High porosity cordierite composition

• US 20070261378A1
• Filed: 05/10/2006
• Published: 11/15/2007
• Est. Priority Date: 05/10/2006
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Wang, Jianguo, Miao, Weiguo, Shustack, Paul, Ogunwumi, Steven
• Granted Patent: US 7,648,548 B2
• Time in Patent Office: Days
• US Class Current: 55/523
• CPC Class Codes: B01D 2275/30 Porosity of filtering material
• CPC Class Codes: B01D 2279/30 for treatment of exhaust gases from IC Engines
• CPC Class Codes: B01D 39/2093 Ceramic foam
• CPC Class Codes: B01D 46/2425 characterized by parameters related to the physical properties of the honeycomb structure material
• CPC Class Codes: B01D 46/24491 Porosity
• CPC Class Codes: B01D 46/24492 Pore diameter
• CPC Class Codes: B01D 46/24494 Thermal expansion coefficient, heat capacity or thermal conductivity
• CPC Class Codes: B01D 46/2498 The honeycomb filter being defined by mathematical relationships
• CPC Class Codes: C04B 2111/00129 Extrudable mixtures
• CPC Class Codes: C04B 2111/00793 as filters or diaphragms
• CPC Class Codes: C04B 2111/0081 as catalysts or catalyst carriers
• CPC Class Codes: C04B 2111/2084 Thermal shock resistance
• CPC Class Codes: C04B 2111/32 Expansion-inhibited materials
• CPC Class Codes: C04B 2111/343 Crack resistant materials
• CPC Class Codes: C04B 35/10 based on aluminium oxide
• CPC Class Codes: C04B 35/195 Alkaline earth aluminosilicates, e.g. cordierite or anorthite
• CPC Class Codes: C04B 38/0006 Honeycomb structures from one or more corrugated sheets by winding or stacking C04B38/0083
• CPC Class Codes: C04B 38/0054 the pores being microsized or nanosized
• CPC Class Codes: C04B 38/0074 expressed as porosity percentage
• CPC Class Codes: C04B 38/0645 Burnable, meltable, sublimable materials
• CPC Class Codes: Y10S 264/48 : Processes of making filters
• CPC Class Codes: Y10S 55/05 : Methods of making filter
• CPC Class Codes: Y10S 55/10 : Residue burned
• CPC Class Codes: Y10S 55/30 : Exhaust treatment
• CPC Class Codes: Y10T 428/24149 : Honeycomb-like

Abstract

Disclosed are ceramic articles, which in one aspect are composed predominately of a cordierite having a composition close to that of Mg₂Al₄Si₅O₁₈. The ceramic articles possess a microstructure characterized by a unique combination of relatively high porosity and relatively narrow pore size distribution, both as measured by mercury porosimetry, that render the ceramic structure useful for ceramic filter applications requiring high thermal durability and high filtration efficiency coupled with low pressure drop along the length of the filter. Such ceramic bodies are particularly well suited for filtration applications, such as diesel exhaust filters or DPFs. Also disclosed are methods for the manufacture of the ceramic articles described herein.

Claims

1. A ceramic honeycomb structure, comprising a porous cordierite composition, having a total porosity (% P) greater than 62%;

a pore size distribution (d_factor) less than 0.4, a median pore size greater than 10 microns; and

a coefficient of thermal expansion in the axial direction less than 10.0×

10<sup>−

7</sup>/°

C. across the temperature range of from 25°

C. to 800°

C., wherein d_factor=(d₅₀-d₁₀/d₅₀.

2. The ceramic honeycomb structure of claim 1, wherein the total porosity % P is greater than 65%.

3. The ceramic honeycomb structure of claim 1, wherein the total porosity % P is in the range of from greater than 62% to less than 75%.

4. The ceramic honeycomb of claim 1, wherein the total porosity P has a median pore size diameter in the range of from 15 μ

m to 30 μ

m.

5. The ceramic honeycomb structure of claim 1, wherein the coefficient of thermal expansion is less than 9.0×

10<sup>−

7</sup>/°

C. across the temperature range of from 25°

C. to 800°

C.

6. The ceramic honeycomb structure of claim 1, wherein the coefficient of thermal expansion is in the range of from 8.0×

10<sup>−

7</sup>/°

C. to 10.0×

10<sup>−

7</sup>/°

C. across the temperature range of from 25°

C. to 800°

C.

7. The ceramic honeycomb structure of claim 1, wherein the pore size distribution (d_factor) is less than 0.35.

8. The ceramic honeycomb structure of claim 1, wherein the pore size distribution (d_factor) is in the range of from 0.30 to less than 0.40.

9. The ceramic honeycomb structure of claim 1, further exhibiting a bulk density in the range of from 200 g/l to 900 g/l.

10. The ceramic honeycomb structure of claim 9, wherein the bulk density is in the range of from 400 g/l to 500 g/l.

11. A method for manufacturing a ceramic honeycomb article, comprising the steps of:

providing a plasticized cordierite precursor batch composition containing;

inorganic batch components selected from a magnesium oxide source;

an alumina-forming source; and

a silica source;

a pore former comprising a potato starch having a dp_breadth less than 1.00, wherein dp_breadth=(dp₉₀-dp₁₀)/dp₅₀;

a liquid vehicle; and

a binder;

forming a honeycomb green body from the plasticized cordierite precursor batch composition; and

firing the honeycomb green body under conditions effective to convert the green body into a porous ceramic honeycomb article containing cordierite and having a total porosity (% P) greater than 60%;

a pore size distribution (dfactor) less than 0.5, a median pore size greater than 10 microns; and

a coefficient of thermal expansion in the axial direction less than 10.0×

10<sup>−

7</sup>/°

C. across the temperature range of from 25°

C. to 800°

C.

12. The method of claim 11, wherein the pore former comprises Katakuriko potato starch.

13. The method of claim 11, wherein the potato starch is present in an amount of from 10 wt. % to 30 wt. % relative to the total weight of the inorganic batch components.

14. The method of claim 13, wherein the potato starch is present in an amount of from 15 wt % to 25 wt. % relative to the total weight of the inorganic batch components.

15. The method of claim 11, wherein the potato starch has a dp_breadth less than 0.9.

16. The method of claim 11, wherein the inorganic batch components are selected to provide a sintered phase cordierite composition as characterized on an oxide weight basis, consisting essentially of:

about 49 to about 53 percent by weight SiO₂,

about 33 to about 38 percent by weight Al₂O₃, and

about 12 to about 16 percent by weight MgO.

17. The method of claim 11, wherein the effective firing conditions comprise firing the honeycomb green body at a soak temperature in range of from 1350°

C. to 1450°

C. and subsequently holding the soak temperature for a period of time sufficient to convert the honeycomb green body into a ceramic honeycomb article.

18. The method of claim 17, wherein the soak temperature is in the range of from approximately 1400°

C. to approximately 1430°

C.

19. The method of claim 11, wherein the effective firing conditions comprise a firing schedule having a total duration in the range of from 20 to 100 hours.

20. A ceramic article manufactured by the method of claim 11.