High porosity cordierite composition
Disclosed are ceramic articles, which in one aspect are composed predominately of a cordierite having a composition close to that of Mg 2 Al 4 Si 5 O 18 . 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.
1. A ceramic honeycomb structure, comprising a porous cordierite composition, having a total porosity (% P) greater than 65%; 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 −7 /° C. across the temperature range of from 25° C. to 800° C., wherein d factor =(d 50 −d 10 )/d 50 .
2. The ceramic honeycomb structure of claim 1 , wherein the total porosity % P is in the range of from greater than 65% to less than 75%.
3. The ceramic honeycomb of claim 1 , wherein the total porosity P has a median pore size diameter in the range of from 15 μm to 30 μm.
4. The ceramic honeycomb structure of claim 1 , wherein the coefficient of thermal expansion is less than 9.0×10 −7 /° C. across the temperature range of from 25° C. to 800° C.
5. The ceramic honeycomb structure of claim 1 , wherein the coefficient of thermal expansion is in the range of from 8.0×10 −7 /° C. to 10.0×10 −7 /° C. across the temperature range of from 25° C. to 800° C.
6. The ceramic honeycomb structure of claim 1 , wherein the pore size distribution (d factor ) is less than 0.35.
7. 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.
8. The ceramic honeycomb structure of claim 1 , further exhibiting a bulk density in the range of from 200 g/l to 900 g/l.
9. The ceramic honeycomb structure of claim 8 , wherein the bulk density is in the range of from 400 g/l to 500 g/l.
10. 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 =(dp 90 −dp 10 )/dp 50 ;
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 (d factor ) 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 −7 /° C. across the temperature range of from 25° C. to 800° C.
11. The method of claim 10 , wherein the pore former comprises Katakuriko potato starch.
12. The method of claim 10 , 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.
13. The method of claim 12 , 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.
14. The method of claim 10 , wherein the potato starch has a dp breadth less than 0.9.
15. The method of claim 10 , 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 SiO 2 ,
about 33 to about 38 percent by weight Al 2 O 3 , and
about 12 to about 16 percent by weight MgO.
16. The method of claim 10 , 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.
17. The method of claim 16 , wherein the soak temperature is in the range of from approximately 1400° C. to approximately 1430° C.
18. The method of claim 10 , wherein the effective firing conditions comprise a firing schedule having a total duration in the range of from 20 to 100 hours.
19. A ceramic article manufactured by the method of claim 10 .