The honeycomb structure includes a honeycomb structure body having porous partition walls, and a plugging portion disposed in one of open ends of each cell, a thickness of the partition walls is 0.30 mm or more and 0.51 mm or less, a cell density is 30 cells/cm.sup.2 or more and 93 cells/cm.sup.2 or less, a filtration area (cm.sup.2) of inflow cells included per cm.sup.3 of the honeycomb structure body is defined as an inflow side filtration area G (cm.sup.2/cm.sup.3), a value obtained by dividing a pore volume Vp (cm.sup.3) formed in the partition walls by a total volume Va (L) including the cells is defined as a pore volume ratio A (cm.sup.3/L), and in this case, a product of the inflow side filtration area G (cm.sup.2/cm.sup.3) and the pore volume ratio A (cm.sup.3/L) is 1800 cm.sup.2/L or more and 3200 cm.sup.2/L or less.

A honeycomb structure comprising: a honeycomb structure body that includes a plurality of porous partition walls and intersection parts, and a catalyst layer, wherein the porosity of the partition wall is 20 to 70%, the average pore diameter of the pores in the partition wall is 1 to 60 μm, a plurality of the partition walls includes a notched partition wall having a recessed part in which at least one end is notched, the ratio of the notched partition wall in the partition walls is 1 to 100%, the recessed part of the notched partition wall has a depth of 10 to 200% of the standard length, and the recessed part of the notched partition wall is a part having a width of 33 to 100% of the standard width.

A honeycomb structure includes a honeycomb structure body including porous partition walls defining a plurality of cells serving as fluid passages extending from an inflow end face to an outflow end face. A porosity of the partition walls is from 45 to 65%, an open frontal area of pores having an equivalent circle diameter of 10 um or more is from 20 to 40%, a pore density of pores having an equivalent circle diameter of 10 μm or more is from 350 to 1,000 pores/mm.sup.2 and a median opening diameter of the pores having an equivalent circle diameter of 10 μm or more is from 40 to 60 μm, where the median opening diameter is the median value of the equivalent circle diameters.

A heat conduction member includes: a cylindrical ceramic body, a metal pipe on the outer periphery side of the cylindrical ceramic body, and an intermediate member held between the cylindrical ceramic body and the metal pipe. The cylindrical ceramic body has passages passing through from one end face to the other end face and allowing the first fluid to flow therethrough. The intermediate member is made of material having at least a part having a Young's modulus of 150 Gpa or less. The first fluid is allowed to flow through the inside of the cylindrical ceramic body while the second fluid having lower temperature than that of the first fluid is allowed to flow on the outer peripheral face side of the metal pipe to perform heat exchange between the first fluid and the second fluid.

A plugged honeycomb structure has a plurality of cells defined by partition walls to become through channels for fluid, one end of each of the predetermined cells is plugged by a plugging member, the other end of each of the residual cells is plugged by the plugging member, the partition wall is made of a cordierite component as a main component, and a value obtained by dividing Young's modulus of a plugging structure portion formed by the partition walls and the plugging member by Young's modulus of a cell structure portion formed by the partition walls is in a range of 1.05 to 2.00.

A plugged honeycomb structure includes a honeycomb structure body, and a plurality of plugging portions, the honeycomb structure body further includes pass-through hole portions each of which is formed in at least a part of a partition wall intersection portion in which the partition walls intersect in one end face and each of which interconnects a pair of cells facing each other at a position corresponding to the partition wall intersection portion to enable pass-through of a fluid, and a value obtained by dividing a diameter of a first virtual inscribed circle inscribed at a position of a minimum hole width of the pass-through hole portion by a diameter of a second virtual inscribed circle inscribed at a position of a minimum plugging width between the plugging portions facing each other is in a range of 0.05 to 0.74.

A plugged honeycomb segment includes a honeycomb segment having a quadrangular prism shape which includes porous partition walls arranged to surround a plurality of cells and an outermost circumferential wall, and a plugging portion, wherein a porosity of the partition walls is 30 to 70%, in a cross section orthogonal to the cell extending direction, an inflow cell surrounded by the partition walls is a hexagon, and an outflow cell is a square, one outflow cell is surrounded by four inflow cells, the cell located at the outermost circumference includes a complete cell and an incomplete cell, and a thickness of the outermost circumferential wall in contact with the incomplete cell (T1), a thickness of the outermost circumferential wall in contact with the complete cell (T2), and a thickness of the partition walls (WT), satisfy 0.200 mm<T1<T2−(½×WT) and T2≤0.700 mm.

A honeycomb filter includes a honeycomb structure having a porous partition wall disposed to surround a plurality of cells; and a plugging portion provided at one end of the cell, wherein the honeycomb structure has an inflow side region including a range of up to at least 30% with respect to the total length of the honeycomb structure with the inflow end face as the starting point and an outflow side region including a range of up to at least 20% with respect to the total length of the honeycomb structure with the outflow end face as the starting point, in the extending direction of the cell of the honeycomb structure, an average pore diameter of the partition wall in the inflow side region is 9 to 14 μm and an average pore diameter of the partition wall in the outflow side region is 15 to 20 μm.

A honeycomb filter includes a honeycomb structure body having a porous partition wall disposed to surround a plurality of cells and a plugging portion disposed at one end of the cells, wherein the plurality of cells are arranged in a square grid pattern along a first direction and a second direction in a section orthogonal to an extending direction of the cells, the shape in the section is a deformed square having a specific corner, the specific corner includes a first curved portion, a second curved portion, and a connecting portion, a radius of curvature R1 of the first curved portion and a radius of curvature R2 of the second curved portion are 40 to 80 μm, respectively, and a center distance between a center of curvature O1 of the first curved portion and a center of curvature O2 of the second curved portion is 80 to 200 μm.

A method for producing a honeycomb-shaped ceramic structure by extrusion-molding a moldable material including a cordierite-forming material and a pore-forming material, wherein the cordierite-forming material contains 15-25% by mass of silica having an average particle size of 20-30 μm, with 5% or less by mass of particles having particle sizes of 10 μm or less and 5% or less by mass of particles having particle sizes of 100 μm or more, a particle size distribution deviation SD of 0.5 or less, and sphericity of 0.5 or more, and wherein the pore-forming material is present in an amount of 5-40% by mass based on the cordierite-forming material and has an average particle size of 15-50 μm, with 10% or less by mass of particles having particle sizes of 5 μm or less and 5% or less by mass of particles having particle sizes of 80 μm or more.