JP7565145B2 - Nanodiamond manufacturing method and nanodiamond - Google Patents

Description

The present invention relates to a method for producing nanodiamonds and nanodiamonds. More specifically, the present invention relates to a method for producing nanodiamonds and nanodiamonds obtained by the method.

Nanodiamonds are ultrafine diamond particles with a very large specific surface area, and have high mechanical strength, electrical insulation, and excellent thermal conductivity. They also have deodorizing, antibacterial, and chemical resistance properties. For this reason, they are used as abrasives, electrical conductivity agents, insulating materials, deodorizers, antibacterial agents, etc.

Nanodiamonds are generally synthesized by the detonation method. Nanodiamonds obtained by the detonation method often form aggregates, and by subjecting the aggregates to a crushing process using a grinder such as a bead mill, so-called single-digit nanodiamonds with a median particle diameter (D50) of less than 10 nm can be obtained (see Patent Documents 1 and 2).

JP 2005-001983 A JP 2010-126669 A

However, while it was relatively easy to produce nanodiamonds with a specific surface area of about 300 m ² /g using the detonation method, it was difficult to produce nanodiamonds with a larger specific surface area, for example, of about 320 m ² /g or more.

Therefore, the object of the present invention is to provide a method for producing nanodiamonds that can produce nanodiamonds with a large specific surface area.

As a result of intensive research into achieving the above object, the present inventors have found that a nanodiamond having a large specific surface area can be obtained by a method for producing nanodiamonds, which includes a nanodiamond production step in which the ratio of the container volume to the explosive mass [container volume (m ³ )/explosive mass (kg)] is within a specific range in a detonation method. The present invention was completed based on these findings.

In other words, the present invention provides a method for producing nanodiamonds, which includes a nanodiamond production step of detonating the explosive in a container under conditions where the ratio of container volume to explosive mass [container volume ( ^m3 )/explosive mass (kg)] is 10 or less.

The capacity of the container is preferably 0.05 to 10 ^m3 .

The explosive mass is preferably 0.07 to 1 kg.

It is preferable that the nanodiamond content in the nanodiamond crude product obtained by the nanodiamond production process is 5 to 55 mass%.

The particle size of the explosive is preferably 45 to 2360 μm.

The explosive is preferably a mixture of trinitrotoluene and cyclotrimethylenetrinitramine.

The present invention also provides nanodiamonds having a median diameter of 4.0 to 5.5 nm and a specific surface area of 320 to 500 m ² /g.

The nanodiamonds are preferably detonation nanodiamonds.

The method for producing nanodiamonds of the present invention makes it possible to obtain nanodiamonds with a large specific surface area.

FIG. 1 is a process diagram showing one embodiment of the nanodiamond manufacturing method of the present invention.

The method for producing nanodiamonds of the present invention includes a step of producing nanodiamonds by detonation (nanodiamond production step). In this specification, the method for producing nanodiamonds of the present invention may be simply referred to as the "production method of the present invention." In addition to the nanodiamond production step, the production method of the present invention may include other steps such as a purification step, an oxygen oxidation step, and a hydrogenation step. Examples of the purification step include an acid treatment step, an oxidation treatment step, an alkaline peroxide treatment step, and a drying step.

Figure 1 is a process diagram showing one embodiment of the manufacturing method of the present invention. The embodiment of the manufacturing method of the present invention shown in Figure 1 includes at least a nanodiamond production step S1, an acid treatment step S2, an oxidation treatment step S3, an alkaline peroxide treatment step S4, and a drying step S5.

(Nanodiamond production process)
In the nanodiamond production process, nanodiamonds are produced by the detonation method. Specifically, first, a molded explosive with an electric detonator attached is placed inside a pressure-resistant container for detonation, and the container is sealed in a state in which a gas of a specific composition and the explosive used coexist in the container. In the nanodiamond production process, the electric detonator is then detonated to detonate the explosive in the container. Detonation refers to an explosion caused by a chemical reaction in which the flame surface of the reaction moves at a high speed exceeding the speed of sound. During detonation, nanodiamonds are produced by the action of the pressure and energy of the shock wave generated by the explosion, using carbon liberated by partial incomplete combustion of the explosive used as a raw material. Nanodiamonds are products obtained by the detonation method, and first, adjacent primary particles or crystallites are very firmly assembled due to the action of van der Waals forces and the Coulomb interaction between the crystal faces, resulting in an aggregate.

In the nanodiamond production process, the explosive is detonated in the container under the condition that the ratio of container volume to explosive mass [container volume (m ³ )/explosive mass (kg)] is 10 or less. By setting the ratio to 10 or less, the heat dissipation after detonation is slowed down, and the graphitization of the surface of the nanodiamond crude product produced progresses, and as a result, nanodiamonds with a small median diameter and a large specific surface area can be produced. In addition, the ratio is preferably 0.5 to 10, more preferably 1 to 7, and even more preferably 3.5 to 5.5. When the ratio is 0.5 or more, the particle size distribution of the primary particles is narrow, and nanodiamonds with a more uniform particle size can be obtained. In addition, the nanodiamond content in the nanodiamond crude product produced is high.

The container capacity (volume) is preferably 0.05 to 10 ^m3 , more preferably 0.07 to 0.2 ^m3 . When the container capacity is 0.05 ^m3 or more, the productivity of nanodiamonds is excellent. When the container capacity is 10 ^m3 or less, the heat release rate after detonation is slowed down, and the graphitization of the surface of the nanodiamond crude product produced is promoted, thereby making it possible to keep the particle size of the nanodiamonds produced small. Moreover, the container is made of, for example, iron.

The mass of the explosive is preferably 0.07 to 1 kg, and more preferably 0.07 to 0.2 kg. If the mass of the explosive is 0.07 kg or more, the productivity of nanodiamonds is excellent.

The explosive may be a mixture of trinitrotoluene (TNT) and cyclotrimethylenetrinitramine, or hexogen (RDX). The mass ratio of TNT to RDX (TNT/RDX) is, for example, in the range of 40/60 to 60/40.

The particle size of the explosive is preferably 45 to 2360 μm, more preferably 45 to 1700 μm, and even more preferably 75 to 90 μm. According to the manufacturing method of the present invention, even when an explosive having a particle size of 45 μm or more is used, nanodiamonds having a small particle size and a large specific surface area can be produced. The particle size of the explosive can be measured by the small angle X-ray scattering measurement method sieve passing method (%).

The pressure during detonation is, for example, 18 to 35.4 GPa, preferably 24.4 to 29.3 GPa, and more preferably 24.4 to 25.5 GPa. If the pressure is 18 GPa or higher, the graphitization of the surface of the nanodiamond crude product produced tends to be delayed, and the nanodiamond content tends to be high.

In the nanodiamond production process, the container and its interior are then allowed to cool by being left at room temperature for about 24 hours. After this cooling process, the crude nanodiamond product (including the nanodiamond aggregates and soot produced as described above) adhering to the inner wall of the container is scraped off with a spatula, and the crude nanodiamond product is collected. By using the detonation method described above, crude nanodiamond particles can be obtained. Furthermore, by performing the nanodiamond production process described above the required number of times, it is possible to obtain the desired amount of crude nanodiamond product.

The nanodiamond content in the nanodiamond crude product obtained by the nanodiamond production process is preferably 10 to 55% by mass, more preferably 13 to 50% by mass, and even more preferably 15 to 40% by mass. According to the production method of the present invention, it is possible to produce nanodiamonds with a small median diameter and a large specific surface area, and to obtain a nanodiamond crude product with a nanodiamond content of 10% by mass or more, resulting in excellent production efficiency.

(Acid treatment process)
In the acid treatment step, a strong acid is applied to the raw nanodiamond crude product in, for example, an aqueous solvent to remove metal oxides. The nanodiamond crude product obtained by the detonation method is likely to contain metal oxides, and these metal oxides are oxides of Fe, Co, Ni, etc., derived from the container used in the detonation method. For example, by applying a strong acid in an aqueous solvent, metal oxides can be dissolved and removed from the nanodiamond crude product (acid treatment). As the strong acid used in this acid treatment, mineral acids are preferable, and examples include hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia. One type of strong acid may be used, or two or more types may be used. The concentration of the strong acid used in the acid treatment is, for example, 1 to 50 mass%. The acid treatment temperature is, for example, 70 to 150°C. The acid treatment time is, for example, 0.1 to 24 hours. The acid treatment can be performed under reduced pressure, normal pressure, or pressure. After such acid treatment, the solid content (including nanodiamond aggregates) is washed with water, for example by decantation. It is preferable to repeatedly wash the solid matter by decantation until the pH of the precipitation liquid reaches, for example, 2 to 3. When the content of metal oxide in the nanodiamond crude product obtained by the detonation method is small, the acid treatment as described above may be omitted.

(Oxidation treatment process)
The oxidation process is a process of removing graphite from the nanodiamond crude product using an oxidizing agent. The nanodiamond crude product obtained by the detonation method contains graphite, which is derived from the carbon that was liberated by partial incomplete combustion of the explosive used and did not form nanodiamond crystals. For example, after the above-mentioned acid treatment, graphite can be removed from the nanodiamond crude product by applying an oxidizing agent in an aqueous solvent. In addition, oxygen-containing groups such as carboxyl groups and hydroxyl groups can be introduced onto the nanodiamond surface by applying an oxidizing agent.

The oxidizing agent used in this oxidation treatment may be, for example, chromic acid, chromic anhydride, dichromic acid, permanganic acid, perchloric acid, nitric acid, a mixture of these, a mixed acid of at least one acid selected from these with another acid (such as sulfuric acid), or a salt of these. Among these, the use of a mixed acid (particularly a mixed acid of sulfuric acid and nitric acid) is preferred because it is environmentally friendly and has excellent effects of oxidizing and removing graphite.

The mixing ratio of sulfuric acid and nitric acid in the mixed acid (former/latter; mass ratio) is preferably, for example, 60/40 to 95/5, because graphite can be efficiently oxidized and removed at a temperature of, for example, 130°C or higher (particularly preferably 150°C or higher; the upper limit is, for example, 200°C) even under pressure near normal pressure (for example, 0.5 to 2 atm). The lower limit is preferably 65/35, more preferably 70/30. The upper limit is preferably 90/10, more preferably 85/15, and even more preferably 80/20. When the mixing ratio is 60/40 or higher, the content of sulfuric acid, which has a high boiling point, is high, so that under pressure near normal pressure, the reaction temperature becomes, for example, 120°C or higher, and the graphite removal efficiency tends to improve. When the mixing ratio is 95/5 or lower, the content of nitric acid, which contributes greatly to the oxidation of graphite, becomes high, so that the graphite removal efficiency tends to improve.

The amount of the oxidizing agent (particularly the mixed acid) used is, for example, 10 to 50 parts by weight, preferably 15 to 40 parts by weight, and more preferably 20 to 40 parts by weight, per part by weight of the crude nanodiamond product. The amount of sulfuric acid used in the mixed acid is, for example, 5 to 48 parts by weight, preferably 10 to 35 parts by weight, and more preferably 15 to 30 parts by weight, per part by weight of the crude nanodiamond product. The amount of nitric acid used in the mixed acid is, for example, 2 to 20 parts by weight, preferably 4 to 10 parts by weight, and more preferably 5 to 8 parts by weight, per part by weight of the crude nanodiamond product.

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

The oxidation temperature is, for example, 100 to 200°C. The oxidation time is, for example, 1 to 24 hours. The oxidation can be carried out under reduced pressure, normal pressure, or increased pressure.

(Alkaline peroxide treatment process)
Even after the acid treatment process, if the metal oxides that were not completely removed remain in the nanodiamond, they will take the form of aggregates (secondary particles) in which the primary particles interact very strongly with each other. In such cases, an alkali and hydrogen peroxide may be applied to the nanodiamond in an aqueous solvent. This can remove the metal oxides remaining in the nanodiamond, and can promote the separation of the primary particles from the aggregates. Examples of alkalis used in this treatment include sodium hydroxide, ammonia, and potassium hydroxide. In the alkaline peroxide treatment, the concentration of the alkali is, for example, 0.1 to 10% by mass, the concentration of the hydrogen peroxide is, for example, 1 to 15% by mass, the treatment temperature is, for example, 40 to 100° C., and the treatment time is, for example, 0.5 to 5 hours. The alkaline peroxide treatment can be performed under reduced pressure, normal pressure, or pressure.

(Drying process)
It is preferable to provide a drying step after the alkaline hydrogen peroxide treatment step. For example, the liquid is evaporated from the nanodiamond-containing solution obtained through the alkaline hydrogen peroxide treatment step using a spray dryer or evaporator, and the resulting residual solid is dried by heating in a drying oven. The heating and drying temperature is, for example, 40 to 150°C. By passing through such a drying step, a nanodiamond aggregate (an aggregate of nanodiamond particles) is obtained as a powder.

(Oxygen oxidation process)
The nanodiamond powder that has undergone the above purification process may be subjected to an oxygen oxidation process in which the nanodiamond powder is heated in an oxygen-containing gas atmosphere using a gas atmosphere furnace. In the oxygen oxidation process, specifically, the nanodiamond powder is placed in a gas atmosphere furnace, an oxygen-containing gas is supplied to or passed through the furnace, and the temperature inside the furnace is raised to a temperature condition set as the heating temperature, and oxygen oxidation process is performed. The temperature condition of this oxygen oxidation process is, for example, 250 to 500 ° C. In order to realize a negative zeta potential for the nanodiamond particles contained in the nanodiamond dispersion liquid to be produced, the temperature condition of this oxygen oxidation process is preferably relatively high, for example, 400 to 450 ° C. In addition, the oxygen-containing gas used in the oxygen oxidation process may be a mixed gas containing an inert gas in addition to oxygen. Examples of the inert gas include nitrogen, argon, carbon dioxide, and helium. The oxygen concentration of the mixed gas is, for example, 1 to 35 vol.%.

(Hydrogenation step)
In order to realize a positive zeta potential for the nanodiamond particles contained in the nanodiamond dispersion liquid to be produced, it is preferable to carry out a hydrogenation process after the oxygen oxidation process. In the hydrogenation process, the nanodiamond powder that has undergone the oxygen oxidation process is heated in a gas atmosphere containing hydrogen using a gas atmosphere furnace. Specifically, a hydrogen-containing gas is supplied or passed through a gas atmosphere furnace in which the nanodiamond powder is disposed, and the temperature inside the furnace is raised to a temperature condition set as the heating temperature to carry out the hydrogenation process. The temperature condition of this hydrogenation process is, for example, 400 to 800 ° C. The hydrogen-containing gas used in the hydrogenation process may be a mixed gas containing an inert gas in addition to hydrogen. Examples of the inert gas include nitrogen, argon, carbon dioxide, and helium. The hydrogen concentration of the mixed gas is, for example, 1 to 50 vol.%. In order to realize a negative zeta potential for the nanodiamond particles contained in the nanodiamond dispersion liquid to be produced, the crushing process described below may be carried out without carrying out such a hydrogenation process.

By such a manufacturing method of the present invention, it is possible to obtain nanodiamonds having a primary particle median diameter of 4.0 to 5.5 nm and a specific surface area of 320 to 500 ^m2 /g. In this specification, the above-mentioned nanodiamonds having a primary particle median diameter of 4.0 to 5.5 nm and a specific surface area of 320 to 500 ^m2 /g may be referred to as "nanodiamonds of the present invention."

The nanodiamond of the present invention has a median diameter (D50) of the primary particles of 4.0 to 5.5 nm, preferably 4.2 to 5.2 nm, and more preferably 4.4 to 5 nm. The median diameter of the primary particles of nanodiamond can be measured by small-angle X-ray scattering measurement or dynamic light scattering.

The nanodiamond of the present invention has a specific surface area of 320 to 500 m ² /g, preferably 340 to 450 m ² /g, and more preferably 350 to 430 m ² /g. The specific surface area of nanodiamond can be measured by the BET method. For example, the redispersion liquid of nanodiamond can be measured using a product called "BELSORP-max" (manufactured by Nippon BEL Co., Ltd.).

Even after being refined through the above-mentioned purification process, oxygen oxidation process, or hydrogenation process, etc., the detonation nanodiamonds tend to take the form of aggregates (secondary particles) in which primary particles are aggregated through very strong interactions between them. In order to separate many primary particles from the aggregates, a crushing process may be performed after the above-mentioned purification process, oxygen oxidation process, or hydrogenation process. Specifically, first, the nanodiamonds that have been subjected to the oxygen oxidation process or the subsequent hydrogenation process are suspended in pure water to prepare a slurry containing nanodiamonds. In preparing the slurry, a centrifugation process may be performed to remove relatively large aggregates from the nanodiamond suspension, or the nanodiamond suspension may be subjected to ultrasonic treatment. The slurry is then subjected to a wet crushing process. The crushing process may be performed using, for example, a high shear mixer, a high shear mixer, a homomixer, a ball mill, a bead mill, a high-pressure homogenizer, an ultrasonic homogenizer, a colloid mill, etc. The crushing process may be performed by combining these. From the viewpoint of efficiency, it is preferable to use a bead mill.

A bead mill, which is a grinding device or dispersing machine, is equipped with, for example, a cylindrical mill container, a rotor pin, a centrifugal separation mechanism, a raw material tank, and a pump. The rotor pin has a common axis with the mill container and is configured to be able to rotate at high speed inside the mill container. The centrifugal separation mechanism is arranged at the upper part of the mill container. In bead milling using a bead mill in the crushing process, the mill container is filled with beads and the rotor pin is stirring the beads, and the above-mentioned slurry (including nanodiamond aggregates) is introduced as a raw material from the raw material tank to the lower part of the mill container by the action of the pump. The slurry reaches the upper part of the mill container through the beads being stirred at high speed in the mill container. In this process, the nanodiamond aggregates contained in the slurry are subjected to the action of crushing or dispersing by contact with the beads that are moving vigorously. This advances the crushing of the nanodiamond aggregates (secondary particles) into primary particles. The slurry and beads that reach the centrifugal separator at the top of the mill vessel are centrifuged by the centrifugal separator using the difference in specific gravity. The beads remain in the mill vessel, and the slurry is discharged from the mill vessel via a hollow line slidably connected to the centrifugal separator. The discharged slurry is returned to the raw material tank, and then pumped back into the mill vessel (circulation operation). In this type of bead milling, the crushing media used is, for example, zirconia beads, and the diameter of the beads is, for example, 15 to 500 μm. The amount of beads (apparent volume) filled in the mill vessel is, for example, 50 to 80% of the volume of the mill vessel. The circumferential speed of the rotor pin is, for example, 8 to 12 m/min. The amount of the circulated slurry is, for example, 200 to 600 ml, and the flow rate of the slurry is, for example, 5 to 15 L/hour. The processing time (circulation operation time) is, for example, 30 to 300 minutes. In the crushing process, a batch-type bead mill may be used instead of the continuous bead mill described above.

By going through this crushing process, a nanodiamond dispersion liquid containing primary nanodiamond particles dispersed as colloidal particles can be obtained.

The slurry that has been through the crushing process may be subjected to a classification operation to remove coarse particles. For example, a classification device can be used to remove coarse particles from the slurry through a classification operation that utilizes centrifugation. This results in a black, transparent nanodiamond dispersion in which the primary nanodiamond particles are dispersed as colloidal particles.

Nanodiamonds that have been through the crushing process, or nanodiamonds that have been through the crushing and classification processes, may be subjected to a drying process. Specifically, in this drying process, the dispersion liquid containing nanodiamonds is subjected to a drying process to obtain a dry nanodiamond powder. Examples of the drying process include spray drying using a spray drying device and evaporation to dryness using an evaporator.

The nanodiamond dispersion contains nanodiamond particles and a dispersion medium. The nanodiamond particles contained in the nanodiamond dispersion are primary nanodiamond particles or secondary nanodiamond particles derived from nanodiamonds obtained by the manufacturing method of the present invention, and are dispersed as colloidal particles in the dispersion medium while being separated from each other. 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, even more preferably 25 nm or less, even more preferably 22 nm or less, and particularly preferably 20 nm or less. The median diameter of the primary nanodiamond particles constituting 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 using a nanodiamond dispersion as a material for adding or supplying nanodiamonds to a transparent resin or the like when forming a nanodiamond-containing transparent member, the smaller the median diameter of the nanodiamond particles, the more favorable it tends to be in terms of achieving high transparency in the transparent member. On the other hand, the lower limit of the median diameter of the nanodiamond particles is, for example, 1 nm. The median diameter in the dispersion can be measured by dynamic light scattering.

The specific surface area of the nanodiamond particles in the nanodiamond dispersion is preferably 320 to 500 m ² /g, more preferably 340 to 450 m ² /g, and even more preferably 350 to 430 m ² /g. The specific surface area of nanodiamond can be measured by the BET method. For example, the redispersion of nanodiamond can be measured using a product name "BELSORP-max" (manufactured by Nippon BEL Co., Ltd.).

The dispersion medium contained in the nanodiamond dispersion liquid is a medium for properly dispersing the nanodiamond particles in the nanodiamond dispersion liquid. The dispersion medium is preferably a solvent in which nanodiamonds can be dissolved, such as water, methanol, ethanol, ethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone. Only one type of dispersion medium may be used, or two or more types may be used. From the viewpoint of dispersibility of the nanodiamond particles, the dispersion medium is preferably water or an aqueous dispersion medium containing 50% or more by mass of water.

The nanodiamond dispersion liquid having the above-mentioned composition can be used as a nanodiamond supply material when producing a composite material containing nanodiamond. The manufacturing method of the present invention can produce nanodiamond particles that can be used, for example, to prepare such nanodiamond dispersion liquid.

The manufacturing method of the present invention includes a nanodiamond production step by detonation, in which the explosive is detonated in the container under conditions where the ratio of container volume to explosive mass [container volume ( ^m3 )/explosive mass (kg)] is 10 or less. The detonation in the manufacturing method of the present invention is characterized by a small ratio, i.e., container volume relative to explosive mass, and by carrying out the detonation under such conditions, heat dissipation after detonation is slowed down, and graphitization of the surface of the nanodiamond crude product produced progresses, resulting in a smaller diameter of the nanodiamond portion, i.e., the diameter of the nanodiamond particles after the purification step, and a larger specific surface area.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1
Nanodiamonds and nanodiamond dispersions were produced through the following steps.
(Nanodiamond production process)
In the nanodiamond production process, first, the formed explosive with an electric detonator was placed inside a pressure-resistant container for detonation, and the container was sealed. The container was made of iron and had a volume of 0.2 ^m3 . 0.2 kg of a mixture of TNT and RDX was used as the explosive. The mass ratio of TNT to RDX in the explosive (TNT/RDX) was 60/40. Next, the electric detonator was detonated to detonate the explosive in the container. Next, the container and its inside were allowed to cool by leaving it at room temperature for 24 hours. After this cooling, the nanodiamond crude product (including the aggregates and soot of nanodiamond particles generated by the above-mentioned detonation method) attached to the inner wall of the container was scraped off with a spatula, and the nanodiamond crude product was collected.

(Acid treatment process)
Next, the nanodiamond crude product obtained by performing the nanodiamond production process multiple times was subjected to acid treatment. Specifically, 200 g of the nanodiamond crude product was added with 6 L of 10% by mass hydrochloric acid to obtain a slurry, which was then heated for 1 hour under reflux at normal pressure. The heating temperature in this acid treatment was 85 to 100°C. Next, after cooling, the solids (including nanodiamond aggregates and soot) were washed with water by decantation. The solids were repeatedly washed with water by decantation until the pH of the precipitation liquid reached 2 from the low pH side.

(Oxidation treatment process)
Next, an oxidation treatment was performed. Specifically, 6 L of 98% by mass sulfuric acid aqueous solution and 1 L of 69% by mass nitric acid aqueous solution were added to the precipitate liquid (including nanodiamond aggregates) obtained by decantation after the acid treatment to form a slurry, and then the slurry was subjected to a heat treatment for 48 hours under reflux at normal pressure. The heating temperature in this oxidation treatment was 140 to 160°C. Next, after cooling, the solid matter (including nanodiamond aggregates) was washed with water by decantation. The supernatant liquid at the beginning of the washing was colored, and the solid matter was repeatedly washed with water by decantation until the supernatant liquid became visually transparent.

(Drying process)
Next, the precipitate (containing nanodiamond aggregates) obtained by decantation after the oxidation treatment was subjected to a drying treatment to obtain a dry powder. The drying method used was evaporation to dryness using an evaporator. In this way, the nanodiamond powder of Example 1 was obtained.

(Crushing process)
Next, a crushing process was performed. Specifically, 0.3 g of the nanodiamond powder that had undergone the drying process and 29.7 ml of pure water were added to a 50 ml sample bottle and mixed to obtain a slurry. Next, the pH of the slurry was adjusted to 11 using a 3 mol/L aqueous sodium hydroxide solution. This resulted in 30 ml of a slurry containing 1 mass% solids and having a pH of 11. Next, an ultrasonic irradiator (product name "ultrasonic cleaner AS-3", manufactured by AS ONE Co., Ltd.) was used to irradiate the slurry with ultrasonic waves for 1 hour. After this, bead milling was performed using a bead milling device (product name "parallel four-cylinder sand grinder LSG-4U-2L type", manufactured by IMEX Co., Ltd.). Specifically, 30 ml of the ultrasonically irradiated slurry and zirconia beads with a diameter of 30 μm were charged and sealed in a 100 ml mill vessel (manufactured by Imex Co., Ltd.), and the device was driven to perform bead milling. In this bead milling, the amount of zirconia beads charged was, for example, 33% of the volume of the mill vessel, the rotation speed of the mill vessel was 2570 rpm, and the milling time was 1 hour.

Next, the slurry or suspension that had undergone the above-mentioned disintegration process was centrifuged using a centrifuge. The centrifugal force in this centrifugation process was 20,000 x g, and the centrifugation time was 10 minutes. Next, 10 ml of the supernatant of the nanodiamond-containing solution that had undergone the centrifugation process was collected. In this way, the nanodiamond dispersion of Example 1, in which nanodiamonds are dispersed in pure water, was obtained.

Examples 2 and 3, and Comparative Example 1
In the nanodiamond production process, a container with the volume shown in Table 1 and an explosive with the mass shown in Table 1 were used, and the same procedure as in Example 1 was repeated to obtain a crude nanodiamond product, nanodiamond powder, and nanodiamond dispersion.

The nanodiamond crude products, nanodiamond powder, and nanodiamond dispersions obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

(1) Median diameter of primary particles For the nanodiamond powder obtained after the drying process, small angle X-ray scattering measurement was performed using an X-ray diffraction device (trade name "SmartLab", manufactured by Rigaku Corporation), and the primary particle diameter of the nanodiamond was estimated in the scattering angle range of 1° to 3° using particle size distribution analysis software (trade name "NANO-Solver", manufactured by Rigaku Corporation). In this estimation, it was assumed that the nanodiamond primary particles were spherical and had a particle density of 3.51 g/cm ³ .

(2) Specific Surface Area The specific surface area of the nanodiamond dispersion was measured using an automatic specific surface area/pore distribution measuring device (product name "BELSORP-max", manufactured by BEL Japan Co., Ltd.).

(3) Nanodiamond content The nanodiamond content of the crude product was calculated according to the following formula.
Nanodiamond content [mass%] = dry powder mass after drying process / nanodiamond crude product mass after nanodiamond production process × 100

S1 Nanodiamond production process S2 Acid treatment process S3 Oxidation treatment process S4 Alkaline hydrogen peroxide treatment process S5 Drying process

Claims (6)

The container capacity is 0.05 to 0.2 ^m3 , and the ratio of the container capacity to the explosive mass [container capacity ( ^m3
A method for producing nanodiamonds, comprising a nanodiamond production step of detonating the explosive in the container under conditions in which the ratio of the explosive mass (kg) to the explosive mass (kg) is 1 to 10. The method for producing nanodiamonds according to claim 1, wherein the explosive mass is 0.07 to 1 kg. The method for producing nanodiamonds according to claim 1 or 2, wherein the nanodiamond content in the crude nanodiamond product obtained by the nanodiamond production process is 5 to 55 mass%. The method for producing nanodiamonds according to any one of claims 1 to 3, wherein the particle size of the explosive is 45 to 2360 μm. The method for producing nanodiamonds according to any one of claims 1 to 4, wherein the explosive is a mixture of trinitrotoluene and cyclotrimethylenetrinitramine. The method for producing nanodiamonds according to any one of claims 1 to 5, wherein the nanodiamonds have a primary particle median diameter of 4.0 to 5.5 nm and a specific surface area of 360 to 430 m ² /g.

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