Mullite-cordierite composite ceramic

Claim 2

A process for producing a polycrystalline body comprised of from about 50% by weight to about 95% by weight of crystalline mullite and from about 5% by weight to about 50% by weight of crystalline cordierite which comprises providing a mixture comprised of Al 2 0 3 1 MgO and Si0 2 and a nucleating agent, said Al 2 O 3 , MgO and SiO 2 being used in amounts required to produce said polycrystalline body, shaping said mixture into a compact, sintering said compact at a temperature ranging from about 1290°C to about 1550°C at which sufficient liquid phase is generated to liquid phase sinter the compact and produce a densified body having a porosity of less than about 10% by volume of said body, said sintering temperature having no significant deleterious effect on said compact or body, said sintered body containing said mullite phase and a glassy phase of said cordierite, nucleation-annealing said sintered body at a temperature ranging from about 600°C to about 800°C to nucleate said glassy cordierite phase, crystallization-annealing the resulting nucleated body at a temperature ranging from about 1200°C to below the temperature at which liquid forms in said body to produce said polycrystalline body, said nucleating agent being an agent for nucleating said glassy cordierite phase, said nucleating agent being used in an amount sufficient to nucleate said glassy cordierite phase to produce said polycrystalline body, said sintering, said nucleation-annealing and said crystallization-annealing being carried out in an atmosphere or vacuum which has no significant deleterious effect on said compact or body.

Claim 3

The process according to claim 1 wherein said nucleation-annealing temperature ranges from about 650°C to about 750°C.

Claim 4

The process according to claim 1 wherein said atmosphere is selected from the group consisting of air, hydrogen, wet hydrogen, nitrogen, argon and mixtures thereof.

Claim 5

The process according to claim 1 wherein said compact is in the form of a tape.

Claim 6

The process according to claim 1 wherein said polycrystalline body is comprised of from about 60% by weight to about 70% by weight of said mullite and from about 30% by weight to about 40% by weight of said cordierite.

Claim 7

The process according to claim 1 wherein said polycrystalline body is comprised of about 36% by weight of said mullite and about 64% by weight of said cordierite.

Claim 8

A process for producing a polycrystalline body comprised of from about 50% by weight to about 95% by weight of crystalline mullite and from about 5% by weight to about 50% by weight of crystalline cordierite which comprises providing a mixture comprised of Al 2 O 3 , MgO and SiO 2 and a nucleating agent, said A1 2 0 3 , MgO and SiO 2 being used in amounts required to produce said polycrystalline body, said nucleating agent being selected from the group consisting of titanium dioxide, titanium isopropoxide, lithium fluoride, magnesium fluoride and mixtures thereof, shaping said mixture into a compact, sintering said compact at a temperature ranging from about 1290°C to about 1490°C at which sufficient liquid phase is generated to liquid phase sinter the compact and produce a densified body having a porosity of less than about 10% by volume of said body, said sintering temperature having no significant deleterious effect on said body, said sintered body containing said mullite phase and a glassy phase of said cordierite, nucleation-annealing said sintered body at a temperature ranging from about 600°C to about 800°C to nucleate said glassy cordierite phase, crystallization-annealing the resulting nucleated body at a temperature ranging from about 1200°C to below the temperature at which liquid forms in said body, said nucleating agent being used in an amount sufficient to nucleate said glassy cordierite phase to produce said polycrystalline body, said sintering, said nucleation-annealing and said crystallization-annealing being carried out in an atmosphere or vacuum which has no significant deleterious effect on said compact or body.

Claim 9

A process for producing a polycrystalline body comprised of from about 50% by weight to about 95% by weight of crystalline mullite and from about 5% by weight to about 50% by weight of crystalline cordierite which comprises providing a mixture comprised of Al 2 O 3 , MgO and SiO 2 and a nucleating agent, said A1 2 0 3 , MgO and SiO 2 being used in amounts required to produce said polycrystalline body, said nucleating agent being selected from the group consisting of titanium dioxide, titanium isopropoxide, lithium fluoride, magnesium fluoride and mixtures thereof, shaping said mixture into a compact, sintering said compact at a temperature ranging from about 1290°C to about 1490°C at which sufficient liquid phase is generated to liquid phase sinter the compact and produce a densified body having a porosity of less than about 10% by volume of said body, said sintering temperature having no significant deleterious effect on said body, said sintered body containing said mullite phase and a glassy phase of said cordierite, nucleation-annealing said sintered body at a temperature ranging from about 600°C to about 800°C to nucleate said glassy cordierite phase, crystallization-annealing the resulting nucleated body at a temperature ranging from about 1200°C to below the temperature at which liquid forms in said body, said nucleating agent being used in an amount sufficient to nucleate said glassy cordierite phase to produce said polycrystalline body, said sintering, said nucleation-annealing and said crystallization-annealing being carried out in an atmosphere or vacuum which has no significant deleterious effect on said compact or body.

Claim 10

The process according to claim 7 wherein said nucleation-annealing temperature ranges from about 650°C to about 750°C.

Claim 11

The process according to claim 7 wherein said atmosphere is selected from the group consisting of air, hydrogen, wet hydrogen, nitrogen, argon and mixtures thereof.

Claim 12

The process according to claim 7 wherein said compact is in the form of a tape.

Claim 13

The process according to claim 7 wherein said polycrystalline body is comprised of from about 60% by weight to about 70% by weight of said mullite and from about 30% by weight to about 40% by weight of said cordierite.

Claim 14

The process according to claim 7 wherein said polycrystalline body is comprised of about 36% by weight of said mullite and about 64% by weight of said cordierite.

Claim 15

A polycrystalline body comprised of crystalline mullite in an amount ranging from about 50% by weight to about 95% by weight of the total weight of the body and crystalline cordierite in an amount ranging from about 5% by weight to about 50% by weight of the total weight of the body, said body having a porosity of less than about 10% by volume of the total volume of said body.

Claim 16

A polycrystalline body comprised of crystalline mullite in an amount ranging from about 50% by weight to about 95% by weight of the total weight of the body and crystalline cordierite in an amount ranging from about 5% by weight to about 50% by weight of the total weight of the body, said body having a porosity of less than about 10% by volume of the total volume of said body.

Claim 17

The polycrystalline body of claim 13 in the form of a tape.

Claim 18

A polycrystalline body comprised of crystalline mullite ranging from about 60% by weight to about 70% by weight of the total weight of the body, and crystalline cordierite ranging from about 30% by weight to about 40% by weight of the total weight of the body, said body having a porosity of less than about 10% by volume of the total volume of said body.

Claim 19

A polycrystalline body comprised of crystalline mullite ranging from about 60% by weight to about 70% by weight of the total weight of the body, and crystalline cordierite ranging from about 30% by weight to about 40% by weight of the total weight of the body, said body having a porosity of less than about 10% by volume of the total volume of said body.

Claim 20

The polycrystalline body of claim 15 in the form of a tape.

Claim 21

A polycrystalline body comprised of crystalline mullite in an amount ranging from about 50% by weight to about 95% by weight of the total weight of the body, crystalline cordierite in an amount ranging from about 5% by weight to about 50% by weight of the total weight of the body, a phase consisting essentially of a nucleating agent useful for nucleating glassy cordierite phase, said phase of nucleating agent ranging up to about 5% by weight of said body, and a glassy phase ranging from a detectable amount up to about 5% by volume of the total volume of said body.

Claim 22

A polycrystalline body comprised of crystalline mullite in an amount ranging from about 50% by weight to about 95% by weight of the total weight of the body, crystalline cordierite in an amount ranging from about 5% by weight to about 50% by weight of the total weight of the body, a phase consisting essentially of a nucleating agent useful for nucleating glassy cordierite phase, said phase of nucleating agent ranging up to about 5% by weight of said body, and a glassy phase ranging from a detectable amount up to about 5% by volume of the total volume of said body.

Claim 23

The polycrystalline body of claim 17 in the form of a tape.

Claim 24

The polycrystalline body of claim 17 wherein said phase of nucleating agent is Ti0 2 .

Claim 25

A polycrystalline body comprised of crystalline mullite phase in an amount ranging from about 50% by weight to about 95% by weight of the total weight of the body and crystalline cordierite phase in an amount ranging from about 5% by weight to about 50% by weight of the total weight of the body, said mullite phase being comprised of from about 71.8 weight % to about 73.3 weight % Al 2 0 3 balance SiO 2 , said cordierite phase being comprised of about 13.7 weight % MgO, about 34.9 weight % Al203 and about 51.4 weight % SiO 2 , said body having a porosity of less than about 10% by volume of the total volume of said body.

Claim 26

A polycrystalline body comprised of crystalline mullite phase in an amount ranging from about 50% by weight to about 95% by weight of the total weight of the body and crystalline cordierite phase in an amount ranging from about 5% by weight to about 50% by weight of the total weight of the body, said mullite phase being comprised of from about 71.8 weight % to about 73.3 weight % Al 2 0 3 balance SiO 2 , said cordierite phase being comprised of about 13.7 weight % MgO, about 34.9 weight % Al203 and about 51.4 weight % SiO 2 , said body having a porosity of less than about 10% by volume of the total volume of said body.