Patent Publication Number: US-10323463-B2

Title: Methods of making diamond tables, cutting elements, and earth-boring tools

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/493,777, filed Sep. 23, 2014, now U.S. Pat. No. 9,611,699, issued Apr. 4, 2017, which is a continuation of U.S. patent application Ser. No. 13/166,557, filed Jun. 22, 2011, now U.S. Pat. No. 8,840,693, issued Sep. 23, 2014. The subject matter of this application is related to the subject matter of provisional U.S. Patent Application Ser. No. 61/408,382, which was filed Oct. 29, 2010 and is titled “Graphene-Coated Diamond Particles, Polycrystalline Compacts, Drill Bits, and Compositions of Graphene-Coated Diamond Particles, and Methods of Forming Same,” the disclosure of each of which is incorporated herein in its entirety by this reference. The subject matter of this application is also related to the subject matter of nonprovisional U.S. patent application Ser. No. 13/283,021, now U.S. Pat. No. 9,103,173, issued Aug. 11, 2015, which was filed Oct. 27, 2011, now U.S. Pat. No. 9,103,173, which issued Aug. 11, 2015, which claims the benefit of provisional U.S. Patent Application Ser. No. 61/408,382. 
    
    
     FIELD 
     Embodiments of the disclosure relate generally to coated particles, methods of forming coated particles, and methods of forming polycrystalline compacts from coated particles. Specifically, embodiments of the disclosure relate to particles of superhard material that have nanoparticles coated thereon. 
     BACKGROUND 
     Superhard materials have proven to be useful in a wide variety of applications. For example, cutting elements used in earth-boring tools often include a polycrystalline diamond (PCD) material, which may be used to form polycrystalline diamond cutters (often referred to as “PDCs”). Such polycrystalline diamond cutting elements are conventionally formed by sintering and bonding together relatively small diamond grains or crystals under conditions of high temperature and high pressure in the presence of a catalyst (e.g., cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high temperature/high pressure (or “HTHP”) processes. The cutting element substrate may comprise a cermet material (i.e., a ceramic-metal composite material) comprising a plurality of particles of hard material in a metal matrix, such as, for example, cobalt-cemented tungsten carbide. In such instances, catalyst material in the cutting element substrate may be drawn into the diamond grains or crystals during sintering and catalyze formation of a diamond table from the diamond grains or crystals. In other methods, powdered catalyst material may be mixed with the diamond grains or crystals prior to sintering the grains or crystals together in an HTHP process. 
     Earth-boring tools for forming wellbores in subterranean earth formations that may include a plurality of cutting elements secured to a body include, for example, fixed-cutter earth-boring rotary drill bits (also referred to as “drag bits”). Such fixed-cutter bits include a plurality of cutting elements that are fixedly attached to a bit body of the drill bit, conventionally in pockets formed in blades and other exterior portions of the bit body. Other earth-boring tools may include rolling cone earth-boring drill bits, which include a plurality of cutters attached to bearing pins on legs depending from a bit body. The cutters may include cutting elements (sometimes called “teeth”) milled or otherwise formed on the cutters, which may include hardfacing on the outer surfaces of the cutting elements, or the cutters may include cutting elements (sometimes called “inserts”) attached to the cutters, conventionally in pockets formed in the cutters. Cutting elements that include superhard materials increase the useful life of the earth-boring tools to which they are attached because the superhard materials increase the strength and abrasion resistance of the tools. 
     Some superhard materials have desirable properties that render them useful in still other applications. For example, the high strength and abrasion resistance of such materials renders them useful in grinding, polishing, and machining applications. Increased thermal conductivity of some superhard materials renders them useful as particles dispersed in lubricants, such as motor and pump oils, because such lubricants often serve to cool the parts they lubricate. Furthermore, increased electrical conductivity of some superhard materials renders them useful as fillers in polymers and elastomers, where increased electrical conductivity in at least some portion of the polymers and elastomers is desirable. 
     Some attempts have been made to enhance or alter the properties of superhard materials through layering other materials thereon. For example,  Core - Shell Diamond as a Support for Solid - Phase Extraction and High - Performance Liquid Chromatigraphy,  82 Analytical Chem. 4448 (Jun. 1, 2010), by Gaurav Saini, David S. Jensen, Landon A. Wiest, Michael A. Vail, Andrew Dadson, Milton L. Lee, V. Shutthanandan, and Matthew R. Linford discloses, among other things, layer-by-layer deposition of an amine-containing polymer and nanodiamond on an amine functionalized microdiamond. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, various features and advantages of embodiments of the disclosure may be more readily ascertained from the following description of embodiments of the disclosure when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view of a core particle; 
         FIG. 2  depicts a cross-sectional view of the core particle of  FIG. 1  after being coated with a coating material; 
         FIG. 3  illustrates a cross-sectional view of the coated core particle of  FIG. 2  after nanoparticles have been disposed on the coating material; 
         FIG. 4  is a cross-sectional view of the coated core particle of  FIG. 3  after coating the nanoparticles with another coating; 
         FIG. 5  depicts a cross-sectional view of the coated core particle of  FIG. 4  after other nanoparticles have been disposed on the other coating; 
         FIG. 6  illustrates a cross-sectional view of an alternative embodiment of the nanoparticles shown in  FIG. 5 ; 
         FIG. 7  is a cross-sectional view of another embodiment of the coated core particle shown in  FIG. 5  wherein the other nanoparticles are disposed directly on the first nanoparticles; 
         FIG. 8  depicts a cross-sectional view of the coated core particle of  FIG. 5  after coating the other nanoparticles with yet another coating; 
         FIG. 9  illustrates a cross-sectional view of the coated core particle of  FIG. 8  after still other nanoparticles have been disposed on the yet other coating; 
         FIG. 10  is a cross-sectional view of the coated core particle of  FIG. 9  after coating the still other nanoparticles have been coated in a final coating; 
         FIG. 11  depicts a cross-sectional view of a mold that may be used to form a cutting element; 
         FIG. 12  illustrates a partial cutaway perspective view of a cutting element that may be attached to an earth-boring tool; and 
         FIG. 13  is a perspective view of an earth-boring tool to which cutting elements may be attached. 
     
    
    
     DETAILED DESCRIPTION 
     The illustrations presented herein are not meant to be actual views of any particular particle, cutting element, or earth-boring tool, but are merely idealized representations that are employed to describe the embodiments of the disclosure. Thus, the drawings are not necessarily to scale and relative dimensions may have been exaggerated for the sake of clarity. Additionally, elements common between figures may retain the same or similar numerical designation. 
     Embodiments of the disclosure relate to particles of superhard material that have nanoparticles coated thereon. In some embodiments, a coating material comprising an amine terminated group may be successively interposed between the particles and/or the nanoparticles. 
     The terms “earth-boring tool” and “earth-boring drill bit,” as used herein, mean and include any type of bit or tool used for drilling during the formation or enlargement of a wellbore in a subterranean formation and include, for example, fixed-cutter bits, rolling cone bits, impregnated bits, core bits, eccentric bits, bicenter bits, hybrid bits as well as reamers, mills, and other drilling bits and tools known in the art. 
     As used herein, the term “polycrystalline material” means and includes any structure comprising a plurality of grains (i.e., crystals) of material (e.g., superhard material) that are bonded directly together by inter-granular bonds. The crystal structures of the individual grains of the material may be randomly oriented in space within the polycrystalline material. 
     As used herein, the terms “inter-granular bond” and “interbonded” mean and include any direct atomic bond (e.g., covalent, metallic, etc.) between atoms in adjacent grains of superabrasive material. 
     As used herein, the term “superhard material” means and includes any material having a Knoop hardness value of about 3,000 Kg f /mm 2  (29,420 MPa) or more. Superhard materials include, for example, diamond and cubic boron nitride. Superhard materials may also be characterized as “superabrasive” materials. 
     As used herein, the terms “nanoparticle” and “nanoscale” mean and include any particle, such as, for example, a crystal or grain, having an average particle diameter of between about 1 nm and 500 nm. 
     As used herein, the term “tungsten carbide” means any material composition that contains chemical compounds of tungsten and carbon, such as, for example, WC, W 2 C, and combinations of WC and W 2 C. Tungsten carbide includes, for example, cast tungsten carbide, sintered tungsten carbide, and macrocrystalline tungsten carbide. 
     Referring to  FIG. 1 , a cross-sectional view of a core particle  100  is shown. The core particle  100  is shown having a circular cross-section for the sake of simplicity, but core particles  100  in practice may have cross-sections of any shape, including irregular shapes. The core particle  100  may comprise a superhard material. For example, the core particle  100  may comprise synthetic diamond, natural diamond, cubic boron nitride, or any superhard material known in the art. Thus, the core particle  100  may comprise a single grain of diamond, for example. The core particle  100  may comprise an average diameter of between 1 μm and 500 μm. The core particle  100  may be provided as one of a plurality of similar core particles  100 . Such a plurality of core particles  100  may be free of nanoscale particles. 
     An outer surface  102  of the core particle  100  may be modified by a surface treatment in some embodiments. For example, the outer surface  102  of the core particle  100  may be derivatized to exhibit a net negative charge or a net positive charge. Thus, a net charge may be imparted to the outer surface  102  of the core particle  100 . Surface treatment may be accomplished using, for example, corona treatment, plasma treatment, chemical vapor treatment, wet etch, ashing, primer treatment (e.g., polymer-based or organosilane primer treatments), and other surface treatments known in the art. 
     Referring to  FIG. 2 , a cross-sectional view of the core particle  100  of  FIG. 1  after being coated with a coating material  104  is shown. Though the coating material  104  is shown as a coating of uniform thickness covering the entire outer surface  102  of the core particle  100 , the coating material  104  may be of non-uniform thickness and may cover only a portion of the outer surface  102  of the core particle  100  in practice. The coating material  104  may carry a net charge opposite the net charge of the outer surface  102  of the core particle  100 , which may facilitate adhesion of the coating material  104  to the outer surface  102  of the core particle  100 , for example, by adsorption. The coating material  104  may comprise an amine terminated group. For example, the coating material  104  may comprise polyallylamine, polyethylenimine, polyethylenamine. As continuing examples, the coating material  104  may comprise a polyamine prepared by the polymerization of aziridene and including polyethylemeamines and polyethylenimines having a branched structure derived from aziridene and tris(aminoethyl)amine, a hyperbranched or dendrimeric polyamine such as polyamidoamine (PAMAM) dendrimer, a polyaminoacrylate such as poly(N,N-dimethylaminoethyl-(meth)acrylate), a copolymer thereof with an alkyl or aralkyl (meth)acrylate such as methyl (meth)acrylate, ethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, (meth)acrylonitrile, poly(N,N-dimethylaminoethyl-(meth)acrylate)-co-(methyl(meth)acrylate), and combinations comprising at least one of these. As a specific example, the coating material  104  may comprise polyethylenimine, which carries a net positive charge and is water soluble. 
     The coating material  104  may be disposed on the outer surface  102  of the core particle  100  by any of several well-known processes. For example, the coating material  104  may be disposed on the outer surface  102  of the core particle  100  by wet chemistry processes (e.g., dip coating, solid-gel processing, etc.), physical deposition processes (e.g., sputtering, also known as physical vapor deposition (PVD), etc.), chemical deposition processes (e.g., chemical vapor deposition (CVD), atomic layer deposition (ALD), etc.), or combinations of these. As a specific example, a plurality of core particles  100  that have been surface treated using a corona treatment to impart a net negative charge to the outer surfaces  102  of particles of the plurality of core particles  100  may be disposed in an aqueous solution of polyallylamine, which carries a net positive charge, and the polyallylamine may adhere to the outer surfaces  102  of particles of the plurality of core particles  100 . 
     Referring to  FIG. 3 , a cross-sectional view of the coated core particle  100  of  FIG. 2  after a plurality of nanoparticles  106  has been disposed on the coating material  104  is shown. Though the plurality of nanoparticles  106  is depicted as having a circular cross-section for the sake of simplicity, the plurality of nanoparticles  106  may comprise any shape, and specifically may have irregular shapes, in practice. In addition, though the plurality of nanoparticles  106  is depicted as being disposed on the coating material  104  at fairly regular intervals over the entire coating material  104 , the plurality of nanoparticles  106  may be disposed on the coating material  104  at irregular intervals and/or over only a portion of the coating material  104 . The plurality of nanoparticles  106  may comprise, for example, surface modified nanodiamonds, oxidized nanodiamonds, carbon nanotubes, nanographite, nanographene, other nanoscale non-diamond allotropes of carbon (e.g., amorphous carbon, fullerenes, carbon nanobuds, Lonsdaleite, etc.), nanoscale particles of BeO, and nanoscale particles comprising a Group VIIIA element (e.g., iron, cobalt, nickel, etc.), known in the art as catalyst materials. Thus, the material of the plurality of nanoparticles  106  may be the same as the material of the core particle  100  in some embodiments. In other embodiments, the plurality of nanoparticles  106  may comprise a different material from the material of the core particle  100 . In some embodiments, the plurality of nanoparticles  106  may comprise at least some nanoparticles  106  of one material (e.g., graphite), and at least some other nanoparticles  106  of another material (e.g., a Group VIIIA element catalyst material). 
     Prior to being deposited onto the coating material  104 , the plurality of nanoparticles  106  may be modified by a surface treatment in some embodiments. For example, an outer surface  108  of the plurality of nanoparticles  106  may be derivatized to exhibit a net charge opposite a net charge of the coating material  104 , which may be a net negative charge or a net positive charge. Surface treatment may be accomplished using, for example, any of the surface treatments described previously in connection with the core particle  100  and other surface treatments known in the art. By alternating the net charge carried by the successive components of the coated core particle  100 , each successive component (e.g., the core particle  100 , the coating material  104 , and the plurality of nanoparticles  106 ) may be adhered to its adjacent components using non-covalent intermolecular interactions (e.g., van der Waals forces) and mechanical interference. 
     The plurality of nanoparticles  106  may be disposed on the coating material  104  by, for example, dispersing the plurality of nanoparticles  106  in a continuous phase material to form a dispersion. The resulting dispersion may be, for example, a suspension, a colloid, or a solution, depending on the type of continuous phase material used and the material of the plurality of nanoparticles  106 . As a specific example, the plurality of nanoparticles  106  may comprise carbon nanotubes suspended in water. The plurality of nanoparticles  106  shown disposed on the coating material  104  in  FIG. 3  may represent only a small proportion of an overall plurality of nanoparticles  106  in the dispersion to ensure that a sufficient quantity of nanoparticles  106  is present for adhering to the coating material  104 . A plurality of core particles  100  at least partially coated with the coating material  104  may then be exposed to the dispersed plurality of nanoparticles  106  by disposing the plurality of coated core particles  100  in the dispersion. In some embodiments, the dispersion may then be agitated to circulate the plurality of coated core particles  100  and the plurality of nanoparticles  106  and increase the likelihood that at least some of the plurality of nanoparticles  106  may adhere to the coating material  104  disposed on the coated core particles  100 . As a result, at least some nanoparticles of the plurality of nanoparticles  106  may be disposed on and adhered to the coating material  104 , which is disposed on and adhered to the plurality of core particles  100 . 
     The plurality of nanoparticles  106  may impart desirable characteristics to the core particle  100 . Where the core particle  100  comprises diamond and the plurality of nanoparticles  106  comprises nanographite, for example, the plurality of nanoparticles  106  may increase the ability to lubricate, increase the electrical insulation, and increase the thermal insulation of the resulting coated core particle  100  as compared to the core particle  100  without any nanoparticles  106  coated thereon. Such a combination of characteristics may be desirable in, for example, a lubricant in which the coated core particles  100  may be dispersed. Thus, the core particles  100 , the coating materials  104 , and the nanoparticles  106  used will depend on the application for which they are intended and the properties of each. In some embodiments, a single application of coating material  104  and nanoparticles  106  may be sufficient. In other embodiments, the coated core particle  100  may undergo subsequent processing. 
     Referring to  FIG. 4 , a cross-sectional view of the coated core particle  100  of  FIG. 3  is shown after the plurality of nanoparticles  106  has been coated with a second coating material  104 ′. Though the second coating material  104 ′ is shown as a coating of uniform thickness covering the entire exposed outer surface  108  of the plurality of nanoparticles  106  and the underlying coating material  104 , the second coating material  104 ′ may be of non-uniform thickness and may cover only a portion of the exposed outer surfaces of components (e.g., the underlying coating material  104  and the plurality of nanoparticles  106 ) of the coated core particle  100  in practice. The second coating material  104 ′ may carry a net charge opposite the net charge of the outer surface  108  of the plurality of nanoparticles  106 , which may facilitate adhesion of the second coating material  104 ′ to the outer surface  108  of the plurality of nanoparticles  106 , for example, by adsorption. The second coating material  104 ′ may comprise an amine terminated group, such as, for example, any of the amine terminated group materials described previously in connection with the underlying coating material  104 . The second coating material  104 ′ may comprise the same material as the underlying coating material  104  in some embodiments. In other embodiments, the second coating material  104 ′ may comprise a different material from the underlying coating material  104 . 
     The second coating material  104 ′ may be disposed on the coated core particle  100  by any of several well-known processes. For example, the second coating material  104 ′ may be disposed on the coated core particle  100  by any of the processes described previously in connection with the underlying coating material  104 . As a specific example, a plurality of coated core particles  100  having a coating material  104  interposed between and adhered to each core particle  100  and a plurality of nanoparticles  106  that have been surface treated using a corona treatment to impart a net negative charge to the outer surface  108  of the plurality of nanoparticles  106  may be disposed in an aqueous solution of polyallylamine, which carries a net positive charge, and the polyallylamine may thereby be disposed on and adhered to the outer surface  108  of the plurality of nanoparticles  106 . 
     Referring to  FIG. 5 , a cross-sectional view of the coated core particle  100  of  FIG. 4  is shown after a second plurality of nanoparticles  106 ′ has been disposed on the second coating material  104 ′. Though the second plurality of nanoparticles  106 ′ is depicted as having a circular cross-section for the sake of simplicity, the second plurality of nanoparticles  106 ′ may comprise any shape, and specifically may have irregular shapes, in practice. In addition, though the second plurality of nanoparticles  106 ′ is depicted as being disposed on the second coating material  104 ′ at fairly regular intervals over the entire second coating material  104 ′, the second plurality of nanoparticles  106 ′ may be disposed on the second coating material  104 ′ at irregular intervals over only a portion of the second coating material  104 ′. The second plurality of nanoparticles  106 ′ may comprise any of the materials described previously in connection with the first plurality of nanoparticles  106 . Thus, the material of the second plurality of nanoparticles  106 ′ may be the same as the material of the core particle  100  and the material of the first plurality of nanoparticles  106  in some embodiments. In other embodiments, the second plurality of nanoparticles  106 ′ may comprise a different material from one or both of the materials of the core particle  100  and the first plurality of nanoparticles  106 . In some embodiments, the second plurality of nanoparticles  106 ′ may comprise at least some nanoparticles  106 ′ of one material (e.g., graphite), and at least some other nanoparticles  106 ′ of another material (e.g., a Group VIIIA element catalyst material). As a specific, non-limiting example, the core particle  100  shown in  FIG. 5  may comprise a diamond crystal, the first plurality of nanoparticles  106  may comprise nanographite, and the second plurality of nanoparticles  106 ′ may comprise nanographene. 
     Prior to being deposited onto the second coating material  104 ′, the second plurality of nanoparticles  106 ′ may be modified by a surface treatment in some embodiments. For example, an outer surface  110  of the second plurality of nanoparticles  106 ′ may be derivatized to exhibit a net charge opposite a net charge of the second coating material  104 ′, which may be a net negative charge or a net positive charge. Surface treatment may be accomplished using, for example, any of the surface treatments described previously in connection with the core particle  100  and other surface treatments known in the art. By alternating the net charge carried by the successive components of the coated core particle  100 , each successive component (e.g., the core particle  100 , the first coating material  104 , the first plurality of nanoparticles  106 , the second coating material  104 ′, and the second plurality of nanoparticles  106 ′) may be adhered to its adjacent components. 
     The second plurality of nanoparticles  106 ′ may be disposed on the second coating material  104 ′ by, for example, dispersing the second plurality of nanoparticles  106 ′ in a continuous phase material to form a dispersion. The resulting dispersion may be, for example, a suspension, a colloid, or a solution, depending on the type of continuous phase material used and the material of the second plurality of nanoparticles  106 ′. As a specific example, the second plurality of nanoparticles  106 ′ may comprise nanoscale particles of cobalt suspended in water. The second plurality of nanoparticles  106 ′ shown disposed on the second coating material  104 ′ in  FIG. 5  may represent only a small proportion of an overall second plurality of nanoparticles  106 ′ in the dispersion to ensure that a sufficient quantity of nanoparticles  106 ′ is present for adhering to the second coating material  104 ′. A plurality of coated core particles  100 , such as that shown in  FIG. 4 , may then be exposed to the dispersed second plurality of nanoparticles  106 ′ by disposing the plurality of coated core particles  100  in the dispersion. In some embodiments, the dispersion may then be agitated to circulate the plurality of coated core particles  100  and the second plurality of nanoparticles  106 ′ and increase the likelihood that at least some of the second plurality of nanoparticles  106 ′ may adhere to the second coating material  104 ′ disposed on the coated core particles  100 . As a result, at least some of the second plurality of nanoparticles  106 ′ may be disposed on and adhered to the second coating material  104 ′. 
     Referring to  FIG. 6 , a cross-sectional view of an alternative embodiment of the second plurality of nanoparticles  106 ′ of  FIG. 5  is shown. Specifically, the core particle  100  shown in  FIG. 6  may comprise a diamond crystal, the first plurality of nanoparticles  106  may comprise nanographite, and the second plurality of nanoparticles  106 ′ may comprise nanoscale particles of cobalt. Such a coated particle may be used as a precursor in a process for making a polycrystalline diamond material of a PDC cutting element. By locating nanoparticles comprising carbon allotropes and catalyst material proximate one another and proximate a larger core diamond particle, such a coated core particle  100  may facilitate the in situ nucleation of diamond grains. For example, the catalyst material of the coated core particle  100  may more easily access and catalyze in situ nucleation of diamond grains from the nanographite particles because the catalyst material does not have to flow, as from a cobalt-cemented carbide substrate, through the often tortuous path to the presence of the nanographite. U.S. Application Publication No. 2011/0031034, published Feb. 10, 2011, now U.S. Pat. No. 8,579,052, issued Nov. 12, 2013, the disclosure of which is incorporated by reference herein in its entirety, discloses that in situ nucleation of diamond grains may result in a stronger and more abrasion resistant polycrystalline diamond material. 
     Referring to  FIG. 7 , a cross-sectional view of another alternative embodiment of the coated core particle  100  shown in  FIG. 5  is shown. In this embodiment, the second plurality of nanoparticles  106 ′ is adhered directly to the first plurality of nanoparticles  106 . To facilitate adhesion, the second plurality of nanoparticles  106 ′ may be modified by a surface treatment. For example, the outer surface  110  of the second plurality of nanoparticles  106 ′ may be derivatized to exhibit a net charge opposite a net charge of the outer surface  108  of the first plurality of nanoparticles  106 , which may be a net negative charge or a net positive charge. Surface treatment may be accomplished using, for example, any of the surface treatments described previously in connection with the core particle  100  and other surface treatments known in the art. In embodiments where particles are adhered directly to one another, coating materials, such as, for example, the second coating material  104 ′ shown in  FIGS. 5 and 6  may be omitted. Thus, any of the coating materials  104  and  104 ′ described previously and any of those described subsequently herein may optionally be omitted where alternating net charge carried by the outer surface or other factors permit adjacent particles to be directly adhered to one another. 
     Referring to  FIG. 8 , a cross-sectional view of the coated core particle  100  of  FIG. 5  after coating the second plurality of nanoparticles  106 ′ with a third coating material  104 ″ is shown. Though the third coating material  104 ″ is shown as a coating of uniform thickness covering the entire exposed outer surface  110  of the second plurality of nanoparticles  106 ′ and the underlying second coating material  104 ′, the third coating material  104 ″ may be of non-uniform thickness and may cover only a portion of the exposed outer surfaces of components (e.g., the underlying second coating material  104 ′ and the second plurality of nanoparticles  106 ′) of the coated core particle  100  in practice. The third coating material  104 ″ may carry a net charge opposite the net charge of the outer surface  110  of the second plurality of nanoparticles  106 ′, which may facilitate adhesion of the third coating material  104 ″ to the outer surface  110  of the second plurality of nanoparticles  106 ′, for example, by adsorption. The third coating material  104 ″ may comprise an amine terminated group, such as, for example, any of the amine terminated group materials described previously in connection with the first coating material  104 . The third coating material  104 ″ may comprise the same material as the first coating material  104  and the second coating material  104 ′ in some embodiments. In other embodiments, the third coating material  104 ″ may comprise a different material from at least one of the first coating material  104  and the second coating material  104 ′. 
     The third coating material  104 ″ may be disposed on the coated core particle  100  by any of several well-known processes. For example, the third coating material  104 ″ may be disposed on the coated core particle  100  by any of the processes described previously in connection with the first coating material  104 . As a specific example, a plurality of coated core particles  100  having adhered thereto an outer second plurality of nanoparticles  106 ′ that have been surface treated using a corona treatment to impart a net negative charge to the outer surface  110  of the second plurality of nanoparticles  106 ′ may be disposed in an aqueous solution of polyallylamine, which carries a net positive charge, and the polyallylamine may thereby be disposed on and adhered to the outer surface  110  of the second plurality of nanoparticles  106 ′. 
     Referring to  FIG. 9 , a cross-sectional view of the coated core particle  100  of  FIG. 8  is shown after a third plurality of nanoparticles  106 ″ has been disposed on the third coating material  104 ″. Though the third plurality of nanoparticles  106 ″ is depicted as having a circular cross-section for the sake of simplicity, the third plurality of nanoparticles  106 ″ may comprise any shape, and specifically may have irregular shapes, in practice. In addition, though the third plurality of nanoparticles  106 ″ is depicted as being disposed on the third coating material  104 ″ at fairly regular intervals over the entire third coating material  104 ″, the third plurality of nanoparticles  106 ″ may be disposed on the third coating material  104 ″ at irregular intervals over only a portion of the third coating material  104 ″. The third plurality of nanoparticles  106 ″ may comprise any of the materials described previously in connection with the first plurality of nanoparticles  106 . Thus, the material of the third plurality of nanoparticles  106 ″ may be the same as the material of the core particle  100 , the material of the first plurality of nanoparticles  106 , and the material of the second plurality of nanoparticles  106 ′ in some embodiments. In other embodiments, the third plurality of nanoparticles  106 ″ may comprise a different material from one, some, or all of the materials of the core particle  100 , the first plurality of nanoparticles  106 , and the second plurality of nanoparticles  106 ′. In some embodiments, the third plurality of nanoparticles  106 ″ may comprise at least some nanoparticles  106 ″ of one material (e.g., graphite), and at least some other nanoparticles  106 ″ of another material (e.g., a Group VIIIA element catalyst material). As a specific non-limiting example, the core particle  100  shown in  FIG. 9  may comprise a diamond crystal, the first plurality of nanoparticles  106  may comprise nanographite, the second plurality of nanoparticles  106 ′ may comprise nanographene, and the third plurality of particles  106 ″ may comprise carbon nanotubes. 
     Prior to being deposited onto the third coating material  104 ″, the third plurality of nanoparticles  106 ″ may be modified by a surface treatment in some embodiments. For example, an outer surface  112  of the third plurality of nanoparticles  106 ″ may be derivatized to exhibit a net charge opposite a net charge of the third coating material  104 ″, which may be a net negative charge or a net positive charge. Surface treatment may be accomplished using, for example, any of the surface treatments described previously in connection with the core particle  100  and other surface treatments known in the art. By alternating the net charge carried by the successive components of the coated core particle  100 , each successive component (e.g., the core particle  100 , the first coating material  104 , the first plurality of nanoparticles  106 , the second coating material  104 ′, the second plurality of nanoparticles  106 ′, the third coating material  104 ″, and the third plurality of particles  106 ″) may be adhered to its adjacent components. 
     The third plurality of nanoparticles  106 ″ may be disposed on the third coating material  104 ″ by, for example, dispersing the third plurality of nanoparticles  106 ″ in a continuous phase material to form a dispersion. The resulting dispersion may be, for example, a suspension, a colloid, or a solution, depending on the type of continuous phase material used and the material of the third plurality of nanoparticles  106 ″. As a specific example, the third plurality of nanoparticles  106 ″ may comprise nanoscale particles of BeO suspended in water. The third plurality of nanoparticles  106 ″ shown disposed on the third coating material  104 ″ in  FIG. 9  may represent only a small proportion of an overall third plurality of nanoparticles  106 ″ in the dispersion to ensure that a sufficient quantity of nanoparticles  106 ″ is present for adhering to the third coating material  104 ″. A plurality of coated core particles  100 , such as coated core particle  100  shown in  FIG. 8 , may then be exposed to the dispersed third plurality of nanoparticles  106 ″ by disposing the plurality of coated core particles  100  in the dispersion. In some embodiments, the dispersion may then be agitated to circulate the plurality of coated core particles  100  and the third plurality of nanoparticles  106 ″ and increase the likelihood that at least some of the third plurality of nanoparticles  106 ″ may adhere to the third coating material  104 ″ disposed on the plurality of coated core particles  100 . As a result, at least some of the third plurality of nanoparticles  106 ″ may be disposed on and adhered to the third coating material  104 ″. 
     Referring to  FIG. 10 , a cross-sectional view of the coated core particle  100  of  FIG. 9  after coating the third plurality of nanoparticles  106 ″ with a fourth coating material  104 ′″ is shown. Though the fourth coating material  104 ′″ is shown as a coating of uniform thickness covering the entire exposed outer surface  112  of the third plurality of nanoparticles  106 ″ and the underlying third coating material  104 ″, the fourth coating material  104 ′″ may be of non-uniform thickness and may cover only a portion of the exposed outer surfaces of components (e.g., the underlying third coating material  104 ″ and the third plurality of nanoparticles  106 ″) of the coated core particle  100  in practice. The fourth coating material  104 ′″ may carry a net charge opposite the net charge of the outer surface  112  of the third plurality of nanoparticles  106 ″, which may facilitate adhesion of the fourth coating material  104 ′″ to the outer surface  112  of the third plurality of nanoparticles  106 ″, for example, by adsorption. The fourth coating material  104 ′″ may comprise an amine terminated group, such as, for example, any of the amine terminated group materials described previously in connection with the first coating material  104 . The fourth coating material  104 ′″ may comprise the same material as the first coating material  104 , the second coating material  104 ′, and the third coating material  104 ″ in some embodiments. In other embodiments, the third coating material  104 ″ may comprise a different material from at least one of the first coating material  104 , the second coating material  104 ′, and the third coating material  104 ″. 
     The fourth coating material  104 ′″ may be disposed on the coated core particle  100  by any of several well-known processes. For example, the fourth coating material  104 ′″ may be disposed on the coated core particle  100  by any of the processes described previously in connection with the first coating material  104 . As a specific example, a plurality of coated core particles  100  having adhered thereto an outer third plurality of nanoparticles  106 ″ that has been surface treated using a corona treatment to impart a net negative charge to the outer surface  112  of the third plurality of nanoparticles  106 ″ may be disposed in an aqueous solution of polyallylamine, which carries a net positive charge, and the polyallylamine may thereby be disposed on and adhered to the outer surface  112  of the third plurality of nanoparticles  106 ″. 
     Successive deposition of pluralities of nanoparticles and coating materials, a process known in the art as layer-by-layer or “LbL” deposition, may continue for as many times as desired or practicable. For example, fourth, fifth, sixth, seventh, etc., pluralities of nanoparticles may be disposed on fourth, fifth, sixth, seventh, etc., coating materials. Such subsequent deposition of pluralities of nanoparticles and coating materials may comprise materials and may be accomplished using processes such as those described previously in connection with the first plurality of nanoparticles  106  and the first coating material  104  ( FIG. 3 ). 
     After a desired number of iterations of deposition of coating materials and pluralities of nanoparticles has occurred, the coating materials may be cross-linked. Cross-linking the coating materials may enhance the mechanical strength and stability of the coating materials. Cross-linking may be accomplished using, for example, addition of a cross-linking reagent, ultraviolet radiation, electron beam radiation, heat, or other processes for cross-linking known in the art. 
       FIG. 11  depicts a cross-sectional view of a mold  114  that may be used to form a cutting element. The mold  114  may include one or more generally cup-shaped members, such as a cup-shaped member  114   a , a cup-shaped member  114   b , and a cup-shaped member  114   c , which may be assembled and swaged and/or welded together to form the mold  114 . A plurality of particles  116  comprising a superhard material may be disposed within the inner cup-shaped member  114   c , as shown in  FIG. 11 , which has a circular end wall and a generally cylindrical lateral side wall extending perpendicularly from the circular end wall, such that the inner cup-shaped member  114   c  is generally cylindrical and includes a first closed end and a second, opposite open end. 
     The plurality of particles  116  may comprise at least one coated particle, such as any of those shown in  FIGS. 3 through 10 . In some embodiments, each particle of the plurality of particles  116  may comprise a coated particle similar to the other coated particles of the plurality of coated particles. In other embodiments, at least some of the particles may comprise coated particles with a different number of coatings and/or a different combination of materials than others of the particles of the plurality of particles  116 . In still other embodiments, coated particles, such as any of those shown in  FIGS. 3 through 10 , may be intermixed with or interlayered with uncoated particles, such as that shown in  FIG. 1 , within the plurality of particles  116 . In some embodiments, an optional catalyst material  118  in the form of a powder may be interspersed among the plurality of particles  116  comprising a superhard material. The plurality of particles  116  may comprise a mono-modal or a multi-modal grain size distribution. 
     A substrate  120  comprising a hard material suitable for use in earth-boring applications may be disposed adjacent the plurality of particles  116  in the mold  114 . The hard material of the substrate  120  may comprise, for example, a ceramic-metal composite material (i.e., a “cermet” material) comprising a plurality of hard ceramic particles dispersed throughout a metal matrix material. The hard ceramic particles may comprise carbides, nitrides, oxides, and borides (including boron carbide (B 4 C)). More specifically, the hard ceramic particles may comprise carbides and borides made from elements such as W, Ti, Mo, Nb, V, Hf, Ta, Cr, Zr, Al, and Si. By way of example and not limitation, materials that may be used to form hard ceramic particles include tungsten carbide, titanium carbide (TiC), tantalum carbide (TaC), titanium diboride (TiB 2 ), chromium carbides, titanium nitride (TiN), aluminum oxide (Al 2 O 3 ), aluminum nitride (AlN), and silicon carbide (SiC). The metal matrix material of the ceramic-metal composite material may include, for example, cobalt-based, iron-based, nickel-based, iron- and nickel-based, cobalt- and nickel-based, and iron- and cobalt-based alloys. The matrix material may also be selected from commercially pure elements such as cobalt, iron, and nickel. As a specific, non-limiting example, the hard material may comprise a plurality of tungsten carbide particles in a cobalt matrix, known in the art as cobalt-cemented tungsten carbide. 
     The plurality of particles  116 , the optional catalyst material  118 , and the substrate  120  may then be subjected to a high temperature/high pressure (HTHP) process. Although the exact operating parameters of HTHP processes will vary depending on the particular compositions and quantities of the various materials being sintered, the pressures in the heated press may be greater than about 5.0 GPa and the temperatures may be greater than about 1,400° C. The pressures in the heated press may be greater than about 6.5 GPa (e.g., about 6.7 GPa), and may even exceed 8.0 GPa in some embodiments. Furthermore, the materials being sintered may be held at such temperatures and pressures for a time period between about 30 seconds and about 20 minutes. If necessary or desirable, the temperature may be reduced to about 1,000° C. and held for up to about one hour, or more to assist in the in situ nucleation of grains of superhard material. Additionally, the temperature may be reduced and maintained at a temperature between about 400° C. and about 800° C. for at least about 30 minutes (e.g., up to about 24 hours or more) in a process similar to those known in the art of metallurgy as “re-crystallization annealing” process. 
     Referring to  FIG. 12 , a partial cutaway perspective view of a cutting element  122  formed by an HTHP process is shown. The cutting element  122  includes a polycrystalline table  124  attached to an end of a substrate  120 . The polycrystalline table  124  comprises a polycrystalline superhard material, such as, for example, polycrystalline diamond. Though the cutting element  122  is depicted as having a cylindrical shape, coated core particles, such as any of those shown in  FIGS. 3 through 10 , may be used to form polycrystalline tables  124  having any shape, such as, for example, dome-shaped, conic, tombstone, and other shapes for superhard polycrystalline materials known in the art. 
     Referring to  FIG. 13 , a perspective view of an earth-boring tool  126  to which cutting elements  122  may be attached is shown. The earth-boring tool  126  includes a bit body  128  having blades  130  extending from the bit body  128 . The cutting elements  122  may be secured within pockets  132  formed in the blades  130 . However, cutting elements  122  and polycrystalline tables  124  as described herein may be bonded to and used on other types of earth-boring tools, including, for example, roller cone drill bits, percussion bits, impregnated bits, core bits, eccentric bits, bicenter bits, reamers, expandable reamers, mills, hybrid bits, and other drilling bits and tools known in the art. 
     While the present invention has been described herein with respect to certain embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Rather, many additions, deletions, and modifications to the embodiments described herein may be made without departing from the scope of the invention as hereinafter claimed, including legal equivalents. In addition, features from one embodiment may be combined with features of another embodiment while still being encompassed within the scope of the invention as contemplated by the inventor. 
     CONCLUSION 
     In some embodiments, coated particles comprise a core particle comprising a superhard material and having an average diameter of between 1 μm and 500 μm. A coating material is adhered to and covers at least a portion of an outer surface of the core particle, the coating material comprising an amine terminated group. A plurality of nanoparticles selected from the group consisting of carbon nanotubes, nanographite, nanographene, non-diamond carbon allotropes, surface modified nanodiamond, nanoscale particles of BeO, and nanoscale particles comprising a Group VIIIA element is adhered to the coating material. 
     In other embodiments, methods of coating a particle comprise at least partially coating a core particle comprising a superhard material and having an average diameter of between 1 μm and 500 μm with a coating material comprising an amine terminated group. The coating material adheres to an outer surface of the core particle. The at least partially coated core particle is disposed in a dispersion comprising a plurality of nanoparticles comprising a material selected from the group consisting of graphite, graphene, a non-diamond allotrope of carbon, surface modified diamond, BeO, and a Group VIIIA element dispersed in a continuous phase material. At least some nanoparticles of the plurality of nanoparticles adhere to the coating material. 
     In additional embodiments, methods of forming a polycrystalline compact comprise at least partially coating a plurality of core particles comprising a superhard material and having an average particle size of between 1 μm and 500 μm with a coating material comprising an amine terminated group. The coating material adheres to an outer surface of the plurality of core particles. The at least partially coated plurality of core particles is disposed in a dispersion comprising a plurality of nanoparticles comprising a material selected from the group consisting of graphite, graphene, a non-diamond allotrope of carbon, surface modified diamond, BeO, and a Group VIIIA element dispersed in a continuous phase material. At least some nanoparticles of the plurality of nanoparticles adhere to the coating material. At least some of the at least partially coated plurality of core particles are interbonded by subjecting them to a high temperature/high pressure process to form a polycrystalline material.