U.S. patent application number 15/977493 was filed with the patent office on 2018-12-20 for extended length tube structures.
The applicant listed for this patent is SAINT-GOBAIN CERAMICS & PLASTICS, INC.. Invention is credited to Lawrence M. BANACH, JOHN BEVILACQUA, STEVEN W. LANZONE.
Application Number | 20180363811 15/977493 |
Document ID | / |
Family ID | 49223382 |
Filed Date | 2018-12-20 |
United States Patent
Application |
20180363811 |
Kind Code |
A1 |
BANACH; Lawrence M. ; et
al. |
December 20, 2018 |
EXTENDED LENGTH TUBE STRUCTURES
Abstract
An extended length tube structure includes a first ceramic tube
segment having a first end and a second end, and a second ceramic
tube segment having a first end and a second end, in which the
second end of the first ceramic tube segment is arranged to face
the first end of the second ceramic tube segment. A ceramic
coupling component is positioned to circumscribe the end-to-end
configuration of the tube segments, and is sinter-bonded to the
tube segments to form a continuous, extended length tube structure
having a seal, such as a sinter bond or an interference bond, that
is free of bond materials.
Inventors: |
BANACH; Lawrence M.;
(Lockport, NY) ; BEVILACQUA; JOHN; (Williamsville,
NY) ; LANZONE; STEVEN W.; (Williamsville,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAINT-GOBAIN CERAMICS & PLASTICS, INC. |
Worcester |
MA |
US |
|
|
Family ID: |
49223382 |
Appl. No.: |
15/977493 |
Filed: |
May 11, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13849354 |
Mar 22, 2013 |
9995417 |
|
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15977493 |
|
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61614499 |
Mar 22, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 2237/84 20130101;
C04B 2235/96 20130101; C04B 2237/78 20130101; C04B 2235/612
20130101; C04B 35/565 20130101; C04B 2235/72 20130101; C04B 2235/94
20130101; C04B 2237/52 20130101; C04B 2235/721 20130101; C04B
37/001 20130101; C04B 37/005 20130101; C04B 2237/365 20130101; C04B
2235/48 20130101; C04B 2237/765 20130101; C04B 2235/767 20130101;
C04B 2235/421 20130101; C04B 2237/083 20130101; F16L 13/02
20130101 |
International
Class: |
F16L 13/02 20060101
F16L013/02; C04B 35/565 20060101 C04B035/565; C04B 37/00 20060101
C04B037/00 |
Claims
1. An extended length tube structure comprising: a first ceramic
tube segment having a first end and a second end; a second ceramic
tube segment having a first end and a second end, the second end of
the first ceramic tube segment being arranged to face the first end
of the second ceramic tube segment, each of the first and second
ceramic tube segments having an inner diameter and an outer
diameter; and a ceramic coupling component sinter bonded to the
second end of the first tube segment and the first end of the
second tube segment such that the first and second tube segments
are arranged end to end to form a continuous tube structure,
wherein each of the ceramic tube segments forms a seal with the
coupling component, wherein the seal has at least one performance
characteristic selected from the group consisting of: i) a Shear
Strength not less than about 25 MPa; ii) a Nitrogen Seal
Performance of not greater than 10%; iii) a Helium Seal Performance
of not greater than 10%; iv) a Vacuum Seal Performance of not
greater than 10%.
2. The extended length tube structure of claim 1, wherein the
second end of the first ceramic tube segment is in abutting contact
with the first end of the second ceramic tube segment.
3. The extended length tube structure of claim 1, wherein the
second end of the first tube segment has an end face and the first
end of the second ceramic tube structure has an end face, and
wherein the end faces have complementary structures.
4. The extended length tube structure of claim 3, wherein the end
faces are planar.
5. The extended length tube structure of claim 3, wherein the end
faces lie in a plane perpendicular to a longitudinal axis of the
first or second ceramic tube segment.
6. The extended length tube structure of claim 1, wherein the
extended length tube structure has an outer diameter (OD) and a
length (L), and an aspect ratio of L:OD of not less than about 10:1
and not greater than 300:1.
7. The extended length tube structure of claim 1, wherein the first
ceramic tube segment, the second ceramic tube segment, the coupling
component, or any combination thereof comprises silicon
carbide.
8. The extended length tube structure of claim 7, wherein each of
the first ceramic tube segment, the second ceramic tube segment,
the coupling component comprise silicon carbide.
9. The extended length tube structure of claim 8, wherein the
silicon carbide comprises a content of the silicon carbide from at
least about 91 wt % to no greater than about 99.85 wt %, wherein at
least about 95 wt % of the silicon carbide is alpha phase.
10. The extended length tube structure of claim 9, wherein the
silicon carbide further comprises: a carbonized organic material in
an amount no greater than about 5.0 wt %; boron in an amount from
at least about 0.15 wt % to no greater than about 3.0 wt %;
additional carbon in an amount no greater than about 1.0 wt %; and
a predominantly equiaxed microstructure.
11. The extended length tube structure of claim 1, wherein the
first tube segment, the second tube segment, and the coupling
component are coaxial.
12. The extended length tube structure of claim 1, wherein the
coupling component comprises a cylindrical body.
13. The extended length tube structure of claim 1, wherein
crystallographic grains from each of the first tube segment and the
coupling component extend across and bridge a sinter bond interface
between the first tube segment and the coupling component, and
wherein crystallographic grains from each of the second tube
segment and the coupling component extend across and bridge a
sinter bond interface between the first tube segment and the
coupling component.
14. The extended length tube structure of claim 1, wherein at least
one of the seals has a Shear Strength of not less than about 40
MPa.
15. The extended length tube structure of claim 1, wherein the seal
is a hermetic seal.
16. A method of forming an extended length ceramic tube structure,
comprising: providing a first ceramic tube segment having a first
end and a second end, providing a second ceramic tube segment
having a first end and a second end; pre-sintering the first and
second ceramic tube segments; surface cleaning an outer surface of
each of the tube segments; providing an un-sintered or partially
sintered ceramic coupling component; arranging the first and second
tube segments and the coupling component such that the second end
of the first ceramic tube segment faces the first end of the second
ceramic tube segment, and the coupling component overlies the
second end of the first tube segment and the first end of the
second tube segment; and co-sintering the first and second tube
segments and the coupling component to form a seal between the
coupling component and each of the first and second tube
segments.
17. The method of claim 16, further comprising: forming
crystallographic grains from each of the first tube segment and the
coupling component such that the crystallographic extend across and
bridge an interface defined by the seal between the first tube
segment and the coupling component, and forming crystallographic
grains from each of the second tube segment and the coupling
component such that the crystallographic grains extend across and
bridge an interface defined by the seal between the first tube
segment and the coupling component.
18. The method of claim 16, wherein the second end of the first
ceramic tube segment is in abutting contact with the first end of
the second ceramic tube segments.
19. The method of claim 16, wherein the second end of the first
tube segment has an end face, and the first end of the second
ceramic tube structure has an end face, wherein the end faces have
complementary structures.
20. The method of claim 16, wherein the first ceramic tube segment,
the second ceramic tube segment, the coupling component, or any
combination thereof comprises silicon carbide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/849,354 entitled "EXTENDED LENGTH TUBE
STRUCTURES," by Lawrence M. Banach et al., filed Mar. 22, 2013,
which claims priority under 35 U.S.C. .sctn. 119(e) to U.S. Patent
Application No. 61/614,499 entitled "EXTENDED LENGTH TUBE
STRUCTURES," by Lawrence M. Banach et al., filed Mar. 22, 2012,
both of which applications are assigned to the current assignee
hereof and incorporated herein by reference in their
entireties.
FIELD OF THE DISCLOSURE
[0002] This disclosure, in general, relates to extended-length tube
structures, and more particularly, to ceramic tube structures
joined together by sinter bonds.
BRIEF DESCRIPTION OF THE INVENTION
[0003] Embodiments of the present invention are generally drawn to
extended-length tube structures, formed as ceramic materials,
particularly including silicon carbide-based materials. Embodiments
of extended length tube structure of the present invention
generally include a first tube segment and a second tube segment
joined together by a ceramic coupling component. The first tube
segment has first and second ends, the second tube segment has
first and second ends, and the two segments are arranged in an
end-to-end configuration such that the second end of the first
ceramic tube segment and the first end of the second tube segment
face each other. The ceramic coupling component serves to bond the
first and second tube segments together, and is positioned so as to
be sinter-bonded to the second end of the first tube segment and to
the first end of the second tube segment. In particular, the
ceramic coupling component is positioned to circumscribe the
end-to-end configuration of the tube segments, and is sinter-bonded
to the tube segments to form an continuous, extended length, tube
structure having a seal, such as a sinter bond or an interference
bond, free of bond materials.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The present disclosure may be better understood, and its
numerous features and advantages made apparent to those skilled in
the art by referencing the accompanying drawings.
[0005] FIG. 1 shows a cross-section of an extended length tube
structure according to an embodiment of the present invention, in
which tube structures are abutted end-to-end and joined to each
other by a ceramic coupling component and a sinter bond
therebetween.
[0006] FIG. 2 shows a plan view of the extended length tube
structure embodiment shown in FIG. 1.
[0007] FIG. 3 shows an exploded plan view of the end faces of
adjacent tube segments to be abutted together according to an
embodiment of the present invention.
[0008] FIG. 4 shows an exploded cross-section view of the end faces
of adjacent tube segments of another embodiment, in which the
adjacent tube segments have complementary L-shaped end faces.
[0009] FIG. 5 shows the sinter-bond interface between a
pre-sintered silicon carbide segment and a ceramic coupling
component.
[0010] FIG. 6 shows a graph of a pressure test of one embodiment of
a ceramic article at 200 psi.
[0011] FIG. 7 shows a graph of a pressure test at 20.degree. C. of
three embodiments of a ceramic article.
[0012] FIG. 8 shows a graph of a pressure test at 1000.degree. C.
of the three embodiments of FIG. 7.
[0013] FIG. 9 shows a graph of pressure vs. temperature of a
pressure test of an embodiment of a ceramic article through five
(5) thermal cycles.
[0014] FIG. 10 shows a graph of a pressure test at 20.degree. C. of
three embodiments of a ceramic article.
[0015] FIG. 11 shows a graph of a pressure test at 1000.degree. C.
of the three embodiments of FIG. 10.
[0016] FIG. 12 shows a graph of pressure vs. temperature of a long
duration test of three embodiments of a ceramic article.
[0017] The use of the same reference symbols in different drawings
indicates similar or identical items.
DETAILED DESCRIPTION
[0018] Embodiments of the present invention are generally drawn to
extended-length tube structures, formed as ceramic materials,
particularly including silicon carbide-based materials.
Large-sized, such as high thermal mass and/or extended dimension
bodies are difficult to manufacture as monolithic ceramic parts.
Typically, extended dimensions have notable challenges in terms of
sourcing appropriate furnaces, have high thermal budgets, and have
extended and slowly-ramping sinter and anneal times. Consequently,
certain structures are made in segmented form and joined
together.
[0019] According to an embodiment of the present invention,
extended length tube structure is provided that includes a first
tube segment and a second tube segment joined together by a ceramic
coupling component. The first tube segment has first and second
ends, the second tube segment has first and second ends, and the
two segments are arranged in an end-to-end configuration such that
the second end of the first ceramic tube segment and the first end
of the second tube segment face each other. The ceramic coupling
component serves to bond the first and second tube segments
together, and is positioned so as to be sinter-bonded to the second
end of the first tube segment and to the first end of the second
tube segment. The ceramic coupling component may circumscribe the
first and second tube segments at a portion on the segments where
they meet each other. Notably, the tube segments form a seal with
the coupling component, a Shear Strength of the seal being not less
about 25 MPa, not less than about 40 MPa, not less than about 50
MPa, not less than about 75 MPa, not less than about 100 MPa, not
less than about 100 MPa, not less than about 120 MPa, not less than
about 140 MPa, not less than about 170 MPa, or not less than about
200 MPa. In one embodiment, the interface between the tube and the
base component exhibits a Shear Strength not greater than about
1000 MPa, such as not greater than about 700 MPa, not greater than
about 500 MPa, or not greater than about 300 MPa.
[0020] As used herein, reference to Shear Strength as a particular
Shear Strength value is measured by testing a sample having
standardized dimensions under load. In particular, the Shear
Strength is measured by preparing and testing a standardized sample
as follows. The sample is prepared from a ceramic tube and a
ceramic ring, each having a length of 76.2 mm. The ceramic tube has
an outer diameter (OD.sub.t) of 14 mm and an inner diameter
(ID.sub.t) of 11 mm. The ceramic ring has an outer diameter
(OD.sub.r) of 20 mm, and an inner diameter (ID.sub.r) of 14 mm. The
ceramic ring is placed around the ceramic tube so that the ends of
each are flush, and the tube-ring assembly is then co-sintered.
After cooling, a cross-sectional center segment is sliced from the
sintered assembly and thickness grinded to a final thickness (t) of
3 mm. The center segment comprises an inner ring sliced from the
ceramic tube and an outer ring sliced from the ceramic ring. The
area of contact between the inner and outer rings represents the
total bond area (A.sub.b), and is calculated according to the
following formula:
A.sub.b=.pi.OD.sub.tt (Formula I)
[0021] The Shear Strength of the center segment sample is tested at
room temperature using an Instron 8562 using a 100 kN load cell at
a speed of 0.05 mm/min, which applies equal but opposing force to
the inner and outer rings, respectively. The magnitude of the
applied force is gradually increased until the rings break apart.
The force (F) required to break the rings apart is measured in
Newtons. The Shear Strength value is obtained according to the
following formula:
.tau.=FA.sub.b10.sup.6 (Formula II)
[0022] It should be understood that ceramic articles as described
herein can be a wide variety of dimensions and overall sizes, but
the Shear Strength values are based on a standardized geometry and
testing approach as described above. Consequently, validating the
Shear Strength of a sample having differing dimensions larger or
smaller than the standardized sample described above requires the
fabrication of a standardized sample under identical compositional
and processing conditions to that of the sample having differing
dimensions.
[0023] The ceramic tube segments may be formed by various
techniques, such as form molding, slip casting, machining,
isopressing, extrusion, and other shape forming techniques.
However, embodiments of the present invention are particularly
drawn to large-scale tubes, typically having an outside diameter
greater than 7-9 inches, and lengths on the order of 0.5 to 3
meters and above. Consequently, extruded tubes tend not to be
practical, and various shape forming techniques have their
practical limitations. Accordingly, various embodiments are formed
by isopressing. Indeed, the extended length tube structures may
have an aspect ratio defined as the ratio of length (L) to outer
diameter (OD) of not less than 10:1, such as not less than about
20:1, such as not less than about 30:1, or not less than about
40:1. Since there is an ultimate limit on the length of such tubes
relative to diameter, most embodiments will not exceed an aspect
ratio of 300:1.
[0024] According to a particular embodiment, the second end of the
first tube segment is in abutting contact with the first end of the
second ceramic tube segment. The end faces may have various
configurations, including simple, planar structures, but also
including complementary structures that "key" together when in
abutting contact. One of example of this keyed relationship or
interconnected relationship is through use of a shiplapped joint,
in which facing surfaces have complementary L-shaped outer
contours, as shown in a cross-sectional view, such that they
interlock each other. In the case of planar end faces, they may be
oriented in a plane perpendicular to the longitudinal access of the
tube segments, or alternatively, be oriented off-angle at some
acute angle relative to the access smaller than 90.degree.,
resembling an offcut tube structure, such as a quill pen or
hypodermic needle. In such a case, the tube segments would be
oriented such that the off-angle faces are complementary to one
another.
[0025] As mentioned briefly above, the ceramic tube segments may be
formed of a ceramic material, most notably silicon carbide.
Additionally, the coupling components may be formed of a ceramic
material, notably silicon carbide. The ceramic tube segments and
the coupling components may comprise silicon carbide, and in
certain embodiments comprise principally silicon carbide, such that
silicon carbide is the majority compositional species of the tube,
typically greater than at least about 70 wt %, such as greater than
at least about 80 wt %, or greater than at least about 90 wt %. In
another embodiment, the tube may comprise silicon carbide in an
amount greater than at least about 91 wt %, such as greater than at
least about 99.85 wt %.
[0026] One particular form of silicon carbide is used according to
certain embodiments, known as HEXOLOY.RTM.-brand silicon carbide
(manufactured by Saint-Gobain Advanced Ceramics Corporation of
Worcester, Mass., USA), described in U.S. Pat. No. 4,179,299
incorporated herein by reference. Suitable silicon carbides
generally contain silicon carbide in an amount greater than at
least about 91 wt %, such as greater than at least about 99.85 wt
%, up to about 5.0 wt % carbonized organic material, from at least
about 0.15 wt % to not greater than about 3.0 wt % boron, and up to
about 1.0 wt % additional carbon. The "carbonized organic material"
is free carbon or uncombined carbon produced in situ by the
carbonization of the organic material used as a raw material in the
process of forming the ceramic tube. The carbonizable organic
materials that can be used in forming the ceramic tube include but
are not limited to phenolic resin, coal tar pitch, polyphenylene,
or polymethylphenylene.
[0027] Sintered ceramic bodies of silicon carbide according to an
embodiment may be characterized by a predominantly equiaxed
microstructure, meaning the presence of grains having an aspect
ratio of less than 3:1 (i.e., the ratio of the maximum dimension of
the grains of the crystal microstructure to the minimum dimension
of the grains of the crystal microstructure is less than 3:1).
Moreover, the silicon carbide comprises at least about 95 wt %,
such as at least about 99 wt % alpha-phase, non-cubic crystalline
silicon carbide.
[0028] The density of silicon carbide according to an embodiment is
at least about 2.40 g/cm.sup.3, such as at least about 2.90
g/cm.sup.3, or at least about 3.05 g/cm.sup.3.
[0029] According to certain embodiments, the first and second tube
segments, as well as the coupling component are all coaxial.
Additionally, the coupling component can take on any one of various
outer contours, but it is generally desirable that the coupling
component have an inner contour matching the outer contour of the
second end of the first tube segment and the first end of the
second tube segment. This inner contour of tube segment is
generally cylindrical, having a generally circular cross-sectional
shape. The outer contour can vary, but for ease of fabrication and
for predictable shrinkage rates, the outer contour of the coupling
may also be cylindrical. According to one particular feature of an
embodiment, an inner face between the coupling component and each
of the tubes segments to which it is bonded forms a seal, that
seals characterized by Shear Strength of the seal being not less
about 25 MPa, not less than about 40 MPa, not less than about 50
MPa, not less than about 75 MPa, not less than about 100 MPa, not
less than about 100 MPa, not less than about 120 MPa, not less than
about 140 MPa, not less than about 170 MPa, or not less than about
200 MPa. In one embodiment, the interface between the tube and the
base component exhibits a Shear Strength not greater than about
1000 MPa, such as not greater than about 700 MPa, not greater than
about 500 MPa, or not greater than about 300 MPa.
[0030] A Nitrogen Seal Performance is determined according to a
nitrogen seal performance test, wherein nitrogen is applied at an
interface of a seal at a given initial positive pressure, and
pressure loss is measured by a pressure gauge. Nitrogen Seal
Performance is then the percent pressure drop occurring across the
seal interface over a period of 2 hours at an applied gauge
pressure of 200 psi. Embodiments herein achieve a Nitrogen seal
performance of not greater than 10%, not greater than 9%, not
greater than 8%, not greater than 7%, not greater than 6%, not
greater than 5%, not greater than 4%, not greater than 3%, not
greater than 2%, not greater than 1.9%, not greater than 1.8%, not
greater than 1.7%, not greater than 1.6%, not greater than 1.5%,
not greater than 1.4%, not greater than 1.3%, not greater than
1.2%, not greater than 1.1%, not greater than 1.0%, not greater
than 0.9%, not greater than 0.8%, not greater than 0.7%, not
greater than 0.6%, not greater than 0.5%, not greater than 0.4%,
not greater than 0.3%, not greater than 0.2%, or not greater than
0.1% of an initial pressure differential of 200 PSI (gauge
pressure).
[0031] A Helium Seal Performance is determined according to a
helium seal performance test, wherein helium is applied at an
interface of a seal at a given initial positive pressure and
pressure loss is measured by a pressure gauge. Helium Seal
Performance is achieved if the pressure drop occurring across the
seal interface over a period of 2 hours is not greater than 10%,
not greater than 9%, not greater than 8%, not greater than 7%, not
greater than 6%, not greater than 5%, not greater than 4%, not
greater than 3%, not greater than 2%, not greater than 1.9%, not
greater than 1.8%, not greater than 1.7%, not greater than 1.6%,
not greater than 1.5%, not greater than 1.4%, not greater than
1.3%, not greater than 1.2%, not greater than 1.1%, not greater
than 1.0%, not greater than 0.9%, not greater than 0.8%, not
greater than 0.7%, not greater than 0.6%, not greater than 0.5%,
not greater than 0.4%, not greater than 0.3%, not greater than
0.2%, or not greater than 0.1% of an initial pressure differential
of 87 PSI (gauge pressure)), an initial pressure differential of
about 200 psi (about 13.8 bar), or an initial pressure differential
of about 6 barg (bar gauge).
[0032] A Vacuum Seal Performance is determined according to a
vacuum seal performance test. In the vacuum seal performance test,
a vacuum is applied to a seal. The nitrogen gas atmosphere inside
the tube is then lowered from 1 ATM (760 torr) to a pressure of 10
torr thereby having a pressure differential of 750 torr. Vacuum
Seal Performance is achieved if the gain inside the tube occurring
across the seal interface over a period of 2 hours is not greater
than 10%, not greater than 9%, not greater than 8%, not greater
than 7%, not greater than 6%, not greater than 5%, not greater than
4%, not greater than 3%, not greater than 2%, not greater than
1.9%, not greater than 1.8%, not greater than 1.7%, not greater
than 1.6%, not greater than 1.5%, not greater than 1.4%, not
greater than 1.3%, not greater than 1.2%, not greater than 1.1%,
not greater than 1.0%, not greater than 0.9%, not greater than
0.8%, not greater than 0.7%, not greater than 0.6%, not greater
than 0.5%, not greater than 0.4%, not greater than 0.3%, not
greater than 0.2%, or not greater than 0.1% of the pressure
differential (750 torr).
[0033] In each of the seal performance tests, the bond or interface
is subjected to the above-described pressure differential.
Depending on the geometry of the part, an inner volume is
pressurized or evacuated, and holes plugged. In a case of an
external seal, such as in the case of a flange on a tube, an
end-cap is positioned to cover the flange and exposed bore of the
tube, the cap being offset from the bore to allow fluid
communication (and hence pressure/vacuum) extending radially up to
the bond region. Caps/plugs can have varying geometries to fit the
part undergoing test, and can be sealed with a vacuum grease to
ensure a pressure tight, hermetic seal.
[0034] Sintered ceramic articles as described herein can be formed
through a multi-step sintering approach. For example, a green
ceramic tube is formed through any one of suitable shape forming
technologies, such as molding, slip casting, isopressing,
machining, and particularly extrusion. As is generally understood
in the art, the green ceramic tube generally contains a water or
organic liquid phase combined with various processing aids and
binders. For additional information on compositional details,
reference can be made to U.S. Pat. No. 4,179,299 incorporated
herein by reference.
[0035] Extended length tube structures according to embodiments
here and may be formed by various techniques. According to one, the
first and second tube segments are provided, each having first and
second ends. Each of the first and second tube segments are
pre-sintered, at a temperature above 2000.degree. C., such as above
2050.degree. C., but generally below 2400.degree. C., such as below
2300.degree. C., such as below 2250.degree. C. A suitable target
range for sintering the green ceramic tube in the case of silicon
carbide can lie within a range of 2100-2200.degree. C. Sintering
times can vary, and are largely dependent on the thermal mass of
the tube. However, typically sintering times range from 15 minutes
to 10 hours, such as not less than about 30 minutes, such as not
less than about 1 hour, such as not less than about 1.5 hours.
While large, high mass tubes may require extended sintering times,
typically sintering times do not exceed 30 hours, such as not great
than 20 hours, such as not greater than 10 hours.
[0036] After the sintering step is completed, at least a portion of
an outer surface of the sintered tube is subjected to surface
cleaning. Typically, at least the portion of the tube that will
contact the base component will be subjected to surface cleaning.
In this respect, it has been found that the outer surface of the
tube can carry contaminates, such as contaminates that are
deposited during the sintering process, or which form as a
consequence of the sintering process and changes in the
crystallographic and compositional structure of the tube. For
example, binders within the composition may burn-out, leaving
behind a carbonaceous reside on the outer surface of the tube. That
carbonaceous residue, generally in the form of free carbon, can
negatively impact the quality of bond between the tube and the base
component, inhibiting a hermetic seal.
[0037] Processing to form an extended length ceramic tube structure
continues with provision of an un-sintered or partially sintered
ceramic coupling component. That ceramic coupling component is
arranged so as to overlie or circumscribe the first and second tube
segments, particularly at the second end of the first tube segment
and the first end of the second tube segment, and more particularly
at the portions on the first and second tube segments where they
first and second tube segments meet each other. Subsequently, the
arrangement of the first and second tube segments and the
positioned coupling component is then subjected to a sintering step
during which the coupling component shrinks to its final
dimensions.
[0038] Further, before the pre-sintering step, each of the ceramic
tube segments may be subjected to a machining operation. Stated
alternatively, this machining step is carried out in the green
state, where the tube is in a state that allows easier material
removal than in the sintered state. The machining may be effective
to reduce or even completely remove dimensional or surface
irregularities of the green tube. For example, in the case of
extrusion, the green tube may have characteristic score lines
extending partially or wholly along the entire length of the tube.
Those score lines can inhibit the formation of a strong interfacial
sinter bond, as well as a hermetic seal. In the case of other
formation technologies, machining may still be desirable. For
example, in the case of isopressing or molding, characteristic
imperfections may be left behind on the green tube, such as
flashing.
[0039] Sintered ceramic bodies of silicon carbide according to an
embodiment may be characterized by the amount the bodies shrink
from a green state to a fully sintered state. For example, green
ceramic bodies of silicon carbide according to an embodiment may
shrink more than about 10% from their original size, more than
about 12%, more than about 15%, more than about 17%, less than
about 25%, less than about 20%, less than about 17%, less than
about 15% upon being fully sintered. In a particular embodiment, a
green ceramic body of silicon carbide may shrink approximately 17%
from its original size upon being fully sintered. When combining a
pre-sintered first component, such as a tube, with a green second
component, such as an un-sintered or incompletely sintered coupling
component that circumvents the pre-sintered first component, the
shrinkage relationship, and the amount of interference bond, can be
expressed as follows.
ID.sub.c,FS=OD.sub.p-.DELTA., where
[0040] ID.sub.c,FS is the inside diameter (ID) of a fully sintered
coupling component, OD.sub.t is IDc,FS/(1-Rs)=IDc, where outside
diameter, of 2.0'' (i.e. OD.sub.t=2.0). An interference bond of 5%
(i.e. A=5%) of a second body, such as the coupling component,
requires a fully sintered coupling component ID (ID.sub.c,FS) to be
0.10'' less than the OD.sub.t (i.e. 2.0*5%=0.10), or 1.90'' (i.e.
ID.sub.c,FS=OD.sub.t-.DELTA., or 1.90''=2.0''-0.10''). Thus, to
attain a 5% interference of a fully sintered coupling component on
the pre-sintered tube, the green coupling component will be made to
have a theoretically fully sintered inner diameter (if it were
sintered by itself) of 1.90''.
[0041] Further, the ID of the green second component (i.e. the
un-sintered coupling component) can be expressed as follows.
ID.sub.c,FS/(1-R.sub.s)=ID.sub.c, where
[0042] ID.sub.c is the inner diameter of the green second
component, or un-sintered coupling component, and R.sub.s is the
shrinkage rate of the second component (expressed as a decimal).
Thus, in accordance with the example given above, and assuming the
shrinkage rate of the second component is 17.0%, the inner diameter
of the green coupling component (ID.sub.c) can be calculated as
1.9/(1-0.170)=2.289''.
[0043] Turning to specific embodiments, a first embodiment of an
extended length tube structure is shown in FIGS. 1 and 2. FIG. 1 is
a cross-section of an extended length tube segment containing 3
segments, and FIG. 2 shows that same structure but in plan view.
The extended length tube segment includes a first tube segment 14,
a second tube segment 12, and a third tube segment 10, each being
arranged in end-end relationship. As particularly shown in FIG. 1,
the first tube segment 14 includes a first end 15 and a second end
16. The second tube segment 12 includes a first end 18. Further,
the first and second coupling components 22, 20, respectively are
shown, and are disposed about the interfaces between the second end
16 of the first component 14 and the first end 18 of the second
component 12.
[0044] FIGS. 3 and 4 show different geometric configurations for
the end faces of adjacent tube segments. FIG. 3 illustrates a
simplified structure having a first tube segment 30, a second tube
segment 35, the first tube segment 30 having a planar end face 31,
the second tube segment 35 having a planar end face 36.
[0045] FIG. 4 illustrates what can be referred to as a "shiplapped"
engagement structure between adjacent tube segments, including a
first tube segment 40 having an L-shaped end face 41, and a second
tube-segment 45 having an L-shaped end face 46. As shown, the
L-shaped structures are inverted with respect to each other so as
to be complementary in nature, and achieve a "keyed"
configuration.
[0046] FIG. 5 is an SEM cross-section showing the interfacial bond
between a pre-sintered silicon carbide tube 50, and a base
component, such as a coupling component, 52. Between the components
50 and 52 is an interface 54, which provides a hermetic seal
between components 50 and 52. The interface 54 may also be defined
as a sinter bond (e.g. sintered bond) or an interference bond or
fit. While the interface may be easily seen in the figure, it
should be noted that portions of the interface are obscured by a
non-colored or white depiction. These areas indicate areas where
grain growth occurred across the interface (i.e. crystallographic
grains extend across and bridge, functioning to strengthen and
enhance the hermetic seal across the interface. Stated
alternatively, grains, formed of crystals from each of the two
components joined and grew or extended so as to bridge the
interface creating a strong chemical or crystallographic bond
across the interface. Consequently, the bond is more complex than a
typical friction-fit direct bond structure, but includes both
mechanical and crystallographic components to improve the
robustness of the interface.
[0047] The following examples include helium pressure testing on
embodiments of articles having silicon carbide components including
a sinter bond, or interference bond, according to the embodiments
discussed above. The embodiments tested generally included a
pre-sintered tube with a flange, cap, or other component sintered
to the pre-sintered tube. Although the articles and components
tested may vary in some respects to those disclosed herein, the
tested seals (e.g. interference bonds, sintered-bonds) in the
following examples are similar or identical to the embodiments of
the seals described and disclosed herein, and thus the results are
relevant to the performance of the disclosed embodiments.
Example 1
[0048] Several ceramic articles were formed to include an
interference bond between a ceramic tube and ceramic flange as
follows. A 14 mm OD ceramic tube was prepared according to the
methods discussed above. One end of the tube was capped, and the
tube and cap was pre-sintered according to the methods discussed
above in order to provide a pre-sintered tube with a closed end and
an open end. Several green ceramic flanges were prepared according
to the methods above to fit over the open end of the pre-sintered
tube. The green ceramic flanges were engineered to provide a
fully-sintered ID that was less than the OD of the 14 mm tube (e.g.
interference) by about 0% to about 15%. The green ceramic flanges
were provided on the open end of the pre-sintered tube and was
co-sintered with the pre-sintered tube to provide an interference
bond according to the methods discussed above.
[0049] After the ceramic articles were formed, they were pressure
tested by providing 200 psi (about 13.8 bar) of helium (He) on one
side of the interference bond to determine the integrity of the
interference bond of each ceramic article. FIG. 6 shows that the
majority of the samples of ceramic articles having a flange
engineered to have between about 0% to about 5% fully-sintered ID
failed in holding pressure. FIG. 6 also shows that a majority of
the sample of ceramic articles having a flange engineered to have
between about 5% to about 15% fully-sintered ID succeeded in
holding pressure. In particular, FIG. 6 tends to show that a
threshold value of about 5% is successful in holding pressure.
Example 2
[0050] A ceramic article having a 100 mm OD tube was prepared and
pre-sintered according to the methods discussed above, and was
fitted with a green flange engineered to have a fully-sintered ID
of 3% less than the pre-sintered tube. The tube and flange were
co-sintered to form a ceramic article having an interference bond
according to the methods discussed above, and pressure tested at
20.degree. C. with 6 barg (bar gauge) of helium on one side of the
interference bond to determine the integrity of the interference
bond of the ceramic article. The ceramic article lost about 0.2 bar
over a 12 hour period.
Example 3
[0051] Three ceramic articles having a 35 mm OD tube were prepared
and pre-sintered according to the methods discussed above, and each
was fitted with a green flange and subsequently co-sintered to form
a ceramic article having an interference bond according to the
methods discussed above. A first ceramic article included a flange
engineered to have a fully-sintered ID of 3% less than the
pre-sintered tube, a second ceramic article included a flange
engineered to have a fully-sintered ID of 5% less than the
pre-sintered tube, and a third ceramic article included a flange
engineered to have a fully-sintered ID of 11% less than the
pre-sintered tube. The three ceramic articles were subjected to
five (5) thermal cycles from 20.degree. C. to 1000.degree. C., and
pressurized with 6 barg of helium on one side of the interference
bond to determine the integrity of the interference bond of each
ceramic article. Pressure readings were taken at 20.degree. C. and
1000.degree. C. for each ceramic article at each iteration of
thermal cycling. The results of the 20.degree. C. readings are
shown in FIG. 10, and the results for the 1000.degree. C. are shown
in FIG. 11, where sample "A" is the 3% sample and depicted as a
triangle, sample "B" is the 5% sample and depicted as a diamond,
and sample "C" is the 11% sample and depicted as a square.
[0052] As shown in FIG. 7, samples A and B lost less than 0.1
(-0.1) bar/H at 20.degree. C. The average pressure loss for sample
A at 20.degree. C. is less than about 0.03 bar/H, and the average
pressure loss for sample B at 20.degree. C. is less than about 0.01
bar/H. FIG. 10 also shows that sample C increasingly lost pressure
at each thermal cycle reading taken at 20.degree. C. It is unclear
why sample C readings show a continuous loss in pressure as this is
contrary to the expectations of that sample.
[0053] Turning to FIG. 8, sample A (the 3% sample) actually shows
an increase in pressure at each thermal cycle reading taken at
1000.degree. C. It is unclear why pressure increased in sample A at
1000.degree. C. The average pressure gain of sample A taken at
1000.degree. C. is about 0.06 bar/H. In FIG. 8, sample B (the 5%
sample) shows less than 0.2 (-0.2) bar/H pressure loss. The average
pressure loss for sample B taken at 1000.degree. C. is less than
about 0.03 bar/H. FIG. 8 also shows that sample C (the 11% sample)
has a continuous increase in pressure loss at each thermal cycle,
which is consistent with the data of FIG. 7. The results of the
thermal cycle pressure readings of FIGS. 7 and 8 tend to show that
sample B (the 5% sample) provides a tighter interference bond than
either sample A or C.
Example 4
[0054] A ceramic article was prepared according to sample B (the 5%
sample) in Example 3 above, and was tested for pressure loss at
intermediate temperatures by pressurizing one side of the
interference bond of the ceramic article with 2 barg of helium
while heating the ceramic article up to 1000.degree. C. As FIG. 9
shows, frequent measurements were taken at several temperatures
between the thermal cycle of about 100.degree. C. to about
900.degree. C. As FIG. 9 also indicates, the pressure in the tube
(measured in barg) remained between about 2 barg and 2.5 barg
through the thermal cycle. The results of this example indicate
little to no loss or degradation of tightness in the interference
bond throughout a thermal cycle, also suggesting that the secondary
component (cap, flange, etc.) bonds well to the tube because both
components have identical, or nearly identical, coefficients of
thermal expansion (CTE). It is also noted that, although not shown
in the FIGS., several samples have been known to operate at greater
than about 1000.degree. C., greater than about 1300.degree. C., and
even greater than 2000.degree. C. with no appreciable increase in
pressure loss when subsequently tested at temperatures at or below
1000.degree. C.
Example 5
[0055] Three ceramic articles (samples A, B, and C) were prepared
according to example 3 above, and subjected to five (5) testing
iterations of thermal cycles between 20.degree. C. and 1000.degree.
C. while provided with 6 barg of helium on one side of the
interference bond of each sample. The results are shown in FIGS. 10
and 11. As shown in FIG. 10, sample A (3% sample) had an average
pressure loss at 20.degree. C. of about 0.05 bar/H, sample B (5%
sample) had an average pressure loss at 20.degree. C. of about 0.03
bar/h, and sample C (11% sample) had an average pressure loss of
about 0.13 bar/H. FIG. 11 shows that sample B tends to provide a
pressure increase at 1000.degree. C. It is unclear why sample B
increases pressure in the tube at 1000.degree. C. However, FIGS. 10
and 11 appear to indicate that sample B provides the tightest
interference bond and, thus, provides higher fidelity in pressure
retention at thermal cycling than the other samples.
Example 6
[0056] Three ceramic articles (samples A, B, and C) were prepared
according to example 3 above, and subjected to a long duration
(about 72-80 hours) pressure test at 1000.degree. C. with 6 barg of
helium on one side of the interference bond of each sample. The
results of the long duration pressure test are shown in FIG. 12. As
shown in FIG. 12, sample B (5% sample) lost all pressure at the end
of the long duration test, at approximately 72 hours. The results
are anomalous, and it is believed that a hermetic seal was not
fully achieved with sample B.
* * * * *