JP2023156281A - Production method of nanodiamond and nanodiamond - Google Patents

Abstract

To provide a production method of nanodiamond, with which nanodiamond with a large specific surface area can be obtained.SOLUTION: A production method of nanodiamond of this invention includes a nanodiamond generation step to detonate an explosive in a vessel under a condition in which a ratio of a capacity of the vessel to a mass of the explosive [(the capacity of the vessel (m3))/(the mass of the explosive (kg))] is 10 or less. The capacity of the vessel is preferably 0.05-10 m3. The mass of the explosive is preferably 0.07-1 kg. A content of nanodiamond in a crude product of nanodiamond obtained by the nanodiamond generation step is preferably 5-55 mass%.SELECTED DRAWING: Figure 1

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. It also has deodorizing effects, antibacterial effects, and chemical resistance. Therefore, it is used as an abrasive, a conductive material, an insulating material, a deodorant, an antibacterial agent, 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 crusher such as a bead mill, the median diameter (D50) of the particles can be reduced. So-called single-digit nanodiamonds with a diameter of less than 10 nm can be obtained (see Patent Documents 1 and 2).

Japanese Patent Application Publication No. 2005-001983 Japanese Patent Application Publication No. 2010-126669

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

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

As a result of intensive studies to achieve the above object, the present inventor has determined that in the detonation method, the ratio of container volume to explosive mass [container volume (m ³ )/explosive mass (kg)] is within a specific range. It has been found that nanodiamonds with a large specific surface area can be obtained according to a nanodiamond manufacturing method including a nanodiamond generation step of detonating the explosive in the container. The present invention was completed based on these findings.

That is, the present invention includes a nanodiamond generation step in which 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. Provided is a method for producing nanodiamonds.

The capacity of the container is preferably 0.05 to 10 m ³ .

The mass of the explosive is preferably 0.07 to 1 kg.

The nanodiamond content in the nanodiamond crude product obtained by the nanodiamond production step is preferably 5 to 55% by mass.

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

Preferably, the explosive is a mixture of trinitrotoluene and cyclotrimethylene trinitramine.

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.

According to the method for producing nanodiamonds of the present invention, it is possible to obtain nanodiamonds with a large specific surface area.

FIG. 1 is a process diagram showing an 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 (nanodiamond production step) by a detonation method. Note that in this specification, the nanodiamond manufacturing method of the present invention may be simply referred to as "the manufacturing method of the present invention." The manufacturing method of the present invention may include other steps such as a purification step, an oxygen oxidation step, and a hydrogenation step in addition to the nanodiamond generation step. Examples of the purification process include an acid treatment process, an oxidation treatment process, an alkaline perhydration treatment process, and a drying process.

FIG. 1 is a process diagram showing an embodiment of the manufacturing method of the present invention. An embodiment of the manufacturing method of the present invention shown in FIG. 1 includes at least a nanodiamond generation step S1, an acid treatment step S2, an oxidation treatment step S3, an alkaline perhydration treatment step S4, and a drying step S5.

(Nanodiamond generation process)
In the nanodiamond generation step, nanodiamonds are generated by a detonation method. Specifically, first, a shaped explosive equipped with an electric detonator is placed inside a pressure-resistant container for detonation, and a gas of a specific composition coexists with the explosive used inside the container. , seal the container. In the nanodiamond generation process, an electric detonator is then detonated to detonate the explosive within the container. A detonation is an explosion associated with a chemical reaction in which the flame front from which the reaction occurs moves at high speeds exceeding the speed of sound. During detonation, the explosive used partially burns incompletely, liberating carbon as a raw material, and nanodiamonds are produced by the pressure and energy of the shock wave generated by the explosion. Nanodiamonds are products obtained by the detonation method, and first of all, adjacent primary particles or crystallites become extremely strong due to the contribution of Coulomb interactions between crystal planes in addition to the effect of van der Waals forces. It aggregates and becomes a cohesive body.

In the nanodiamond generation step, the explosive is detonated in the container under conditions such that the ratio of container capacity to explosive mass [container capacity (m ³ )/explosive mass (kg)] is 10 or less. When the above ratio is 10 or less, the heat dissipation after detonation is delayed, so the surface of the generated nanodiamond crude product progresses to graphitization, and as a result, nanodiamonds with a small median diameter and a large specific surface area are produced. can be generated. Further, the above ratio is preferably 0.5 to 10, more preferably 1 to 7, and even more preferably 3.5 to 5.5. When the above 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. Moreover, the nanodiamond content in the nanodiamond crude product produced increases.

The container capacity (volume) is preferably 0.05 to 10 m ³ , more preferably 0.07 to 0.2 m ³ . When the container capacity is 0.05 m ³ or more, the productivity of nanodiamonds is excellent. When the container capacity is 10 m ³ or less, the particle size of the nanodiamonds produced can be kept small by slowing down the heat dissipation rate after detonation and promoting graphitization of the surface of the crude nanodiamond products produced. can. Further, the container is made of iron, for example.

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

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

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

The pressure during detonation is, for example, 18 to 35.4 GPa, preferably 24.4 to 29.3 GPa, more preferably 24.4 to 25.5 GPa. When the pressure is 18 GPa or more, graphitization of the surface of the generated nanodiamond crude product is slowed down, and the nanodiamond content tends to increase.

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

The nanodiamond content in the nanodiamond crude product obtained by the above nanodiamond production step is preferably 10 to 55% by mass, more preferably 13 to 50% by mass, and even more preferably 15 to 40% by mass. be. According to the production method of the present invention, nanodiamonds with a small median diameter and a large specific surface area can be produced, and a nanodiamond crude product with a nanodiamond content of 10% by mass or more can be obtained. Excellent efficiency.

(Acid treatment process)
In the acid treatment step, metal oxides are removed by treating the nanodiamond crude product as a raw material with a strong acid in, for example, an aqueous solvent. The nanodiamond crude product obtained by the detonation method tends to contain metal oxides, and these metal oxides are oxides of Fe, Co, Ni, etc. derived from the containers used in the detonation method. . For example, metal oxides can be dissolved and removed from the nanodiamond crude product by applying a strong acid to the nanodiamond crude product (acid treatment). The strong acid used in this acid treatment is preferably a mineral acid, such as hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia. The above strong acids may be used alone or in combination of two or more. The concentration of the strong acid used in the acid treatment is, for example, 1 to 50% by mass. The acid treatment temperature is, for example, 70 to 150°C. The acid treatment time is, for example, 0.1 to 24 hours. Further, the acid treatment can be performed under reduced pressure, normal pressure, or increased 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 content by decantation with water until the pH of the precipitate reaches, for example, 2 to 3. When the content of metal oxides in the nanodiamond crude product obtained by the detonation method is low, the above acid treatment may be omitted.

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

Examples of the oxidizing agent used in this oxidation treatment include chromic acid, chromic anhydride, dichromic acid, permanganic acid, perchloric acid, nitric acid, mixtures thereof, and at least one acid selected from these. Mixed acids with other acids (for example, sulfuric acid, etc.) and salts thereof can be mentioned. Among these, it is preferable to use a mixed acid (particularly a mixed acid of sulfuric acid and nitric acid) because it is environmentally friendly and has an excellent effect of oxidizing and removing graphite.

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

The amount of the oxidizing agent (particularly the above-mentioned 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 1 part by weight of the nanodiamond crude product. The amount of sulfuric acid used in the mixed acid is, for example, 5 to 48 parts by mass, preferably 10 to 35 parts by mass, and more preferably 15 to 30 parts by mass, per 1 part by mass of the nanodiamond crude 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 1 part by weight of the nanodiamond crude product.

Moreover, when using the above-mentioned mixed acid as an oxidizing agent, a catalyst may be used together with the mixed acid. By using a catalyst, graphite removal efficiency can be further improved. Examples of the catalyst include copper (II) carbonate. The amount of the catalyst used is, for example, about 0.01 to 10 parts by mass based on 100 parts by mass of the nanodiamond crude product.

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

(Alkaline perhydration treatment process)
Even after the above acid treatment process, if metal oxides that could not be completely removed remain on the nanodiamonds, aggregates (secondary particles). In such a case, an alkali and hydrogen peroxide may be applied to the nanodiamonds in an aqueous solvent. Thereby, metal oxides remaining on the nanodiamonds can be removed, and separation of the primary particles from the aggregate can be promoted. Examples of the alkali used in this treatment include sodium hydroxide, ammonia, potassium hydroxide, and the like. In alkaline perhydration treatment, the concentration of alkali is, for example, 0.1 to 10% by mass, the concentration of 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, it is 0.5 to 5 hours. Further, the alkaline perhydration treatment can be performed under reduced pressure, normal pressure, or increased pressure.

(drying process)
It is preferable to provide a drying step after the alkaline perhydration treatment step. For example, after evaporating the liquid from the nanodiamond-containing solution obtained through the above alkaline perhydration process using a spray dryer or evaporator, the remaining solids resulting from this are heated in a drying oven. Dry by drying. The heat drying temperature is, for example, 40 to 150°C. Through such a drying process, 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 step may be subjected to an oxygen oxidation step in which it is heated in an oxygen-containing gas atmosphere using a gas atmosphere furnace. Specifically, in the oxygen oxidation process, nanodiamond powder is placed in a gas atmosphere furnace, oxygen-containing gas is supplied or passed through the furnace, and the furnace is heated to a temperature condition set as the heating temperature. is heated to perform oxygen oxidation treatment. The temperature conditions for this oxygen oxidation treatment are, for example, 250 to 500°C. In order to achieve a negative zeta potential for the nanodiamond particles contained in the nanodiamond dispersion to be produced, the temperature condition for this oxygen oxidation treatment is preferably a relatively high temperature, for example, 400 to 450°C. be. Further, the oxygen-containing gas used in the oxygen oxidation step 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% by volume.

(Hydrogenation process)
In order to achieve a positive zeta potential of the nanodiamond particles contained in the nanodiamond dispersion to be produced, it is preferable to perform a hydrogenation step after the oxygen oxidation step. In the hydrogenation step, the nanodiamond powder that has undergone the oxygen oxidation step is heated in a gas atmosphere containing hydrogen using a gas atmosphere furnace. Specifically, hydrogen-containing gas is supplied or passed through a gas atmosphere furnace in which nanodiamond powder is placed, and the temperature inside the furnace is raised to a temperature condition set as the heating temperature, and the hydrogen processing is carried out. The temperature conditions for this hydrogenation treatment are, for example, 400 to 800°C. Further, the hydrogen-containing gas used in the hydrogenation step 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% by volume. In order to achieve a negative zeta potential of the nanodiamond particles contained in the nanodiamond dispersion to be produced, the crushing step described below may be performed without performing such a hydrogenation step.

By such a manufacturing method of the present invention, it is possible to obtain, for example, nanodiamonds whose primary particles have a median diameter of 4.0 to 5.5 nm and a specific surface area of 320 to 500 m ² /g. Note that in this specification, nanodiamonds whose primary particles have a median diameter of 4.0 to 5.5 nm and a specific surface area of 320 to 500 m ² /g are sometimes referred to as "nanodiamonds of the present invention". be.

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

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

Even after being purified through the above purification process, oxygen oxidation process, hydrogenation process, etc., detonation nanodiamonds are aggregates (aggregates) in which the primary particles interact very strongly. They tend to take the form of secondary particles). In order to separate many primary particles from this aggregate, a crushing step may be performed after the purification step, oxygen oxidation step, or hydrogenation step. Specifically, first, nanodiamonds that have undergone an oxygen oxidation step or a subsequent hydrogenation step 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, and the nanodiamond suspension may be subjected to ultrasonication. Then, the slurry is subjected to wet crushing treatment. The crushing treatment can 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, or the like. 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 crushing device or a dispersing machine, includes, 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 centrifuge mechanism is located at the top inside the mill container. In bead milling using a bead mill in the crushing process, with the mill container filled with beads and the rotor pin stirring the beads, the slurry as a raw material ( (containing nanodiamond aggregates) is introduced. The slurry reaches the upper part of the mill vessel through the beads being stirred at high speed within the mill vessel. During this process, the nanodiamond aggregates contained in the slurry are crushed or dispersed by contact with the rapidly moving beads. This progresses the disintegration of nanodiamond aggregates (secondary particles) into primary particles. The slurry and beads that have reached the centrifugal separation mechanism at the top of the mill container are centrifuged using the difference in specific gravity by the operating centrifugal separation mechanism, the beads remain in the mill container, and the slurry is It is discharged out of the mill vessel via a slidably connected hollow line. The discharged slurry is returned to the raw material tank, and then put into the mill container again by the action of the pump (circulation operation). In such bead milling, the crushing media used are, for example, zirconia beads, and the beads have a diameter of, for example, 15 to 500 μm. The amount of beads (apparent volume) filled into the mill container is, for example, 50 to 80% of the volume of the mill container. The circumferential speed of the rotor pin is, for example, 8 to 12 m/min. The amount of slurry to be circulated is, for example, 200 to 600 ml, and the flow rate of the slurry is, for example, 5 to 15 L/hour. Further, the processing time (circulation operation time) is, for example, 30 to 300 minutes. In the crushing step, a batch type bead mill may be used instead of the continuous type bead mill as described above.

Through such a crushing step, a nanodiamond dispersion containing primary nanodiamond particles dispersed as colloidal particles can be obtained.

The slurry that has undergone the crushing step may be subjected to a classification operation to remove coarse particles. For example, coarse particles can be removed from the slurry by a classification operation using centrifugation using a classification device. As a result, a black transparent nanodiamond dispersion liquid in which primary particles of nanodiamonds are dispersed as colloidal particles is obtained.

Nanodiamonds that have undergone a crushing process or nanodiamonds that have undergone a crushing process and a classification operation may be subjected to a drying process. In the drying step, specifically, the dispersion containing nanodiamonds is subjected to a drying treatment to obtain a dry powder of nanodiamonds. Examples of drying methods include spray drying using a spray dryer and evaporation to dryness using an evaporator.

The nanodiamond dispersion liquid contains nanodiamond particles and a dispersion medium. The nanodiamond particles contained in the nanodiamond dispersion are nanodiamond primary particles or nanodiamond secondary particles derived from nanodiamonds obtained by the production method of the present invention, and are separated from each other in a dispersion medium to form colloidal particles. It is distributed as. 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, still more preferably 22 nm or less, particularly preferably 20 nm or less. Further, the median diameter of the nanodiamond primary 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 etc. when forming a nanodiamond-containing transparent member, the smaller the median diameter of nanodiamond particles, the higher the This trend is favorable from the perspective of achieving transparency. On the other hand, the lower limit of the median diameter of nanodiamond particles is, for example, 1 nm. The median diameter in the above dispersion can be measured by a dynamic light scattering method.

Further, 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 still more preferably 350 to 430 m ² /g. Note that the specific surface area of nanodiamonds can be measured by the BET method. For example, a nanodiamond redispersion liquid can be measured using the product name "BELSORP-max" (manufactured by Nippon Bell Co., Ltd.).

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

The nanodiamond dispersion having the above structure can be used as a nanodiamond supply material when producing a composite material containing nanodiamonds. The production method of the present invention can produce nanodiamond particles that can be used, for example, to prepare such a nanodiamond dispersion.

The manufacturing method of the present invention includes a nanodiamond production step using a detonation method, and in the nanodiamond production step, the ratio of container volume to explosive mass [container volume (m ³ )/explosive mass (kg)] is 10 or less. The explosive is detonated in the container under the following conditions. The detonation in the production method of the present invention is characterized by the above ratio, that is, the container capacity to the mass of the explosive is small, and by performing the detonation under such conditions, the heat dissipation after detonation is delayed. Graphitization of the surface of the resulting crude nanodiamond product progresses, and as a result, the diameter of the nanodiamond portion, that is, the diameter of the nanodiamond particles after the purification step, becomes smaller and the specific surface area becomes larger.

The present invention will be explained in more detail below based on Examples, but the present invention is not limited to these Examples.

Example 1
Nanodiamonds and nanodiamond dispersions were manufactured through the following steps.
(Nanodiamond generation process)
In the nanodiamond production process, first, a shaped explosive with an electric detonator attached was placed inside a pressure-resistant container for detonation, and the container was sealed. The container is made of iron and has a volume of 0.2 m ³ . As the explosive, 0.2 kg of a mixture of TNT and RDX was used. The mass ratio of TNT to RDX (TNT/RDX) in the explosive is 60/40. An electric detonator was then detonated, causing the explosives to detonate inside the container. Next, the temperature of the container and its interior was lowered by leaving it at room temperature for 24 hours. After this cooling, the nanodiamond crude products (including soot and aggregates of nanodiamond particles produced by the above detonation method) adhering to the inner wall of the container are scraped off with a spatula, and the nanodiamond The crude product was collected.

(Acid treatment process)
Next, acid treatment was performed on the nanodiamond crude product obtained by performing the nanodiamond generation step multiple times. Specifically, a slurry obtained by adding 6 L of 10 mass % hydrochloric acid to 200 g of the nanodiamond crude product was heat-treated for 1 hour under reflux under normal pressure conditions. The heating temperature in this acid treatment is 85 to 100°C. Next, after cooling, the solid content (including nanodiamond aggregates and soot) was washed with water by decantation. The solid content was repeatedly washed with water by decantation until the pH of the precipitate reached 2 from the low pH side.

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

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

(Crushing process)
Next, a crushing process was performed. Specifically, first, 0.3 g of the nanodiamond powder that had undergone the above 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. Thereby, 30 ml of slurry containing 1% by mass of solids and having a pH of 11 was prepared. Next, the slurry was subjected to ultrasonic irradiation for 1 hour using an ultrasonic irradiator (trade name "Ultrasonic Cleaner AS-3", manufactured by AS ONE). Thereafter, bead milling was performed using a bead milling device (trade name: "Parallel four-barrel sand grinder LSG-4U-2L type", manufactured by Imex Co., Ltd.). Specifically, 30 ml of the slurry after ultrasonic irradiation and zirconia beads with a diameter of 30 μm are charged into a 100 ml mill container (manufactured by Imex Corporation) and sealed, and the device is driven to perform bead milling. was executed. In this bead milling, the input amount of zirconia beads is, for example, 33% of the volume of the mill container, the rotation speed of the mill container is 2570 rpm, and the milling time is 1 hour.

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

Examples 2, 3, and comparative example 1
In the nanodiamond production step, the nanodiamond crude product, nanodiamond powder, and nanodiamond A dispersion was obtained.

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

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

(2) Specific surface area The nanodiamond dispersion was measured using an automatic specific surface area/pore distribution measuring device (trade name "BELSORP-max", manufactured by Nippon Bell Co., Ltd.).

(3) Nanodiamond content ratio The nanodiamond crude product was calculated according to the following formula.
Nanodiamond content ratio [mass%] = Dry powder mass after drying process / Nanodiamond crude organism mass after nanodiamond generation process x 100

S1 Nanodiamond generation process S2 Acid treatment process S3 Oxidation treatment process S4 Alkaline perhydration treatment process S5 Drying process

Claims (8)

Production of nanodiamonds, including a nanodiamond generation step of detonating the explosive in the container under conditions such that the ratio of container capacity to explosive mass [container capacity (m ³ )/explosive mass (kg)] is 10 or less. Method. The method for producing nanodiamonds according to claim 1, wherein the container capacity is 0.05 to 10 m ³ . The method for producing nanodiamonds according to claim 1 or 2, wherein the mass of the explosive is 0.07 to 1 kg. The method for producing nanodiamonds according to any one of claims 1 to 3, wherein the nanodiamond content in the nanodiamond crude product obtained by the nanodiamond production step is 5 to 55% by mass. The method for producing nanodiamonds according to any one of claims 1 to 4, wherein the explosive has a particle size of 45 to 2360 μm. The method for producing nanodiamonds according to any one of claims 1 to 5, wherein the explosive is a mixture of trinitrotoluene and cyclotrimethylene trinitramine. A nanodiamond whose primary particles have a median diameter of 4.0 to 5.5 nm and a specific surface area of 320 to 500 m ² /g. The nanodiamond according to claim 7, which is a detonation method nanodiamond.

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