JP3814660B2 - Manufacturing method of high-hardness ultrafine diamond composite sintered body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrafine diamond composite sintered body and a method for producing the same.
[0002]
[Prior art]
Conventionally, it is known that a diamond sintered body or a fine diamond sintered body using a metal such as Co as a sintering aid is manufactured by a normal ultrahigh pressure synthesizer (Patent Documents 1 and 2). Also, without using metal sintering aids at all, by using alkaline earth metal carbonates as sintering aids and sintering under higher pressure and temperature conditions, they have superior heat resistance. A synthesis method for obtaining a high-hardness diamond sintered body is known (Non-Patent Document 1). However, these sintered bodies are limited to a relatively large particle diameter with a diamond particle diameter of about 5 μm in the sintered body.
[0003]
The present inventors prepared a mixed powder obtained by adding oxalic acid dihydrate, which is a source of a CO ₂ —H ₂ O fluid phase, to a carbonate, and natural diamond having a particle size range of 0 to 1 μm on the mixed powder. A method of laminating powder and producing a fine diamond sintered body has been reported (Patent Document 3, Non-Patent Documents 2 and 3), but the production requires a high temperature of 2200 ° C. or higher.
[0004]
The present inventors have reported an example in which a finer diamond powder, for example, a diamond powder having a particle size width of 0 to 0.1 μm, is sintered by the same method (Non-patent Document 4). However, abnormal grain growth of diamond occurred, and a high-hardness diamond sintered body could not be manufactured.
[0005]
Recently, a method of synthesizing a diamond sintered body without sintering aids under conditions of 12 to 25 GPa and 2000 to 2500 ° C. by direct conversion reaction from graphite to diamond has been announced and reported to become a translucent sintered body. (Non-Patent Document 5).
[0006]
[Patent Document 1]
Japanese Patent Publication No. 52-12126 [Patent Document 2]
Japanese Patent Publication No. 4-50270 [Patent Document 3]
Japanese Patent Laid-Open No. 2002-187775
[Non-Patent Document 1]
Diamond and Related Mater. , 5 pp. 2-7 , Elsevier Science S. A, 1996 [Non-Patent Document 2]
108 pages of the 41st High Pressure Discussion Meeting Abstract, Japan Society of High Pressure, 2000 [Non-Patent Document 3]
Proceedings of the 8th NIRIM International Symposium on Advanced Materials, 33-34, Institute for Inorganic Materials, 2001 [Non-Patent Document 4]
Abstracts of the 42nd high-pressure discussion meeting, 89 pages, Japan Society of High Pressure, 2001 [Non-Patent Document 5]
T.A. Irifune et al. , “Characterization of polycrystalline diamonds synthesized by direct conversion of graphs using a large amount of the two”, 6th High Pressure
[0008]
[Problems to be solved by the invention]
Since the diamond sintered body containing a sintering aid contains a solid aid, the volume of diamond particles decreases by the amount of volume occupied by the aid. As a result, the diamond sintered body containing the sintering aid has a lower Vickers hardness than the ideal diamond sintered body containing no auxiliary.
[0009]
Conventionally, the present inventors have searched for a new diamond synthesis catalyst under high pressure and high temperature conditions of 7.7 GPa and ˜2500 ° C. As a result, it was discovered and reported that a fluid phase such as a C—O—H fluid phase composed of CO 2 and H 2 O belonging to the third category in addition to a metal catalyst and a non-metal catalyst becomes a diamond synthesis catalyst (for example, C-O-H fluid catalyst diamond synthesis, M. Akashishi and S. Yamaoka, "Crystallization of diamond from C-O-fluids under high-pressure and high-temperature Jr." 999 (2000).
[0010]
Conventional diamond powder sintering aids are metallic aids such as Co and non-metallic carbonates such as MgCO ₃ . Existing sintering aids, whether metallic or non-metallic, all belong to the category of diamond synthesis catalysts.
Therefore, the present inventors have newly clarified that the catalyst becomes a diamond synthesis catalyst. Oxalic acid dihydrate (hereinafter abbreviated as “OAD”) that decomposes under high pressure and high temperature conditions to become a C—O—H fluid catalyst. If it functions as a sintering aid for diamond, synthesis of a sintered body in which no solid sintering aid remains in the diamond sintered body was expected.
[0011]
However, natural diamond powder having a particle diameter of 0 to 1 μm is desilicated, and then these powders are laminated on an OAD powder and filled into a Ta capsule, and a wide range of 7.7 GPa to 9.4 GPa. Even when heated and pressed under various pressure conditions, OAD did not function as a diamond sintering aid at all. That is, the diamond sample collected after the treatment under conditions of 7.7 GPa and 2000 ° C. was a milky white block having innumerable cracks, but had no grinding resistance.
[0012]
Moreover, the diamond sample recovered by treatment with the pressure increased to 9.4 GPa was a slightly grayish white. This sample had almost no cracking, but had no grinding resistance.
As described above, it has been difficult to produce an ideal high-hardness diamond sintered body containing no sintering aid.
[0013]
[Means for Solving the Problems]
The present inventors filled a Ta capsule with a powder prepared by freeze-drying ultrafine natural diamond powder having a particle size width of 0 to 0.1 μm and then lyophilized it, and 9.4 GPa using an ultrahigh pressure synthesizer. When the sample was recovered after treatment at 2150 ° C. for 20 minutes, a sintered body having a very large grinding resistance was obtained. As a result, it was discovered that an organic acid composed of carbon, oxygen, and hydrogen is an effective sintering aid for sintering ultrafine natural diamond. When the particle diameter of diamond is reduced, the surface energy of the particles increases, and this energy is considered to work as a driving force for sintering.
[0014]
In addition, this sintered body is gray, but the reason is not clear. When the X-ray diffraction pattern of the sample was measured, surprisingly, in addition to the diffraction lines of diamond, Ta oxide and carbide were confirmed. It was done. These compounds are thought to be produced by the reaction of oxygen or carbon, which is a decomposition product of OAD, with Ta, which is a cylindrical capsule material, or Ta foil laminated on a diamond powder layer. The relative intensity of the strongest diffraction line of the Ta oxide was 68 when the intensity of the strongest diffraction line of diamond was 100, and the relative intensity of the strongest diffraction line of Ta carbide was 50.
[0015]
That is, the present invention is as follows.
[0016]
(1) A powder prepared by desiccating ultrafine natural diamond powder having a particle size range of 0 to 0.1 μm and then freeze-drying using an aqueous solution is enclosed in a Ta capsule, and the capsule is then combined with an ultrahigh pressure synthesizer The diamond powder is obtained by heating and pressing organic acid powder composed of carbon, oxygen, and hydrogen as a sintering aid at a temperature of 1900 ° C. or higher and a pressure of 8.5 GPa or higher, which is the thermodynamic stability condition of diamond. High-hardness ultrafine diamond composite firing characterized by obtaining a sintered body containing a product composed of a Ta compound in the sintered body by sintering and having a diamond particle diameter of 100 nm or less in the sintered body. A manufacturing method of a knot.
[0017]
The particle diameter of diamond in the diamond sintered body of the present invention is 100 nm or less as observed with an electron microscope, the hardness is a high Vickers hardness of 80 GPa or higher, and no homogeneous grain growth is observed at all. Because it is made of fine particles, it has excellent wear resistance and heat resistance, and can be machined into a sharp edge shape.For example, finish cutting of difficult-to-cut materials such as high Si-Al alloy, Excellent cutting performance when applied to ultra-precision machining of alloys.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The desiccated ultrafine natural diamond powder used to produce the diamond sintered body of the present invention is specifically prepared as follows. In addition, this method is the same method as the preparation method of the diamond powder which suppressed formation of the secondary particle disclosed by Japanese Patent Application No. 2002-030863.
[0019]
A commercially available natural diamond powder having a particle size range of 0 to 0.1 μm is treated in molten sodium hydroxide using a zirconium crucible to convert silicate contained as an impurity in the diamond into water-soluble sodium silicate.
In addition, although there is no particle size standard based on a standardized measurement method for fine powder diamond, the particle size range is 0 to 1/4, 0 to 1/2, 0 to 1, 0 to 2, 1 to 3, It is marketed based on the standard particle size standard (the center particle size is the intermediate value of the particle size width) divided into 2 to 4 and 4 to 8, and in this specification, the particle size of natural diamond powder The width is based on these categories.
[0020]
Diamond powder is recovered from the molten sodium hydroxide in an aqueous alkaline solution, neutralized with hydrochloric acid, and then washed several times with distilled water to remove sodium chloride.
Aqua regia is added to the solution in which the diamond powder is dispersed, and the diamond powder is treated in hot aqua regia to remove zirconium that may be mixed in from the zirconium crucible. After the hot aqua regia treatment, it is washed with distilled water three times or more, and the diamond powder is recovered in the weakly acidic solution. The treatment solution in which the diamond powder is dispersed is weakly acidic with a pH of about 3-5.
[0021]
The weakly acidic aqueous solution in which the desilicated diamond powder is dispersed is preferably sufficiently shaken with a shaker in a plastic container or the like for about 20 to 30 minutes. Freeze in a short time while stirring the container. The time from the shaker to immersion in liquid nitrogen is as short as possible, preferably within 30 seconds. As a result, the sedimentation of diamond powder on the bottom of the plastic container is suppressed, and the formation of secondary particles is also suppressed. Liquid nitrogen is suitable for use in refrigeration because it is inexpensive and the solution can be easily frozen.
[0022]
In lyophilization, the lid of a container containing frozen diamond powder is loosened and placed in a vacuum, and when the frozen material is brought into a vacuum state, the frozen weakly acidic ice sublimes. The container containing the frozen material is cooled by sublimation heat and can be kept frozen. The vaporized water is trapped by placing a freezer at −100 ° C. or lower in the middle of the exhaust system of the vacuum pump. In this case, lyophilization takes about 4 days in a 15 gr diamond powder / 100 ml solution system.
[0023]
In this method, fine diamond powder is dispersed in an aqueous solution in a container, the surface of the diamond particles is frozen in a state of being covered with the aqueous solution, and then freeze-dried as it is to suppress the formation of secondary particles. It is. When freeze-dried, the diamond powder becomes a discrete powder, which is completely different from those of the conventional filtration and heat drying methods, and a smooth powder with high fluidity can be obtained. The powder prepared by the above lyophilization method is a primary particle having an average particle diameter of about 80 nm as observed with an electron microscope. In addition, although specific numerical conditions were illustrated above, it is only necessary to obtain a free-flowing powder that suppresses the formation of secondary particles as described above by freeze drying, and the specific numerical conditions can be changed as appropriate.
[0024]
In the method for producing a diamond sintered body of the present invention, natural ultrafine diamond powder prepared by lyophilization by the above method is used as a starting material. FIG. 1 is a cross-sectional view showing an example of a state in which diamond powder is filled into a capsule for sintering a fluid phase sealable sintered body for sintering diamond powder in the production method of the present invention.
[0025]
As shown in FIG. 1, a graphite disc 5A for suppressing capsule deformation is placed on the bottom of a cylindrical Ta capsule 3, and a hydrocarbon compound powder 4 such as OAD is filled through Ta foil or Mo foil 1A. Then, diamond powder 2 is pressure-filled thereon. Ta or Mo foil is used for separating diamond powders for synthesizing a sintered body having a desired thickness, separating graphite and diamond powders, preventing intrusion of a pressure medium, sealing a fluid phase, and the like.
[0026]
The hydrocarbon compound is in a solid state when charged, but decomposes under high pressure and high temperature conditions to produce CO ₂ , H ₂ O and C. The decomposed _CO 2 -H ₂ O fluid infiltrates between diamond particles. It is considered that Ta and the infiltrated C—O—H fluid react with each other to generate oxides and carbides. Therefore, in the ultrafine sintered body of the present invention, a product mainly composed of tantalum oxide and tantalum carbide is uniformly dispersed. As the hydrocarbon compound, organic acids such as malonic acid, succinic acid, and oxalic anhydride, which are composed of carbon, oxygen, and hydrogen, which are diamond synthesis catalysts other than OAD, may be used. A Ta foil 1B is disposed on the diamond powder 2, and a graphite disk 5B for suppressing capsule deformation is disposed thereon.
[0027]
The capsule is housed in a pressure medium, and pressurized to 8.5 GPa or more at room temperature using an ultra-high pressure apparatus such as a belt-type ultra-high pressure synthesizer, and 1900 ° C. or more under the same pressure condition. Is heated to a predetermined temperature and sintered. When the pressure is less than 8.5 GPa, a desired high-hardness sintered body cannot be obtained even at a temperature of 1900 ° C. or higher. Moreover, if the sintering temperature is less than 1900 ° C., a desired high hardness sintered body cannot be obtained even at a pressure of 8.5 GPa or more. Even if the temperature and pressure are set higher than necessary, the energy efficiency is only deteriorated. Therefore, it is desirable to set the required minimum in consideration of the corresponding limit of the apparatus.
[0028]
【Example】
Hereinafter, the manufacturing method of the diamond sintered compact of this invention is demonstrated concretely by an Example.
Example 1
A powder prepared by a freeze-drying method as described above was prepared using a commercially available natural diamond powder having a particle size range of 0 to 0.1 μm as a starting material. This powder was determined to have an average particle diameter of 80 nm by electron microscope observation. A 0.6 mm thick graphite disk for suppressing capsule deformation is placed on the bottom of a cylindrical Ta capsule having a wall thickness of 0.2 mm and an outer diameter of 6 mm, and 15 mg of OAD powder is pressed and laminated through a Ta foil. On top, 60 mg of this diamond powder was filled in layers at a pressure of 100 MPa. A Ta foil was placed on the diamond powder, and a 0.6 mm thick graphite disc was placed on the Ta foil in order to suppress capsule deformation.
[0029]
Next, the capsule was filled in a cesium chloride pressure medium, treated with a belt-type ultrahigh pressure synthesizer under conditions of 9.4 GPa and 2000 ° C. for 30 minutes, and then the capsule was taken out of the synthesizer.
[0030]
The TaC or the like formed on the surface of the sintered body hydrofluoric acid - was removed by treatment with nitric acid solution. The upper and lower surfaces of the sintered body were ground with a diamond wheel. The Vickers hardness of the sintered body after grinding was as extremely high as 105 GPa. As a result of measuring the X-ray diffraction pattern of the sintered body, it was a composite sintered body made of diamond, Ta oxide and carbide.
As shown in (A) and FIG. 2 (B) which is an enlarged view thereof , the diamond particle diameter in the sintered body was 100 nm or less from the observation of the structure of the fractured surface of the sintered body with an electron microscope.
[0031]
(Comparative Example 1)
The MgCO ₃ -0.1mol and OAD mixed powder instead of OAD in Example 1 except for using 20mg were sintered in the same manner as in Example 1. As a result of observing the obtained sintered body with an optical microscope, it was a homogeneous milky white sintered body without cracks. The Vickers hardness of the sintered body was 70 GPa, which was sufficiently high as a diamond sintered body in a system using a sintering aid, but was lower than that in Example 1.
[0032]
(Comparative Example 2)
Sintering was performed in the same manner as in Example 1, except that 20 mg of an equal molar mixture of IrO ₂ and graphite powder was used instead of OAD in Example 1. As a result of observing the obtained sintered body with an optical microscope, it was a sintered body in which a cracked product Ir entered between diamond particles and a large number of cracks were present. The ability of the CO ₂ fluid produced from IrO ₂ + C to be sintered was investigated, but it was found that this mixed powder is not effective as a sintering aid because Ir enters the diamond.
[0033]
(Comparative Example 3)
Sintering was performed in the same manner as in Example 1 except that the sintering temperature was 1800 ° C. The grinding resistance of the sintered body after the treatment was not high. Under this processing condition, it can be said that OAD does not function as a sintering aid.
[0034]
【The invention's effect】
The high-hardness ultrafine diamond composite sintered body synthesized by the production method of the present invention has characteristics as an excellent high-hardness material different from a sintered body synthesized from a conventional natural diamond powder.
[0035]
Furthermore, since this diamond sintered body is a composite sintered body composed of a compound of Ta, which is a high-temperature stable substance, in addition to diamond, it exhibits excellent characteristics even under high temperature conditions in the atmosphere. it is conceivable that. From the standpoint of protecting the global environment, emission-free machining that uses almost no cutting oil is required for future machining from the viewpoint of suppressing carbon dioxide emissions. Also from this viewpoint, the high temperature stability of the cutting tool material is one of the extremely important characteristics required for the tool material. The diamond composite sintered body of the present invention is expected to be used in the field of various cutting tools and the like as an earth-friendly high-hardness material.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a state in which diamond powder is filled into a capsule for sintering a fluid phase sealable sintered body for sintering diamond powder in the method of the present invention.
FIG. 2 is a drawing-substitute electron micrograph of the fracture surface of the sintered body obtained in Example 1. FIG.
[Explanation of symbols]
1A, 1B Ta foil 2 Diamond powder 3 Ta capsule 4 Oxalic acid dihydrate 5A, 5B Graphite disk

Claims (1)

A powder prepared by desiccating ultrafine natural diamond powder having a particle size range of 0 to 0.1 μm and then freeze-drying using an aqueous solution is enclosed in a Ta capsule, and the capsule is encapsulated using an ultrahigh pressure synthesizer. Diamond powder is sintered by heating and pressurizing organic acid powder composed of carbon, oxygen and hydrogen under sintering thermodynamic stability conditions at a temperature of 1900 ° C. or higher and pressure of 8.5 GPa or higher. A sintered body having a high hardness ultrafine diamond composite sintered body comprising a sintered body containing a product composed of a Ta compound and having a diamond particle diameter of 100 nm or less in the sintered body. Manufacturing method.

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