JP2018070412A - Process for manufacturing nanodiamond dispersion and nanodiamond dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for manufacturing a nanodiamond dispersion which is suitable for obtaining a nanodiamond dispersion of low electrolyte concentration, which contains nanodiamond particles of positive zeta potential, and provide such a nanodiamond dispersion.SOLUTION: The process for manufacturing a nanodiamond dispersion of the present invention comprises an oxygen oxidation step S3 for oxidizing nanodiamond with oxygen, and a hydrogenation step S4 for hydrogenating the nanodiamond which has been processed in the above step. The nanodiamond dispersion of the present invention contains an aqueous dispersion medium, and nanodiamond particles which are dispersed in the medium and have positive zeta potential, and are 30 μS/cm wt% or less in electric conductivity.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a dispersion of nanodiamond and a nanodiamond dispersion.

  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. The technology relating to the production of such nanodiamonds is described in, for example, the following Patent Documents 1 to 3.

JP-A-2005-001983 JP 2010-126669 A JP-T-2006-520035 Publication

  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). Therefore, the sum of van der Waals forces that can act between surface atoms of adjacent particles is large, causing aggregation. Prone to occur. 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 superimposing interaction can occur between crystallites or primary particles. For example, nanodiamond creates a state in which nanodiamond primary particles are dispersed in a solvent, and so on. Maintaining the correct state often involves technical difficulties. Nanodiamond is a product obtained by detonation, for example. First, it forms an aggregate (secondary particle) in which primary particles are aggregated due to a very strong interaction between primary particles. However, there are technical difficulties associated with pulverization from secondary particles to primary particles and maintaining the dispersed state of primary particles in a desired solvent.

  A wet crushing process such as bead milling is known as an effective crushing technique from secondary particles of nanodiamond to primary particles. The nanodiamond-containing slurry to be subjected to the treatment and the nanodiamond aqueous dispersion obtained through the treatment ensure a large zeta potential for the nanodiamond particles in the aqueous dispersion to stabilize the dispersion. In many cases, the pH is adjusted by adding a pH adjusting agent for the purpose of achieving the above. For example, in order to ensure a large positive zeta potential for nanodiamond particles in an aqueous dispersion, an acid such as hydrochloric acid is used as a pH adjuster.

  However, the addition of such a pH adjuster causes an increase in the electrolyte concentration of the obtained nanodiamond aqueous dispersion, which is not preferable. In the process of preparing a composite material of nanodiamond and, for example, a resin, a mixture process of a predetermined organic material such as an organic solvent and a nanodiamond aqueous dispersion is often performed. The electrolyte concentration of the nanodiamond aqueous dispersion The higher the is, the lower the miscibility or dispersibility of the aqueous dispersion with respect to the organic material. As a result, the nanodiamond dispersion in the organic material phase in the solution obtained by mixing the aqueous dispersion with the organic material, etc. The amount tends to decrease, which is not preferable for producing a composite material. Moreover, the addition of an acid as a pH adjuster causes an increase in the acid concentration of the resulting nanodiamond aqueous dispersion, which is not preferable. In using the nanodiamond aqueous dispersion, the higher the acid concentration of the nanodiamond aqueous dispersion, the easier the nanodiamond aqueous dispersion causes corrosion of the metal material. When a nanodiamond aqueous dispersion is used in the production of a composite material of nanodiamond and resin, the higher the acid concentration of the nanodiamond aqueous dispersion, the more the nanodiamond aqueous dispersion will cause degradation and decomposition of the resin. Easy to make.

  The present invention has been conceived under the circumstances as described above, and is suitable for obtaining a nanodiamond dispersion having a positive zeta potential of nanodiamond particles and a low electrolyte concentration. It is an object to provide a method and to provide such a nanodiamond dispersion.

  According to a first aspect of the present invention, a method for producing a nanodiamond dispersion is provided. This manufacturing method includes an oxygen oxidation step for subjecting nanodiamond to oxygen oxidation treatment, and a hydrogenation step for subjecting nanodiamond subjected to the oxygen oxidation step to hydrogenation treatment. 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. In the present invention, the hydrogenation treatment is a treatment for causing a hydrogenation reaction in a state where nanodiamonds are placed in an atmosphere in which hydrogen 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. Further, when an oxygen oxidation reaction occurs on the surface of the nanodiamond itself, the surface of the nanodiamond is modified with oxygen. 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. On the other hand, when a functional group such as a carboxyl group containing oxygen atoms or a partial structure is present on the surface of the nanodiamond, if a hydrogenation reaction occurs on the functional group or the like, does the functional group form a hydrogen reductant? Or it will be removed from the nanodiamond surface. The nano-diamond is subjected to an oxygen oxidation treatment for causing the above-described oxygen oxidation reaction before the hydrogenation treatment for causing such a hydrogenation reaction, thereby performing wet crushing after the hydrogenation treatment. The present inventors have found that a nanodiamond dispersion having a positive zeta potential of nanodiamond particles can be obtained without adjusting pH with addition of a pH adjuster before and after the process. For example, as shown in the examples described later. In order to obtain a nanodiamond dispersion liquid in which the nanodiamond particles have a positive zeta potential, it is not necessary to adjust the pH before and after the wet crushing process. Suitable for obtaining a low nanodiamond dispersion.

  The method for producing a nanodiamond dispersion liquid according to the first aspect of the present invention is preferably a production process for producing nanodiamonds by a detonation method in an inert gas atmosphere, and the nanodiamond obtained in the production process A purification step for purifying the crude product prior to the oxygen oxidation step. The purification step preferably includes a mixed acid treatment performed using a mixed acid containing sulfuric acid and nitric acid. According to the detonation method, it is possible to appropriately generate nanodiamond having a primary particle size of 10 nm or less. The detonation method under an inert gas atmosphere is suitable for producing nanodiamond having a small particle size and a small amount of functional groups on the surface of primary particles. As the inert gas, for example, at least one selected from nitrogen, argon, carbon dioxide, and helium can be used. The configuration in which the present production method includes the above-described purification step preferably including a mixed acid treatment prior to the oxygen oxidation step is suitable for increasing the degree of purification of the nanodiamond used in the oxygen oxidation step. The higher the degree of purification of the nanodiamond subjected to the oxygen oxidation process, that is, the less non-diamond carbon such as graphite or amorphous carbon present on the surface of the nanodiamond subjected to the oxygen oxidation process, It is easy to achieve a large positive zeta potential for nanodiamond particles in a diamond dispersion.

  According to a second aspect of the present invention, a nanodiamond dispersion is provided. This nanodiamond dispersion liquid includes an aqueous dispersion medium and nanodiamond particles dispersed in the dispersion medium and having a positive zeta potential, and has an electric conductivity of 30 μS / cm · wt% or less. In the present invention, the aqueous dispersion medium is a dispersion medium containing 50% by mass or more of water as a dispersion medium component having the largest mass ratio. The nanodiamond particles in this dispersion include nanodiamond primary particles and / or nanodiamond secondary particles. The nanodiamond primary particles are nanodiamonds having a particle diameter of 10 nm or less. In the present invention, the zeta potential of the nanodiamond particles contained in the nanodiamond dispersion is a value measured at 25 ° C. for the nanodiamond particles in the nanodiamond dispersion having a nanodiamond concentration of 0.2 mass%. When it is necessary to dilute the nanodiamond dispersion liquid for the preparation of the nanodiamond dispersion having a nanodiamond concentration of 0.2% by mass, ultrapure water is used as the diluent. The electrical conductivity of the solution can be measured according to the method described in JIS K 0130 (2008) “General Rules for Electrical Conductivity Measurement”.

  As described above, nanodiamond particles having a positive zeta potential are dispersed in this nanodiamond dispersion. Such a nanodiamond dispersion liquid can be used as a material for supplying nanodiamond particles having a positive zeta potential, for example, in producing a nanodiamond-containing composite material. And the electrical conductivity used as the parameter | index of the electrolyte concentration of this nano diamond dispersion liquid is 30 microS / cm * wt% or less as mentioned above. The lower the electrolyte concentration of the nanodiamond dispersion, the higher the dispersibility of the dispersion with respect to the organic material. However, the electrical conductivity of the nanodiamond dispersion is less than 30 μS / cm · wt%. The configuration is suitable for realizing sufficiently high dispersibility with respect to the organic material. The low electrolyte concentration constitution in which the electrical conductivity of the nano-diamond dispersion is 30 μS / cm · wt% or less is eventually transferred to the organic material phase in a solution obtained by mixing the aqueous dispersion and the organic material. This is suitable for realizing a high nano-diamond dispersion amount. In addition, the low-electrolyte concentration configuration in which the electrical conductivity of the nanodiamond dispersion is 30 μS / cm · wt% or less is applicable even if the nanodiamond dispersion contains an acid as an electrolyte. The use of an aqueous diamond dispersion is suitable for suppressing corrosion of metal materials as other materials and deterioration / decomposition of resin materials.

  The zeta potential of the nanodiamond dispersion is preferably 30 mV or more. Such a configuration is suitable for stably maintaining the dispersion state of the nanodiamond particles.

  The pH of the nanodiamond dispersion is preferably in the range of 5 or more. Such a configuration is suitable for suppressing the above-described corrosion, deterioration, decomposition, etc. of other materials when the nano-diamond aqueous dispersion is used.

It is process drawing of the nano diamond dispersion liquid manufacturing method which concerns on one Embodiment of this invention. It is an expansion schematic diagram of the nano diamond dispersion liquid concerning one embodiment of the present invention.

  FIG. 1 is a process diagram of a method for producing a nanodiamond dispersion according to an embodiment of the present invention. This method is a method for producing a dispersion in which nanodiamond particles having a positive zeta potential are dispersed, and includes a production step S1, a purification step S2, an oxygen oxidation step S3, a hydrogenation step S4, and a solution. And crushing step S5.

In the production step S1, nanodiamonds are generated, 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 gas and a used explosive coexist in the container. To seal. 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. The above gas sealed in the container together with the explosive used may have an atmospheric composition or may be an inert gas. From the viewpoint of producing nanodiamonds having a small amount of functional groups on the surface of the primary particles, the gas sealed in the container together with the explosive used is preferably an inert gas. That is, from the viewpoint of generating nanodiamonds having a small amount of functional groups on the surface of primary particles, it is preferable that the detonation method for generating nanodiamonds is performed in an inert gas atmosphere. As the inert gas, for example, at least one selected from nitrogen, argon, carbon dioxide, and helium can be used.

  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. 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.

  As such a solution oxidation treatment, a mixed acid treatment using a mixed acid is preferable from the viewpoint of increasing the degree of purification of nanodiamonds used in the oxygen oxidation step described later. The ratio (volume ratio) of concentrated sulfuric acid and concentrated nitric acid for preparing the mixed acid is preferably 1: 1 to 10: 1, more preferably 2: 1 to 9: 1, more preferably 3: 1 to 8: 1. When the mixed acid treatment is adopted as the solution oxidation treatment, the mixed acid treatment temperature is preferably 80 to 200 ° C, more preferably 100 to 190 ° C, more preferably 120 to 180 ° C, and the mixed acid treatment time is preferably 1 to It is 96 hours, More preferably, it is 5-84 hours, More preferably, it is 10-72 hours.

  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, an oxygen oxidation step S3 is performed. 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 preferably 250 to 500 ° C. The lower limit of the temperature condition for the oxygen oxidation treatment is more preferably 280 ° C, more preferably 320 ° C. The upper limit of the temperature condition of the oxygen oxidation treatment is more preferably 450 ° C., more preferably 400 ° C. In the present embodiment, the oxygen-containing gas is a mixed gas containing an inert gas in addition to oxygen. Examples of the inert gas include nitrogen, argon, carbon dioxide, and helium. The oxygen content of the mixed gas, that is, the oxygen concentration, is preferably 1 to 35% by volume, more preferably 1 to 10% by volume, and more preferably 2 to 5% by volume.

  In this method, next, hydrogenation process S4 is performed. In this step, the nanodiamond powder that has undergone the oxygen oxidation step S3 is heated in a gas atmosphere having a predetermined composition containing hydrogen using a gas atmosphere furnace. Specifically, a hydrogen-containing gas is supplied to or passed through a gas atmosphere furnace in which nanodiamond powder is arranged, and the temperature in the furnace is increased to a temperature condition set as a heating temperature. Processing is performed. The temperature condition for the hydrogenation treatment is preferably 400 to 800 ° C. The lower limit of the temperature condition of the hydrogenation treatment is more preferably 500 ° C, and more preferably 550 ° C. The upper limit of the temperature condition of the hydrotreatment is more preferably 700 ° C., more preferably 650 ° C. In the present embodiment, the hydrogen-containing gas is a mixed gas containing an inert gas in addition to hydrogen. Examples of the inert gas include nitrogen, argon, carbon dioxide, and helium. The hydrogen content of the mixed gas, that is, the hydrogen concentration, is preferably 0.1 to 99.9% by volume, more preferably 0.5 to 50% by volume, and more preferably 1 to 10% by volume.

  Through a series of processes including the production step S1, the purification step S2, the oxygen oxidation step S3, and the hydrogenation step S4 as described above, nanodiamonds that can be used for the preparation of the nanodiamond dispersion liquid can be obtained.

  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 the primary particles from the adherend, in the present method, the crushing step S5 is then performed. Specifically, first, nanodiamonds that have undergone the hydrogenation step S4 are suspended in pure water to prepare a slurry containing nanodiamonds. In preparing the slurry, a centrifugal separation treatment may be performed to remove a relatively large assembly from the nanodiamond suspension, or an ultrasonic treatment may be applied to the nanodiamond suspension. And the said slurry is attached | subjected to a wet 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 S5, a predetermined amount of beads are filled in the mill container and the rotor pin is stirring the beads, and the raw material is supplied 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 S5, a nanodiamond dispersion containing primary particles of nanodiamond dispersed as colloidal particles can be obtained.

  About the slurry which passed through crushing process S5, 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.

  As described above, a nanodiamond dispersion liquid in which primary particles of nanodiamond are dispersed as colloidal particles can be produced.

  In the oxygen oxidation step S3 described above, when non-diamond carbon such as graphite or amorphous carbon is present on the surface of the nanodiamond, if an oxygen oxidation reaction occurs in the non-diamond carbon, carbon dioxide is generated and the non-diamond carbon is generated. Diamond carbon is removed from the nanodiamond surface. In the oxygen oxidation step S3 described above, when an oxygen oxidation reaction occurs on the surface of the nanodiamond itself, the surface of the nanodiamond is modified with oxygen. 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. In the hydrogenation step S4 described above, when a functional group such as a carboxyl group containing oxygen atoms or a partial structure exists on the surface of the nanodiamond, a hydrogenation reaction occurs on the functional group or the like. The group or the like forms a hydrogen reductant or is removed from the nanodiamond surface. The nano-diamond is subjected to an oxygen oxidation treatment for causing the above-described oxygen oxidation reaction before the hydrogenation treatment for causing such a hydrogenation reaction, thereby performing wet crushing after the hydrogenation treatment. The present inventors have found that a nanodiamond dispersion having a positive zeta potential of nanodiamond particles can be obtained without adjusting the pH with addition of a pH adjuster before and after step S5. For example, as shown in the examples described later. In order to obtain a nanodiamond dispersion liquid in which the nanodiamond particles have a positive zeta potential, the present manufacturing method, which does not require pH adjustment before and after the wet crushing step S5, has a positive zeta potential of the nanodiamond particles and an electrolyte concentration. Is suitable for obtaining a nanodiamond dispersion having a low particle size.

  FIG. 2 is an enlarged schematic view of the ND dispersion 10 which is a nanodiamond dispersion according to an embodiment of the present invention. The ND dispersion 10 contains ND particles 11 and an aqueous dispersion medium 12 and has an electric conductivity of 30 μS / cm · wt% or less. The ND dispersion 10 can be used, for example, as a nanodiamond supply material when producing a composite material containing nanodiamond.

  The ND particles 11 contained in the ND dispersion 10 are primary or secondary particles of nanodiamond, and are dispersed as colloidal particles in the aqueous dispersion medium 12 so as to be separated from each other. 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. The particle diameter D50 of the particles in the dispersion can be measured by a so-called dynamic light scattering method.

  The zeta potential of the ND particles 11 contained in the ND dispersion 10 is positive (that is, takes a positive value), and is preferably 30 mV or more from the viewpoint of stably maintaining the dispersion state of the ND particles 11. More preferably, it is 35 mV or more, more preferably 40 mV or more. In the present invention, the zeta potential of the nanodiamond particles contained in the nanodiamond dispersion is a value measured at 25 ° C. for the nanodiamond particles in the nanodiamond dispersion having a nanodiamond concentration of 0.2 mass%. When it is necessary to dilute the nanodiamond dispersion liquid for the preparation of the nanodiamond dispersion having a nanodiamond concentration of 0.2% by mass, ultrapure water is used as the diluent.

  The aqueous dispersion medium 12 contained in the ND dispersion 10 is a medium for appropriately dispersing the ND particles 11 in the ND dispersion 10. The aqueous dispersion medium 12 is a dispersion medium containing 50% by mass or more of water as a dispersion medium component having the largest mass ratio, and is preferably water. Examples of the dispersion medium component other than water of the aqueous dispersion medium 12 include methanol, ethanol, ethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone.

  As described above, the electrical conductivity of the ND dispersion 10 is 30 μS / cm · wt% or less, preferably 28 μS / cm · wt% or less, more preferably 26 μS / cm · wt% or less, and more preferably 25 μS / wt%. It is not more than cm · wt%, more preferably not more than 23 μS / cm · wt%, more preferably not more than 20 μS / cm · wt%. The electrical conductivity of the solution is an index of the electrolyte concentration of the solution, and can be measured in accordance with the method described in JIS K 0130 (2008) “General Rules for Electrical Conductivity Measurement”.

  The pH of the ND dispersion 10 is preferably in the range of 5 or more, more preferably 6 to 10, more preferably 7 to 9.

  The ND dispersion 10 having the above-described configuration can be manufactured by, for example, the nanodiamond dispersion manufacturing method described above with reference to FIG.

  As described above, ND particles 11 having a positive zeta potential are dispersed in the ND dispersion liquid 10. Such an ND dispersion liquid 10 can be used as a material for supplying ND particles 11 having a positive zeta potential in producing a nanodiamond-containing composite material. The electrical conductivity that serves as an index of the electrolyte concentration of the ND dispersion 10 is 30 μS / cm · wt% or less as described above, preferably 28 μS / cm · wt% or less, more preferably 26 μS / cm · wt. % Or less, more preferably 25 μS / cm · wt% or less, more preferably 23 μS / cm · wt% or less, more preferably 20 μS / cm · wt% or less. The lower the electrolyte concentration of the ND dispersion liquid 10 is, the higher the dispersibility of the dispersion liquid with respect to the organic material tends to be higher. In contrast, it is suitable for realizing sufficiently high dispersibility. The low electrolyte concentration configuration in which the ND dispersion 10 exhibits such low electrical conductivity is, as a result, high nanodiamond dispersion in the organic material phase in a solution obtained by mixing the water dispersion and the organic material. It is suitable for realizing the quantity. In addition, the low electrolyte concentration configuration in which the ND dispersion 10 exhibits such a low electrical conductivity is the use of the nanodiamond aqueous dispersion even when the ND dispersion 10 contains an acid as an electrolyte. In this case, it is suitable for suppressing corrosion of a metal material as another material and deterioration / decomposition of a resin material.

  Further, as described above, the pH of the ND dispersion 10 is preferably 5 or more, more preferably 6 to 10, and more preferably 7 to 9. Such a configuration is suitable for suppressing the above-described corrosion, deterioration, and decomposition of other materials when using the ND dispersion liquid 10.

[Nanodiamond dispersion]
A nanodiamond dispersion was produced through the following production process, purification process, oxygen oxidation process, hydrogenation process, and crushing process.

In the production process, first, a molded explosive with an electric detonator was installed inside a pressure-resistant container for detonation, and the container was sealed. The container is made of iron and the volume of the container is 15 m ³ . As the explosive, 0.50 kg of a mixture of trinitrotoluene (TNT) and cyclotrimethylenetrinitroamine or hexogen (RDX) was used. The mass ratio (TNT / RDX) of TNT and RDX in the explosive is 50/50. Next, the electric detonator was detonated, and the explosive was detonated in the container. Next, the container and its interior were cooled by being left at room temperature for 24 hours. After this cooling, the nanodiamond crude product (including the nanodiamond particle aggregates and soot produced by the above detonation method) adhering to the inner wall of the container is scraped off with a spatula. The crude product was recovered.

  Next, the acid treatment of the refinement | purification process was performed with respect to the nano diamond crude product acquired by performing the above production | generation processes in multiple times. 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, 6 L of 98% by mass sulfuric acid aqueous solution and 1 L of 69% by mass nitric acid aqueous solution were added to a precipitate obtained by decantation after acid treatment (including nano-diamond adherends) to form a slurry. Thereafter, the slurry was heated for 48 hours under reflux under normal pressure conditions. The heating temperature in this oxidation treatment is 140 to 160 ° 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, an oxygen 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 350 ° C. The rate of temperature increase was 10 ° C./min up to 330 ° C., which is 20 ° C. lower than the heating set temperature, and then 1 ° C./min from 330 ° C. to the heating set temperature 350 ° C. And the oxygen oxidation process was performed about the nano diamond powder in a furnace, maintaining the temperature conditions in a furnace at 350 degreeC. The processing time was 3 hours. As described above, nano-diamond powder subjected to an oxygen oxidation process or an oxygen oxidation treatment was obtained.

  Next, the hydrogenation process was performed using the above-mentioned gas atmosphere furnace. Specifically, after continuously flowing nitrogen gas at a flow rate of 1 L / min for 30 minutes through a gas atmosphere furnace in which nano-diamond powder that has undergone an oxygen oxidation step is arranged, the flow gas is changed from nitrogen. Switching to a mixed gas of hydrogen and nitrogen, the mixed gas was kept flowing through the core tube at a flow rate of 1 L / min. The hydrogen concentration in the mixed gas is 2% by volume. After switching to the mixed gas, the temperature in the furnace was raised to a heating set temperature of 600 ° C. The heating rate was 10 ° C./min. And the hydrogen oxidation process was performed about the nano diamond powder in a furnace, maintaining the temperature conditions in a furnace at 600 degreeC. The processing time was 5 hours. As described above, nano-diamond powder subjected to a hydrogen oxidation step or a hydrogen oxidation treatment was obtained.

  Next, the crushing process was performed. Specifically, first, 0.9 g of nanodiamond powder that had undergone the above hydrogenation step and 29.1 ml of pure water were added to a 50 ml sample bottle and mixed to obtain about 30 ml of slurry. Next, the slurry was subjected to centrifugation (centrifugal force 20000 × g for 10 minutes) and subsequent ultrasonic treatment. In the ultrasonic treatment, an ultrasonic irradiator (trade name “ultrasonic cleaner AS-3”, manufactured by AS ONE) was used, and the slurry was subjected to ultrasonic irradiation for 2 hours. . 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 2 hours.

  Next, about the slurry thru | or suspension which passed through the above crushing processes, the centrifugation process was performed using the centrifuge (classification operation). 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 in which nanodiamonds are dispersed in pure water was obtained. With respect to this nanodiamond dispersion, the solid content concentration or nanodiamond concentration was 2.1 mass%, and the pH was 8.07.

<Particle size D50>
With respect to the nanodiamond dispersion liquid obtained as described above, the particle size distribution of nanodiamond was measured by a dynamic light scattering method. Specifically, the particle size distribution of the nano diamond was measured by a dynamic light scattering method (non-contact back scattering method) using a device (trade name “Zetasizer Nano ZS”) manufactured by Malvern. The nanodiamond dispersion liquid subjected to the measurement has a solid content concentration or a nanodiamond concentration of 2.1% by mass, and is subjected to ultrasonic irradiation by an ultrasonic cleaner. As a result of the measurement, the particle diameter D50 (median diameter) of nanodiamond was 5.05 nm, and the particle diameter D90 of nanodiamond was 7.54 nm.

<Zeta potential>
The zeta potential of nanodiamond particles contained in the nanodiamond dispersion obtained as described above was measured by laser Doppler electrophoresis using a device (trade name “Zetasizer Nano ZS”) manufactured by Malvern. It was measured. The nanodiamond dispersion subjected to the measurement is diluted with ultrapure water so that the solid content concentration or the nanodiamond concentration is 0.2% by mass, and then subjected to ultrasonic irradiation with an ultrasonic cleaner. The zeta potential measurement temperature is 25 ° C. As a result of this measurement, the zeta potential of the nanodiamond dispersion was 41.8 mV.

<Electrical conductivity measurement>
About the nanodiamond dispersion liquid obtained as described above, electrical conductivity was measured at a measurement temperature of 25 ° C. using an electrical conductivity measuring device (trade name “TWIN-COND B-771”, manufactured by Horiba, Ltd.). The degree was measured. The nanodiamond dispersion liquid subjected to the measurement has a solid content concentration or a nanodiamond concentration of 2.1% by mass, and is subjected to ultrasonic irradiation by an ultrasonic cleaner. As a result of this measurement, the electric conductivity of the nanodiamond dispersion liquid was 25.2 μS / cm · wt%.

[Evaluation]
The nanodiamond dispersion liquid obtained by the above-described nanodiamond manufacturing method has a zeta potential of nanodiamond particles of 41.8 mV, a relatively large positive value, and an electrolyte concentration of 25.2 μS / cm · wt%. And pH is 8.07 in the alkaline region. On the other hand, the electrical conductivity of “Nanoamand”, an aqueous nanodiamond dispersion of zeta potential positive manufactured by Nanocarbon Laboratory, Inc. was measured and found to be as high as 66.6 μS / cm.

10 ND dispersion (nanodiamond dispersion)
11 ND particles (nanodiamond particles)
12 Aqueous dispersion medium S1 Production process S2 Purification process S3 Oxygen oxidation process S4 Hydrogenation process S5 Crushing process

Claims (6)

An oxygen oxidation process for subjecting nanodiamond to oxygen oxidation,
And a hydrogenation step for hydrotreating the nanodiamond that has undergone the oxygen oxidation step. A production process for producing nanodiamonds by detonation under an inert gas atmosphere;
The method for producing a nanodiamond dispersion according to claim 1, further comprising a purification step for purifying the nanodiamond crude product obtained in the generation step before the oxygen oxidation step.   The method for producing a nanodiamond dispersion according to claim 2, wherein the purification step includes a mixed acid treatment using a mixed acid. An aqueous dispersion medium;
Comprising nanodiamond particles dispersed in the aqueous dispersion medium and having a positive zeta potential,
A nanodiamond dispersion liquid having an electric conductivity of 30 μS / cm · wt% or less.   The nanodiamond dispersion liquid according to claim 4, wherein the zeta potential is 30 mV or more.   The nanodiamond dispersion liquid according to claim 4 or 5, wherein the pH is in the range of 5 or more.

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