Methods for forming ceramic cores

Patent metadata

Field	Value
Publication number	US-10364189-B2
Application number	US-201715586390-A
Country	US
Kind code	B2
Filing date	May 4, 2017
Priority date	May 4, 2017
Publication date	Jul 30, 2019
Grant date	Jul 30, 2019

Abstract

Methods for forming ceramic cores are disclosed. A ceramic core formed using the method of the present application includes a silica depletion zone encapsulating an inner zone. The inner zone includes mullite and the silica depletion zone includes alumina. The method includes heat-treating a ceramic body in a non-oxidizing atmospheric condition for an effective temperature and time combination at a pressure less than 10 −2 atmosphere to form the silica depletion zone at a surface of the ceramic core.

First claim

The invention claimed is:

1. A method for forming a ceramic core, the method comprising:
heat-treating a sintered ceramic body comprising mullite in a non-oxidizing atmospheric condition for an effective temperature and time combination at a pressure less than 10 −2 atmosphere to form a silica depletion zone at a surface of the ceramic core, wherein the sintered ceramic body further comprises alumina and free silica.

2. The method of claim 1 , wherein the pressure of the non-oxidizing atmospheric condition is less than 10 −3 atmosphere.

3. The method of claim 1 , wherein a partial pressure of oxygen in the non-oxidizing atmospheric condition is less than 10 −4 atmosphere.

4. The method of claim 1 , wherein the non-oxidizing atmospheric condition comprises a reducing atmospheric condition.

5. The method of claim 4 , wherein the reducing atmospheric condition comprises at least one of methane or hydrogen.

6. The method of claim 1 , wherein heat-treating the sintered ceramic body comprises heat-treating in presence of carbon.

7. The method of claim 1 , wherein the effective temperature of heat-treating the sintered ceramic body is greater than 1400° C.

8. The method of claim 7 , wherein the effective temperature of heat-treating the sintered ceramic body is in a range from 1500° C. to 1700° C.

9. The method of claim 7 , wherein an effective time duration of heat-treating the sintered ceramic body is greater than one hour.

10. The method of claim 1 , wherein the method comprises forming the ceramic core in a monolithic form, wherein the monolithic form comprises a silica depletion zone encapsulating an inner zone, wherein the inner zone comprises alumina and mullite, and the silica depletion zone comprises alumina.

11. The method of claim 1 , wherein the method further comprises:
providing a slurry comprising a precursor of silica and at least one of alumina or a precursor of alumina;
injecting the slurry into a die;
curing the slurry in the die to form a cured ceramic body;
separating the die and the cured ceramic body; and
sintering the cured ceramic body to form the sintered ceramic body comprising mullite.

12. The method of claim 11 , wherein the precursor of silica comprises siloxane binder.

13. The method of claim 11 , wherein a temperature of sintering is greater than 1200° C.

14. A method comprising:
providing a slurry comprising a precursor of silica and at least one of alumina or a precursor of alumina;
injecting the slurry into a die;
curing the slurry in the die to form a cured ceramic body;
separating the die and the cured ceramic body;
sintering the cured ceramic body to form the sintered ceramic body comprising mullite; and
heat-treating the sintered ceramic body in a non-oxidizing atmospheric condition at a temperature greater than 1600 degree Celsius for a time duration greater than 2 hours at less than 10 −3 atmosphere pressure to form a silica depletion zone encapsulating an inner zone comprising alumina and mullite.

15. The method of claim 14 , wherein heat-treating the sintered ceramic body comprises heat-treating in presence of carbon.

16. The method of claim 14 , wherein the precursor of silica comprises siloxane binder.

17. The method of claim 14 , wherein a temperature of sintering is greater than 1200° C.

Assignees

• Gen Electric

Inventors

• Ku Anthony Yu-Chung
• Yang Xi
• Li Tao
• Pollinger John Patrick
• Mowry Zachary Kenneth
• Klug Frederic Joseph

Classifications

• C22C9/10

  with silicon as the next major constituent · CPC title

• C04B41/009

  characterised by the material treated · CPC title

• C04B2235/662

  Annealing after sintering · CPC title

• C04B2235/75

  Products with a concentration gradient · CPC title

• C04B2235/80

  Phases present in the sintered or melt-cast ceramic products other than the main phase · CPC title