Methods of fabricating polycrystalline diamond, and cutting elements and earth-boring tools comprising polycrystalline diamond

1. A method of fabricating polycrystalline diamond, comprising:

functionalizing surfaces of carbon-free nanoparticles comprising a ceramic material with one or more functional groups;

combining the functionalized nanoparticles with diamond nanoparticles and diamond grit to form a particle mixture; and

subjecting the particle mixture to high pressure and high temperature (HPHT) conditions to form inter-granular bonds between the diamond nanoparticles and the diamond grit.

2. The method of claim 1 , wherein functionalizing the surfaces of the carbon-free nanoparticles with one or more functional groups comprises functionalizing the surfaces of the carbon-free nanoparticles with methyl functional groups.

3. The method of claim 1 , wherein functionalizing the surfaces of the carbon-free nanoparticles with one or more functional groups comprises functionalizing the surfaces of the carbon-free nanoparticles with acetylene functional groups.

4. The method of claim 1 , further comprising selecting the carbon-free nanoparticles to comprise one or more of an oxide and a nitride.

5. The method of claim 1 , further comprising selecting the carbon-free nanoparticles to comprise alumina or magnesia.

6. The method of claim 1 , wherein combining the functionalized nanoparticles with the diamond nanoparticles and the diamond grit to form the particle mixture comprises:

suspending the functionalized nanoparticles and the diamond nanoparticles in a liquid to form a suspension; and

drying the suspension.

7. The method of claim 6 , wherein drying the suspension comprises one or more of spray drying, freeze drying, and flash drying the suspension.

8. The method of claim 6 , further comprising suspending the diamond grit in the liquid.

9. The method of claim 6 , wherein drying the suspension comprises drying the suspension to form a powder product.

10. A method of fabricating polycrystalline diamond, comprising:

functionalizing surfaces of carbon-free nanoparticles with one or more functional groups;

combining the functionalized nanoparticles with diamond nanoparticles and diamond grit to form a particle mixture, the combining comprising:

suspending the functionalized nanoparticles and the diamond nanoparticles in a liquid to form a suspension;

drying the suspension to form a powder product; and

mixing the powder product with the diamond grit to form the particle mixture; and

subjecting the particle mixture to high pressure and high temperature (HPHT) conditions to form inter-granular bonds between the diamond nanoparticles and the diamond grit.

11. The method of claim 10 , further comprising milling the particle mixture prior to subjecting the particle mixture to the HPHT conditions.

12. The method of claim 9 , further comprising milling the powder product.

13. The method of claim 1 , wherein subjecting the particle mixture to the HPHT conditions comprises subjecting the particle mixture to a temperature of at least about 1400° C. and a pressure of at least about 5.0 GPa.

14. A cutting element for use in an earth-boring tool, the cutting element comprising a polycrystalline diamond material formed by a method comprising:

functionalizing surfaces of carbon-free nanoparticles comprising a ceramic material with one or more functional groups;

combining the functionalized nanoparticles with diamond nanoparticles and diamond grit to form a particle mixture; and

subjecting the particle mixture to high pressure and high temperature (HPHT) conditions to form inter-granular bonds between the diamond nanoparticles and the diamond grit.

15. The cutting element of claim 14 , wherein functionalizing the surfaces of the carbon-free nanoparticles with one or more functional groups comprises functionalizing the surfaces of the carbon-free nanoparticles with methyl or acetylene functional groups.

16. An earth-boring tool comprising a cutting element, the cutting element comprising a polycrystalline diamond material formed by a method comprising:

functionalizing surfaces of carbon-free nanoparticles comprising a ceramic material with one or more functional groups;

combining the functionalized nanoparticles with diamond nanoparticles and diamond grit to form a particle mixture; and

subjecting the particle mixture to high pressure and high temperature (HPHT) conditions to form inter-granular bonds between the diamond nanoparticles and the diamond grit.

17. The earth-boring tool of claim 16 , wherein the earth-boring tool comprises an earth-boring rotary drill bit.