Method for the separation of diamond particle clusters

Abstract

A method for the separation of diamond particle clusters into discrete diamond particles and/or into smaller diamond particle clusters comprising fewer diamond particles is disclosed. The diamond particle clusters are combined with at least one liquid phase organic or inorganic compound, or with a solution of at least one organic or inorganic compound in at least one solvent to form a reaction mixture. Mechanical means are then used to separate the diamond particle clusters into discrete diamond particles and/or into smaller clusters within the reaction mixture producing diamond particles with dangling bonds or free bonding sites on the surface of the diamond particles. The at least one organic or inorganic compound then reacts with these dangling bonds present on the diamond particle surface. The surfaces of the diamond particles are functionalized by the reaction with the organic or inorganic compounds and the diamond particles and/or smaller clusters produced are well dispersed in dry powder form, as well as in solution.

Claims

1. A method for the separation of diamond particle clusters having a diameter of less than or equal to 1.0 mm into discrete diamond particles and/or into smaller clusters comprising fewer diamond particles, the method comprising the steps of: a) combining the diamond particle clusters with at least one liquid phase unsaturated organic compound, or with a solution of at least one unsaturated organic compound in at least one solvent, to form a reaction mixture, the unsaturated organic compound comprising at least one carbon-carbon double bond or carbon-carbon triple bond; and b) introducing milling beads to the reaction mixture and producing diamond particles with dangling bonds on the surface of the diamond particles by imparting kinetic energy to the diamond particle clusters within the reaction mixture using mechanical means to break up the diamond particle clusters into discrete diamond particles and/or into smaller clusters comprising fewer diamond particles causing the at least one unsaturated organic compound to react with at least some of the dangling bonds on the diamond particles; wherein imparting kinetic energy to the diamond particle clusters is performed in a plurality of cycles, with each cycle of imparting kinetic energy to the diamond particle clusters being followed by a period of cooling the reaction mixture.

2. A method according to claim 1, wherein step b) includes shaking or stirring the reaction mixture or applying ultrasonication to the reaction mixture.

3. A method according to claim 2, wherein the reaction mixture is shaken at a frequency of at least 10 Hz.

4. A method according to claim 2, wherein ultrasonication is applied to the reaction mixture at a frequency of not more than 80 kHz.

5. A method according to claim 1, wherein the milling beads are ceramic milling beads.

6. A method according to claim 5, wherein the milling beads are selected from the group comprising zirconia beads and silica beads and mixtures thereof.

7. A method according to claim 1, wherein the milling beads are larger than the diamond particles by a factor of between 100 and 100000.

8. A method according to claim 1, wherein the diamond particles have a diameter of 0.5 mm or less.

9. A method according to claim 1, wherein the diamond particles are nanodiamond particles and have a diameter in the range 1 to 1000 nm.

10. A method according to claim 1, wherein the at least one unsaturated organic compound is a straight chain alkene.

11. A method according to claim 1, wherein the at least one unsaturated organic compound is unsaturated at the first position.

12. A method according to claim 1, wherein the at least one unsaturated organic compound comprises a number of carbon atoms in the range 6 to 12.

13. A method according to claim 1, wherein the period of cooling the reaction mixture cools the liquid phase unsaturated organic compound to a temperature of not more than the boiling point of the reaction mixture.

14. A method according to claim 1, further comprising: c) separating the discrete diamond particles from the milling beads.

15. A method according to claim 14, wherein in step c) the diamond particles are separated from the milling beads using a method selected from the group comprising: filtration, centrifugation, extraction, precipitation, decantation and combinations thereof.

16. A method according to claim 1, further comprising the step of isolating the discrete diamond particles in solid form.

17. A method for the separation of diamond particle clusters having a diameter of less than or equal to 1.0 mm into discrete diamond particles and/or into smaller clusters comprising fewer diamond particles, the method comprising the steps of: a) combining the diamond particle clusters with at least one liquid phase unsaturated organic compound, or with a solution of at least one unsaturated organic compound in at least one solvent, to form a reaction mixture, the unsaturated organic compound comprising at least one carbon-carbon double bond or carbon-carbon triple bond; and b) creating diamond particles with dangling bonds on the surface of the diamond particles by imparting kinetic energy to the diamond particle clusters within the reaction mixture using mechanical means to break up the diamond particle clusters into discrete diamond particles and/or into smaller clusters comprising fewer diamond particles causing the at least one unsaturated organic compound to react with at least some of the dangling bonds on the diamond particles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings, which illustrate preferred embodiments of the invention:

(2) FIG. 1 is an FTIR spectrum of nanodiamonds alkylated with 1-undecene;

(3) FIG. 2 is a C1s X-ray photoemission spectrum of nanodiamonds alkylated with 1-undence;

(4) FIG. 3 illustrates Super STEM images of nanodiamond powder functionalised with 1-undecene that has been re-suspended in solution and deposited by a drop cast method onto a carbon lacey TEM grid;

(5) FIG. 3a illustrates a bright-field (BF) image of separated nanodiamond particles;

(6) FIG. 3b is a BF image of twinned particles;

(7) FIGS. 3c and 3d illustrate a HAADF image of nanodiamond crystallinity;

(8) FIG. 4 illustrates HRTEM images and an associated fast Fourier transform (FFT) of evaporated nanodiamond powder evaporated at 200 C. for 15 minutes, on a lacey carbon TEM grid.

(9) FIG. 4a is a BF image of sparsely distributed nanodiamonds;

(10) FIG. 4b is a magnification of a box-selected area in FIG. 4a;

(11) FIG. 4c is a BF image of an isolated nanodiamond; and

(12) FIG. 4d is an FFT analysis of the nanodiamond crystalline structure from FIG. 4c.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(13) Nanodiamonds used in the examples were produced by the detonation of explosives with a negative oxygen balance in hermetic tanks.

EXAMPLES

Example 1: Alkylation with 1-Undecene

(14) The detonation nanodiamond powder was boiled in a mixture of concentrated sulphuric and perchloric acids (1:1) for a period of two hours in order to remove any non-diamond forms of carbon. After this purification step the powder was dried in air at 50 C. to produce dry nanodiamond powder containing clusters of nanodiamonds.

(15) 200 mg of the dry nanodiamond powder was mixed with 1 g of zirconia/silica beads with an average diameter of approximately 0.1 mm. The mixture was placed in a plastic vial (2 ml) and filled with 1-undecene (C.sub.11H.sub.22).

(16) The vial containing the mixture was shaken in a MiniBeadbeater 3110BX (Stratech Scientific Ltd) at a frequency of 4500 Hz. Shaking was performed in cycles lasting 5 minutes. After each cycle the sample was cooled to avoid excessive heating by immersing the vial in water with a temperature of approximately 15 C. Shaking and cooling was repeated twelve times to give a total shaking time of 1 hour.

(17) After shaking, the slurry containing the beads, the nanodiamonds and the 1-undecene was transferred to a Whatman cellulose extraction thimble and placed inside a Quickfit Sohxhlet exctrator to recover the nanodiamond material. Extraction of the nanodiamond particles was performed with undecane at 174 C. for 15 hours.

(18) After the extraction, the solution was centrifuged at 16000 g for 1 hour.

(19) The solution was left to evaporate completely to leave the alkylated nanodiamonds as a pale white powder residue.

(20) Confirmation of 1-undecene attachment to the nanodiamonds was performed by Fourier transform infrared spectroscopy (FTIR). FIG. 1 shows the FTIR spectrum of the alkylated nanodiamonds. The peak at 2955 cm.sup.1 indicates the presence of the CH.sub.3 asymmetric stretch mode, while bands at 2924 cm.sup.1 and 2854 cm.sup.1 confirm the presence of CH.sub.2 asymmetric and symmetric stretch modes. The appearance of a terminal methyl group can be demonstrated by vibrational absorption at 1463 and 1375 cm.sup.1 corresponding to CCH.sub.3 asymmetric and symmetric bending vibration, respectively. The complete absence of CC groups which would appear at 1610-1680 cm.sup.1 confirms that the 1-undecene is involved directly in bonding to the surface. It is suggested that the bond of the alkene is broken, transforming into a bond linking the alkene to the nanodiamond surface.

(21) A sample of the alkylated nanodiamond powder was dissolved in pentane and several drops were deposited and allowed to dry upon a pre-cleaned, and Argon ion sputter tantalum foil for X-ray photoemission spectroscopy (XPS) characterisation.

(22) FIG. 2 illustrates the C1s X-ray photoemission spectrum of the nanodiamonds treated with 1-undecene. A single peak at a binding energy of 285.8 eV is observed, with a full width at half maximum (FWHM) of 1.7 eV indicating the presence of CC sp.sup.3 bonding within the material. This confirms that the sp.sup.2 component present in pristine nanodiamond powder has been removed.

(23) The SuperSTEM micrographs shown in FIG. 3 demonstrate that a solution of the alkyl-coated nanodiamonds with diameters of approximately 5 nm can be sparsely dispersed onto the surface of a lacey carbon TEM grid wand subsequently allowed to dry at ambient temperature (see FIG. 3a). FIGS. 3a and 3b confirm that the diamond particles are largely spherical in shape with an average diameter of 5 nm. These results confirm that the diamond particles remain as discrete particles after drying.

(24) FIG. 4 illustrates HRTEM images and an associated fast Fourier transform (FFT) of evaporated nanodiamond powder. FIG. 4a in particular illustrates that the diamond nanoparticles are well-separated and deposited successfully onto a lacey carbon grid by evaporation at 200 C. for 15 minutes. Enlargement of the micrograph, FIG. 4b, shows that separated nanodiamond particles have diameters ranging from 2-4 nm. FIG. 3c shows an isolated particle with a diameter of 4 nm, which was subsequently used to determine the crystalline structure of the evaporated nanodiamonds. Determination of the crystal structure was carried out by FFT analysis which can be seen in FIG. 3d.