Silicon carbide ceramic honeycomb structure and its production method
A silicon carbide ceramic honeycomb structure having large numbers of axially penetrating flow paths partitioned by porous silicon carbide cell walls and being formed by integrally bonding honeycomb segments by binder layers, the cell walls having porosity of 40-50% and a median pore diameter of 8-18 μm, an average pore width W determined by averaging the lengths (pore widths) of all measured pore portions being 10-25 μm, the number N of pores per length determined by dividing the total number of the measured pores by the total length of the straight lines used for measurement being 20-40/mm, and the volume of pores having pore diameters of 20 μm or more being 10-20% of the total pore volume in the cell walls and the volume of pores having pore diameters of 9 μm or less being 3-25% of the total pore volume in the cell walls, measured by mercury porosimetry.
1. A silicon carbide ceramic honeycomb structure having large numbers of axially penetrating flow paths partitioned by porous silicon carbide cell walls,
the silicon carbide ceramic honeycomb structure being formed by integrally bonding large numbers of honeycomb segments by binder layers, so as to have an outer periphery having a circular shape in a cross section perpendicular to the axial direction, and forming an outer peripheral wall on the outer periphery,
each honeycomb segment being composed of a sintered body of ceramic particles comprising aggregate and a binder,
said binder being at least one selected from the group consisting of alumina particles, aluminum hydroxide particles, magnesium oxide particles, and magnesium hydroxide particles,
said cell walls having porosity of 40-50% and a median pore diameter of 8-18 μm, and
when a straight line C is drawn in parallel with the cell wall surface such that it passes a center in the direction of the thickness T of said cell wall, and straight lines are drawn in parallel with said straight line C such that they are separate from said straight line C by ±T/5 and ±2T/5 in the thickness direction of said cell wall, to measure the lengths (pore widths) of pore portions crossing each straight line, and the number of pores crossing each straight line, in a cell wall cross section perpendicular to the axial direction,
an average pore width W determined by averaging the lengths (pore widths) of all measured pore portions being 10-25 μm,
the number N of pores per length determined by dividing the total number of the measured pores by the total length of the straight lines used for measurement being 20-40/mm,
the volume of pores having pore diameters of 20 μm or more being 10-20% of the total pore volume in said cell walls, and the volume of pores having pore diameters of 9 μm or less being 3-25% of the total pore volume in said cell walls, in the relation between the pore diameter and cumulative pore volume of said cell walls measured by mercury porosimetry.
2. The silicon carbide ceramic honeycomb structure according to claim 1 , wherein the flow paths of each honeycomb segment are composed of inlet-side-sealed flow paths having plugs on the inlet-side end surface and outlet-side-sealed flow paths having plugs on the outlet-side end surface, the inlet-side-sealed flow paths and the outlet-side-sealed flow paths being alternately positioned in a checkerboard pattern.
3. A method for producing the silicon carbide ceramic honeycomb structure according to claim 1 , comprising (1) integrally bonding large numbers of honeycomb segments by binder layers, each honeycomb segment being formed by formulating, mixing and blending ceramic particles comprising aggregate and a binder with an organic binder to form a moldable material, extrusion-molding said moldable material to a honeycomb shape, and drying and then sintering the resultant green body, (2) machining the resultant composite structure to have an outer periphery having a circular, and then (3) covering the machined outer periphery with a coating material to form an outer peripheral wall,
said aggregate being silicon carbide particles,
said binder being at least one selected from the group consisting of alumina particles, aluminum hydroxide particles, magnesium oxide particles and magnesium hydroxide particles,
said ceramic particles having a median particle diameter D50 of 37-45 μm, and
in a curve showing the relation between particle diameter and cumulative particle volume,
the particle diameter D10 at a cumulative particle volume corresponding to 10% of the total particle volume being 5-20 μm,
the particle diameter D90 at a cumulative particle volume corresponding to 90% of the total particle volume being 52-65 μm, and
the particle size distribution deviation SD being 0.20-0.40, wherein SD=log(D80)−log(D20), D20 is a particle diameter at a cumulative particle volume corresponding to 20% of the total particle volume, D80 is a particle diameter at a cumulative particle volume corresponding to 80% of the total particle volume, and D20<D80.
4. The method for producing the silicon carbide ceramic honeycomb structure according to claim 3 , wherein the sintering is conducted in a temperature range of 1200-1350° C. in an oxidizing atmosphere.