AU2019250113A1

AU2019250113A1 - Method of manufacturing nanodiamonds and nanodiamonds

Info

Publication number: AU2019250113A1
Application number: AU2019250113A
Authority: AU
Inventors: Tomohide Ina; Tomoaki Mahiko
Original assignee: Daicel Corp
Current assignee: Daicel Corp
Priority date: 2018-12-07
Filing date: 2019-10-15
Publication date: 2020-06-25
Also published as: JP2023156281A; JP2020089864A; CN111282514A

Abstract

Abstract Object Provided is a method capable of producing nanodiamonds having a large specific surface area. Solution to Problem The method of manufacturing nanodiamonds according to the present invention includes producing nanodiamonds by detonating an explosive in a container under a condition where a ratio of volume of the container to mass of the explosive [the volume of the container (m3)/the mass of the explosive (kg)] is 10 or less. The volume of the container is preferably from 0.05 to 10 M3. The mass of the explosive is preferably from 0.07 to 1 kg. A nanodiamond content in a nanodiamond crude product obtained in the producing nanodiamonds is preferably from 5 to 55 mass%. Selected Drawing: FIG. 1 si PRODUCING NANODIAMONDS ____ ____ ___ _ __ ___ ____ ___S2 ACID-TREATING )f__ _ S4 ALKALI AND HYDROGEN PEROXIDE-TREATING ____ ___ ____ _ _ ____ ___ ___S5

Description

METHOD OF MANUFACTURING NANODIAMONDS AND NANODIAMONDS

Technical Field

[0001]

The present invention relates to a method of manufacturing nanodiamonds and nanodiamonds. More specifically, the present invention relates to a method of manufacturing nanodiamonds and nanodiamonds obtained by the method of manufacturing the same.

Background Art

[0002]

Nanodiamonds are ultrafine diamond particles having an extremely large specific surface area, and have high mechanical strength, and excellent electrical insulating properties and heat conductive properties. In addition, nanodiamonds exhibit a deodorizing effect, antimicrobial effect, and chemical resistance. Therefore, nanodiamonds are used as abrasive materials, conductivity imparting materials, insulating materials, deodorizing agents, and antimicrobial agents, for example.

[0003]

Typically, nanodiamonds are synthesized by a detonation method. The nanodiamonds obtained by the detonation method often form aggregates. By crushing the aggregates using a mill such as a bead mill, so-called single-digit nanodiamonds having a median diameter (D50) of less than 10 nm are obtained (see Patent Documents 1 and 2).

Citation List

Patent Document

[0004]

Patent Document 1: JP 2005-001983 A

Patent Document 2: JP 2010-126669 A

Summary of Invention [0005]

With the detonation method, it is relatively easy to manufacture nanodiamonds with a specific surface area of approximately 300 m²/g, but it is difficult to manufacture nanodiamond having an even larger specific surface area, for example, a specific surface area of approximately 320 m²/g or greater.

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[0006]

An embodiment of the present invention provides a method of manufacturing nanodiamonds that may be capable of producing nanodiamonds having a large specific surface area.

[0007]

The present inventors discovered that nanodiamonds having a large specific surface area can be obtained by a method of manufacturing nanodiamonds. Embodiments provide a method of manufacturing nanodiamonds, comprising producing nanodiamonds by detonating an explosive 10 in a container under a condition where a ratio of volume of the container to mass of the explosive [the volume of the container (m³)/the mass of the explosive (kg)] is in a specific range. Embodiments of the present invention have been completed based on these findings. [0008]

An aspect of the present invention provides a method of manufacturing nanodiamonds that includes producing nanodiamonds by detonating an explosive in a container under a condition where a ratio of volume of the container to mass of the explosive [the volume of the container (m³)/the mass of the explosive (kg)] is 10 or less.

[0009]

The volume of the container may preferably be from 0.05 to 10m³. [0010]

The mass of the explosive may preferably be from 0.07 to 1 kg. [0011]

A nanodiamond content in a nanodiamond crude product obtained in the producing nanodiamonds may preferably be from 5 to 55 mass%.

[0012]

A particle diameter of the explosive may preferably be from 45 to 2360 pm.

[0013]

The explosive may preferably be a mixture of trinitrotoluene and cyclotrimethylenetrinitramine.

[0014]

Another aspect of the present invention further provides nanodiamonds 35 having a median diameter from 4.0 to 5.5 nm and a specific surface area from 320 to 500 m²/g.

[0015]

The nanodiamonds may preferably be detonation nanodiamonds.

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[0016]

With the method of manufacturing nanodiamonds according to an embodiment of the present invention, it may be possible to produce nanodiamonds having a large specific surface area.

Brief Description of Drawing [0017]

Embodiments of the disclosure will now be described by way of example only with reference to the accompanying non-limiting Figure:

FIG. 1 is a flow chart of an embodiment of a method of manufacturing nanodiamonds according to the present invention.

Description of Embodiments [0018]

The method of manufacturing nanodiamonds according to embodiments of the present invention includes producing nanodiamonds by a detonation method (producing nanodiamonds). Note that the method of manufacturing nanodiamonds according to embodiments of the present invention may be referred to herein simply as “the manufacturing method according to the present invention”. The manufacturing method according to the present invention may include another process, such as purifying, oxygen-oxidizing, or hydrogenating, in addition to the producing nanodiamonds. Examples of the purifying include acid-treating, oxidizing, alkali and hydrogen peroxide-treating, and drying.

[0019]

FIG. 1 is a flow chart of an embodiment of the manufacturing method according to the present invention. The embodiment of the manufacturing method according to the present invention illustrated in FIG. 1 includes at least producing nanodiamonds SI, acid-treating S2, oxidizing S3, alkali and hydrogen peroxide-treating S4, 30 and drying S5.

[0020]

Producing Nanodiamonds

In producing nanodiamonds, nanodiamonds are produced by a detonation method. More specifically, first, an electric detonator is attached to a molded explosive, and then placed inside a pressure-resistant container for detonation, and the container is sealed in a state in which a gas having a specific composition and the explosive to be used coexist inside the container. In the producing nanodiamonds, then, the electric detonator is ignited, whereby the

11786948_1 (GHMatters) P112226.AU

2019250113 15 Oct 2019 explosive is detonated in the container. Detonation refers to, among explosive reactions associated with chemical reactions, one that includes a flame surface, where the reaction occurs, traveling at a high speed exceeding the speed of sound. During the detonation, the explosive that is used undergoes partially 5 incomplete combustion and releases carbon, and with the carbon being used as a raw material, nanodiamonds are produced by the action of the pressure and energy of shock waves that are produced in the explosion. In the production of the nanodiamonds, first a product obtained through the detonation method is subjected to Coulomb interaction between crystal planes, in addition to Van der 10 Walls forces between adjacent primary particles or crystallites, to be, as a result, very strongly assembled, thereby forming an aggregate.

[0021]

In the producing nanodiamonds, the explosive is detonated in the container under a condition where a ratio of the volume of the container to the 15 mass of the explosive [the volume of the container (m³)/the mass of the explosive (kg)] is 10 or less. When the ratio is 10 or less, heat dissipation after the detonation becomes slower, and thus graphitization on the surface of the resulting nanodiamond crude product is promoted. As a result, it is possible to produce nanodiamonds having a small median diameter and a large specific 20 surface area. The above-described ratio is preferably from 0.5 to 10, more preferably from 1 to 7, and still more preferably from 3.5 to 5.5. When the ratio is greater than or equal to 0.5, the primary particles of the resulting nanodiamonds exhibit narrow particle diameter distribution, and enhanced uniformity in particle diameter can be achieved. Furthermore, the nanodiamond 25 content in the produced nanodiamond crude product increases.

[0022]

The volume (capacity) of the container is preferably from 0.05 to 10 m³, and more preferably from 0.07 to 0.2 m³. When the volume of the container is 0.05 m³ or greater, nanodiamond productivity increases. When the volume of 30 the container is less than or equal to 10 m³, heat dissipation after the detonation becomes slower, whereby graphitization on the surface of the produced nanodiamond crude product is promoted. As a result, the particle diameter of the produced nanodiamonds can be reduced. Furthermore, the container is, for example, made from iron.

[0023]

The mass of the above-described explosive is preferably from 0.07 to 1 kg, and more preferably from 0.07 to 0.2 kg. When the mass of the explosive is not less than 0.07 kg, nanodiamond productivity increases.

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2019250113 15 Oct 2019

[0024]

A mixture of trinitrotoluene (TNT) and cyclotrimethylenetrinitramine,

i.e., hexogen (RDX), can be used for the explosive. The mass ratio (TNT/RDX) of TNT and RDX is, for example, in a range from 40/60 to 60/40.

[0025]

The particle diameter of the explosive is preferably from 45 to 2360 pm, more preferably from 45 to 1700 pm, and still more preferably from 75 to 90 pm. With the manufacturing method according to an embodiment of the present invention, it is possible to produce nanodiamonds having a small particle 10 diameter and a large specific surface area, even when the explosive having a particle diameter of 45 pm or greater, as described above, is used. Note that the particle diameter of the explosive can be measured by using a small angle X-ray scattering measurement method sieving method (%). [0026]

The pressure during the detonation is, for example, from 18 to 35.4 GPa, preferably from 24.4 to 29.3 GPa, and more preferably from 24.4 to 25.5 GPa. When the pressure is greater than or equal to 18 GPa, graphitization on the surface of the produced nanodiamond crude product becomes slower, and thus the nanodiamond content tends to increase.

[0027]

In the producing nanodiamonds, subsequently the container and the content therein are left for approximately 24 hours at room temperature, and thus, are cooled. After the cooling, the nanodiamond crude product (including soot and the nanodiamond aggregates produced as described above), which is 25 deposited on the inner wall of the container, is scraped with a spatula, whereby the nanodiamond crude product is collected. By the detonation method described above, the crude product of nanodiamond particles can be obtained. Furthermore, by implementing the producing of nanodiamonds described above several times, if necessary, a desired amount of the nanodiamond crude product 30 can be obtained.

[0028]

The nanodiamond content in the nanodiamond crude product obtained by the producing nanodiamonds is preferably from 10 to 55 mass%, more preferably from 13 to 50 mass%, and still more preferably from 15 to 40 35 mass%. With the manufacturing method according to an embodiment of the present invention, nanodiamonds having a small median diameter and a large specific surface area can be produced, and a nanodiamond crude product having

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2019250113 15 Oct 2019 a nanodiamond content of 10 mass% or greater can be obtained, whereby excellent production efficiency is achieved.

[0029]

Acid-Treating

In acid-treating, a strong acid is allowed to act on a nanodiamond crude product, i.e., a raw material, in an aqueous solvent, for example, to remove metal oxides. The nanodiamond crude product obtained by a detonation method is prone to include metal oxide, and this metal oxide is an oxide of metals, such as Fe, Co, or Ni, derived from the container or the like used in the detonation method. The metal oxide can be dissolved and removed from the nanodiamond crude product by allowing a strong acid to act thereon (acid treatment) in an aqueous solvent, for example. The strong acid used in the acid treatment is preferably a mineral acid, and examples thereof include hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia. A single kind of the 15 strong acid may be used, or two or more kinds of the strong acids may be used.

The concentration of the strong acid used in the acid treatment is, for example, from 1 to 50 mass%. The acid treatment temperature is from 70 to 150°C, for example. The duration of the acid treatment is, for example, from 0.1 to 24 hours. Furthermore, the acid treatment can be performed under reduced pressure, at atmospheric pressure, or under pressurization. After such acid treatment, the solid content (including nanodiamond aggregates) is washed with water by decantation, for example. Washing of the solid content by decantation is preferably repeated until the pH of the precipitate solution reaches 2 to 3, for example. When the content amount of metal oxide in the nanodiamond crude product obtained by the detonation method is small, the acid treatment such as that described above may be omitted.

[0030]

Oxidizing

Oxidizing is performed to remove graphite from a nanodiamond crude product by using an oxidizing agent. A nanodiamond crude product obtained by a detonation method contains graphite, and the graphite is derived from carbon that did not form nanodiamond crystals from among the carbons released when the explosive used underwent partially incomplete combustion. For example, an oxidizing agent can be allowed to act, in an aqueous solvent, on the nanodiamond crude product which is subjected to the acid treatment described above, thereby removing the graphite. Furthermore, an oxidizing agent can be allowed to act on the nanodiamond crude product, whereby an

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2019250113 15 Oct 2019 oxygen-containing group, such as a carboxyl group or a hydroxyl group, can be introduced to surfaces of the nanodiamonds.

[0031]

Examples of the oxidizing agent used in the oxidation treatment include 5 chromic acid, chromic anhydride, dichromic acid, permanganic acid, perchloric acid, nitric acid, and mixtures thereof, a mixed acid of at least one acid selected therefrom and another acid (for example, sulfuric acid), and salts thereof. Among these, a mixed acid (in particular, a mixed acid of sulfuric acid and nitric acid) is preferably used since such a mixed acid is environmentally friendly and exhibits excellent performance in oxidizing and removing graphite. [0032]

The mixture ratio of sulfuric acid to nitric acid (the former/the latter, mass ratio) in the above-described mixed acid is preferably, for example, from 60/40 to 95/5, since when the mixture ratio is in that range, it is possible to 15 efficiently oxidize and remove graphite at, for example, a temperature of 130°C or higher (particularly preferably 150°C or higher, and with the upper limit being 200°C, for example), even under approximately atmospheric pressure (for example, from 0.5 to 2 atm). The lower limit of the mixture ratio is preferably 65/35, and more preferably 70/30. The upper limit of the mixture ratio is preferably 90/10, more preferably 85/15, and still more preferably 80/20. When the mixing ratio is not less than 60/40, the reaction temperature becomes, for example, 120°C or higher under approximately atmospheric pressure, since sulfuric acid having a high boiling point is contained in a larger amount. Therefore, efficiency in graphite removal tends to be improved. When the mixing ratio is less than or equal to 95/5, nitric acid that greatly contributes to oxidation of graphite is contained in a larger amount, and thus efficiency in graphite removal tends to be improved.

[0033]

The amount of use of an oxidizing agent (in particular, the mixed acid 30 described above) is, for example, from 10 to 50 parts by mass, preferably from 15 to 40 parts by mass, and more preferably from 20 to 40 parts by mass, based on 1 part by mass of the nanodiamond crude product. In addition, the amount of use of sulfuric acid in the mixed acid is, for example, from 5 to 48 parts by mass, preferably from 10 to 35 parts by mass, and more preferably from 15 to 35 30 parts by mass, based on 1 part by mass of the nanodiamond crude product. In addition, the amount of use of nitric acid in the mixed acid is, for example, from 2 to 20 parts by mass, preferably from 4 to 10 parts by mass, and more

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2019250113 15 Oct 2019 preferably from 5 to 8 parts by mass, based on 1 part by mass of the nanodiamond crude product.

[0034]

Furthermore, when the mixed acid is used as the oxidizing agent, a catalyst may be used together with the mixed acid. When the catalyst is used, the removal efficiency of graphite can be further improved. Examples of the catalyst include copper carbonate (II), etc. The amount of use of the catalyst is, for example, from about 0.01 to about 10 parts by mass per 100 parts by mass of the nanodiamond crude product.

[0035]

The oxidation treatment temperature is, for example, from 100 to 200°C. The duration of the oxidation treatment is, for example, from 1 to 24 hours. The oxidation treatment can be performed under reduced pressure, at atmospheric pressure, or under pressurization.

[0036]

Alkali and Hydrogen Peroxide-Treating

In a case where metal oxides still remain in the nanodiamonds even after the above-described acid-treating, the nanodiamonds are in the form of aggregates (secondary particles) in which primary particles interact very strongly with each other and aggregate. In this case, an alkali and hydrogen peroxide may be allowed to act on the nanodiamonds in an aqueous solvent. As a result, the metal oxides remaining in the nanodiamonds can be removed, and separation of the primary particles from the aggregates can be promoted. Examples of the alkali used in this treatment include sodium hydroxide, ammonia, and potassium hydroxide. In alkali and hydrogen peroxide treatment, the concentration of the alkali is, for example, from 0.1 to 10 mass%, the concentration of hydrogen peroxide is, for example, from 1 to 15 mass%, the treatment temperature is, for example, from 40 to 100°C, and the duration for the treatment is, for example, from 0.5 to 5 hours. Furthermore, the alkali and hydrogen peroxide treatment can be performed under reduced pressure, at atmospheric pressure, or under pressurization.

[0037]

Drying

After the alkali and hydrogen peroxide-treating, drying is preferably performed. For example, by using a spray drying apparatus, an evaporator, etc., the liquid content is evaporated from the nanodiamond-containing solution obtained through the alkali and hydrogen peroxide-treating, and then the resulting residual solid content is dried by being heated and dried in a drying

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2019250113 15 Oct 2019 oven. The temperature during the drying by heating is, for example, from 40 to

150°C. Through the drying, powdery nanodiamond aggregates (nanodiamond particle aggregates) can be obtained.

[0038]

Oxygen-oxidizing

After the purifying, the nanodiamond powder may be subject to oxygen-oxidizing by being heated in an atmosphere of gas containing oxygen using a gas atmosphere furnace. Specifically, in the oxygen-oxidizing, the nanodiamond powder is placed in the gas atmosphere furnace, an oxygen-containing gas is fed into or passed through the furnace, the inside of the furnace is heated until reaching a temperature, at which a temperature condition set as the heating temperature is satisfied, whereby the oxygen oxidation treatment is performed. The temperature condition of this oxygen oxidation treatment is, for example, from 250 to 500°C. To achieve a negative zeta potential for the nanodiamond particles contained in a nanodiamond dispersion to be produced, the temperature of this oxygen oxidation treatment is preferably relatively high, namely from 400 to 450°C, for example.

Additionally, the oxygen-containing gas used in the oxygen-oxidizing may be a mixed gas containing, in addition to oxygen, an inert gas. Examples of the inert gas include nitrogen, argon, carbon dioxide, and helium. The oxygen concentration of the mixed gas is, for example, from 1 to 35 vol.%. [0039]

Hydrogenating

To achieve a positive zeta potential for the nanodiamond particles contained in a nanodiamond dispersion to be produced, hydrogenating is preferably performed after the oxygen-oxidizing described above. In the hydrogenating, the nanodiamond powder that was subjected to the oxygen-oxidizing is heated using a gas atmosphere furnace, in an atmosphere of gas containing hydrogen. Specifically, a hydrogen-containing gas is fed into or passed through the gas atmosphere furnace, in which the nanodiamond powder is placed, the inside of the furnace is heated until reaching a temperature at which a temperature condition set as the heating temperature is satisfied, whereby the hydrogenation treatment is performed. The temperature condition of this hydrogenation treatment is, for example, from 400 to 800°C.

Furthermore, the hydrogen-containing gas that is used in the hydrogenating may be a mixed gas containing, in addition to hydrogen, an inert gas. Examples of the inert gas include nitrogen, argon, carbon dioxide, and helium. The hydrogen concentration of the mixed gas is, for example, from 1 to 50 vol.%. To achieve a

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2019250113 15 Oct 2019 negative zeta potential for the nanodiamond particles contained in the nanodiamond dispersion to be produced, crushing, which will be described later, may be performed without performing the above-described hydrogenating.

[0040]

By the manufacturing method according to an embodiment of the present invention, it is possible to produce, for example, nanodiamonds, the primary particles of which have a median diameter from 4.0 to 5.5 nm, and the specific surface area of which is from 320 to 500 m²/g. Note that, the nanodiamonds, the primary particles of which have a median diameter from 4.0 to 5.5 nm, and the 10 specific surface area of which is from 320 to 500 m²/g may be referred to herein as “the nanodiamonds according to the present invention”.

[0041]

The median diameter (D50) of primary particles of the nanodiamonds according to an embodiment of the present invention is from 4.0 to 5.5 nm, 15 preferably from 4.2 to 5.2 nm, and more preferably from 4.4 to 5 nm. Note that the median diameter of the primary particles of nanodiamonds can be measured by a small angle X-ray scattering measurement method or a dynamic light scattering method.

[0042]

The nanodiamonds according to an embodiment of the present invention has a specific surface area of 320 to 500 m²/g, preferably from 340 to 450 m²/g, and more preferably from 350 to 430 m²/g. Note that the specific surface area of the nanodiamonds can be measured by the BET method. For example, by using a redispersion liquid of the nanodiamonds, the specific surface area of the nanodiamonds can be measured using an apparatus, BELSORP-max (available from BEL JAPAN, Inc.).

[0043]

Even after being purified by undergoing the purifying, the oxygen-oxidizing, the hydrogenating, etc. described above, the detonation nanodiamonds have strong tendency to be in the form of aggregates (secondary particles) in which the primary particles interact very strongly with each other and aggregate. After the purifying, the oxygen-oxidizing, or the hydrogenating, the crushing may be performed to cause more primary particles to be separated from the aggregates. Specifically, first, nanodiamonds that have undergone the 35 oxygen-oxidizing or subsequent hydrogenating are suspended in pure water to prepare a slurry containing nanodiamonds. In preparing the slurry, centrifugation may be carried out to remove relatively large aggregates from the nanodiamond suspension, or ultrasonic treatment may be performed on the

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2019250113 15 Oct 2019 nanodiamond suspension. The slurry is then subjected to a wet crushing treatment. The crushing treatment can be performed using, for example, a high shearing mixer, a high shear mixer, a homomixer, a ball mill, a bead mill, a high pressure homogenizer, an ultrasonic homogenizer, or a colloid mill. The crushing treatment may also be performed by combining these. From the viewpoint of efficiency, a bead mill is preferably used.

[0044]

A bead mill, which is a grinding device or a disperser, is provided with, for example, a cylindrical mill container, a rotor pin, a centrifugation mechanism, a raw material tank, and a pump. The rotor pin has an axial center serving also as an axial center of the mill container, and is configured to be rotatable at high speeds within the mill container. The centrifugation mechanism is disposed at an upper part inside the mill container. In bead milling using a bead mill in the crushing, the slurry (including nanodiamond aggregates) is charged as a raw material from the raw material tank into a lower part of the mill container by the action of the pump, in a state where the inside of the mill container is filled with beads and the rotor pin of the bead mill stirs the beads. The slurry passes through the beads, which are under high-speed stirring in the mill container, and reaches the upper part of the inside of the mill container. In this process, the nanodiamond aggregates contained in the slurry are subjected to action of grinding or dispersion through contact with the vigorously moving beads. As a result, crushing of the nanodiamond aggregates (secondary particles) into primary particles proceeds. The slurry and beads that have reached the centrifugation mechanism at the upper part in the mill container are subjected to centrifugation that is based on differences in specific gravity by the centrifugation mechanism being in operation. The beads remain in the mill container, and the slurry is discharged out of the mill container via a hollow line that is slidably coupled to the centrifugation mechanism. The discharged slurry is returned to the raw material tank, and then pumped back into the mill container by the action of the pump (circulation operation). In such bead milling, zirconia beads, for example, are used as crushing media, and the bead diameter is, for example, from 15 to 500 pm. The amount (apparent volume) of beads used to fill the mill container is, for example, from 50 to 80% of the capacity of the mill container. The circumferential speed of the rotor pin is, for example, from 8 to 12 m/minute. The amount of slurry to be circulated is, for example, from 200 to 600 ml, and the flow rate of the slurry is, for example, from 5 to 15 L/hour. Furthermore, the duration for treatment (circulation operation time) is, for example, from 30 to 300 minutes. In the crushing, instead

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2019250113 15 Oct 2019 of a continuous bead mill as described above, a batch-type bead mill may be used.

[0045]

By performing the crushing, a nanodiamond dispersion, in which 5 colloidal nanodiamond primary particles are dispersed, can be obtained. [0046]

After undergoing the crushing, the slurry may be subjected to a classification operation to remove coarse particles. For example, a classifier can be used to remove coarse particles from the slurry through a classification operation that uses centrifugation. As a result, a black transparent nanodiamond dispersion, in which primary particles of nanodiamonds are dispersed as colloidal particles, can be obtained.

[0047]

The nanodiamonds that have undergone the crushing, or the nanodiamonds that have undergone the crushing and the classification operation may be subjected to drying. In the drying, specifically, the dispersion containing nanodiamonds is subjected to the drying treatment thereby producing a dry powder of nanodiamonds. Examples of the drying treatment include spray drying performed using a spray drying apparatus or evaporating to dryness by using an evaporator.

[0048]

The nanodiamond dispersion contains nanodiamond particles and dispersion medium. The nanodiamond particles contained in the nanodiamond dispersion are nanodiamond primary particles or nanodiamond secondary particles derived from nanodiamonds obtained by the manufacturing method according to an embodiment of the present invention, and are dispersed as colloidal particles separated from each other in the dispersion medium. The median diameter of the nanodiamond particles is, for example, 60 nm or less, preferably 30 nm or less, more preferably 28 nm or less, still more preferably 25 30 nm or less, even more preferably 22 nm or less, and particularly preferably 20 nm or less. The median diameter of the nanodiamond primary particles included in the nanodiamond particles is, for example, 5.5 nm or less, preferably 5.2 nm or less, and more preferably 5 nm or less. For example, when nanodiamond dispersion is used as a material for adding or supplying nanodiamonds to a transparent resin or the like when producing a nanodiamond-containing transparent material, the nanodiamond particles having a smaller median diameter tends to be preferable, from the viewpoint of achieving high transparency of the transparent material. On the other hand, the lower limit of

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2019250113 15 Oct 2019 the median diameter of the nanodiamond particles is 1 nm, for example. The median diameter in the dispersion can be measured by a dynamic light scattering method.

[0049]

The specific surface area of the nanodiamond particles in the nanodiamond dispersion is preferably from 320 to 500 m²/g, more preferably from 340 to 450 m²/g, and still more preferably from 350 to 430 m²/g. Note that the specific surface area of the nanodiamonds can be measured by the BET method. For example, by using a redispersion liquid of the nanodiamonds, the 10 specific surface area of the nanodiamonds can be measured using an apparatus, BELSORP-max (available from BEL JAPAN, Inc.).

[0050]

The dispersion medium contained in the nanodiamond dispersion is a medium for appropriately dispersing nanodiamond particles in the nanodiamond 15 dispersion. The dispersion medium is preferably a solvent with which the nanodiamonds can be dissolved, and examples of the dispersion medium include water, methanol, ethanol, ethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone. Only one kind of dispersion medium may be used, or two or more kinds of dispersion media may be used. From the viewpoint of the dispersibility of the nanodiamond particles, the dispersion medium is preferably water or a water-based dispersion medium containing 50 mass% or greater of water.

[0051]

The nanodiamond dispersions constituted as described above can be used 25 as a material serving as a nanodiamond source when producing a composite material containing nanodiamonds. Furthermore, by the manufacturing method according to an embodiment of the present invention, it is possible to manufacture nanodiamond particles that can be used to prepare such nanodiamond dispersions, for example.

[0052]

The manufacturing method according to an embodiment of the present invention includes producing nanodiamonds by using a detonation method, and in the producing nanodiamonds, an explosive is detonated in a container under a condition where a ratio of volume of the container to mass of the explosive [the 35 volume of the container (m³)/the mass of the explosive (kg)] is 10 or less. The detonation in the manufacturing method according to an embodiment of the present invention is characterized in that the above-described ratio, i.e., the ratio of the volume of the container to the mass of the explosive is set to a small

11786948_1 (GHMatters) P112226.AU

2019250113 15 Oct 2019 value. With detonation being performed under the condition, heat dissipation after the detonation becomes slower, and thus graphitization on the surface of the resulting nanodiamond crude product is promoted. As a result, the diameter of the nanodiamond parts, i.e., the diameter of the nanodiamond particles obtained after the purifying, becomes smaller, and the specific surface area increases.

Examples [0053]

Hereinafter, embodiments of the present invention will be described in more detail based on examples, but the present invention is not limited by these examples.

[0054]

Example 1

Nanodiamonds and nanodiamond dispersions were made according to the following process.

Producing Nanodiamonds

In producing nanodiamonds, first, an electric detonator was attached to a molded explosive, and then placed inside a pressure-resistant container for detonation, and the container was sealed. The container was made from iron, and the capacity of the container was 0.2 m³. As the explosive, 0.2 kg of a mixture of TNT and RDX was used. The mass ratio (TNT/RDX) of TNT and RDX in the explosive was 60/40. Next, the electric detonator was ignited, and the explosive was detonated in the container. Subsequently, the container and its interior were left standing for 24 hours at room temperature, and were thereby cooled. After the cooling, a nanodiamond crude product deposited on the inner wall of the container (including soot and the nanodiamond particle aggregates produced by the detonation method described above) was scraped by using a spatula, thereby collecting the nanodiamond crude product.

[0055]

Acid-Treating

Next, the nanodiamond crude product obtained by performing the producing of nanodiamonds described above multiple times was subjected to an acid treatment. Specifically, a slurry obtained by adding 6 L of 10 mass% hydrochloric acid to 200 g of the nanodiamond crude product was subjected to heating treatment for 1 hour under reflux at normal pressure conditions. The heating temperature in this acid treatment was from 85 to 100°C. Next, after cooling, the solid content (including nanodiamond aggregates and soot) was

11786948_1 (GHMatters) P112226.AU

2019250113 15 Oct 2019 washed with water by decantation. Washing of the solid content by decantation was repeated until the pH of a precipitate solution reached 2 from the low pH side.

[0056]

Oxidizing

Oxidation treatment was then performed. Specifically, a slurry was formed by adding 6 L of a 98 mass% sulfuric acid aqueous solution and 1 L of a 69 mass% nitric acid aqueous solution to the precipitate solution (containing nanodiamond aggregates) obtained through decantation after the acid treatment, 10 and subsequently, the slurry was subjected to heat treatment under reflux for 48 hours at normal pressure conditions. The heating temperature in this oxidation treatment was from 140 to 160°C. Next, after cooling, the solid content (including nanodiamond aggregates) was washed with water by decantation. The initial supernatant liquid from the water washing was colored, and 15 therefore the washing of the solid content with water by decantation was repeated until the supernatant liquid became visually clear.

[0057]

Drying

Next, the precipitate solution (including nanodiamond aggregates) 20 obtained through decantation after the oxidation treatment was then subjected to drying treatment and a dried powder was obtained. As a technique for the drying treatment, evaporation to dryness by using an evaporator was adopted. In this way, the nanodiamond powder of Example 1 was obtained.

[0058]

Crushing Treatment

The crushing treatment was then performed. Specifically, first, 0.3 g of the nanodiamond powder that had undergone the drying, and 29.7 ml of pure water were mixed in a 50 ml sample bottle to obtain a slurry. Next, pH of the slurry was adjusted to 11 using a 3 mol/L sodium hydroxide aqueous solution. 30 As a result, 30 ml of a slurry having pH of 11 and containing 1 mass% of solid content was prepared. Next, the slurry was subjected to ultrasonic irradiation for 1 hour using an ultrasonic irradiator (trade name Ultrasonic Cleaner AS-3, available from AS ONE). Subsequently, bead milling was performed using a bead milling device (trade name Parallel 4-Tube Sand Grinder Model

LSG-4U-2L, available from Aimex Co., Ltd.). Specifically, 30 ml of the slurry after ultrasonic irradiation, and zirconia beads having a diameter of 30 pm were charged in a 100 ml vessel (available from Aimex Co., Ltd.), which was the mill container, and then the vessel was sealed. Then, the device was actuated to

11786948_1 (GHMatters) P112226.AU

2019250113 15 Oct 2019 perform bead milling. In this bead milling, the amount of zirconia beads that were charged was, for example, 33% of the capacity of the mill container, the rotational speed of the mill container was 2570 rpm, and the duration of the milling was 1 hour.

[0059]

Next, the slurry or suspension that had undergone the above-described crushing treatment was subjected to centrifugation treatment using a centrifuge device. The centrifugal force in this centrifugation treatment was 20000 xg, and the duration of the centrifugation was 10 minutes. Next, 10 ml of supernatant of 10 the nanodiamond-containing solution that had been subjected to this centrifugation treatment was collected. In this way, a nanodiamond dispersion of Example 1, in which the nanodiamonds are dispersed in pure water, was obtained.

[0060]

Examples 2 and 3 and Comparative Example 1

Nanodiamond crude products, nanodiamond powders, and nanodiamond dispersions were prepared in the same manner as in Example 1 except that, in the producing nanodiamonds, containers having volumes as shown in Table 1 and explosives according to masses as shown in Table 1 were used. 20 [0061]

The nanodiamond crude products, nanodiamond powders, and nanodiamond dispersions obtained in Examples and Comparative Example were evaluated as follows. The results are shown in Table 1. [0062]

1. Median Diameter of Primary Particles

For the obtained nanodiamond powders after the drying, the small angle X-ray scattering measurement using an X-ray diffractometer (trade name SmartLab, available from Rigaku Corporation) was performed and the primary particle diameters of the nanodiamonds were estimated, for scattering angles 30 ranging from 1° to 3°, by using particle diameter distribution analysis software (trade name NANO-Solver, available from Rigaku Corporation). In the estimate, it was assumed that the nanodiamond primary particles were spherical and had a particle density of 3.51 g/c m³. [0063]

2. Specific Surface Area

For the nanodiamond dispersions, the specific surface area was measured by using an automatic specific surface area/pore distribution measurement apparatus (trade name BELSORP-max, available from BEL JAPAN, Inc.).

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2019250113 15 Oct 2019

[0064]

3. Nanodiamond Content

The nanodiamond contents of the nanodiamond crude products were calculated according to the following equation:

Nanodiamond content [mass%] = mass of dried powder after drying/mass of nanodiamond crude product after producing nanodiamonds x 100 [0065] Table 1 (Table 1)

	Example 1	Example 2	Example 3	Comparative Example 1
Volume of container (m³)	0.2	0.2	0.2	31
Mass of explosive (kg)	0.2	0.1	0.7	1
Volume of container/Mass of explosive	1	2	3	31
Median diameter of primary particles (nm)	4.4	4.7	5.0	5.6
Specific Surface Area (m²/g)	423	385	360	311
Nanodiamond content (mass%)	16.0	24.3	33.1	61.2

Reference Signs List

[0066]

SI Producing nanodiamonds

S2 Acid-treating

S3 Oxidizing

S4 Alkali and hydrogen peroxide-treating

S5 Drying

[0067]

It is to be understood that, if any prior art publication is referred to herein, 20 such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. [0068]

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary 25 implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not

11786948_1 (GHMatters) P112226.AU to preclude the presence or addition of further features in various embodiments of the invention.

Claims

Claims [Claim 1]

A method of manufacturing nanodiamonds, comprising producing nanodiamonds by detonating an explosive in a container under a condition where a ratio of volume of the container to mass of the explosive [the volume of the container (m³)/the mass of the explosive (kg)] is 10 or less.
[Claim 2]

The method of manufacturing nanodiamonds according to claim 1, wherein the volume of the container is from 0.05 to 10m³.
[Claim 3]

The method of manufacturing nanodiamonds according to claim 1 or 2, wherein the mass of the explosive is from 0.07 to 1 kg.
[Claim 4]

The method of manufacturing nanodiamonds according to any one of claims 1 to 3, wherein a nanodiamond content in a nanodiamond crude product obtained in the producing nanodiamonds is from 5 to 55 mass%.
[Claim 5]

The method of manufacturing nanodiamonds according to any one of claims 1 to 4, wherein a particle diameter of the explosive is from 45 to 2360 pm.
[Claim 6]

The method of manufacturing nanodiamonds according to any one of claims 1 to 5, wherein the explosive is a mixture of trinitrotoluene and cyclotrimethylenetrinitramine.
[Claim 7]

Nanodiamonds comprising primary particles having a median diameter of 4.0 to 5.5 nm and a specific surface area from 320 to 500 m²/g.

11786948_1 (GHMatters) P112226.AU

2019250113 15 Oct 2019 [Claim 8]

The nanodiamonds according to claim 7, wherein the nanodiamonds are detonation nanodiamonds.