Graphite intercalation and exfoliation process
The invention relates to expanded graphite and methods of making the graphite and products that can be made from the graphite made from the inventive process. The invention includes the step of introducing a fluid into at least one of a plurality of interstices of graphite flake, wherein the fluid comprises at least one of a sub-critical point fluid, a near critical point fluid, or a supercritical fluid. The graphite flake is also intercalated with an intercalant and optionally an oxidizing agent. The invention may further include novel techniques of exfoliating the graphite. The invention may be practiced to make nano-sized graphite particles and also graphite composites. Preferred composites which may be made in accordance with the invention include conductive polymeric composites (thermally or electrically), paint composites, battery composites, capacitor composites, and pollution abatement catalyst support composites.
1. A method of modifying graphite comprising:
introducing an intercalant into at least one interstice of at least one flake of natural graphite; and
introducing a supercritical fluid into said at least one interstices of said flake.
2. The method according to claim 1 wherein said fluid comprises at least one of carbon dioxide, water, and helium.
3. The method according to claim 1 wherein said introducing said intercalant further Comprises introducing an oxidizing agent.
4. The method according to claim 1 further comprising heating said flake to a temperature of about 700° C. to about 1200° C.
5. The method according to claim 1 wherein said introducing of said fluid occurred in a pressurized vessel having an internal pressure greater than atmospheric pressure and further comprising reducing said internal pressure of said vessel.
6. The method according to claim 1 further comprising exfoliating said flake at a maximum temperature of less than about 700° C.
7. The method according to claim 1 wherein said fluid in said interstices of said flake occupies a predetermined volume within said interstices, further comprising increasing said volume occupied by said fluid.
8. The method according to claim 1 wherein a temperature of said introducing of said intercalant comprises at least a temperature associated with a triple point of said fluid and no more than a temperature associated with a supercritical point of said fluid.
9. The method according to claim 1 wherein a pressure of said introducing of said intercalant comprises at least a pressure associated with a triple point of said fluid and no more than a pressure associated with a supercritical point of said fluid.
10. The method according to claim 1 wherein a temperature of said introducing of said intercalant comprises at least a temperature associated with a supercritical point of said fluid and a pressure associated with said supercritical point of said fluid.
11. The method according to claim 1 wherein said discharging comprises spraying said flake and said fluid from said vessel.
12. The method according to claim 1 further comprising exfoliating said flake and wherein said steps of introducing said intercalant, introducing said fluid, and said exfoliating occur substantially at about the same time.
13. The method according to claim 3 wherein said oxidizing agent comprises ozone.
14. The method according to claim 5 wherein said reducing said pressure comprises recirculating said flake and said fluid into said vessel.
15. The method according to claim 1 further comprising blending an effective amount of said flake with a polymeric material, thereby forming a graphite-polymeric composite having a loading rate of less than about 20%.
16. The method according to claim 1 wherein said intercalating step comprises no more than about stage 5 .
17. The method according to claim 1 further comprising washing said graphite.
18. A method of making at least one nano-sized flexible graphite particle comprising:
introducing into at least one flake of natural graphite an intercalant; and
introducing a supercritical fluid into at least one of a plurality of interstices of said flake.
19. The method according to claim 18 wherein said fluid comprises at least one of supercritical water oxidation, supercritical carbon dioxide, supercritical helium, and supercritical water.
20. The method according to claim 18 further comprising heating said flake to a temperature of about 700° C. to about 1200° C.
21. The method according to claim 18 wherein said introducing of said fluid occurred in a pressurized vessel having an internal pressure of greater than atmospheric pressure and further comprising reducing said internal pressure of said vessel.
22. The method according to claim 18 further comprising exfoliating said flake at a maximum temperature of less than about 700° C.
23. The method according to claim 18 wherein said fluid in said interstices of said flake occupies a predetermined volume within said interstices, further comprising increasing said volume occupied by said fluid.
24. The method according to claim 18 wherein a temperature of said introducing of said intercalant comprises at least a temperature associated with a triple point of said fluid.
25. The method according claim 24 wherein a pressure of said introducing of said intercalant comprises more than atmospheric pressure and up to about a pressure associated with a triple point of said fluid.
26. The method according to claim 21 wherein said reducing said pressure comprises discharging said flake and said fluid from said vessel.
27. The method according to claim 18 further comprising blending an effective amount of said flake with a polymeric material, thereby forming a graphite-polymeric composite having a loading rate of less than about 20%.
28. The method according to claim 1 further comprising blending an effective amount of said flake with a polymeric material, thereby forming a graphite-polymeric composite having a loading rate of at least about 70%.
29. The method according to claim 18 further comprising blending an effective amount of said flake with a polymeric material, thereby forming a graphite-polymeric composite having a loading rate of at least about 70%.