Ceramic honeycomb structure and its production method
A ceramic honeycomb structure having a large number of flow paths partitioned by porous cell walls, the cell walls having porosity of 40-60%; pores opening on the cell wall surface having an opening area ratio (the total opening area of pores opening on the cell wall surface per a unit area) of 15% or more; the median opening diameter of the opening pores being 10 μm or more and less than 40 μm, when the opening diameter of each pore opening on the cell wall surface is expressed by an equivalent circle diameter (a diameter of a circle having the same area as the opening area of each pore); the density of pores having equivalent circle diameters of 10 μm or more and less than 40 μm being 350/mm 2 or more; and the average circularity of pores having equivalent circle diameters of 10 μm or more and less than 40 μm being 1-2.
1. A ceramic honeycomb structure having a large number of flow paths partitioned by porous cell walls,
said cell walls having porosity of 40-60%;
pores opening on the cell wall surface having an opening area ratio (the total opening area of pores opening on the cell wall surface per a unit area) of 15% or more;
when the opening diameter of each pore opening on the cell wall surface is expressed by an equivalent circle diameter (a diameter of a circle having the same area as the opening area of each pore), the median opening diameter of said opening pores being 10 μm or more and less than 40 μm;
the density of pores having equivalent circle diameters of 10 μm or more and less than 40 μm being 350/mm 2 or more; and
the average circularity of pores having equivalent circle diameters of 10 μm or more and less than 40 μm being 1-2.
2. The ceramic honeycomb structure according to claim 1 , wherein said cell walls have a Darcy's coefficient of permeability of 0.1×10 −12 m 2 to 2×10 −12 m 2 .
3. The ceramic honeycomb structure according to claim 1 , having a median pore diameter of 5 μm or more and less than 20 μm when the pore diameters of said cell walls are measured by mercury porosimetry;
the volume of pores having diameters of less than 2 μm being 10% or less of the total pore volume;
the volume of pores having diameters of 40 μm or more being 10% or less of the total pore volume; and
the pore size distribution deviation σ=log(D 20 )−log(D 80 ) being 0.5 or less, wherein D 20 represents a pore diameter (μm) at a pore volume corresponding to 20% of the total pore volume, and D 80 similarly represents a pore diameter (μm) at a pore volume corresponding to 80% of the total pore volume, on a curve showing the relation between a pore diameter and a cumulative pore volume obtained by accumulating a pore volume from the maximum pore diameter to a particular pore diameter, and D 80 <D 20 .
4. The ceramic honeycomb structure according to claim 1 , wherein the exhaust gas inlet or outlet sides of said flow paths are alternately plugged for use as a filter.
5. The ceramic honeycomb structure according to claim 1 , wherein it has an average cell wall thickness of 9.0-12 mil and an average cell density of 150-300 cpsi.
6. The ceramic honeycomb structure according to claim 1 , wherein said ceramic honeycomb structure has a thermal expansion coefficient of 13×10 −7 /° C. or less between 20° C. and 800° C.