Production method of ceramic honeycomb structure, and ceramic honeycomb structure

Abstract

A method for producing a ceramic honeycomb structure comprising a ceramic honeycomb body having large numbers of longitudinal cells partitioned by porous cell walls having porosity of 50% or more, and a peripheral wall formed on a peripheral surface of the ceramic honeycomb body, comprising the steps of extruding moldable ceramic material to form a honeycomb-structured ceramic green body; machining a peripheral portion of the green body or a sintered body obtained from the green body to remove part of cell walls in the peripheral portion to obtain a ceramic honeycomb body having longitudinal grooves on a peripheral surface; applying colloidal metal oxide to a peripheral surface of the ceramic honeycomb body and drying it, and then applying a coating material comprising ceramic aggregate having an average particle size of 1 μm or more to form the peripheral wall.

Claims

1. A method for producing a ceramic honeycomb structure comprising a ceramic honeycomb body having a plurality of longitudinal cells partitioned by porous cell walls having a porosity of 50% or more, and a peripheral wall formed on a peripheral surface of said ceramic honeycomb body, comprising the steps of extruding a moldable ceramic material to form a honeycomb-structured ceramic green body; machining a peripheral portion of said green body or a sintered body obtained from said green body to remove part of cell walls in the peripheral portion, thereby obtaining a ceramic honeycomb body having longitudinal grooves on a peripheral surface; coating said ceramic honeycomb body with a composition consisting of an aqueous dispersion of colloidal metal oxide so that the colloidal metal oxide intrudes into pores in cell walls constituting the grooves on the peripheral surface, wherein said coating clogs the pores so that the porosity of said cell walls constituting the grooves on the peripheral surface is 0.9 times or less a porosity of cell walls in an inner portion of the ceramic honeycomb body, and drying it; and further coating said peripheral surface coated with the composition consisting of the aqueous dispersion of colloidal metal oxide with a coating material comprising ceramic aggregate having an average particle size of 1 μm or more to form said peripheral wall.

2. The method for producing a ceramic honeycomb structure according to claim 1, wherein said colloidal metal oxide is colloidal silica or colloidal alumina.

3. The method for producing a ceramic honeycomb structure according to claim 1, wherein the amount of said colloidal metal oxide coated is 2.0×10.sup.−3-150×10.sup.−3 g/cm.sup.3 on a solid basis, per a unit volume of said ceramic honeycomb body.

4. The method for producing a ceramic honeycomb structure according to claim 1, wherein said colloidal metal oxide has an average particle size of 5-100 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1(a) is a schematic view longitudinally showing one example of ceramic honeycomb structures produced by the method of the present invention.

(2) FIG. 1(b) is a schematic, longitudinal cross-sectional view showing one example of ceramic honeycomb structures produced by the method of the present invention.

(3) FIG. 2(a) is an enlarged schematic view showing part of an end surface of a ceramic honeycomb body produced by the method of the present invention.

(4) FIG. 2(b) is an enlarged, longitudinal, partial cross-sectional view showing a ceramic honeycomb body produced by the method of the present invention.

(5) FIG. 3(a) is a schematic view longitudinally showing grooves coated with colloidal metal oxide on a peripheral surface of the ceramic honeycomb body.

(6) FIG. 3(b) is a longitudinal, partial cross-sectional view showing grooves coated with colloidal metal oxide on a peripheral surface of the ceramic honeycomb body.

(7) FIG. 4(a) is a schematic view longitudinally showing grooves coated with colloidal metal oxide and a coating material on a peripheral surface of the ceramic honeycomb body.

(8) FIG. 4(b) is a longitudinal, partial cross-sectional view showing grooves coated with colloidal metal oxide and a coating material on a peripheral surface of the ceramic honeycomb body.

(9) FIG. 5 is a schematic cross-sectional view showing the ceramic honeycomb structure described in JP 2003-284923 A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) The embodiments of the present invention will be explained below, without intention of restricting the present invention thereto. Within the scope of the present invention, any modifications and improvements, etc. may be made properly based on the knowledge of those skilled in the art.

[1] PRODUCTION METHOD OF CERAMIC HONEYCOMB STRUCTURE

(11) The method of the present invention for producing a ceramic honeycomb structure 1 comprising a ceramic honeycomb body 10 having large numbers of longitudinal cells 14 partitioned by porous cell walls 13 having porosity of 50% or more, and a peripheral wall 11 formed on a periphery of the ceramic honeycomb body 10 as shown in FIGS. 1(a) and 1(b), comprises the steps of

(12) (a) extruding a moldable ceramic material to form a honeycomb-structured ceramic green body;

(13) (b) machining a peripheral portion of the green body or a sintered body obtained from the green body to remove part of cell walls in the peripheral portion, thereby obtaining a ceramic honeycomb body having longitudinal grooves on a peripheral surface; and

(14) (c) coating a peripheral surface of the ceramic honeycomb body with colloidal metal oxide, and drying it, and further coating the peripheral surface of the ceramic honeycomb body with a coating material comprising ceramic aggregate having an average particle size of 1 μm or more to form the peripheral wall.

(15) (a) Formation of Green Body

(16) The honeycomb-structured ceramic green body is produced by extruding a moldable ceramic material. Ceramic powder is fully dry-mixed with a binder, a lubricant, and if necessary, a pore-forming material, and sufficiently blended with water to form a plasticized ceramic material. This ceramic material is extruded, cut to a predetermined length, and dried to obtain a honeycomb-structured ceramic green body integrally comprising a peripheral wall and cell walls.

(17) (b) Production of Ceramic Honeycomb Body

(18) The honeycomb-structured ceramic green body is sintered to provide a sintered body having porosity of 50% or more. This sintered body is deprived of part of cell walls in the peripheral portion by machining, to form a ceramic honeycomb body 10 having longitudinal grooves 140 on a peripheral surface 11a as shown in FIGS. 2(a) and 2(b). Though a peripheral surface is machined after the green body is sintered in this example, the green body before sintering may be machined and then sintered to form the ceramic honeycomb body 10.

(19) Materials preferable for the ceramic honeycomb body 10 include cordierite, alumina, silica, silicon nitride, silicon carbide, aluminum titanate, LAS, etc. Among them, ceramic comprising cordierite as a main crystal phase is most preferable because it is inexpensive and has excellent heat resistance and chemical stability.

(20) (c) Formation of Peripheral Wall

(21) (i) Application of Colloidal Metal Oxide

(22) As shown in FIGS. 3(a) and 3(b), colloidal metal oxide 21 is applied to grooves 140 on a peripheral surface 11a of the ceramic honeycomb body 10 by a brush, a roller, etc. The colloidal metal oxide 21 applied intrude into pores in cell walls 13a constituting the grooves 140 on the peripheral surface 11a as well as in cell walls 13b inside the cell walls 13a, thereby clogging the pores to increase the strength of cell walls 13a on the peripheral surface 11a. Colloidal metal oxide 21 applied to the grooves 140 is dried by spontaneous drying, hot-air drying in a drying furnace, etc.

(23) The colloidal metal oxide 21 includes colloidal silica, colloidal alumina, titania sol, water glass, etc. Among them, colloidal silica and colloidal alumina are preferable. The colloidal metal oxide 21 is used preferably in the form of an aqueous dispersion, with the concentration of a solid component properly adjusted to have viscosity suitable for coating.

(24) The amount of colloidal metal oxide 21 coated is preferably 2.0×10.sup.−3 g/cm.sup.3 to 150×10.sup.−3 g/cm.sup.3 on a solid basis, per a unit volume of the ceramic honeycomb body 10. When the amount of the coating is less than 2.0×10.sup.−3 g/cm.sup.3 on a solid basis less, pores in the cell walls 13a constituting the grooves 140 and in the cell walls 13b inside the cell walls 13a may not be sufficiently clogged, failing to obtain sufficient isostatic strength. On the other hand, when it exceeds 150×10.sup.−3 g/cm.sup.3, a large amount of colloidal metal oxide 21 fills the grooves 140, resulting in low heat shock resistance. The amount of the coating is preferably 4.0×10.sup.−3 g/cm.sup.3 to 90×10.sup.−3 g/cm.sup.3 on a solid basis. The amount [g/cm.sup.3] of a solid component coated per a unit volume is a value obtained by dividing the solid-basis amount [g] of colloidal metal oxide 21 coated by the volume [cm.sup.3] of the ceramic honeycomb body, which is expressed, for example, by [(π/4)×D.sup.2×L] in the case of a cylindrical shape having an outer diameter of D and a length of L.

(25) The colloidal metal oxide 21 preferably has a particle size of 5-100 nm. The use of colloidal metal oxide 21 having a particle size in such a range makes it easy for the colloidal metal oxide 21 enter pores in the cell walls 13a constituting the grooves 140, resulting in sufficient isostatic strength. The particle size of less than 5 nm undesirably decreases heat shock resistance. On the other hand, the particle size exceeding 100 nm makes it difficult for the colloidal metal oxide to enter pores in the cell walls 13a constituting the grooves 140, resulting in insufficient clogging of pores in the cell walls 13a, and thus likely failing to obtain sufficient isostatic strength. The particle size is preferably 10-90 nm.

(26) (ii) Application of Coating Material

(27) As shown in FIGS. 4(a) and 4(b), a coating material 22 is applied in a thickness of 0.1-3 mm onto the dried colloidal metal oxide 21 to fill the grooves 140 on the peripheral surface 11a of the ceramic honeycomb body 10. The applied coating material 22 is dried by a known method such as hot-air drying, microwave drying, etc. to remove moisture in the coating material 22, thereby obtaining a ceramic honeycomb structure 1 having a peripheral wall 11.

(28) The coating material 22 used is a paste obtained by blending ceramic aggregate having an average particle size of 1 μm or more, colloidal silica or colloidal alumina, a binder, water, and if necessary, a dispersant, ceramic fibers, etc. The use of ceramic aggregate having an average particle size of 1 μm or more in the coating material 22 increases the strength of the peripheral wall 11, and thus the isostatic strength of the ceramic honeycomb structure 1. However, when the average particle size of the ceramic aggregate is less than 1 μm, a large amount of colloidal silica or colloidal alumina is needed to bind the ceramic aggregate, providing the peripheral wall 11 with low heat shock resistance. On the other hand, ceramic aggregate having too large an average particle size provides the peripheral wall 11 with low strength, resulting in easy detachment of the peripheral wall 11 from the ceramic honeycomb structure. Accordingly, the average particle size of the ceramic aggregate is preferably 2-50 μm.

(29) Materials for the ceramic aggregate used in the coating material 22 may be the same as or different from those of the ceramic honeycomb body 10, preferably cordierite, alumina, mullite, silica, etc. The use of a material having a smaller thermal expansion coefficient than that of the ceramic honeycomb body 10 preferably provides high heat shock resistance during use. For example, amorphous silica is preferable.

(30) When colloidal metal oxide 21 applied to the grooves 140 is the same as ceramic aggregate in the coating material 22 applied thereon, the colloidal metal oxide 21 and the coating material 22 preferably have good adhesion to the cell walls 13a, resulting in high bonding strength between the cell walls 13a and the peripheral wall 11.

(31) In the ceramic honeycomb structure 1 produced by the method of the present invention, the colloidal metal oxide 21 applied to cell walls 13a constituting the longitudinal grooves 140 on the peripheral surface 11a intrude into pores in the cell walls 13a as well as in the cell walls 13b inside the cell walls 13a, and are strongly bonded thereto. As a result, colloidal metal oxide 21 and the coating material 22 applied thereon are integrated with the cell walls 13a, resulting in high adhesion (bonding strength) between the cell walls 13a and the peripheral wall 11. Accordingly, even a ceramic honeycomb structure 1 comprising cell walls 13 having as high porosity as 50% or more has extremely high isostatic strength because of a peripheral wall 11 formed by the colloidal metal oxide 21 and the coating material 22 applied thereon, so that the peripheral wall 11 is not easily detached from the peripheral surface 11a of the ceramic honeycomb structure.

(32) When the method of the present invention is used to produce a ceramic honeycomb structure 50 having cells 54 whose ends on one side are sealed by a peripheral wall 52 as shown in FIG. 5, the detachment of the peripheral wall can be prevented, and cells sealed by the peripheral wall exhibit higher heat insulation, because colloidal metal oxide applied to the grooves of the sealed cells 54 intrude into pores of cell walls constituting the grooves, and because the pores of the cell walls are clogged by the coating material applied thereon. Accordingly, the ceramic honeycomb structure 50 enjoys such high-speed temperature elevation that high catalytic activity can be achieved in a short period of time from the start of operation.

[2] CERAMIC HONEYCOMB STRUCTURE

(33) As shown in FIGS. 1(a), 1(b), 2(a) and 2(b), the ceramic honeycomb structure 1 of the present invention comprises a ceramic honeycomb body 10 having large numbers of longitudinal cells 14 partitioned by porous cell walls 13, and a peripheral wall 11 formed on a peripheral surface 11a of the ceramic honeycomb body 10,

(34) the ceramic honeycomb body 10 having longitudinal grooves 140 on the peripheral surface 11a; and

(35) the peripheral wall 11 being filled in the longitudinal grooves 140, so that cell walls 13a constituting the grooves 140 on the peripheral surface 11a have smaller porosity than that of cell walls 13 in an inner portion of the ceramic honeycomb body 10.

(36) The porosity of cell walls 13 in the ceramic honeycomb structure 1 is preferably 50% or more. Also, it is preferably 80% or less to provide the ceramic honeycomb structure 1 with sufficient strength. Because the colloidal metal oxide 21 intrudes into cell walls 13a constituting the grooves 140 on the peripheral surface 11a of the ceramic honeycomb body 10, the porosity of the cell walls 13a is smaller than the porosity of cell walls 13 in an inner portion of the ceramic honeycomb body 10. To have sufficient isostatic strength, the porosity of cell walls 13a constituting the grooves 140 on the peripheral surface 11a is preferably 0.9 times or less, more preferably 0.8 times or less, the porosity of cell walls 13 in an inner portion of the ceramic honeycomb body 10. To prevent the deterioration of heat shock resistance, the porosity of cell walls 13a constituting the grooves 140 on the peripheral surface 11a is preferably 0.1 times or more the porosity of cell walls 13 in an inner portion of the ceramic honeycomb body 10.

(37) Because the colloidal metal oxide 21 enters not only pores of the cell walls 13a constituting the grooves 140 on the peripheral surface 11a of the ceramic honeycomb body 10, but also pores of cell walls 13b inside the cell walls 13a, the porosity of the inside cell walls 13b is also preferably smaller than the porosity of the cell walls 13 in an inner portion of the ceramic honeycomb body 10, like the porosity of cell walls 13a constituting the grooves 140 of the peripheral surface 11a. Up to 20 cells below the peripheral surface 11a preferably have cell walls 13b having smaller porosity than that of cell walls 13 in an inner portion of the ceramic honeycomb body 10. More than 20 such cells lead to large pressure loss. The number of such cells is preferably up to 15, more preferably up to 10. The porosity of the cell walls 13b preferably becomes larger from the peripheral surface 11a toward inside gradually or stepwise.

(38) The cell walls 13 of the ceramic honeycomb body 10 preferably have thickness of 0.1-0.4 mm, and a cell pitch of 1-3 mm. The ceramic honeycomb body 10 with such structure more effectively exhibits high isostatic strength.

[3] EXAMPLES

(39) The present invention will be explained in further detail by Examples below, without intention of restricting the present invention thereto.

Example 1

(1) Production of Ceramic Honeycomb Body

(40) Kaolin powder, talc powder, silica powder and alumina powder were mixed to form a cordierite-forming material powder comprising 50% by mass of SiO.sub.2, 36% by mass of Al.sub.2O.sub.3, and 14% by mass of MgO. This material powder was fully dry-mixed with methylcellulose and hydroxypropyl methylcellulose as a binder, a lubricant, and a foamed resin as a pore-forming material, and then sufficiently blended with water to prepare a plasticized ceramic material. This ceramic material was extruded, cut to a predetermined length, and dried to obtain a honeycomb-structured ceramic green body comprising a peripheral portion integral with cell walls. This green body was sintered, and machined to remove part of cell walls from the peripheral portion, thereby obtaining a cordierite honeycomb body comprising longitudinal grooves on a peripheral surface, which had an outer diameter of 266 mm, a length of 305 mm, a cell wall thickness of 0.3 mm, a cell pitch of 1.57 mm, and a cell wall porosity of 61%.

(2) Formation of Peripheral Wall

(41) An aqueous dispersion of colloidal silica (average particle size: 15 nm, and solid concentration: 20% by mass) as colloidal metal oxide was applied to a peripheral surface of each of the resultant four ceramic honeycomb bodies, in an amount of 20×10.sup.−3 g/cm.sup.3 on a solid basis per a unit volume of the ceramic honeycomb body. After the applied colloidal metal oxide was dried at room temperature for 2 hours, it was coated with a coating material obtained by blending 100 parts by mass of ceramic aggregate (silica powder having an average particle size of 15 μm) with 12 parts by mass of colloidal silica on a solid basis, and then blending 100 parts by mass in total of ceramic aggregate and colloidal silica with 1.2 parts by mass of methylcellulose together with water. The coated material was dried at 130° C. for 2 hours to produce four ceramic honeycomb structures.

(42) The ceramic honeycomb structures were evaluated with respect to isostatic strength, and the adhesion and heat shock resistance of the peripheral wall. Also, with respect to the ceramic honeycomb structure used for the above evaluation, samples were cut out of cell walls in an inner portion of the ceramic honeycomb body, and cell walls in the grooves on the peripheral surface, to measure their porosities by mercury porosimetry. Further, cell walls in the peripheral portion were cut out for observation by an electron microscope, to count how many cells having walls into which colloidal metal oxide intruded existed from below the peripheral surface toward inside.

(43) Isostatic Strength

(44) The isostatic strength test was conducted under the automobile standards M505-87 of the Japanese Automotive Standards Organization (JASO). Both ends of the ceramic honeycomb structure were sealed by 20-mm-thick aluminum plates abutting its longitudinal both end surfaces, and a 2-mm-thick rubber sheet was closely attached to a peripheral wall surface of the ceramic honeycomb structure. This sample was placed in a pressure-resistant container, into which water was introduced to isostatically exert pressure onto the peripheral wall surface. The pressure at which the ceramic honeycomb structure was broken was regarded as isostatic strength, which was evaluated by the following standards. The results are shown in Table 1.

(45) Excellent: The isostatic strength was 2 MPa or more.

(46) Good: The isostatic strength was 1.5 MPa or more and less than 2 MPa.

(47) Fair: The isostatic strength was 1.0 MPa or more and less than 1.5 MPa.

(48) Poor: The isostatic strength was less than 1.0 MPa.

(49) Adhesion

(50) The ceramic honeycomb structure was cut at three arbitrary points perpendicularly to the longitudinal direction, and the resultant three cross sections were observed by the naked eye with respect to gaps between the peripheral wall and the ceramic honeycomb body, thereby evaluating the adhesion of the peripheral wall to the ceramic honeycomb body by the following standards.

(51) Excellent: There were no gaps in all of three cross sections.

(52) Good: There were one or more gaps in one of three cross sections.

(53) Fair: There were one or more gaps in two of three cross sections.

(54) Poor: There were one or more gaps in all of three cross sections.

(55) Heat Shock Resistance

(56) Three ceramic honeycomb structures were heated at a constant temperature for 30 minutes in an electric furnace, and then rapidly cooled to room temperature to observe cracks by the naked eye for the evaluation of heat shock resistance. Because cracking occurs more at a higher temperature, the heating temperature was elevated by every 25° C. until cracking occurred. The same evaluation was conducted on three samples, and the difference between the heating temperature and room temperature in a sample, in which cracking occurred at the lowest temperature among the three samples, was regarded as a heat shock resistance temperature. The heat shock resistance temperature was evaluated by the following standards.

(57) Excellent: The heat shock resistance temperature was 600° C. or higher.

(58) Good: The heat shock resistance temperature was 550° C. or higher and lower than 600° C.

(59) Fair: The heat shock resistance temperature was 500° C. or higher and lower than 550° C.

(60) Poor: The heat shock resistance temperature was lower than 500° C.

Examples 2-15 and Comparative Examples 3-7

(61) Ceramic honeycomb structures were produced in the same manner as in Example 1, except for changing the type and solid-base amount of colloidal metal oxides applied, and the type and average particle size of ceramic aggregates in the coating material as shown in Table 1, and their isostatic strength, peripheral wall adhesion, and heat shock resistance were evaluated. The colloidal metal oxide was used in these Examples in the form of an aqueous dispersion having a solid concentration of 20% by mass.

Comparative Example 1

(62) A ceramic honeycomb structure was produced in the same manner as in Example 1, except that a coating material obtained by changing the average particle size of silica powder used as ceramic aggregate from 15 μm to 20 μm was directly applied to a peripheral surface of the ceramic honeycomb body without applying colloidal metal oxide, and its isostatic strength, peripheral wall adhesion, and heat shock resistance were evaluated.

Comparative Example 2

(63) A ceramic honeycomb structure was produced in the same manner as in Comparative Example 1, except that after a coating material directly applied to a peripheral surface of the ceramic honeycomb body was dried, colloidal silica (average particle size: 20 nm, and solid concentration: 20% by mass) as colloidal metal oxide was applied thereonto in an amount of 50×10.sup.−3 g/cm.sup.3 on a solid basis per a unit volume of the ceramic honeycomb body, and then dried, and its isostatic strength, peripheral wall adhesion, and heat shock resistance were evaluated.

(64) TABLE-US-00001 TABLE 1 Colloidal Metal Oxide Applied to Grooves on Peripheral Surface Amount of Solid Average Component Coated.sup.(1) Particle No. Type (×10.sup.−3 g/cm.sup.3) Size (nm) Example 1 Colloidal Silica 20 15 Example 2 Colloidal Silica 20 20 Example 3 Colloidal Alumina 20 25 Example 4 Colloidal Silica 20 100 Example 5 Colloidal Silica 20 5 Example 6 Colloidal Silica 150 20 Example 7 Colloidal Silica 2.0 20 Example 8 Colloidal Silica 50 60 Example 9 Colloidal Silica 50 2 Example 10 Colloidal Silica 155 20 Example 11 Colloidal Silica 1.0 20 Example 12 Colloidal Silica 20 20 Example 13 Colloidal Silica 20 20 Example 14 Colloidal Silica 20 20 Example 15 Colloidal Alumina 20 20 Com. Ex. 1 — — — Com. Ex. 2 — — — Com. Ex. 3 Colloidal Silica 50 20 Com. Ex. 4 Colloidal Silica 50 200 Com. Ex. 5 Colloidal Silica 50 2 Com. Ex. 6 Colloidal Silica 160 20 Com. Ex. 7 Colloidal Silica 1.0 20 Note: .sup.(1)The amount of a solid component coated per a unit volume of a ceramic honeycomb body. Coating Material Evaluation Results Average Porosity of Type of Particle Cell Walls (%) Ceramic Size Inner No. Aggregate (μm) Portion.sup.(2) Grooves.sup.(3) Example 1 Silica 15 60 15 Example 2 Silica 15 58 20 Example 3 Silica 15 59 22 Example 4 Silica 15 59 46 Example 5 Silica 15 58 8 Example 6 Silica 15 58 15 Example 7 Silica 20 58 30 Example 8 Silica 20 58 25 Example 9 Silica 20 58 5 Example 10 Silica 20 58 10 Example 11 Silica 20 60 35 Example 12 Cordierite 50 60 22 Example 13 Cordierite 80 60 22 Example 14 Cordierite 1 60 22 Example 15 Cordierite 15 75 30 Com. Ex. 1 Silica 20 60 55 Com. Ex. 2.sup.(4) Silica 20 60 55 Com. Ex. 3 Silica 0.5 60 20 Com. Ex. 4 Silica 0.5 60 30 Com. Ex. 5 Silica 0.5 60 10 Com. Ex. 6 Silica 0.5 60 20 Com. Ex. 7 Silica 0.5 60 20 Note: .sup.(2)Cells in the inner portion of the ceramic honeycomb body. .sup.(3)Cells in grooves on the peripheral surface. .sup.(4)After the coated material was dried, colloidal metal oxide was applied. Evaluation Results Number of Intruded Isostatic Heat Shock No. Cells.sup.(1) Strength Adhesion Resistance Example 1 16 Excellent Excellent Excellent Example 2 15 Excellent Excellent Excellent Example 3 14 Excellent Good Excellent Example 4 12 Good Excellent Excellent Example 5 18 Excellent Excellent Good Example 6 25 Excellent Excellent Excellent Example 7 9 Excellent Excellent Excellent Example 8 19 Good Excellent Excellent Example 9 21 Excellent Excellent Fair Example 10 27 Excellent Excellent Good Example 11 7 Good Good Good Example 12 15 Good Good Good Example 13 15 Fair Fair Good Example 14 15 Excellent Good Fair Example 15 15 Good Good Good Com. Ex. 1 — Poor Poor Poor Com. Ex. 2 — Poor Poor Poor Com. Ex. 3 20 Excellent Excellent Poor Com. Ex. 4 15 Fair Excellent Poor Com. Ex. 5 25 Excellent Excellent Poor Com. Ex. 6 30 Excellent Excellent Poor Com. Ex. 7 7 Good Good Poor Note: .sup.(1)The number of cells into which colloidal metal oxide intruded.

(65) As is clear from Table 1, the ceramic honeycomb structures of Examples 1-15 each obtained by applying colloidal metal oxide to grooves on a peripheral surface and then applying a coating material comprising ceramic particles having an average particle size of 1 μm or more onto the colloidal metal oxide layer had sufficient isostatic strength, peripheral wall adhesion and heat shock resistance. On the other hand, Comparative Example 1, in which the above coating material was directly applied to grooves on a peripheral surface without applying colloidal metal oxide, did not have sufficient isostatic strength, and was low in peripheral wall adhesion and heat shock resistance. Like Comparative Example 1, Comparative Example 2, in which the coating material was directly applied to grooves on a peripheral surface, and colloidal metal oxide was applied thereonto, did not have sufficient isostatic strength. The ceramic honeycomb structures of Comparative Examples 3-7 each obtained by applying colloidal metal oxide to grooves on a peripheral surface, and applying a coating material comprising ceramic particles having an average particle size of less than 1 μm thereonto had poor heat shock resistance, despite relatively good isostatic strength and peripheral wall adhesion.

EFFECT OF THE INVENTION

(66) Because the present invention provides a ceramic honeycomb structure having sufficient isostatic strength even when its cell walls have as high porosity as 50% or more, the peripheral wall is unlikely detached from the ceramic honeycomb body even under heat shock during use.