Pitch-based carbon foam heat sink with phase change material

• US 6,399,149 B1
• Filed: 01/24/2000
• Issued: 06/04/2002
• Est. Priority Date: 09/02/1997
• Status: Expired due to Term

• Current Assignee: UT-Battelle LLC
• Original Assignee: UT-Battelle LLC
• Inventors: Klett, James W., Burchell, Timothy D.
• Primary Examiner(s): BARR, MICHAEL E
• Application Number:
  US09/489,799
• Time in Patent Office: 862 Days
• Field of Search: 427/243, 427/244, 427/230, 427/430.1
• US Class Current: 427/230
• CPC Class Codes: B32B 2266/04 Inorganic
• CPC Class Codes: B32B 2305/022 Foam
• CPC Class Codes: B32B 2309/68 Vacuum
• CPC Class Codes: B32B 5/18 characterised by features of a layer of foamed material
• 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: C09K 5/06 the change of state being from liquid to solid or vice versa
• CPC Class Codes: F24F 5/0035 using evaporation
• CPC Class Codes: F28D 20/023 the latent heat storage material being enclosed in granular particles or dispersed in a porous, fibrous or cellular structure
• CPC Class Codes: F28D 5/00 Heat-exchange apparatus having stationary conduit assemblies for one heat-exchange medium only, the media being in contact with different sides of the conduit wall, using the cooling effect of natural or forced evaporation
• CPC Class Codes: F28F 13/003 by using permeable mass, perforated or porous materials F28F13/18 takes precedence
• CPC Class Codes: Y02B 30/54 Free-cooling systems
• CPC Class Codes: Y02E 60/14 Thermal energy storage
• CPC Class Codes: Y02P 20/10 Process efficiency
• CPC Class Codes: Y10S 428/913 Material designed to be responsive to temperature, light, moisture
• CPC Class Codes: Y10T 428/233 Foamed or expanded material encased
• CPC Class Codes: Y10T 428/249954 With chemically effective material or specified gas other than air, N, or carbon dioxide in void-containing component
• CPC Class Codes: Y10T 428/249956 Void-containing component is inorganic
• CPC Class Codes: Y10T 428/249994 Composite having a component wherein a constituent is liquid or is contained within preformed walls [e.g., impregnant-filled, previously void containing component, etc.]
• CPC Class Codes: Y10T 428/2991 Coated

Abstract

A process for producing a carbon foam heat sink is disclosed which obviates the need for conventional oxidative stabilization. The process employs mesophase or isotropic pitch and a simplified process using a single mold. The foam has a relatively uniform distribution of pore sizes and a highly aligned graphic structure in the struts. The foam material can be made into a composite which is useful in high temperature sandwich panels for both thermal and structural applications. The foam is encased and filled with a phase change material to provide a very efficient heat sink device.

Claims

1. A process comprising:

(1) heating a liquified pitch under non-oxidizing, superatmospheric conditions below about 500°

C. sufficient to produce a carbon foam;

(2) cooking said carbon foam by heating said carbon foam at a temperature above about 500°

C. under non-oxidizing, superatmospheric conditions;

(3) heating the coked carbon foam under conditions sufficient to produce an essentially graphitic carbon foam; and

(4) at least partially filling porous regions in the essentially graphitic carbon foam with a phase change material.

2. The process of claim 1 wherein the temperature in step (2) is held constant for at least 15 minutes.

3. The process of claim 1 wherein the pressure is held substantially constant during each of steps (1) and (2).

4. The process of claim 3 wherein the pressure in steps (1) and (2) is substantially identical.

5. The process of claim 1 wherein the temperature during the cooking in step (2) is no more than about 1000°

C.

6. The process of claim 5 wherein at least some foaming in step (1) occurs at a temperature between about 420 and about 480°

C. and wherein said pitch is selected from the group consisting of liquified mesophase petroleum pitch and liquified mesophase synthetic pitch.

7. The process of claim 1 wherein said heating under conditions sufficient to produce an essentially graphitic carbon foam in step (3) includes a temperature in the range of about 2500°

to 2800°

C.

8. The process of claim 1 wherein said heating in step (3) comprises heating the coked carbon foam from step (2) at a temperature above that for coking in step (2) to produce a carbonized carbon foam, followed by further heating at a yet higher temperature to produce said essentially graphitic carbon foam.

9. The process of claim 1 wherein between steps (2) and (3) the cooked carbon foam is cooled.

10. The process of claim 1 wherein said pitch is a liquified mesophase pitch.

11. The process of claim 1 wherein said pitch is a liquified pitch of petroleum or synthetic origin.

12. The process of claim 1 wherein said pitch is selected from the group consisting of liquefied mesophase petroleum pitch and liquified mesophase synthetic pitch.

13. The process of claim 3 wherein said pitch is a liquified mesophase petroleum pitch.

14. The process of claim 1 wherein at least some foaming in step (1) occurs at a temperature between about 4200 and about 480°

C.

15. The process of claim 14 wherein said pitch is a liquified mesophase pitch.

16. The process of claim 14 wherein said pitch is a liquified pitch of petroleum or synthetic origin.

17. The process of claim 1 wherein (a) at least some foaming in step (1) occurs at a temperature between about 420°

and about 480°

C. and (b) the temperature during the cooking in step (2) is no more than about 1000°

C. and is held at a substantially constant value for at least 15 minutes.

18. The process of claim 17 wherein said pitch is selected from the group consisting of liquified mesophase petroleum pitch and liquified mesophase synthetic pitch.

19. The process of claim 17 wherein said pitch is a liquified mesophase pitch.

20. The process of claim 7 yielding in step (3) an essentially graphitic carbon foam having a bulk thermal conductivity between about 58 and 106 W/m·

°

K.

21. The process of claim 7 yielding in step (3) an essentially graphitic carbon foam having a specific thermal conductivity greater than four times that of copper.

22. The process of claim 7 yielding in step (3) an essentially graphitic carbon foam having a specific thermal conductivity greater than copper.

23. The process of claim 7 yielding in step (3) an essentially graphitic carbon foam characterized by an X-ray diffraction pattern substantially as depicted in FIG. 14.

24. The process of claim 7 to yielding in step (3) an essentially graphitic carbon foam characterized by an X-ray diffraction pattern exhibiting doublet peaks at 2θ

angles between 40 and 50 degrees.

25. The process of claim 7 yielding in step (3) an essentially graphitic carbon foam characterized by an X-ray diffraction pattern having an average d002 spacing of about 0.336.

26. The process of claim 25 wherein the average d002 spacing is 0.336.

27. The process of claim 20 wherein said pitch is a liquified mesophase pitch.

28. The process of claim 27 wherein at least some foaming in step (1) occurs at a temperature between about 420°

and 480°

C.

29. The process of claim 21 wherein said pitch is a liquified pitch of petroleum or synthetic origin.

30. The process of claim 29 wherein at least some foaming in step (1) occurs at a temperature between about 420°

and 480°

C. and the temperature during the cooking in step (2) is no more than about 1000°

C.

31. The process of claim 20 wherein said pitch is selected from the group consisting of liquified mesophase petroleum pitch and liquified mesophase synthetic pitch.

32. The process of claim 31 wherein at least some foaming in step (1) occurs at a temperature between about 420 and 480 C. and the pressure is held substantially constant during each of steps (1) and (2).

33. The process of claim 21 wherein said pitch is a liquified mesophase petroleum pitch.

34. The process of claim 33 wherein (a) at least some foaming in step (1) occurs at a temperature between about 420°

and 480°

C., (b) the temperature during the cooking in step (2) is no more than about 1000°

C. and is held at a substantially constant value for at least 15 minutes; and

(c) the pressure is held to substantially the same constant value in steps (1) and (2).

35. The process of claim 20 wherein at least some foaming in step (1) occurs at a temperature between about 420°

and 480°

C.

36. The process of claim 1 wherein the phase change material freezes at a temperature above 0°

C. but does not boil below room temperature.

37. The process of claim 1 wherein the phase change material changes phase from a solid to a liquid below 1800°

C. but remains in the liquid state up to a temperature as high as 1800°

C.

38. The process of claim 1 wherein the phase change material changes phase from a solid to a liquid below 1200°

C. but remains in the liquid state up to a temperature as high as 1200°

C.

39. The process of claim 1 wherein the phase change material is selected from the group consisting of water, acetic acid, germanium, germanium-silicon, and paraffin wax.

40. A process comprising at least partially filling the porous region of a thermally conductive, non-oxidatively stabilized, mesophase pitch-derived carbon foam with a phase change material.

41. The process of claim 40 wherein the carbon foam has a bulk thermal conductivity between about 58 and 106 W/m·

°

K.

42. The process of claim 40 wherein the carbon foam has a specific thermal conductivity greater than four times that of copper.

43. The process of claim 40 wherein the carbon foam has a specific thermal conductivity greater than copper.

44. The process of claim 40 wherein the carbon foam has a bulk thermal conductivity less than or equal to 106 W/m°

K.

45. The process of claim 40 wherein the carbon foam has a specific thermal conductivity of at least about 109 W·

cm³/m·

°

K.g.

46. The process of claim 40 wherein the carbon foam has a specific thermal conductivity of between about 109 and about 200 W·

cm³/m·

°

K.g.

47. The process of claim 40 wherein the carbon foam is characterized by an x-ray diffraction pattern substantially as depicted in FIG. 14.

48. The process of claim 40 wherein the carbon foam is characterized by an X-ray diffraction pattern having an average d002 spacing of about 0.336.

49. The process of claim 40 wherein the carbon foam is characterized by an X-ray diffraction pattern exhibiting doublet peaks at 2θ

angles between 40 and 50 degrees.

50. The process of claim 49 wherein the average d002 spacing of the X-ray diffraction pattern is 0.336.

51. The process of claim 40 wherein the carbon foam, when initially at a temperature of approximately 21°

C. and saturated with acetone, cools to a temperature of −

50°

C. in no more than about 4 minutes when under a reduced vacuum pressure of about 1.2 torr.

52. The process of claim 40 wherein the carbon foam, when initially at a temperature of approximately 21°

C. and saturated with ethanol, cools to a temperature of −

28°

C. in no more than about 6 minutes when under a reduced vacuum pressure of about 1.0 torr.

53. The process of claim 40 wherein the carbon foam, when initially at a temperature of approximately 21°

C. and saturated with water, cools to a temperature of −

5.5°

C. in no more than about 9 minutes when under a reduced vacuum pressure of about 29 torr.

54. The process of claim 40 wherein the carbon foam, when initially at a temperature of approximately 21°

C. and saturated with acetone, cools to a temperature of 0.50°

C. in no more than about 38 minutes when under ambient room temperature conditions.

55. The process of claim 40 wherein the carbon foam, when initially at a temperature of approximately 21°

C. and saturated with ethanol, cools to a temperature of 14°

C. in no more than about 38 minutes when under ambient room temperature conditions.

56. The process of claim 40 wherein the carbon foam, when initially at a temperature of approximately 21°

C. and saturated with water, cools to a temperature of 19°

C. in no more than about 38 minutes when under ambient room temperature conditions.