U.S. patent application number 14/445665 was filed with the patent office on 2016-07-28 for article comprising environmental barrier coating.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Julin WAN.
Application Number | 20160215631 14/445665 |
Document ID | / |
Family ID | 53887178 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160215631 |
Kind Code |
A1 |
WAN; Julin |
July 28, 2016 |
ARTICLE COMPRISING ENVIRONMENTAL BARRIER COATING
Abstract
An article includes a substrate, a substantially hermetic
sealing layer disposed on the substrate, and a porous transition
layer disposed on the substrate between the sealing layer and the
substrate. The article also includes one or more openings extending
through the substrate to the porous transition layer.
Inventors: |
WAN; Julin; (Rexford,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenectady |
NY |
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
53887178 |
Appl. No.: |
14/445665 |
Filed: |
July 29, 2014 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 41/52 20130101;
C04B 41/89 20130101; C04B 41/52 20130101; F23R 3/002 20130101; C04B
41/009 20130101; C04B 41/52 20130101; C04B 41/5024 20130101; C04B
41/5059 20130101; C04B 41/4572 20130101; C04B 41/009 20130101; C04B
41/52 20130101; C04B 41/009 20130101; C04B 35/584 20130101; C04B
41/52 20130101; C04B 41/009 20130101; C04B 41/5071 20130101; C04B
41/4572 20130101; C04B 41/5066 20130101; C04B 35/00 20130101; C04B
41/522 20130101; C04B 41/5024 20130101; C04B 2103/001 20130101;
C04B 41/522 20130101; C04B 2103/0021 20130101; C04B 41/5024
20130101; C04B 35/806 20130101; C04B 41/4582 20130101; C04B 41/5042
20130101; C04B 41/4572 20130101; C04B 41/5024 20130101; C04B 41/522
20130101; C04B 41/522 20130101; C04B 35/58092 20130101; C04B 41/522
20130101; C04B 41/5032 20130101; C04B 2103/0021 20130101; C04B
41/4572 20130101; C04B 2103/0021 20130101; C04B 41/522 20130101;
C04B 41/5096 20130101; C04B 41/4582 20130101; C04B 35/565 20130101;
C04B 41/522 20130101; C04B 2103/0021 20130101; C04B 41/5096
20130101; C04B 41/52 20130101; C04B 41/009 20130101; C04B 41/52
20130101; C04B 41/52 20130101; F01D 5/288 20130101; C04B 41/52
20130101; C04B 41/52 20130101; C04B 41/52 20130101; C04B 41/52
20130101 |
International
Class: |
F01D 5/28 20060101
F01D005/28; F23R 3/00 20060101 F23R003/00 |
Claims
1. An article comprising: a substrate; a substantially hermetic
sealing layer disposed on the substrate; and a porous transition
layer disposed on the substrate between the sealing layer and the
substrate, wherein the article comprises one or more openings
extending through the substrate to the porous transition layer.
2. The article according to claim 1, further comprising a bond coat
disposed on the substrate, wherein the porous transition layer is
disposed between the sealing layer and the bondcoat.
3. The article according to claim 2, wherein the substrate
comprises a ceramic matrix composite material.
4. The article according to claim 3, wherein the substrate
comprises silicon carbide (SiC).
5. The article according to claim 3, wherein the composite
comprises a matrix phase and a reinforcement phase, and wherein the
matrix phase and the reinforcement phase comprise silicon
carbide.
6. The article according to claim 1, wherein the bondcoat comprises
silicon carbide and/or silicon nitride.
7. The article according to claim 2, wherein the sealing layer
comprises a rare earth silicate and/or an alkaline earth
aluminosilicate.
8. The article according to claim 2, wherein the porous transition
layer comprises a rare earth silicate and/or silicon carbide.
9. The article according to claim 2, wherein the porous transition
layer has a porosity of 10 to 90%.
10. The article according to claim 2, wherein the porous transition
layer has an average pore diameter of 0.1 to 100 .mu.m.
11. The article according to claim 2, wherein the one or more
openings have an average diameter of 1 to 1000 .mu.m.
12. The article according to claim 2, said article comprising a
substrate cavity, and wherein said one or more openings open into
the cavity.
13. The article according to claim 2, further comprising a topcoat
disposed over the sealing layer.
14. The article according to claim 13, wherein the topcoat
comprises a ceramic material selected from the group consisting of
silicates, aluminates, and yttria-stabilized zirconia.
15. The article according to claim 13, wherein the topcoat
comprises a rare earth monosilicate, a rare earth disilicate, or
combinations thereof.
16. The article according to claim 2, further comprising an
intermediate layer disposed between the sealing layer and the
porous transition layer, wherein the intermediate layer comprises a
barrier material that is substantially inert with respect to
silica.
17. The article according to claim 16, wherein the barrier material
comprises a rare-earth disilicate.
18. The article according to claim 17, wherein the barrier material
comprises yttrium disilicate.
19. The article according to claim 1, wherein the article comprises
a component of a gas turbine assembly.
20. A method for making an article, said method comprising:
disposing a bondcoat over a substrate; disposing a porous
transition layer over the bondcoat; disposing a sealing layer over
the porous transition layer, wherein the sealing layer comprises a
rare earth silicate or an alkaline-earth aluminosilicate; and
forming one or more openings, said openings extending through the
substrate and bondcoat to the porous transition layer.
21. The method according to claim 20, wherein the substrate and the
bondcoat comprise silicon carbide, said method further comprising:
disposing an intermediate layer over the porous transition layer,
said intermediate layer comprising a barrier material that is
substantially inert with respect to silica; and disposing a topcoat
over the sealing layer.
Description
BACKGROUND
[0001] This invention relates to articles comprising an
environmental barrier coating (EBC), for example, high-temperature
machine components. More particularly, this invention relates to
coating systems and articles comprising the same for protecting
machine components from exposure to high-temperature environments.
This invention also relates to methods for making and protecting
articles.
[0002] High-temperature materials, such as, for example, ceramics,
alloys, and intermetallics, offer attractive properties for use in
structures designed for service at high temperatures in such
applications as gas turbine engines, heat exchangers, and internal
combustion engines, for example. However, the environments
characteristic of these applications often contain reactive
species, such as water vapor, which at high temperatures may cause
significant degradation of the material structure. For example,
water vapor has been shown to cause significant surface recession
and mass loss in silicon-bearing materials. The water vapor reacts
with the structural material at high temperatures to form volatile
silicon-containing species, often resulting in unacceptably high
recession rates.
[0003] Environmental barrier coatings (EBC's) are applied to
silicon-bearing materials and other material susceptible to attack
by reactive species, such as high temperature water vapor. EBC's
provide protection by prohibiting contact between the environment
and the surface of the material. EBC's applied to silicon-bearing
materials, for example, are designed to be relatively stable
chemically in high-temperature, water vapor-containing
environments. One exemplary conventional EBC system, as described
in U.S. Pat. No. 6,410,148, comprises a silicon or silica bond
layer applied to a silicon-bearing substrate; an intermediate layer
comprising mullite or a mullite-alkaline earth aluminosilicate
mixture deposited over the bond layer; and a top layer comprising
an alkaline earth aluminosilicate deposited over the intermediate
layer. In another example, U.S. Pat. No. 6,296,941, the top layer
is a yttrium silicate layer rather than an alumino silicate. U.S.
Pat. No. 6,299,988 and U.S. Publication No. 2011/0052925 also
describe EBC's.
BRIEF DESCRIPTION
[0004] The above coating systems can provide suitable protection
for articles in demanding environments, but opportunities for
improvement in coating performance exist. Implementation of
different materials in EBC's offers an opportunity for use in an
expanded array of applications and environments, yet use of
different materials can also result in new technical problems that
can detrimentally impact the integrity of an EBC and/or the article
comprising the EBC.
[0005] Therefore, there is a need for articles protected by
improved coating systems that offer utility in expanded
applications, without sacrificing the integrity of the EBC and/or
the article. There is also a further need for methods to produce
these articles economically and reproducibly.
[0006] In one aspect, the invention provides an article comprising
a substrate, a substantially hermetic sealing layer disposed on the
substrate, and a porous transition layer disposed on the substrate
between the sealing layer and the substrate, wherein the article
comprises one or more openings extending through the substrate to
the porous transition layer.
[0007] In a second aspect, the invention provides a method for
making an article. The method includes: disposing a bondcoat over a
substrate, disposing a porous transition layer over the bondcoat,
disposing a sealing layer over the porous transition layer, wherein
the sealing layer comprises a rare earth silicate or an
alkaline-earth aluminosilicate, and forming one or more openings,
the openings extending through the substrate and bondcoat to the
porous transition layer. In embodiments that do not include a
bondcoat, the method does not comprise disposing a bondcoat over
the substrate.
[0008] In some embodiments, the method further comprises: disposing
an intermediate layer over the porous transition layer, the
intermediate layer comprising a barrier material that is
substantially inert with respect to silica; and optionally
disposing a topcoat over the sealing layer.
DRAWINGS
[0009] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0010] FIG. 1 is a schematic cross-section illustration of one
exemplary embodiment of the present invention.
[0011] FIG. 2 is a simplified schematic cross-section illustration
of another exemplary embodiment of the present invention.
DETAILED DESCRIPTION
[0012] As used herein, the substantially hermetic sealing layer,
which may be referred to herein as a "sealing layer," refers to a
layer/coating, or multiple layers/coatings, that can prevent gases
in the environment from accessing the substrate from the coated
side. The term "substantially hermetic" as used herein means that
the coating has a gas permeability that is below about
2.times.10.sup.-14 cm.sup.2 (about 2.times.10.sup.-6 Darcy), the
detection limit of commonly used measurement techniques. In some
non-limiting embodiments, the sealing layer comprises material
("sealing material") capable of forming a flowable phase, such as a
liquid or a glassy phase, at or above a known temperature ("sealing
temperature") that is below a melting temperature of the bulk of
the coating. This liquid or glassy phase has a viscosity at the
sealing temperature suitable to allow the flowable phase to flow
into and at least partially fill defects such as cracks and pores,
thereby enhancing the ability of the coating to block the movement
of detrimental species from the external environment into the
substrate. Examples of non-limiting sealing layers that may be used
in the present invention are described, for example, in U.S.
Publication No. 2011/0052925.
[0013] FIG. 1 depicts an exemplary article 200 of the present
invention. In this particular embodiment, sealing layer 210 is
disposed over a substrate 202. Substrate 202 may be made from any
suitable material, such as a ceramic, a metal alloy, or an
intermetallic material. In some embodiments the substrate comprises
a ceramic, for example an oxide, nitride, or carbide. Substrate 202
may include a silicon-containing material, such as silicon nitride,
molybdenum disilicide, or silicon carbide. This material, in
certain embodiments, is a ceramic-matrix composite material, such
as a material made of a matrix phase and a reinforcement phase; in
particular embodiments, the matrix phase and the reinforcement
phase comprise silicon carbide (SiC). In certain embodiments,
article 200 is a component of a gas turbine assembly, such as, for
example, a combustion liner, transition piece, shroud, vane, or
blade. In some embodiments, the ability of the sealing layer to
protect substrate 202 from exposure to water vapor at high
temperatures may be advantageous for its application to
silicon-bearing turbine components. It will be understood that
although the application of embodiments of the present invention
may be described with reference to applications on silicon-bearing
substrates for protection against attack by water vapor, such
references are exemplary and that embodiments of the present
invention include substrate materials other than silicon-bearing
materials.
[0014] In some embodiments, a bondcoat 204 is disposed over
substrate 202, between the sealing layer 210 and the substrate 202.
Bondcoat 204 may be used, for example, to mitigate thermal stresses
or to inhibit chemical reactions between, e.g., substrate 202 and
sealing layer 210. In some embodiments, bondcoat 204 is a nonoxide
layer that serves as an oxygen getter that inhibits and/or prevents
oxidation of the substrate.
[0015] In some embodiments, such as, for example, where substrate
202 is a silicon-bearing material, the bondcoat 204 may comprise
silicon. For example, bondcoat 204, in some embodiments, comprises
elemental silicon or a silicide. In some embodiments, bondcoat 204
comprises silicon carbide and/or silicon nitride. In some
embodiments, bond coat 204 comprises a carbide, nitride, and/or
silicide.
[0016] In various applications, articles (e.g., articles comprising
environmental barrier coatings (EBCs)) for substrates (e.g.,
silicon carbide-based ceramic matrix composites) employ silicon as
the bondcoat (i.e., a silicon bond coat). However, this can limit
the temperature application of, e.g., an EBC/CMC system to below
the melting point of silicon. Accordingly, in some embodiments, the
bondcoat comprises a material that is more refractory than silicon.
Such embodiments offer utility in that they allow articles (e.g.,
turbines that use ceramic matrix composites (CMCs) on, e.g.,
hot-section parts), to benefit from a higher firing
temperature.
[0017] Many potential options for a refractory bondcoat generate a
gaseous reaction product upon oxidation. For example, carbides
oxidize to release carbon monoxide or carbon dioxide, nitrides
oxidize to release nitrogen gas, and some silicides oxidize to
release metal oxides that may, in some cases, be in a gaseous
state. These gaseous reaction products cause spallation in
traditional EBC's because they include a hermetic layer and
therefore do not permit permeation of these gaseous products. As a
result, gas bubbles build up underneath the hermetic layer(s),
which, overtime, lead to spallation of the EBC. Thus, while
expanded, non-silicon bond coats offer advantages such as expanded
temperature applications, they can also introduce new problems,
such as potential article spallation due to gas bubbles caused by
gaseous reactant products, thereby necessitating new EBC/CMC
design.
[0018] The present invention addresses, inter alia, the problem of
spallation due to bubbles caused by gaseous reactant products via
the inclusion of porous transition layer 208, which is disposed on
substrate 202 between the sealing layer 210 and the substrate 202,
and by inclusion of one or more openings 212 extending through the
substrate 202 to the porous transition layer 208. As shown in the
embodiment depicted in FIG. 1, where bondcoat 204 is present, the
one or more openings 212 also extend through the bondcoat.
[0019] The porosity of porous transition layer 208 allows for
redistribution of gaseous reaction product. The porous transition
layer comprises an oxide or non-oxide ceramic or a combination
thereof, which is thermally and chemically compatible with the
substrate and the sealing layer. For example, in the case that the
substrate is composed of silicon carbide based CMC, and the
component within the sealing layer right next to the porous layer
is composed of rare earth silicate, the porous layer in some
embodiment can be a rare earth silicate. In another embodiment it
can be silicon carbide. Persons having ordinary skill in the art
will readily recognize that the desired porosity of the porous
transition layer may change depending on the intended application
of the inventive article, and the on the nature of the other
materials used in the article (e.g., on the nature of the bond
coat, where present). While the porous transition layer may have
any porosity that effectuates the intended purpose of the layer, in
some embodiments, the porous transition layer has a porosity of 10
to 90% (e.g., 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,
75, 80, 85, or 90%), including any and all ranges and subranges
therein (e.g., 15-85%, 12-75%, etc.), preferably 20.about.50%. In
some embodiments, the porous transition layer will have a
specified, and optionally pre-determined average pore diameter,
which again, may vary depending on application and nature of the
inventive article. In some embodiments, the porous transition layer
has an average pore diameter of 0.1 to 100 .mu.m (e.g., 0.1, 0.2,
0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 10, 15, 20, 25,
30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100
.mu.m), including any and all ranges and subranges therein (e.g.,
0.1 to 20 .mu.m, 0.1 to 15 .mu.m, etc.).
[0020] The chemical composition and physical features of the porous
layer described as above are subject to change during the service
of the article, and thereby may drift out of the ranges specified
above. For example, sintering and coarsening may occur which lead
to reduced porosity and increased pore diameter. In the case that
silicon carbide is used to form the porous layer, oxidation will
turn this layer into a silica based layer partially or entirely.
The material that is used to make the porous layer can be applied
in its pure form, or in mixture with a second phase or as an alloy
with a minor dopant, to enhance the property of the layer according
to specific application requirements.
[0021] Article 200 includes openings 212, which extend through the
substrate 202 to the porous transition layer 208. The openings 212
serve as escape holes for gaseous species, which are first
redistributed through porous transition layer 208. The openings 212
may be created in any desired or art/acceptable fashion. For
example, in some embodiments, the openings 212 are created by
drilling through the layer(s) preceding the porous transition layer
208 (e.g., drilling through substrate 202 and bond coat 204). In
some embodiments, the openings 212 extend into the porous
transition layer 208. The one or more openings 212 may have
equivalent or differing diameters, and diameters may be selected
depending on the nature and application of the article. In some
embodiments, the one or more openings have an average diameter of 1
to 1000 .mu.m (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50,
60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, or
1000 .mu.m), including any and all ranges and subranges therein
(e.g., 1-20 .mu.m, 2 to 40 .mu.m, etc.). While reference is made
above to an average diameter, the cross section of the opening can
be of any shape, including but not limited to circular, oval,
square, rectangular, triangular, or any other regular or irregular
geometry. The spacing between the openings can be periodical or
random, and can range from 10 .mu.m to 100 mm, depending on the
application requirements. Longitudinally the openings can be
straight or tortuous through the substrate and the coating
layers.
[0022] Upon, for example, oxidation of the bond coat, gaseous
product is conducted through the porous transition layer 208 to the
openings 212, from which the gaseous product escapes.
[0023] FIG. 2 depicts another exemplary article 300 of the present
invention. In this particular embodiment, the article comprises a
substrate cavity 214, and the openings 212 enter into the cavity
214. In some embodiments (not pictured), the cavity 214 is an open
chamber that is optionally in pressure equilibrium with the
external environment (e.g., combustion environment), and may
optionally be protected by a flux of dry air. In other embodiments
(e.g., in the embodiment depicted in FIG. 2), the cavity 214 is a
self-contained closed chamber that is isolated from the external
(e.g., combustion) environment. In such embodiments, upon long term
use, gas-generating reactions (e.g., oxidation) can cause gas
pressure buildup within the cavity 214, which could rise to levels
that could threaten article and/or EBC integrity. In such cases,
periodical venting of gas from the cavity 214 is desirable, and may
be accomplished through optional vent 216. In some embodiments,
vent 216 is a controlled valve, or a thermal-expansion enabled seal
that can close at high temperatures and open at low temperatures,
such that, for example, pressure inside the cavity 214 may be
released during a service cycle.
[0024] In some embodiments, an intermediate layer (not shown) may
be disposed between sealing layer 210 and bond coat 204 (e.g.,
between the sealing layer 210 and the porous transition layer 208,
or between the porous transition layer 208 and the bondcoat 204).
In some embodiments, the bond coat 204 comprises silicon or silicon
oxide, and the intermediate layer comprises a barrier material that
is substantially inert with respect to silicon oxide to promote
chemical stability in the coating system. "Substantially inert"
means that there is at most only incidental interaction (solubility
or reactivity) between silica and the barrier material. Rare-earth
disilicates, such as disilicates of yttrium, ytterbium, lutetium,
scandium, and other rare-earth elements, are non-limiting examples
of suitable barrier materials.
[0025] As shown in FIG. 1, in some embodiments, a topcoat 206 is
disposed over sealing layer 210. Topcoat 206 may be used to provide
thermal insulation (a thermal barrier coating), environmental
protection (an environmental barrier coating), or a combination of
these functions. The selection of a suitable topcoat material will
depend on the type of environment the article is to be exposed to,
the composition of the underlying coatings and substrate, the cost
of processing, and other factors known in the art. In some
embodiments, topcoat 206 is a ceramic material. Many classes of
ceramic materials may serve as thermal and/or environmental barrier
coatings; these materials include, but are not limited to,
silicates, aluminosilicates, and yttria-stabilized zirconia. In
certain embodiments, topcoat 206 contains a rare earth monosilicate
and/or rare earth disilicate; in particular embodiments, topcoat
206 is a dual-layer coating, with an outer layer of rare earth
monosilicate and an inner layer of rare earth disilicate. The rare
earth elements associated with these monosilicate and disilicate
materials, in some embodiments, may include one or more of yttrium,
ytterbium, lutetium, and scandium. A particular example is where
the outer layer is yttrium monosilicate and the inner layer is a
rare earth disilicate (such as yttrium disilicate, for
instance).
[0026] The thickness of any of the various coating layers described
above is generally chosen to provide adequate protection for a
given service time while keeping thermal stresses to a sustainable
level. Moreover, coating thickness may also be determined by the
ability of a selected coating method to produce a continuous layer
over the deposition area. Non-limiting examples of approximate
thickness ranges for the various coatings include the following:
for the sealing layer, from about 25 micrometers to about 1000
micrometers; for the porous transition layer, from about 25
micrometers to about 1000 micrometers; for the bondcoat, from about
25 micrometers to about 200 micrometers; for the intermediate
layer, from about 50 micrometers to about 100 micrometers; for the
topcoat layer, from about 50 micrometers to about 500 micrometers.
For the dual-layer topcoat embodiment described above, the yttrium
monosilcate outer layer can be from about 25 micrometers to about
50 micrometers in certain embodiments.
[0027] The coatings described above can be deposited using coating
technology that may result in a substantial amount of cracking and
internal open porosity. Plasma spray technology and slurry-based
coating processes are examples of coating methods that generate
coatings with such features. In such cases, the presence of the
sealing layer serves to considerably enhance the hermeticity, and
thus the efficacy of protection, of the coating. Moreover, in some
embodiments the sealing layer may be effective in sealing cracks or
other damage to the coating that may occur after processing,
including for instance damage created during installation of
components, or service of components.
[0028] In order to activate the optional self-sealing nature of the
sealing layer, the sealing layer may be heated to the sealing
temperature (described above) at which at least a portion of the
sealing layer will flow; the flowable portion thus moves into
cracks and pores and, upon solidification, seals off these defects
that would otherwise serve as pathways for detrimental species,
such as water vapor, from the environment to the substrate.
Depending upon the nature of the coating, the economics of the
processing, and other factors, the heating step may be performed
immediately after depositing the sealing layer, after all coatings
have been deposited but prior to putting the finished article into
service, or even during service itself if the service temperature
is allowed to be sufficiently high.
[0029] The sealing temperature is maintained for an effective time
to allow time for the flowable material to reach and at least
partially fill or otherwise seal off the defects. The length of
time needed to achieve this is generally selected based on the
number and nature of the defects to be sealed and the quantity of
flowable material available in the sealing layer. In one
embodiment, the sealing layer is heated to a sealing temperature in
a range from about 950 degrees Celsius to about 1350 degrees
Celsius for a time in the range from about 30 minutes to about 10
hours; in particular embodiments the time is in the range from
about 30 minutes to about 4 hours. In some embodiments, the
temperature is in the range from about 950 degrees Celsius to about
1050 degrees Celsius for a time in the range from about 30 minutes
to about 4 hours, while in other embodiments the temperature is
from about 1250 degrees Celsius to about 1350 degrees Celsius for a
time in the range from about 30 minutes to about 4 hours. The
heating step to seal the coating may be performed in air, vacuum,
an inert atmosphere, or other environment, depending at least in
part on the requirements of the materials being heated (i.e., the
substrate and other coating layers, if present).
[0030] The method that is applied to deposit the porous layer is
selected to fulfill the geometric requirements as described above.
In some embodiments, the layer is applied by thermal spray with
parameters selected to target a specific porosity, such as
controlling the spray gun energy, standoff distance, and particle
size of the powder feed. In other embodiments, a sacrificial phase
is added to the powder feed to enhance the porosity. For example,
organic particles such as but not limited to polystyrene particles,
are added to the powder feed during the coating process, which can
be burned off during subsequent steps and leave behind pores in the
coating. In another example, a dissolvable salt is added and
subsequently dissolved away to generate the pores. In yet another
example, glass particles are added to the powder feed, after
applying the layer, the glass phase is leached away by soaking the
part in a hydrofluoric acid solution to leave behind a porous
structure. In yet another example, a glass layer is deposited and
then a subsequent heat-treatments is applied to lead to partial
crystallization or phase separation of the glass, subsequently the
coating is soaked in an acid solution to leach out one phase and
leave behind a porous structure.
[0031] Similar technology can be applied in slurry coating, wherein
either controlling parameters to facilitate partial sintering, or
otherwise employment of a sacrificial phase can be used to achieve
a structure that contain appropriate porosity. Partial sintering
can be realized by solid phase or liquid sintering of coarse
particle compact at lower temperatures, or use a bonding agent to
facilitate necking with minimal volume shrinkage, or sintering of a
multimodal powder mixture. Sacrificial phases, as stated above, can
be an organic or carbonaceous phase, or a dissolvable salt or a
glass phase that can be etched away. In general, any technologies
known by those skilled in the art of making porous ceramics can be
applied in this invention.
[0032] All publications and patent references cited in this
specification are herein incorporated by reference as if each
individual publication were specifically and individually indicated
to be incorporated by reference herein as though fully set
forth.
[0033] Subject matter incorporated by reference is not considered
to be an alternative to any claim limitations, unless otherwise
explicitly indicated.
[0034] Where one or more ranges are referred to throughout this
specification, each range is intended to be a shorthand format for
presenting information, where the range is understood to encompass
each discrete point within the range as if the same were fully set
forth herein.
[0035] It is to be understood that the above description is
intended to be illustrative, and not restrictive. For example, the
above-described embodiments (and/or aspects thereof) may be used in
combination with each other. In addition, many modifications may be
made to adapt a particular situation or material to the teachings
of the various embodiments without departing from their scope.
While the dimensions and types of materials described herein are
intended to define the parameters of the various embodiments, they
are by no means limiting and are merely exemplary. Many other
embodiments will be apparent to those of skill in the art upon
reviewing the above description. The scope of the various
embodiments should, therefore, be determined with reference to the
appended claims, along with the full scope of equivalents to which
such claims are entitled. In the appended claims, the terms
"including" and "in which" are used as the plain-English
equivalents of the respective terms "comprising" and "wherein."
Moreover, in the following claims, the terms "first," "second," and
"third," etc. are used merely as labels, and are not intended to
impose numerical requirements on their objects. Further, the
limitations of the following claims are not written in
means-plus-function format and are not intended to be interpreted
based on 35 U.S.C. .sctn.112, sixth paragraph, unless and until
such claim limitations expressly use the phrase "means for"
followed by a statement of function void of further structure. It
is to be understood that not necessarily all such objects or
advantages described above may be achieved in accordance with any
particular embodiment. Thus, for example, those skilled in the art
will recognize that the systems and techniques described herein may
be embodied or carried out in a manner that achieves or optimizes
one advantage or group of advantages as taught herein without
necessarily achieving other objects or advantages as may be taught
or suggested herein.
[0036] While the invention has been described in detail in
connection with only a limited number of embodiments, it should be
readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the disclosure
may include only some of the described embodiments. Accordingly,
the invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended
claims.
[0037] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal language of the claims.
* * * * *