Abstract: A purification catalyst for exhaust gas is provided that uses a hexagonal cell monolithic carrier which is able to demonstrate purification performance that is superior to the case of using a square cell monolithic carrier. This purification catalyst for exhaust gas comprises a monolithic carrier (10) provided with hexagonal cells (15) of 200 cells/in2 or more in which the porosity of partition walls (11) that form the cells (15) is 25% or more; and, a catalyst layer (2) arranged on the surface of the partition walls (11) of the monolithic carrier (10) that contains a catalyst component for purification of exhaust gas. The thickness of catalyst layer (2) is 10-70 &mgr;m at its thin portion (21), and its thick portion (22) has a thickness of no more than 12 times that of thin portion (21).

Abstract: A ceramic carrier and ceramic catalyst body used as NOx purification catalysts for lean burn engines, which are inexpensive, exhibit high temperature durability and can maintain their catalytic function for extended periods. The ceramic carrier has a diffusion-inhibiting layer formed on the surface of a cordierite honeycomb structure, to inhibit diffusion of alkali metals, alkaline earth metals, etc. carried as NOx storage materials. The diffusion-inhibiting layer is composed of a ceramic material such as Y2O3, NiO or CeO2 which does not react with alkali metals or alkaline earth metals at temperatures of up to 1000° C. and has a melting point of higher than 1000° C., and the diffusion-inhibiting layer inhibits diffusion of catalyst components such as potassium into the interior to prevent their reaction with cordierite, so that the durability is greatly enhanced without reducing catalytic performance.

Abstract: A metal mold for molding a hexagonal honeycomb structure, having feed holes for feeding a material, pool grooves formed in the shape of a triangular lattice and communicated with the feed holes, and slit grooves formed in the shape of a hexagonal lattice and communicated with the pool grooves. Each hexagonal lattice of the slit grooves is so formed as to come into agreement with a hexagon shaped by combining six triangular lattices of the pool grooves.

Abstract: There is provided a cordierite honeycomb structural body that allows the thickness of the cell walls to be reduced and heat capacity to be decreased by improving the fluidity of the molding material when passing through a mold for extrusion molding while maintaining the shape retention of the molding material. A water-soluble cellulose ether is used as a binder that is added to a cordierite-converted starting material. This water-soluble cellulose ether contains methoxyl groups substituted for the cellulose hydroxyl groups within the range of a substitution rate of 27.5 to 31.5%, does not contain hydroxypropoxyl groups and hydroxyethoxyl groups in an amount greater than the amount of unavoidable impurities (0.1 wt %), and has a viscosity in a 2 wt % aqueous solution at 20° C. of less than 8000 centipoise.

Abstract: A metal mold for molding a hexagonal honeycomb structure, having feed holes for feeding a material, pool grooves formed in the shape of a triangular lattice and communicated with the feed holes, and slit grooves formed in the shape of a hexagonal lattice and communicated with the pool grooves. Each hexagonal lattice of the slit grooves is so formed as to come into agreement with a hexagon shaped by combining six triangular lattices of the pool grooves. The invention is further concerned to a method of producing a metal mold for molding a hexagonal honeycomb structure, having feed holes for feeding a material, pool grooves formed in the shape of a triangular lattice, and slit grooves formed in the shape of a hexagonal lattice.

Abstract: A method of producing a metal mold for molding a honeycomb structure, wherein the slit grooves are formed by electric discharge machining that is executed a plural number of times by using a small electrode for electric discharge machining having a working surface of an area smaller than the area of the groove-forming surface.

Abstract: The present invention provides a production process of a hexagonal honeycomb structure having low deformation of hexagonal cells. This process comprises an extrusion step for obtaining moldings (7) in which partitions (71) are provided in the form of a hexagonal matrix by extrusion molding of a mixed raw material using a horizontal extruder having an extrusion die provided with slits in the form of a hexagonal matrix and in which the direction of extruding is substantially the horizontal direction, a drying step for drying moldings (7), and a baking step for baking moldings (7). The extrusion step is performed such that c axis (700) parallel to two parallel sides (702) and (705) of the six sides (701) through (706) of each hexagon formed by partitions (71) of extruded moldings (7) is substantially vertical relative to the horizontal plane.

Abstract: A ceramic carrier and ceramic catalyst body used as NOx purification catalysts for lean burn engines, which are inexpensive, exhibit high temperature durability and can maintain their catalytic function for extended periods. The ceramic carrier has a diffusion-inhibiting layer formed on the surface of a cordierite honeycomb structure, to inhibit diffusion of alkali metals, alkaline earth metals, etc. carried as NOx storage materials. The diffusion-inhibiting layer is composed of a ceramic material such as Y2O3, NiO or CeO2 which does not react with alkali metals or alkaline earth metals at temperatures of up to 1000° C. and has a melting point of higher than 1000° C., and the diffusion-inhibiting layer inhibits diffusion of catalyst components such as potassium into the interior to prevent their reaction with cordierite, so that the durability is greatly enhanced without reducing catalytic performance.

Abstract: The present invention provides a production process of a hexagonal honeycomb structure having low deformation of hexagonal cells. This process comprises an extrusion step for obtaining moldings (7) in which partitions (71) are provided in the form of a hexagonal matrix by extrusion molding of a mixed raw material using a horizontal extruder having an extrusion die provided with slits in the form of a hexagonal matrix and in which the direction of extruding is substantially the horizontal direction, a drying step for drying moldings (7), and a baking step for baking moldings (7). The extrusion step is performed such that c axis (700) parallel to two parallel sides (702) and (705) of the six sides (701) through (706) of each hexagon formed by partitions (71) of extruded moldings (7) is substantially vertical relative to the horizontal plane.

Abstract: There is provided a process for obtaining a cordierite honeycomb structural body with thin cell walls and no molding defects such as cell breakage or the like. Cell breakage is prevented by limiting the maximum particle size of the cordierite starting material powder to no greater than 85% of the slit width of the extrusion molding die so that the starting material particles will not clog inside the slits or the introduction port of the slits. As one cordierite starting material, talc with a mean particle size of 5 &mgr;m or greater is used to give a honeycomb structural body with a void volume of greater than 30%, for production of a honeycomb structural body, with good moldability, having a small thickness and a low heat capacity. It is preferred to add to the starting material at least a lubricant/humectant, a binder and/or a mixture of a water-soluble polyhydric alcohol derivative and a polyhydric alcohol.

Abstract: A reinforcing layer 4 of nearly a cylindrical shape is formed along the outer circumferential portion of a ceramic honeycomb structure which comprises a cylindrical outer circumferential skin layer 1 and cell walls 2, the reinforcing layer 4 being formed at a position maintaining a one-cell pitch from the outer circumferential skin layer 1 and extending from one end surface of the ceramic honeycomb structure toward the other end surface thereof. The reinforcing layer 4 is integrally formed, of the same material, with the outer circumferential skin layer 1 and the cell walls 2 to reinforce the strength in the circumferential direction. This makes it possible to decrease the thickness of the cell walls 2 to not larger than 100 &mgr;m yet maintaining moldability and resistance to thermal shock.

Abstract: The present invention discloses a ceramic honeycomb structure comprising partition walls 3 that form mutually adjacent flow paths having a polygonal cross-section, and a peripheral wall 5 provided around the circumference of partition walls that hold the partition walls integrated into a single unit; wherein, the mean thickness of partition walls 3 is 0.05 mm to 0.13 mm, the mean thickness of peripheral wall 5 is greater than the mean thickness of partition walls 3, and the mean contact width between partition walls 3 and peripheral wall 5 satisfies a predetermined relationship. This ceramic honeycomb structure is able to inhibit the occurrence of chipping in the vicinity of the peripheral wall.