Ceramic porous body and method for evaluating its permeability
A ceramic porous body is provided, inclusing a plurality of pores formed in a ceramic substrate at a specified porosity. A pore part is discriminated from a non-pore part by binarizing a cross-sectional plane image of the substrate by image analysis. When a center line passing the central part of the pore part is drawn, the porosity (ε (%)), a mean width (D P (μm)) of the pore part represented by a mean value of a distance, between outlines specifying the pore part, perpendicular to the center line, a mean length (L (μm)) of the pore part represented by a mean value of a length of the center line between adjacent branch points and a length of the center line between an end of the center line and the branch point, and a mean pore size (D H (μm)) satisfy a specified relationship.
1. A ceramic porous body including a plurality of pores formed in a substrate made of a ceramic at a specified porosity; the substrate having predetermined end faces; and the pores connecting through the end faces of the substrate to each other and having branches,
wherein when a cross-sectional plane image of the substrate cut along a predetermined plane is binarized by image analysis to distinguish a specified pore part derived from the pores from a specified non-pore part derived from the substrate, and a center line passing a central part of the pore part is drawn on the distinguished image,
the porosity (ε (%)), a mean width (D P (μm)) of the pore part represented by a mean value of a distance, between outlines specifying the pore part and facing each other, perpendicular to the center line, a mean length (L (μm)) of the pore part represented by a mean value of a length of the center line between adjacent branch points among a plurality of specified branch points derived from the center line and a length of the center line between an end of the center line and the branch point adjacent to the end of the center line, and a mean pore size (D H (μm)) satisfy relations of the following equations (1) and (2):
200≦ε×( D P /2) 2 /L (1);
and
L≦D H /2 (2).
2. The ceramic porous body according to claim 1 , wherein the permeability is 5×10 −12 m 2 or more.
3. The ceramic porous body according to claim 2 , wherein the ceramic includes at least one type selected from the group consisting of alumina, mullite, cordierite, silicon nitride, and silicon carbide.
4. The ceramic porous body according to claim 2 , wherein a four-point bending strength is 10 MPa or more.
5. The ceramic porous body according to claim 1 , wherein the permeability is 1×10 −11 m 2 or more.
6. The ceramic porous body according to claim 5 , wherein the ceramic includes at least one type selected from the group consisting of alumina, mullite, cordierite, silicon nitride, and silicon carbide.
7. The ceramic porous body according to claim 5 , wherein a four-point bending strength is 10 MPa or more.
8. The ceramic porous body according to claim 1 wherein the ceramic includes at least one type selected from the group consisting of alumina, mullite, cordierite, silicon nitride, and silicon carbide.
9. The ceramic porous body according to claim 4 , wherein a four-point bending strength is 10 MPa or more.
10. The ceramic porous body according to claim 1 wherein a four-point bending strength is 10 MPa or more.
11. An evaluation method capable of clarifying superiority/inferiority of a permeability of a ceramic porous body as a member constituting a diesel particulate filter, and a factor for the superiority/inferiority of the permeability, the ceramic porous body including a plurality of pores formed in a substrate made of a ceramic at a specified porosity; the substrate having predetermined end faces: the pores connecting through the end faces of the substrate to each other and having branches,
wherein in a case where a cross-sectional plane image of the substrate obtained by cutting the ceramic porous body along a predetermined plane is binarized by image analysis to thereby distinguish a specified pore part derived from the pores from a specified non-pore part derived from the substrate, and a center line passing a central part of the pore part is drawn on the distinguished image,
when the porosity (μ(%)), a mean width (D p (μm)) of the pore part represented by a mean value of a distance, between outlines specifying the pore part and facing each other, perpendicular to the center line, a mean length (L (μm)) of the pore part represented by a mean value of a length of the center line between adjacent branch points among a plurality of specified branch points derived from the center line and a length of the center line between an end of the center line and the branch point adjacent to the end of the center line, and a mean pore size (D H (μm)) satisfy relations of the following equations (1) and (2), it is judged that the ceramic porous body has a superior permeability and a superior pore shape as the member constituting the diesel particulate filter:
200≦ε×( D P /2) 2 /L (1);
and
L≦D H /2 (2).