Cordierite-type ceramic honeycomb structure and its production method
A cordierite-type ceramic honeycomb structure having large numbers of flow paths partitioned by porous cell walls; the cell walls having (a) porosity of more than 65% and 75% or less, (b) in a pore diameter distribution measured by mercury porosimetry, (i) a pore diameter d 10 at a cumulative pore volume corresponding to 10% of the total pore volume being less than 50 μm, a pore diameter (median pore diameter) d 50 at 50% being 18-27 μm, a pore diameter d 90 at 90% being 10 μm or more, and (d 10 −d 90 )/d 50 being 2.3 or less; (ii) σ [=log(d 20 )−log(d 80 )] being 0.25 or less, wherein σ represents the difference between a logarithm of a pore diameter d 20 at a cumulative pore volume corresponding to 20% of the total pore volume and a logarithm of a pore diameter d 80 at a cumulative pore volume corresponding to 80% of the total pore volume; and (iii) the maximum of the inclination S n =−(V n −V n-1 )/[log(d n )−log(d n-1 )] of a curve of a cumulative pore volume to a pore diameter being 3 or more, wherein d n and V n are respectively a pore diameter and a cumulative pore volume at an n-th measurement point, and d n-1 and V n-1 are respectively a pore diameter and a cumulative pore volume at a (n−1)-th measurement point.
1. A method for producing a cordierite-type ceramic honeycomb structure comprising the steps of extruding a moldable material comprising a ceramic material and a pore-forming material constituted by hollow resin particles coated with inorganic powder to form a predetermined green body, and drying and sintering said green body;
said moldable material comprising 8-16% by mass of said pore-forming material per 100% by mass of said ceramic material;
said pore-forming material having a median diameter D 50 of 25-35 μm, a particle diameter D 10 (at a cumulative volume corresponding to 10% of the total volume) of 14-24 μm, and a particle diameter D 90 (at a cumulative volume corresponding to 90% of the total volume) of 45-60 μm, in a curve expressing the relation of a particle diameter to a cumulative volume (cumulative volume of particles having diameters equal to or smaller than a particular particle diameter), a particle diameter distribution deviation SD [=log(D 80 )−log(D 20 )] being 0.4 or less, wherein D 20 is a particle diameter at a cumulative volume corresponding to 20% of the total volume, and D 80 is a particle diameter at a cumulative volume corresponding to 80% of the total volume, D 20 <D 80 ; and
said pore-forming material having the maximum compression recovery Lmax of 3.0 mm or more, and a compression recovery L in a compression stress range of 2-6 MPa, which is 80% or more of said maximum compression recovery Lmax, the compression recovery L being defined by the returning distance (mm) of a piston having an outer diameter of 8 mm applying a predetermined compression stress to 0.3 g of a pore-forming material in a metal cylinder having an inner diameter of 8 mm and a depth of 100 mm, when the pore-forming material is relieved of the compression stress, and the maximum compression recovery Lmax being the maximum of the compression recovery L.
2. The method for producing a cordierite-type ceramic honeycomb structure according to claim 1 , wherein
said ceramic material and said inorganic powder constitute a cordierite-forming material;
15-25% by mass of silica, 27-43% by mass of talc, and 15-30% by mass of alumina are contained in 100% by mass of said cordierite-forming material, a sum of said ceramic material and said inorganic powder;
said silica has a median diameter D 50 of 15-30 μm, the percentage of particles having diameters of 10 μm or less being 3% or less by mass, the percentage of particles having diameters of 100 μm or more being 3% or less by mass, and the particle diameter distribution deviation SD being 0.4 or less;
said talc has a median diameter D 50 of 1-10 μm, and a particle diameter distribution deviation SD of 0.6 or less; and
said alumina has a median diameter D 50 of 1-8 μm, a particle diameter D 90 at a cumulative volume corresponding to 90% of the total volume being 5-15 μm in a curve expressing the relation of a particle diameter to a cumulative volume.
3. The method for producing a cordierite-type ceramic honeycomb structure according to claim 1 , wherein the inorganic powder on said pore-forming material is at least one selected from the group consisting of kaolin, silica, talc, cordierite, alumina, aluminum hydroxide, calcium carbonate, and titanium oxide.
4. The method for producing a cordierite-type ceramic honeycomb structure according to claim 1 , wherein the inorganic powder on said pore-forming material has a median diameter D 50 of 0.5-10 μm.