Mullite-aluminum titanate diesel exhaust filter

• US 6,849,181 B2
• Filed: 07/31/2002
• Issued: 02/01/2005
• Est. Priority Date: 07/31/2002
• Status: Expired due to Term

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Tepesch, Patrick D., Ogunwumi, Steven B.
• Primary Examiner(s): KIM, SUN U
• Application Number:
  US10/209,684
• Publication Number:
  US 20040020846A1
• Time in Patent Office: 916 Days
• Field of Search: 501/80, 501/127, 501/128, 501/134, 501/153, 555/23, 55D/IG.30, 210/503, 210/510.1, 502/439, 502/527.19
• US Class Current: 210/510.1
• CPC Class Codes: B01D 39/2093 Ceramic foam
• CPC Class Codes: B01J 21/063 Titanium; Oxides or hydroxides thereof
• CPC Class Codes: B01J 35/56 Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
• CPC Class Codes: C04B 2235/3217 Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
• CPC Class Codes: C04B 2235/3218 Aluminium (oxy)hydroxides, e.g. boehmite, gibbsite, alumina sol
• CPC Class Codes: C04B 2235/322 Transition aluminas, e.g. delta or gamma aluminas
• CPC Class Codes: C04B 2235/3232 Titanium oxides or titanates, e.g. rutile or anatase
• CPC Class Codes: C04B 2235/3234 Titanates, not containing zirconia
• CPC Class Codes: C04B 2235/327 Iron group oxides, their mixed metal oxides, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3272 Iron oxides or oxide forming salts thereof, e.g. hematite, magnetite
• CPC Class Codes: C04B 2235/3418 Silicon oxide, silicic acids, or oxide forming salts thereof, e.g. silica sol, fused silica, silica fume, cristobalite, quartz or flint glass constituents C04B2235/36
• CPC Class Codes: C04B 2235/3463 Alumino-silicates other than clay, e.g. mullite
• CPC Class Codes: C04B 2235/36 Glass starting materials for making ceramics, e.g. silica glass
• CPC Class Codes: C04B 2235/449 Organic acids, e.g. EDTA, citrate, acetate, oxalate
• CPC Class Codes: C04B 2235/5292 Flakes, platelets or plates
• CPC Class Codes: C04B 2235/5436 micrometer sized, i.e. from 1 to 100 micron
• CPC Class Codes: C04B 2235/5481 Monomodal
• CPC Class Codes: C04B 2235/6021 Extrusion moulding
• CPC Class Codes: C04B 2235/77 Density
• CPC Class Codes: C04B 2235/80 Phases present in the sintered or melt-cast ceramic products other than the main phase
• CPC Class Codes: C04B 2235/96 : Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
• CPC Class Codes: C04B 2235/9607 : Thermal properties, e.g. thermal expansion coefficient
• CPC Class Codes: C04B 2235/9615 : Linear firing shrinkage
• CPC Class Codes: C04B 35/478 : based on aluminium titanates
• CPC Class Codes: C04B 35/63 : using additives specially adapted for forming the products , e.g.. binder binders
• CPC Class Codes: C04B 35/632 : Organic additives
• CPC Class Codes: Y10S 55/30 : Exhaust treatment

Abstract

The invention is directed at a mullite-aluminum titanate porous diesel particulate filter constituting a porous ceramic body containing, expressed in terms of weight percent of the total body, of 60-90%, preferably 70-80%, most preferably 70% iron-aluminum titanate solid solution having a stoichiometry of Al_2(1−x)Fe_2xTiO₅, where x is 0-0.1, and 10-40%, preferably 20-30%, most preferably 30% mullite (3Al₂O₃.2SiO₂), and consists essentially, expressed in terms of weigh percent on the oxide basis, of 3 to 15% SiO₂, 55 to 65% Al₂O₃, 22 to 40% TiO₂, and 0 to 10% Fe₂O₃, and being useful for filtration of diesel exhaust. The inventive diesel particulate filter exhibits high interconnected open porosity and large median pore size, in combination with high permeability when fired to a temperature of between 1650° to 1700° C., along with high thermal shock resistance and good filtration capability.

Claims

1. A diesel exhaust particulate filter comprising a plugged, wall-flow honeycomb filter body composed of porous ceramic material and comprising a plurality of parallel end-plugged cell channels traversing the body from a frontal inlet end to an outlet end thereof, wherein:

the ceramic contains, expressed in terms of weight percent of the total body, of 60-90% iron-aluminum titanate solid solution having a stoichiometry of Al<sub>2(1−

x)</sub>Fe_2xTiO₅, where x is 0-0.1, and 10-40% mullite (3Al₂O₃.2SiO₂), and consists essentially, expressed in terms of weigh percent on the oxide basis, of 3 to 15% SiO₂, 55 to 65% Al₂O₃, 22 to 40% TiO₂, and 0 to 10% Fe₂O₃; and

,

the filter has a porosity of 35% to 55% by volume, a median pore size of 8 to 20 micrometers, a permeability of at least 0.30×

10<sup>−

12</sup> m² when fired to a temperature of between 1650°

to 1700°

C., and, an increment in a linear dimension of less than 1% after the filter has been exposed one hundred times to thermal cycling at a temperature of 200°

to 1100°

C. in a time of 7 minutes, and cooling from 1100°

to 200°

C. in a time of 7 minutes.

2. The diesel exhaust particulate filter of claim 1 wherein:

the ceramic contains, expressed in terms of weight percent of the total body, of 70-80% iron-aluminum titanate solid solution having a stoichiometry of Al<sub>2(1−

x)</sub>Fe_2xTiO₅, where x is 0-0.1, and 20-30% mullite (3Al₂O₃.2SiO₂), and consists essentially, expressed in terms of weigh percent on the oxide basis, of 6 to 12% SiO₂, 57 to 61% Al₂O₃, 26 to 35% TiO₂, and 0.5 to 5% Fe₂O₃; and

,

the filter has a porosity of 40% to 50% by volume, a median pore size of 10 to 15 micrometers, and a permeability of 0.33 to 1.00×

10<sup>−

12</sup> m².

3. The diesel exhaust particulate filter of claim 2 wherein the ceramic contains, expressed in terms of weight percent of the total body, of 70% iron-aluminum titanate solid solution having a stoichiometry of Al₂₍₁₋

x)Fe_2xTiO₅, where x is 0-0.1, and 30% mullite (3Al₂O₃.2SiO₂).

4. The diesel exhaust particulate filter of claim 1 further having a CTE, as measured from room temperature to 1000°

C. of 5 to 15×

10<sup>−

7</sup>/°

C., a heat capacity of at least 3.2 J cm<sup>−

3</sup>K<sup>−

1</sup> at 500°

C., and a four-point modulus of rupture as measured on a solid rod of circular cross section of at least 500 pounds per square inch.

5. The diesel exhaust particulate filter of claim 4 wherein the CTE, as measured from room temperature to 1000°

C. is 5 to 10×

10<sup>−

7</sup>/°

C., a heat capacity of at least 3.9 J cm<sup>−

3</sup>K<sup>−

1</sup> at 500°

C., and a four-point modulus of rupture as measured on a solid rod of circular cross section of at least 800 pounds per square inch.

6. A method of making a structure for use in filtration of diesel exhaust, the method comprising:

a. forming a mixture of powdered raw materials selected to obtain a ceramic article consisting essentially, expressed in terms of weigh percent on the oxide basis, of 3 to 15% SiO₂, 55 to 65% Al₂O₃, 22 to 40% TiO₂, and 0 to 10% Fe₂O₃;

b. shaping the mixture into a green ceramic article;

c. firing the green ceramic article to a temperature of between 1650°

to 1700°

C. for a duration of time sufficient to produce a mullite-aluminum titanate ceramic article having a porosity of 35% to 55% by volume, a median pore size of 8 to 20 micrometers, a permeability of at least 0.30×

10<sup>−

12</sup> m², and, an increment in a linear dimension of less than 1% after the filter has been exposed one hundred times to thermal cycling at a temperature of 200°

to 1100°

C. in a time of 7 minutes, and cooling from 1100°

to 200°

C. in a time of 7 minutes.

7. The method of claim 6 wherein the raw materials comprise oxide sources including:

silica (SiO₂) having a particle size of 5 to 20 micrometers;

alumina (Al₂O₃) having a particle size of 5 to 25 micrometers;

titania (TiO₂) having a particle size of 4 to 20 micrometers; and

,

iron oxide (Fe₂O₃) added at about 0 to 6% weight of the total batched raw materials.

8. The method of claim 7 wherein:

the silica (SiO₂) has a particle size of 8 to 15 micrometers;

alumina (Al₂O₃) having a particle size of 10 to 15 micrometers;

titania (TiO₂) having a particle size of 8 to 16 micrometers; and

,

iron oxide (Fe₂O₃) added at about 0 to 5% weight of the total batched raw materials.

9. The method of claim 6 wherein the mixture is shaped by extrusion into a honeycomb having an inlet and outlet end and a multiplicity of cells extending from inlet end to outlet end, the cells having porous walls.

10. The method of claim 9 wherein the cells are plugged at one end only, either at the inlet end or the outlet end of the honeycomb structure.

11. The method of claim 9 wherein the firing step includes heating from room temperature (22-25°

C.) to 1500°

-1600°

C. over a period of about 8 to 10 hours, with a hold at top temperature of about 4 to 8 hours, followed by heating over a period of about 2 to 3 hours to a top temperature of 1650°

to 1700°

C., with a hold thereat of about 30 to 60 minutes, followed by a ramp down to a temperature of about 1575°

to 1600°

C. over a period of about 1 hour, with a hold thereat of about 4 to 5 hours.