Honeycomb bodies with controlled porosity gradient and firing methods thereof

1. A honeycomb firing method, comprising:

providing a green honeycomb body comprising a honeycomb structure with a matrix of intersecting walls having an interior portion, and having a skin disposed on at least a portion of an outer periphery of the matrix; and

firing the green honeycomb body in a furnace;

wherein firing comprises:

ramping up, at a first rate, a temperature in the furnace to reach a first temperature,

after reaching the first temperature, ramping up, at a second rate, the temperature in the furnace to reach a spike temperature,

after reaching the spike temperature, ramping down, at a third rate, the temperature in the furnace to reach a soak temperature,

after reaching the soak temperature, maintaining the soak temperature for a predetermined period of time; and

after the predetermined period of time, ramping down, at a fourth rate, the temperature in the furnace from the soak temperature to a handling temperature, and

wherein, after firing, the interior portion of the matrix has a first average bulk porosity, and the skin has a second average bulk porosity that is less than the first average bulk porosity.

2. The method of claim 1 , wherein providing the green honeycomb body comprises extruding the green honeycomb body comprising aluminum-titanate-forming batch mixture.

3. The method of claim 1 , further comprising:

controlling an oxygen level in the furnace by introducing nitrogen and/or recycling products of combustion into the furnace; and

wherein the first rate is nonlinear throughout the ramping, the first temperature is 1,000° C. or greater, the second rate is nominally linear throughout the ramping, the spike temperature is 1,420° C.±5%, the third rate is nominally linear throughout the ramping, the soak temperature is 1,350° C. or greater, the fourth rate is nominally linear throughout the ramping, and the handling temperature is less than 400° C.

4. The method of claim 1 , further comprising:

varying an oxygen level in the furnace during at least a portion of a time required to ramp up the temperature in the furnace; and

wherein the soak temperature is 1,350° C. or greater, the spike temperature is 1,420° C.±5%, the second rate is nominally 100° C./hour or greater throughout the ramping, the third rate is negative 150° C./hour or more negative throughout the ramping, the fourth rate is negative 150° C./hour or more negative throughout the ramping, and the handling temperature is less than 400° C.

5. The method of claim 1 , further comprising:

extruding the green honeycomb body wherein the matrix includes a halo portion adjacent to the skin.

6. A honeycomb firing method, comprising:

providing a green honeycomb body comprising a honeycomb structure with a matrix of intersecting walls having an interior portion, and having a skin disposed on at least a portion of an outer periphery of the matrix; and

firing the green honeycomb body in a furnace;

wherein firing comprises:

ramping up, at a first rate, a temperature in the furnace to a soak temperature,

after reaching the soak temperature, maintaining the soak temperature for a predetermined period of time;

after maintaining the soak temperature for the predetermined period of time, ramping up, at a second rate, the temperature in the furnace to reach a spike temperature,

after reaching the spike temperature, ramping down, at a third rate, the temperature in the furnace to a handling temperature, and

wherein, after firing, the interior portion of the matrix has a first average bulk porosity, and the skin has a second average bulk porosity that is less than the first average bulk porosity.

7. The method of claim 6 , wherein providing the green honeycomb body comprises extruding the green honeycomb body comprising aluminum-titanate-forming batch mixture.

8. The method of claim 6 , further comprising:

controlling an oxygen level in the furnace by introducing nitrogen and/or recycling products of combustion into the furnace, and

wherein the first rate is nonlinear or piecewise-linear throughout the ramping, the second rate is nominally linear throughout the ramping, the spike temperature is 1,420° C.±5%, the third rate is nominally linear throughout the ramping, the soak temperature is 1,350° C. or greater, and the handling temperature is less than 400° C.

9. The method of claim 6 , further comprising:

varying an oxygen level in the furnace during at least a portion of a time required to ramp up the temperature in the furnace, and

wherein the soak temperature is 1,350° C. greater, the spike temperature is 1,420° C.±5%, the second rate is 100° C./hour or greater throughout the ramping, the third rate is negative 150° C./hour or more negative throughout the ramping, and the handling temperature is less than 400° C.

10. The method of claim 6 , further comprising:

extruding the green honeycomb body wherein the matrix comprises a halo portion adjacent to the skin.

11. A honeycomb firing method, comprising:

providing a green honeycomb body comprising a honeycomb structure with a matrix of intersecting walls having an interior portion, and having a skin disposed on at least a portion of an outer periphery of the matrix; and

firing the green honeycomb body in a furnace;

wherein firing comprises:

ramping up, at a first rate, a temperature in the furnace to a soak temperature,

after reaching the soak temperature, maintaining the soak temperature for a predetermined period of time;

after maintaining the soak temperature for the predetermined period of time, ramping down, at a second rate, the temperature in the furnace to reach a pre-spike temperature,

after reaching the pre-spike temperature, ramping up, at a third rate, the temperature in the furnace to reach a spike temperature that is greater than the soak temperature,

after reaching the spike temperature, ramping down, at a fourth rate, the temperature in the furnace from the spike temperature to a handling temperature, and

wherein, after firing, the interior portion of the matrix has a first average bulk porosity, and the skin has a second average bulk porosity that is less than the first average bulk porosity.

12. The method of claim 11 , wherein providing the green honeycomb body comprises extruding the green honeycomb body comprising an aluminum-titanate-forming batch mixture.

13. The method of claim 11 , further comprising:

controlling an oxygen level in the furnace by introducing nitrogen and/or recycling products of combustion into the furnace, and

wherein the first rate is nonlinear or piecewise-linear throughout the ramping, the second rate is nominally linear throughout the ramping, the spike temperature is 1,420° C.±5%, the third rate is nominally linear throughout the ramping, the soak temperature is 1,350° C.±5%, the fourth rate is nominally linear throughout the ramping, and the handling temperature is less than 400° C.

14. The method of claim 11 , further comprising:

varying an oxygen level in the furnace during at least a portion of a time required to ramp up the temperature in the furnace, and

wherein the soak temperature is 1,350° C. or greater, the spike temperature is 1,420° C.±5%, the second rate is 100° C./hour or greater throughout the ramping, the third rate is negative 150° C./hour or more negative throughout the ramping, the fourth rate is negative 150° C./hour or more negative throughout the ramping, and the handling temperature is less than 400° C.

15. The method of claim 11 , further comprising:

extruding the green honeycomb body wherein the matrix includes a halo region adjacent to the skin.