A mat material including: a base mat containing inorganic fibers and having a first main surface and a second main surface; and a sheet material disposed on at least one of the first main surface or the second main surface, wherein the sheet material is a stacked sheet material in which longitudinally oriented fibers and transversely oriented fibers are stacked, the sheet material has openings surrounded by the longitudinally oriented fibers and the transversely oriented fibers, and an average opening area of the sheet material is more than 0 mm.sup.2/piece and 0.7 mm.sup.2/piece or less.

Provided is a honeycomb fired body in which the pressure loss in the initial state where PM has not accumulated is sufficiently low, the strength is sufficiently high, and the heat capacity is not small. The honeycomb fired body of the present invention is a honeycomb fired body including a plurality of cells in each of which one end is plugged and which serve as channels of exhaust gas, and porous cell partition walls that define the cells, wherein the honeycomb fired body is formed of SiC, the plurality of cells include peripheral cells located at an outermost peripheral region of the honeycomb fired body and inner cells located more inward than the peripheral cells, all the inner cells have the same cross-sectional shape that is a rectangle in a plane perpendicular to the longitudinal direction thereof, each peripheral cell is defined by the cell partition walls and an outer wall forming a periphery of the honeycomb fired body, the cell partition walls in contact with the outer wall each have a thick wall region where the wall thickness gradually increases toward the outer wall, the cross-sectional shape of the peripheral cells in a plane perpendicular to the longitudinal direction thereof is a shape formed by reducing the rectangular cross-sectional shape of the inner cells to obtain a reduced rectangle and chamfering or rounding two corners of the reduced rectangle, the cross-sectional area of each peripheral cell in a plane perpendicular to the longitudinal direction thereof is 60 to 80% of the cross-sectional area of each inner cell in a plane perpendicular to the longitudinal direction thereof, the cell partition walls include inter-peripheral-cell cell partition walls each located between the peripheral cells and inter-inner-cell cell partition walls each located between the inner cells, and the minimum thickness of the inter-peripheral-cell cell partition walls is greater than the thickness of the inter-inner-cell cell partition walls.

The present invention provides a honeycomb filter including a honeycomb fired body including porous cell partition walls, exhaust gas introduction cells each having an open end at an exhaust gas inlet side and a plugged end at an exhaust gas outlet side, exhaust gas emission cells each having an open end at the exhaust gas outlet side and a plugged end at the exhaust gas inlet side, and an outer wall on the periphery thereof. The cross-sectional shape of each exhaust gas introduction cell in a plane perpendicular to the longitudinal direction thereof is entirely uniform from the end at the exhaust gas inlet side to the end at the exhaust gas outlet side excluding the plugged portion. The cross-sectional shape of each exhaust gas emission cell in a plane perpendicular to the longitudinal direction thereof is entirely uniform from the end at the exhaust gas inlet side to the end at the exhaust gas outlet side excluding the plugged portion. The exhaust gas emission cells, except for the cells adjacent to the outer wall, are each adjacently surrounded fully by the exhaust gas introduction cells across the porous cell partition walls. The cells adjacent to the outer wall include the exhaust gas introduction cells and the exhaust gas emission cells. A substantial ratio of the number of the exhaust gas introduction cells to the number of the exhaust gas emission cells (exhaust gas introduction cells:exhaust gas emission cells) is 4:1. All the exhaust gas introduction cells, except for the cells adjacent to the outer wall, have the same cross-sectional area in a plane perpendicular to the longitudinal direction thereof, the cross-sectional area of each exhaust gas introduction cell being smaller than that of each exhaust gas emission cell in a plane perpendicular to the longitudinal direction thereof.

A honeycomb filter including a honeycomb fired body including porous cell partition walls, exhaust gas introduction cells, exhaust gas emission cells, and an outer wall on the periphery thereof. Provided that the hydraulic diameter is given by the following equation (1) and the area based on the given hydraulic diameter is given by the following equation (2), the ratio of the area based on the hydraulic diameter of an exhaust gas introduction cell to the cross-sectional area of the exhaust gas introduction cell is 0.95 to 0.98, and the ratio of the area based on the hydraulic diameter of an exhaust gas emission cell to the cross-sectional area of the exhaust gas emission cell is 0.7 to 0.9: Hydraulic diameter=(4cross-sectional area of cell)/Cross-sectional peripheral length of cell (1), Area based on the hydraulic diameter=(Hydraulic diameter/2).sup.2(2).

A honeycomb structure includes a honeycomb substrate having a porous partition wall that defines a plurality of cells that extend from an inlet end face as an inlet side for a fluid to an outlet end face as an outlet side for the fluid, and a porous circumferential wall that is monolithically formed with the partition wall, and a coat layer that is disposed on at least a part of the outer surface of the circumferential wall. Here, a part of the coat layer penetrates into the pores of the circumferential wall, and a thickness of the part of the coat layer that penetrates into the pores of the circumferential wall is from 1 to 90% of the thickness of the circumferential wall.

An exhaust system includes an exhaust gas treatment article having a porous ceramic honeycomb body mounted in a housing. The exhaust gas treatment article includes a thermal barrier disposed at the outer peripheral surface of the honeycomb body, wherein the thermal barrier comprises blocked peripheral cell channels adjacent to and around the entire peripheral surface and/or a thermal barrier skin.

A method to form a laminar integral skin of a honeycomb structure is provided. The method includes extruding a ceramic precursor batch through a die with feedholes in entry side and slots in exit face of the die to form the honeycomb structure. In a region on the periphery of the die configured to form the cell matrix, a series of concentric slots around the matrix in the exit face of the die are configured to feed skin onto the matrix. Ring sections between concentric slots are angled away from the center and a mask is disposed on top of the periphery producing a channel for extruded skin to meet and bond to extruded matrix. Optionally, slots in the skin-forming ring sections enhance knitting between laminar skin layers. The die and honeycomb body having uniform integral skin are also provided.

A method for drying at least one unfired columnar honeycomb formed body, the honeycomb formed body comprising a raw material composition containing at least one raw material of ceramics, water and at least one heat-gelling binder, and comprising plurality of cells comprising flow paths penetrating from a first bottom surface to a second bottom surface in an inside of an outer sidewall, the cells being defined by partition walls, the method comprising a step of drying the honeycomb formed body by allowing hot gas satisfying 0.8T2/T13.3 in which T1 represents a gelation temperature of the binder ( C.) and T2 represents a wet-bulb temperature of hot gas ( C.), to pass through the flow paths of the plurality of cells such that the hot gas flows into the first bottom surface and flows out of the second bottom surface, while surrounding an outer side surface of the honeycomb formed body by a correction mold comprising an inner side surface shape corresponding to the outer side surface shape of the honeycomb formed body, wherein during the step of drying the honeycomb formed body, at least a part of the outer side surface of the honeycomb formed body receives pressure from the inner side surface of the correction mold, whereby the honeycomb formed body is subjected to shape correction.

A first circumferential wall disposed in a circumference of partition walls has no interface with the outermost circumference partition wall in a circumferential portion constituted by the partition walls whose wall thickness is larger than that of a central portion constituted by the partition walls in a central region. A maximum thickness of a total of the first circumferential wall and a second circumferential wall disposed to surround an outer side of the first circumferential wall is 1.2-3.0 mm, a difference between the maximum thickness and a minimum thickness of the total is 0.2-1.5 mm, and there is satisfied a relation, 0.5(TBTA)SB/SA100(%)9.0 in which TB and TA indicate average thicknesses (m) of the partition walls in the circumferential and central portion respectively, and SB and SA indicate areas (cm.sup.2) of the circumferential portion and the honeycomb structure in the cross section respectively.

A honeycomb filter includes a plurality of honeycomb fired bodies and adhesive layers. Each of the plurality of honeycomb fired bodies includes a plurality of cells, porous cell walls, and an outer wall. The plurality of cells includes exhaust gas introduction cells and exhaust gas emission cells. The exhaust gas introduction cells and the exhaust gas emission cells each have a uniform cross-sectional shape throughout from the exhaust gas inlet side to the exhaust gas outlet side excluding a plugged portion in a cross section perpendicular to a longitudinal direction of the plurality of cells. Each of the exhaust gas emission cells is adjacently surrounded fully by the exhaust gas introduction cells across the porous cell walls. The plurality of cells includes outer cells which are adjacent to the outer wall and which include the exhaust gas introduction cells.