JP5411210B2 - Method for producing metal-supported diamond fine powder and metal-supported diamond fine powder - Google Patents

Description

  The present invention relates to a finely sized diamond fine powder having an average particle diameter of 5 μm or less carrying a metal on its surface, particularly a submicron class, that is, a diamond fine powder having an average particle diameter of less than 1 μm and a method for producing the same.

  Surface coating, which has been implemented with the aim of increasing the functionality of diamond particles, is an intermediate film that aims to improve the bonding strength with the matrix that fixes diamond particles as abrasive grains during the production of diamond-containing tools. There are protective films for preventing particle deterioration, conductive films for the purpose of developing composite functions, etc., nickel coating on diamond particles for resin bond tools, metal carbide coating on particles for high-temperature fired tools, conductivity imparting to the surface Vapor-deposited films for the purpose are widely put into practical use. In particular, metal coatings are used as particles for metal bond tools, as binders in the production of diamond sintered bodies, and as magnetic abrasives.

  As metal coating methods for these applications, physical methods such as vapor deposition and sputtering, chemical methods such as plating (electroplating, chemical plating, immersion plating), chemical vapor deposition (CVD), and thermal spraying are known. It has been. Among them, chemical plating is widely used as a simple coating method for diamond as an electrical insulator, and in particular, a method of using sodium hypophosphite as a reducing agent and precipitating as a Ni-P alloy is common.

Japanese Patent Publication No.52-027875 JP-A-8-209360

  In order to form a uniform coating on the surface of diamond particles, it is essential that the entire surface of each particle faces or is in contact with the coating raw material. For this reason, in the physical method, the vibration / rotation operation of the particles is used in combination, and in the chemical method, the entire surface of the particles is in contact with the coating raw material.

  However, when the particle size becomes smaller, especially when it becomes a so-called submicron-class fine powder of 1 μm or less, the aggregation phenomenon due to the interaction between the fine powder particles becomes prominent. It is necessary to devise a method for uniformly dispersing the particles in the form of primary particles (isolated particles). Furthermore, measures for preventing the joining of the fine powder particles via the deposited metal are also required. For example, in chemical plating on submicron grade diamond, the interaction between fine particles is reduced by using a dilute solution with a diamond concentration in the plating bath of 0.01% by mass or less, and agglomerates via precipitated metal. In order to prevent formation, it is necessary to keep the metal deposition rate small by using a sufficiently diluted metal salt solution, and the low productivity is an obstacle.

In the present invention, diamond particles having an average particle diameter of 5 μm or less (D ₅₀ value display, the same applies hereinafter) as primary particles, which has been difficult to form metal-coated isolated particles in the past, particularly submicron grade diamond particles or fine particles The main object is to provide a method for forming a uniform support layer thereon.

  The method for producing a metal-supported diamond fine powder of the present invention is essentially a process of creating diamond powder with high dispersibility and chargeability in water, such diamond fine powder is dispersed in water as primary particles, and negatively charged and suspended. A step of adding positively charged metal ions, a step of neutralizing the charge of metal ions and attaching a metal precursor on diamond fine powder, and reducing the precursor to metal to form diamond-supported metal powder Each process to include.

More specifically, the method of the present invention includes the following steps.
(1) Oxidizing diamond sized powder having an average particle size of 5 μm or less, and adding oxygen-containing functional groups to the surface of the diamond particles constituting the powder;
(2) The above diamond fine powder is placed in a polar solvent such as water or alcohol to form negatively charged diamond fine powder, and dispersed and suspended in a solvent to obtain a suspension,
(3) Add positively charged metal ions to the suspension, then neutralize the charge of the metal ions, convert the metal ions around the surface of the diamond fine powder to hydroxide or hydrated oxide, A step of forming a metal precursor deposited and supported thereon,
(4) heating the diamond fine powder in a reducing atmosphere, reducing the metal precursor to metal, and
(5) A step of recovering the metal-carrying diamond.

  Since the method of the present invention can be easily applied to nanometer-class diamond fine powder, it is possible to effectively obtain diamond powder having such a fine particle size in which metal is uniformly supported on all particles. In the present invention, the metal is deposited on the surface of the diamond particles of the substrate in the form of particles, coatings, or other shapes depending on the deposition conditions. The term “support” includes the metal and engages or adheres to the substrate particles. It represents what you are doing.

FIG. 1 is an X-ray diffraction pattern (XRD) when MD100 (average particle size 105 nm) grade diamond carrying a metal precursor is heated to several stages of temperature in a hydrogen atmosphere. (Example 1)

  In the method of the present invention, in order to disperse submicron-sized diamond in water without being agglomerated, that is, as primary particles, an operation of positively attaching a hydrophilic functional group by oxidation of the diamond fine powder surface is effective. is there. Although surface oxidation can be realized by heating to around 400 ° C. in an oxygen atmosphere, wet oxidation is preferred for reliable full surface oxidation, in which heating is performed while dispersed in an oxidant solution.

  Examples of the oxidant solution that can be used include concentrated sulfuric acid, concentrated nitric acid, and perchloric acid. In such a solution, diamond is suspended and dispersed and heated to near the boiling point. In this case, it is more effective to add an oxidizing agent, and as such an oxidizing agent, potassium nitrate, chromium oxide and potassium permanganate are suitable. The diamond fine powder after wet oxidation is washed with deionized water, dried at 120 ° C or lower, and sent to the next step.

  The diamond fine powder treated by the wet oxidation method shows strong absorption attributed to carbonyl, carboxyl and hydroxyl by infrared absorption analysis. By performing this treatment, the zeta (ζ) potential of the diamond to which the hydrophilic functional group is added becomes a value of −40 mV or less at pH 9.

  The above diamond fine powder is negatively charged in a polar solvent such as water or alcohol, and repels each other to be suspended in the solvent in the form of primary particles. The application of ultrasonic waves is effective as a treatment for solving the aggregation of fine powder particles that tend to aggregate lightly.

  A metal compound is charged into the obtained diamond fine powder dispersion to bind positively charged metal ions to the diamond surface. The type of metal can be selected according to the diamond application, and it is composed of nickel and copper when used as abrasive grains for metal bonding and resin bonding tools, and iron, nickel, and finely divided diamond when used as a magnetic abrasive. Cobalt is mainly selected as the material for producing the sintered body.

  These metals are added in the form of water-soluble salts such as nitrates and chlorides. Instead of introducing the metal compound into the diamond dispersion aqueous solution, diamond fine powder may be introduced into an aqueous solution in which a metal salt is dissolved, and an ultrasonic wave may be applied to suspend and disperse.

  Next, the metal ions on the surface of the diamond fine powder are precipitated by neutralization treatment, washed with water, and dried to obtain diamond fine powder to which the metal compound is adhered. As the neutralizing agent, metal hydroxide such as sodium hydroxide, ammonia, various alkali salts, urea and the like can be used, and dimethylamine borane (DMAB) and pyrophosphate used as reducing agents for chemical plating. Hypophosphite, borohydride compounds, hydrazine and the like can also be used.

  The compound on the surface of the above-mentioned dry diamond fine powder does not yet exhibit the properties specific to metals. For example, a ferromagnetic signal is not detected in susceptibility measurement from diamond powder dispersed in nickel nitrate solution and using DMAB as a neutralizing agent. For this reason, there is no appearance of agglomerated particles due to the joining of fine powders via precipitated metal, which often occurs in electroplating and electroless plating on fine powders, and each powder particle is separated by fine precipitated compounds, and the form of isolated particles is reduced. The retained feature is recognized.

  This deposited compound can be regarded as a metal precursor in a treatment operation aimed at metal plating. The size of the deposited compound is estimated to be several nanometers by transmission electron microscope observation, and since there is no tendency to join together to form a solid lump, it differs from the case of chemical plating for the purpose of metallic precipitation. In addition, it became possible to carry a metal plating finally by loading a metal precursor on each fine powder particle of fine diamond having a diameter of 100 nm or less.

  The metal precursor formed on the surface of the diamond fine powder may obtain a diffraction pattern that matches the metal hydroxide by X-ray diffraction, and is regarded as a hydroxide or hydrated oxide generated by neutralization or hydrolysis. It is done. For example, in a product obtained by adding nickel nitrate solution to a diamond suspension and neutralizing with a diluted solution of DMAB or sodium hydroxide, an X-ray diffraction pattern consistent with nickel hydroxide was obtained.

  When this product was heated in a hydrogen atmosphere, a weak diffraction pattern attributed to nickel was observed near 300 ° C., and a broad diffraction pattern of nickel was observed near 400 ° C. When the heating temperature is 500 ° C., a sharp peak attributed to nickel is obtained. In transmission electron microscope observation of this sample, the presence of fine particles having a lattice image corresponding to nickel was observed at various locations on the diamond fine powder of the base material. When the temperature was further raised and heated at 800 ° C., the sharp diffraction peak attributed to nickel did not change, but the surface of the fine diamond powder was observed to become spherical with a diameter of about 10 nm by transmission electron microscopy. It was estimated that the nickel in the molten state became aggregated particles due to surface tension. Therefore, the reduction temperature to metallic nickel using hydrogen for the purpose of forming a thin film was estimated to be 700 ° C or less, considering the sintering experience of fine nickel, and 600 ° C or less for safety.

  However, the reduction temperature in the case of aiming at a diamond sintered compact raw material or magnetic abrasive grains for magnetic polishing may be 800 ° C., and the merit of improving oxidative stability is recognized by reducing the surface area of the deposited metal.

According to the method of the present invention, when a single-crystal submicron diamond fine powder subjected to heat treatment is coated with a metal as a base and used as an abrasive, good sharpness is secured. A method for producing heat-treated abrasive grains is disclosed in JP-A-2000-136376. According to this method, fine cracks can be generated in the diamond fine powder, and it has been recognized that the polishing performance is improved as the self-generated blades are sustained by the fine crushing.
JP 2000-136376 A

  However, the surface of the heat-treated diamond fine powder appears to have a hexagonal network structure similar to graphite and exhibits hydrophobicity. Further, the apparent particle size is increased by the joining of the fine powder particles during the heat treatment. Therefore, the surface hydrophilization treatment for dispersing in the form of isolated particles in water is essential, and the above-described oxidation treatment method, particularly the wet oxidation treatment method is used. The obtained diamond particles have a hydrophilic functional group while maintaining a part of the surface structure similar to graphite and have good dispersibility in water.

  This method can also be applied to carbon nanofibers and carbon nanotubes, and it is possible to create new functional materials in which metal is supported on the surface of carbon nanofibers and carbon nanotubes that are substantially free of entanglement.

  The method of the present invention can also be used for detonation diamond aggregates synthesized by an impact pressure method and polycrystalline diamond particles. These commercially available diamonds can be dispersed in water as obtained when the surface is hydrophilic as a result of purification treatment, followed by addition of metal ions, precursor formation by neutralization, drying, and gas reduction. Through various steps, a metal-supported or coated diamond can be obtained. On the other hand, when it is difficult to disperse the obtained product in water, single-particle diamond particles coated with metal can be obtained by performing surface oxidation treatment according to the aforementioned heat-treated particles.

  As described above, the method of the present invention can be applied to all carbon materials of submicron or nanometer size.

  By using the method of the present invention in which a precursor mainly composed of metal hydroxide is formed on the surface of diamond fine powder and the metal is supported on the surface of diamond fine powder by subsequent reduction treatment, fine particles having a particle size of 5 μm or less, particularly 1 μm or less are obtained. It became possible to attach a thin metal film or fine metal particles to the surface in the state of isolated (primary) particles.

  The resulting metal-supported diamond fine powder, such as fine powder covered with a nickel thin film, can be firmly fixed as abrasive grains having a compatible surface in a nickel or bronze matrix in the field of metal bond polishing tools for precision polishing. In addition, when fixed in a resin-based matrix as a resin bond tool, it functions as a protective film to prevent the grains from falling off by preventing local burning of the resin and holding fine powder that has cracked. This contributes to improved tool life.

  Particularly in sub-micron size abrasive grains, conventional abrasive grains have a strong tendency to agglomerate with each other, making it difficult to fix them in the matrix as isolated particles, and the agglomerated particles scratch the work as apparent coarse particles. Because of its detriment, it was not used as a fixed abrasive but was suspended in a dispersion as a free abrasive. However, when used as free abrasive grains, it is necessary to use a large amount of abrasive grains because the ratio of abrasive grains contributing to actual processing is low, and it is also necessary to treat a large amount of used dispersion as waste. There is a negative effect that the load on the environment is large.

  The diamond fine powder according to the present invention does not cause an agglomeration phenomenon between the diamond fine powders due to the metal loading on the surface. Therefore, the diamond fine powder can be dispersed and fixed in the tool matrix as fixed abrasive grains regardless of the fine powder. Therefore, substantially all the fine powder particles contribute to the polishing process, and there is a merit that it is not necessary to take measures against waste because the amount of abrasive grains used is greatly reduced and the dispersion liquid is unnecessary.

  On the other hand, particles carrying cobalt in the form of a thin film or particles serve as a raw material for a sintered body having fine toughness and high toughness. Diamond sintered bodies with diamond particles having an average particle diameter of several μm to several tens of μm as starting materials have small constituent particles and random arrangement directions. It is not seen and is widely used as a cutting tool. In the production, a liquid phase sintering method based on a dissolution / precipitation mechanism is adopted in which a cobalt-based metal sintering aid is infiltrated between diamond particles.

  Sintered diamond blades are used for cutting a wide range of materials except ferrous metals, but they have higher toughness for high-functional materials such as high silicon / aluminum alloys and carbon fiber reinforced resins. Is required. In order to cope with this problem, it is known that the constituent particle size is set to a smaller submicron class. However, it is practically impossible to conduct the sintering reaction by infiltrating the sintering aid metal into fine diamond particles.

  In the present invention, by preparing a starting material in which a required amount of a sintering aid metal is previously supported on the surface of diamond fine powder, it is possible to manufacture a sintered body with high toughness composed of submicron diamond.

  The optimum amount of the sintering aid metal to be supported varies depending on the size of the diamond fine powder to be used, but is usually in the range of 10 to 20% by mass relative to diamond. The form of the sintering aid metal (cobalt) to be supported is generally in the form of a thin film, and for this reason, a hydrogen reduction temperature for obtaining a metallic state is less than 600 ° C.

  Also, particles carrying iron or nickel are expected to be used for precision finish polishing as magnetic abrasive grains for magnetic polishing. Magnetic abrasive grains restrained by a magnetic field can behave like fixed abrasive grains while being free abrasive grains, and use efficiency of abrasive grains is significantly higher than free abrasive grains used as a dispersion (slurry). Is the feature. In addition, it is possible to process a complicated shape that cannot be processed with a tool in which particles are fixed.

  From the viewpoint of maintaining high polishing performance with diamond, a thick coating is not preferable. On the other hand, when the amount of supported metal is small, the responsiveness to the magnetic force of the driving source is reduced. The amount is preferably 20 to 100% by mass with respect to the diamond particles. By supporting these magnetic metals in the form of a film or particles, it is possible to perform free polishing in a magnetic field without impairing the polishing performance of the diamond abrasive grains.

  As a starting material for the metal-coated particles, fine powder of MD100 (average particle size 105 nm) manufactured by Tomei Dia Co., Ltd. was used. The raw diamond powder was previously boiled in a concentrated nitric acid / concentrated sulfuric acid mixed solution to bond hydrophilic functional groups to the surface. The zeta potential at pH 9 was estimated to be about -40 mV from the measurement by Rank Brother electrophoresis type colloidal particle zeta potential measuring device model MARK II.

  5 g of this diamond fine powder was placed in 5 liters of deionized water and sufficiently dispersed and suspended by an ultrasonic bath. Add 3 g of nickel nitrate hexahydrate as a metal salt to this aqueous solution, stir well, and keep a small amount of 0.2 mol DMAB (dimethylamine borane) liquid as a reducing agent while maintaining the liquid temperature at 55 ° C. The solution was added dropwise to deposit a nickel compound as a precursor on the surface of the fine powder.

  The product precursor was dried at 120 ° C. and subjected to X-ray diffraction and magnetic measurements. From the results of X-ray diffraction, a broad diffraction line attributed to metallic nickel found in normal chemical plating (electroless plating) was not observed, but a diffraction line corresponding to nickel hydroxide was observed instead. Moreover, since the difference from the baseline was not recognized in the magnetic measurement, it was judged that the precipitate was not metallic.

  On the other hand, from the observation result by transmission electron microscope, it was estimated that nickel was present on the entire surface of the fine particles. Scanning electron microscopic images also confirmed that the entire surface of the diamond fine powder was covered with precipitates.

  When this product was heated in a hydrogen atmosphere, the XRD pattern changed as shown in FIG. That is, a broad diffraction pattern attributed to nickel was observed around 400 ° C., and a sharp peak attributed to nickel was obtained when the heating temperature was 490 ° C. Further heating and heating at 800 ° C showed no change in the sharp diffraction peak attributed to nickel, but by observation with transmission electron microscope, metallic nickel became a spherical shape with a diameter of around 10 nm on the surface of diamond fine powder. It was estimated that the nickel film covering the surface of the fine powder melted and aggregated into droplets, and heating at 800 ° C. was found to be too high for the purpose of surface coating.

  For the purpose of comparison, a sodium hydroxide diluted solution was added at room temperature instead of DMAB to a diamond suspension to which the same nickel nitrate was added as described above, and the precursor was precipitated while maintaining pH 9. The behavior of the obtained dried product in heating in hydrogen was exactly the same as when DMAB was used, and it was confirmed that the precipitation precursor by DMAB was a hydroxide.

  As a starting material for metal-coated diamond fine powder, a fine powder of MD250 (average particle size 255 nm) manufactured by Tomei Dia Co., Ltd. was used. The surface was oxidized by adding potassium nitrate to concentrated nitric acid / concentrated sulfuric acid mixture and boiling. 50 g of diamond fine powder is dispersed in 15 liters of deionized water, 25 g of cobalt nitrate hexahydrate is added and stirred well, then 30 g of urea is added in powder form and heated to 85 ° C., and a cobalt-containing precursor The diamond fine powder covered with was obtained. The diamond fine powder dried at 120 ° C. was heated to 600 ° C. in hydrogen to obtain diamond fine powder covered with about 5% by mass of a cobalt film.

  This powder is filled in a tantalum capsule on the surface of a cemented carbide substrate with a 13% Co-WC composition to a thickness of 0.8mm and kept at 5.5GPa and 1350 ° C for 15 minutes. The material was obtained.

  As a starting material for the metal-coated particles, diamond fine powder of HM3-8 (average particle size 4.3 μm) manufactured by Tomei Dia Co., Ltd. was used. This variety is single-crystal diamond particles that have been heat-treated at 1300 ° C in a nitrogen atmosphere, and the surface is hydrophobic. In order to make the surface hydrophilic, an oxidation treatment was performed by adding potassium nitrate to a mixture of concentrated nitric acid and concentrated sulfuric acid and boiling.

Disperse 40 g of diamond fine powder in 10 liters of deionized water, add 50 g of nickel chloride hexahydrate, maintain the liquid temperature at 50 ° C., add ammonia water to pH 9.0, and cover with nickel-containing precursor. A fine diamond powder was obtained. Diamond particles covered with about 10% by mass of nickel film were obtained by heating at 600 ° C. in hydrogen.
A grindstone in which these particles were fixed with a phenol resin was suitable for final polishing of a cemented carbide mold.

Examples of starting materials and coating treatment conditions are shown in Table 1. In both cases, the dispersion medium was 10 liters of deionized water.

Submicron-class metal-supported diamond fine powder produced according to the present invention is
* Since it can be used as a tool in a matrix or fixed to a support member as a precision polishing abrasive, it can be used effectively as a loose abrasive in the processing field that was previously used as a loose abrasive. Reduction is achieved;
* The ability to perform effective sintering under ultra-high pressure and high temperature regardless of the fineness of the primary particles enables the production of cutting tools with high toughness composed of fine particles as raw materials for diamond sintered bodies. In particular, it facilitates the processing of difficult-to-cut materials represented by silicon / aluminum alloy and carbon fiber reinforced resin;
* As a fine magnetic abrasive used in magnetic fluids, it enables precision finish polishing using the superior polishing performance of diamond;
It has various applicability.

Claims (13)

A method for producing metal-supported diamond fine powder having the following steps:
(1) Oxidizing diamond sized powder having an average particle size of 5 μm or less, and imparting oxygen-containing functional groups to the surface of the diamond particles constituting the diamond powder;
(2) The above diamond particles are placed in a polar solvent to form negatively charged diamond particles, and dispersed and suspended in the solvent to form a suspension,
(3) Add positively charged metal ions to the suspension, then neutralize the charge of the metal ions, convert the metal ions around the surface of the diamond particles to hydroxide or hydrated oxide, A step of forming a metal precursor deposited and supported thereon,
(4) heating the diamond particles carrying the metal precursor in a reducing atmosphere to reduce the metal precursor to metal;
(5) A step of recovering the metal-supported diamond particles obtained in the step (4) .   The method of claim 1, wherein the polar solvent is water or alcohol.   The method according to claim 1, wherein the neutralization in the step (3) is performed by adding a metal hydroxide, ammonia, various alkali salts, urea, or a reducing agent for chemical plating. The neutralization in the step (3) is performed by adding a reducing agent for chemical plating including one selected from dimethylamine borane (DMAB), pyrophosphate, hypophosphite, borohydride compound, and hydrazine . The method of claim 1 . The method according to claim 1, wherein an average particle diameter of the diamond fine powder is 1 μm or less in D ₅₀ value display. The average particle diameter of the diamond fine powders is 0.2μm or less in the D ₅₀ value display method of claim 1 or claim 5.   The method according to claim 1, wherein the metal of the step (4) is obtained in a thin film form.   The method according to claim 1, wherein the metal of step (4) is obtained in the form of particles.   The method according to claim 1, wherein the metal in step (4) is ferromagnetic or paramagnetic.   The method according to claim 1, wherein the diamond fine powder in the step (1) is a fine powder obtained by pulverization of single crystalline diamond synthesized under a static ultrahigh pressure.   2. The diamond fine powder of the step (1) is composed of polycrystalline particles obtained by fusing nanometer-scale primary diamond particles synthesized by impact pressurization using graphite as a starting material. The method described.   The method according to claim 1, wherein the diamond fine powder in the step (1) is an aggregate of nanometer-scale diamond particles synthesized from detonation using a high-performance explosive as a starting material.   The method according to claim 1, wherein the diamond fine powder constituting particles of the step (1) incorporate microcracks as a result of the heat treatment.

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