JP2011037693A - Method for refining nanodiamond and refined nanodiamond - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for refining nanodiamond by efficiently removing graphite phase from nanodiamond containing the graphite phase with high rate at a low cost, and to provide high purity refined nanodiamond. <P>SOLUTION: In the method for refining the nanodiamond containing the graphite phase and having ≤250 nm median diameter measured by a dynamic light scattering method, (1) the nanodiamond having the graphite phase is subcritically or supercritically treated in a fluid, where oxygen and a treating solvent composed of water and/or alcohol coexist, at a temperature equal to or above the standard boiling point of the treating solvent under pressure equal to or above ≥1 atmospheric pressure (gauge pressure); or (2) the nanodiamond having the graphite phase is supercritically treated with a solution containing an acidic compound. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for purifying nanodiamond that efficiently removes a graphite phase from nanodiamond having a graphite phase at a high rate and at a low cost, and a highly purified nanodiamond.

  Nanodiamond has high hardness and is excellent in smoothness, so it is used as an abrasive or a lubricant. Nanodiamond also has a low dielectric constant and is excellent in electrical insulation, heat resistance, thermal conductivity, optical properties and biocompatibility, so it can be used in fields such as insulating materials for semiconductors and circuit boards, materials for optical components, etc. The use in is expected.

  A typical method for producing nanodiamond is an explosion method (a method in which an explosive containing carbon atoms is exploded and nanosized diamond is generated by an impact associated therewith). However, since the nanodiamond obtained by this method contains carbon impurities mainly composed of graphite, the original properties of diamond are hindered.

  Japanese Patent Laid-Open No. 2003-146637 (Patent Document 1) discloses that a graphite phase-containing nanodiamond is oxidized with nitric acid at a temperature of 150 to 250 ° C. and a pressure of 1.4 to 2.5 MPa, and then neutralized with a base such as ammonia. The method of purification is described. However, this method cannot sufficiently remove the graphite phase.

  Japanese Patent Application Laid-Open No. 2004-43265 (Patent Document 2) describes a method of purifying a graphite phase-containing nanodiamond by treating it with supercritical water. However, in order to sufficiently remove the graphite phase by this method, a temperature of 700 to 800 ° C and a pressure of 100 to 200 MPa are necessary, and it is relatively close to the critical point of water (critical temperature 374 ° C, critical pressure 22.1 MPa). There is a problem that the temperature and pressure are not enough, and the cost of energy and equipment is high.

  Therefore, Yury Gogotsi, four others, "Journal of American Chemical Society", 2006, Vol. 128, pp. 11635-11642 (Non-Patent Document 1) contains graphite phase. A method for purifying nanodiamonds by oxidizing them with air under atmospheric pressure is described. However, in this method, oxygen does not sufficiently penetrate into the graphite phase at the grain boundary, so that only the graphite phase on the nanodiamond surface may be removed.

JP2003-146637 JP 2004-43265 A

Yury Gogotsi, 4 others, "Journal of American Chemical Society", 2006, 128, pp.11635-11642

  Accordingly, an object of the present invention is to provide a method for purifying nanodiamond, which efficiently removes the graphite phase from the nanodiamond having a graphite phase at a high rate and at a low cost, and a highly purified nanodiamond. It is.

  As a result of diligent research in view of the above object, the present inventor has (1) a nanodiamond having a graphite phase in a fluid in which oxygen and a processing solvent comprising water and / or alcohol coexist, and the normal boiling point of the processing solvent. When subcritical or supercritical processing is performed at the above temperature and pressure of 1 atm (gauge pressure) or (2) supercritical processing of nanodiamond having a graphite phase with a solution containing an acidic compound, a high proportion of graphite The inventors have discovered that high-purity nanodiamonds from which phases have been removed can be obtained efficiently and at low cost, and have arrived at the present invention.

  That is, the first purification method of nanodiamonds of the present invention for purifying nanodiamonds containing a graphite phase and having a median diameter of 250 nm or less determined by a dynamic light scattering method comprises oxygen, water and / or alcohol. In the fluid coexisting with the processing solvent, the nanodiamond is subjected to subcritical processing or supercritical processing at a temperature equal to or higher than the normal boiling point of the processing solvent and a pressure equal to or higher than one atmospheric pressure (gauge pressure).

  The treatment conditions are preferably a temperature equal to or higher than (critical temperature of the treatment solvent−100 ° C.) and a pressure of 50% or more of the critical pressure of the treatment solvent. The pressure condition for the treatment is more preferably 70% or more of the critical pressure of the treatment solvent.

  The second method for purifying nanodiamonds of the present invention is characterized in that the graphite layer-containing nanodiamond is supercritically treated in a solution containing at least an acidic compound and a treatment solvent comprising water and / or alcohol. It is preferable to use nitric acid as the acidic compound and water as the treatment solvent.

  In order to further increase the removal rate of the graphite phase, in the first and second methods, the nanodiamond containing the graphite phase is synthesized by an explosion method in which an explosive containing a carbon atom is exploded, and then the median diameter is 50 nm or less. It is preferable to be pulverized so as to be, and more preferable to be pulverized to be 30 nm or less.

Nanodiamond of the present invention purified by the first and second method, the peak intensity I _a of 1,330 ± 10 cm ^-1 in the Raman spectrum, the ratio of the peak intensity I _b of 1,610 ± 100 cm ^-1 It is characterized by 1.2 or more.

  In the method for purifying nanodiamonds of the present invention, (1) whether a fluid in which oxygen and a processing solvent comprising water and / or alcohol coexist is used as a subcritical or supercritical solution having vigorous reactivity (first) (Method 1), (2) Since a supercritical solution containing an acidic compound and having intense reactivity is used (second method), it is relatively high from a graphite phase-containing nanodiamond at a relatively low temperature and pressure. The graphite phase can be removed in proportions. Therefore, the cost for energy and equipment is low and the productivity is good. In particular, in the first method, no acidic compound is used, so there is no problem such as device corrosion. The nanodiamond purified by the method of the present invention has high purity and can fully exhibit the original properties of diamond, and thus is suitable for applications such as abrasives, smoothing materials, insulating materials, and optical component materials.

It is sectional drawing which shows the apparatus which manufactures a blend diamond. It is a typical infrared absorption spectrum of purified nanodiamond. It is the schematic which shows the structure of the apparatus used for the supercritical process. 2 is a Raman measurement chart of UDD and purified nanodiamond before supercritical processing in Example 1. FIG. 7 is a Raman measurement chart of UDD and purified nanodiamond before supercritical processing in Example 7. FIG. It is an infrared absorption spectrum of UDD and the refined nano diamond before supercritical processing of Examples 1 and 7. It is an infrared absorption spectrum of the refined nanodiamond of Examples 1-3. It is an infrared absorption spectrum of the refined nanodiamond of Examples 7-9.

[1] Graphite phase-containing nanodiamonds Graphite phase-containing nanodiamonds purified by the method of the present invention are produced by the explosive method (explosives containing carbon atoms are exploded in an inert gas atmosphere, and nanosized diamonds are bombarded by the accompanying impact. And the like. The graphite phase-containing nanodiamond may be as-synthesized crude diamond (blended diamond, hereinafter referred to as BD), or obtained by selectively oxidizing BD and then neutralizing with a base. Ultra-dispersed diamond (Ultra Dispersed Diamond, hereinafter referred to as UDD) from which a part has been removed may be used, but UDD is preferred.

  For example, Japanese Laid-Open Patent Publication No. 56-26711, Japanese Laid-Open Patent Publication No. 63-303806, Japanese Laid-Open Patent Publication No. 1-234311, Japanese Laid-Open Patent Publication No. 2-14414, Japanese Laid-Open Patent Publication No. 3-271109, and Special Tables. JP 6-505694 (WO 93/13016), JP 7-505831 (WO 94/18123), JP 2003-146637, JP 2006-239511, US Pat. No. 5,861,349, British Patent 1154633 No., Science, Vol. 133, No. 3467 (1961), pp. 1821-1822, Carbon, Vol. 22, No. 2, pp. 189-191 (1984), Van Thiei. M. & Rec., FH, J. Appl. Phys. 62, pp. 1761-1767 (1987), K. Xu. Z. Jin, F. Wei and T. Jiang, Energetic Materials, 1, 19 (1993), Chemical Physics Letters, 222 (1994) ), pp. 343-346, Carbon, Vol. 33, No. 12 (1995), pp. 1663-1671, Bull. Soc. Chem. Fr. Vol. 134 (1997), pp. 875-890, Diamond and Related materials Vol. 9 (2000), pp. 861-865, Physics of the Solid State, Vol. 42, No. 8 (2000), pp. 1575-1578, etc. Specifically, as shown in FIG. 1, an electric detonator 6 is installed in the body, and an explosive [for example, TNT (trinitrotoluene) and HMX (cyclotetramethylenetetranitroamine) or RDX (cyclotrimethylenetrinitroamine) is used. ) In a mass ratio of (40/60) to (60/40)] A steel pipe 4 with a single-sided plug containing 5 is submerged in ice water 1 placed in a pressure vessel 2 made of pure titanium, When the steel helmet 4 is put on the steel pipe 4 and the explosive is exploded, BD is generated in the ice water 1.

  A method for producing UDD is described in, for example, Japanese Patent Application Laid-Open No. 2003-146637. Specifically, (1) Pressurize and heat BD for 10-30 minutes in acid (concentrated nitric acid, concentrated sulfuric acid, mixtures of these, etc.) at a pressure of about 1.4 MPa and a temperature of about 150-180 ° C. (2) The resulting dispersion is pressurized and heated at a pressure of about 1.8 MPa and a temperature of about 200 to 240 ° C., thereby subjecting the BD to a primary oxidizing etching treatment, (3 ) BD is subjected to secondary oxidative etching by pressurizing and heating at a pressure of about 2.5 MPa and a temperature of about 230 to 250 ° C. as necessary. (4) The resulting dispersion is subjected to acid oxidation. 1 to 1.5 equivalents of a base (such as ammonia) is added to neutralize the acid, (5) the obtained UDD is washed with water, and (6) the resulting suspension is centrifuged. . The UDD that has been dehydrated in step (6) may be made into a suspension by adding water, or dried to a fine powder. UDD may be a commercially available product, for example, sold by Vision Development Co., Ltd.

  The BD obtained by the explosion method and the UDD obtained by subjecting the BD to the above steps (1) to (6) are composed of particles in which nano-sized diamond having a diameter of about 1 to 10 nm is aggregated. However, it is preferable that 95 volume% or more has a particle size of 1,000 nm or less, and it is preferable that the particle | grains exceeding a particle size of 1,000 nm are not included substantially. The particle size can be determined by a dynamic light scattering method. Since BD and UDD have a median diameter of 250 nm or less, the graphite phase can be removed efficiently and at a high rate. In order to further increase the removal rate of the graphite phase, it is preferable to further grind BD and UDD. By grinding, the median diameter of BD and UDD is preferably 100 nm or less, more preferably 50 nm or less, and most preferably 30 nm or less.

  A wet pulverization process is preferable as the BD and UDD pulverization process. Examples of the wet pulverization method include a bead mill method, a jet mill method, a vibration mill method, a meteor type ball mill method, a sand mill method, a roll mill method, and a hammer mill method, but the bead mill method is preferable. Examples of the beads include zirconia beads, glass beads, and alumina beads. Among them, zirconia beads having high wear resistance are preferable. The particle size of the beads is preferably 1.0 mm or less, and more preferably 0.5 mm or less. If the particle size exceeds 1.0 mm, the grinding effect is low. If desired, treatment with relatively large particle size beads (eg, about 0.1 mm) may be followed by treatment with smaller particle size beads (eg, about 50 nm).

  The concentration of the aqueous suspension of BD and UDD to be processed by the bead mill is preferably 0.05 to 16% by mass. The circumferential speed of the rotor and the pulverization time may be appropriately set according to the desired degree of grinding, but the circumferential speed of the rotor is preferably 5 m / second or more. Examples of the bead mill include “Star Mill LMZ” and “Star Mill Nano Getter” manufactured by Ashizawa Finetech Co., Ltd.

  If necessary, a wet grinding method other than the bead mill method may be used in combination. Other wet pulverization methods include those described above. The treatment by other wet pulverization method is preferably performed before the treatment by the bead mill.

  BD and UDD mainly have a graphite phase at grain boundaries and surfaces. BD and UDD are impurities other than graphite, including (i) amorphous carbon, (ii) hydrocarbon impurities such as hydrocarbons and heteroatom-containing hydrocarbons, and (iii) metals such as iron and their oxides and salts ( (Metal sulfates, metal carbonates, etc.), carbides, etc., and (iv) non-metallic inorganic substances such as silicon and sulfur and their oxides, carbides, etc. BD and UDD have functional groups and bonds possessed by these impurities mainly composed of graphite. As functional groups, methyl group, methylene group, methine group, carbonyl group, ketone group, ester group, carboxyl group, ether group, aldehyde group, amino group, amide group, nitro group, nitrate ester group, sulfonic acid group, carbon atom And a hydroxyl group (bonding hydroxyl group) bonded to. In the present invention, the above impurities can be sufficiently decomposed or dissolved.

[2] Purification method
(a) First method The first purification method of the graphite phase-containing nanodiamond is: (1) preparing a mixture comprising the graphite phase-containing nanodiamond and a treatment solvent comprising water and / or alcohol; (2) In the presence of oxygen in the nanodiamond-solvent mixture, the nanodiamond containing graphite phase is subcritically or supercritically treated at a temperature higher than the normal boiling point of the processing solvent and at a pressure higher than 1 atm (gauge pressure). 3) A step of centrifuging the liquid containing the purified nanodiamond obtained to remove the processing solvent. After the step (3), a step (4) of washing the purified nanodiamond that has been subjected to the detreatment solvent and a step (5) of centrifuging may be provided. The purified nanodiamond obtained in the step (3) or (5) may be added to a suspension by adding a dispersion solvent or dried to a fine powder. The dispersion solvent may be water, an organic solvent (alcohol or the like), or a mixture thereof. A dispersant may be added to the suspension as necessary.

(1) Preparation process of nanodiamond-solvent mixture The concentration of the nanodiamond containing graphite phase in the nanodiamond-solvent mixture is preferably 0.05 to 16% by mass, more preferably 0.1 to 12% by mass, and most preferably 1 to 10% by mass. preferable. If this concentration exceeds 16% by mass, purification may be insufficient. On the other hand, if it is less than 0.05% by mass, the productivity is poor.

  As the processing solvent, water, alcohol or a mixture thereof is used. The alcohol is preferably a lower alcohol having 1 to 3 carbon atoms (hereinafter simply referred to as “lower alcohol”). Specific examples of the lower alcohol include methanol, ethanol, n-propanol, isopropanol, and a mixture thereof.

(2) Purification process step Place the nanodiamond-solvent mixture in an autoclave and introduce oxygen. You may add a catalyst (boron oxide etc.) as needed. If there is air in the autoclave, it is preferably replaced with oxygen. The amount of oxygen introduced is preferably 0.1 mol or more, more preferably 0.15 mol or more, and most preferably 0.2 mol or more with respect to 1 g of graphite in the graphite phase-containing nanodiamond. The upper limit of the introduction amount is not particularly limited. The proportion of graphite in the nano-diamond, for example, in conformity with JIS K2249 to measure the specific gravity of the nano-diamond, from the specific gravity, the specific gravity of the diamond and 3.50 g / cm ^3, the specific gravity of graphite as 2.25 g / cm ³ Can be calculated.

  The temperature and pressure in the autoclave are adjusted so that the processing solvent has a normal boiling point Tb or higher and one atmospheric pressure (gauge pressure) or higher. As long as the processing solvent is at least Tb and at least one atmospheric pressure (gauge pressure), the processing solvent is in a subcritical state [temperature above Tb and pressure above one atmospheric pressure (gauge pressure) and below the critical temperature Tc and / or critical pressure. It may be in a state less than Pc] or in a supercritical state. In the present invention, the graphite phase can be efficiently and selectively oxidized by subcritical or supercritical oxygen and the treatment solvent.

  The lower limit of the treatment temperature is preferably (critical temperature of treatment solvent Tc-150 ° C), more preferably (Tc-100 ° C). The upper limit of the treatment temperature is preferably 800 ° C, more preferably 600 ° C. The lower limit of the processing pressure is preferably 30% of the critical pressure Pc of the processing solvent, more preferably 50% of Pc, and most preferably 70% of Pc. The upper limit of the treatment pressure is preferably 70 MPa, more preferably 50 MPa. The treatment time may be appropriately set depending on the temperature and pressure, but is preferably 0.1 to 24 hours.

  Table 1 below shows Tb, Tc and Pc of oxygen, water and lower alcohol. The Tc of water and lower alcohol is much higher than that of oxygen (−118 ° C.), and the Pc of water and lower alcohol is higher than the Pc of oxygen (5.1 MPa). Therefore, when the processing solvent consisting of water and / or lower alcohol is set to Tb or more and one atmospheric pressure (gauge pressure) or more, oxygen remains in a subcritical state or a supercritical state, and when the processing solvent is set to a supercritical state, Oxygen is also in a supercritical state.

(3) Desolvation step The obtained liquid containing purified nanodiamond is centrifuged to remove the processing solvent.

(4) Washing step The purified nanodiamond that has been desolvated may be washed with water by a decantation method. The washing operation is preferably performed three times or more.

(5) Dehydration process The purified nanodiamond washed with water is preferably centrifuged and dehydrated.

(b) Second method The second purification method of the graphite phase-containing nanodiamond is as follows. (1) A mixture containing a graphite phase-containing nanodiamond, an acidic compound, and a treatment solvent comprising water and / or alcohol is prepared. (2) Treat this nanodiamond-acidic compound-solvent mixture at a temperature and pressure above the critical point of the processing solvent, and (3) centrifuge the resulting liquid containing purified nanodiamond to remove the processing solvent. The process of carrying out. After the step (3), it is preferable to provide a step (4) for washing the desolvated purified nanodiamond with water and a step (5) for centrifuging. Between steps (3) and (4), a step (6) of neutralizing the desolvated purified nanodiamond with a basic solution and a step (7) of treating with a weak acid may be provided as necessary. . The purified nanodiamond obtained in the step (3) or (5) may be made into a suspension or fine powder in the same manner as described above.

(1) Preparation process of nanodiamond-acidic compound-solvent mixture An acidic compound or a solution thereof is added to a processing solvent dispersion of graphite phase-containing nanodiamond, or an acidic compound and a processing solvent are added to dried graphite phase-containing nanodiamond. A nanodiamond-acidic compound-solvent mixture is prepared by adding.

  Acidic compounds include inorganic acids such as nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrobromic acid, and organic acids such as formic acid, acetic acid, methanesulfonic acid, benzenesulfonic acid, and p-toluenesulfonic acid. Although an acid is mentioned, an inorganic acid is preferable and nitric acid is more preferable.

  If necessary, an oxidizing compound may be further added. Examples of oxidizing compounds include hydrogen peroxide, sodium percarbonate, potassium percarbonate, sodium perborate, potassium perborate, sodium hypochlorite, potassium hypochlorite, sodium chlorite, potassium chlorite, Lithium chlorate, sodium chlorate, potassium chlorate, lithium perchlorate, sodium perchlorate, potassium perchlorate, sodium permanganate, potassium permanganate, sodium manganate, potassium manganate, sodium persulfate, persulfate Examples include potassium sulfate, potassium dichromate, and potassium chromate, and hydrogen peroxide is preferable. A preferred combination of an acidic compound and an oxidizing compound is a combination of nitric acid and hydrogen peroxide.

  The concentration of the nanodiamond containing graphite phase in the nanodiamond-acidic compound-solvent mixture may be the same as in the first method. In order to sufficiently purify, the concentration of the compound in the nanodiamond-acidic compound-solvent mixture is preferably 0.01 to 10 mol / L, more preferably 0.1 to 5 mol / L.

(2) Supercritical processing step The nanodiamond-acidic compound-solvent mixture is processed at a temperature and pressure above the critical point of the processing solvent. The critical temperature Tc and critical pressure Pc of water and lower alcohol are as shown in Table 1 above. The temperature is preferably from the critical temperature of the processing solvent to 600 ° C. The upper limit of the temperature is more preferably 550 ° C. The pressure is preferably a critical pressure of the processing solvent to 100 MPa. The upper limit of the pressure is more preferably 70 MPa, and most preferably 50 MPa. The treatment time may be appropriately set depending on the temperature and pressure, but is preferably 1 to 24 hours.

(3) Desolvation step, (4) Washing step and (5) Dehydration step Steps (3) to (5) may be the same as in the first method.

(6) Neutralization step The purified nanodiamond removed from the solvent in the step (3) may be neutralized with a basic solution. As the basic solution, an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution are preferred. The concentration of the basic solution is preferably 0.01 to 0.5 mol / L. It is preferable to add a basic solution to the desolvated purified nanodiamond and perform ultrasonic treatment. After neutralization, the mixture is centrifuged to remove the basic solution.

(7) Weak acid treatment step The purified nanodiamond neutralized in step (6) is preferably washed with a weak acid solution. With the weak acid solution, metal ions such as sodium remaining after the neutralization treatment can be removed. Examples of the weak acid solution include 0.01 to 0.5 mol / L hydrochloric acid. It is preferable to add a weak acid solution to the neutralized purified nanodiamond and perform ultrasonic treatment. After washing, centrifuge to remove the weak acid solution.

[3] Properties and use of purified nanodiamond The graphite phase of nanodiamond purified by the method of the present invention is removed at a high rate. Specifically, the peak intensity I _a of 1,330 ± 10 cm ⁻¹ attributed to diamond in the Raman spectrum is greater than the peak intensity I _b of 1,610 ± 100 cm ⁻¹ attributed to graphite (the former peak is the latter Higher than the peak). The intensity ratio I _a / I _b is preferably 1.2 or more, and more preferably 1.5 or more.

Purified nanodiamonds also have many functional groups removed with the removal of the graphite phase. FIG. 2 shows a typical infrared absorption spectrum of purified nanodiamond after drying for 2 hours at a temperature of 100 ° C. Purification nanodiamonds, (i) appear in the range of approximately 3,000~3,700 cm ^-1, the peak 1 is considered attributable to the stretching vibration of the hydroxyl groups, it appears in the range of (ii) approximately 2,800~3,000 cm ^-1, methylene group Peak 2, which is considered to be attributed to stretching vibration, (iii) Peak which appears in the range of approximately 1,700 to 1,800 cm ^-1 and is attributed to stretching vibration of carbonyl group of ketone group, aldehyde group, ester group, carboxyl group, etc. 3, (iv) Peak 4, which appears in the range of about 1,500 to 1,700 cm ^-1 and is attributed to the stretching vibration of the carbonyl group of the amide group, carboxyl group, etc., the bending vibration of the hydroxyl group, etc., (v) about 1,200 Peak 5 which appears in the range of ˜1,400 cm ⁻¹ and is attributed to nitrate group, CN single bond, CH bond, hydroxyl group, etc., (vi) in the range of approximately 1,100 to 1,200 cm ⁻¹ and approximately 1,000 to 1,100 cm ⁻ appears in the ^first range, nitrate ester groups, aliphatic et Ether group, SO double bonds, and the like peaks 6 and 7 is considered to belong to, (vii) appears in the range of approximately 800 to 1000 cm ^-1, a peak considered to nitrate ester groups, CCC bond, attributable to the aldehyde group 8 and (viii) approximately range from 750 to 800 cm ^-1, approximately 650 to 750 range cm ^-1, appears in range and approximately 400-500 range cm ^-1 approximately 500 to 650 cm ^-1, aliphatic ethers The peaks 9 to 12 are considered to belong to groups, aromatic groups, etc., but the intensities I _{2 to} I 12 of the peaks 2 to ₁₂ are all smaller than the intensity I _{1 of the} peak 1. The ratio of each of the intensities I _{2 to} I ₁₂ of the peaks _{2 to 12} and the intensity I _{1 of the} peak 1 is preferably 2.5 or less, and more preferably 2.0 or less.

  Purified nanodiamond is a particle having a median diameter of about 30 nm to 1 μm (dynamic light scattering method) formed by agglomeration of primary particles of nanosized diamond, and contains a minute amount of coarse particles of 10 μm or more. Therefore, it is preferable that the purified nanodiamond is separated into relatively fine particles and coarse particles by a method such as filtration, centrifugation, and decantation according to the purpose of use.

  As described above, refined nanodiamonds have a high proportion of graphite phase removed, so the original properties of diamond (excellent mechanical properties, chemical stability, electrical insulation, low dielectric properties, thermal conductivity, heat resistance) Etc.). Purified nanodiamond is suitable for applications such as insulating materials, abrasives, heat dissipation materials, etc. used for semiconductors, circuit boards, capacitors and the like. Purified nanodiamonds have a high refractive index and excellent dispersibility in other materials (transparent resin, glass, etc.), so optical components (glasses lenses, optical information recording / reproducing device pickup lenses, backs It is also useful as a material for light lenses and lens sheets.

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

Example 1
Synthesis of blended diamond Using the apparatus shown in Fig. 1, 0.65 kg of explosive containing TNT (trinitrotoluene) and RDX (cyclotrimethylenetrinitroamine) at a mass ratio of 60/40, and a pressure vessel with a capacity of 3m ³ The diamond was exploded in 2 to synthesize blended diamond (BD). After the explosion product expanded and reached thermal equilibrium, the gas mixture was allowed to flow out of the pressure vessel 2 through a supersonic Laval nozzle having a cross section of 15 mm for 35 seconds. Due to heat exchange with the vessel wall and work done by the gas (adiabatic expansion and vaporization), the product cooling rate was 280 ° C./min. The product (black powder, BD) captured by the cyclone had a specific gravity of 2.55 g / cm ³ and a median diameter (dynamic light scattering method) of 220 nm. From this specific gravity, assuming that the specific gravity of diamond is 3.50 g / cm ³ and the specific gravity of graphite is 2.25 g / cm ³ , the ratio of diamond to graphite is calculated, and the composition is 24% by volume of diamond and 76% by volume of graphite. Estimated.

Preparation of ultra-dispersed diamond The above BD is placed in a 60 mass% nitric acid aqueous solution, selectively oxidized for 20 minutes at a temperature of 160 ° C and a pressure of 1.4 MPa, and then an oxidative etching treatment at a temperature of 230 ° C and a pressure of 1.8 MPa for 1 hour. After neutralization by adding ammonia and refluxing at a temperature of 210 ° C. and a pressure of 2.0 MPa for 20 minutes, the separated ultradispersed diamond (UDD) was washed and dried. The median diameter of this UDD was 130 nm (dynamic light scattering method), and the specific gravity measured according to JIS K2249 was 3.38 g / cm ³ . The composition calculated from this specific gravity was estimated to be a composition of 90% by volume of diamond and 10% by volume of graphite.

Grinding The above UDD 243 g was put into a water / triethylene glycol mixed solvent (volume ratio 1: 1) and stirred to prepare a 5 mass% aqueous dispersion. The above aqueous dispersion is supplied at a rate of 0.12 L / min to a bead mill (equipment: “Star Mill LMZ” manufactured by Ashizawa Finetech Co., Ltd.) filled with zirconia beads having a particle size of 0.1 mm in a vessel, and 10 m / sec. The UDD was continuously pulverized while rotating the rotor at a peripheral speed (residence time in the mill: 2 hours). The median diameter of UDD after pulverization was 25 nm.

Purification 30 mL of a 2.0% by mass aqueous dispersion of pulverized UDD was prepared, placed in an autoclave (capacity 50 mL, made of SUS316), and sealed with a lid having an oxygen introduction tube, a temperature sensor, and a pressure regulating valve. The air in the autoclave was replaced with oxygen, oxygen was introduced at room temperature so that the pressure in the autoclave was 1.0 MPa (gauge pressure), the autoclave was installed in the furnace, and the average heating rate was 6.5 ° C / min. Heated. After reaching 400 ° C., it was treated at a temperature of 400 ± 5 ° C. and a pressure of 24.8 ± 1 MPa for 1 hour. After cooling to room temperature, the pressure was reduced to atmospheric pressure, and a liquid containing purified nanodiamond was recovered. This liquid was separated into a supernatant and a precipitate of purified nanodiamonds showing a light gray color.

The purified nanodiamond-containing liquid was centrifuged, the supernatant liquid was removed, the dehydrated purified nanodiamond was washed with water three times by a decantation method, centrifuged, and the dehydrated purified nanodiamond was heated and dried at 120 ° C. The removal rate calculated from the difference in dry mass between UDD and purified nanodiamond was 5.9% by mass with UDD as 100% by mass. The specific gravity of the purified nanodiamond was 3.49 g / cm ³ . The composition calculated from this specific gravity was 99% by volume of diamond and 1% by volume of graphite.

Example 2
The UDD was treated in the same manner as in Example 1 except that the amount of UDD aqueous dispersion was 25 mL, the temperature was raised to a temperature of 397.5 ° C. and a pressure of 19.85 MPa, and then immediately cooled to room temperature. The obtained liquid containing the purified nanodiamond was separated into a supernatant and a precipitate of purified nanodiamond exhibiting a light gray color.

The purified nanodiamond was washed with water and dried in the same manner as described above, and the removal rate was determined. As a result, it was 5.5% by mass. The specific gravity of the purified nanodiamond was 3.47 g / cm ³ . The composition calculated from this specific gravity was diamond 98 volume% and graphite 2 volume%.

Example 3
UDD was treated in the same manner as in Example 1 except that the amount of UDD aqueous dispersion was 15 mL, the treatment pressure was 16 ± 1 MPa, and the treatment time was 2 hours. The obtained liquid containing the purified nanodiamond was separated into a supernatant and a precipitate of purified nanodiamond exhibiting a light gray color.

The purified nanodiamond was washed with water and dried in the same manner as described above, and the removal rate was determined. The specific gravity of the purified nanodiamond was 3.46 g / cm ³ . The composition calculated from this specific gravity was 97% by volume of diamond and 3% by volume of graphite.

Example 4
The UDD was treated in the same manner as in Example 1 except that the amount of UDD aqueous dispersion was 15 mL, the treatment temperature was 300 ± 5 ° C., and the treatment pressure was 20 ± 1 MPa. The purified nanodiamond was washed with water and dried in the same manner as described above, and the removal rate was determined. The result was 2.7% by mass. The specific gravity of the purified nanodiamond was 3.42 g / cm ³ . The composition calculated from this specific gravity was 94% by volume of diamond and 6% by volume of graphite.

Example 5
UDD was treated in the same manner as in Example 1 except that the amount of UDD aqueous dispersion was 15 mL, the treatment temperature was 350 ± 5 ° C., and the treatment pressure was 20 ± 1 MPa. The purified nanodiamond was washed with water and dried in the same manner as described above, and the removal rate was determined. The result was 3.7% by mass. The specific gravity of the purified nanodiamond was 3.44 g / cm ³ . The composition calculated from this specific gravity was 95% by volume of diamond and 5% by volume of graphite.

Example 6
UDD was supercritically treated in the same manner as in Example 1 except that the treatment temperature was 500 ± 5 ° C. The purified nanodiamond was washed with water and dried in the same manner as described above, and the removal rate was determined. As a result, it was 6.5% by mass. Specific gravity of the purified nanodiamonds is the same as 3.50 g / cm ³ and the diamond was estimated to almost all of the graphite has been removed.

  From Examples 1 to 6, it was found that when UDD is subcritically or supercritically treated in a fluid in which oxygen and water coexist, impurities mainly composed of graphite are significantly removed.

Example 7
FIG. 3 shows the apparatus used to supercritically treat UDD with nitric acid. This device includes a Hastelloy (registered trademark) autoclave (capacity 10 mL) 11, a furnace 12 for heating the same, a back pressure control valve 13 for controlling the pressure in the autoclave 11, and a front stage of the back pressure control valve 13. Detected by the cooling coil 14 provided, the waste liquid container 15 provided downstream of the back pressure control valve 13, the temperature sensor 16 for detecting the temperature of the contents, and the back pressure control valve 13 and the temperature sensor 16, respectively. And a computer 17 for recording pressure and temperature. An ultrapure water tank 18 and a pump 19 for feeding ultrapure water are connected to a pipe 110 connecting the autoclave 11 and the back pressure control valve 13 via a three-way joint 111.

  A 2.0 mass% aqueous dispersion of ground UDD (median diameter 25 nm, estimated composition: diamond 90 volume% / graphite 10 volume%) prepared in the same manner as in Example 1 and 13.4 N nitric acid (61 mass%, specific gravity 1.38) , Manufactured by Wako Pure Chemical Industries, Ltd.) at a volume ratio of 9: 1. The obtained mixture (7 mL) was put into the autoclave 11, the pipe 110 and the temperature sensor 16 were attached to the autoclave 11, and the autoclave 11 was set in the furnace 12. Ultrapure water was fed from tank 18 at a flow rate of 0.5 mL / min until the pressure in autoclave 11 reached 30 MPa, and then the flow rate of ultrapure water was reduced to 0.1 mL / min and temperature increase was started. . In order to prevent water containing impurities such as graphite discharged from the three-way joint 111 from flowing back into the autoclave 11, the inside of the autoclave 11 is maintained at 30 ± 1 MPa while maintaining the flow rate of ultrapure water at 0.1 mL / min. The UDD was supercritically treated with nitric acid by holding at a pressure of 5 ° C and a temperature of 500 ± 5 ° C for 3 hours. After cooling to room temperature while maintaining the flow rate of ultrapure water at 0.1 mL / min, the pressure was reduced to atmospheric pressure, and a liquid containing purified nanodiamond was recovered.

The purified nanodiamond was washed with water and dried in the same manner as described above, and the removal rate was determined. As a result, it was 4.7% by mass. The specific gravity of the purified nanodiamond was 3.46 g / cm ³ . The composition calculated from this specific gravity was estimated to be a composition of 97 vol% diamond and 3 vol% graphite.

Example 8
UDD was supercritically treated with nitric acid in the same manner as in Example 7 except that the treatment time was 5 hours. The removal rate obtained in the same manner as described above was 5.0% by mass. The specific gravity of the purified nanodiamond was 3.46 g / cm ³ . The composition calculated from this specific gravity was estimated to be a composition of 97 vol% diamond and 3 vol% graphite.

Example 9
UDD was supercritically treated with nitric acid in the same manner as in Example 8 except that the temperature was 400 ° C. ± 5. The removal rate determined in the same manner as described above was 2.5% by mass. The specific gravity of the purified nanodiamond was 3.45 g / cm ³ . The composition calculated from this specific gravity was estimated to be a composition of 96 volume% diamond and 4 volume% graphite.

Example 10
UDD was supercritically treated with nitric acid in the same manner as in Example 7 except that the temperature was 580 to 600 ° C., the pressure was 60 MPa, and the time was 8 hours. The removal rate obtained in the same manner as above was 6.5% by mass. Specific gravity of the purified nanodiamonds is the same as 3.50 g / cm ³ and the diamond was estimated to almost all of the graphite has been removed.

  From Examples 7 to 10, it was found that when UDD was treated with nitric acid in a supercritical state, impurities mainly composed of graphite were significantly removed.

Comparative Example 1
UDD was treated with supercritical water in the same manner as in Example 7 except that nitric acid was not added. The removal rate calculated in the same manner as described above was 0.7% by mass. The specific gravity of the nanodiamond was 3.39 g / cm ³ . When calculated from this specific gravity, it was estimated that the purified nanodiamond had a composition of 91% by volume of diamond and 9% by volume of graphite. From the above, it was found that the supercritical water treatment of Comparative Example 1 was significantly inferior in the removal amount of the graphite phase as compared with the treatment using Examples 1 to 10 using oxygen or nitric acid.

  For the purified nanodiamonds and UDDs obtained in Examples 1 to 3 and 7 to 9, Raman spectra were measured under the following conditions. The results of Examples 1 and 7 are shown in FIGS.

Apparatus: Microscopic Raman spectrometer (JRS-SYSTEM 2000 manufactured by Renishaw Co., Ltd.)
Laser wavelength: 532 nm
Laser power: 100%
Grating: 1800 line / mm
Measurement time: 30 seconds Integration: 5 times Sample: Dry at 100 ° C

As is clear from FIGS. 4 and 5, in the purified nanodiamond, the peak intensity I _a near 1,333 cm ⁻¹ attributed to diamond is larger than the peak intensity I _b near 1,620 cm ⁻¹ attributed to graphite. On the other hand, in UDD, intensity _Ia is smaller than intensity _Ib . As a result of measuring five sites on the purified nanodiamond and UDD and determining the average value of the intensity ratio I _a / I _b , the purified nanodiamond of Examples 1 and 7 was 8.0 and 1.6, respectively. The UDD was 0.86. For Examples 2, 3, 8, and 9, the intensity ratios I _a / I _b (average values) obtained in the same manner as described above were 4.2, 2.1, 1.8, and 1.2, respectively. In addition, the peak near 1,620 cm ^-1 attributed to graphite is detected with a very large intensity due to the resonance Raman effect, so it is impossible to quantify graphite, but relative comparison between samples based on the intensity ratio of diamond and graphite peaks. Can do.

About the refined nanodiamond and UDD obtained in Examples 1 to 3 and 7 to 9, using a Fourier transform infrared spectrophotometer (Nicolet MAGNA 760 manufactured by Thermo Fisher Scientific Co., Ltd.), 100 ° C. by the transmission method. The infrared spectrum after drying for 2 hours at a temperature of was measured. The results are shown in FIGS. 7 and 8, the upper limit value of the vertical axis is made smaller than in FIG. As apparent from FIGS. 6 to 8, the purified nanodiamonds obtained in Examples 1 to 3 and 7 to 9 show (i) a range of approximately 2,800 to 3,000 cm ⁻¹ compared to UDD, and methylene. The peak that is considered to be attributed to the stretching vibration of the group, (ii) appears in the range of approximately 1,700 to 1,800 cm ⁻¹ , and is considered to be attributed to the stretching vibration of the carbonyl group of the ketone group, aldehyde group, ester group, carboxyl group, etc. Peak, (ii) Appears in the range of approximately 1,500 to 1,700 cm ⁻¹ , Peak considered to be attributed to the stretching vibration of the carbonyl group possessed by the amide group, carboxyl group, etc., the bending vibration of the hydroxyl group, etc. Peak appearing in the range of 1,400 cm ^-1 and attributed to nitrate group, CN single bond, CH bond, hydroxyl group, etc. (iv) in the range of approximately 1,100 to 1,200 cm ^-1 and in the range of approximately 1,000 to 1,100 cm ^-1 Appears in range, nitrate group, aliphatic ether group Peak thought to belong to the SO double bonds, and the like, (v) appear in a range of approximately 800 to 1000 cm ^-1, nitrate group, CCC bond peak is believed attributable to the aldehyde group and the like, and (vi) approximately 750 range to 800 cm ^-1, generally range from 650 to 750 cm ^-1, appears in range and approximately 400-500 range cm ^-1 approximately 500 to 650 cm ^-1, aliphatic ether group, an aromatic group, etc. All of the peaks considered to be attributed decreased.

Intensities I _{2 to} I ₁₂ (see FIG. 2) of the above peaks in the infrared absorption spectra of the purified nanodiamonds of Examples ^{1 to 3} and 7 to 9 appear in the range of 3,000 to 3,700 cm ⁻¹ , and the expansion and contraction of the hydroxyl group. The ratio with the peak intensity I ₁ (see FIG. 2) that is considered to be attributed to vibration was determined. The results are shown in Table 2.

As is apparent from Table 2, the peak intensity ratios (I ₂ / I ₁ ) to (I ₁₂ / I ₁ ) are all 2.0 or less, particularly 1.0 to 3 in Examples 1 to 3, In 2, it was 0.6 or less.

DESCRIPTION OF SYMBOLS 1 ... Ice water 2 ... Pressure-resistant container 3 ... Helmet 4 ... Steel pipe 5 ... Explosive 6 ... Electric detonator
11 ... Autoclave
12 ... heating furnace
13 ... Back pressure control valve
14 ... Cooling coil
15 ... Waste liquid container
16 ... Temperature sensor
17 ... Computer
18 ... Ultra pure water tank
19 ... Pump
110 ... pipe
111 ・ ・ ・ Three-way fitting

Claims (11)

A method for purifying nanodiamond containing a graphite phase and having a median diameter of 250 nm or less determined by a dynamic light scattering method, wherein a fluid containing oxygen and a treatment solvent comprising water and / or alcohol coexists. A method comprising subjecting the graphite layer-containing nanodiamond to a subcritical or supercritical treatment at a temperature not lower than the normal boiling point of the processing solvent and a pressure not lower than 1 atm (gauge pressure). 2. The method for purifying nanodiamond according to claim 1, wherein the graphite layer-containing nanodiamond is formed at a temperature of (critical temperature of the processing solvent−100 ° C.) or higher and a pressure of 50% or higher of the critical pressure of the processing solvent. A method characterized by processing. The method for purifying nanodiamond according to claim 1 or 2, wherein the graphite layer-containing nanodiamond is treated at a pressure of 70% or more of a critical pressure of the treatment solvent. A method for purifying nanodiamond containing a graphite phase and having a median diameter of 250 nm or less determined by a dynamic light scattering method, in a solution containing at least an acidic compound and a treatment solvent comprising water and / or alcohol And a method of supercritically treating the graphite layer-containing nanodiamond. 5. The method for purifying nanodiamond according to claim 4, wherein nitric acid is used as the acidic compound and water is used as the treatment solvent. The method for purifying nanodiamond according to any one of claims 1 to 5, wherein the graphite phase-containing nanodiamond is synthesized by an explosion method in which an explosive containing a carbon atom is exploded, and then has a median diameter of 50 nm or less. A method comprising pulverizing as described above. The method for purifying nanodiamond according to claim 6, wherein the graphite phase-containing nanodiamond is pulverized so as to have a median diameter of 30 nm or less. A nanodiamond containing a graphite phase and having a median diameter of 250 nm or less determined by a dynamic light scattering method, in a fluid in which oxygen and a processing solvent comprising water and / or alcohol coexist, exceed the standard boiling point of the processing solvent. Nanodiamond purified by subcritical or supercritical treatment at a temperature of 1 atmosphere (gauge pressure) or higher, with a peak intensity I _a of 1,330 ± 10 cm ⁻¹ in the Raman spectrum and 1,610 ± 100 A purified nanodiamond having a ratio of cm ^{−1 to} a peak intensity I _b of 1.2 or more. Supercritical treatment of nanodiamond containing a graphite phase and having a median diameter of 250 nm or less determined by dynamic light scattering method in a solution containing at least an acidic compound and water and / or alcohol. a nanodiamond purified by purification, characterized in that the peak intensity I _a of 1,330 ± 10 cm ^-1 in the Raman spectrum, the ratio of the peak intensity I _b of 1,610 ± 100 cm ^-1 is 1.2 or more Nano diamond. 10. The refined nanodiamond according to claim 8 or 9, wherein the graphite phase-containing nanodiamond is pulverized so as to have a median diameter of 50 nm or less after being synthesized by an explosion method in which an explosive containing a carbon atom is exploded. A refined nanodiamond characterized by comprising: 11. The purified nanodiamond according to claim 10, wherein the graphite phase-containing nanodiamond is pulverized so as to have a median diameter of 30 nm or less.

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