JP3855029B2 - Manufacturing method of translucent ultrafine diamond sintered body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a light-transmitting ultrafine diamond sintered body .
[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]
In the method of manufacturing a diamond sintered body, it is difficult to synthesize a translucent diamond sintered body by the conventional method using a sintering aid, and reaction sintering by direct conversion from graphite to diamond without using any sintering aid. Then, since the synthesis conditions of translucent diamond require a very high pressure of 12 to 25 GPa and a high temperature of 2000 to 2500 ° C., the size of the obtained sintered body is limited.
[0009]
Thus, the synthesis conditions of the diamond sintered body that becomes translucent are very severe conditions, and since the sintered body that can be synthesized is as small as about 1 to 2 mm in diameter, application as an ultra-hard material is limited. Yes.
An object of the present invention is to provide a means for producing a translucent diamond sintered body under pressure conditions that are far lower than those of the prior art.
[0010]
[Means for Solving the Problems]
The present inventors use a sintering aid, but finally, no solid sintering aid remains in the sintered body, and the crystal phase in the sintered body is examined with an X-ray diffractometer. In this case, intensive research has been conducted to develop a translucent diamond sintered body in which only diamond is detected.
[0011]
As a result, if a powder prepared by freeze-drying after ultra-fine natural diamond powder having a particle size range of 0 to 0.1 μm is used, an aromatic hydrocarbon composed of carbon and hydrogen such as anthracene is obtained. It has been found that it can function as a sintering aid and a light-transmitting diamond sintered body can be synthesized.
[0012]
That is, the present invention is as follows.
[0013]
( 1 ) Super fine natural diamond powder having a particle size range of 0 to 0.1 μm is desilicated, and the powder prepared by lyophilization using an aqueous solution is laminated on anthracene, naphthalene, or phenanthrene, and Ta or The diamond powder is sintered by encapsulating it in a Mo capsule and heating and pressing the capsule at a temperature of 1900 ° C. or higher under the thermodynamic stability condition of diamond under a pressure of 7.5 GPa or higher using an ultrahigh pressure synthesizer. A process for producing a light-transmitting ultrafine diamond sintered body.
[0014]
( 2 ) A powder prepared by lyophilizing an ultrafine natural diamond powder having a particle size range of 0 to 0.1 μm by desilicate treatment using an aqueous solution is laminated on anthracene, naphthalene, or phenanthrene, and Ta or Enclosed in a Mo capsule, and the capsule is heated and pressed at a temperature of 1800 ° C. or higher and a pressure of 9.0 GPa or higher, which is the thermodynamic stability condition of diamond, using an ultra-high pressure synthesizer to sinter diamond powder. A process for producing a light-transmitting ultrafine diamond sintered body.
[0015]
In the production method of the present invention, anthracene , naphthalene, or phenanthrene is used as a sintering aid, but the decomposition product from this compound is a molecule represented by hydrogen or C _n H _{2n + 2} under ultra high pressure. It is considered that these supercritical molecules function as sintering aids. About the obtained sintered compact, since absorption resulting from the stretching vibration of C—H was confirmed in the IR spectrum, it is considered that either hydrogen or CH ₄ is present in the sintered compact.
[0016]
In the conventional commercially available sintered body, the sintering aid exists as a crystal phase in the sintered body, but in the diamond sintered body according to the present invention, only diamond exists in the X-ray diffraction pattern as the crystal phase. For this reason, it is thought that a translucent diamond sintered body is synthesized.
[0017]
The average particle size of the diamond particles in the sintered diamond of the present invention is 100 nm or less by electron microscope observation, and is composed of uniform fine particles in which no abnormal grain growth is observed, so that excellent wear resistance and heat resistance are achieved. It can be machined into a sharp cutting edge shape, so it exhibits excellent machining performance when applied to, for example, finish cutting of difficult-to-cut materials such as high Si-Al alloys and ultra-precision machining tools for metals and alloys. To do.
[0018]
Moreover, the diamond sintered body of the present invention is a high-purity sintered body using a sintering aid, in which diffraction lines other than diamond are not observed in powder X-ray diffraction, and there are no non-transparent impurities. Is opaque, but has sufficient translucency so that characters can be clearly seen through the sintered body by transmitted light. Therefore, wear-resistant materials that require translucency (missile window materials and water It is useful as a window material for a thermal reaction vessel or a pressure member for generating high pressure), and also exhibits value as a jewelry.
[0019]
Furthermore, the diamond sintered body of the present invention has an electrical conductivity that can clearly confirm electrical conduction in a 1 kΩ range by a tester. Although the mechanism of conduction is unknown, it is considered that if a considerable amount of graphite is present in the sintered body, it does not become translucent. Therefore, electrical conductivity is caused by hydrocarbons such as hydrogen or methane in the sintered body. It may be present and contribute to conduction.
[0020]
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.
[0021]
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.
[0022]
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.
[0023]
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.
[0024]
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.
[0025]
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.
[0026]
For the production of the sintered body of the present invention, 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.
[0027]
As shown in FIG. 1, after placing a graphite disk 1A for suppressing capsule deformation on the bottom of a cylindrical Ta or Mo capsule 4 and pressurizing and filling diamond powder 2A in layers through Ta or Mo foil 5A Then, a condensed ring aromatic hydrocarbon 3A such as anthracene is layered and pressurized at the same pressure. Further, the same diamond powder 2B is laminated on the layer of the hydrocarbon compound 3A in the same shape with the same molding pressure. Further, Ta or Mo foil 5B, diamond powder 2C, hydrocarbon compound 3B, and diamond powder 2D are repeatedly pressed and filled in layers. A Ta or Mo foil 5C is disposed on the uppermost diamond powder 2D, and a graphite disk 1B for suppressing capsule deformation is disposed 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.
[0028]
Examples of the sintering aid include naphthalene and phenanthrene, which are similar condensed ring aromatic hydrocarbons , in addition to anthracene. The amount of anthracene is preferably about 5 to 10% by weight with respect to the total amount of diamond powder. For example, 20 to 40 mg of anthracene is suitable between two layers of 200 mg of diamond powder. Thus, a layer structure of Ta / diamond 200 mg / anthracene 20 to 40 mg / diamond 200 mg / Ta / diamond 200 mg / anthracene 20 to 40 mg / diamond 200 mg / Ta is obtained.
[0029]
This capsule is housed in a pressure medium, and is pressurized to 7.5 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 7.5 GPa, the condensed ring aromatic hydrocarbon is difficult to function as a diamond synthesis catalyst even at a temperature of 1900 ° C. or higher. Further, when the pressure is increased to 9.0 GPa or higher, a translucent sintered body can be obtained at a sintering temperature of 1800 ° C. or higher. 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.
[0030]
【Example】
Hereafter, the manufacturing method of the diamond sintered compact of this invention is demonstrated concretely based on 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 2.5 mm thick graphite disk for suppressing capsule deformation is placed on the bottom of a cylindrical Ta capsule having a wall thickness of 0.8 mm and an inner diameter of 10 mm, and 200 mg of this diamond powder is layered at a pressure of 100 MPa through a Ta foil. Filled.
The diamond powder layer was filled with 40 mg of anthracene at the same pressure. Furthermore, 200 mg of diamond powder was filled on the same pressure. A Ta foil was placed on the upper diamond powder, and a 2.5 mm-thick graphite disk was placed on the Ta foil in order to suppress capsule deformation.
[0031]
Next, the capsule was filled in a pressure medium of cesium chloride, treated with a belt-type ultrahigh pressure synthesizer at 7.7 GPa and 2300 ° C. for 30 minutes, and then the capsule was taken out from the synthesizer.
[0032]
TaC and the like formed on the surface of the sintered body were removed by treatment with a hydrofluoric acid-nitric acid solution, and the upper and lower surfaces of the sintered body were ground with a diamond wheel. As a result of observing the fracture surface of the sintered body with an electron microscope, as shown in FIG. 2 (A) and an enlarged view of FIG. 2 (B), a homogeneous firing in which diamond fine particles having an average particle diameter of 80 nm are sintered is obtained. It was a ligation. Is an enlargement of (A). Further, as a result of observing the sintered body with transmitted light, it was found that the sintered body is translucent as shown in FIG.
[0033]
(Comparative Example 1)
It sintered by the same manufacturing method as Example 1 except having made sintering temperature 1800 degreeC. The sample after recovery was opaque and unsintered without any mechanical strength. This is because the temperature during sintering is less than 1900 ° C. and the pressure is low.
[0034]
(Comparative Example 2)
A sintered body was obtained by the same production method as in Example 1 except that natural diamond powder having a particle size range of 0 to 1 μm was used as a starting material. The obtained sintered body was far from a milky white translucent sintered body having layered cracks and standing cracks.
[0035]
(Comparative Example 3)
Sintering was performed in the same manner as in Example 1 except that natural diamond powder having a particle size range of 0 to 0.25 μm was used as a starting material. The sample after collection was collected as a lump, but was gray and lacking in the circumferential portion, and was far from the translucent sintered body.
[0036]
(Example 2)
Sintering was performed by the same manufacturing method as in Example 1 except that the sintering temperature was set to 2000 ° C. lower than that in Example 1. The obtained sintered body was observed with an optical microscope. The sintered body was translucent without exception, but the central part of the sintered body remained partially opaque.
[0037]
Example 3
The amount of anthracene was 15 mg, the amount of diamond powder in each layer was 60 mg, the pressure was 9.4 GPa, and the sintering temperature was 1800 ° C. Other conditions were the same as in Example 1. The obtained sintered body was subjected to acid treatment and then observed with an optical microscope. As a result, a part of the grain growth layer was observed in the diamond sintered body in contact with the anthracene. In order to scrape off the grain growth layer and to flatten the sintered body, the upper and lower surfaces of the sintered body were ground. The Vickers hardness of the sintered body after grinding was measured. The hardness was as high as 80 GPa. The sintered body was translucent.
[0038]
【The invention's effect】
The translucent ultrafine diamond sintered body synthesized by the production method of the present invention not only has the characteristics as an excellent high hardness material different from the sintered body synthesized from the conventional natural diamond powder. Its application as a translucent high hardness material and jewelry is expected.
Since the diamond sintered body obtained by the production method of the present invention is a high-purity, high-hardness sintered body with diamond particles in the sintered body of 100 nm or less, it has characteristics not found in conventional sintered bodies. Applications in fields such as ultra-precision machining tools and difficult-to-cut material machining tools are expected.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a state in which a fluid phase sealable capsule for synthesis of a sintered body for sintering diamond powder is filled with diamond powder in the production method of the present invention. .
FIG. 2 is a drawing-substituting electron micrograph of the fracture surface of the diamond sintered body obtained in Example 1. FIG.
FIG. 3 is a drawing-substituting optical photograph showing the translucency of the diamond body obtained in Example 1. FIG.
[Explanation of symbols]
1A, 1B Graphite disks 2A, 2B, 2C, 2D Diamond powders 3A, 3B Condensed aromatic hydrocarbons such as anthracene 4 Ta or Mo capsules 5A, 5B, 5C Ta or Mo foil

Claims (2)

A powder prepared by desiccating ultrafine natural diamond powder with a particle size range of 0 to 0.1 μm and then freeze-drying using an aqueous solution is laminated on anthracene, naphthalene, or phenanthrene to form a capsule made of Ta or Mo. The diamond powder is sintered by encapsulating and heating and pressing the capsule at a temperature of 1900 ° C. or higher and a pressure of 7.5 GPa or higher, which is a thermodynamic stability condition of diamond, using an ultrahigh pressure synthesizer. A manufacturing method of translucent ultrafine diamond sintered body. A powder prepared by desiccating ultrafine natural diamond powder with a particle size range of 0 to 0.1 μm and then freeze-drying using an aqueous solution is laminated on anthracene, naphthalene, or phenanthrene to form a capsule made of Ta or Mo. The diamond powder is sintered by encapsulating and heating and pressing the capsule at a temperature of 1800 ° C. or higher and a pressure of 9.0 GPa or higher, which is a thermodynamic stability condition of diamond, using an ultrahigh pressure synthesizer. A manufacturing method of translucent ultrafine diamond sintered body.

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