JP2017202940A - Nano diamond production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nano diamond production method suitable for obtaining nano diamond with good production efficiency with achieving high dispersibility.SOLUTION: The nano diamond production method include a heat oxidation process S3 for oxygen oxidation treating a powder of nano diamond under a temperature condition of 230 to 320°C. Prior the heat oxidation process S3, a purification process S2 for purifying a nano diamond crude product can be conducted. After the heat oxidation process S3, a pulverization process S4 for pulverizing nano diamond secondary particles to nano diamond primary particles can be conducted.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing nanodiamonds.

  In recent years, development of fine-grained diamond materials called nanodiamonds has been promoted. As for nanodiamonds, so-called single-digit nanodiamonds having a particle size of 10 nm or less may be required depending on applications. Techniques relating to the production of such nanodiamonds are described in, for example, the following Patent Documents 1 to 3 and Non-Patent Document 1.

JP-A-2005-001983 JP 2006-273704 A JP 2010-126669 A

O.Shenderova et al., “Modification of detonation nanodiamonds by heat treatment in air”, DIAMIOND AND RELATED MATERIALS, ELSEVIER B.V., October 13, 2006, Vol. 15, p.1799-1803

  Nanodiamonds having a primary particle size of 10 nm or less can exhibit high mechanical strength, high thermal conductivity, high refractive index, and the like, as do bulk diamonds. Nanoparticles, which are fine particles, generally have a large proportion of surface atoms (coordinately unsaturated), so that the sum of van der Waals forces that can act between surface atoms of adjacent particles is large and aggregates. Cheap. In addition to this, in the case of nanodiamond particles, a phenomenon called agglutination can be generated in which coulomb interaction between crystal planes of adjacent crystallites contributes and is very strongly assembled. Nanodiamond has such a unique property that crystallites or primary particles can interact with each other in a superimposed manner, and the primary particles are dispersed in, for example, a solvent by dissociating the primary particles of nanodiamond. Creating a technology involves technical difficulties. Nanodiamond is a product obtained by detonation, for example. First, it takes the form of an aggregate (secondary particle) in which primary particles are very strongly interacting and assembled. It is technically difficult to disintegrate into primary particles and maintain the dispersion state of primary particles in a desired solvent.

  Patent Document 2 and Non-Patent Document 1 describe a technique in which such nanodiamond is subjected to an air oxidation treatment prior to the crushing step so as to realize a good dispersion state in water. Patent Document 2 has a description that air oxidation treatment of nanodiamond powder was performed under the temperature conditions of 550 ° C., 600 ° C., or 650 ° C. in Examples 1 to 3. Non-Patent Document 1 describes that air oxidation treatment of nanodiamond powder was performed under a temperature condition within a range of 350 to 450 ° C.

  In the above-described air oxidation treatment, the higher the heating temperature of the nanodiamond powder, the more the amount of energy consumed in the treatment tends to increase, and from the time required for raising the temperature to the heating temperature and the heating temperature. The time required for lowering the temperature tends to be longer. Increasing the energy consumption in air oxidation treatment and increasing the temperature rise / fall time are not preferable for efficiently producing nanodiamonds dispersed in a solution system.

  The present invention has been conceived under the circumstances as described above, and provides a nanodiamond production method suitable for obtaining high production efficiency while realizing high dispersibility in a solution system for nanodiamonds. That is the purpose.

  The nanodiamond manufacturing method provided by the present invention includes a thermal oxidation process for subjecting nanodiamond powder to an oxygen oxidation treatment at a temperature of 230 to 320 ° C. In the present invention, the oxygen oxidation treatment is a treatment for causing an oxygen oxidation reaction in a state where nanodiamonds are placed in an atmosphere in which oxygen is present.

  When non-diamond carbon such as graphite or amorphous carbon exists on the surface of nano-diamond, if oxygen oxidation reaction occurs on the non-diamond carbon, carbon dioxide is generated and the non-diamond carbon is removed from the nano-diamond surface. The Rukoto. The more non-diamond carbon such as graphite and amorphous carbon present on the nanodiamond surface, the lower the dispersibility of the nanodiamond particles in the solution system. However, the non-diamond carbon on the nanodiamond surface is removed by oxygen oxidation treatment. Alternatively, the reduction contributes to achieving high dispersibility in a solution system for nanodiamonds. On the other hand, when an oxygen oxidation reaction occurs on the surface of the nanodiamond itself, the nanodiamond surface is oxygen-modified. Specifically, functional groups and partial structures containing oxygen atoms are generated on the nanodiamond surface. Examples of such a functional group or partial structure include a carbonyl group, a carboxy group, a lactone structure, and an acid anhydride structure. The more functional groups and partial structures containing oxygen atoms are present on the nanodiamond surface, the higher the dispersibility of the nanodiamond particles in the solution system. However, the nanodiamond surface is subject to oxygen modification by oxygen oxidation treatment. This contributes to the high dispersibility of nanodiamonds in solution systems.

  In the thermal oxidation process of the present invention, the nano-diamond powder is subjected to oxygen oxidation treatment at a temperature condition of 230 to 320 ° C., but is manufactured even if the oxygen oxidation treatment is not performed at a high temperature condition of, for example, 350 ° C. or higher. The present inventors have found that high dispersibility in a solution system can be realized for nanodiamonds. In addition, when the oxygen oxidation treatment is performed under a low temperature condition of 200 ° C., the oxygen oxidation reaction does not proceed sufficiently to achieve high dispersibility in the solution system for the manufactured nanodiamond. The inventors have found. These are the examples and comparative examples described later. In the oxygen oxidation treatment, the lower the heating temperature of the nanodiamond powder, the more the energy consumption in the treatment is suppressed, and the time required for the temperature to rise to or fall from the heating temperature tends to be shorter. The method in which the oxygen oxidation treatment in the thermal oxidation process is performed at a relatively low temperature of 230 to 320 ° C. is suitable for suppressing energy consumption in the process, and shortens the temperature rising time and the temperature falling time. Suitable for Suppressing energy consumption in the thermal oxidation process in the nanodiamond manufacturing process and shortening the temperature rise time and temperature fall time contribute to the production efficiency of nanodiamonds exhibiting high dispersibility in a solution system.

  As described above, the nanodiamond production method of the present invention is suitable for obtaining high production efficiency while realizing high dispersibility in a solution system for nanodiamonds.

  Preferably, the thermal oxidation step is performed in an atmosphere of a mixed gas containing an inert gas and oxygen. The inert gas is preferably nitrogen. The oxygen content of such a mixed gas is preferably 1 to 10% by volume. These configurations are suitable for appropriately performing the oxygen oxidation treatment at a relatively low temperature of 230 to 320 ° C.

  The nanodiamond production method of the present invention may include a purification step for purifying the nanodiamond crude product before the thermal oxidation step. This purification step may include a solution oxidation treatment in which an oxidizing agent is allowed to act on the nanodiamond. According to the solution oxidation treatment, non-diamond carbon such as graphite and amorphous carbon existing on the nanodiamond surface is reduced. The oxidizing agent preferably contains sulfuric acid and nitric acid. These structures are suitable for increasing the degree of purification of the nanodiamond used for the thermal oxidation process. The higher the degree of purification of the nanodiamond subjected to the thermal oxidation process, that is, the less non-diamond carbon such as graphite and amorphous carbon present on the surface of the nanodiamond subjected to the thermal oxidation process, In the oxidation treatment, the amount of oxygen acting on the surface of the nanodiamond itself tends to increase, and thus the nanodiamond surface is susceptible to oxygen modification.

  The nanodiamond production method of the present invention may include a crushing step for crushing the nanodiamond secondary particles into nanodiamond primary particles after the thermal oxidation step. Such a crushing step is preferable for appropriately dispersing the nanodiamond in a solution system.

  Preferably, the nano diamond is a nano diamond (detonation nano diamond) generated by a detonation method. According to the detonation method, it is possible to appropriately generate nanodiamond having a primary particle size of 10 nm or less.

It is process drawing of an example of the nano diamond manufacturing method of this invention. It is an expansion schematic diagram of the solution (nanodiamond dispersion liquid) which the nanodiamond disperse | distributed by the nanodiamond manufacturing method of this invention.

  FIG. 1 is a process diagram of a nanodiamond manufacturing method according to an embodiment of the present invention. This production method is a method for producing nanodiamonds that can be used, for example, in the preparation of a nanodiamond dispersion. In this embodiment, the production method includes at least a generation step S1, a purification step S2, and a thermal oxidation step S3. .

In the production step S1, nanodiamonds are produced, for example, by detonation. Specifically, first, a molded explosive equipped with an electric detonator is installed inside a pressure-resistant container for detonation, and in a state where a predetermined composition of gas and a used explosive coexist in the container, Seal the container. The container is made of, for example, iron, and the volume of the container is, for example, 0.5 to 40 m ³ . As the explosive, a mixture of trinitrotoluene (TNT) and cyclotrimethylenetrinitroamine, ie hexogen (RDX), can be used. The mass ratio (TNT / RDX) between TNT and RDX is, for example, in the range of 40/60 to 60/40. The amount of explosive used is, for example, 0.05 to 2.0 kg.

  Next, in the generation step S1, the electric detonator is detonated, and the explosive is detonated in the container. Detonation refers to an explosion associated with a chemical reaction in which the reaction flame surface moves at a speed exceeding the speed of sound. At the time of detonation, the diamond used is generated by the action of the pressure and energy of the shock wave generated by the explosion, using the carbon that is liberated due to partial incomplete combustion of the explosive used. According to the detonation method, it is possible to appropriately generate nanodiamond having a primary particle size of 10 nm or less. Nanodiamond is a product obtained by the detonation method. First, the adjacent primary particles or crystallites are very strong due to the coulomb interaction between crystal planes in addition to the action of van der Waals force. Gather and form a cohesive.

  In the production step S1, the temperature of the container and its interior is then lowered by leaving it at room temperature, for example, for 24 hours. After this cooling, the nanodiamond coarse product (including the nanodiamond adherends and wrinkles produced as described above) adhering to the inner wall of the container is scraped off with a spatula, and the nanodiamond coarse product is scraped off. The product is recovered. A crude product of nanodiamond particles can be obtained by the detonation method as described above. Moreover, it is possible to obtain a desired amount of the nanodiamond crude product by performing the generation step S1 as described above as many times as necessary.

  In the present embodiment, the purification step S2 includes an acid treatment in which a strong acid is allowed to act on the raw nanodiamond product as a raw material in, for example, an aqueous solvent. The nano-diamond crude product obtained by the detonation method is likely to contain a metal oxide. This metal oxide is an oxide such as Fe, Co, Ni, etc. derived from the container used for the detonation method. is there. For example, by applying a predetermined strong acid in an aqueous solvent, the metal oxide can be dissolved and removed from the nanodiamond crude product (acid treatment). The strong acid used for this acid treatment is preferably a mineral acid, and examples thereof include hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia. In the acid treatment, one type of strong acid may be used, or two or more types of strong acid 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 such an acid treatment, the solid content (including the nanodiamond adherend) is washed with water, for example, by decantation. It is preferable to repeat the washing of the solid content by decantation until the pH of the precipitation liquid reaches, for example, 2 to 3. When the content of the metal oxide in the nanodiamond crude product obtained by the detonation method is small, the above acid treatment may be omitted.

  In the present embodiment, the purification step S2 is a solution oxidation treatment for removing non-diamond carbon such as graphite and amorphous carbon from a crude nanodiamond product (nanodiamond aggregate before purification is finished) using an oxidizing agent. Including. The nano-diamond crude product obtained by the detonation method contains non-diamond carbon such as graphite and amorphous carbon. This non-diamond carbon causes partial incomplete combustion of the explosive used. It originates from the carbon which did not form the nano diamond crystal among the free carbon. For example, after the acid treatment described above, non-diamond carbon can be removed from the nanodiamond crude product by applying a predetermined oxidizing agent in an aqueous solvent, for example (solution oxidation treatment). Examples of the oxidizing agent used in the solution oxidation treatment include chromic acid, chromic anhydride, dichromic acid, permanganic acid, perchloric acid, and salts thereof, nitric acid, and mixed acid (a mixture of sulfuric acid and nitric acid). Can be mentioned. The ratio of concentrated sulfuric acid and concentrated nitric acid for preparing the mixed acid is, for example, 1: 1 to 10: 1 (volume ratio). In the solution oxidation treatment, one kind of oxidizing agent may be used, or two or more kinds of oxidizing agents may be used. The concentration of the oxidizing agent used in the solution oxidation treatment is, for example, 3 to 50% by mass. The usage-amount of the oxidizing agent in a solution oxidation process is 300-2000 mass parts with respect to 100 mass parts of nano diamond rough products attached | subjected to a solution oxidation process, for example. The solution oxidation treatment temperature is, for example, 50 to 250 ° C. The solution oxidation treatment time is, for example, 1 to 72 hours. The solution oxidation treatment can be performed under reduced pressure, normal pressure, or increased pressure. After such solution oxidation treatment, the solid content (including the nanodiamond adherend) is washed with water, for example, by decantation. When the supernatant liquid at the beginning of water washing is colored, it is preferable to repeat the washing of the solid content by decantation until the supernatant liquid becomes transparent visually.

  Even after the acid treatment and solution oxidation treatment as described above, detonation nanodiamonds are in the form of aggregates (secondary particles) in which the primary particles are assembled with very strong interactions. Take. In this embodiment, in order to promote separation of the primary particles from the adherend, a predetermined alkali and hydrogen peroxide may be allowed to act on the nanodiamond in an aqueous solvent. Thereby, for example, when the metal oxide that could not be removed even by the above-mentioned acid treatment remains in the nanodiamond, the metal oxide can be removed, and the primary nanodiamond from the nanodiamond adherend is removed. Separation of particles is promoted (alkaline overwater treatment). Examples of the alkali used for this treatment include sodium hydroxide, ammonia, potassium hydroxide and the like. In this 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. .5-5 hours. In addition, this treatment can be performed under reduced pressure, normal pressure, or increased pressure. After the supernatant is removed from the nanodiamond-containing solution that has undergone this treatment, for example, by decantation, the residual fraction is subjected to a drying treatment to obtain a dry powder. Examples of the drying treatment include spray drying performed using a spray drying apparatus and evaporation to dryness performed using an evaporator.

  Next, in this method, a thermal oxidation step S3 is performed. The thermal oxidation step S3 is a step for subjecting nanodiamond to oxygen oxidation treatment in order to realize high dispersibility in a solution system. In this step, the nanodiamond powder that has undergone the purification step S2 is heated in a gas atmosphere having a predetermined composition containing oxygen using a gas atmosphere furnace. Specifically, nano-diamond powder is disposed in a gas atmosphere furnace, oxygen-containing gas is supplied to or passed through the furnace, and the furnace is heated to a temperature condition set as a heating temperature. Oxygen oxidation treatment is performed. The temperature condition of this oxygen oxidation treatment is 230 to 320 ° C. The lower limit of the temperature condition for the oxygen oxidation treatment is preferably 240 ° C, more preferably 245 ° C, and more preferably 250 ° C. The upper limit of the temperature condition of the oxygen oxidation treatment is preferably 310 ° C, more preferably 300 ° C, more preferably 290 ° C, more preferably 280 ° C, more preferably 270 ° C, more preferably 260 ° C. In the present embodiment, the oxygen-containing gas is a mixed gas containing an inert gas and oxygen. Examples of the inert gas include nitrogen, argon, carbon dioxide, and helium. The oxygen content of the mixed gas, that is, the oxygen concentration is, for example, 1 to 35% by volume, preferably 1 to 10% by volume, and more preferably 2 to 5% by volume. The said oxygen content rate is suitable when performing the oxygen oxidation process which concerns on a nano diamond appropriately by comparatively low temperature conditions of 230-320 degreeC.

  In the oxygen oxidation treatment in the thermal oxidation step S3, the oxygen oxidation reaction proceeds by heating in a state where nanodiamonds are placed in an atmosphere in which oxygen exists. When non-diamond carbon such as graphite or amorphous carbon exists on the surface of nano-diamond, if oxygen oxidation reaction occurs on the non-diamond carbon, carbon dioxide is generated and the non-diamond carbon is removed from the nano-diamond surface. The Rukoto. The more non-diamond carbon such as graphite and amorphous carbon present on the nanodiamond surface, the lower the dispersibility of the nanodiamond particles in the solution system. However, the non-diamond carbon on the nanodiamond surface is removed by oxygen oxidation treatment. Alternatively, the reduction contributes to achieving high dispersibility in a solution system for nanodiamonds. On the other hand, when an oxygen oxidation reaction occurs on the surface of the nanodiamond itself, the nanodiamond surface is oxygen-modified. Specifically, functional groups and partial structures containing oxygen atoms are generated on the nanodiamond surface. Examples of such a functional group or partial structure include a carbonyl group, a carboxy group, a lactone structure, and an acid anhydride structure. The more functional groups and partial structures containing oxygen atoms are present on the nanodiamond surface, the higher the dispersibility of the nanodiamond particles in the solution system. However, the nanodiamond surface is subject to oxygen modification by oxygen oxidation treatment. This contributes to the high dispersibility of nanodiamonds in solution systems.

  By going through a series of processes including the production step S1, the purification step S2, and the thermal oxidation step S3 as described above, nanodiamonds that can be used for the preparation of the nanodiamond dispersion can be manufactured.

  Even after being refined through a series of processes as described above, detonation nanodiamonds are formed of aggregates (secondary particles) in which the primary particles are assembled with very strong interactions. Takes form. In order to separate many primary particles from the adherend, a crushing step S4 may be performed after the thermal oxidation step S3. Prior to the crushing step S4, the nano diamond that has undergone the thermal oxidation step S3 is suspended in pure water, and the pH of the suspension is adjusted to 8 to 12, for example. In this way, a slurry containing nanodiamond is prepared. And in crushing process S4, the said slurry is attached | subjected to a crushing process. 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, or a colloid mill. You may implement a crushing process combining these. From the viewpoint of efficiency, it is preferable to use a bead mill.

  A bead mill as a pulverizer or a disperser 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 rotatable at high speed inside the mill container. The centrifugal separation mechanism is arranged at the upper part in the mill container. In the bead milling by the bead mill in the crushing step S4, a predetermined amount of beads are filled in the mill container and the rotor pin is stirring the beads, and the raw material tank is used as a raw material from the raw material tank to the lower part of the mill container by the action of the pump. The above slurry (including nano-diamond adherends) is charged. The slurry reaches the upper part in the mill container through the bead being rapidly stirred in the mill container. In this process, the nanodiamond aggregate contained in the slurry is subjected to the action of pulverization or dispersion by contact with the beads moving vigorously. Thereby, the crushing from the nanodiamond adherend (secondary particles) to the primary particles proceeds. The slurry and beads that have reached the centrifuge mechanism in the upper part of the mill container are centrifuged using the specific gravity difference by the operating centrifuge mechanism, the beads remain in the mill container, and the slurry is in contact with the centrifuge mechanism. It is discharged out of the mill container via a slidably connected hollow line. The discharged slurry is returned to the raw material tank, and then charged again into the mill container by the action of the pump (circulation operation). In such bead milling, the crushing medium used is, for example, zirconia beads, and the diameter of the beads is, for example, 15 to 500 μm. The amount (apparent volume) of beads filled in the mill container is, for example, 50 to 80% with respect to the volume of the mill container. The peripheral speed of the rotor pin is, for example, 8 to 12 m / min. The amount of the 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. The processing time (circulation operation time) is, for example, 30 to 300 minutes. In the present embodiment, a batch type bead mill may be used instead of the continuous bead mill as described above.

  By passing through such a crushing step S4, a nanodiamond dispersion containing primary particles of nanodiamond dispersed as colloidal particles can be obtained.

  About the slurry which passed through crushing process S4, you may perform classification operation for removing a coarse particle. For example, using a classifier, coarse particles can be removed from the slurry by a classification operation utilizing centrifugation. Thereby, a black transparent nanodiamond dispersion liquid in which primary particles of nanodiamond are dispersed as colloidal particles is obtained.

  About the nano diamond which passed through crushing process S4, or the nano diamond which passed through crushing process S4 and classification operation, you may perform a drying process. In the drying step, specifically, the dispersion containing nanodiamond is subjected to a drying treatment to obtain a dry powder of nanodiamond. Examples of the drying treatment include spray drying performed using a spray drying apparatus and evaporation to dryness performed using an evaporator.

  FIG. 2 is an enlarged schematic view of the ND dispersion 10 which is a nanodiamond dispersion containing nanodiamonds manufactured as described above. The ND dispersion 10 contains ND particles 11 and a dispersion medium 12.

  The ND particles 11 contained in the ND dispersion 10 are nanodiamond primary particles or nanodiamond secondary particles derived from nanodiamonds produced as described above, and are separated from each other in the dispersion medium 12 to form a colloid. Dispersed as particles. The particle size D50 (median diameter) of the ND particles 11 is, for example, 60 nm or less, preferably 30 nm or less, more preferably 28 nm or less, more preferably 25 nm or less, more preferably 22 nm or less, and more preferably 20 nm or less. Moreover, the particle diameter D50 (median diameter) of the nanodiamond primary particles forming the ND particle 11 is, for example, 10 nm or less, preferably 8 nm or less, more preferably 6 nm or less. For example, when the ND dispersion 10 is used 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 particle diameter D50 of the ND particles 11 is, It tends to be favorable in realizing high transparency. On the other hand, the lower limit of the particle size D50 of the ND particles 11 is, for example, 1 nm. In this specification, the particle size D50 in the dispersion is a value measured by a so-called dynamic light scattering method.

  The dispersion medium 12 contained in the ND dispersion liquid 10 is a medium for appropriately dispersing the ND particles 11 in the ND dispersion liquid 10. The dispersion medium 12 is preferably a solvent in which nanodiamonds can exhibit solubility, and examples thereof include water, methanol, ethanol, ethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone. As the dispersion medium 12, one type of dispersion medium may be used, or two or more types of dispersion media may be used. From the viewpoint of dispersibility of the ND particles 11, the dispersion medium 12 is preferably water or an aqueous dispersion medium containing 50% by mass or more of water.

  The ND dispersion 10 having the above-described configuration can be used as a nanodiamond supply material when producing a composite material containing nanodiamonds. And the above-mentioned nanodiamond production method can produce ND particles 11 that can be used for the preparation of such an ND dispersion 10, for example.

  In the oxygen oxidation treatment in the thermal oxidation step S3 in the nanodiamond manufacturing method, as described above, when non-diamond carbon such as graphite or amorphous carbon exists on the nanodiamond surface, the non-diamond carbon is oxidized by oxygen. It is removed from the nanodiamond surface by reaction. The removal or reduction of non-diamond carbon on the nanodiamond surface by the oxygen oxidation treatment contributes to achieving high dispersibility in the solution system of nanodiamond as described above. In addition, in the oxygen oxidation treatment of the thermal oxidation step S3, as described above, the nanodiamond surface is oxygen-modified by an oxygen oxidation reaction, and a functional group or partial structure containing an oxygen atom (carbonyl group, carboxy group, lactone structure, An acid anhydride structure, etc.) occurs on the nanodiamond surface. As the number of functional groups and partial structures containing oxygen atoms increases on the nanodiamond surface, the dispersibility of the nanodiamond particles in a solution system tends to be higher. The modification contributes to achieving high dispersibility in a solution system for nanodiamonds.

  In the thermal oxidation step S3, the nano-diamond powder is subjected to oxygen oxidation treatment at a temperature condition of 230 to 320 ° C., and manufactured even if the oxygen oxidation treatment is not performed at a high temperature condition of, for example, 350 ° C. or higher. The present inventors have found that high dispersibility in a solution system can be realized for nanodiamonds. In addition, when the oxygen oxidation treatment is performed under a low temperature condition of 200 ° C., the oxygen oxidation reaction does not proceed sufficiently to achieve high dispersibility in the solution system for the manufactured nanodiamond. The inventors have found. These are the examples and comparative examples described later. In the oxygen oxidation treatment, the lower the heating temperature of the nanodiamond powder, the more the energy consumption in the treatment is suppressed, and the time required for the temperature to rise to or fall from the heating temperature tends to be shorter. The above-described nanodiamond manufacturing method in which the oxygen oxidation treatment in the thermal oxidation step S3 is performed at a relatively low temperature of 230 to 320 ° C. is suitable for suppressing the energy consumption in the thermal oxidation step S3. Suitable for shortening time and cooling time. The suppression of energy consumption in the thermal oxidation step S3 in the nanodiamond manufacturing process and the shortening of the temperature rise time and temperature fall time contribute to the production efficiency of nanodiamonds exhibiting high dispersibility in a solution system.

  As described above, the nanodiamond manufacturing method described above with reference to FIG. 1 is suitable for obtaining high production efficiency while realizing high dispersibility in a solution system for nanodiamond.

  The above-described nanodiamond manufacturing method includes a purification step S2 for purifying a nanodiamond crude product before the thermal oxidation step S3, and such a configuration is used for the nanodiamond to be subjected to the thermal oxidation step S3. It is suitable for increasing the degree of purification. The higher the degree of purification of the nanodiamond used for the thermal oxidation step S3, that is, the less non-diamond carbon such as graphite or amorphous carbon present on the surface of the nanodiamond used for the thermal oxidation step S3, In the oxygen oxidation treatment in step S3, the amount of oxygen acting on the surface of the nanodiamond itself tends to increase, and therefore the nanodiamond surface is easily subjected to oxygen modification.

[Example 1]
The nanodiamond crude product obtained by the detonation method was subjected to an acid treatment in the purification process. Specifically, the slurry obtained by adding 6 L of 10 mass% hydrochloric acid to 200 g of the nanodiamond crude product was subjected to a heat treatment 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 the nanodiamond adherend and soot) was washed with water by decantation. The solid content was washed repeatedly with decantation until the pH of the precipitate reached 2 from the low pH side.

  Next, solution oxidation treatment or mixed acid treatment in the purification step was performed. Specifically, 3 L of 98 mass% sulfuric acid aqueous solution and 1 L of 69 mass% nitric acid aqueous solution were added to a precipitation liquid (including nanodiamond adherend) obtained through decantation after acid treatment to form a slurry. Thereafter, the slurry was subjected to a heat treatment for 5 hours under reflux under normal pressure conditions. The heating temperature in this oxidation treatment is 120 to 140 ° C. Next, after cooling, the solid content (including the nanodiamond adherend) was washed with water by decantation. The supernatant liquid at the beginning of water washing was colored, and the solid contents were washed repeatedly by decantation until the supernatant liquid became transparent visually.

  Next, 1 L of a 10% by mass sodium hydroxide aqueous solution and 1 L of a 30% by mass hydrogen peroxide aqueous solution are added to the precipitate (including the nanodiamond adherend) obtained through decantation after the solution oxidation treatment. Then, the slurry was subjected to heat treatment for 1 hour under reflux under normal pressure conditions (alkaline overwater treatment). The heating temperature in this treatment is 50 to 105 ° C. Next, after cooling, the supernatant was removed by decantation. The residual fraction was subjected to a drying treatment to obtain a dry powder. As a drying process, evaporation to dryness using an evaporator was employed.

  Next, a thermal oxidation process was performed using a gas atmosphere furnace (trade name “Gas Atmosphere Tube Furnace KTF045N1”, manufactured by Koyo Thermo System Co., Ltd.). Specifically, 4.5 g of the nanodiamond powder obtained as described above was placed in the core tube of a gas atmosphere furnace, and nitrogen gas was continuously passed through the core tube at a flow rate of 1 L / min for 30 minutes. Thereafter, the flow gas was switched from nitrogen to a mixed gas of oxygen and nitrogen, and the mixed gas was continuously passed through the reactor core tube at a flow rate of 1 L / min. The oxygen concentration in the mixed gas is 4% by volume. After switching to the mixed gas, the temperature in the furnace was raised to a heating set temperature of 250 ° C. The rate of temperature increase was 10 ° C./min up to 230 ° C., which is 20 ° C. lower than the heating set temperature. And the oxygen oxidation process was performed about the nano diamond powder in a furnace, maintaining the temperature conditions in a furnace at 250 degreeC. The processing time was 1 hour. As described above, the nanodiamond powder of Example 1 that had undergone the thermal oxidation process or oxygen oxidation treatment was obtained. Further, when the ratio (yield) of the amount of nanodiamond powder after undergoing the thermal oxidation step or oxygen oxidation treatment to the amount of nanodiamond powder before being subjected to the thermal oxidation step or oxygen oxidation treatment, 97%. This value is listed in Table 1 (the same applies to Examples and Comparative Examples described later).

  Next, the crushing process was performed. Specifically, first, 0.3 g of nanodiamond powder that had undergone the above-described thermal oxidation step 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. As a result, 30 ml of a slurry containing 1% by mass of solid and having a pH of 11 was prepared. Next, ultrasonic irradiation for 1 hour was performed with respect to the said slurry using the ultrasonic irradiation apparatus (Brand name "ultrasonic cleaning machine AS-3", the product made by AS ONE). Then, bead milling was performed using a bead milling device (trade name “parallel four-cylinder sand grinder LSG-4U-2L type”, manufactured by Imex Corporation). Specifically, 30 ml of slurry after ultrasonic irradiation and zirconia beads with a diameter of 30 μm are placed in a 100 ml mill vessel (Imex Co., Ltd.) and sealed, and the apparatus is driven to perform bead milling. did. In this bead milling, the input amount of zirconia beads is, for example, 33% with respect to 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 centrifuge process was performed about the slurry thru | or suspension which passed through the above crushing processes using the centrifuge. The centrifugal force in this centrifugation treatment was 20000 × g, and the centrifugation time was 10 minutes. Next, 10 ml of the supernatant of the nanodiamond-containing solution that had undergone the centrifugation treatment was collected. In this way, a nanodiamond dispersion liquid of Example 1 in which nanodiamonds are dispersed in pure water was obtained. Then, 10 g of the supernatant of the nanodiamond-containing solution that has undergone the above centrifugation treatment is weighed, and the supernatant liquid is dried by an evaporation to dryness operation using a rotary evaporator, and then the nanodiamond powder that is a dry residue Were weighed. Based on the weighed value of 10 g of the weighed supernatant liquid and the weighed value of the dried product remaining after the moisture was evaporated from the weighed supernatant liquid by heating, the solid of the nanodiamond-containing supernatant liquid subjected to the centrifugal separation treatment The partial concentration was calculated to be 0.95% by mass.

<Particle size D50>
About the nano diamond dispersion liquid of Example 1, the particle size distribution of the nano diamond in the said recovery solution was measured by the dynamic light scattering method. Specifically, using a device made by Malvern (trade name “Zetasizer Nano ZS”), the particle size distribution of nanodiamond in the recovered liquid is measured by a dynamic light scattering method (non-contact backscattering method). did. The nanodiamond dispersion subjected to the measurement was diluted with ultrapure water so that the solid content concentration or the nanodiamond concentration was 0.5 to 2.0 mass%, and then subjected to ultrasonic irradiation with an ultrasonic cleaner. Is. As a result of the measurement, the particle diameter D50 (median diameter) of the nanodiamond was 18.4 nm. The results are listed in Table 1 (the same applies to Examples and Comparative Examples described later).

<Zeta potential>
The zeta potential of the nanodiamond particles contained in the nanodiamond dispersion liquid of Example 1 was measured by laser Doppler electrophoresis using a device (trade name “Zetasizer Nano ZS”) manufactured by Malvern. With respect to the nanodiamond dispersion liquid of Example 1 subjected to the measurement, the solid content concentration or the nanodiamond concentration is adjusted within the range of 0.5 to 2.0 mass%, and the pH is 8.38. The zeta potential measurement temperature is 25 ° C. As a result of the measurement, the zeta potential of the nanodiamond dispersion liquid of Example 1 was −36.0 mV. The results are listed in Table 1 (the same applies to Examples and Comparative Examples described later).

<FT-IR analysis>
About the nano diamond powder of Example 1 which passed through the above-mentioned thermal oxidation process, Fourier transform infrared spectroscopic analysis (FT-IR) using an FT-IR apparatus (trade name “FT-720”, manufactured by Horiba, Ltd.) ), A peak attributed to the carbonyl group (C═O) was confirmed at 1747 cm ⁻¹ . The results are listed in Table 1 (the same applies to Examples and Comparative Examples described later).

<Elemental analysis>
About the nanodiamond powder of Example 1 which passed through the above-mentioned thermal oxidation process, when elemental analysis was performed using an elemental analyzer (trade name “JM10”, manufactured by J Science Co., Ltd.), carbon element, hydrogen element Regarding the ratio of the total amount of nitrogen element and oxygen element, carbon element was 88.9%, hydrogen element was 0.56%, nitrogen element was 2.29%, and oxygen element was 8.16%. The ratio of the oxygen element is listed in Table 1 (the same applies to Examples and Comparative Examples described later).

[Example 2]
A nanodiamond powder of Example 2 was obtained in the same manner as in Example 1 except that the time for maintaining at 250 ° C. in the oxygen oxidation treatment in the thermal oxidation process was changed to 3 hours instead of 1 hour. The ratio (yield) of the amount of nanodiamond powder after the thermal oxidation step or oxygen oxidation treatment to the amount of nanodiamond powder before being subjected to the thermal oxidation step or oxygen oxidation treatment is the same as that of Example 2. The diamond powder was 96%. Further, the crushing step described above with respect to Example 1 and the subsequent centrifugation are performed in the same manner as Example 1 except that the nanodiamond powder of Example 2 described above is used instead of the nanodiamond powder of Example 1. Processed. This obtained the nano diamond dispersion liquid of Example 2 in which nano diamond is dispersed in pure water.

With respect to the nanodiamond dispersion liquid of Example 2, when the particle size distribution of nanodiamond was measured by the dynamic light scattering method in the same manner as in Example 1, the particle size D50 (median diameter) of nanodiamond was 26.7 nm. . When the zeta potential of the nanodiamond particles contained in the nanodiamond dispersion liquid of Example 2 was measured in the same manner as in Example 1, it was -40 mV. About the nanodiamond dispersion liquid of Example 2 attached | subjected to zeta potential measurement, solid content concentration is adjusted in the range of 0.5-2.0 mass%, and pH is 9.45. The zeta potential measurement temperature is 25 ° C. Further, when the above-described nanodiamond powder of Example 2 was subjected to Fourier transform infrared spectroscopic analysis in the same manner as in Example 1, the peak attributed to the carbonyl group (C═O) was confirmed at 1747 cm ^−1. It was. In addition, elemental analysis was performed on the nanodiamond powder of Example 2 in the same manner as in Example 1. As a percentage of the total amount of carbon element, hydrogen element, nitrogen element, and oxygen element, carbon element was 88%. It was 0.60%, hydrogen element was 0.51%, nitrogen element was 2.25%, and oxygen element was 8.64%.

Example 3
A nanodiamond powder of Example 3 was obtained in the same manner as in Example 1 except that the temperature condition in the oxygen oxidation treatment in the thermal oxidation process was changed to 300 ° C instead of 250 ° C. The ratio (yield) of the amount of nanodiamond powder after undergoing the thermal oxidation step or oxygen oxidation treatment to the amount of nanodiamond powder before being subjected to the thermal oxidation step or oxygen oxidation treatment is the same as that of Example 3. The diamond powder was 98%. Further, in the same manner as in Example 1 except that the nanodiamond powder of Example 3 described above was used instead of the nanodiamond powder of Example 1, the crushing step described above with respect to Example 1 and subsequent centrifugation were performed. Processed. This obtained the nano diamond dispersion liquid of Example 3 in which nano diamond is dispersed in pure water.

With respect to the nanodiamond dispersion liquid of Example 3, when the particle size distribution of nanodiamond was measured by the dynamic light scattering method in the same manner as in Example 1, the particle size D50 (median diameter) of nanodiamond was 21.3 nm. . When the zeta potential of the nanodiamond particles contained in the nanodiamond dispersion liquid of Example 3 was measured in the same manner as in Example 1, it was -37.3 mV. About the nanodiamond dispersion liquid of Example 3 attached | subjected to zeta potential measurement, solid content concentration is adjusted in the range of 0.1-2.0 mass%, and pH is 8.41. The zeta potential measurement temperature is 25 ° C. Further, when the nanodiamond powder of Example 3 was subjected to Fourier transform infrared spectroscopic analysis in the same manner as in Example 1, the peak attributed to the carbonyl group (C═O) was confirmed at 1756 cm ^−1. It was. In addition, elemental analysis was performed on the nanodiamond powder of Example 3 in the same manner as in Example 1. As a result, the carbon element was 88.90% of the total amount of carbon element, hydrogen element, nitrogen element, and oxygen element. 28%, hydrogen element 0.42%, nitrogen element 2.36%, oxygen element 8.94%.

[Comparative Example 1]
A nanodiamond powder of Comparative Example 1 was obtained in the same manner as in Example 1 except that the temperature condition in the oxygen oxidation treatment in the thermal oxidation process was changed to 200 ° C instead of 250 ° C. The ratio (yield) of the amount of nanodiamond powder after undergoing the thermal oxidation step or oxygen oxidation treatment to the amount of nanodiamond powder before being subjected to the thermal oxidation step or oxygen oxidation treatment is the nano of Comparative Example 1. The diamond powder was 96%. Moreover, it replaced with the nano diamond powder of Example 1, and the crushing process mentioned above regarding Example 1 and subsequent centrifugation were carried out similarly to Example 1 except having used the nano diamond powder of the above-mentioned comparative example 1. Processed. However, the nanodiamond settled by the centrifugal separation treatment, and the particle size distribution measurement and the zeta potential measurement by the dynamic light scattering method could not be performed for the nanodiamond of Comparative Example 1. On the other hand, the nanodiamond precipitated by the centrifugal separation treatment was dried by an evaporating and drying operation performed using a rotary evaporator to obtain a nanodiamond powder of Comparative Example 1. When this nanodiamond powder of Comparative Example 1 was subjected to Fourier transform infrared spectroscopic analysis in the same manner as in Example 1, the peak attributed to the carbonyl group (C═O) was confirmed at 1739 cm ⁻¹ . The elemental analysis of the nanodiamond powder of Comparative Example 1 was performed in the same manner as in Example 1. As a result, the carbon element 88.98 was in proportion to the total amount of carbon element, hydrogen element, nitrogen element, and oxygen element. %, Hydrogen element 0.68%, nitrogen element 2.30%, oxygen element 8.04%.

[Comparative Example 2]
Nanodiamond powder of Comparative Example 2 in the same manner as in Example 1 except that the temperature condition in the oxygen oxidation treatment in the thermal oxidation process was changed to 200 ° C. instead of 250 ° C. and the treatment time was changed to 3 hours instead of 1 hour. Got the body. The ratio (yield) of the amount of nanodiamond powder after the thermal oxidation step or oxygen oxidation treatment to the amount of nanodiamond powder before being subjected to the thermal oxidation step or oxygen oxidation treatment is the nano of Comparative Example 2. The diamond powder was 95%. Moreover, it replaced with the nano diamond powder of Example 1, and the crushing process mentioned above regarding Example 1 and the subsequent centrifugation were carried out similarly to Example 1 except having used the nano diamond powder of the above-mentioned comparative example 2. Processed. However, the nanodiamond settled by the centrifugal separation treatment, and the particle size distribution measurement and the zeta potential measurement by the dynamic light scattering method could not be performed for the nanodiamond of Comparative Example 2. On the other hand, the nanodiamond precipitated by the centrifugal separation treatment was dried by an evaporating and drying operation performed using a rotary evaporator to obtain a nanodiamond powder of Comparative Example 2. When this nanodiamond powder of Comparative Example 2 was subjected to Fourier transform infrared spectroscopic analysis in the same manner as in Example 1, a peak attributed to the carbonyl group (C═O) was confirmed at 1747 cm ⁻¹ . Further, when the elemental analysis was performed on the nanodiamond powder of Comparative Example 2 in the same manner as in Example 1, the proportion of the carbon element, hydrogen element, nitrogen element, and oxygen element in the total amount of carbon element 89.31 %, Hydrogen element was 0.75%, nitrogen element was 2.31%, and oxygen element was 7.63%.

[Comparative Example 3]
A nanodiamond powder of Comparative Example 3 was obtained in the same manner as in Example 1, except that the temperature condition in the oxygen oxidation treatment in the thermal oxidation process was changed to 425 ° C instead of 250 ° C. The ratio (yield) of the amount of nanodiamond powder after the thermal oxidation step or oxygen oxidation treatment to the amount of nanodiamond powder before being subjected to the thermal oxidation step or oxygen oxidation treatment is the nano of Comparative Example 3. The diamond powder was 22%. Further, the crushing step described above with respect to Example 1 and the subsequent centrifugation are performed in the same manner as Example 1 except that the nanodiamond powder of Comparative Example 3 described above is used instead of the nanodiamond powder of Example 1. Processed. Thus, a nanodiamond dispersion liquid of Comparative Example 3 in which nanodiamonds are dispersed in pure water was obtained.

When the nanodiamond particle size distribution of the nanodiamond dispersion liquid of Comparative Example 3 was measured by the dynamic light scattering method in the same manner as in Example 1, the particle size D50 (median diameter) of the nanodiamond was 11.4 nm. . When the zeta potential of the nanodiamond particles contained in the nanodiamond dispersion liquid of Comparative Example 3 was measured in the same manner as in Example 1, it was -45.8 mV. The nanodiamond dispersion liquid of Comparative Example 3 subjected to zeta potential measurement has a solid content concentration of 0.5 to 3% by mass and a pH of 9.88. The zeta potential measurement temperature is 25 ° C. Further, when the nanodiamond powder of Comparative Example 3 was subjected to Fourier transform infrared spectroscopic analysis in the same manner as in Example 1, the peak attributed to the carbonyl group (C═O) was confirmed at 1783 cm ^−1. It was. In addition, the nanodiamond powder of Comparative Example 3 was subjected to elemental analysis in the same manner as in Example 1. As a result, the amount of carbon as a proportion of the total amount of carbon, hydrogen, nitrogen, and oxygen was The element was 81.62%, the hydrogen element was 0.36%, the nitrogen element was 2.12%, and the oxygen element was 15.9%.

[Evaluation]
Just as the nanodiamond of Comparative Example 3 showed high dispersibility in water, the nanodiamonds of Examples 1 to 3 also showed high dispersibility in water. Specifically, the nanodiamonds of Examples 1 to 3 exhibited a particle size distribution with a relatively small particle size D50 (median diameter) in water as a dispersion medium. This is considered to be because the nanodiamonds of Examples 1 to 3 were subjected to sufficient oxygen oxidation reaction in the oxygen oxidation treatment of the thermal oxidation process. The oxygen amount (%) of each Example and each Comparative Example shown in Table 1 as a part of the elemental analysis result tends to increase as the temperature condition of the oxygen oxidation treatment increases. The higher the temperature condition of the oxygen oxidation treatment, the more the oxygen oxidation reaction on the nanodiamond surface proceeds. In addition, the positions of the carbonyl group-assigned peaks in Examples 1 and Comparative Examples shown in Table 1 as part of FT-IR analysis are shifted to higher wavenumbers as the temperature condition of the oxygen oxidation treatment is higher. This also suggests that the oxygen oxidation reaction on the nanodiamond surface proceeds as the temperature condition of the oxygen oxidation treatment is higher. Specifically, the carboxy group, the carbonyl group, the lactone structure, and the acid anhydride structure on the surface of the nanodiamond are considered to increase as the position of the carbonyl group-affected peak shifts to the higher wavenumber side. In contrast, the nanodiamonds of Comparative Examples 1 and 2 in which the temperature condition of the oxygen oxidation treatment in the thermal oxidation process was 200 ° C. were not dispersed as described above.

10 ND dispersion 11 ND particles 12 Dispersion medium S1 Production process S2 Purification process S3 Thermal oxidation process S4 Crushing process

Claims (9)

  A method for producing nanodiamond, comprising a thermal oxidation step for subjecting nanodiamond powder to an oxygen oxidation treatment at a temperature of 230 to 320 ° C.   The nano-diamond manufacturing method according to claim 1, wherein the thermal oxidation step is performed in an atmosphere of a mixed gas containing an inert gas and oxygen.   The nanodiamond manufacturing method according to claim 2, wherein the inert gas is nitrogen.   The method for producing nanodiamond according to claim 2 or 3, wherein the mixed gas has an oxygen content of 1 to 10% by volume.   The method for producing nanodiamond according to any one of claims 1 to 4, further comprising a purification step for purifying the crude nanodiamond product before the thermal oxidation step.   The said refinement | purification process is a nano diamond manufacturing method of Claim 5 including the solution oxidation process which makes an oxidizing agent act on nano diamond.   The nano-diamond manufacturing method according to claim 6, wherein the oxidizing agent contains sulfuric acid and nitric acid.   The nanodiamond manufacturing method according to any one of claims 1 to 7, further comprising a crushing step for crushing the nanodiamond secondary particles into nanodiamond primary particles after the thermal oxidation step.   The nanodiamond manufacturing method according to any one of claims 1 to 8, wherein the nanodiamond is a detonation nanodiamond.

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