Spherical carbon allotropes for lubricants
Carbon materials having carbon aggregates, where the aggregates include carbon nanoparticles and no seed particles, are disclosed. In various embodiments, the nanoparticles include graphene, optionally with multi-walled spherical fullerenes and/or another carbon allotrope. In various embodiments, the nanoparticles and aggregates have different combinations of: a Raman spectrum with a 2D-mode peak and a G-mode peak, and a 2D/G intensity ratio greater than 0.5, a low concentration of elemental impurities, a high Brunauer-Emmett and Teller (BET) surface area, a large particle size, and/or a high electrical conductivity. Methods are provided to produce the carbon materials.
1. A lubricant comprising:
a liquid; and
carbon aggregates within the liquid, each of the carbon aggregates including a plurality of carbon nanoparticles, wherein each of the plurality of carbon nanoparticles comprises:
at least two connected multi-walled spherical fullerenes; and
one or more layers of graphene coating the at least two connected multi-walled spherical fullerenes.
2. The lubricant of claim 1 , wherein the surface area of the carbon aggregates is from 10 m 2 /g to 200 m 2 /g, when measured via a Brunauer-Emmett-Teller (BET) method with nitrogen as the adsorbate.
3. The lubricant of claim 1 , wherein the carbon aggregates, when compressed, have an electrical conductivity from 500 S/m to 20,000 S/m.
4. The lubricant of claim 1 , wherein the carbon aggregates are post-processed using a method selected from the group consisting of milling, grinding, and exfoliating.
5. The lubricant of claim 1 , wherein a median size of the carbon aggregates is from 1 micron to 100 microns.
6. The lubricant of claim 1 , wherein a percentage of carbon to other elements, except hydrogen, in the carbon aggregates is greater than 99%.
7. The lubricant of claim 1 , wherein:
a Raman spectrum of the carbon aggregate using 532 nm incident light has a first Raman peak at approximately 1350 cm −1 and a second Raman peak at approximately 1580 cm −1 ; and
a ratio of an intensity of the first Raman peak to an intensity of the second Raman peak is from 0.9 to 1.1.
8. The lubricant of claim 1 , wherein:
the multi-walled spherical fullerenes do not comprise a seed particle or a void at the center of the multi-walled spherical fullerenes.
9. The lubricant of claim 1 , wherein:
the ratio of graphene to multi-walled spherical fullerenes in the carbon aggregates is from 10% to 80%.
10. The lubricant of claim 1 , wherein:
the lubricant is for high-speed applications, high-stress applications, high-temperature environments, high-thermal conductivity applications, or anti-stiction applications.
11. The lubricant of claim 1 , wherein the carbon aggregates are post-processed using a method selected from the group consisting of annealing, sintering, and steaming.
12. The lubricant of claim 1 , wherein the carbon aggregates are post-processed using a method selected from the group consisting of filtering and lypolizing.
13. The lubricant of claim 1 , wherein the carbon aggregates are post-processed using a method selected from the group consisting of doping and adding elements.
14. The lubricant of claim 1 , wherein the carbon aggregates are produced using a process comprising:
flowing a process gas into a reaction zone;
cracking the process gas in the reaction zone using a microwave plasma;
reacting the cracked molecules to form carbon aggregates, each carbon aggregate comprising at least two connected multi-walled spherical fullerenes coated in layers of graphene; and
collecting the carbon aggregates.
15. The lubricant of claim 14 , wherein:
the flow rate of the process gas is from 1 slm to 1000 slm; and
the carbon aggregates are formed at a production rate from 0.1 kg/hr to 100 kg/hr.
16. The lubricant of claim 14 , wherein:
the flow rate of the process gas is from 1 L/min to 100 L/min; and
the carbon aggregates are formed at a production rate from 0.1 g/hr to 15 g/hr.
17. The lubricant of claim 14 , wherein the process gas comprises methane.
18. The lubricant of claim 14 , wherein, after the carbon aggregates are collected, the carbon aggregates are post-processed by annealing at a temperature from 1000° C. to 2200° C. in an inert atmosphere for a duration from 60 minutes to 600 minutes.