Doped ceramic materials and methods of forming the same

• US 20060138715A1
• Filed: 12/01/2005
• Published: 06/29/2006
• Est. Priority Date: 12/01/2004
• Status: Abandoned Application

• Current Assignee: National University of Singapore
• Original Assignee: National University of Singapore
• Inventors: Liu, Ping, Lim, Leong Chew
• Application Number:
  US11/291,271
• Publication Number:
  US 20060138715A1
• Time in Patent Office: Days
• US Class Current: 264/642
• CPC Class Codes: B23B 2226/18 Ceramic
• CPC Class Codes: C04B 2111/00405 Materials with a gradually increasing or decreasing concentration of ingredients or property from one layer to another
• CPC Class Codes: C04B 2235/3241 Chromium oxides, chromates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/5445 submicron sized, i.e. from 0,1 to 1 micron
• CPC Class Codes: C04B 2235/6027 Slip casting
• CPC Class Codes: C04B 2235/6581 Total pressure below 1 atmosphere, e.g. vacuum
• CPC Class Codes: C04B 2235/661 Multi-step sintering
• CPC Class Codes: C04B 2235/75 Products with a concentration gradient
• CPC Class Codes: C04B 2235/77 Density
• CPC Class Codes: C04B 2235/785 Submicron sized grains, i.e. from 0,1 to 1 micron
• CPC Class Codes: C04B 2235/786 Micrometer sized grains, i.e. from 1 to 100 micron
• CPC Class Codes: C04B 2235/96 Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
• CPC Class Codes: C04B 35/10 based on aluminium oxide
• CPC Class Codes: C04B 35/64 Burning or sintering processes C04B33/32 takes precedence ; powder metallurgy B22F
• CPC Class Codes: C04B 38/00 Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof treating slag with gases or gas generating material C04B5/06 ; expanded graphite C04B35/536
• CPC Class Codes: C04B 41/009 characterised by the material treated
• CPC Class Codes: C04B 41/4535 applied as a solution, emulsion, dispersion or suspension
• CPC Class Codes: C04B 41/455 the coating or impregnating process including a chemical conversion or reaction
• CPC Class Codes: C04B 41/457 Non-superficial impregnation or infiltration of the substrate
• CPC Class Codes: C04B 41/5033 Chromium oxide
• CPC Class Codes: C04B 41/87 : Ceramics

Abstract

A doped ceramic material comprising: a first layer comprising ceramic material and an amount of dopant, a second layer comprising the ceramic material, and a transitional layer connecting the first layer and the second layer. The transitional layer comprises the dopant in an amount which decreases in a direction from the first layer to the second layer. A method of forming the doped ceramic material is also disclosed.

Claims

1. A doped ceramic material comprising:

(a) a first layer comprising ceramic material and an amount of dopant,

(b) a second layer comprising the ceramic material, and

(c) a transitional layer connecting the first layer and the second layer, said transitional layer comprising the dopant in an amount which decreases in a direction from the first layer to the second layer.

2. A doped ceramic material according to claim 1, wherein the ceramic material is formed from at least two elements selected from the group consisting of:

Group IIIA elements, Group IVA elements, Group IVB elements, Group VA elements and Group VIA elements of the periodic table of elements.

3. A doped ceramic material according to claim 2, wherein the ceramic material is selected from the group consisting of SiC, Si₃N₄, Al₂O₃, AlN, ZrO₂, SiO₂ and composites thereof.

4. A doped ceramic material according to claim 3, wherein the ceramic material is Al₂O₃.

5. A doped ceramic material according to claim 1, wherein the dopant is a metal oxide.

6. A doped ceramic material according to claim 5, wherein the metal oxide is a transition metal oxide.

7. A doped ceramic material according to claim 6, wherein the transition metal oxide is chromium oxide (Cr₂O₃).

8. A doped ceramic material according to claim 1, wherein the amount of dopant in the first layer is selected from the group consisting of:

about 0.1 mol % to about 5 mol %;

about 0.3 mol % to about 5 mol %;

about 0.6 mol % to about 5 mol %;

about 1 mol % to about 5 mol %;

about 2 mol % to about 5 mol %;

about 3 mol % to about 5 mol %;

about 4 mol % to about 5 mol %;

about 0.1 mol % to about 4 mol %;

about 0.1 mol % to about 3 mol %;

about 0.1 mol % to about 2 mol %;

about 0.1 mol % to about 1 mol %;

about 0.1 mol % to about 0.6 mol %; and

about 0.1 mol % to about 0.3 mol %.

9. A doped ceramic material according to claim 1, wherein the second layer has substantially no dopant.

10. A doped ceramic material according to claim 1, wherein the doped ceramic material has a sintered relative density of at least about 97%.

11. A doped ceramic material according to claim 1, wherein the doped ceramic material has an average grain size selected from the group consisting of:

about 0.5 μ

m to about 5 μ

m;

about 0.5 μ

m to about 4 μ

m;

about 0.5 μ

m to about 3 μ

m;

about 0.5 μ

m to about 2 μ

m;

about 0.5 μ

m to about 1 μ

m;

about 1 μ

m to about 5 μ

m;

about 2 μ

m to about 5 μ

m;

about 3 μ

m to about 5 μ

m; and

about 4 μ

m to about 5 μ

m.

12. A doped ceramic material according to claim 1, wherein the doped ceramic material has a surface hardness of at least about 17 GPa.

13. A doped ceramic material according to claim 1, wherein the doped ceramic material has a fracture toughness of at least about 3.6 MPa(m^1/2).

14. A method of forming a doped ceramic material comprising the steps of:

(a) providing a high sinterability ceramic preform having a first layer, a second layer and a transitional layer connecting the first layer and the second layer;

(b) doping the first layer of the ceramic preform with an amount of dopant to thereby cause the amount of dopant in said transitional layer to decrease in a direction from the first layer to the second; and

(c) sintering the ceramic preform at a temperature for a period of time to form the doped ceramic material.

15. A method of forming a doped ceramic material according to claim 14, wherein the first layer, the second layer and the transitional layer form an integral structure.

16. A method of forming a doped ceramic material according to claim 14, wherein the providing step (a) comprises the steps of:

(a1) casting a suspension of ceramic powder into a mould to form a green body;

(a2) pre-firing the green body at a temperature for a period of time to form the high sinterability ceramic preform.

17. A method of forming a doped ceramic material according to claim 16, wherein the casting step (al) comprises the step of:

(a3) selecting an average particle size of the ceramic powder from the group consisting of;

about 0.05 μ

m to about 1 μ

m;

about 0.05 μ

m to about 0.8 μ

m;

about 0.05 μ

m to about 0.6 μ

m;

about 0.05 μ

m to about 0.4 μ

m;

about 0.05 μ

m to about 0.2 μ

m;

about 0.05 μ

m to about 0.1 μ

m;

about 0.1 μ

m to about 1 μ

m;

about 0.2 μ

m to about 1 μ

m;

about 0.4 μ

m to about 1 μ

m;

about 0.6 μ

m to about 1 μ

m;

about 0.8 μ

m to about 1 μ

m; and

about 0.1 μ

m to about 0.2 μ

m.

18. A method of forming a doped ceramic material according to claim 16, wherein the pre-firing step (a2) comprises the step of:

(a4) pre-firing the green body at a temperature selected from the group consisting of;

about 700°

C. to about 1100°

C.;

about 800°

C. to about 1100°

C.;

about 9000°

C. to about 1100°

C.;

about 1000°

C. to about 1100°

C.;

about 700°

C. to about 1000°

C.;

about 700°

C. to about 900°

C.; and

about 700°

C. to about 800°

C.

19. A method of forming a doped ceramic material according to claim 16, wherein the pre-firing step (a2) comprises the step of:

(a5) pre-firing the green body for a time period selected from the group consisting of;

about 1 hour to about 4 hours;

about 2 hours to about 4 hours;

about 3 hours to about 4 hours;

about 1 hour to about 3 hours; and

about 1 hour to about 2 hours.

20. A method of forming doped ceramic material according to claim 14, wherein the providing step (a) comprises the step of:

(a6) selecting the ceramic preform from compounds formed from at least two elements selected from the group consisting of;

Group IIIA elements, Group IVA elements, Group IVB elements, Group VA elements and Group VIA elements of the periodic table of elements.

21. A method of forming a doped ceramic material according to claim 20, wherein the selecting step (a6) comprises the step of:

(a7) selecting the ceramic preform from the group consisting of SiC, Si₃N₄, Al₂O₃, AlN, ZrO₂, SiO₂ and composites thereof.

22. A method of forming a doped ceramic material according to claim 14, wherein the providing step (a) comprises the steps of:

(a8) shaping the ceramic preform.

23. A method of forming a doped ceramic material according to claim 21, wherein the selecting step (a7) comprises the step of:

(a7) selecting Al₂O₃ as the ceramic preform.

24. A method of forming a doped ceramic material according to claim 14, wherein the doping step (b) comprises the step of:

(b1) selecting a metal oxide as the dopant.

25. A method of forming a doped ceramic material according to claim 24, wherein the selecting step (b1) comprises the step of:

(b2) selecting a transition metal oxide as the metal oxide.

26. A method of forming a doped ceramic material according to claim 25, wherein the selecting step (b2) comprises the step of:

(b3) selecting chromium oxide (Cr₂O₃) as the transition metal oxide.

27. A method of forming a doped ceramic material according to claim 14, wherein the doping step (b) comprises the step of:

(b4) selecting the amount of dopant in the first layer from the group consisting of;

about 0.1 mol % to about 5 mol %;

about 0.3 mol % to about 5 mol %;

about 0.6 mol % to about 5 mol %;

about 1 mol % to about 5 mol %;

about 2 mol % to about 5 mol %;

about 3 mol % to about 5 mol %;

about 4 mol % to about 5 mol %;

about 0.1 mol % to about 4 mol %;

about 0.1 mol % to about 3 mol %;

about 0.1 mol % to about 2 mol %;

about 0.1 mol % to about 1 mol %;

about 0.1 mol % to about 0.6 mol %; and

about 0.1 mol % to about 0.3 mol %.

28. A method of forming a doped ceramic material according to claim 14, wherein the doping step (b) comprises the step of:

(b5) selecting the amount of dopant in the second layer as about 0 mol %.

29. A method of forming a ceramic material according to claim 14, wherein the doping step (b) comprises the step of:

(b6) immersing the ceramic preform into a solution having a selected concentration of the dopant for a selected period of time to dope the first layer with the selected amount of dopant and to cause infiltration of the dopant into the ceramic preform.

30. A method of forming a ceramic material according to claim 29, wherein the immersing step (b6) comprises the step of:

(b7) immersing the ceramic preform into a solution of dopant for a period of time selected from the group consisting of;

about 15 minutes to about 5 hours;

about 30 minutes to about 5 hours;

about 1 hour to about 5 hours;

about 2 hours to about 5 hours;

about 3 hours to about 5 hours;

about 4 hours to about 5 hours;

about 15 minutes to about 4 hours;

about 15 minutes to about 3 hours;

about 15 minutes to about 2 hours;

about 15 minutes to about 1 hour; and

about 15 minutes to about 30 minutes.

31. A method of forming a ceramic material according to claim 29, wherein the immersing step (b6) comprises the step of:

(b8) immersing the ceramic preform in a saturated solution of the dopant.

32. A method of forming a ceramic material according to claim 14, wherein said sintering step (c) comprises the step of:

(c1) sintering the ceramic preform at a temperature selected from the group consisting of;

about 1200°

C. to about 1600°

C.;

about 1200°

C. to about 1500°

C.;

about 1200°

C. to about 1400°

C.;

about 1200°

C. to about 1300°

C.;

about 1300°

C. to about 1600°

C.;

about 1400°

C. to about 1600°

C.;

about 1500°

C. to about 1600°

C.; and

about 1350°

C. to about 1550°

C.

33. A method of forming a ceramic material according to claim 14, wherein the sintering step (c) comprises the step of:

(c2) sintering the ceramic preform for a period of time selected from the group consisting of;

about 1 hour to about 24 hours;

about 5 hours to about 24 hours;

about 10 hours to about 24 hours;

about 15 hours to about 24 hours;

about 20 hours to about 24 hours;

about 1 hour to about 20 hours;

about 1 hour to about 15 hours;

about 1 hour to about 10 hours; and

about 1 hour to about 5 hours.

34. A method of forming a ceramic material according to claim 14, wherein the sintering step (c) comprises the step of:

(c3) sintering the ceramic preform in a vacuum.

35. A method of forming a ceramic material according to claim 14, wherein the sintering step (c) comprises the step of:

(c4) sintering the ceramic preform in an environment of gases selected from the group consisting of;

oxygen gas, nitrogen gas, argon gas, air and combinations thereof.

36. A chromium oxide (Cr₂O₃) doped alumina (Al₂O₃) material comprising:

(a) a first layer comprising Al₂O₃ and an amount of Cr₂O₃,

(b) a second layer comprising Al₂O₃, and

(c) a transitional layer connecting the first layer and the second layer, said transitional layer comprising Cr₂O₃ in an amount which decreases in a direction from the first layer to the second layer.

37. A method of forming Chromium Oxide (Cr₂O₃) doped alumina (Al₂O₃) material comprising the steps of:

(a) providing a high sinterability Al₂O₃ preform having a first layer, a second layer and a transitional layer connecting the first layer and the second layer;

(b) doping the first layer with an amount of Cr₂O₃ to thereby cause the amount of Cr₂O₃ in said transitional layer to decrease in a direction from the first layer to the second; and

(c) sintering the Al₂O₃ preform at a temperature for a period of time to form the Cr₂O₃ doped Al₂O₃ material.