Ceramic honeycomb structure and its production method
A ceramic honeycomb structure comprising a ceramic honeycomb body having cell walls defined by a large number of longitudinally extending cells, and an outer peripheral wall formed on an outer peripheral surface of the ceramic honeycomb body, the outer peripheral wall being formed by coating longitudinally extending grooves defined by cell walls on the outer peripheral surface of the ceramic honeycomb body with a coating material, and the outer peripheral wall having higher hardness in its outer peripheral portion than in its inside portion in a thickness direction.
1. A ceramic honeycomb structure, comprising:
a ceramic honeycomb body having cell walls defining longitudinally extending cells, and
an outer peripheral wall formed on the outer peripheral surface of said ceramic honeycomb body, said outer peripheral wall being formed by coating longitudinally extending grooves defined by cell walls on the outer peripheral surface of the ceramic honeycomb body with a coating material comprising colloidal silica having an average particle size of 10-40 nm and ceramic particles selected from the group consisting of cordierite and amorphous silica, and said outer peripheral wall having a thickness of 1.5-5 mm and having higher hardness in its outer peripheral portion than in its inside portion in a thickness direction, wherein the B-type durometer hardness (ASTM D2240) of said outer peripheral wall is 90-95 in said outer peripheral portion, and 85-90 in said inside portion,
wherein the isostatic strength and the heat shock resistant temperature of said ceramic honeycomb structure are 2 MPa or more and 600° C. or higher, respectively, and wherein said outer peripheral wall is formed by drying it with hot air at 150-400° C.
2. The ceramic honeycomb structure according to claim 1 , wherein said outer peripheral wall has hardness gradually decreasing from said outer peripheral portion to said inside portion.
3. A method for producing a ceramic honeycomb structure according to claim 1 , comprising:
forming said outer peripheral wall having a thickness 1.5-5 mm by coating longitudinally extending grooves defined by cell walls on the outer peripheral surface of the ceramic honeycomb body with a coating material comprising 100 parts by mass of ceramic particles and 2-30 parts by mass of colloidal silica, and then drying it with hot air at 150-400° C.,
wherein said colloidal silica has an average particle size of 10-40 nm, and said ceramic particles are selected from the group consisting of cordierite and amorphous silica, and wherein said coating material is kneaded under reduced pressure of −80 kPa or less.