Ceramic honeycomb structure and its production method

1. A ceramic honeycomb structure comprising a plurality of cells partitioned by porous cell walls, said cell walls having

(a) porosity of 50-80%; and

when measured by mercury porosimetry,

(b) a median pore diameter being 25-50 μm;

(c) (i) a cumulative pore volume in a pore diameter range of 20 μm or less being 25% or less of the total pore volume;

(ii) a cumulative pore volume in a pore diameter range of more than 20 μm and 50 μm or less being 50% or more of the total pore volume; and

(iii) a cumulative pore volume in a pore diameter range of more than 50 μm being 12% or more of the total pore volume;

wherein an opening area ratio of pores open on said cell wall surfaces (a total opening area of pores per a unit cell wall surface area) is 30% or more; and

wherein said ceramic honeycomb structure has an A-axis compression strength of 1.0 MPa or more.

2. The ceramic honeycomb structure according to claim 1 , wherein pores open on said cell wall surfaces have a median opening diameter (expressed by an equivalent circle diameter) of 60 μm or more.

3. The ceramic honeycomb structure according to claim 1 , wherein a cumulative opening area of pores open on said cell wall surfaces, which have opening diameters (each expressed by an equivalent circle diameter) of 30 μm or less, is 20% or less of the total opening area.

4. The ceramic honeycomb structure according to claim 1 , wherein a cumulative opening area of pores open on said cell wall surfaces, which have opening diameters (each expressed by an equivalent circle diameter) of 100 μm or more, is 30-70% of the total opening area.

5. The ceramic honeycomb structure according to claim 1 , wherein said cell walls have permeability of 10×10 −12 m 2 to 30×10 −12 m 2 .