C04B035/505 |
Claims
1. A method of sintering a ceramic to produce a sintered ceramic
plate, comprising: heating a ceramic precursor material between a
first mesh and a second mesh; wherein at least a first portion of
the ceramic precursor material contacts the first mesh and at least
a second portion of the ceramic precursor material contacts the
second mesh during heating, thereby producing a sintered ceramic
plate.
2. The method of claim 1, wherein either or both of the first mesh
and the second mesh comprise heat conductive material, the heat
conductive material comprising stainless steel, iron, iron alloys,
copper, copper alloys, niobium, niobium alloys, molybdenum,
molybdenum alloys, nickel, nickel alloys, platinum, platinum
alloys, tantalum, tantalum alloys, titanium, titanium alloys,
tungsten, tungsten alloys, rhenium, rhenium alloys, or any
combination thereof.
3. The method of claim 2, wherein the heat conductive material
comprises a tungsten:molybdenum alloy.
4. The method of claim 3, wherein the tungsten:molybdenum alloy is
about 3% molybdenum.
5. The method of claim 1, wherein the ceramic precursor material
slidably contacts the first mesh and/or the second mesh at a
plurality of substantially periodic and/or substantially uniformly
distributed contact points or lines.
6. The method of claim 5, further comprising applying sufficient
pressure to the precursor material to reduce camber of the sintered
ceramic plate but allow sliding engagement of the ceramic precursor
material with the first mesh and the second mesh, wherein the
applying sufficient pressure comprises placing a metal plate of
about 0.1 gm/cm2 to about 20 gm/cm2 on the first mesh.
7. The method of claim 1, wherein the ceramic precursor material is
a product of a slurry of solvent, binder and ceramic particles that
have been heated at a sufficiently high temperature to evaporate or
burn substantially all of the binder and solvent.
8. The method of claim 1, wherein camber of the sintered ceramic
plate is less than 50 .mu.m/mm2 vertical displacement.
9. The method of claim 1, wherein either or both of the first mesh
and the second mesh have a mesh size of more than about 30 wires
per inch to about 100 wires per inch, and a wire diameter of less
than 400 .mu.m.
10. The method of claim 1, wherein either or both of the first mesh
and the second mesh is configured as a plain weave or as a twill
weave.
11. The method of claim 1, wherein the ceramic precursor material
is in the form of an unsintered ceramic compact comprising an oxide
material, a garnet material, a nitride material, and/or an
oxynitride material.
12. The method of claim 11, wherein the oxide material comprises a
metallic element or silicon.
13. The method of claim 11, wherein the garnet material comprises
yttrium.
14. The method of claim 11, wherein the oxynitride material
comprises a metallic element or silicon.
15. The method of claim 1, wherein either or both of the first mesh
and the second mesh comprise wires intersecting at an angle of
about 10.degree., about 15.degree., about 30.degree., about
45.degree., about 60.degree., about 80.degree., or about
90.degree..
16. The method of claim 1, wherein either or both of the first mesh
and the second mesh have a mesh size that is the same in both
dimensions, and the mesh size is about 40.times.40 wires per inch,
about 50.times.50 wires per inch, about 60.times.60 wires per inch,
about 70.times.70 wires per inch, or about 80.times.80 wires per
inch.
17. The method of claim 1, wherein the sintered ceramic plate
comprises an optionally doped yttrium aluminum garnet and/or an
optionally doped lutetium aluminum garnet.
18. The method of claim 17, wherein the yttrium aluminum garnet is
a gadolinium-doped yttrium aluminum garnet.
19. A sintered ceramic plate produced according to the method of
claim 1.
20. A lighting device comprising the sintered ceramic plate of
claim 19.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/865,950 (U.S. Publication No. 2013/0277613
A1) filed on Apr. 18, 2013, which is a continuation-in-part of U.S.
patent application Ser. No. 13/842,878 (U.S. Publication No.
2013/0288875 A1) filed on Mar. 15, 2013, which claims the benefit
of U.S. Provisional Patent Application No. 61/635,129, filed Apr.
18, 2012, the entire disclosure of all these documents are
incorporated herein by reference.
FIELD OF THE DISCLOSURE
[0002] Disclosed herein are methods in which ceramic materials,
such as phosphors, can be sintered by heating a precursor material
between two mesh structures. Such methods reduce camber, warping
and cracking of the ceramic materials. Also disclosed herein are
ceramic materials made according to such methods, and devices
comprising these ceramic materials.
BACKGROUND
[0003] Sintering of powders is part of the process in manufacturing
various ceramic materials. Generally speaking, sintering includes
mixing water, a binder, a deflocculant, and ceramic powder to form
a slurry, then drying the slurry to form a dried powder such as by
spray-drying, pressing the dried powder such as in a mold to form a
green body (i.e., an unsintered ceramic item), heating the green
body at low temperature to burn off the binder, then sintering at
high temperature to fuse the ceramic particles together into the
ceramic material.
[0004] It is known that sintering is associated with great
shrinkage of the ceramic material as the ceramic powder is
consolidated. Shrinkage in turn gives rise to camber, or warping
and cracking, and surface damage of the ceramic material.
[0005] The present disclosure relates to methods of sintering
ceramic materials which reduces or eliminates such difficulties
associated with sintering of ceramic materials.
SUMMARY
[0006] The present disclosure relates to methods of sintering
ceramic materials, such as phosphors, comprising heating a
precursor material between two mesh (or lattice) structures. These
methods reduce camber, or warping and cracking, of the ceramic
materials. In certain embodiments, these methods can be used when
the heating step(s) in the sintering process is done under
pressure.
[0007] Some embodiments include a method of sintering a ceramic
comprising: heating a ceramic precursor material between a first
mesh and a second mesh, wherein at least a first portion of the
ceramic precursor material contacts the first mesh and at least a
second portion of the ceramic precursor contacts the second mesh
during heating, thereby producing a sintered ceramic plate. In
further embodiments, the ceramic precursor material is in the form
of an unsintered ceramic compact comprising ceramic particles. In
certain embodiments, the ceramic precursor material slidably
contacts the first mesh and the second mesh.
[0008] In certain embodiments, the mesh comprises heat conductive
material. In further embodiments, the heat conductive material has
a degradation temperature greater than the sintering temperature of
the unsintered ceramic compact. In some embodiments the degradation
temperature is at least 200.degree. C. greater than the sintering
temperature.
[0009] In some embodiments of the methods, the ceramic precursor
material is a product of a slurry of solvent, binder and ceramic
particles that have been heated at a sufficiently high temperature
to evaporate or burn substantially all of the binder and solvent.
In certain embodiments, the ceramic precursor material is in the
form of an unsintered green sheet comprising ceramic particles.
[0010] In some embodiments, the ceramic precursor material slidably
contacts the first mesh and/or the second mesh at a plurality of
substantially periodic distributed contact points or lines. In
certain embodiments, the number of contact points or lines is
approximately 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500,
5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, or
10000.
[0011] Certain embodiments of the present methods further comprise
applying sufficient pressure to the precursor material to reduce
camber of the sintered ceramic plate but allow sliding engagement
of the ceramic precursor material with the first mesh and/or the
second mesh. In some embodiments, the camber of the sintered
ceramic plate is less than 50 .mu.m/mm.sup.2 vertical displacement.
In some embodiments, the applying sufficient pressure comprises
placing a metal plate of about 0.1 gm/cm2 to about 20 gm/cm2 on the
first mesh.
[0012] In certain embodiments of the present methods, the heat
conductive material comprises stainless steel, iron, iron alloys,
copper, copper alloys, niobium, niobium alloys, molybdenum,
molybdenum alloys, nickel, nickel alloys, platinum, platinum
alloys, tantalum, tantalum alloys, titanium, titanium alloys,
tungsten, tungsten alloys, rhenium, rhenium alloys, or any
combination thereof. In some embodiments, the heat conductive
material substantially comprises tungsten. In other embodiments,
the heat conductive material comprises a tungsten:molybdenum alloy.
In certain embodiments, the tungsten:molybdenum alloy is about 3%
molybdenum.
[0013] In some embodiments, either or both of the first mesh and
the second mesh is configured as a plain weave. In other
embodiments, either or both of the first mesh and the second mesh
is configured as a twill weave.
[0014] In some embodiments, the ceramic precursor material is in
the form of an unsintered ceramic compact comprising an oxide
material. In certain embodiments, the oxide material comprises a
metallic element such as, for example but without limitation,
silicon. In other embodiments, the ceramic precursor material is in
the form of an unsintered ceramic compact comprising a garnet
material such as, for example but without limitation, yttrium. In
other embodiments, the ceramic precursor material is in the form of
an unsintered ceramic compact comprising a nitride material. In
other embodiments, the ceramic precursor material is in the form of
an unsintered ceramic compact comprising an oxynitride material. In
certain embodiments, the oxynitride material comprises a metallic
element such as, for example but without limitation, silicon.
[0015] In some embodiments, either or both of the first mesh and
the second mesh comprise wires intersecting at an angle of about
10.degree., about 15.degree., about 30.degree., about 45.degree.,
about 60.degree., or about 80.degree.. In some embodiments, either
or both of the first mesh and the second mesh comprise wires
intersecting at an angle of 90.degree..
[0016] In some embodiments, either or both of the first mesh and
the second mesh have a mesh size that is about 5 wires per inch to
about 500 wires per inch. In certain embodiments, the mesh size is
about 40 wires per inch, about 50 wires per inch, about 60 wires
per inch, about 70 wires per inch, or about 80 wires per inch. In
certain embodiments, either or both of the first mesh and the
second mesh have a mesh size of about 30 wires per inch to about
100 wires per inch, and a wire diameter of less than about 400
.mu.m.
[0017] In some embodiments, either or both of the first mesh and
the second mesh have a mesh size that is the same in both
dimensions. In certain embodiments, the mesh size is about
40.times.40 wires per inch, about 50.times.50 wires per inch, about
60.times.60 wires per inch, about 70.times.70 wires per inch, or
about 80.times.80 wires per inch.
[0018] In some embodiments, either or both of the first mesh and
the second mesh have a mesh size that is not the same in both
dimensions.
[0019] Further embodiments relate to a sintered ceramic plate
produced according to any of the methods described herein. Yet
other embodiments relate to a lighting device comprising a sintered
ceramic plate produced by the any of the methods as disclosed
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 1A-C illustrate contact points in embodiment of a mesh
comprising intersecting wires. FIGS. 1A and 1B specifically depict
an embodiment of a mesh of the interwoven type.
[0021] FIG. 1D depicts contact lines for twill weave.
[0022] FIGS. 2A and 2B illustrate an embodiment of a mesh in which
intersecting wires overlay each other.
[0023] FIG. 3 illustrates an embodiment of a configuration of
plates for sintering ceramic materials.
[0024] FIG. 4 illustrates an embodiment of a light-emitting device
that includes a ceramic phosphor.
[0025] FIG. 5 illustrates a measurement of camber as described in
certain embodiments herein.
[0026] FIG. 6 illustrates the correlation between measured warpage
and the number of contact points or lines in the mesh.
[0027] FIG. 7 illustrates the correlation between measured surface
roughness (Ra) and the number of contact points or lines in the
mesh.
DETAILED DESCRIPTION
[0028] In the methods described herein, a ceramic precursor
material is heated between two mesh structures, such as a first
mesh and a second mesh. The precursor material is often in the form
of a flat plate. Generally a first portion, or side in the case of
a plate, of the precursor material comes in contact with the first
mesh and a second portion, or side of the plate, comes in contact
with the second mesh. The first mesh and the second mesh may be of
the same or different type of mesh, and may comprise the same or
different materials.
[0029] A first mesh or a second mesh (referred to collectively
herein as "a mesh") refers to any structure that comprises
intersecting strips or wires (referred to collectively hereafter as
"wires"). By "intersecting" as used herein is meant simply that
contact points 50 are created where the wires are in contact. See,
e.g., FIGS. 1A-1C. Intersecting wires create a mesh opening 60.
FIG. 1C. The mesh count or size 70 of a mesh refers to the number
of wires in any one direction (commonly referred to as the "warp"
in one direction, and the "weft" or "shute" in the other) per inch,
cm or other unit of measure. See FIG. 1C. The specific
characteristics of the mesh in any of various embodiments can vary
depending upon the circumstances; e.g., the mesh size, the size and
shape of the mesh opening, etc.
[0030] In some embodiments, the mesh is configured such that the
intersecting wires of the mesh are interwoven. By "interwoven" is
meant that each wire passes over and under one or more of its
intersecting wires. FIG. 1A depicts an example of one type of
interwoven mesh configuration, wherein wires 10, 20, and 30 are
interwoven with wires 15, 25, 35, and 45. See also FIG. 1B, in
which wire 30 is interwoven with wires 15, 25, 35 and 45. In such
embodiments, contact points are formed when one wire is positioned
above another. See, e.g., FIG. 1B, in which a contact points 50 are
formed at each point where wire 30 intersects wires 15, 25, 35 and
45 in the interwoven structure. In some embodiments, the mesh is
configured such that the intersecting wires of the mesh overlay
each other. See, e.g., FIG. 2A, in which wires 205, 215, 225, and
235 overlay wires 210, 220, and 230. See also FIG. 2B, in which
wire 210 overlays wires 205, 215, 225, and 235.
[0031] In some embodiments, the mesh can be configured as a
combination of interwoven and overlaid wires; i.e., the
intersecting wires of the mesh alternately overlay and are
interwoven with each other.
[0032] For a weave such as a twill weave (FIG. 1D), wherein the
intersecting wires of mesh overlay and underlay two (or more)
intersecting wires at a time, instead of one, contact lines can be
formed instead of contact points. Such a contact line 85 can be
formed by the portion of the wire that overlays the two or more
intersecting wires.
[0033] Wires may intersect one another at nearly any angle. For
example, a mesh may comprise intersecting wires that are
substantially perpendicular to one another; i.e., the intersecting
wires are at right angles or 90.degree. to each other. FIG. 1A
depicts an example of such a mesh configuration, wherein wires 10,
20, and 30, and wires 15, 25, 35, and 45 are at substantially right
angles. See also FIG. 1C and FIG. 2A. A mesh may also comprise
intersecting wires that are at another angle to one another, such
as 10.degree., 15.degree., 30.degree., 45.degree., 60.degree.,
80.degree., or any angle in a range bounded by, or between, any of
these values.
[0034] In some embodiments, the mesh opening is square. In other
embodiments, the mesh opening is rectangular.
[0035] In some embodiments, the contact points or lines can be
periodically distributed throughout the mesh. In some embodiments
the contact points or lines can be substantially regularly or
uniformly distributed or spaced throughout the mesh. Contact points
or lines may be substantially the same as one another throughout a
mesh.
[0036] Spacing between wires in a mesh may vary in various
embodiments, depending upon the circumstance, resulting in various
mesh sizes. In some embodiments, a mesh may have a mesh size of
about 5 wires/inch to about 500 wires/inch, about 7 wires/inch to
about 200 wires/inch, about 10 wires/inch to about 200 wires/inch,
about 10 wires/inch to about 100 wires/inch, about 15 wires/inch to
about 200 wires/inch, about 15 wires/inch to about 100 wires/inch,
about 20 wires/inch to about 200 wires/inch, about 20 wires/inch to
about 100 wires/inch, about 10 wires/inch, about 30 wires/inch,
about 40 wires/inch, about 50 wires/inch, about 60 wires/inch, or
any mesh size in a range bounded by, or between, any of these
values. The mesh size may be the same in both dimensions, e.g.
10.times.10, 20.times.20, 30.times.30, 40.times.40, 50.times.50,
60.times.60, 70.times.70, 80.times.80, 90.times.90, 100.times.100,
etc. (such as in a square-shaped mesh), or may be different, e.g.
10.times.20, 20.times.30, etc. (such as in a rectangular-shaped
mesh).
[0037] The mesh may be in any shape, such as a square, rectangle,
circle, oval, etc.
[0038] The cross section of a wire in a mesh may be substantially
circular (see, e.g., FIGS. 1A and 1B), or may have another shape
such as square, rectangular (see, e.g., FIG. 2B), oval,
semicircular, etc. The sizes of the wires in the mesh can also vary
in various embodiments. A wire may have a diameter or thickness in
any suitable range. For example, some wires may have a diameter of
about 10 .mu.m to about 1 mm, about 20 .mu.m to about 500 .mu.m,
about 50 .mu.m to about 400 .mu.m, about 50 .mu.m, about 70 .mu.m,
about 69 .mu.m, about 100 .mu.m, about 102 .mu.m, about 120 .mu.m,
about 127 .mu.m, about 130 .mu.m, about 380 .mu.m, about 381 .mu.m,
or any diameter in a range bounded by, or between, any of these
values. The intersecting wires of a mesh can be of the same or
different sizes.
[0039] A mesh may be composed of any material capable of conducting
heat, including a metal such as stainless steel, an iron, copper,
niobium, molybdenum, nickel, platinum, tantalum, titanium,
tungsten, or rhenium, or alloys containing any of the above metals,
or any combination thereof. In some embodiments, the mesh can
substantially comprise tungsten. In some embodiments, the mesh can
comprise molybdenum. In some embodiments, the mesh can comprise
tungsten and molybdenum. In some embodiments, the mesh can comprise
0.1-99.9% molybdenum:99.9%-0.01% tungsten. In some embodiments, the
mesh can comprise 40 atom %-60 atom % molybdenum:60 atom %-40 atom
% tungsten. In one embodiment, the mesh can comprise 50 atom %
molybdenum:50 atom % tungsten. In some embodiments, the mesh can
comprise at least one of tungsten and molybdenum and further
comprise rhenium. Normally, the material of a mesh will have a
higher degradation or melting temperature than the sintering
temperature of the precursor material to be sintered. In some
embodiments the metal has a melting temperature at least
200.degree. C. greater than the desired sintering temperature.
[0040] In some embodiments, the mesh is configured as a "plain
weave," in which intersecting wires are interwoven at right angles.
In some embodiments, the mesh is configured as a "twilled weave,"
in which heavier wires are used to produce a square mesh opening,
and each wire alternately overlays two wires and underlays two
wires. (Such as depicted in FIG. 1D) By "staggering" the overlay of
the wires, a diagonal pattern is produced in the twill weave mesh.
In some embodiments, the mesh is configured as a "plain filter
cloth" weave or "Dutch weave." In this configuration, intersecting
wires are interwoven at right angles as in the "plain weave," but
heavier warp and lighter shute wires are used, the shute wires
being crimped to result in a smaller, triangular mesh opening. In
some embodiments, the mesh is configured as a "twilled filter
cloth" weave. In this configuration each wire alternately overlays
two wires and underlays two wires, as in the "twilled weave," but
different wire sizes are used for warp and shute. This permits
twice the mesh count as the regular twilled weave. In some
embodiments, the mesh is configured as a "micron" weave, in which
finer wires overlap heavier wires with specialized wire placement,
to create a higher mesh count. A micron weave mesh is extremely
durable, and with such a configuration it is possible to have as
many as 1,000,000 mesh openings per square inch. In some
embodiments, the mesh is configured as a "grid" (or "grid
specifications") weave, in which very fine wire is used, the wire
comprising for example stainless steel. Such a mesh configuration
can result in very high percent of mesh opening area.
[0041] In some embodiments, one or both meshes are not bonded to a
precursor material before sintering. In some embodiments, a mesh
may be slidably contacted with the precursor material. In some
embodiments, the precursor material, such as a ceramic compact, may
be slidably contacted with the meshes at a plurality of contact
points or lines. A ceramic compact may comprise ceramic particles.
"Slidably contacted" includes a situation in which solid precursor
material can shrink or move in the direction of the plane of
contact between the precursor material and a mesh. This may help to
reduce the formation of cracks or cambering in a solid ceramic
compact.
[0042] Any suitable heating regime may be used to heat a precursor
material between two mesh structures. For example, the precursor
material may be heated to a maximum temperature of about
1000.degree. C. to about 3000.degree. C., about 1500.degree. C. to
about 2000.degree. C., or about 1800.degree. C. Heating may occur
for as long as desired to obtain the sintering effect sought, such
as about 1 hour to about 50 hours, about 3 hours to about 20 hours,
about 5 hours to about 20 hours, or, e.g., about 5 hours. In some
embodiments, heating to maximum temperature, e.g. 1000-3000.degree.
C., may occur over a period of about 1 hour to about 10 hours, and
the material may then be held at the maximum temperature for about
1 hour to about 20 hours.
[0043] In some embodiments, the mesh structures may be heated by a
conductive plate, which may be composed of a conductive material
such as a metal. Such conductive metal may include an iron alloy, a
copper alloy, niobium, molybdenum, a nickel alloy, platinum,
tantalum, titanium, tungsten, etc. Heating may be accomplished by
using a configuration such as that depicted in FIG. 3. In such a
configuration, a precursor material 310 is sandwiched between, and
has thermal contact with, a first mesh 320 and a second mesh 330.
Mesh 320 in turn has thermal contact with thermal conductive plate
340 and mesh 330 has thermal contact with thermal conductive plate
350. Thus, plate 340 and plate 350 can heat precursor material
through the mesh 320 and 330. Mesh 320 and mesh 330 may comprise
the same material, or different materials.
[0044] This type of configuration may also permit a precursor
material, such as precursor material 310, to be pressurized by
conductive plates, such as conductive plate 340 and conductive
plate 350, which helps to reduce the warping and cracking
associated with heating. In some embodiments, sufficient pressure
may be applied to the precursor material to reduce camber. In some
embodiments, pressure applied is sufficiently low to still permit
sliding engagement between the mesh and the precursor materials. In
some embodiments, pressure is applied by of the weight of the top
plate, which presses through the first and second meshes and the
precursor material to the bottom plate. In some embodiments, the
top plate e.g. plate 350 (which, for the sake of reference, can be
described as being placed on the first mesh), has a weight of about
0.01 g/cm.sup.2 to about 100 g/cm.sup.2 or about 0.1 g/cm.sup.2 to
about 20 g/cm.sup.2. In some embodiments, a plate has a weight of
about 2.5 g/cm.sup.2 to about 7.5 g/cm.sup.2. In some embodiments,
the plates may be 2 inch.times.2 inch squares of a heat conductive
material, such as tungsten, and may weigh about 15 g, about 23 g,
or about 25 g.
[0045] In some embodiments, cambering is less than about 20%, about
10%, or about 5%, quantified as the amount of cambering as a
percentage of the thickness of the flat ceramic piece. In some
embodiments, cambering is less than about 100 .mu.m/mm.sup.2, about
50 .mu.m/mm.sup.2, or about 10 .mu.m/mm.sup.2.
[0046] A precursor composition may include any composition
comprising at least two different atomic elements; e.g.,
Al.sub.2O.sub.3, ZrO.sub.2, Y.sub.2O.sub.3, etc.
[0047] A precursor composition may comprise a bi-elemental oxide,
including a compound containing at least two different atomic
elements, wherein at least one of the two different elements
includes oxygen.
[0048] A precursor composition may comprise a bi-elemental
non-oxide, including a compound containing at least two different
atomic elements, wherein the two different elements do not include
oxygen.
[0049] In some embodiments, a precursor material may comprise a
single or multiple oxide materials.
[0050] In some embodiments, a precursor composition can be a
precursor host material. In some embodiments, the host material may
be powder comprising a single inorganic chemical compound; e.g.,
Y.sub.3Al.sub.5O.sub.12 (YAG) powder as compared to yttria and
alumina. The host materials can have an average grain size diameter
of about 0.1 .mu.m to about 20 .mu.m.
[0051] In some embodiments, a precursor composition can comprise
phosphor powders. Phosphor powders can include, but are not limited
to, oxides, such as oxides of metallic elements or silicon,
including silicate, phosphate, aluminate, borate, tungstate,
vanatate, titanate, molybdate or combinations of those oxides.
Phosphor powders can also include sulfides, oxysulfides,
oxyfluorides, nitrides, carbides, nitridobarates, chlorides,
phosphor glass or combinations thereof.
[0052] In some embodiments, a precursor composition may comprise
one or more oxynitrides, such as an oxynitride comprising a
metallic element or silicon.
[0053] A precursor composition may include a host-dopant material,
such as a material that is primarily a single solid state compound,
or host material, having a small amount of one or more atoms in the
host structure substituted by one or more non-host atoms, or dopant
atoms. In some embodiments, a precursor composition can be a garnet
host material or a nitride host material. In some embodiments the
precursor composition can further comprises a dopant material.
[0054] In some embodiments, the precursor composition can include a
garnet host material. As used herein, a "garnet" includes any
material that would be identified as a garnet by a person of
ordinary skill in the art, and any material identified as a garnet
herein. In some embodiments, the term "garnet" refers to the
tertiary structure of an inorganic compound, such as a mixed metal
oxide.
[0055] In some embodiments, the garnet may be composed of oxygen
and at least two different elements comprising groups II, III, IV,
V, VI, VII, VIII, or Lanthanide metals. For example, the garnet may
be composed of oxygen and a combination of two or more of the
following elements: Ca, Si, Fe, Eu, Ce, Gd, Tb, Lu, Nd, Y, La, In,
Al, and Ga.
[0056] In some embodiments, a synthetic garnet may be described
with the formula A.sub.3D.sub.2(EO.sub.4).sub.3, wherein A, D, and
E are elements comprising group II, III, IV, V, VI, VII, VIII
elements, and Lanthanide metals. A, D, and E may either represent a
single element, or they may represent a primary element that
represents the majority of A, D, or E, and a small amount of one or
more dopant elements also comprising group II, III, IV, V, VI, VII,
VIII elements, and Lanthanide metals. Thus, the above formula may
be expanded to: (primary A+dopants).sub.3(primary
D+dopants).sub.2([primary E+dopants]O.sub.4).sub.3.
[0057] In a garnet particle, the primary element or dopant element
atom of A (e.g., Y.sup.3+) may be in a dodecahedral coordination
site or may be coordinated by eight oxygen atoms in an irregular
cube. Additionally, the primary element or dopant element atom of D
(e.g., Al.sup.3+, Fe.sup.3+, etc.) may be in an octahedral site.
Finally, the primary element or dopant element atom of E (e.g.,
Al.sup.3+, Fe.sup.3+, etc.) may be in a tetrahedral site.
[0058] In some embodiments, a garnet can crystallize in a cubic
system, wherein the three axes are of substantially equal lengths
and perpendicular to each other. In these embodiments, this
physical characteristic may contribute to the transparency or other
chemical or physical characteristics of the resulting material. In
some embodiments, the garnet may be yttrium iron garnet (YIG),
which may be represented by the formula
Y.sub.3Fe.sub.2(FeO.sub.4).sub.3 or (Y.sub.3Fe.sub.5O.sub.12). In
YIG, the five iron(III) ions may occupy two octahedral and three
tetrahedral sites, with the yttrium(III) ions coordinated by eight
oxygen ions in an irregular cube. In YIG, the iron ions in the two
coordination sites may exhibit different spins, which may result in
magnetic behavior. By substituting specific sites with rare earth
elements, for example, interesting magnetic properties may be
obtained.
[0059] Some embodiments comprise metal oxide garnets, such as YAG
or Gd.sub.3Ga.sub.5O.sub.12 (GGG), which may have desired optical
characteristics such as transparency or translucency. In these
embodiments, the dodecahedral site can be partially doped or
completely substituted with other rare-earth cations for
applications such as phosphor powders for electroluminescent
devices. In some embodiments, specific sites are substituted with
rare earth elements, such as cerium. In some embodiments, doping
with rare earth elements or other dopants may be useful to tune
properties such as optical properties. For example, some doped
compounds can luminesce upon the application of electromagnetic
energy. In phosphor applications, some embodiments are represented
by the formula (A.sub.1-xRE.sub.x).sub.3D.sub.5O.sub.12, wherein A
and D are divalent, trivalent, quadrivalent or pentavalent
elements; A may comprise, for example, Y, Gd, La, Lu, Yb, Tb, Sc,
Ca, Mg, Sr, Ba, Mn and combinations thereof; D may comprise, for
example, Al, Ga, In, Mo, Fe, Si, P, V and combinations thereof;
and, RE may be rare earth metal or a transition element comprising,
for example, Ce, Eu, Tb, Nd, Pr, Dy, Ho, Sm, Er, Cr, Ni, and
combinations thereof. This compound may be a cubic material having
useful optical characteristics such as transparency, translucency,
or emission of a desired color.
[0060] In some embodiments, a garnet may comprise yttrium aluminum
garnet, Y.sub.3Al.sub.5O.sub.12 (YAG). In some embodiments, YAG may
be doped with neodymium (Nd.sup.3+). YAG prepared as disclosed
herein may be useful as the lasing medium in lasers. Embodiments
for laser uses may include YAG doped with neodymium and chromium
(Nd:Cr:YAG or Nd/Cr:YAG); erbium-doped YAG (Er:YAG),
ytterbium-doped YAG (Yb:YAG); neodymium-cerium double-doped YAG
(Nd:Ce:YAG, or Nd,Ce:YAG); holmium-chromium-thulium triple-doped
YAG (Ho:Cr:Tm:YAG, or Ho,Cr,Tm:YAG); thulium-doped YAG (Tm:YAG);
and chromium (IV)-doped YAG (Cr:YAG). In some embodiments, YAG may
be doped with cerium (Ce.sup.3+). Cerium doped YAG may be useful as
phosphors in light emitting devices; e.g., light emitting diodes
and cathode ray tubes. Other embodiments include dysprosium-doped
YAG (Dy:YAG); and terbium-doped YAG (Tb:YAG), which are also useful
as phosphors in light emitting devices. Some embodiments include
gadolinium-doped YAG (Gd:YAG), such as gadolinium-doped YAG having
about 0.1 atom % to 40 atom %, about 1 atom % to about 35 atom %,
about 5 atom % to about 25 atom %, about 8 atom % to about 15 atom
%, or about 10% atom % gadolinium, based upon the total number of
atoms of yttrium and gadolinium.
[0061] In some embodiments, the sintered ceramic plate may be a
lutetium aluminum oxide, such as an optionally doped lutetium
aluminum garnet (LuAG). In some embodiments, the LuAG is
undoped.
[0062] In some embodiments, the garnet host material can be a
precursor material comprising an oxide of yttrium, an oxide of
aluminum, an oxide of lutetium, and an oxide of gadolinium.
[0063] In some embodiments, the nitride host material can be a
material having a quaternary host material structure represented by
a general formula M-A-B--N:Z. Such a structure may increase the
emission efficiency of a phosphor. In some embodiments, M is a
divalent element, A is a trivalent element, B is a tetravalent
element, N is nitrogen, and Z is a dopant/activator in the host
material.
[0064] M may be Mg, Be, Ca, Sr, Ba, Zn, Cd, Hg, or a combination
thereof. A may be B (boron), Al, Ga, In, Ti, Y, Sc, P, As, Sb, Bi,
or a combination thereof. B may be C, Si, Ge, Sn, Ni, Hf, Mo, W,
Cr, Pb, Zr, or a combination thereof. Z may be one or more
rare-earth elements, one or more transition metal elements, or a
combination thereof.
[0065] In the nitride material, a mol ratio Z/(M+Z) of the element
M and the dopant element Z may be about 0.0001 to about 0.5. When
the mol ratio Z/(M+Z) of the element M and the activator element Z
is in that range, it may be possible to avoid decrease of emission
efficiency due to concentration quenching caused by an excessive
content of the activator. On the other hand, when the mole ratio is
in that range, it may also be possible to avoid a decrease of
emission efficiency due to an excessively small amount of light
emission contributing atoms caused by an excessively small content
of the activator. Depending on the type of the activating element Z
to be added, an optimum percentage of Z/(M+Z) may vary. In some
embodiments, a Z/(M+Z) mol ratio in a range from 0.0005 to 0.1 may
provide improved emission.
[0066] For a composition wherein M is Mg, Ca, Sr, Ba, Zn, or a
combination thereof, raw materials can be easily obtained and the
environmental load is low. Thus, such a composition may be
preferred.
[0067] For a composition wherein M is Ca, A is Al, B is Si, and Z
is Eu in a material, raw materials can be easily obtained and the
environmental load is low. Additionally, the emission wavelength of
a phosphor having such a composition is in the red range. A red
based phosphor may be capable of producing warm white light with
high Color Rendering Index (CRI) at adjusted color temperature when
combined with blue light emitting diode (LED) and yellow phosphors.
Thus, such a composition may be preferred.
[0068] Some examples of a nitride host precursor include
Ca.sub.3N.sub.2 (such as Ca.sub.3N.sub.2 having at least 2N), AlN
(such as AlN having at least 3N), Si.sub.3N.sub.4 (such as
Si.sub.3N.sub.4 having at least 3N). The term 2N refers to a purity
of at least 99% pure. The term 3N refers to a purity of at least
99.9% pure.
[0069] In some embodiments, a precursor composition can further
include a dopant precursor. In some embodiments, the dopant can be
a rare earth compound or a transition metal. In some embodiments,
the dopants can comprise Ce.sup.3+, Gd.sup.3+, and or Eu.sup.2+.
Suitable precursor dopant materials include, but are not limited
to, CeO.sub.2, Ce(NO.sub.3).sub.3,
[Ce(NO.sub.3).sub.3].[6H.sub.2O], Ce.sub.2O.sub.3, Gd.sub.2O.sub.3,
and/or EuN. Other suitable precursor dopant materials include the
respective metal oxide of the desired dopant material; e.g., oxides
of Tm, Pr, and/or Cr.
[0070] In some embodiments, a precursor material may be in the form
of a ceramic compact. A ceramic compact includes precursor material
that is compacted or preformed to some extent. Ceramic compacts may
include materials to aid in sintering such as a solvent or a
binder. Before or during sintering, the material may be heated to a
sufficiently high temperature to remove any solvent, binder, and/or
any other organic material.
[0071] In some embodiments, a ceramic compact may be in the form of
a green sheet comprising ceramic particles.
[0072] In some embodiments, the garnet material, and other
materials such as flux additives, plasticizers, solvents useful to
create a slurry or green sheet, can be those materials as described
in U.S. Pat. No. 8,283,843, filed Jan. 28, 2011 and U.S. Pat. No.
8,169,136, filed Feb. 19, 2009, which are incorporated by reference
herein for all they disclose regarding materials for creating
slurries or green sheets.
[0073] FIG. 4 shows an example of one way that a phosphor ceramic
may be integrated into an LED. A phosphor ceramic 101 may be
disposed above an LED 102 so that light from the LED passes through
the phosphor ceramic before leaving the system. Part of the light
emitted from the LED may be absorbed by the phosphor ceramic and
subsequently converted to light of a lower wavelength by
luminescent emission. Thus, the color of light-emitted by the LED
may be modified by a phosphor ceramic such as phosphor ceramic
101.
[0074] Further embodiments include, but are not limited to, the
following:
[0075] 1. A method of sintering a ceramic to produce a sintered
ceramic plate, comprising: heating a ceramic precursor material
between a first mesh and a second mesh; wherein at least a first
portion of the ceramic precursor material contacts the first mesh
and at least a second portion the ceramic precursor material
contacts the second mesh during heating, thereby producing a
sintered ceramic plate.
[0076] 2. The method of (1), wherein the ceramic precursor material
is in the form of an unsintered ceramic compact comprising ceramic
particles.
[0077] 3. The method of (1) or (2), wherein the ceramic precursor
material slidably contacts the first mesh and the second mesh.
[0078] 4. The method of any one of (1)-(3), wherein either or both
of the first mesh and the second mesh comprise heat conductive
material.
[0079] 5. The method of (4), wherein the heat conductive material
has a degradation temperature greater than the sintering
temperature of the unsintered ceramic compact.
[0080] 6. The method of (5), wherein the degradation temperature is
at least 200.degree. C. greater than the sintering temperature.
[0081] 7. The method of any one of (1)-(6), wherein the ceramic
precursor material is a product of a slurry of solvent, binder and
ceramic particles that have been heated at a sufficiently high
temperature to evaporate or burn substantially all of the binder
and solvent.
[0082] 8. The method of any one of (1)-(7), wherein the ceramic
precursor material is in the form of an unsintered green sheet
comprising ceramic particles.
[0083] 9. The method of any one of (1)-(8), wherein the ceramic
precursor material slidably contacts the first mesh and/or the
second mesh at a plurality of substantially periodic distributed
contact points or lines.
[0084] 10. The method of any one of (1)-(9), wherein the ceramic
precursor material slidably contacts the first mesh and/or the
second mesh at a plurality of substantially uniformly distributed
contact points or lines.
[0085] 11. The method of any one of (1)-(10), wherein the number of
contact points or lines per square inch is approximately 500, 1000,
1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500,
7000, 7500, 8000, 8500, 9000, 9500, or 10000.
[0086] 12. The method of any one of (1)-(11), further comprising
applying sufficient pressure to the precursor material to reduce
camber of the sintered ceramic plate but allow sliding engagement
of the ceramic precursor material with the first mesh and/or the
second mesh.
[0087] 13. The method of (12), wherein the camber of the sintered
ceramic plate is less than 50 .mu.m/mm2 vertical displacement.
[0088] 14. The method of (12) or (13), wherein the applying
sufficient pressure comprises placing a metal plate of about 0.1
gm/cm2 to about 20 gm/cm2 on the first mesh.
[0089] 15. The method of (4), wherein the heat conductive material
comprises stainless steel, iron, iron alloys, copper, copper
alloys, niobium, niobium alloys, molybdenum, molybdenum alloys,
nickel, nickel alloys, platinum, platinum alloys, tantalum,
tantalum alloys, titanium, titanium alloys, tungsten, tungsten
alloys, rhenium, rhenium alloys, or any combination thereof.
[0090] 16. The method of (15), wherein the heat conductive material
substantially comprises tungsten.
[0091] 17. The method of (15), wherein the heat conductive material
comprises a tungsten:molybdenum alloy.
[0092] 18. The method of (17), wherein the tungsten:molybdenum
alloy is about 50 atom % molybdenum.
[0093] 19. The method of any one of (1)-(18), wherein either or
both of the first mesh and the second mesh comprise plural
interwoven wires, wherein the plural interwoven wires provide a
plurality of substantially uniformly distributed contact points or
lines in a plane.
[0094] 20. The method of any one of (1)-(19), wherein either or
both of the first mesh and the second mesh is configured as a plain
weave.
[0095] 21. The method of any one of (1)-(19), wherein either or
both of the first mesh and the second mesh is configured as a twill
weave.
[0096] 22. The method of any one of (1)-(21), wherein the ceramic
precursor material is in the form of an unsintered ceramic compact
comprising an oxide material.
[0097] 23. The method of (22), wherein the oxide material comprises
a metallic element.
[0098] 24. The method of (22), wherein the oxide material comprises
silicon.
[0099] 25. The method of any one of (1)-(24), wherein the ceramic
precursor material is in the form of an unsintered ceramic compact
comprising a garnet material.
[0100] 26. The method of (25), wherein the garnet material
comprises yttrium.
[0101] 27. The method of any one of (1)-(26), wherein the ceramic
precursor material is in the form of an unsintered ceramic compact
comprising a nitride material.
[0102] 28. The method of any one of (1)-(27), wherein the ceramic
precursor material is in the form of an unsintered ceramic compact
comprising an oxynitride material.
[0103] 29. The method of (28), wherein the oxynitride material
comprises a metallic element.
[0104] 30. The method of (28), wherein the oxynitride material
comprises silicon.
[0105] 31. The method of any one of (1)-(30), wherein either or
both of the first mesh and the second mesh comprise wires
intersecting at an angle of 90.degree..
[0106] 32. The method of any one of (1)-(30), wherein either or
both of the first mesh and the second mesh comprise wires
intersecting at an angle of about 10.degree., about 15.degree.,
about 30.degree., about 45.degree., about 60.degree., or about
80.degree..
[0107] 33. The method of any one of (1)-(32), wherein either or
both of the first mesh and the second mesh have a mesh size that is
about 5 wires per inch to about 500 wires per inch.
[0108] 34. The method of (33), wherein the mesh size is about 10
wires per inch to about 200 wires per inch.
[0109] 35. The method of (34), wherein the mesh size is about 30
wires per inch to about 100 wires per inch.
[0110] 36. The method of (35), wherein the mesh size is about 40
wires per inch, about 50 wires per inch, about 60 wires per inch,
about 70 wires per inch, or about 80 wires per inch.
[0111] 37. The method of any one of (1)-(36), wherein either or
both of the first mesh and the second mesh have a mesh size of
about 30 wires per inch to about 100 wires per inch, and a wire
diameter of less than about 400 .mu.m.
[0112] 38. The method of any one of (1)-(37), wherein either or
both of the first mesh and the second mesh have a mesh size that is
the same in both dimensions.
[0113] 39. The method of (38), wherein the mesh size is about
40.times.40 wires per inch, about 50.times.50 wires per inch, about
60.times.60 wires per inch, about 70.times.70 wires per inch, or
about 80.times.80 wires per inch.
[0114] 40. The method of any one of (1)-(37), wherein either or
both of the first mesh and the second mesh have a mesh size that is
not the same in both dimensions.
[0115] 41. The method of any one of (1)-(21) and (31)-(39), wherein
the sintered ceramic plate comprises an optionally doped yttrium
aluminum garnet.
[0116] 42. The method of (41), wherein the sintered ceramic plate
comprises gadolinium-doped yttrium aluminum garnet.
[0117] 43. The method of (41), wherein the yttrium aluminum garnet
is undoped.
[0118] 44. The method of any one of (1)-(21) and (31)-(39), wherein
the sintered ceramic plate comprises an optionally doped lutetium
aluminum garnet.
[0119] 45. The method of (44), wherein the lutetium aluminum garnet
is undoped.
[0120] 46. A sintered ceramic plate produced according to the
method of any one of (1)-(45).
[0121] A lighting device comprising the sintered ceramic plate of
(46).
EXAMPLES
Example 1
[0122] In this Example, 57.06 g of Y.sub.2O.sub.3 particles with a
Brunauer-Emmett-Teller (BET) surface area of approximately 4.5
m.sup.2/g, and 42.94 g of Al.sub.2O.sub.3 particles with a BET
surface area of 5.6 m.sup.2/g, were added to a 250 ml ZrO.sub.2
ball mill jar (Torrey Hills Technologies, LLC, San Diego, Calif.).
The total powder weight was 100.00 g and the mixing ratio of
Y.sub.2O.sub.3 to Al.sub.2O.sub.3 was at a stoichiometric ratio of
3:5 in mol % for forming YAG. Dispersant (2.00 pph, 2.00 g) and
tetraethyl orthosilicate (0.50 pph, 0.50 g) as a sintering aid were
also added to the mill jar. Toluene (33.33 g) was added to the mill
jar, and the contents in the mill jar were then stirred by hand
until the mixture seemed liquid-like. Then 130 g of ZrO.sub.2
milling media of 3 mm diameter were added to the mill jar, and the
mixture in the mill jar was milled by a bench-top planetary ball
mill (MTI Corporation, Richmond, Calif.) for about 24 h. as a first
mixing step.
[0123] Concurrently, a binder solution of polymeric binder and
plasticizers was prepared by dissolving 21.00 g poly(vinyl
butyral-co-vinyl alcohol-co-vinyl acetate) (PVB), 10.50 g benzyl
n-butyl phthalate (BBP), and 10.50 g polyethylene glycol (PEG) in
90 g toluene while stirring all for about 24 h.
[0124] Binder solution (47.14 g) prepared as above was added to the
milled solution of ceramic particles in the mill jar so as to
contain 7.50 pph PVB, 3.75 pph BBP, and 3.75 pph PEG in the final
slurry. Then this mixture was further ball-milled by the bench-top
planetary ball mill for about an additional 24 h. When the entire
ball milling process was completed, the resultant slurry was
filtered through a syringe-aided metal screen filter with pore size
of 0.05 mm, in order to remove aggregated ceramic particles.
Viscosity of the resulted slurry was in the range of 400 cP to 800
cP. The slurry was then cast on silicone-coated polyethylene
teraphthalate substrate film (Paul N. Gardner Company, Inc.,
Pompano Beach, Fla.) with an adjustable film applicator (Gardner
Company) at a cast rate of 1.1 m/min. The blade gap of the film
applicator was adjusted depending on the desired green sheet
thickness. The cast tape was dried at ambient atmosphere to finally
obtain an approximately 80-100 .mu.m thick ceramic green sheet.
[0125] The dried green sheet was cut to the appropriate size by
razor blade, the cut green sheets were detached from the PET
substrate, and plural sheets were layered to obtain the desired
thickness of the green sheet laminates in the range of 80 micron to
3.0 mm thick. This assembly was laminated at 24 MPa at room
temperature for about 5 min., followed by 16 MPa at about
85.degree. C. for about 5 min. using a TBH-100H heating press
(Sansho Industry, Japan). The laminated compacts were then cut
using the VLS 2.30 laser engraving and cutting system (Universal
Laser Systems) with a 25 W CO.sub.2 laser to obtain green laminate
compacts of 12 mm.times.12mm, 18.5 mm.times.18.5 mm, 30 mm.times.30
mm, or 50 mm.times.50 mm square shapes, or an 80 mm diameter disc.
Each size of the cut laminate compacts was 10 mm.times.10 mm, 15
mm.times.15 mm, 25 mm.times.25 mm, or 40 mm.times.40 mm square
shapes, or a 65 mm diameter disc-shape flat ceramic piece,
respectively.
[0126] As the next step, the polymeric binder was removed from the
laminated compacts. The laminated compacts were sandwiched between
Al.sub.2O.sub.3 porous cover plates with 40% nominal porosity, in
order to avoid the warping, cambering and bending of the laminated
compacts during the debinding process. A plurality of green
laminate compacts was stacked between porous Al.sub.2O.sub.3 cover
plates (ESL ElectroScience, King of Prussia, Pa.), alternately. The
laminated compacts were heated to about 1200.degree. C. for about 2
h. in air using a ST-1700C-445 box furnace (SentroTech Corporation,
Brea, Ohio) for de-binding and Bisk-firing. The heating and cooling
rates were <0.7.degree. C./min. and <4.0.degree. C./min.,
respectively. The debinded/Bisk-fired blank samples were fully
sintered at 1800.degree. C. for about 5 hours under 10.sup.-3 Torr
vacuum using a high temperature furnace whose heating elements were
made of tungsten and which was attached with a mechanical pump.
Inside the furnace chamber, the blank samples were sandwiched with
tungsten mesh and tungsten plates, alternately. The mesh types used
are summarized in Table 1, below. See also Comparative Example
4.
[0127] The heating rate of this final sintering process was about
16.7.degree. C./min. (.about.400.degree. C.), 8.0.degree. C./min.
(400-1000.degree. C.), 5.0.degree. C./min. (1000-1400.degree. C.),
3.3.degree. C./min. (1400-1500.degree. C.), and 1.5.degree. C./min.
(1500-1800.degree. C.), whereas the cooling rate was 8.0.degree.
C./min. in order to minimize cracking during sintering.
[0128] Tungsten mesh can provide "point contact" and/or
"2-dimensional (2-D) line contact" (not "area contact") support
during sintering. This point or 2-D line contact allows the thin
green compact to shrink during sintering at high temperature. As a
result, the YAG flat ceramic pieces were sintered at 1800.degree.
C. without cracking due to the tungsten mesh.
[0129] In summary, the green compacts were successfully sintered to
be substantially flat, thin ceramic pieces without cracking
regardless of (a) slurry type, with xylene-ethanol mixed solvent,
toluene, or water; or, (b) the doping elements for the YAG
ceramics; or, (c) different sintering temperatures between
1700-1800.degree. C.; or, (e) existing air voids in the final
sintered YAG plates (instead of fully transparent YAG plates) for
light scattering. These methods should be applicable not only to
vacuum sintering but also H.sub.2, N.sub.2, Ar, and mixed gas
sintering.
[0130] Table 1 shows a summary of the various types of mesh used
for sintering the flat ceramics of this Example 1 and the remaining
Examples ("M"=Mesh; "CE"=Comparative Example; "W"=tungsten;
"Mo"=molybdenum). Note that Mesh 1-7 were square-shaped mesh; i.e.,
the mesh size (at [warp wires per inch].times.[shute wires per
inch]) was the same in both dimensions.
TABLE-US-00001 TABLE 1 M1 M2 M3 M4 M5 M6 M7 CE2 CE3 CE4 CE5 Wire
100 70 50 100 125 100 381 diam. (.mu.m) Wire W/3% W W W W W W W
plate W plate W plate W plate material Mo alloy M size 80 .times.
50 .times. 50 .times. 60 .times. 40 .times. 30 .times. 10 .times.
(in.) 80 50 50 60 40 30 10 M type Plain Plain Plain Twill Plain
Plain Plain # contact 6400 2500 2500 2100 1600 900 100
pts./in..sup.2 Sample 250 200 100 250 300 225 381 381 1,000 50
thickness .mu.m .mu.m .mu.m .mu.m .mu.m .mu.m (0.015) (0.015)
(0.002) in .mu.m (in.) Surface 8.62 8.43 8.43 8.32 7.55 6.88 0.65
3.46 roughness (Ra) in .mu.m Results Good Good Good Good Good Good
Not Not Not Not Not good good good good good
Example 2
[0131] Aqueous slurry was prepared as set forth in Example 1,
excepting as follows: 133.55 g Y.sub.2O.sub.3 particles, 23.82 g
Gd.sub.2O.sub.3 particles with a BET surface area of 2.9 m.sup.2/g,
111.68 g Al.sub.2O.sub.3 particles, 45.00 g aqueous acrylic polymer
solution (solid content: 35 wt %) as a main component of polymeric
binder for final green sheet, 0.49 g aqueous solution of
2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate solution as a
de-foamer for aqueous slurry, 4.87 g of aqueous 2-amino-2-methyl-1
propanol solution as a plasticizer, and 125.00 g milli-Q water were
added to a 1.0 L high density polyethylene (HDPE) thick wall jar,
with an inner diameter of 124 mm (BHB-1100, Kinki Youki, Japan),
for an aqueous slurry preparation.
[0132] The contents in the HDPE jar were then shaken by hand until
the mixture seemed liquid-like. A 1.5 kg ZrO.sub.2 milling media of
5-10 mm diameter was added to the HDPE jar, and the mixture in the
HDPE jar was milled at 70 rpm by 700 series "roller-type" jar mill
(US Stoneware, East Palestine, Ohio) for about 16 h. Afterwards, an
additional 55.59 g aqueous acrylic polymer solution was added to
the milled solution of ceramic particles in the HDPE jar to finally
contain 60 vol % ceramic particles in the final aqueous slurry.
Then this mixture was further milled by the roller-type jar mill
for an additional approximately 4 h. When the entire ball milling
process was completed, the resultant slurry was filtered through a
syringe-aided metal screen filter with pore size of 0.05 mm, in
order to remove aggregated ceramic particles. Viscosity of the
resulted slurry was in the range of 200 cP to 350 cP. The slurry
was then cast on 75 .mu.m thick silicone-coated polyethylene
terephthalate Mylar substrate film (Hansung Systems Inc., South
Korea) using an automated roll-to-roll Model 102 tape caster
(DreiTek, Valley Center, Calif.) at a cast rate of 200 mm/min. The
blade gap of the film applicator was adjusted depending on the
desired green sheet thickness. The cast tape was dried at
55-80.degree. C. at five different heat zones with a length of 0.5
m each, to finally obtain a YAG ceramic green sheet either 45 or 60
.mu.m thick.
[0133] The dried green sheet was cut to be about 135 mm.times.135
mm using a razor blade. Either four layers of the 45 .mu.m thick
green sheets or three layers of the 60 .mu.m thick green sheets
having the same composition were assembled on an anodized aluminum
plate, and this assembly was vacuum-bagged before pressing. This
assembly was laminated using a cold isostatic press (CIP) at 40 MPa
at 80.degree. C. for 10 min. using an ILS-66 isostatic lamination
press (Keko Equipment, Slovenia). As a result, an approximately 135
mm.times.135 mm.times.0.17 mm laminated green laminate was
obtained. The green laminate was then laser-cut to the size of an
18.5 mm.times.18.5 mm cubic shape using a VLS 2.30 laser engraving
and cutting system (Universal Laser Systems) with a 25W CO.sub.2
laser for the following Bisk firing and sintering processes, which
were the same as those outlined in Example 1.
[0134] The debinded/Bisk-fired blank samples were fully sintered at
1800.degree. C. for about 5 hours under a 10.sup.-5 Torr vacuum
using a high temperature furnace, in which the heating elements
were made of tungsten and which was attached with a diffusion pump
for a higher vacuum level. The heating rate of this final sintering
process was about 16.7.degree. C./min. (.about.400.degree. C.),
8.0.degree. C./min. (400-1000.degree. C.), 2.5.degree. C./min.
(1000-1400.degree. C.), (1.7.degree. C./min. 1400-1500.degree. C.),
and 0.8.degree. C./min (1500-1800.degree. C.), whereas the cooling
rate was 8.0.degree. C./min. in order to minimize cracking during
sintering. Finally, ceramic plates of 15 mm.times.15 mm size were
obtained.
[0135] Mesh 7 (see Table 1) displayed significant warpage in this
Example. See Table 3, and explanation of warpage measurement,
below.
Example 3
[0136] Similar YAG ceramics were processed as detailed in Example
2, except that 4.47 g of polymeric beads, which were made of
cross-linked poly(methyl methacrylate) and with a bead diameter of
8 .mu.m, were also added to the milled solution in the HDPE jar to
create 6.0 vol % voids, after the initial 16 h. ball-milling. These
beads would create air voids after the Bisk-firing, and these voids
remained even after the end of sintering using a tungsten furnace.
Eventually these voids lead to the light scattering.
[0137] Mesh 7 (see Table 1) displayed significant warpage in this
Example. See Table 3, and explanation of warpage measurement,
below.
Example 4
[0138] Similar YAG ceramics were processed as detailed in Example
2, except that 97.50 g Y.sub.2O.sub.3 particles, 73.38 g
Al.sub.2O.sub.3 particles, 27.00 g aqueous acrylic polymer
solution, 0.32 g aqueous solution of
2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate solution as a
de-foamer for aqueous slurry, 3.18 g of aqueous 2-amino-2-methyl-1
propanol solution as a plasticizer, and 60.00 g milli-Q water were
added to a 16 oz. (0.45 L) polypropylene (PP) thick wall jar, with
an inner diameter of 80 mm (Parkway Plastics Inc., Piscataway,
N.J.).
[0139] Then 760 g ZrO.sub.2 milling media of 5-10 mm diameter was
added to the PP jar, and the mixture in the PP jar was milled at 96
rpm by a 700 series "roller-type" jar mill (US Stoneware, East
Palestine, Ohio) for about 16 h. Afterwards, an additional 38.63 g
of aqueous acrylic polymer solution was added to the milled
solution of ceramic particles in the PP jar to finally contain 60
vol % ceramic particles in the final slurry. Then this mixture was
further milled by the roller-type jar mill for about an additional
4 h. The slurry was tape-cast to finally obtain an approximately 60
.mu.m thick ceramic green sheet. The dried green sheet was cut to
be about 135 mm.times.135 mm using a razor blade. Seven layers of
the 60 .mu.m thick green sheets having the same composition were
assembled on an anodized aluminum plate. This assembly was
vacuum-bagged and then isostatically pressed at 40 MPa at
80.degree. C. for 10 min.
Example 5
[0140] Transparent LuAG ceramics were processed as detailed for YAG
ceramics in Example 2, except that 75.24 g Lu.sub.2O.sub.3
particles with a BET surface area of 2.0 m.sup.2/g, 32.13 g
Al.sub.2O.sub.3 particles, 15.00 g aqueous acrylic polymer
solution, 0.14 g aqueous solution of
2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate solution as a
de-foamer for aqueous slurry, 1.35 g of aqueous 2-amino-2-methyl-1
propanol solution as a plasticizer, and 30.00 g milli-Q water were
added to an 8 oz. (0.23 L) polypropylene (PP) thick wall jar, with
an inner diameter of 80 mm (Parkway Plastics Inc., Piscataway,
N.J.).
[0141] Then 380 g ZrO.sub.2 milling media of 5-10 mm diameter was
added to the PP jar, and the mixture in the PP jar was milled at 96
rpm by a 700 series "roller-type" jar mill (US Stoneware, East
Palestine, Ohio) for about 16 h. Afterwards, an additional 12.81 g
of aqueous acrylic polymer solution was added to the milled
solution of ceramic particles in the PP jar to finally contain 60
vol % ceramic particles in the final slurry. Then this mixture was
further milled by the roller-type jar mill for about an additional
4 h. The slurry was tape-cast to finally obtain an approximately 65
.mu.m thick ceramic green sheet. The dried green sheet was cut to
be about 135 mm.times.135 mm using a razor blade. Three layers of
the 65 .mu.m thick green sheets having the same composition were
assembled on an anodized aluminum plate. This assembly was
vacuum-bagged and then isostatically pressed at 40 MPa at
80.degree. C. for 10 min.
Example 6
[0142] Transparent LuAG ceramics were processed as detailed in
Example 5, except that two layers of the 65 .mu.m thick green
sheets having the same composition were assembled on an anodized
aluminum plate. This assembly was vacuum-bagged and then
isostatically pressed at 40 MPa at 80.degree. C. for 10 min.
[0143] A summary of the ceramic samples prepared according to
Examples 1-6 above are summarized in Table 2.
TABLE-US-00002 TABLE 2 Example 1 2 3 4 5 6 Solvent Toluene Milli-Q
water Milli-Q water Milli-Q water Milli-Q water Milli-Q water
Garnet type YAG YAG YAG YAG LuAG LuAG Gd-doping N/A 10 10 N/A N/A
N/A % Void vol % N/A N/A 6 N/A N/A N/A for light scattering Final
150 150 150 350 150 100 ceramic thickness (.mu.m)
Comparative Example 1
[0144] Garnet ceramic plates, derived as in Examples 1-6, were
sintered on a tungsten plate without a top cover plate. All samples
were warped after sintering in a high temperature vacuum furnace
(1800.degree. C.) made of tungsten. There were hardly any flat
ceramics obtained, due to the lack of a top cover plate during
sintering.
Comparative Example 2
[0145] Four pieces of 18.5 mm.times.18.5 mm blank samples of garnet
ceramics were sandwiched between 15 mg tungsten plates of a
diameter of 50 mm.times.50 mm.times.0.38 mm (w/o tungsten mesh) to
reduce warpage as seen in Comparative Example 1. The surface
roughness, represented by the arithmetic mean value Ra, of the
tungsten plates was 0.65 micron. All garnet ceramics of less than
150 micron thick were cracked, whereas approximately 50% of the 350
micron thick garnet ceramics were cracked, after sintering using a
high temperature vacuum tungsten furnace (1800.degree. C.). The
reason for sample cracking appeared to be due to a small area of
the samples sticking to the tungsten plate. Such area contact (as
distinguished from spot contact, as when mesh is used) constrained
sample shrinkage during sintering, which thus led to the cracking
during the sintering process, which was especially pronounced in
the thinner ceramics.
Comparative Example 3
[0146] Four pieces of 18.5 mm.times.18.5 mm blank samples of garnet
ceramic were sandwiched between 15 mg tungsten plates with a
diameter of 50 mm.times.50 mm.times.0.38 mm (w/o tungsten mesh) to
reduce warpage. The surface roughness (Ra) of the tungsten plates
in this Example was 3.46 micron. As in Comparative Example 2, all
garnet ceramics of less than 150 micron thick were cracked, whereas
approximately 50% of the 350 micron thick garnet ceramics were
cracked, after sintering using high temperature vacuum tungsten
furnace (1800.degree. C.). The reason for sample cracking of again
appeared to be due to a small area of the samples sticking to the
tungsten plate, which area contact constrained sample shrinkage
during sintering, leading to cracking during sintering.
Comparative Example 4
[0147] Four pieces of 18.5 mm.times.18.5 mm blank samples of garnet
ceramics were sandwiched between 10 mg of porous zirconia plates
(instead of tungsten mesh+tungsten plates) having a size of 50
mm.times.50 mm.times.1.0 mm, to prevent warpage. Zirconia plates
were selected due to zirconia's high melting point
(.about.2400.degree. C.). Although the utility of zirconia cover
plates occasionally resulted in the desired level of flatness of
the obtained YAG ceramics, the surface of the YAG plates often
reacted with the zirconia cover plates above 1675.degree. C., which
lead to a non-homogeneous surface roughness on the YAG plate
surface, which could easily be found visually. Additionally, YAG
ceramics cannot be sintered above 1700.degree. C., since the YAG
and zirconia often reacted at high temperature, and two of the
oxide flat ceramic pieces adhered at such high temperature.
Comparative Example 5
[0148] YAG flat ceramic pieces were sandwiched with molybdenum foil
(instead of tungsten mesh) to reduce warpage. This enabled the YAG
plates to be sintered at a higher temperature (>1700.degree.
C.). Additionally, the YAG ceramics were not cracked during the
sintering, and a uniform and high transparency was maintained. This
may have been due to the lack of the reaction between YAG and
molybdenum during sintering at high temperature. However, the
desired level of flatness of the sintered YAG plates was not
achieved. Only warped flat ceramic pieces were obtained. During the
sintering at high temperature, the molybdenum foil was also warped,
and this may have caused the warpage of the sintered YAG
ceramics.
Comparative Example 6
[0149] YAG flat ceramic pieces were sandwiched with very rough
tungsten 6 mesh with a very thick tungsten filament diameter. Due
to the rough mesh structure, the sintered YAG ceramics showed
slight warpage which followed the mesh structure, although no
observable cracking was observed and the yield remained 100%.
[0150] Using zirconia at 1800.degree. C., all of the ceramic pieces
were cracked and stuck to the zirconia. Using molybdenum at
1800.degree. C., there was no cracking, but the foil warped at high
temperature. Using tungsten plate at 1800.degree. C., 75%-50% of
the ceramic pieces were cracked (i.e., visible cracks).
[0151] Warpage and Roughness Measurements
[0152] One example of a method of measuring warpage is as follows.
Two flat plates are disposed parallel to each other a given
distance apart. See FIG. 5. The total thickness (D) of the plates
(distance A+B) and the vertical displacement of the sample with
warpage (distance C+E) are measured by a micrometer, where C is the
known thickness of sample without warpage, and E is amount of
warpage. The outside surfaces of the two parallel plates are placed
within the measuring distances of a micrometer. The plates are
disposed a distance sufficient to insert the sample between the
plates. Once inserted, the jaws are closed until the jaws touch the
plates, and the total distance between the jaws is measured by the
micrometer (D). The amount of warpage (E) of the sample, then, can
be calculated by D-(A+B+C), in which the known distance values of
the plates and unwarped sample are subtracted from the total
distance measured.
[0153] Warpage measurements of the ceramic samples from Examples
1-6 demonstrated that the methods of the present disclosure reduce
warpage of the ceramic materials. All ceramic samples described in
Examples 1-6 were measured for camber using a micrometer and a
caliper. A micrometer has a measuring interface (tip, about 5 mm
diameter) with a smaller surface area. A caliper has a larger
surface area measuring interface (jaw face about 30 mm). Ceramic
samples were measured with both instruments. "Good" samples have
substantially similar thickness when measured by micrometer or
caliper, indicating little or no warpage. The thickness
measurements by micrometer were conducted at five different
locations on each ceramic plane. The average values of these
warpage measurements is presented in Table 3, showing the
experimental results of warpage of 15 mm.times.15 mm ceramic plates
in Examples 1-6, using micrometer and caliper.
TABLE-US-00003 TABLE 3 Example Example Example Example Example
Example Mesh types 1 2 3 4 5 6 Mesh 1 0.41 0.18 0.19 0.36 0.17 0.11
Caliper, mm 404 143 140 346 143 98 Micrometer, .mu.m 0.01 0.04 0.05
0.01 0.02 0.01 Warpage, mm Mesh 2 0.41 0.18 0.19 0.38 0.2 0.13 404
143 141 345 142 96 0.01 0.04 0.05 0.03 0.06 0.04 Mesh 3 0.41 0.18
0.18 0.36 0.17 0.12 405 140 140 342 140 96 0.01 0.04 0.04 0.02 0.03
0.03 Mesh 4 0.41 0.16 0.18 0.37 0.17 0.11 404 140 142 347 144 96
0.01 0.02 0.03 0.01 0.03 0.02 Mesh 5 0.43 0.18 0.16 0.38 0.17 0.12
406 140 141 347 143 95 0.03 0.03 0.02 0.03 0.03 0.02 Mesh 6 0.43
0.15 0.19 0.37 0.17 0.11 406 142 140 347 141 96 0.03 0.01 0.05 0.02
0.03 0.01 Mesh 7 0.43 0.41 0.42 0.36 0.22 0.24 406 143 142 346 142
97 0.03 0.27 0.31 0.01 0.08 0.15 Comparative 0.82 0.76 0.81 0.41
1.20 1.24 Example 1 406 140 137 344 142 95 0.41 0.62 0.67 0.07 1.06
1.15 Comparative 50% All All 50% All All Example 2 cracked cracked
cracked cracked cracked cracked Comparative 50% All All 50% All All
Example 3 cracked cracked cracked cracked cracked cracked
Comparative All All All All All All Example 4 adhered adhered
adhered adhered adhered adhered Comparative 0.65 0.53 0.55 0.54
0.42 1.09 Example 5 404 143 142 346 142 97 0.25 0.39 0.41 0.19 0.28
0.99
[0154] Note that Mesh 7 (see Table 1) displayed significant warpage
under the conditions of Examples 2 and 3, with warpage of 0.27 mm
and 0.31 mm, respectively.
[0155] The correlation between measured warpage, summarized in
Table 3, and the number of contact points or lines in the mesh is
presented in FIGS. 6A and B for each of Examples 1-6. From this it
is clear that warpage was minimized for all ceramics produced under
the currently described process where the number of contact points
or lines in the mesh used was increased.
[0156] While maintaining the flatness of the ceramics, it is also
important to minimize the surface roughness of the sintered
ceramics. Otherwise, great roughness of the sintered ceramics may
affect the thickness measurements. Therefore, the surface roughness
(represented by the arithmetic mean value Ra) of the garnet
ceramics sintered using mesh was measured at five different
locations on the ceramic plane, by a portable roughness tester
(Model 54-400-110, Fred V. Fowler Company Inc., Newton Mass.). Any
warped and/or cracked samples were excluded from this measurement
due to the measurement difficulty. A summary of the average value
of the surface roughness measurements of all flat samples is
presented in Table 4.
TABLE-US-00004 TABLE 4 Mesh type Example 1 Example 2 Example 3
Example 4 Example 5 Example 6 Mesh 1 0.35 0.25 0.30 0.41 0.20 0.26
Mesh 2 0.37 0.33 0.38 0.43 0.27 0.25 Mesh 3 0.38 0.30 0.36 0.39
0.27 0.36 Mesh 4 0.35 0.23 0.28 0.39 0.30 0.26 Mesh 5 0.36 0.29
0.29 0.40 0.28 0.37 Mesh 6 0.36 0.30 0.31 0.37 0.26 0.26 Mesh 7
0.55 0.52 0.59 0.45 0.49 0.59 Comparative example 1 N/A N/A N/A
0.44 0.96 N/A
[0157] The correlation between measures Ra, as presented in Table
4, and the mesh is presented in FIGS. 7A and B. From this it is
clear that surface roughness was minimized for all ceramics
produced under the currently described process where contact number
of the number of contact points or lines in the mesh used was
increased.
[0158] Unless otherwise indicated, all numbers expressing
quantities of ingredients, properties such as molecular weight,
reaction conditions, and so forth used in the specification and
claims are to be understood as being modified in all instances by
the term "about." Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the specification and
attached claims are approximations that may vary depending upon the
desired properties sought to be obtained. At the very least, and
not as an attempt to limit the application of the doctrine of
equivalents to the scope of the claims, each numerical parameter
should at least be construed in light of the number of reported
significant digits and by applying ordinary rounding
techniques.
[0159] The terms "a," "an," "the" and similar referents used in the
context of describing the invention (especially in the context of
the following claims) are to be construed to cover both the
singular and the plural, unless otherwise indicated herein or
clearly contradicted by context. All methods described herein can
be performed in any suitable order unless otherwise indicated
herein or otherwise clearly contradicted by context. The use of any
and all examples, or exemplary language (e.g., "such as") provided
herein is intended merely to better illuminate the invention and
does not pose a limitation on the scope of any claim. No language
in the specification should be construed as indicating any
non-claimed element essential to the practice of the invention.
[0160] Groupings of alternative elements or embodiments disclosed
herein are not to be construed as limitations. Each group member
may be referred to and claimed individually or in any combination
with other members of the group or other elements found herein. It
is anticipated that one or more members of a group may be included
in, or deleted from, a group for reasons of convenience and/or
patentability. When any such inclusion or deletion occurs, the
specification is deemed to contain the group as modified thus
fulfilling the written description of all Markush groups used in
the appended claims.
[0161] Certain embodiments are described herein, including the best
mode known to the inventors for carrying out the invention. Of
course, variations on these described embodiments will become
apparent to those of ordinary skill in the art upon reading the
foregoing description. The inventor expects skilled artisans to
employ such variations as appropriate, and the inventors intend for
the invention to be practiced otherwise than specifically described
herein. Accordingly, the claims include all modifications and
equivalents of the subject matter recited in the claims as
permitted by applicable law. Moreover, any combination of the
above-described elements in all possible variations thereof is
contemplated unless otherwise indicated herein or otherwise clearly
contradicted by context.
[0162] In closing, it is to be understood that the embodiments
disclosed herein are illustrative of the principles of the claims.
Other modifications that may be employed are within the scope of
the claims. Thus, by way of example, but not of limitation,
alternative embodiments may be utilized in accordance with the
teachings herein. Accordingly, the claims are not limited to
embodiments precisely as shown and described.
* * * * *