Thermal graphitization of encapsulated micron size and submicron size diamond particles

Abstract

The disclosure relates to a method for forming surface-modified or graphitized diamond particles. The method includes heat treating encapsulated diamond composites to form a plurality of surface-modified diamond particles, with each particle including at least a surface portion of non-diamond carbon (NDC). The encapsulated diamond composites include a plurality of encapsulated particles, where each encapsulated particle includes a plurality of diamond particles and an inert inorganic material encapsulating the plurality of diamond particles. After heat treatment, the inorganic material is removed from the encapsulated diamond composites. Removal of the inorganic material releases the plurality of surface- modified diamond particles from their encapsulating binder or matrix, for example being released as individual particles in a non-aggregated powder form substantially free from interparticle fused or sintered bridging regions.

Description

THERMAL GRAPHITIZATION OF ENCAPSULATED MICRON SIZE AND SUBMICRON SIZE DIAMOND PARTICLESCROSS REFERENCE TO RELATED APPLICATION

[0001] Priority is claimed to U.S. Provisional Application No. 63 / 653,449 (filed May 30, 2024), which is incorporated herein in its entirety.STATEMENT OF GOVERNMENT INTEREST

[0002] None.BACKGROUND OF THE DISCLOSUREField of the Disclosure

[0003] The present disclosure relates to a process by which micron and submicron diamond particles may be subjected to a high temperature thermal treatment that graphitizes the surface of said diamond particles and allows the recovery of these particles in a nearly completely dispersed state, i.e. the particles are almost completely free of particle clumps or agglomerates.Background

[0004] Diamonds possess remarkable mechanical, thermal, and optical properties. It’s chemically inert and has a low coefficient of friction and high electrical conductivity. Diamond powders are mainly used in abrasive applications, in which diamond particles are bonded on a variety of tools for drilling, sawing, grinding, cutting and slicing applications. They can be bonded to form diamond films or incorporated into slurries and compounds for lapping and polishing applications.

[0005] Changing the surface chemistries of diamond particles are presumed capable of delivering improved properties including better surface finishes and less random scratching in lapping and polishing applications. There has been works to chemically functionalize the surface of diamond particles to increase the bond strength within the matrix. Changing the surface chemistry may also lead to good particle dispersion in slurries and compounds.

[0006] Graphitized diamond particles have been used in high precision lapping applications for more than 20 years. It has been found that diamond particles which have undergone a thermal treatment in an inert atmosphere and whose surfaces are graphitized have significant performance improvement over non-graphitized diamond particles. High precision lapping involves a lap plate charged or embedded with submicron diamond particles that can be used to abrade or polish a work surface.

[0007] Different surface treatments have been applied to diamond surfaces to improve their functionality and / or performance. Chemical treatments are used to functionalize diamond particles to enable them to be chemically active. US patents #8609188, and #6372001 teach modification of nano-diamond surface by graphitizing organic polymers, which will make it more dispersible in a polymer system. Diamond and diamond-like materials have been photochemically modified in US patent #5593783 to make them amenable to chemical reactions. Some diamond modifications as in US patent #7115325, make them easily dispersible in aqueous solutions.

[0008] Depending on the thermal treatment conditions, one can produce diamonds with highly modified surface characteristics such as oxidized hydrophilic surface or reduced hydrophobic surface. Most often thermal treatment of monocrystalline diamond under inert atmosphere induces graphitization of the diamond surface at elevated temperatures (US pat. #8609188, and #6565618, Chinese pat appl. CN 200710193071 ). The problem is that after graphitization, the diamond particles are aggregated together forming bridges between particles. And this phenomenon is even worse for submicron diamond particles. These sintered particles are hard to re-disperse even with strong mechanical forces. The yield on the desired diamond particle size distribution is usually very low and makes the operation expensive.

[0009] The current process for graphitization of diamond particles, for example as described in U.S. Pat. No. 6,565,618, treats diamond powder in an inert atmosphere at temperatures greater than 1000 °C, but it includes no method to prevent aggregation of submicron diamond particles during thermal treatment.

[0010] Encapsulation of submicron size (nanometer size) particles has been utilized to prevent agglomeration and sintering during calcination of ceramic and oxide nanoparticles at temperatures up to 1100 °C, but has never been applied to the surface graphitization of diamond particles (Nanoscale Adv., “Supraparticles with silica protection for redispersible, calcined nanoparticles,” 2019, 1 , 4277-4281).SUMMARY

[0011] In an aspect, the disclosure relates to a method for forming surface-modified (or graphitized) diamond particles, the method comprising: providing a plurality of encapsulated diamond composites (e.g., beads, such as diamond abrasive composites or beads), each encapsulated diamond composite comprising (i) a plurality of diamond particles, and (ii) an (inert) inorganic material encapsulating the plurality of diamond particles; heat (or thermally) treating the encapsulated diamond composites at (i) a temperature in a range of OOTD to 1500 °C, (ii) optionally for a time in a range of 0.1 hr to 48 hr, and (iii) optionally at a pressure ina range of 0.001 bar to 2 bar, thereby forming a plurality of surface-modified diamond particles each comprising at least a surface portion of non-diamond carbon (NDC); and removing the inorganic material, thereby releasing the plurality of surface-modified diamond particles.

[0012] In another aspect, the disclosure relates to a method for forming surface-modified (or graphitized) diamond particles, the method comprising: providing a plurality of encapsulated diamond composites, each encapsulated diamond composite comprising (i) a plurality of diamond particles, and (ii) an (inert) inorganic material encapsulating the plurality of diamond particles; heat treating the encapsulated diamond composites at a temperature, pressure, and time sufficient to form a plurality of surface-modified diamond particles each comprising at least a surface portion of non-diamond carbon (NDC); and removing the inorganic material, thereby releasing the plurality of surface-modified diamond particles. In embodiments, the surface- modified diamond particles can have at least one of the following properties (A), (B), and (C): (A) the surface-modified diamond particles have a non-diamond carbon (NDC) content in a range of 0.2 wt.% to 20 wt.% or 0.2 wt.% to 50 wt.%; (B) the surface-modified diamond particles have a diamond carbon (DC) content in a range of 50 wt.% to 99.8 wt.% or 80 wt.% to 99.8 wt.%; and (C) the surface-modified diamond particles have a G-D ratio as determined by Raman spectroscopy in a range of 0.1 to 4.

[0013] In another aspect, the disclosure relates to a plurality of (non-aggregated) surface- modified diamond particles formed according to any of the methods disclosed herein.

[0014] In another aspect, the disclosure relates to a plurality of (non-aggregated) surface- modified diamond particles having at least one of the following properties (A), (B), and (C): (A) the surface-modified diamond particles have a non-diamond carbon (NDC) content in a range of 0.2 wt.% to 20 wt.% or 0.2 wt.% to 50 wt.%; (B) the surface-modified diamond particles have a diamond carbon (DC) content in a range of 50 wt.% to 99.8 wt.% or 80 wt.% to 99.8 wt.%; and (C) the surface-modified diamond particles have a G-D ratio as determined by Raman spectroscopy in a range of 0.1 to 4.

[0015] Various refinements of the disclosed surface-modified diamond particles and corresponding methods are possible.

[0016] In a refinement, the encapsulated diamond composites have an average particle size in a range of 5 pm to 50 pm; the plurality of diamond particles has an average particle size in a range of 5 nm to 1.5 pm; and the inorganic material encapsulating the plurality of diamond particles is selected from the group of inorganic metal oxides (or metal oxide binders). In a further refinement, the inorganic material is an inorganic metal oxide selected from the groupconsisting of silicon dioxide, aluminum oxide, calcium oxide, magnesium oxide, titanium dioxide, cerium oxide, zirconium oxide, and mixtures thereof.

[0017] In a refinement, the plurality of diamond particles is present in an amount in a range of 1 wt.% to 50 wt.% relative to the plurality of encapsulated diamond composites; and the inorganic material is present in an amount in a range of 50 wt.% to 99 wt.% relative to the plurality of encapsulated diamond composites.

[0018] In a refinement, providing the plurality of encapsulated diamond beads comprises performing one or more of oven drying, spray drying, and freeze drying of a colloidal mixture of (i) the plurality of diamond particles and (ii) nanoparticles of the inorganic material.

[0019] In a refinement, the method comprises performing the heat treating of the encapsulated diamond beads in an inert atmosphere.

[0020] In a refinement, the surface-modified diamond particles comprise (non-aggregated) individual diamond particles in which (i) a surface portion of each diamond particle has a nondiamond carbon (NDC) structure, and (ii) an interior portion of each diamond particle retains its original diamond carbon (DC) structure. In a further refinement, the NDC structure comprises one or more of (outer) graphite or graphene layers, sheets, or lattice structures.

[0021] In a refinement, the surface-modified diamond particles have at least one of the following properties (A), (B), and (C): (A) the surface-modified diamond particles have a nondiamond carbon (NDC) content in a range of 0.2 wt.% to 20 wt.% or 0.2 wt.% to 50 wt.%; (B) the surface-modified diamond particles have a diamond carbon (DC) content in a range of 50 wt.% to 99.8 wt.% or 80 wt.% to 99.8 wt.%; and (C) the surface-modified diamond particles have a G- D ratio as determined by Raman spectroscopy in a range of 0.1 to 4. In a further refinement, the surface-modified diamond particles have all three of the properties (A), (B), and (C), or any combination of two of the properties (A), (B), and (C).

[0022] In a refinement, the plurality of diamond particles in the (initial) encapsulated diamond composites has an initial D50i particle size; the plurality of surface-modified diamond particles has a final D50f particle size; and a particle size ratio D50f / D50i is in a range of 0.7 to 1 .3.

[0023] In a refinement, the plurality of surface-modified diamond particles has a final D50f particle size and a final D90f particle size; and a particle size ratio D90f / D50f is in a range of 1 .0 to 3.0.

[0024] In a refinement, the plurality of diamond particles in the (initial) encapsulated diamond composites has an initial D50; particle size and an initial D90i particle size;the plurality of surface-modified diamond particles has a final D50f particle size and a final D90f particle size; and a particle size ratio ( D90f / D50f) / (D90i / D50i) is in a range of 0.7 to 2.0.

[0025] In a refinement, the plurality of diamond particles in the (initial) encapsulated diamond composites has an initial D90i particle size; the plurality of surface-modified diamond particles has a final D90f particle size; and a particle size ratio D90f / D90i is in a range of 0.7 to 2.0.

[0026] In a refinement, removing the inorganic material comprises contacting the heat treated encapsulated diamond composites with a basic solution at elevated temperature for a time sufficient to dissolve the inorganic material and release the plurality of surface-modified diamond particles.

[0027] In a refinement, the method comprises heat treating the encapsulated diamond composites for a time in a range of 0.1 hr to 48 hr.

[0028] In a refinement, the method comprises heat treating the encapsulated diamond composites at a pressure in a range of 0.001 bar to 2 bar.

[0029] In a refinement, the surface-modified diamond particles are not subjected to subsequent size-reduction and / or subsequent size-classification. The disclosed method can form non-agg regated surface-modified diamond particles that have a suitable size distribution (i.e., average size and / or width of size distribution) that is usable directly in a machining slurry without the need for (i) milling or other mechanical means for breaking aggregates and reducing diamond particle size, and / or (ii) sieving or other classification / size-based separation methods to only use the smaller / non-aggregated diamond particles.

[0030] In a refinement, the surface-modified diamond particles have surface metal contents (e.g., as determined by the Surface Analysis Test) as follows: a titanium content of not more than 0.001 wt.%; an iron content of not more than 0.002 wt.%; an aluminum content of not more than 0.001 wt.%; a zirconium content of not more than 0.0001 wt.%; a chromium content of not more than 0.0001 wt.%; a tungsten content of not more than 0.0001 wt.%; a first combined metals content of not more than 0.003 wt.%, the first combined metals consisting of titanium, iron, aluminum, zirconium, chromium, and tungsten; and a second combined metals content of not more than 0.01 wt.%, the second combined metals consisting of magnesium, titanium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, molybdenum, and tungsten. The foregoing wt.% values can be expressed as analyte(s) content relative to total weight of surface-modified diamond particles.

[0031] In a refinement, the surface-modified diamond particles have surface metal extract concentrations (e.g., as determined by the Surface Analysis Test) as follows: a titaniumconcentration of not more than 100 ng / ml; an iron concentration of not more than 200 ng / ml; an aluminum concentration of not more than 100 ng / ml; a zirconium concentration of not more than 10 ng / ml; a chromium concentration of not more than 10 ng / ml; a tungsten concentration of not more than 10 ng / ml; a first combined metals concentration of not more than 300 ng / ml, the first combined metals consisting of titanium, iron, aluminum, zirconium, chromium, and tungsten; and a second combined metals concentration of not more than 1000 ng / ml, the second combined metals consisting of magnesium, titanium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, molybdenum, and tungsten. The foregoing concentrations can be expressed as analyte(s) content relative to a 1-ml sample volume containing a 1 wt.% aqueous suspension of the surface-modified diamond particles.

[0032] In another aspect, the disclosure relates to slurry composition comprising: 0.002 wt.% to 5 wt.% (or 0.01 -1 wt.%) surface-modified diamond particles according to the disclosure;50 wt.% to 98 wt.% (or 70-90 wt.%) water; up to 3 wt.% (or up to 1 wt.%) dispersing agent; 0.01 wt.% to 9 wt.% (or 0.1 -3 wt.%) emulsifier; and 2 wt.% to 50 wt.% (or 5-20 wt.%) oil.BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is an image illustrating encapsulated diamond beads according to the disclosure. These illustrated spherical composites are made by spray drying an aqueous colloidal mixture of silica and 50nm-diameter diamond particles, resulting in diamond particles embedded in a silica matrix.

[0034] Figure 2A is a graph showing particle size distributions of recovered 50nm diamond particles after thermal treatment (1100 °C for 1 hr) and dissolution of the silica matrix in a strong alkaline solution. The percentage labels give the wt% of diamond in the silica matrix.

[0035] Figure 2B is a graph showing corresponding cumulative particle size distributions for the thermally treated diamond particles in Figure 2A.

[0036] Figure 3 includes images of 50nm diamond particles embedded in a porous silica matrix. This composite material was made by freeze drying an aqueous mixture of diamond and fumed silica. Panel (a) has a scale bar of 2 pm, and panel (b) has a scale bar of 1 pm.

[0037] Figure 4 is a graph showing Raman Spectra of a) untreated monocrystalline diamond and b) thermally treated monocrystalline diamond. The diamond peak intensity decreased due to conversion to graphite.

[0038] Figure 5 includes TEM images of graphitized 50nm diamond at 1100 °C for 3hrs. Panel (a) has a scale bar of 5 nm, and panel (b) is an enlarged image from the indicated rectangular portion of panel (a).

[0039] Figure 6A is a graph showing particle size distributions (PSD) of 50nm A) untreated monocrystalline diamond, B) heat treated graphitized monocrystalline diamond after milling for 30 min, C) silica encapsulated and heat-treated graphitized monocrystalline diamond after removing silica, and D) PSD of 50nm commercially available, heat-treated graphitized diamond, after milling for 30 min.

[0040] Figure 6B is a graph showing corresponding cumulative particle size distributions for the thermally treated diamond particles in Figure 6A.

[0041] Figure 7 is a graph showing surface finish of the alumina component of an AITiC row bar lapped using plate charged with 100nm diamond that was graphitized at 1100°C for different times.DETAILED DESCRIPTION

[0042] This disclosure relates to diamond particle graphitization reduces the aggregation of the diamond particles and makes them easier to re-disperse into water or other media. The disclosed method involves encapsulating the diamond into an inert inorganic material before subjecting the encapsulated diamond to thermal treatment. The inert inorganic media can be nanoparticles of silica or alumina. The encapsulation methods include spray drying, freeze drying, freeze granulation, forced air drying or heat assisted drying. If the diamonds are well dispersed into the encapsulating media, there will be reduced aggregation, thereby reducing bridging between particles. In the case of silica as the encapsulating material, it is removed after graphitization by dissolution in a strong alkaline solution which allows the recovery of dispersed, graphitized, submicron diamond particles. The unaggregated, graphitized submicron diamonds are used to make slurries which are applied in the lapping of AITiC materials in both the 3-body and 2-body systems.

[0043] A method for forming surface-modified (or graphitized) diamond particles according to the disclosure includes heat treating encapsulated diamond composites at a temperature, pressure, and time sufficient to form a plurality of surface-modified diamond particles, with each particle including at least a surface portion of non-diamond carbon (NDC). The heat treatment can thermally convert at least some surface diamond carbon (DC) in the encapsulated diamond composites to NDC. The encapsulated diamond composites or encapsulated diamond beads (e.g., diamond abrasive composites or beads) include a plurality of encapsulated particles, where each encapsulated particle includes a plurality of diamond particles and an (inert) inorganic material encapsulating the plurality of diamond particles. After heat treatment, the inorganic material is removed from the encapsulated diamond composites, for example by dissolving, destroying, or otherwise separating the encapsulating inorganic material from thegraphitized diamond particles. Removal of the inorganic material releases the plurality of surface-modified diamond particles from their encapsulating binder or matrix, for example being released as individual particles in a non-aggregated powder form substantially free from interparticle fused or sintered bridging regions.

[0044] In embodiments, the encapsulated diamond composites can have an average particle size in a range of 5 pm to 50 pm. For example, the encapsulated diamond composites can have a size or average size of at least 5, 7, 10, 12, 15, 20, or 25 pm and / or up to 10, 15, 20, 25, 30, 35, 40, 45, or 50 pm. In embodiments, the plurality of diamond particles can have an average particle size in a range of 5 nm to 1 .5 pm. For example, the diamond particles can have a size or average size of at least 0.005, 0.01 , 0.02, 0.025, 0.035, 0.05, 0.1 , 0.2, 0.5, or 3 pm and / or up to 0.05, 0.1 , 0.2, 0.3, 0.4, 0.5, 0.7, 1 , 1 .2, or 1 .5 pm. The average sizes disclosed herein can represent weight-, volume-, or area-average sizes. Similarly, the size ranges disclosed herein can represent upper and lower bounds of a weight-, volume-, or areabased size distribution (e.g., 1 % / 99%, 2% / 98%, 5% / 95%, or 10% / 90% cuts of a cumulative size distribution). Alternatively, or additionally, the sizes disclosed herein can represent minimum or maximum sizes in a particle size distribution, for example resulting from sieving, grading, or other size classification means.

[0045] In embodiments, the inorganic material encapsulating the plurality of diamond particles can include one or more inorganic metal oxides and / or metal oxide binders. Examples of suitable inorganic metal oxides include silicon dioxide, aluminum oxide, calcium oxide, magnesium oxide, titanium dioxide, cerium oxide, zirconium oxide, and mixtures thereof. The encapsulated diamond beads can be formed, for example, by drying, spray drying, or freeze drying a colloidal mixture of the plurality of diamond particles and nanoparticles of the inorganic material.

[0046] In embodiments, the plurality of diamond particles can be present in an amount in a range of 1 wt.% to 50 wt.% relative to the plurality of encapsulated diamond composites, for example at least 1 , 2, 5, 10, 15, 20, 25, or 30 wt.% and / or up to 10, 15, 20, 25, 30, 35, 40, 45, or 50 wt.%; relative to combined weight of diamond particles and inorganic material binder. In embodiments, the inorganic material can be present in an amount in a range of 50 wt.% to 99 wt.% relative to the plurality of encapsulated diamond composites for example at least 50, 55, 60, 60, 75, or 80 wt.% and / or up to 55, 60, 65, 70, 75, 80, 85, 90, 95, 98, or 99 wt.%. The foregoing amounts can be expressed relative to the combined weight of diamond particles and inorganic material binder. Suitably, the composites contain not more than 0.01 , 0.1 , 1 , 2, 5, or 10 wt.% materials other than the diamond particles and inorganic material binder.

[0047] Heat (or thermal) treatment of the encapsulated diamond composites can be performed at a variety of different conditions. In embodiments, heat treatment can include heating the encapsulated diamond composites at or to a temperature in a range of 1000 °C to 1500 °C, for example at least 1000, 1100, or 1200 °C and / or up to 1200, 1300, 1400, or 1500 °C. In embodiments, heat treatment can include heating the encapsulated diamond composites for a time in a range of 0.1 hr to 48 hr, for example at least 0.1 , 0.2, 0.5, 1 , 2, or 4 hr and / or up to 1 , 2, 4, 6, 8, 12, 16, 24, 36, or 48 hr. In embodiments, heat treatment can include heating the encapsulated diamond composites at or to a pressure in a range of 0.001 bar to 2 bar, for example at least 0.001 , 0.01 , 0.1 , 0.2, 0.4, 0.6, 0.8, or 0.9 bar and / or up to 0.05, 0.15, 0.25, 0.5, 0.75, 1 , 1.1 , 1.2, 1 .5, or 2 bar. In embodiments, heat treatment can be performed in an inert atmosphere, for example a non-oxidizing atmosphere for diamond, such as a vacuum (e.g., up to 10, 100, or 1000 Pa) or an inert gas such as nitrogen, helium, and / or argon.

[0048] Removal of the inorganic material can be performed under a variety of different conditions. In embodiments, removing the inorganic material can include contacting the heat treated encapsulated diamond composites with a basic solution at elevated temperature for a time sufficient (e.g., 15 wt.% KOH at 80 °C for 24 hr) to dissolve the inorganic material and release the plurality of surface-modified diamond particles. More generally, the inorganic material can be dissolved and removed with a sufficiently acidic or basic (aqueous) solution to release the non-aggregated particles. For example, suitable acids can include hydrofluoric acid, other mineral acids, or mixtures thereof. Similarly, suitable bases can include potassium hydroxide, other alkali metal hydroxides, or mixtures thereof.Encapsulated Diamond Beads

[0049] Encapsulated diamond beads can be formed by a spray drying process as described in U.S. Pat. No. 1 1 ,565,374, incorporated herein by reference in its entirety. A slurry of diamond abrasive particles is made by dispersing abrasive grains in a liquid carrier in the presence of inorganic binder, dispersing agent and / or plasticizer. The constituents were mixed thoroughly with a propeller mixer or ultrasonic mixer or other appropriate dispersing mechanisms to give a uniformly dispersed abrasive slurry. The slurry is then spray dried to form spherical diamond beads (Figure 1 ). Micron-sized spherical diamond beads formed have an average particle size of 5 microns to 50 microns.

[0050] The diamond grains come in different sizes from nano sizes to micron sizes and shapes from 3-D blocky shapes to 2-D shapes, and surface roughnesses ranging from smooth to rough. The size range of the abrasive grains may be from about 5 nm to about 5 microns in some embodiments. The abrasive grain composition of the slurry for spray drying is betweenabout 1 wt.% and about 50 wt.% in some embodiments, and between about 5 wt.% and about 35 wt. % in other embodiments, based on the weight of the slurry for spray drying.

[0051] The abrasive grains are subsequently mixed with inorganic metal oxide binder to form sprayable slurries / sols in some embodiments. The metal oxide binder encapsulates the plurality of the diamond particles in a continuous friable matrix as shown in Figure 1 . Suitable metal oxide binders include ceria, silica, zirconia, alumina, titanium dioxide, magnesium oxide, and mixtures thereof. In many embodiments, silica is used as the metal oxide binder. Silica is available as colloidal silica from many commercial manufactures. Some suitable commercially available colloidal silica are: NexSil 5, NexSil 6, NexSil 8, NexSil 12, NexSil 20, NexSil 20A, NexSil 20K-30, NexSil 20NH4, Nyacol DP9711 (from Nyacol Nano Technologies, Inc. Ashland, Massachusetts), Bendzil 2040, Levasil 2050, Levasil FO1440, Megasol S50, (Wesbond Corporation, Wilmington, Delaware), Nalco 1050, Nalco 1060, Nalco 1130, Nalco 2326, Nalco 2360 (Nalco, Naperville, Illinois ) Ludox SM30, Ludox HS30, Ludox AM30, Ludox PX30, Remasol SP30, Remasol LP40 and Remasol LP40 (from Remet Corporation, Utica, New York). Different sizes of colloidal silica could be used from about 5 nm to about 200 nm in some embodiments, from about 5 nm to about 100 nm in other embodiments, and from about 5 nm to about 60 nm in yet other embodiments. The sprayable abrasive grain and metal oxide binder slurry has a solid content of about 5 wt.% to about 60 wt.% in some embodiments and about 10 wt.% to about 50 wt.% in other embodiments, based on the weight of the slurry. The metal oxide binder content of the sprayable abrasive mixture is between about 1 wt.% and about 90 wt.%, in some embodiments and between about 10 wt.% and about 80 wt.% in other embodiments on a basis of the dry components.

[0052] In another embodiment, the diamond grains were dispersed into aqueous fumed silica to form a gelled slurry. The well dispersed gel slurry was then transferred into a Lyoguard tray and freeze dried in a Virtis Genesis freeze dryer to encapsulate the diamonds. The freeze-dried encapsulated diamond was transferred into a ceramic crucible ready for thermal treatment. Fumed silica is a thickening agent in many formulations exhibiting thixotropic behavior. The highly dispersed silica particles hydrogen bond with each other to form a three-dimensional network, which results in increased viscosity. When shear forces are applied, the hydrogen bonds are broken and the material flows as a liquid substance. The material recovers its gel structure after shear force is removed. This thixotropic effect will aid in the suspension of diamond particles and minimize particle -particle interaction.

[0053] Fumed silica may be supplied as fluffy powder or aqueous dispersion and comes in different grades. Some suitable commercially available fumed silica for the invention are cab-O-sil TS720, cab-O-sil HS5, cab-O-sil EH5, cab-O-sil M5, cab-O-sil PTG; cab-O-sperse 1015A, cab-O-sperse 1017A, cab-O-sperse 1030K, cab-O-sperse 2020K ( from Cabot Corporation, Billerica, Massachusetts); Aerosil 200, Aerosil 300, Aerosil 380, Aerosil R106, Aerosil R972,(from Evonik Corporation, Piscataway, New Jersey); Konasil K200, and Konasil KD15 (from Akrochem Corporation, Akron, Ohio); HDK D05, HDK H15, HDK H21 , HDK N20, HDK T30, HDK T40 (from Wacker Chemie AG, Munich, Germany).

[0054] The ratio of diamond to fumed silica is important to get a well dispersed diamond particles with minimal particle-particle interaction. The amount of diamond in fumed silica is between 1 % to 50% by weight on dry basis and preferably between 5% and 40% by weight and more preferably between 5% to 30%. After thermal treatment of the freeze-dried diamond / silica mixture at 1 100 °C for 1 hr in flowing nitrogen gas, the color of the mixture changed from light blue / gray to black indicating modification of the surface to non-diamond carbon. The diamond powder was recovered from the thermally treated diamond / silica mixture by dissolving the silica in a 15wt% KOH aqueous solution at 80°C for 24hrs. The strong alkaline solution dissolved the silica and released the entrapped diamond particles. The supernatant was decanted, and the left-over sludge was rinsed multiple times with deionized water to very low conductivity.Preferably to conductivity of less than 60pS / cm and more preferable less than 30pS / cm or most preferable less than 20|iS / cm. At this conductivity, the diamond is well stabilized by electrostatic repulsion of the surface charge of the particles. The recovered diamond has good particle size distribution similar to the initial monocrystalline diamond as shown in Figure 6A and Figure 6B, where sample A represents the initial or untreated diamond, and sample C represents silica-encapsulated, heat-treated graphitized diamond after silica removal according to the disclosure.

[0055] The recovered diamond was analyzed by Raman spectroscopy and Transmission Emission Microscopy. Figure 4 shows a less intense diamond peak compared to the original monocrystalline diamond, and broadening of the D peak. The G peak shifts to higher wavelength on graphitization. The broadening of the D and G peaks and shifts in peak positions are indications of the presence of amorphous carbon layer on the surface of the diamond after thermal treatment. The disclosed method gives a graphitized diamond surface that is easy to recover without aggregation. Figure 5 is the T ransmission electron micrograph of the graphitized diamond showing the thickness of the graphite layer. The average thickness of the graphite layer of a 50nm diamond treated at 1100 °C for 3hrs is about 4nm.

[0056] The recovered graphitized diamond dispersion is used in making water-based and oilbased diamond slurries for charging, lapping and polishing of AITiC and other semiconductormaterials. Diamond slurries were prepared by combining appropriate amounts of diamond dispersion in water, wetting agents, buffering agents, dispersing agents, cosolvents, and vegetable oil, to make an oil in water emulsion slurry. Diamond slurries made with graphitized diamond according to the disclosure were applied in the polishing of AITiC row bars. The rough lap step involves the free and fixed abrasive lapping method, where work piece is brought into contact with a turning plate and a conditioning ring for planarization, while dripping diamond slurry on the plate. Some of the diamond grains embed into the metal turning plate (typically made from zinc, tin or tin-alloy) to form a 2-body system while others roll between the plate and the workpiece in a 3-body system. The use of free and fixed abrasive diamond delivers a higher material removal rate, but high surface roughness. The surface roughness is improved by adding another step of fixed abrasive lapping, where the work piece is brought into contact with a turning plate pre-embedded with graphitized diamond grains according to the disclosure and lapped with a lubricant vehicle. The lubricant vehicle does not contain abrasives. The fixed abrasive lapping gives a lower lap rate and better surface finish.Surface-Modified Diamond Particles

[0057] As described above, the surface-modified diamond particles according to the disclosure include at least a surface portion of non-diamond carbon (NDC). The heat treatment can thermally convert at least some surface diamond carbon (DC) in the encapsulated diamond composites to NDC without minimal or essentially no interparticle sintering or other aggregation of individual diamond particles in the encapsulated diamond composites. Subsequent removal of the inorganic encapsulating material releases the surface-modified diamond particles in substantially non-aggregated form that retains or only deviates slightly from the size distribution characteristics of the diamond particles prior to heat treatment. In embodiments, the surface- modified diamond particles can include non-aggregated, individual diamond particles in which a surface portion of each diamond particle has a non-diamond carbon (NDC) structure, for example where some or all of the outer surface includes NDC structure(s), although some outer surface regions can also have a DC structure. Further, an interior portion of each diamond particle retains its original diamond carbon (DC) structure (i.e., each diamond particle contains at least some internal DC structure). Examples of suitable NDC structures include one or more of (outer) graphite or graphene layers, sheets, or lattice structures.

[0058] The surface-modified diamond particles can be characterized according to one or more of their NDC content, DC content, and / or their G-D ratio. In embodiments, the surface- modified diamond particles can have a non-diamond carbon (NDC) content in a range of 0.2 wt.% to 20 wt.% or 0.2 wt.% to 50 wt.%, for example at least 0.2, 0.5, 0.7, 1 , 1.5, 2, 3, 4, 5,6, 8, 10, 15, 20, or 30 wt.% and / or up to 3, 6, 8, 10, 12, 14, 16, 18, 20, 30, 40, or 50 wt.% relative to the surface-modified diamond particles as a whole. In embodiments, the surface- modified diamond particles can have a diamond carbon (DC) content in a range of 50 wt.% to 99.8 wt.% or 80 wt.% to 99.8 wt.%, for example at least 50, 60, 70, 80, 82, 84, 86, 88, 90, 92, 94, or 97 wt.% and / or up to 60, 70, 80, 90, 92, 94, 95, 96, 97, 98, 98.5, 99, 99.3, 99.5, or 99.8 wt.% relative to the surface-modified diamond particles as a whole. In embodiments, the surface-modified diamond particles can have a G-D ratio as determined by Raman spectroscopy in a range of 0.1 to 4, for example at least 0.1 , 0.2, 0.3, 0.4, 0.5, or 0.8 and / or up to 0.3, 0.6, 1 , 1 .5, 2, 3 or 4. The foregoing ranges can apply to a collective sample or distribution of particles. The properties can be determined as generally described in US 6,565,618, incorporated herein by reference, for example by wet oxidation in a strong acid for NDC, balance / difference with NDC for DC, Raman spectroscopy peak height between about 1500 and 1600 cm-1for G (graphite or amorphous carbon), and Raman spectroscopy peak height at about 1330 cm-1for D (diamond carbon.

[0059] The surface-modified diamond particles can be characterized according to one or more size / diameter properties of their particle size distribution.

[0060] In embodiments, the plurality of diamond particles in the (initial) encapsulated diamond composites has an initial D50i particle size, the plurality of surface-modified diamond particles (e.g., after heat treatment and release from the inorganic material) has a final D50f particle size, and a particle size ratio D50f / D50i can be in a range of 0.7 to 1 .3. For example, the ratio D50f / D50i can be at least 0.7, 0.8, 0.85, 0.9, 0.93, 0.95, 0.98, or 1 and / or up to 1 , 1 .02, 1 .05, 1 .07, 1.1 , 1.15, 1 .2, or 1 .3. The D50 is a weight-average particle size in a distribution or sample of the diamond particles, with the two different values representing the average size before and after thermal heat treatment (i.e., the 50 wt.% cut point in the cumulative size distribution). The disclosed heat treatment method advantageously can essentially maintain the original particle size distribution, or at least minimize / reduce aggregation relative to the method of US 6,565,618.

[0061] In embodiments, the plurality of surface-modified diamond particles (e.g., after heat treatment and release from the inorganic material) has a final D50f particle size and a final D90f particle size, and a particle size ratio D90f / D50f can be in a range of 1 .0 to 3.0. For example, the ratio D90f / D50t can be at least 1 .0, 1 .05, 1.1 , 1.2, 1.3, 1 .4, 1 .5, 1 .6, or 1 .8 and / or up to 1 .4, 1 .6, 1 .8, 2.0, 2.2, 2.4, 2.7, or 3.0. The D90 represents a 90 wt.% cut point in the cumulative size distribution corresponding to a weight-average particle size in a distribution or sample of the diamond particle. The particle size ratio D90f / D50f can reflect a relative non-broadening of thePSD after heat treatment according to the disclosure, which contrasts the conventional heat treatment method according to US 6,565,618.

[0062] In embodiments, the plurality of diamond particles in the (initial) encapsulated diamond composites has an initial D50i particle size and an initial D90i particle size, the plurality of surface-modified diamond particles (e.g., after heat treatment and release from the inorganic material) has a final D50f particle size and a final D90f particle size, and a particle size ratio (D90f / D50f) / (D90i / D50i) can be in a range of 0.7 to 2.0. For example, the ratio (D90f / D50f) / (D90i / D50i) can be at least 0.7, 0.8, 0.85, 0.9, 0.93, 0.95, 0.98, or 1 and / or up to 1 , 1 .02, 1 .05, 1 .07, 1.1 , 1.15, 1 .2, 1 .3, 1 .4, 1 .5, 1 .6, 1 .8, or 2.0. Similar ranges can apply to the ratio (D90f / D90i) / (D50f / D50i).

[0063] In embodiments, the plurality of diamond particles in the (initial) encapsulated diamond composites has an initial D90i particle size, the plurality of surface-modified diamond particles (e.g., after heat treatment and release from the inorganic material) has a final D90f particle size; and a particle size ratio D90f / D90i can be in a range of 0.7 to 2.0. For example, the ratio D90f / D90i can be at least 0.7, 0.8, 0.85, 0.9, 0.93, 0.95, 0.98, or 1 and / or up to 1 , 1.02, 1.05, 1.07, 1.1 , 1.15, 1.2, 1.3, 1.4, 1.5, 1.6, 1.8, or 2.0.

[0064] The surface-modified diamond particles can be characterized as being free from, substantially free from, or otherwise having very low concentrations or amounts of non-carbon materials, for example metals or metal-containing materials, in particular on an outer surface of the particles. The presence of such non-carbon materials as impurities on the outer particle surface can be particularly undesirable when using the particles in a subsequent machining process (e.g., as a slurry component as described below) where very high purity and / or a lack of surface contamination is required or otherwise desirable for the workpiece. More specifically, non-carbon impurities on the outer particle surface can be undesirably transferred to the workpiece surface during machining, introducing an impurity to the final machined workpiece product. For example, workpieces or substrates used in semiconductor materials, computer components, hard disk drive components (e.g., disk plates, read / write heads, etc.), etc. can be particularly sensitive to such impurities, leading to an increased fraction of non-functional or low- performing machined products. Examples of such workpieces or substrates include sapphire, titanium carbide reinforced alumina (AITiC), silicon carbide (SiC; e.g., (a)3C-SiC, 4H-SiC, (P)6H- SiC), gallium nitride (GaN), aluminum nitride (AIN), zinc selenide (ZnSe), silicon wafers (e.g., semiconducting silicon, such as crystalline silicon), ceramic substrates, optical substrates (e.g., transparent glass or polymeric materials), and metal or metal alloy workpieces or substrates. While surface impurities can be imparted to the surface-modified diamond particles from avariety sources, a prominent source of surface impurities includes milling media such as zirconia balls, tungsten carbide balls, stainless steel balls, etc., which can degrade during milling and impart milling media component residue(s) to the surface-modified diamond particles. As described above, such milling is conventionally employed to break aggregates formed during a conventional thermal graphitization process, and it results in substantial levels of metallic surface impurities, such as one or more of aluminum, titanium, chromium, iron, zirconium, and / or tungsten. In contrast, the method for forming surface-modified diamond particles according to the disclosure substantially maintains the initial particle size distribution and does not result in substantial formation of aggregates. As a result, the surface-modified diamond particles according to the disclosure do not generally require or otherwise benefit from milling or other mechanical size reduction techniques, which in turn provides surface-modified diamond particles with very low or absent surface metal or metal-containing impurities, making the particles particularly suitable as a machining abrasive where workpiece purity in desirable.

[0065] In embodiments, the surface-modified diamond particles can be characterized as having one or both of a surface metal content and / or a surface metal extract concentration at or below a threshold amount, or within a specific range. The surface metal content and the surface metal extract concentration can be determined according to the Surface Analysis Test described below. More generally, the surface metal content and the surface metal extract concentration can be determined according to any suitable analytical method to determine the amount of a given metal (or group of metals) on the outer surface of the particles, which can be expressed on a weight basis relative to the total particle weight or on a volume basis in a specified extraction sample (e.g., concentration in a 10-ml sample volume extract of 0.01 g diamond particles as a basis). Example metals can include one or more of magnesium, titanium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, molybdenum, and tungsten. The metal amounts can represent a combined or total amount of the metal originally present in any oxidation state on the diamond particle surface, for example an elemental metal or alloyed metal (e.g., zero oxidation state), and / or an oxidized metal in compound form (e.g., a metal oxide, a metal nitride, etc. with the metal in a positive oxidation state). In some embodiments, an individual surface metal component can have a (surface) content of not more than 0.0001 , 0.0005, 0.001 , 0.002, 0.003, or 0.01 wt.%, for example at least and / or up to 0.000001 , 0.000002, 0.000005, 0.00001 , 0.00002, 0.00005, 0.0001 , 0.0002, 0.0003, 0.0005, 0.0007, 0.001 , 0.002, 0.003, 0.005, or 0.01 wt.%. In some embodiments, an individual surface metal component can have an extract concentration (e.g., relative to a 1 -ml sample volume containing a 1 wt.% aqueous suspension of the surface-modified diamond particles) of not more than 10, 50, 100, 200, 300, or 1000 ng / ml, for example at least and / or upto 0.1 , 0.2, 0.5, 1 , 2, 5, 10, 20, 30, 50, 70, 100, 200, 300, 500, or 1000 ng / ml. The foregoing ranges also can apply to groups of metals, for example a first combined group of metals including titanium, iron, aluminum, zirconium, chromium, and tungsten. Similarly, a second combined group of metals can include magnesium, titanium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, molybdenum, and tungsten. Other combined groups of metals can include any selections from the foregoing.

[0066] The surface-modified diamond particles can be incorporated into a slurry composition for various machining processes known in the art. Suitable slurries can be water-based and / or oil-based slurries for charging, lapping and polishing of AITiC and other semiconductor materials. The slurries can be in the form of an emulsion including an aqueous phase and an oil or other water-immiscible non-aqueous phase. In embodiments, the slurry can include the surface-modified diamond particles, water, optionally a dispersing agent, an emulsifier, and an oil. The surface-modified diamond particles can be included in the slurry in an amount of 0.002 wt.% to 5 wt.% (or 0.01 -1 wt.%), for example at least 0.002, 0.005, 0.01 , 0.02, 0.05, or 0.1 wt.% and / or up to 0.5, 0.7, 1 , 1 .5, 2, 3, 4, or 5 wt.% relative to the slurry. The water can be included in the slurry in an amount of 50 wt.% to 98 wt.% (or 70-90 wt.%), for example at least 50, 60, 70, or 75 wt.% and / or up to 80, 85, 90, 95, or 98 wt.% relative to the slurry. The dispersing agent can be included in the slurry in an amount up to 3 wt.% (or up to 1 wt.%), for example at least 0.002, 0.005, 0.01 , 0.02, 0.05, or 0.1 wt.% and / or up to 0.5, 0.7, 1 , 1.5, 2, or 3 wt.% relative to the slurry. The emulsifier can be included in the slurry in an amount of 0.01 wt.% to 9 wt.% (or 0.1 -3 wt.%), for example at least 0.01 , 0.02, 0.05, 0.1 , 0.2, 0.3, or 0.5 wt.% and / or up to 0.5, 1 , 1 , 1 .5, 2, 3, 5, 7, or 9 wt.% relative to the slurry. The oil can be included in the slurry in an amount of 2 wt.% to 50 wt.% (or 5-20 wt.%), for example at least 2, 3, 5, 7, 10, 12, 15, or 20 wt.% and / or up to 10, 12, 15, 18, 20, 25, 30, 40 or 50 wt.% relative to the slurry. Suitable dispersing agents include sodium tripolyphosphate, sodium hexametaphosphate, sulfonated polyacrylic acid copolymer, polycarboxylates and polymeric dispersants. Suitable emulsifiers include polyethylene glycol (20) sorbitan monooleate, polyethylene glycol (20) sorbitan monolaurate, polyethylene glycol 40) sorbitol hexaoleate, polyethylene glycol (4) lauryl alcohol, polyethylene glycol (5) sorbitan monooleate. Suitable oils can include natural or synthetic oils, for example vegetable oils and vegetable oil esters such as soy (or soybean) oil, soy (or soybean) oil ester, canola oil, methyl ester of canola oil, coconut oil and tall oil. The slurry composition can be formed by adding the oil phase to the water phase containing the graphitized diamond while mixing to form an emulsion diamond slurry. Buffering agents and cosolvents may be added to stabilize the emulsion.Examples

[0067] The following examples illustrate the disclosed compositions, articles, and methods, but are not intended to be limiting.Examples 1 -4 - Graphitized Diamond Formed from Colloidal Silica-Encapsulated Diamond

[0068] 50nm monocrystalline diamond powder (from Engis Corp.) was dispersed into 60nm colloidal silica of 50wt% silica (from Nalco, Naperville, IL) in the ratios given in Table 1 . The diamond / silica slurry was then spray dried in a Yamato ADL31 1 spray dryer, to form spherical porous diamond in silica beads. The diamond grains are discretely held in place by the silica binder. The composite diamond beads were poured into a ceramic crucible and heat treated at 1 100 °C for 1 hour under flowing nitrogen gas at 1.5psi. The powder color changed from a light gray to black. After thermal treatment, the diamond powder was recovered by treating the powder in a 15wt% KOH solution at 80C for 24hrs. The strong alkaline solution dissolved the silica and released the entrapped diamond particles. After repeated rinsing with deionized water, the graphitized diamond was recovered as stable dispersion in water with conductivity of 14 pS / cm. The particle size distributions of each example are shown in Figure 2A and Figure 2B with the median D50 of each example is given in Table 1. The initial D50 of the untreated diamond was 52.6nm and the initial D90 of the untreated diamond was about 75 nm. Table 1 shows that at high diamond concentrations, aggregation of particles is common, and the initial particle size distribution is not obtained without further grading process.Table 1. Effect of Encapsulating Material Amount on Graphitized Diamond FormationComparative Example 1 - Graphitized Diamond Formed from Non-Encapsulated Diamond

[0069] 50nm monocrystalline diamond powder (Engis Corp., Wheeling, IL) was poured into a ceramic crucible and thermally treated at 1 100 °C for 1 hr in hermetic furnace with flowing nitrogen gas at 1 .5psi. The diamond became darker in color after thermal treatment and obviously agglomerated; it is not wettable in aqueous solution due to the hydrophobic nature ofthe treated surface. In a 250 ml high density polyethylene container, add 10g of the thermally treated diamond powder and 1 .Og sulfonated polyacrylic acid copolymer as dispersing agent. Fill the container with milling media to 60% by volume and add water to cover the milling media. Shake in a paint shaker for 30mins to de-aggregate the particles. Recover the diamond particles by rinsing with de-ionized water. Particle size distribution of the recovered diamond is shown in Figure 6A (sample B) and the corresponding cumulative particle size distribution is shown in Figure 6B (sample B). The D50 measurement and the distribution data showed evidence of aggregation which is very hard to disperse even at a high milling force. Specifically, relative to the initial D50 of the untreated diamond (52.6 nm), the D50 after treatment was about 72 nm (i.e., D50 / D50i of about 1 .36) and the D90 after treatment was about 240 nm (i.e., D90 / D50 of about 3.33 and (D90 / D90i) / (D50 / D50i) of about 2.35). The particles can be graded to the desired D50 of 50nm, but the process yield is only 15-20%.Comparative Example 2 - Commercial Graphitized Diamond

[0070] A sample of commercially available, heat-treated graphitized diamond having a nominal (average) size of 50 nm was obtained and milled for 30 minutes to reduce aggregates. The particle size distribution of the milled, heat-treated graphitized diamond is shown in Figure 6A (sample D) and the corresponding cumulative particle size distribution is shown in Figure 6B (sample D). The distribution data showed evidence of aggregation which is very hard to disperse even at a high milling force. Specifically, relative to the nominal average size of 50 nm, the D50 after milling was about 88 nm, and the D90 after milling was about 430 nm. The bimodal size distribution in Figure 6A (sample D) having a first peak at about 68 nm and a second peak at about 360 nm suggests the presence of a substantial amount of aggregates, even after milling.Examples 5-9 - Graphitized Diamond Formed from Fumed Silica-Encapsulated Diamond

[0071] 100g of a 10wt% diamond powder in deionized water was dispersed into 600g of 15wt% fumed silica in deionized water using an ultrasonic probe. The slurry was then poured into LYOGUARD trays and freeze dried in a VIRTIS GENESIS freeze dryer. The freeze-dried diamond / silica composite contained 10 wt.% diamond and 90 wt.% fumed silica (i.e., 10 g diamond and 90 g fumed silica from respective slurries after drying). The freeze-dried diamond / silica composite was transferred into a ceramic crucible for thermal treatment in a hermetic furnace. The freeze-dried diamond / silica composite was heat treated at 1100 °C under flowing nitrogen atmosphere according to the schedule in Table 2. After thermal treatment, the diamond powder was recovered by treating the powder in a 15wt% KOH solution at 80 °C for 24hrs. The strong alkaline solution dissolved the silica and released the entrapped diamondparticles. After repeated rinsing with deionized water, the graphitized diamond was recovered as stable dispersion in water with conductivity of less than 20pS / cm. The D50 measurements and process yield of the recovered diamond are shown in Table 2.Table 2. Effect of Initial Diamond Size and Treatment Time on Graphitized Diamond FormationExample 10 - Lapping and Polishing Slurries Including Graphitized Diamond

[0072] Graphitized diamond of Example 5-7 was used to prepare diamond slurries for lapping and polishing AITiC row bars. Diamond slurries were prepared by dispersing 0.01g to 1 .0g of graphitized diamond in 70g to 90g of water in the presence of 0.0 to 1 .0g of dispersing agent. Some suitable dispersing agents are sodium tripolyphosphate, sodium hexametaphosphate, sulfonated polyacrylic acid copolymer, polycarboxylates and polymeric dispersants. About 0.1 to 3.0g of emulsifier was added to 5 to 20g of vegetable oil and mixed to dissolve. Suitable emulsifiers are Polyethylene glycol (20) sorbitan monooleate, polyethylene glycol (20) sorbitan monolaurate, polyethylene glycol 40) sorbitol hexaoleate, polyethylene glycol (4) lauryl alcohol, polyethylene glycol (5) sorbitan monooleate. Vegetable oils and vegetable oil esters are suitable for the slurry, example soy oil, soy oil ester, canola oil, methyl ester of canola oil, coconut oil and tall oil. The mixed oil phase was added to the water phase containing the graphitized diamond while mixing to form an emulsion diamond slurry. Buffering agents, and cosolvents may be added to stabilize the emulsion.

[0073] During charging operation, graphitized diamond grains from the slurries were embedded into the tin-antimony lapping plate using Engis F15 Lapping machine (Engis Corp., Wheeling, IL) to make a fixed abrasive tin-antimony plate. The fixed abrasive tin-antimony plate embedded with graphitized diamond particles was used to lap Alumina of row bar work piece with a glycol lubricant. Figure 7 is the plot of Alumina surface finish as a function of graphitization time. Lap rate and surface finish of the work piece was compared to that ofuntreated diamond. While lap rate remained about the same for the different graphitization times, surface finish improved with increase in graphitization time.Example 11 and Comparative Example 12 - Graphitized Diamond Surface Characterization

[0074] For Example 1 1 , a sample of graphitized diamond having a nominal average diameter (D50) of about 50 nm was prepared according to Example 9 above. For Comparative Example 12, a commercially available, heat-treated graphitized diamond sample having a nominal (average) size of 50 nm was obtained and tested in its form as provided by the manufacturer.

[0075] Both samples were tested for their surface composition / components using the following extraction and analysis procedures (“Surface Analysis Test”). Surface components were extracted from each diamond sample using an acid leaching process. Briefly, 1 ml of a 1 wt.% aqueous suspension in water of the graphitized diamond powder sample was combined with 0.5 ml nitric acid (67% nitric acid in water) and 0.125 ml hydrogen peroxide (30% hydrogen peroxide in water), and the mixture (nominally 1 .675 ml) was heated at a temperature of 65 °C for about 12 hours in a sealed vessel. The heated / extracted samples were then diluted to a 10 ml sample volume by adding ultrafiltration membrane purification (MP) water. The samples were then filtered to remove residual solid material (e.g., surface-extracted graphitized diamond remaining after acid leaching). The filtered 10 ml-samples were then analyzed using inductively coupled plasma / mass spectroscopy (ICP-MS) on a computer-controlled (QTEGRA software) THERMO ICAPQ ICP-MS (Thermo Fisher Scientific, Waltham, MA, USA) operating in KED mode and equipped with an ESI SC-2DX PREPFAST autosampler (Omaha, NE, USA). Internal standard was added inline using the PREPFAST system and consisted of 1 ng / mL of a mixed element solution containing Bi, In, 6Li, Sc, Tb, Y (IV-ICPMS-71 D from Inorganic Ventures). A calibration curve was prepared and analyzed using standards from Inorganic Ventures (IV- ICPMS-71 A and 71 B). While ICP-MS was used in these examples, other equivalent analytical techniques for metal or element detection and quantitation can be used, for example atomic absorption, ICP-OES (optical Emission spectroscopy), etc. The result can be expressed as an analyte concentration in the original 1 ml-sample volume of the 1 wt.% sample suspension (e.g., ppb or ng / ml analyte relative to liquid sample medium). Alternatively or additionally, the result can be expressed as an analyte weight fraction (or weight percent) relative to the graphitized diamond, for example the original or total graphitized diamond in the 1 ml of the 1 wt.% sample suspension (e.g., wt.% analyte relative to graphitized diamond). The result for a given analyte can represent a combined or total amount of the metal originally present in any oxidation state on the diamond particle surface.

[0076] The analytical results for various metals in the two samples are shown in Table 3. The amounts shown in ppb (equivalent to ng / ml or pig / l) represent the metal concentration in the original 1 ml-sample of the 1 wt.% suspension after heating with acid and peroxide (i.e., the 10 ml-sample after dilution was analyzed, and the resulting analytical concentration was expressed on the basis of the original 1 ml sample suspension). The amounts shown in wt.% represent the metal amount relative to graphitized diamond (i.e., 10 mg of graphitized diamond in 1 ml of a 1 wt.% suspension). The acid leaching process extracts or removes material from the outer surface of the graphitized diamond particles, leaving bulk graphitized diamond particles intact. Accordingly, the analytical results represent the types and relative amounts of metal components that can be present on the outer surface of the as-produced graphitized diamond particles, for example as a result of various processing steps, such as milling for aggregate reduction or otherwise. As illustrated in Table 3, the graphitized diamond of Comparative Example 12 contains substantially higher levels of various surface metals (or metal-containing compounds), in particular aluminum, titanium, chromium, iron, zirconium, and tungsten. Such metals can result from aggressive milling using one or more milling media such as zirconia balls, tungsten carbide balls, and / or stainless steel balls, and the presence of such metals on the outer surface of graphitized diamond can represent an undesirable impurity that can be transferred as a contaminant to a workpiece being machined using the graphitized diamond as an abrasive. In contrast, the graphitized diamond of Example 1 1 contains substantially less of such metals.Table 3. Surface Components of Graphitized Diamond

[0077] As illustrated in Table 3, the initial sample contains about 0.01 g graphitized diamond (=10 mg or 10,000 pg) based on a 1 wt.% concentration of a 1 ml aqueous sample (i.e., about 1 g aqueous sample). A 1000 ppb (=1000 ng / ml) analyte result for the 1 ml aqueous sample corresponds to 1 ,000 ng analyte (=1 pg) in the sample. Thus, a 1000 ppb analyte result in Table 3 corresponds to 0.01 wt.% analyte relative to graphitized diamond (i.e., 1 pg analyte / 10,000 pg graphitized diamond).

[0078] Because other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the disclosure is not considered limited to the example chosen for purposes of illustration, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this disclosure.

[0079] Accordingly, the foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications within the scope of the disclosure may be apparent to those having ordinary skill in the art.

[0080] All patents, patent applications, government publications, government regulations, and literature references cited in this specification are hereby incorporated herein by reference in their entirety. In case of conflict, the present description, including definitions, will control.

[0081] Throughout the specification, where the compositions, processes, kits, or apparatus are described as including components, steps, or materials, it is contemplated that the compositions, processes, or apparatus can also comprise, consist essentially of, or consist of, any combination of the recited components or materials, unless described otherwise. Component concentrations can be expressed in terms of weight concentrations, unless specifically indicated otherwise. Combinations of components are contemplated to include homogeneous and / or heterogeneous mixtures, as would be understood by a person of ordinary skill in the art in view of the foregoing disclosure.

Claims

What is claimed is:1 . A method for forming surface-modified diamond particles, the method comprising: providing a plurality of encapsulated diamond composites, each encapsulated diamond composite comprising (i) a plurality of diamond particles, and (ii) an inorganic material encapsulating the plurality of diamond particles; heat treating the encapsulated diamond composites at (i) a temperature in a range of 1000°C to 1500 °C, (ii) optionally for a time in a range of 0.1 hr to 48 hr, and (iii) optionally at a pressure in a range of 0.001 bar to 2 bar, thereby forming a plurality of surface-modified diamond particles each comprising at least a surface portion of non-diamond carbon (NDC); and removing the inorganic material, thereby releasing the plurality of surface-modified diamond particles.

2. The method of claim 1 , wherein: the encapsulated diamond composites have an average particle size in a range of 5 pm to 50 pm; the plurality of diamond particles has an average particle size in a range of 5 nm to1 .5 pm; and the inorganic material encapsulating the plurality of diamond particles is selected from the group of inorganic metal oxides.

3. The method of claim 2, wherein the inorganic material is an inorganic metal oxide selected from the group consisting of silicon dioxide, aluminum oxide, calcium oxide, magnesium oxide, titanium dioxide, cerium oxide, zirconium oxide, and mixtures thereof.

4. The method of claim 1 , wherein: the plurality of diamond particles is present in an amount in a range of 1 wt.% to 50 wt.% relative to the plurality of encapsulated diamond composites; and the inorganic material is present in an amount in a range of 50 wt.% to 99 wt.% relative to the plurality of encapsulated diamond composites.

5. The method of claim 1 , wherein providing the plurality of encapsulated diamond beads comprises performing one or more of oven drying, spray drying, and freeze drying of a colloidal mixture of (i) the plurality of diamond particles and (ii) nanoparticles of the inorganic material.

6. The method of claim 1 , comprising performing the heat treating of the encapsulated diamond beads in an inert atmosphere.

7. The method of claim 1 , wherein the surface-modified diamond particles comprise individual diamond particles in which (i) a surface portion of each diamond particle has a nondiamond carbon (NDC) structure, and (ii) an interior portion of each diamond particle retains its original diamond carbon (DC) structure.

8. The method of claim 7, wherein the NDC structure comprises one or more of graphite or graphene layers, sheets, or lattice structures.

9. The method of claim 1 , wherein the surface-modified diamond particles have at least one of the following properties (A), (B), and (C):(A) the surface-modified diamond particles have a non-diamond carbon (NDC) content in a range of 0.2 wt.% to 50 wt.% ;(B) the surface-modified diamond particles have a diamond carbon (DC) content in a range of 50 wt.% to 99.8 wt.%; and(C) the surface-modified diamond particles have a G-D ratio as determined by Raman spectroscopy in a range of 0.1 to 4.

10. The method of claim 9, wherein the surface-modified diamond particles have all three of the properties (A), (B), and (C).11 . The method of claim 1 , wherein: the plurality of diamond particles in the encapsulated diamond composites has an initial D50i particle size; the plurality of surface-modified diamond particles has a final D50f particle size; and a particle size ratio D50f / D50i is in a range of 0.7 to 1 .3.

12. The method of claim 1 , wherein : the plurality of surface-modified diamond particles has a final D50f particle size and a final D90f particle size; and a particle size ratio D90f / D50f is in a range of 1 .0 to 3.0.

13. The method of claim 1 , wherein : the plurality of diamond particles in the encapsulated diamond composites has an initial D50i particle size and an initial D90i particle size; the plurality of surface-modified diamond particles has a final D50f particle size and a final D90f particle size; and a particle size ratio (D90f / D50f) / (D90i / D50i) is in a range of 0.7 to 2.0.

14. The method of claim 1 , wherein : the plurality of diamond particles in the encapsulated diamond composites has an initial D90i particle size; the plurality of surface-modified diamond particles has a final D90f particle size; and a particle size ratio D90f / D90i is in a range of 0.7 to 2.0.

15. The method of claim 1 , wherein removing the inorganic material comprises contacting the heat treated encapsulated diamond composites with a basic solution at elevated temperature for a time sufficient to dissolve the inorganic material and release the plurality of surface-modified diamond particles.

16. The method of claim 1 , comprising heat treating the encapsulated diamond composites for a time in a range of 0.1 hr to 48 hr.

17. The method of claim 1 , comprising heat treating the encapsulated diamond composites at a pressure in a range of 0.001 bar to 2 bar.

18. The method of claim 1 , wherein the surface-modified diamond particles are not subjected to subsequent size-reduction and / or subsequent size-classification.

19. The method of claim 1 , wherein the surface-modified diamond particles have surface metal contents as determined by the Surface Analysis Test as follows: a titanium content of not more than 0.001 wt.%; an iron content of not more than 0.002 wt.%; an aluminum content of not more than 0.001 wt.%; a zirconium content of not more than 0.0001 wt.%; a chromium content of not more than 0.0001 wt.%; a tungsten content of not more than 0.0001 wt.%; a first combined metals content of not more than 0.003 wt.%, the first combined metals consisting of titanium, iron, aluminum, zirconium, chromium, and tungsten; and a second combined metals content of not more than 0.01 wt.%, the second combined metals consisting of magnesium, titanium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, molybdenum, and tungsten.

20. The method of claim 1 , wherein the surface-modified diamond particles have surface metal extract concentrations as determined by the Surface Analysis Test as follows: a titanium concentration of not more than 100 ng / ml;an iron concentration of not more than 200 ng / ml; an aluminum concentration of not more than 100 ng / ml; a zirconium concentration of not more than 10 ng / ml; a chromium concentration of not more than 10 ng / ml; a tungsten concentration of not more than 10 ng / ml; a first combined metals concentration of not more than 300 ng / ml, the first combined metals consisting of titanium, iron, aluminum, zirconium, chromium, and tungsten; and a second combined metals concentration of not more than 1000 ng / ml, the second combined metals consisting of magnesium, titanium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, molybdenum, and tungsten.

21. A method for forming surface-modified diamond particles, the method comprising: providing a plurality of encapsulated diamond composites, each encapsulated diamond composite comprising (i) a plurality of diamond particles, and (ii) an (inert) inorganic material encapsulating the plurality of diamond particles; heat treating the encapsulated diamond composites at a temperature, pressure, and time sufficient to form a plurality of surface-modified diamond particles each comprising at least a surface portion of non-diamond carbon (NDC); and removing the inorganic material, thereby releasing the plurality of surface-modified diamond particles; wherein the surface-modified diamond particles have at least one of the following properties (A), (B), and (C):(A) the surface-modified diamond particles have a non-diamond carbon (NDC) content in a range of 0.2 wt.% to 20 wt.%;(B) the surface-modified diamond particles have a diamond carbon (DC) content in a range of 80 wt.% to 99.8 wt.%; and(C) the surface-modified diamond particles have a G-D ratio as determined by Raman spectroscopy in a range of 0.1 to 4.

22. The method of claim 21 , wherein the surface-modified diamond particles have all three of the properties (A), (B), and (C).

23. A plurality of surface-modified diamond particles formed according to any one of claims 1 to 22.

24. A plurality of surface-modified diamond particles having at least one of the following properties (A), (B), and (C):(A) the surface-modified diamond particles have a non-diamond carbon (NDC) content in a range of 0.2 wt.% to 20 wt.%;(B) the surface-modified diamond particles have a diamond carbon (DC) content in a range of 80 wt.% to 99.8 wt.%; and(C) the surface-modified diamond particles have a G-D ratio as determined by Raman spectroscopy in a range of 0.1 to 4.

25. The surface-modified diamond particles of claim 24, wherein the surface-modified diamond particles have all three of the properties (A), (B), and (C).

26. The surface-modified diamond particles of claim 24, wherein the surface-modified diamond particles have surface metal contents as follows: a titanium content of not more than 0.001 wt.%; an iron content of not more than 0.002 wt.%; an aluminum content of not more than 0.001 wt.%; a zirconium content of not more than 0.0001 wt.%; a chromium content of not more than 0.0001 wt.%; a tungsten content of not more than 0.0001 wt.%; a first combined metals content of not more than 0.003 wt.%, the first combined metals consisting of titanium, iron, aluminum, zirconium, chromium, and tungsten; and a second combined metals content of not more than 0.01 wt.%, the second combined metals consisting of magnesium, titanium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, molybdenum, and tungsten.

27. The surface-modified diamond particles of claim 24, wherein the surface-modified diamond particles have surface metal extract concentrations as follows: a titanium concentration of not more than 100 ng / ml; an iron concentration of not more than 200 ng / ml; an aluminum concentration of not more than 100 ng / ml; a zirconium concentration of not more than 10 ng / ml; a chromium concentration of not more than 10 ng / ml; a tungsten concentration of not more than 10 ng / ml; a first combined metals concentration of not more than 300 ng / ml, the first combined metals consisting of titanium, iron, aluminum, zirconium, chromium, and tungsten; and a second combined metals concentration of not more than 1000 ng / ml, the secondcombined metals consisting of magnesium, titanium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zirconium, molybdenum, and tungsten.

28. A slurry composition comprising:0.002 wt.% to 5 wt.% surface-modified diamond particles according to any one of claims23 to 27;50 wt.% to 98 wt.% water; up to 3 wt.% dispersing agent;0.01 wt.% to 9 wt.% emulsifier; and2 wt.% to 50 wt.% oil.

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