An exhaust gas filter purifies exhaust gas containing particulate matter emitted from an engine. The filter has cell walls and cells surrounded by the cell walls. Through pores formed in the cell walls, adjacent cells are communicated. The cells have open cells opening along an axial direction of the filter, and plugged cells. An upstream end part of the plugged cell is plugged by a plug member. On a cross section perpendicular to the axial direction, a flow-passage sectional area of the plugged cells is larger than a flow-passage sectional area of the open cells. A total length of the filter is not less than a first standard value and is not more than a critical length Lm determined by respective predetermined equations.

The honeycomb filter of the present invention comprises a ceramic honeycomb substrate formed from a porous body of sintered ceramic particles, and a filter layer formed on the surface of the cell walls, wherein a portion of the filter layer penetrates from the surface of the cell walls into pores formed by the ceramic particles to form inter-particle filtration bodies, these inter-particle filtration bodies are formed from a plurality of spherical ceramic particles and crosslinking bodies which bind the spherical ceramic particles to each other, and the spherical ceramic particles and the crosslinking bodies form a three-dimensional network structure.

Disclosed is a honeycomb support structure comprising a honeycomb body and an outer layer or skin formed of a cement that includes an inorganic filler material having a first coefficient of thermal expansion from 25° C. to 600° C. and a crystalline inorganic fibrous material having a second coefficient of thermal expansion from 25° C. to 600° C.

A ceramic honeycomb body, suitable for use in exhaust gas processing, includes a honeycomb structure having a plurality of through-channels, a first portion of the plurality of through-channels have a first hydraulic diameter dh1, a second portion of the plurality of through-channels have a second hydraulic diameter that is smaller than the first hydraulic diameter dh1, the first hydraulic diameter dh1 is equal to or greater than 1.1 mm, and the first and second portions of through-channels, taken together, have a geometric surface area GSA greater than 2.9 mm.sup.−1. Diesel oxidation catalysts and methods of soot removal are also provided, as are other aspects.

A honeycomb structure, including: a plurality of pillar shaped honeycomb segments, each of the pillar shaped honeycomb segments including a partition wall and a plugged portion; and a joining layer arranged so as to join side surfaces of the pillar shaped honeycomb segments to each other. The honeycomb structure satisfies the following equations (1) to (3):
y≤1000  (1);
y≤717.92x.sup.−0.095  (2); and
y≥462.4x.sup.−0.153  (3),
in which y is a maximum temperature (° C.) at which the use of the honeycomb structure is accepted, and x is a thermal conduction factor represented by the following equation:
thermal conduction factor=(thermal conductivity of the partition wall×thermal conductivity of the joining layer)/(average thickness of the joining layer×porosity of the partition wall).

A honeycomb structure includes a pillar-shaped honeycomb structure body including porous partition walls defining and forming a plurality of cells which extend from an inflow end face to an outflow end face, and a porous outer wall surrounding the partition walls, a porous supporting bulge disposed to extend out from a circumference of the outer wall so that at least a part of the outer wall is exposed, and plugging portions arranged in open ends of the cells, and the supporting bulge has support portions and a side wall portion, and the partition walls and the outer wall of the honeycomb structure body and the support portions and the side wall portion of the supporting bulge are all formed monolithically by formation of a ceramic raw material.

A honeycomb filter includes a pillar-shaped honeycomb structure having porous partition walls provided, surrounding a plurality of cells which serve as fluid through channels extending from an inflow end face to an outflow end face, and a porous plugging portion provided either at an end on the inflow end face or the outflow end face of the cells, wherein the plugging portion is composed of a porous material, the honeycomb structure has a central region and a circumferential region, and a ratio of an area of the circumferential region with respect to that of the central region ranges from 0.1 to 0.5, porosity of a central plugging portion in the central region is lower than that of a circumferential plugging portion in the circumferential region, and the porosity of the central plugging portions ranges from 60% to 68%, and that of the circumferential plugging portions ranges from 70% to 85%.

The honeycomb filter includes a honeycomb substrate having porous partition walls defining a plurality of cells and plugging portions. In a cross section, the cells are arranged so that a periphery of an inlet plugged cell including an open end whose shape is a square in which a length of one side is L1 is surrounded with four rectangular outlet plugged cells each including an open end whose shape is a rectangle in which a length of one side is L1 and a length of the other side is L2 (L1>L2) and four square outlet plugged cells each including an open end whose shape is a square in which a length of one side is L2. A partition wall center distance a, a partition wall center distance b and a partition wall thickness t satisfy the following equation (1):
0.95<b/at<1.90   (1).

In a porous body, a surface layer thickness Ts takes a relatively small value satisfying P≧0.54 Ts (formula (1)), the surface layer thickness Ts being derived by a microstructure analysis using the porous-body data that is prepared through three-dimensional scanning of a region including a surface (inflow plane 61) of the porous body. Here, P denotes a porosity [%] of the porous body, and 0%<P<100% and 0 μm<Ts are assumed. The surface layer thickness Ts is derived as a distance in a thickness direction (X direction) between a surface-layer region start plane 92 in which a straight-pore opening ratio becomes 98% or less for the first time and a surface-layer region end plane 93 in which the straight-pore opening ratio becomes 1% or less for the first time.

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.