Nanodiamond manufacturing method and nanodiamond

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

[Technical Field]

[0001] 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. [Background technology]

[0002] 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. Therefore, they are used as abrasives, electrical conductivity enhancers, insulating materials, deodorizers, antibacterial agents, etc.

[0003] 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). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-001983 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-126669 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the detonation method, the specific surface area is 300m 2 Although it has been relatively easy to produce nanodiamonds with a specific surface area of ​​about 320 m / g, 2 It has been difficult to produce nanodiamonds of about 1 / g or more.

[0006] Therefore, an object of the present invention is to provide a method for producing nanodiamonds that can produce nanodiamonds with a large specific surface area. [Means for solving the problem]

[0007] The inventors of the present invention have conducted extensive research to achieve the above object, and have found that in the detonation method, the ratio of the container volume to the explosive mass [container volume (m 3 It has been discovered that nanodiamonds with a large specific surface area can be obtained by a method for producing nanodiamonds that includes a nanodiamond production step of detonating the explosive in the container under conditions where the ratio (mass of explosive (kg) / mass of explosive (kg)) falls within a specific range. The present invention was completed based on these findings.

[0008] That is, the present invention is based on the ratio of the container volume to the explosive mass [container volume (m 3 The present invention provides a method for producing nanodiamonds, which includes a nanodiamond production step of detonating the explosive in the container under conditions where the ratio (mass of explosive (kg) / mass of explosive (kg)) is 10 or less.

[0009] The container capacity is 0.05 to 10 m 3 It is preferable that:

[0010] The explosive mass is preferably 0.07 to 1 kg.

[0011] The nanodiamond content in the crude nanodiamond product obtained by the nanodiamond production step is preferably 5 to 55 mass %.

[0012] The particle size of the explosive is preferably 45 to 2360 μm.

[0013] Preferably, the explosive is a mixture of trinitrotoluene and cyclotrimethylenetrinitramine.

[0014] The present invention also provides a method for producing a carbon nanotube having a median diameter of 4.0 to 5.5 nm and a specific surface area of ​​320 to 500 m 2 / g of nanodiamonds.

[0015] The nanodiamonds are preferably detonation nanodiamonds. [Effects of the Invention]

[0016] According to the method for producing nanodiamonds of the present invention, it is possible to obtain nanodiamonds with a large specific surface area. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a process diagram showing one embodiment of the nanodiamond manufacturing method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The method for producing nanodiamonds of the present invention includes a step of generating nanodiamonds by detonation (nanodiamond generation 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 generation step, the production method of the present invention may also 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 hydrogen peroxide treatment step, and a drying step.

[0019] Figure 1 is a process diagram showing one embodiment of the manufacturing method of the present invention. 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 hydrogen peroxide treatment step S4, and a drying step S5.

[0020] (Nanodiamond production process) In the nanodiamond production process, nanodiamonds are produced by the detonation method. Specifically, a shaped explosive equipped with an electric detonator is first placed inside a pressure-resistant detonation vessel, and the vessel is sealed with a gas of a specific composition coexisting with the explosive. In the nanodiamond production process, the electric detonator is then detonated to detonate the explosive inside the vessel. Detonation refers to an explosion accompanying a chemical reaction in which the flame front of the reaction moves at a speed exceeding the speed of sound. During detonation, nanodiamonds are produced using carbon liberated by partial incomplete combustion of the explosive as a raw material, through the action of the pressure and energy of the shock wave generated by the explosion. Nanodiamonds are a product obtained by the detonation method. First, adjacent primary particles or crystallites are strongly aggregated together to form an aggregate due to the action of van der Waals forces and Coulomb interactions between crystal planes.

[0021] In the nanodiamond production process, the ratio of the container volume to the explosive mass [container volume (m 3 The explosive is detonated in the container under conditions where the ratio (mass of explosive (kg) / mass of explosive (kg)) is 10 or less. A ratio of 10 or less slows down heat dissipation after detonation, promoting graphitization of the surface of the resulting nanodiamond crude product, resulting in the production of nanodiamonds with a small median diameter and a large specific surface area. The ratio is preferably 0.5 to 10, more preferably 1 to 7, and even more preferably 3.5 to 5.5. A ratio of 0.5 or more narrows the particle size distribution of the primary particles, resulting in nanodiamonds with a more uniform particle size. Furthermore, the nanodiamond content in the resulting nanodiamond crude product is high.

[0022] The container capacity (volume) is 0.05 to 10 m 3 is preferable, and more preferably 0.07 to 0.2 m 3 The above container capacity is 0.05m 3 When the capacity of the container is 10m or more, the productivity of nanodiamonds is excellent. 3If the temperature is less than 100°C, the heat release rate after detonation is slowed down, and the particle size of the nanodiamonds produced can be reduced by promoting graphitization of the surface of the nanodiamond crude product produced.

[0023] 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.

[0024] The explosive may be a mixture of trinitrotoluene (TNT) and cyclotrimethylenetrinitramine, i.e., hexogen (RDX). The mass ratio of TNT to RDX (TNT / RDX) is, for example, in the range of 40 / 60 to 60 / 40.

[0025] 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 production 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 sieve passing method (%).

[0026] 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, graphitization of the surface of the generated nanodiamond crude product tends to be slower, resulting in a higher nanodiamond content.

[0027] In the nanodiamond production process, the container is then left to cool at room temperature for about 24 hours, allowing the temperature of the container and its interior to drop. 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 recovered. By using the detonation method described above, crude nanodiamond particles can be obtained. Furthermore, by repeating the nanodiamond production process described above as many times as necessary, it is possible to obtain the desired amount of crude nanodiamond product.

[0028] The nanodiamond content in the nanodiamond crude product obtained by the nanodiamond production step is preferably 10 to 55 mass%, more preferably 13 to 50 mass%, and even more preferably 15 to 40 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 mass% or more, resulting in excellent production efficiency.

[0029] (Acid treatment process) In the acid treatment process, 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, such as Fe, Co, and Ni, which originate 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). Mineral acids are preferred as the strong acid used in this acid treatment, and examples include hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia. One or more of the above strong acids may be used. 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. The acid treatment can be performed under reduced pressure, normal pressure, or increased pressure. After this acid treatment, the solids (including nanodiamond aggregates) are washed with water, for example, by decantation. It is preferable to repeatedly wash the solid matter with water by decantation until the pH of the precipitation liquid reaches, for example, 2 to 3. If the content of metal oxides in the crude nanodiamond product obtained by the detonation method is low, the acid treatment described above may be omitted.

[0030] (Oxidation treatment process) The oxidation treatment process is a process in which graphite is removed from the crude nanodiamond product using an oxidizing agent. The crude nanodiamond product obtained by the detonation method contains graphite, which is derived from the carbon liberated by the partial incomplete combustion of the explosive used and which did not form nanodiamond crystals. For example, after the above-mentioned acid treatment, graphite can be removed from the crude nanodiamond product by applying an oxidizing agent in an aqueous solvent. In addition, applying an oxidizing agent can introduce oxygen-containing groups such as carboxyl groups and hydroxyl groups onto the nanodiamond surface.

[0031] Examples of oxidizing agents used in this oxidation treatment include chromic acid, chromic anhydride, dichromic acid, permanganic acid, perchloric acid, nitric acid, mixtures thereof, mixed acids of at least one acid selected from these with other acids (e.g., sulfuric acid), and salts thereof. Among these, the use of mixed acids (particularly mixed acids of sulfuric acid and nitric acid) is preferred because it is environmentally friendly and has an excellent effect of oxidizing and removing graphite.

[0032] The mixing ratio of sulfuric acid to nitric acid (former / latter; mass ratio) in the mixed acid is preferably, for example, 60 / 40 to 95 / 5, since graphite can be efficiently oxidized and removed at temperatures of, for example, 130°C or higher (particularly preferably 150°C or higher; the upper limit is, for example, 200°C) even under pressures near atmospheric pressures (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 the reaction temperature is, for example, 120°C or higher under pressures near atmospheric pressures, and graphite removal efficiency tends to be improved. When the mixing ratio is 95 / 5 or less, the content of nitric acid, which significantly contributes to graphite oxidation, is high, so that graphite removal efficiency tends to be improved.

[0033] The amount of oxidizing agent (particularly the mixed acid) used is, for example, 10 to 50 parts by mass, preferably 15 to 40 parts by mass, and more preferably 20 to 40 parts by mass per part by mass of the crude nanodiamond 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 part by mass of the crude nanodiamond product. The amount of nitric acid used in the mixed acid is, for example, 2 to 20 parts by mass, preferably 4 to 10 parts by mass, and more preferably 5 to 8 parts by mass per part by mass of the crude nanodiamond product.

[0034] When the mixed acid is used as an oxidizing agent, a catalyst may be used together with the mixed acid. The use of a catalyst can further improve the efficiency of graphite removal. Examples of the catalyst include 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 crude nanodiamond product.

[0035] 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 carried out under reduced pressure, normal pressure, or increased pressure.

[0036] (Alkaline hydrogen peroxide treatment process) Even after the acid treatment process, if metal oxides remain on the nanodiamond, they form aggregates (secondary particles) due to strong interactions between primary particles. In such cases, the nanodiamond may be treated with alkali and hydrogen peroxide in an aqueous solvent. This removes the metal oxides remaining on the nanodiamond and promotes 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 alkali concentration is, for example, 0.1 to 10% by mass, the hydrogen peroxide concentration 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 elevated pressure.

[0037] (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 then dried by heating in a drying oven. The heating and drying temperature is, for example, 40 to 150°C. By undergoing this drying step, a nanodiamond aggregate (an aggregate of nanodiamond particles) is obtained as a powder.

[0038] (Oxygen oxidation process) The nanodiamond powder that has undergone the purification process may be subjected to an oxygen oxidation process in which it is heated in an oxygen-containing gas atmosphere using a gas atmosphere furnace. Specifically, in the oxygen oxidation process, the nanodiamond powder is placed in a gas atmosphere furnace, and an oxygen-containing gas is supplied or passed through the furnace. The temperature inside the furnace is raised to a preset temperature condition, and oxygen oxidation is performed. The temperature condition for this oxygen oxidation process is, for example, 250 to 500°C. To achieve a negative zeta potential for the nanodiamond particles contained in the nanodiamond dispersion liquid produced, the temperature condition for this oxygen oxidation process is preferably relatively high, for example, 400 to 450°C. The oxygen-containing gas used in the oxygen oxidation process may also be a mixed gas containing an inert gas in addition to oxygen. Examples of inert gases include nitrogen, argon, carbon dioxide, and helium. The oxygen concentration of the mixed gas is, for example, 1 to 35% by volume.

[0039] (Hydrogenation process) To achieve a positive zeta potential for the nanodiamond particles contained in the resulting nanodiamond dispersion, a hydrogenation process is preferably performed after the oxygen oxidation process. In the hydrogenation process, the nanodiamond powder that has undergone the oxygen oxidation process is heated in a hydrogen-containing gas atmosphere using a gas atmosphere furnace. Specifically, a hydrogen-containing gas is supplied to or passed through the gas atmosphere furnace containing the nanodiamond powder, and the temperature inside the furnace is raised to a preset temperature condition for hydrogenation. The temperature condition for this hydrogenation process is, for example, 400 to 800 °C. The hydrogen-containing gas used in the hydrogenation process may also be a mixed gas containing an inert gas in addition to hydrogen. Examples of inert gases include nitrogen, argon, carbon dioxide, and helium. The hydrogen concentration of the mixed gas is, for example, 1 to 50% by volume. To achieve a negative zeta potential for the nanodiamond particles contained in the resulting nanodiamond dispersion, the crushing process described below may be performed without performing the hydrogenation process.

[0040] According to the manufacturing method of the present invention, for example, a cellulose having a median diameter of primary particles of 4.0 to 5.5 nm and a specific surface area of ​​320 to 500 m 2 Nanodiamonds having a median diameter of 4.0 to 5.5 nm and a specific surface area of ​​320 to 500 m can be obtained. 2 / g may be referred to as "nanodiamonds of the present invention."

[0041] The nanodiamond of the present invention has a median diameter (D50) of 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 primary particles of nanodiamond can be measured by small-angle X-ray scattering or dynamic light scattering.

[0042] The nanodiamond of the present invention has a specific surface area of ​​320 to 500 m 2 / g, preferably 340 to 450m 2 / g, more preferably 350 to 430 m 2 / g. The specific surface area of ​​nanodiamonds can be measured by the BET method. For example, the redispersion liquid of nanodiamonds can be measured using a product called "BELSORP-max" (manufactured by BEL Japan Co., Ltd.).

[0043] Even after purification through the above-mentioned purification, oxygen oxidation, or hydrogenation processes, detonation nanodiamonds tend to form aggregates (secondary particles) in which primary particles aggregate due to very strong interactions between them. To separate many primary particles from these aggregates, a crushing process may be performed after the above-mentioned purification, oxygen oxidation, or hydrogenation processes. Specifically, nanodiamonds that have undergone the oxygen oxidation or subsequent hydrogenation processes are first suspended in pure water to prepare a nanodiamond-containing slurry. To prepare the slurry, centrifugation 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. Crushing can be performed using, for example, a high-shear mixer, high-shear mixer, homomixer, ball mill, bead mill, high-pressure homogenizer, ultrasonic homogenizer, colloid mill, etc. Crushing can also be performed using a combination of these. From the perspective of efficiency, using a bead mill is preferred.

[0044] A bead mill, which is a grinding or dispersing device, includes, for example, a cylindrical mill container, a rotor pin, a centrifugal separator, a raw material tank, and a pump. The rotor pin has a common axis with the mill container and is configured to rotate at high speed inside the mill container. The centrifugal separator is located at the top 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. The raw material slurry (including nanodiamond aggregates) is then introduced from the raw material tank to the bottom of the mill container by the action of the pump. The slurry reaches the top of the mill container through the beads being stirred at high speed inside the mill container. During this process, the nanodiamond aggregates contained in the slurry are crushed or dispersed by contact with the vigorously moving beads. This promotes the crushing of 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 operating centrifugal separator, utilizing the difference in specific gravity. The beads remain in the mill vessel, while 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, with a diameter of, 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 peripheral speed of the rotor pin is, for example, 8 to 12 m / min. The amount of 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.

[0045] By undergoing such a crushing process, a nanodiamond dispersion liquid containing primary particles of nanodiamond dispersed as colloidal particles can be obtained.

[0046] The slurry that has undergone the crushing process may be classified to remove coarse particles. For example, coarse particles can be removed from the slurry by centrifugal separation using a classification device. This results in a black, transparent nanodiamond dispersion in which the primary nanodiamond particles are dispersed as colloidal particles.

[0047] Nanodiamonds that have undergone the crushing process, or nanodiamonds that have undergone the crushing process and classification operation, may be subjected to a drying process. In this drying process, specifically, the dispersion liquid containing nanodiamonds is subjected to a drying process to obtain a dry powder of nanodiamonds. Examples of drying methods include spray drying using a spray drying device and evaporation to dryness using an evaporator.

[0048] 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 spaced apart from one another. 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 transparent resins, etc., when forming a nanodiamond-containing transparent component, a smaller median diameter of the nanodiamond particles tends to be preferable in terms of achieving high transparency in the transparent component. 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.

[0049] 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, more preferably 350 to 430m 2 / g. The specific surface area of ​​nanodiamonds can be measured by the BET method. For example, the redispersion liquid of nanodiamonds can be measured using a product called "BELSORP-max" (manufactured by BEL Japan Co., Ltd.).

[0050] The dispersion medium contained in the nanodiamond dispersion liquid is a medium for properly dispersing nanodiamond particles in the nanodiamond dispersion liquid. As the dispersion medium, a solvent in which nanodiamonds can be dissolved is preferred, for example, water, methanol, ethanol, ethylene glycol, dimethyl sulfoxide, N-methylpyrrolidone, etc. One type of dispersion medium may be used alone, or two or more types may be used. From the viewpoint of the dispersibility of nanodiamond particles, the dispersion medium is preferably water or an aqueous dispersion medium containing 50 mass% or more of water.

[0051] The nanodiamond dispersion liquid having the above-mentioned structure 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 to prepare such a nanodiamond dispersion liquid.

[0052] The manufacturing method of the present invention includes a step of generating nanodiamonds by a detonation method, and in the nanodiamond generation step, the ratio of the container volume to the explosive mass [container volume (m 3The explosive is detonated in the container under the condition that the ratio (mass of explosive (kg) / mass of explosive (kg)) is 10 or less. The detonation in the manufacturing method of the present invention is characterized by a small container volume relative to the explosive mass, and by carrying out the detonation under such conditions, heat dissipation after detonation is slowed, which promotes graphitization of the surface of the resulting crude nanodiamond product, resulting in a smaller diameter of the nanodiamond portion, i.e., the diameter of the nanodiamond particles after the purification process, and an increased specific surface area. [Example]

[0053] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0054] Example 1 Nanodiamonds and nanodiamond dispersions were produced through the following steps. (Nanodiamond production process) In the nanodiamond production process, the formed explosive, equipped 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 m. 3 The explosive used was a mixture of 0.2 kg of TNT and RDX. The mass ratio of TNT to RDX (TNT / RDX) in the explosive was 60 / 40. Next, an electric detonator was detonated to detonate the explosive inside the container. The container and its interior were then allowed to cool for 24 hours at room temperature. After cooling, the crude nanodiamond product (including the aggregates of nanodiamond particles and soot produced by the detonation method) adhering to the inner wall of the container was scraped off with a spatula, and the crude nanodiamond product was recovered.

[0055] (Acid treatment process) Next, the crude nanodiamond product obtained by repeating the nanodiamond production process multiple times was subjected to acid treatment. Specifically, 200 g of the crude nanodiamond product was added to 6 L of 10 mass % hydrochloric acid to obtain a slurry, which was then heated under reflux at atmospheric pressure for 1 hour. The heating temperature in this acid treatment was 85 to 100°C. Next, after cooling, the solid matter (including nanodiamond aggregates and soot) was washed with water by decantation. The solid matter was repeatedly washed with water by decantation until the pH of the precipitated liquid reached 2 from the low pH side.

[0056] (Oxidation treatment process) Next, an oxidation treatment was carried out. Specifically, 6 L of 98 mass % sulfuric acid aqueous solution and 1 L of 69 mass % nitric acid aqueous solution were added to the precipitate liquid (containing nanodiamond aggregates) obtained through decantation after the acid treatment to form a slurry, and this slurry was then heat-treated for 48 hours under reflux at atmospheric pressure. The heating temperature in this oxidation treatment was 140 to 160°C. Next, after cooling, the solid content (including nanodiamond aggregates) was washed with water by decantation. The supernatant liquid was colored at the beginning of the washing, so the solid content was repeatedly washed with water by decantation until the supernatant liquid became visually transparent.

[0057] (drying process) Next, the precipitated liquid (containing nanodiamond aggregates) obtained through 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.

[0058] (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 a pH of 11. Next, the slurry was subjected to ultrasonic irradiation for 1 hour using an ultrasonic irradiator (product name "Ultrasonic Cleaner AS-3" manufactured by AS ONE Corporation). After this, bead milling was performed using a bead milling machine (product name "Parallel Four-Cylinder Sand Grinder LSG-4U-2L type" manufactured by Aimex Co., Ltd.). Specifically, 30 ml of the ultrasonically irradiated slurry and 30 μm diameter zirconia beads were placed in a 100 ml milling vessel (manufactured by Aimex Co., Ltd.) and sealed, and the machine was operated to perform bead milling. In this bead milling, the amount of zirconia beads charged 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.

[0059] Next, the slurry or suspension that had undergone the above-mentioned crushing treatment was centrifuged using a centrifuge. The centrifugal force in this centrifugation treatment 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 centrifugal treatment was collected. In this way, the nanodiamond dispersion of Example 1, in which nanodiamonds were dispersed in pure water, was obtained.

[0060] Examples 2 and 3 and Comparative Example 1 In the nanodiamond production process, a crude nanodiamond product, nanodiamond powder, and nanodiamond dispersion were obtained in the same manner as in Example 1, except that a container with the capacity shown in Table 1 and an explosive with the mass shown in Table 1 were used.

[0061] The crude nanodiamond products, nanodiamond powders, and nanodiamond dispersions obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

[0062] (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 Corporation), and the primary particle size 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, the primary nanodiamond particles were assumed to be spherical and had a particle density of 3.51 g / cm. 3 It was assumed that this was the case.

[0063] (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 BEL Japan Co., Ltd.).

[0064] (3) Nanodiamond content The crude nanodiamond 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

[0065] [Table 1] [Explanation of symbols]

[0066] S1 Nanodiamond production process S2 Acid treatment process S3 Oxidation treatment process S4 Alkaline peroxide treatment process S5 Drying process

Claims

1. The container capacity is 0.07 to 0.2 m 3 , and the ratio of the container capacity to the explosive mass [container capacity (m ３ A method for producing nanodiamonds, comprising a nanodiamond production step of detonating the explosive in the container under conditions where the ratio [mass of explosive (kg)] is 10 or less.

2. The method for producing nanodiamonds according to claim 1, wherein the explosive mass is 0.07 to 1 kg.

3. 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 step is 5 to 55 mass%.

4. The method for producing nanodiamonds according to any one of claims 1 to 3, wherein the particle diameter of the explosive is 45 to 2360 μm.

5. The method for producing nanodiamonds according to any one of claims 1 to 4, wherein the explosive is a mixture of trinitrotoluene and cyclotrimethylenetrinitramine.

6. The median diameter of the primary particles is 4.0 to 5.5 nm, and the specific surface area is 360 to 430 m ２ / g of detonation nanodiamonds.

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