Cordierite-type ceramic honeycomb structure and its production method

1. A ceramic honeycomb structure having a plurality of flow paths partitioned by porous cell walls comprising cordierite,

(a) said cell walls having porosity of more than 65% and 75% or less; and

(b) in a pore diameter distribution measured by mercury porosimetry,

(i) a pore diameter d 10 at a cumulative pore volume (cumulative volume of pores in a range from the maximum pore diameter to a particular pore diameter) 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 μm or more and 27 μm or less,

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.

2. The ceramic honeycomb structure according to claim 1 , wherein pores open on the cell wall surfaces have (i) an opening area ratio of 25-50%, and (ii) an area-based median opening diameter (expressed by equivalent circle diameter) of 25-50 μm.

3. The ceramic honeycomb structure according to claim 1 , wherein the maximum of said S n is 3.5 or more.

4. The ceramic honeycomb structure according to claim 1 , wherein the maximum of said S n is 4.0 or more.