Title: Methods of fabricating cermet materials and methods of utilizing same
Abstract: Methods of fabricating cermet materials and methods of utilizing the same such as in filtering particulate and gaseous pollutants from internal combustion engines having intermetallic and ceramic phases. The cermet material may be made from a transition metal aluminide phase and an aluminia phase. The mixture may be pressed to form a green compact body and then heated in a nitrogen-containing atmosphere so as to melt aluminum particles and form the cermet. Filler materials may be added to increase the porosity or tailor the catalytic properties of the cermet material. Additionally, the cermet material may be reinforced with fibers or screens. The cermet material may also be formed so as to pass an electrical current therethrough to heat the material during use.
Patent Number: 7,022,647 Issued on 04/04/2006 to Kong
| Inventors:
|
Kong; Peter C. (Idaho Falls, ID)
|
| Assignee:
|
Battelle Energy Alliance, LLC (Idaho Falls, ID)
|
| Appl. No.:
|
213112 |
| Filed:
|
August 5, 2002 |
| Current U.S. Class: |
502/414; 423/210; 502/439 |
| Current Intern'l Class: |
B01J 8/00 (20060101); B01J 20/00 (20060101); B01J 21/04 (20060101) |
| Field of Search: |
423/210
502/414,439
|
References Cited [Referenced By]
U.S. Patent Documents
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| |
| 4909842 | Mar., 1990 | Dunmead et al.
| |
| 4942020 | Jul., 1990 | Whittenberger et al.
| |
| 4990181 | Feb., 1991 | Pierotti et al.
| |
| 4992233 | Feb., 1991 | Swaroop et al.
| |
| 5053062 | Oct., 1991 | Barris et al.
| |
| 5217816 | Jun., 1993 | Brupbacher et al.
| |
| 5496655 | Mar., 1996 | Lessing.
| |
| 5545240 | Aug., 1996 | Tsuru et al.
| |
| 5682740 | Nov., 1997 | Kawamura.
| |
| 5714065 | Feb., 1998 | Huder.
| |
| 5735332 | Apr., 1998 | Ritland et al.
| |
| 5766458 | Jun., 1998 | Sekhar et al.
| |
| 5774779 | Jun., 1998 | Tuchinskiy.
| |
| 5780811 | Jul., 1998 | Kawamura.
| |
| 5827424 | Oct., 1998 | Gillis et al.
| |
| 5951791 | Sep., 1999 | Bell et al.
| |
| 6025065 | Feb., 2000 | Claussen et al.
| |
| 6033623 | Mar., 2000 | Deevi et al.
| |
| 6271461 | Aug., 2001 | Fraas et al.
| |
| 6314722 | Nov., 2001 | Matros et al.
| |
| 6641795 | Nov., 2003 | Abe.
| |
Primary Examiner: Silverman; Stanley S.
Assistant Examiner: Strickland; Jonas N.
Attorney, Agent or Firm: Trask Britt, P.C.
Goverment Interests
STATEMENT OF GOVERNMENT RIGHTS
The United States Government has rights in this invention pursuant to Contract
No. DE-AC07-99ID13727 and Contract No. DE-AC07-05ID14517 between the United States
Department of Energy and Battelle Energy Alliance, LLC.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to U.S. application Ser. No. 10/213,120 entitled
CERMET MATERIALS, SELF-CLEANING CERMET FILTERS, APPARATUS AND SYSTEMS EMPLOYING
SAME, filed on even date herewith.
Claims
What is claimed is:
1. A method of filtering exhaust gases comprising:
providing a porous filter made from a cermet material comprising:
a substantial number of pores;
a transition metal aluminide phase; and
a discontinuous ceramic phase bonded by the transition metal aluminide phase,
wherein the ceramic phase is selected from the group consisting of alumina, zirconia
silicate, zirconia, mullite, cordierite, and iron III oxide, and wherein the ceramic
phase comprises at least approximately 50% by weight of the cermet material; and
operably coupling the porous filter to exhaust gases from an internal combustion
engine to cause the exhaust gases to travel through the pores of the porous filter
in contact with the cermet material thereof.
2. The method of filtering exhaust gases of claim 1, wherein at least a portion
of the exhaust gases are chemically transformed into different chemical species
while passing through the pores of the porous filter.
3. The method of filtering exhaust gases of claim 1, wherein the exhaust gases
include NO
x type gases and chemically reducing at least a portion of
the NO
x type gases while passing through the pores of the porous filter.
4. The method of filtering exhaust gases of claim 1 further comprising trapping
carbon particles from the exhaust gases within the pores of the porous filter.
5. The method of filtering exhaust gases of claim 4, wherein the carbon particles
trapped within the pores of the porous filter chemically reduce at least a portion
of the exhaust gases.
6. The method of filtering exhaust gases of claim 1, wherein the exhaust gases
include CO
x type gases and chemically oxidizing at least a portion of
the CO
x type gases while passing through the pores of the porous filter.
7. The method of filtering exhaust gases of claim 1 further comprising applying
an electrical current to the porous filter.
8. The method of filtering exhaust gases of claim 7, wherein the electrical current
applied heats the porous filter.
9. The method of filtering exhaust gases of claim 7, wherein the electrical current
is continuously applied to the porous filter.
10. The method of filtering exhaust gases of claim 7, wherein the electrical
current is intermittently applied to the porous filter.
11. The method of filtering exhaust gases of claim 1 further comprising providing
the porous filter with a resistive heating element disposed within the porous filter.
12. The method of filtering exhaust gases of claim 11 further comprising providing
the resistive heating element with a ceramic coating.
13. The method of filtering exhaust gases of claim 11 further comprising applying
an electrical current to the resistive heating element.
14. The method of filtering exhaust gases of claim 13, wherein the electrical
current applied to the resistive heating element heats the porous filter.
15. The method of filtering exhaust gases of claim 13, wherein the electrical
current is continuously applied to the resistive beating element.
16. The method of filtering exhaust gases of claim 13, wherein the electrical
current is intermittently applied to the resistive heating element.
17. The method of filtering exhaust gases of claim 1 further comprising providing
a heating element external to the porous filter.
18. The method of filtering exhaust gases of claim 1 further comprising injecting
vapor from a fuel tank headspace into the porous filter.
19. The method of filtering exhaust gases of claim 1 further comprising providing
the cermet material with a structural reinforcement phase.
20. The method of filtering exhaust gases of claim 1 further comprising providing
the cermet material with a structural reinforcement phase selected from the group
consisting of metal fibers, ceramic fibers, and metal screens.
21. The method of filtering exhaust gases of claim 1 further comprising bonding
a housing with the cermet material.
22. The method of filtering exhaust gases of claim 1 further comprising providing
the cermet material with a graded porosity.
23. The method of filtering exhaust gases of claim 1 further comprising providing
electrodes integrally bonded with the cermet material.
24. The method of filtering exhaust gases of claim 1 further comprising providing
the cermet material with an ammonia emitting phase.
25. The method of filtering exhaust gases of claim 24, wherein the ammonia emitting
phase emits ammonia chemically reducing a portion of NO
x in the exhaust gases.
26. The method of filtering exhaust gases of claim 1 further comprising providing
the cermet material with a NO
x absorbing phase.
27. The method of filtering exhaust gases of claim 26, wherein the NO
x
absorbing phase absorbs at least a portion of the exhaust gases.
28. The method of filtering exhaust gases of claim 1 further comprising providing
the cermet material with a hydrocarbon emitting phase.
29. The method of filtering exhaust gases of claim 28, wherein the hydrocarbon
emitting phase emits hydrocarbons that chemically reduce at least a portion of
NO
x in the exhaust gases.
30. The method of filtering exhaust gases of claim 1 further comprising providing
the cermet material with an alkali oxide phase.
31. The method of filtering exhaust gases of claim 30, wherein the alkali oxide
phase absorbs at least a portion of the exhaust gases.
32. A method of filtering exhaust gases comprising:
providing a porous filter made from a cermet material comprising:
a substantial number of pores,
a transition metal aluminide phase,
a ceramic phase selected from the group consisting of alumina, zirconia silicate,
zirconia, mullite, cordierite, and iron III oxide, and
an ammonia emitting phase; and
operably coupling the porous filter to exhaust gases from an internal combustion
engine to cause the exhaust gases to travel through the pores of the porous filter
in contact with the cermet material thereof.
33. The method of filtering exhaust gases according claim 32, further comprising
chemically reducing a portion of NO
x in the exhaust gases with ammonia
from the ammonia emitting phase.
34. The method of filtering exhaust gases according to claim 32, further comprising
applying an electrical current to the porous filter.
35. The method of filtering exhaust gases according to claim 34, further comprising
heating the porous filter with the electrical current.
36. The method of filtering exhaust gases according to claim 32, further comprising
providing the porous filter with a resistive heating element disposed within the
porous filter.
37. The method of filtering exhaust gases according to claim 36, further comprising
providing the resistive heating element with a ceramic coating.
38. The method of filtering exhaust gases according to claim 32, further comprising
injecting vapor from a fuel tank headspace into the porous filter.
39. The method of filtering exhaust gases according to claim 32, further comprising
providing the cermet material with a structural reinforcement phase selected from
the group consisting of metal fibers, ceramic fibers, and metal screens.
40. The method of filtering exhaust gases according to claim 32, further comprising
providing the cermet material with a graded porosity.
41. A method of filtering exhaust gases comprising:
providing a porous filter made from a cermet material comprising:
a substantial number of pores,
a transition metal aluminide phase,
a ceramic phase selected from the group consisting of alumina, zirconia silicate,
zirconia, mullite, cordierite, and iron III oxide, and
a hydrocarbon emitting phase; and
operably coupling the porous filter to exhaust gases from an internal combustion
engine to cause the exhaust gases to travel through the pores of the porous filter
in contact with the cermet material thereof.
42. The method of filtering exhaust gases according to claim 41, further comprising
chemically reducing at least a portion of NO
x in the exhaust gases with
hydrocarbons from the hydrocarbon emitting phase.
43. The method of filtering exhaust gases according to claim 41, further comprising
applying an electrical current to the porous filter.
44. The method of filtering exhaust gases according to claim 43, further comprising
heating the porous filter with the electrical current.
45. The method of filtering exhaust gases according to claim 41, further comprising
providing the porous filter with a resistive heating element disposed within the
porous filter.
46. The method of filtering exhaust gases according to claim 45, further comprising
providing the resistive heating element with a ceramic coating.
47. The method of filtering exhaust gases according to claim 41, further comprising
injecting vapor from a fuel tank headspace into the porous filter.
48. The method of filtering exhaust gases according to claim 41, further comprising
providing the cermet material with a structural reinforcement phase selected from
the group consisting of metal fibers, ceramic fibers, and metal screens.
49. The method of filtering exhaust gases according to claim 41, further comprising
providing the cermet material with a graded porosity.
50. A method of filtering exhaust gases comprising:
providing a porous filter made from a cermet material comprising:
a substantial number of pores,
a transition metal aluminide phase,
a ceramic phase selected from the group consisting of alumina, zirconia silicate,
zirconia, mullite, cordierite, and iron III oxide, and
an alkali oxide phase; and
operably coupling the porous filter to exhaust gases from an internal combustion
engine to cause the exhaust gases to travel through the pores of the porous filter
in contact with the cermet material thereof.
51. The method of filtering exhaust gases according to claim 50, further comprising
absorbing at least a portion of the exhaust gases with the alkali oxide phase.
52. The method of filtering exhaust gases according to claim 51, further comprising
applying an electrical current to the porous filter.
53. The method of filtering exhaust gases according to claim 52, further comprising
heating the porous filter with the electrical current.
54. The method of filtering exhaust gases according to claim 50, further comprising
providing the porous filter with a resistive heating element disposed within the
porous filter.
55. The method of filtering exhaust gases according to claim 54, further comprising
providing the resistive heating element with a ceramic coating.
56. The method of filtering exhaust gases according to claim 50, further comprising
injecting vapor from a fuel tank headspace into the porous filter.
57. The method of filtering exhaust gases according to claim 50, further comprising
providing the cermet material with a structural reinforcement phase selected from
the group consisting of metal fibers, ceramic fibers, and metal screens.
58. The method of filtering exhaust gases according to claim 50, further comprising
providing the cermet material with a graded porosity.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to cermet filters used to filter combustion products
from internal combustion engines. More particularly, this invention relates to
a porous, intermetallic-ceramic composite filter that is self-cleaning and can
improve emissions from internal combustion engines.
2. State of the Art
Emissions from vehicles, such as heavy-duty diesel engine vehicles, contribute
greatly to pollution problems of the United States of America (USA). Heavy-duty
vehicle emissions produce ozone, particulate materials (PM), nitrogen oxides (NO
X),
sulfur oxides (SO
X), and volatile organic compounds (VOCs). These emissions
can cause adverse health effects such as premature mortality, aggravation of respiratory
and cardiovascular disease, chronic bronchitis, changes to lung tissues and structures,
and altered respiratory defense mechanisms, among other things. Further, ozone
is known to cause crop and forestry losses and PM causes damage to materials and
soiling. NO
X and PM also significantly contribute to unsightly smog
and substantial visibility impairment in many parts of the USA.
Emissions from diesel engine heavy-duty trucks significantly contribute
to these problems throughout the country. By 2007, heavy-duty vehicles will account
for 29 percent of NO
X and 14 percent of PM emissions in the USA. These
proportions are even higher in some urban areas. For example in Albuquerque, N.
Mex., heavy-duty vehicles contribute 37 percent of NO
X and 20 percent
of PM emissions.
The United States Environmental Protection Agency (EPA) is proposing a PM emissions
standard for new heavy-duty engines of 0.01 grams per brake-horsepower-per hour
(g/bhp-hr) to take full effect in 2007. The EPA is also proposing more stringent
standards for NO
X and VOC emissions to be phased in between 2007 and
2010. In order to meet these rigorous new standards, new and improved filters are needed.
Engine and catalyst manufacturers have experimented with many catalytic converters
and with a wide variety of regenerative catalytic traps. Precious metal catalytic
traps are somewhat effective in oxidizing gaseous hydrocarbons and CO as well as
the particulate soluble organic fraction (SOF). However, precious metal catalysts
are very expensive. Base metal catalytic traps promote soot oxidation but have
little effect on NO
X, CO
X, or SO
X.
Intermetallic-ceramic catalyst supports have been produced
in the past. For example, U.S. Pat. No. 5,951,791 to Bell et al. discloses using
nickel aluminide to coat the inside of an alumina fiber preform. U.S. Pat. No.
5,774,779 to Tuchinskiy and U.S. Pat. No. 4,990,181 to Pierotti et al. disclose
using nickel aluminide as a catalyst support. U.S. Pat. No. 4,992,233 to Swaroop
et al. discloses using iron aluminide alloys in exhaust filter applications. Also,
U.S. Pat. No. 5,496,655 to Lessing discloses using a porous NiAl or Ni
3Al
with a ceramic filler to catalyze steam reforming of hydrocarbons to power fuel cells.
Porous ceramic filters made from carbide and oxide materials are well known
in the art. However, conventional ceramic filters used with heavy-duty diesel engines
have a significant lifetime problem. These ceramic filters have a short lifetime
due to severe carbon particulate plugging and structural failure due to high vehicle
motion stresses and extreme thermal stresses. Typically, the filters are plugged
after 500 hours of service, which makes them a financial and operational liability
for companies. Further, the filters often require complicated heating and control systems.
BRIEF SUMMARY OF THE INVENTION
The present invention fulfills the need in the art for a strong and tough porous
intermetallic-ceramic composite filter that not only filters particulates but reduces
undesirable gaseous pollutants. The present invention eliminates the need for complicated
systems to heat the filter and is self-cleaning so it does not plug up with particulate
matter. Further, the intermetallic-ceramic composite filters of the present invention
do not require coating with other materials for functioning.
The present invention comprises a self-cleaning filter used for filtering particulate
and gaseous pollutants from internal combustion engines. The filter is made from
a porous cermet-type material having an intermetallic phase and a ceramic phase.
An exemplary embodiment uses a porous cermet filter having a transition metal
aluminide phase such as cobalt, iron, nickel, or titanium-type aluminides and an
alumina phase.
In another exemplary embodiment, a reinforcement material such as metal fibers,
ceramic fibers, or metal screens may be incorporated into the porous cermet filter
for added strength.
In another exemplary embodiment, the porous cermet filter is electrically conductive
and a current may be passed therethrough to heat it during use.
In another exemplary embodiment, at least one resistive heating element may be
incorporated into the porous cermet filter during manufacture. An electrical current
may be applied to the resistive heating element to heat the porous cermet filter
during use.
In another exemplary embodiment, the resistive heating element has a coefficient
of thermal expansion approximately the same as that of the cermet material.
In another exemplary embodiment, the resistive heating element may be coated
with
a ceramic material prior to incorporation into the cermet filter.
In another exemplary embodiment, the ceramic material coating the resistive heating
element electrically insulates it from the cermet material.
In another exemplary embodiment, an external heating element may be provided
to
heat the porous cermet filter during use.
In another exemplary embodiment, the cermet may be manufactured using a combustion
synthesis process by forming a green compact of a transition metal, aluminum, and
alumina particles to produce a transition metal aluminide-alumina porous cermet
filter. Alternatively, aluminum and thermite particles may be used to produce a
nickel aluminide-alumina porous cermet filter.
In another exemplary embodiment, the combustion synthesis process may be performed
under a nitrogen-containing atmosphere to form ammonia-producing phases in the
porous cermet filter.
In another exemplary embodiment, the combustion synthesis process may be performed
with sugar added to the green compact under a nitrogen-containing atmosphere to
form ammonia-producing phases in the porous cermet filter.
In another exemplary embodiment, the combustion synthesis process may be performed
with an alkali carbonate or an alkali bicarbonate and sugar added to the green
compact under a nitrogen-containing atmosphere to form ammonia-producing phases
and hydrocarbon gas-producing phases. In this embodiment, an alkali oxide is formed
during the combustion synthesis process, which may either be leached out to increase
porosity or left in the cermet filter because of its ability to absorb NO
X.
In another exemplary embodiment, a sacrificial filler may be added to the green
compact to increase the porosity of the cermet filter.
In another exemplary embodiment, a porous cermet filter may be produced with a
graded porosity by layering relatively larger and smaller sacrificial filler materials
in the green compact.
In another exemplary embodiment, electrodes may be incorporated into the porous
cermet filter during the combustion synthesis process.
In another exemplary embodiment, a housing may be bonded to the porous cermet
filter during the combustion synthesis process.
The disclosed invention also encompasses methods of manufacture and use of the
inventive cermet filter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
In the drawings, which illustrate what is currently considered to be the best
mode for carrying out the invention:
FIG. 1 is sectional view of a porous cermet filter.
FIGS. 2A and 2B are photomicrographs of the microstructure of the cermet material
in FIG. 1.
FIG. 3A is a sectional view of a porous cermet filter produced with sugar filler materials.
FIG. 3B is a sectional view of a porous cermet filter produced with human hair
sacrificial filler materials.
FIG. 3C is a longitudinal view of a porous cermet filter produced with human
hair sacrificial filler materials.
FIG. 3D is a sectional view of a porous cermet filter having a graded porosity.
FIGS. 3E and 3F are views of a porous cermet filter having a graded porosity
across the length thereof.
FIG. 4A is a longitudinal view of a porous cermet filter with a reinforcement material.
FIG. 4B is a sectional view of a porous cermet filter with a reinforcement material.
FIG. 4C is a sectional view of a porous cermet filter with multiple resistive
heating elements.
FIGS. 5A and 5B are gas chromatography analyses of an activated cermet filter
produced by a combustion synthesis process under a nitrogen atmosphere.
FIGS. 6A and 6B are gas chromatography analyses of an activated cermet filter
produced by a combustion synthesis process using a sodium bicarbonate and sugar
filler material.
FIG. 7 is a view of electrodes bonded to a cermet filter.
FIG. 8A is a sectional view of a cermet filter having multiple resistive heating elements.
FIG. 8B is a view of the cermet filter of FIG. 9A.
FIG. 8C is a sectional view of a resistive heating element coated with a ceramic material.
FIG. 9 is a sectional view of a cermet filter with an external heating element.
FIGS. 10A and 10B are sectional views of a cermet filter bonded to a filter housing.
FIGS. 11A and 11B are flow diagrams showing a porous cermet filter coupled
to an exhaust system of an internal combustion engine from a vehicle.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, a sectional view of filter
10 made from cermet
12 and having pores
14 is shown. For purposes of illustration, the
sizes of pores
14 in relation to filter
10 are exaggerated. The porous
structure of filter
10 is used for its high internal surface area in order
to trap particulate matter and for chemical reactions. In an exemplary embodiment,
pores
14 are irregular in shape and non-linear. In another exemplary embodiment,
filter
10 may be disk or cylinder shaped. Cermet
12 in filter
10
is a metallic-ceramic composite material. Cermet
12 of filter
10
may be coating free, in that it lacks a coating of another material deposited over
the inside of pores
14.
Referring to the photomicrographs of FIGS. 2A and 2B, a representative
microstructure of cermet
12 is shown having a ceramic phase
16 and
a metallic phase
18. As shown in FIGS. 2A and 2B, ceramic phase
16
may be discontinuous and bonded by metallic phase
18. FIG. 2A shows a 50
wt % NiAl-50 wt % alumina cermet
12 formed from fine alumina particles approximately
5-10 μm in size, nickel particles, and aluminum particles. FIG. 2B shows
a 50 wt % NiAl-50 wt % alumina cermet
12 formed from coarse ceramic particles
approximately 100-200 μm in size. Various intermetallic compounds may be
used for metallic phase
18, such as aluminide compounds of the form AB or
A
3B. In an exemplary embodiment, the metallic phase
18 is an
aluminide such as NiAl, Ni
3Al, FeAl, Fe
3Al, CoAl, CO
3Al,
or other transition metal aluminides due to the desirable catalytic properties
of transition metals. Transition metals are defined as the elements Sc, Ti, V,
Cr, Mn, Fe, Co, Ni, Cu, and Zn. Ceramic phase
16 may be oxide or non-oxide
ceramics. Exemplary materials for ceramic phase
16 include alumina (Al
2O
3),
zirconia silicate (ZrSiO
4), zirconia, mullite, cordierite, or iron III
oxide (Fe
2O
3). In an exemplary embodiment, ceramic phase
16 may be a refractory material, allowing filter
10 to be used at
very high temperatures.
Depending on the intended use of filter
10, the composition of cermet
12 may be tailored to affect certain functional characteristics such as
incorporating specific catalysts to perform selected catalysis or control of the
coefficient of thermal expansion (CTE). An exemplary cermet
12 may exhibit
properties such as high melting temperatures (greater than 1500° C.), high
fracture toughness (22 MPa-ml), high strength, high oxidation resistance, controlled
porosity (greater than 50%), inexpensive starting materials, an ability to be formed
into net shapes, electrically conducting, light weight (less than 3 grams/cm
3),
high heat capacity, and controllable CTE.
Cermet
12 may be made using conventional powder metallurgy techniques.
However, an exemplary manufacturing method mixes metallic and ceramic powders and
uses a combustion synthesis process in order to form filter
10 in a single
step. In this process, a net shape filter
10 can be produced. In an exemplary
embodiment, a mixture is formed of aluminum and transition metal powders mixed
together in a 1:1 atomic ratio and alumina powder. A small amount of organic binder,
such as one weight percent polyvinyl alcohol (PVA), may be used. Upon combustion
synthesis, cermet
12 is formed having an alumina ceramic phase
16
and an aluminide metallic phase
18 such as NiAl, CoAl, or FeAl. In another
exemplary embodiment, aluminum and transition metal powders such as nickel, cobalt,
or iron powders are mixed in a ratio of 1:3 to form an aluminide metallic phase
18 such as Ni
3Al, Fe
3Al, or Co
3Al. In another
exemplary embodiment, a sacrificial filler such as polystyrene spheres or fibers
may be added to the mixture to increase formation of pores
14. In all cases,
the green body is placed in a structurally configured mold and pressed into discs
or cylinders to form a green compact.
The green compact is then fired in a furnace between 600° C.-700° C.
or higher to set off the combustion synthesis process. At 660° C., the aluminum
powder melts. The molten aluminum spreads over the surface of the transition metal
particles by capillary action. Molten aluminum reacts with the transition particles
in a highly exothermic reaction to form an aluminide compound. The extremely reactive
molten aluminum reacts with the transition metal powder and sets off a solid flame.
The alumina is not involved in the reaction. The solid flame is an intensely luminous
combustion front separating the initial reactant mixture and the solid combustion
product. In a pure metallic combustion synthesis process, the combustion front
is white-hot and the temperature is extremely high. However, in the exemplary embodiments
of the present invention, the presence of ceramic phase
16 made from alumina
moderates the combustion process. The combustion process continues until the entire
green compact has been reacted to form a net shape cermet
12 with an aluminide
metallic phase
18 and an alumina ceramic phase
16. As an example,
the chemical reaction involved when nickel is used as the transition metal is shown below.
Aluminum combustion synthesis: 3Ni+3Al+Al
2O
3→3NiAl+Al
2O
3 (1)
In another embodiment of the combustion synthesis process, NiAl-alumina cermets
may be formed using aluminum particles and thermite (NiO) particles as starting
materials. When aluminum reaches the melting temperature, it is extremely reactive.
The molten aluminum reduces NiO to Ni. During this reduction step, the Al reacts
with the oxygen to form alumina, and the remaining molten Al combusts with Ni to
form NiAl. The energy released by alumina and NiAl formation is tremendous and
would raise the overall reaction temperature higher than that from the aluminum
combustion synthesis process. Net shape bulk products formed by the aluminum-thermite
reaction would thus achieve higher densities because the reaction temperature is
significantly higher than the reaction in the previous embodiment. The chemical
reaction for the aluminum-thermite reaction is shown below.
Aluminum-thermite combustion synthesis: 5Al+3NiO→3NiAl+Al
2O
3 (2)
If a sacrificial filler is added, it is burned off during this process, assisting
in leaving pores
14 behind. The sacrificial filler and the volume change
due to the formation of aluminide metallic phase
18 all contribute to the
formation of pores
14. In an exemplary embodiment, spherical and fiber sacrificial
filler materials are used to produce a highly porous cermet
12 with non-linear
pore channels. Consolidation pressure affects porosity development of cermet
12.
Higher consolidation pressures lead to a denser, less porous material. Also, the
size and shape of the ceramic particles used for ceramic phase
16 control
the shape and size of pores
14. Larger ceramic particles lead to a large
pore size for pores
14. For example, when the ceramic particle size was
between 5-10 μm, the average porosity of pores
14 is less than 10
μm. When the ceramic particle size was between 100-200 μm, the average
porosity is greater than 50 μm. Exemplary materials for the sacrificial filler
are polystyrene particles, Styrofoam® particles, sugar, corn starch, hair,
and organic long, thin fibers. Referring to FIG. 3A, a photomicrograph of a cross-section
of cermet
12 produced with sugar filler materials is shown. The sizes of
pores
14 in FIG. 3A ranged from submicron to 150 μm.
In another exemplary embodiment, hair fibers are frozen in liquid nitrogen and
then crushed into short fragments. The hair fibers mix well with the metal and
ceramic powders and are compacted into the green compact. The green compact is
fired under the conditions previously discussed herein. During combustion synthesis,
the hair fibers burn out and produce linear or longitudinal pore channels. These
type of pores and channels facilitate good gas and fluid transport through the
filter and produce a lower pressure drop across filter
10 during use. The
photomicrograph in FIG. 3B shows a cross-section of pores
14 produced with
a human hair sacrificial filler. FIG. 3C shows a longitudinal section of pores
14 produced with a human hair sacrificial filler. It is currently believed
by the inventor that animal hairs will produce similar results. The sacrificial
filler materials need not be limited to the examples herein and any suitable combustible
materials may be used in the process as long as they substantially burn off to
assist in formation of pores
14.
Referring to FIGS. 3D-3F, in another exemplary embodiment, a graded porosity
in cermet
12 may be produced during the synthesis process. Relatively smaller
sacrificial filler materials produce smaller pores
14 while relatively larger
sacrificial filler materials produce larger pores
14. Sequential layering
of smaller and larger sacrificial filler materials in the powder mixture in the
mold during the consolidation operation produces a graded porous cermet
12.
Referring to FIG. 3D, the porosity may be graded in the direction from top to bottom
of cermet
12. Referring to FIGS. 3E and 3F, the porosity may be graded across
the length of cermet
12. After combustion synthesis, pores
14 of
cermet
12 will retain layers of pores reminiscent of the sizes of the initial
sacrificial filler materials.
Referring to FIGS. 4A-4C, in another exemplary embodiment, reinforcement
material
17 can be added to the green compact prior to combustion. FIG.
4A is a longitudinal view of cermet
12 synthesized with a metal reinforcement
material
17. FIG. 4B is a sectional view of cermet
12 synthesized
with a metal reinforcement material
17. FIG. 4C is a sectional view of cermet
12 reinforced by multiple resistive heating elements
20. Exemplary
structures suitable for use as metal reinforcement
17 include long, thin
metal fibers or metal screens which are incorporated into the green compact prior
to consolidation. Exemplary metals suitable for use as reinforcement material
17
include stainless steels, nickel superalloys, cobalt alloys, titanium alloys, and
combinations thereof. In another exemplary embodiment, reinforcement material
17
may be ceramic fibers such as alumina, silicon carbide, or silicon nitride. In
an exemplary embodiment, reinforcement material
17 may be fused into cermet
12 during the combustion synthesis process.
In another exemplary embodiment of the combustion synthesis process, the manufacturing
of filter
10 may be performed under a nitrogen atmosphere. Cermet
12
of filter
10 will emit ammonia after activation by water. FIGS. 5A and 5B
show the gas chromatography (GC) analysis of the ammonia standard and the ammonia
generated from a cermet filter after activation. PH paper tests further confirmed
generation of ammonia from cermet
12 by turning dark blue after cermet
12
was activated, indicating the presence of ammonia. During ammonia emission, cermet
12 generates a significant amount of heat. The exothermic reaction indicates
formation of new phases in cermet
12 during the combustion synthesis reaction.
These new phases are currently believed by the inventor to be nitrogen-containing
nitride compounds that will hydrolyze to give off ammonia. It is well known that
bulk AlN and Si
3N
4 can be synthesized from metal powder compacts
by a high pressure nitrogen combustion process. It is currently believed by the
inventor that the combustion synthesis processes can form other metal nitrides.
These new phases formed in cermet
12 are currently believed by the inventor
to be some type of metal nitrides. These nitride phases produce ammonia when they
are activated by water. The ammonia emission phenomenon is also observed with cermet
filters synthesized with sacrificial filler materials such as sugar. The general
combustion synthesis reactions for ammonia-producing cermet filters are represented
by the chemical equations below.
##EQU1##
##EQU2##
- Ω=ammonia-producing phases
Alternatively, the aluminum-thermite combustion synthesis process
may be used instead of the aluminum combustion synthesis process to produce a nickel
aluminide-alumina cermet having ammonia-producing phases.
In another exemplary embodiment, mixed filler materials, sodium carbonate (Na
2CO
3)
or sodium bicarbonate and sugar, are used in the combustion synthesis of cermet
12. Alternatively, any other alkali carbonates or bicarbonates may be used.
When the combustion synthesis is carried out under a nitrogen atmosphere, ammonia-producing
phases and additional new phases are formed in cermet
12. These additional
new phases generate light hydrocarbon gases when cermet
12 is activated
by water. The major hydrocarbon gas produced is methane. However, other light hydrocarbon
gases have also been detected. FIGS. 6A and 6B show the GC analysis after activation.
The primary hydrocarbon produced is methane with minor amounts of other higher
hydrocarbons. These new additional phases are currently believed by the inventor
to be metal carbides. Particularly, alkaline carbides such as sodium carbide will
produce light hydrocarbon gases when hydrolyzed. The compositions of the ammonia-
and hydrocarbon gas-producing phases have not been fully identified. This alternative
formulation for ammonia- and hydrocarbon gas-producing cermet filters is shown
in the following chemical equation.
##EQU3##
- Ω=ammonia-producing phases Φ=light hydrocarbon gas-producing phases
Alternatively, the aluminum-thermite combustion synthesis process
may be used instead of the aluminum combustion synthesis process to produce a nickel
aluminide-alumina cermet having ammonia-producing phases and hydrocarbon gas-producing phases.
Ammonia and hydrocarbon gases are reducing agents for NO
X, which
is present in the diesel exhaust gas. The internal generation capability of reducing
agents has significant implications for destruction of exhaust NO
X.
Further, sodium carbonate (Na
2CO
3) decomposes to CO
2
gas and Na
2O during the combustion synthesis process. If different alkali
carbonates or bicarbonates are used instead of sodium carbonate or bicarbonate,
other types of alkali oxides will be formed during synthesis of cermet
12.
Further, CO
2 escaping from the green compact during the combustion synthesis
process produces pores
14 in cermet
12.
In an exemplary embodiment, post combustion synthesis leaching of cermet
12
dissolving the Na
2O particles further increases the porosity of cermet
12. The leaching may be accomplished by soaking cermet
12 in hot
or cold water to dissolve the sodium oxide. In another exemplary embodiment, the
Na
2O is used to absorb NO
X during use of filter
10.
In an exemplary embodiment, cermet
12 is electrically conductive so that
direct internal electrical heating is possible when a current is passed through
cermet
12. The temperature of cermet
12 is controlled by the magnitude
of the applied current. A larger current will yield a higher temperature for cermet
12. As an example, the battery on a vehicle may be used to provide a DC
power source to accomplish this. However, uniform electrical heating depends on
good contact and continuity between the portions of metallic phase
18 as
well as substantial uniformity throughout cermet
12. The electrical resistance
of cermet
12 may be tailored by adding additional metal powders to the green
compact. To increase the electrical resistance of cermet
12, metals such
as chromium, manganese, silicon, etc. may be added to the powder mixture before combustion.
Referring to FIG. 7, in an exemplary embodiment that uses direct internal
electrical heating, electrodes
23 are incorporated into cermet
12
during the combustion synthesis process. FIG. 7 shows a thin stainless steel ring
electrode
23 that has been bonded to the surface of cermet
12 during
combustion synthesis. An Electrical wire may be attached to the electrode to provide
direct internal heating. During compaction, the powder mixture is sandwiched between
electrodes
23 inside the mold. In an exemplary embodiment, to assist bonding
of electrodes
23 to cermet
12, nickel and aluminum fine powders may
be coated on the underside of the electrodes using silver paint. However, another
metal besides nickel may be used depending on the composition of metallic phase
18. The combustion synthesis process will result in permanent bonding of
electrodes
23 to cermet
12 in one single operation.
Referring to FIGS. 8A-8C, another exemplary embodiment uses internal resistive
heating element
20 incorporated in cermet
12. FIG. 8A shows a cross-sectional
view of cermet
12 containing multiple resistive heating elements
20.
FIG. 8B shows a frontal view of cermet
12. Resistive heating element
20
may be made from nickel-chromium alloys (nichrome), nickel-chromium-iron alloys,
molybdenum disilicide (MoSi
2), or any other appropriate heating element
material known to one of ordinary skill in the art. In another exemplary embodiment,
the coefficient of thermal expansion of resistive heating element
20 may
be selected to be substantially the same as cermet
12.
During combustion synthesis, resistive heating element
20 will be permanently
bonded inside filter
10. Referring to FIG. 8C, in another exemplary embodiment,
resistive heating element
20 may be coated with ceramic material
21
prior to incorporating it inside filter
10. Examples of such ceramic materials
21 are refractory oxides such as zirconium dioxide (ZrO
2), alumina,
magnesium oxide (MgO), silicon dioxide (SiO
2), or titanium dioxide (TiO
2).
These types of ceramic materials are well known to one of ordinary skill in the
art. The ceramic material
21 may be used to electrically insulate resistive
heating element
20 to prevent stray currents from passing through cermet
12. In another exemplary embodiment, resistive heating element
20
structurally strengthens cermet
12. Referring to FIG. 9, in another exemplary
embodiment, filter
10 may be electrically insulated with insulation
19.
An external heating source
22 may generally surround filter
10 and
insulation
19 to heat filter
10. External heating source
22
may be a source such as a resistance heating coil. Other types of external heating
sources will be known to one of ordinary skill in the art.
Referring to FIGS. 10A-10B, in another exemplary embodiment, filter housing
24 is reaction bonded to cermet
12 of filter
10 during the
combustion synthesis process. Exemplary materials for filter housing
24
include stainless steels, nickel superalloys, and cobalt alloys. Other materials
will be known to one of ordinary skill in the art. Prior to compaction of the metal
and ceramic powders of cermet
12, the interior of filter housing
24
is coated with a thin layer of aluminum and nickel powder. Another metal besides
nickel may be used depending on the composition of metallic phase
18. For
instance, iron would be suitable if the metallic phase
18 is an iron aluminide.
The green cermet powder is then compacted in filter housing
24 with the
thin layer of aluminum and nickel powder in place. During combustion synthesis,
the aluminum and nickel powder also combusts. The combustion heat from the process
in-situ bonds filter
10 permanently to the wall of filter housing
24.
FIG. 10B shows good bonding between cermet
12 of filter
10 and filter
housing
24. This exemplary embodiment provides a single-step process to
form and bond the cermet
12 of filter
10 to filter housing
24.
Referring to FIG. 11A, filter
10 is coupled to exhaust system
26
of internal combustion engine
25 on a vehicle
27, such as a heavy-duty
diesel engine truck. Carbon particles present in exhaust gases
28 will be
trapped by pores
14 (not shown) of filter
10. Filtered exhaust gases
30 then exit filter
10 containing substantially less pollutants.
During engine operation, filter
10 may heat up periodically or maintain
continuous heating to burn off collected carbon particles and keep pores
14
open. For instance, electrical source
34 on vehicle
27 may be used
to beat filter
10. Further, the burning off of the carbon particles reduces
NO
X gases in the final exhaust gas. The carbon particles in the exhaust
stream are very fine and have extremely high active surfaces. At elevated temperatures
on a condensable surface such as filter
10, the carbon particles can destroy
NO
X and lower the NO
X level in the final exhaust gas. Further,
under an oxidizing environment, cermet
12 can destroy CO, H
2,
and other hydrocarbon gases. Since intermetallic and oxide compositions have a
profound influence on pollutant destruction, the catalytic properties of cermet
12 and the operating environment can be tailored to oxidize CO and hydrocarbons
while also destroying NO
X. The process by which the NO
X gases
and carbon particles are destroyed is represented by the following chemical equations:
C
(s)+2NO
(g)→N
2(g)+CO
2(g)
C
(s)+NO
2(g)→½N
2(g)+CO
2(g)
In an exemplary embodiment, pores
14 are of sufficient concentration so
that the pressure drop is less than 5 psi across filter
10. Under a fuel
lean condition, non-transient steady state driving conditions, the amount of carbon
particulate generated from a diesel engine may not be enough to reduce all of the
NO
X present. Thus, referring to FIG. 11B, in another exemplary embodiment
using diesel fuel, vapor from the headspace of the fuel tank
32 can be injected
into filter
10 for supplemental NO
X reduction.
The tables below include data from tests of various intermetallic and intermetallic-oxide
cermets used for filter
10. The data in the following tables is merely illustrative
and other variations on the compositions of the cermets used are fully embraced
by the present invention. Tables 1-6 show the test results for several cermet filter
compositions. Table 1 shows nitric oxide (NO) conversion to nitrogen for two cermet
filters and a molybdenum disilicide filter under a reducing atmosphere. Table 2
shows the percent products of incomplete combustion (PICs) destroyed as a function
of temperature for a specific cermet composition. Tables 3-7 show the results of
catalytic steam reforming of various hydrocarbon fuels to synthesis gas (CO and
H
2) by a 50 wt % NiAl-50 wt % alumina cermet filter. Tables 8-9 show
pressure drop data with and without the presence of filtered carbon particles in
a 50 wt % NiAl-50 wt % alumina cermet filter having approximately 30% porosity.
Table 10 shows test data that simulated the removal of exhaust gas-entrained
fine carbon particles generated from an internal combustion engine such as a diesel
engine. The individual carbon grain size was approximately 10 nanometers. Agglomerated
particle size was approximately 0.5-1.0 μm. The carbon particles were generated
by the thermal plasma decomposition of methane. An airflow rate of 60 liters/minute
under high pressure (56 psi) was used. The test lasted 60 minutes. The porosity
of the cermet filter used in the pressure drop tests was approximately 30 percent.
Test data shows that for a filter porosity of approximately 30 percent containing
approximately 0.448 in
2 filter area, the carbon filtration efficiency
was 99.86 percent. No clogging of the cermet filter was observed. The weight of
the trapped carbon after filtering was measured by tapping the cermet filter to
remove all of the carbon particles.
Although the foregoing description of embodiments and test data contains
many specifics, these should not be construed as limiting the scope of the present
invention, but merely as providing illustrations of some exemplary embodiments.
Similarly, other embodiments of the invention may be devised which do not depart
from the spirit or scope of the present invention. The scope of the invention is,
therefore, indicated and limited only by the appended claims and their legal equivalents,
rather than by the foregoing description. All additions, deletions, and modifications
to the present invention, as disclosed herein, which fall within the meaning and
scope of the claims are embraced thereby.
| TABLE 1 |
|
| NO(g) Reduction for NiAl Cermets and MoSi2 |
| Under a Reducing Atmosphere |
| Test Condition: 5% NO + 1.67% C2H4 + 93.33% He |
| |
% NO(g) Conversion to N2 Under a |
| |
Reducing Atmosphere |
| |
50 wt % NiAl + 50 |
50 wt % NiAl + 50 |
|
| Temperature (° C.) |
wt % ZrSiO4 |
wt % Fe2O3 |
MoSi2 |
|
| 300 |
0 |
0 |
0 |
| 400 |
0 |
2.5 |
0 |
| 475 |
0 |
2.6 |
2 |
| 550 |
0 |
4.7 |
2 |
| 623 |
3.8 |
13.3 |
2 |
| 696 |
11.3 |
43.1 |
3 |
| 797 |
38.7 |
98.3 |
7 |
| 904 |
|
100 |
|
| TABLE 2 |
|
| % Products of Incomplete Combustion Destroyed vs. Temperature |
| for a Cermet Composition of (NiAl)0.2/Ni0.02/(ZrSiO4)0.04 |
| |
Temperature (° C.) |
C3H6 |
CH4 |
CO |
| |
|
| |
25 |
0 |
0 |
0 |
| |
101 |
0 |
0 |
0 |
| |
203 |
2.1 |
0 |
5.3 |
| |
302 |
1.4 |
0 |
6.1 |
| |
403 |
0 |
0 |
8.9 |
| |
478 |
11.3 |
15.9 |
24 |
| |
553 |
47.8 |
233 |
81.2 |
| |
627 |
93.8 |
25.2 |
97.0 |
| |
702 |
100 |
36.0 |
100 |
| |
797 |
100 |
52 |
100 |
| |
|
| TABLE 3 |
|
| Steam Reforming of Methanol Using a 50 wt % NiAl—50 wt % Al2O3 |
| Test Conditions: 10 cc CH3OH/H2O = 0.5 mole ratio mixture
+ 5 cc He |
| Temperature (° C.) |
CO2 (vol. %) |
H2 (vol. %) |
CO (vol. %) |
|
| 500 |
0.1 |
13.0 |
3.5 |
| 600 |
1.5 |
43.0 |
11.4 |
| 700 |
4.7 |
46.0 |
9.6 |
| 800 |
2.2 |
47.7 |
12.0 |
| 900 |
2.1 |
50.0 |
15.1 |
| 967 |
3.2 |
50.3 |
12.4 |
|
