JPH06238154A - Synthesizing method for diamond - Google Patents

Abstract

PURPOSE:To obtain diamond particles high in yield and economical by allowing a carbonaceous material to contact the solvent metal consisting of the second metal such as iron and manganese which is composed gradiently of the first metal such as cobalt, nickel and chromium. CONSTITUTION:After allowing the carbon material to contact the contact surface of the carbon material in the solvent metal, the carbonaceous material is synthesized under the pressure and temp. of a diamond stable region, and the carbonaceous material is dissolved into a solvent metal layer. The diamond which becomes supersaturation by dissolving is deposited as nucleus near the contact surface with the carbonaceous material, moreover, a crystal is grown to form a seed crystal. Because the second metal in the solvent metal is incorporated largely so far, the forming density of the nucleus and a crystal growing velocity are small, and an idiomorphic face is allowed to grow and the diamond having a good shape is obtained. In the crystal growth after that, because the ratio of the second metal is decreased and the first metal is increased, growing velosity becomes large and the diamond large in grain size and minimized in impurities is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing diamond, and more specifically, cutting abrasive grains, abrasive grains,
The present invention relates to a method for synthesizing diamond, which can be suitably used in a wide range of fields including a diamond sintered body and the like, which has a good crystal form, a small amount of impurities, and can efficiently obtain large-diameter diamond particles. .

[0002]

2. Description of the Related Art At present, diamond is being attempted to be used or applied in various fields in order to utilize its excellent characteristics. For example, one of them is that it is utilized as cutting abrasive grains and the like by taking advantage of its excellent hardness. Granular diamond used as cutting abrasive grains or the like is generally required to have a large grain size, a small amount of impurities in the crystal, and a good crystal shape.

Conventionally, as a method for obtaining diamond satisfying such requirements, for example, Japanese Patent Publication No. 55-23.
201 and Japanese Patent Publication No. 47-29112.

These are, under the stable region of diamond,
This is a high-pressure synthesis method in which diamond is gradually formed on a small number of nuclei in which the density of initial nuclei for forming diamond is suppressed. In this case, in order to suppress the density of the initial nuclei,
For non-diamond carbon as a raw material, for example, copper, silver, gold,
A non-solvent metal such as lead or zinc or a solvent metal has been brought into contact with or coated with.

However, these methods have the following problems. That is, when non-solvent metal is brought into contact with or coated with non-diamond carbon, the nucleation density becomes extremely small, and the yield of diamond having a large grain size is significantly reduced. In addition, the non-solvent metal may be incorporated into the diamond crystal as an impurity, and the strength of the abrasive grains will be reduced. When a non-diamond carbon is contacted with or coated with a solvent metal, a solvent metal that increases the degree of supersaturation of diamond for crystal growth must be placed in contact with the solvent metal, so that the diamond crystal growth There is a problem that the growth rate rapidly increases in the process of, and defects occur in the crystal and impurities are taken in. The presence of defects and impurities in the diamond crystals reduces the strength of the abrasive grains.

The present invention solves the above problems and
Can be suitably used in a wide range of fields including cutting abrasives, grinding abrasives, and sintered diamond, and has a good crystal morphology, a low impurity content, and efficiently obtains large-diameter diamond particles. Another object of the present invention is to provide a method of synthesizing diamond that can be used.

[0007]

In order to solve the above-mentioned problems, as a result of intensive investigations by the present inventors, as a result of bringing a carbonaceous substance into contact with a specific solvent metal and causing it to react under specific conditions, It has been found that the carbonaceous material can be converted into diamond particles with high yield and economically. In addition, the diamond has a large grain size,
They have found that they are suitable for cutting abrasive grains and the like because they have a low content of impurities and a good shape, and have reached the present invention.

That is, claim 1 for solving the above problems
The invention described in (1) has a first metal selected from cobalt, nickel and chromium and a second metal selected from iron and manganese, and the second metal is provided near the contact surface of the carbonaceous material. In a solvent metal having a graded composition in which the content of the second metal continuously decreases as the distance from the contact surface increases, the carbonaceous material is contacted with diamond A method for synthesizing diamond, which comprises converting the carbonaceous material into diamond by reacting under conditions of pressure and temperature in a stable region.

The present invention will be described in detail below.

(Solvent metal) The solvent metal in the present invention includes a first metal selected from cobalt, nickel and chromium and a second metal selected from iron and manganese, and a carbonaceous material. It is possible to use a mixture or alloy having a high proportion of the second metal near the contact surface with the substance and having a graded composition in which the proportion of the second metal decreases as the distance from the contact surface increases.

Examples of the solvent metal include cobalt-iron, nickel-iron, nickel-manganese, nickel-
Mention may be made of mixtures or alloys of combinations of cobalt-iron, nickel-chromium-iron, nickel-chromium-manganese, nickel-manganese-iron and the like.

The content ratio of the second metal near the contact surface with the carbonaceous material is 35 to 100% by weight.
And preferably 50 to 85% by weight, and particularly preferably 60 to 85% by weight. If the content ratio is less than 35% by weight, the density of nuclei for diamond generation may not be suppressed.

The content ratio of the second metal in the solvent metal is 0 to 85% by weight, and preferably 5 to 15% by weight, in the portion farthest from the carbonaceous material having the minimum content. is there. When the content ratio is more than 85% by weight, the crystal growth rate of diamond becomes low.

The solvent metal of the present invention has a graded composition in which the content ratio of the second metal continuously decreases as the distance from the contact surface with the carbonaceous material increases.

If the composition does not have a gradient composition in which the content ratio of the second metal continuously decreases as the distance from the contact surface with the carbonaceous material increases, that is, the gradient composition does not change continuously, If it is discontinuous and changes stepwise, the crystal growth rate of diamond rapidly increases at the discontinuous interface, so defects and impurities may be mixed into the crystal. Such diamond is not preferable for use as abrasive grains and the like because its strength becomes low.

The solvent metal in the present invention is, for example, as shown in FIG.
It has a gradient composition shown in. Note that FIG. 1 is a conceptual graph for showing the concept of the gradient composition.

In the present invention, the gradient ratio in the gradient composition, that is, the degree of change in the content ratio of the second metal is such that the degree of supersaturation of diamond in the solvent metal is kept low and The crystal growth rate is appropriately selected so as to be small.

If the growth rate is high, impurities may be mixed in the diamond crystal, while if it is too low, it is not economical.

As a method for producing the solvent metal, known methods such as an electrolytic method, a non-electrolytic plating method, a vapor deposition method, a thermal decomposition method and a thermal spraying method using plasma can be used.

The shape of the solvent metal is not particularly limited, but a plate-like one is usually used. In the case of a plate-shaped solvent metal, its thickness is not particularly limited, but it is usually 0.
It is 1 to 5 mm, preferably 0.1 to 2 mm.

When a plate-shaped solvent metal and a carbonaceous substance described later are used and the layers are alternately laminated to carry out a synthesis reaction, two plate-shaped solvent metal plates are each made of carbon. It is possible to use an integrated body in which the contact surface with the quality substance is on the outside. That is, the content of the second metal in both contact surfaces is the highest, and the content ratio decreases continuously toward the center, and the second metal in the vicinity of the center surface in a position parallel to both contact surfaces. It is a solvent metal that minimizes the content of.

When this solvent metal is used, diamond can be obtained efficiently and economically.

(Carbonaceous substance) The carbonaceous substance in the present invention is not particularly limited as long as it can be converted into diamond, and a substance known per se can be used. Examples thereof include substances made of carbon such as graphite and amorphous carbon, and various carbon-containing substances such as coal, coke, charcoal and coal tar pitch.

Of these, graphite and amorphous carbon are preferable.

The shape of the carbonaceous substance is not particularly limited as long as it can be easily brought into contact with the solvent metal, but a plate-like substance is usually used. In the case of plate-like carbonaceous material,
The thickness is not particularly limited, but is usually 0.1 to 5
mm, and preferably 0.1 to 2 mm.

(Synthesis Conditions) In the present invention, after the carbonaceous substance is brought into contact with the contact surface of the solvent metal with the carbonaceous substance, the diamond synthesis reaction is performed under the pressure and temperature conditions in the diamond stable region. To do.

The pressure and temperature conditions in the diamond stable region are the pressure and temperature at which the carbonaceous material can be stably converted into diamond, and the pressure is usually 5
It is 7,000 to 70,000 Kg / cm ² , and the temperature is 1300 to 2000 ° C. The conditions such as preferable pressure and temperature can be determined in consideration of the carbon solubility of the metal used.

The apparatus for carrying out the synthesis reaction is not particularly limited, and a known ultrahigh pressure apparatus can be used.

Examples of the ultra-high pressure device include a belt type high pressure device, a hexagonal push type cubic high pressure device, a four way push tetrahedron high pressure device, a Drickermer type high pressure device, a girdle type high pressure device, and a piston cylinder type high pressure device. Can be used.

There is no particular limitation on the solvent metal and the carbonaceous material contained in these ultra-high pressure devices, and they may be directly contained, or they may be contained in an appropriate sample container in advance. Then, it may be housed in the ultra-high pressure apparatus.

The sample container is not particularly limited, but for example, it has a space for alternately accommodating plates of carbonaceous material and plates of solvent metal therein and accommodating pyrophyllite around it. A container having a pressure medium such as catolinite, a metal electrode and the like can be mentioned.

The synthesis reaction time is usually 1 to 6
It is 0 minutes, preferably 1 to 20 minutes.

The pressure in the diamond stable region
Under the temperature condition, the solvent metal dissolves into a liquid state and catalyzes the diamond synthesis reaction. Even if the solvent metal is in a liquid state, it exists while maintaining its gradient composition.

In the present invention, the diamond crystal growth direction is, as shown in FIG. 2, the direction from the contact surface of the solvent metal with the carbonaceous material to the inside of the carbonaceous material layer. The crystal of diamond grows in the above direction.

In the present invention, the proportion of the second metal decreases continuously as it goes inward in the direction of crystal growth, and conversely the proportion of the first metal increases continuously. The growth rate can be increased continuously and gradually.

According to the above, diamond having a large grain size, a small amount of impurities, and a good crystal shape can be synthesized at a high yield and economically.

[0037]

In the present invention, the carbonaceous substance is brought into contact with the contact surface of the solvent metal with the carbonaceous substance, and then the synthesis reaction is carried out under the pressure and temperature conditions in the diamond stable region. Then, the carbonaceous substance is first dissolved in the solvent metal layer by the action of high pressure and high heat.

Next, PT which is a diamond stable region
In the region, the melted and supersaturated diamond is deposited as nuclei in the vicinity of the contact surface of the solvent metal with the carbonaceous material. At this time, since the contact surface contains a large amount of the second metal, the nucleus generation density is low.

When the nuclei are generated, the diamond crystals are synthesized around the nuclei, the diamond crystals grow, and seed crystals are generated. At this time, since a large amount of the second metal exists near the contact surface, the crystal growth rate is low. When the crystallization rate is low, the self-shaped surface of diamond is well developed, so that the seed crystal has a good shape with the self-shaped surface.

When diamond crystals continue to grow, the proportion of the second metal in the solvent metal gradually decreases, and conversely, the proportion of the first metal gradually increases, so that the crystal growth rate gradually increases. Grows to. At this time, the crystal growth rate does not rapidly increase, so that impurities are not mixed in and defects are not generated in the crystal during the diamond crystal growth process. By the above, diamond particles are generated. This diamond has a large grain size, a small content of impurities, and a good crystal shape.

In the present invention, since diamond particles are generated from each of the initial nuclei generated with a low density,
High yield and economical.

[0042]

EXAMPLES Examples of the present invention will be specifically described below. The present invention is not limited to the following embodiments.

Example 1 As shown in FIG. 3, a capsule having a space for accommodating a synthetic sample inside and a portion filled with water and a metal electrode around the space has a width of 10 mm and a thickness of 10 mm. Is 2 mm, and both ends thereof are solvent metal plates having contact surfaces with the carbonaceous substance and graphite plates having a width of 10 mm and a thickness of 1 mm, which are alternately stacked and accommodated.

As the solvent metal, nickel is 30 wt% and iron is 70 wt% at the contact surface with the carbonaceous substance.
50% by weight of nickel and 50% by weight of iron at the position farthest from the contact surface with the carbonaceous substance.
Nickel having a gradient composition
An iron solvent metal was used. This solvent metal is prepared by iron powder and nickel powder each having a particle size of 10 μm while controlling the supply amount of each powder by plasma spraying. As the solvent metal, a sprayed metal having a gradient composition as shown in FIG. 4 was used.

The capsule containing the laminated body of the graphite and the solvent metal was placed in an ultrahigh pressure / high temperature apparatus, and a synthesis reaction was carried out for 30 minutes under the conditions of a pressure of 55,000 Kg / cm ² and a temperature of 1450 ° C. I did.

As a result, the particle size is 425 to 550 μm.
The diamond particles are obtained. The crystal structure of this diamond was a 6-8 octahedron, which was suitable for abrasive grains. The amount of impurities mixed in the diamond crystal could be reduced by 30 to 40% by weight as compared with the case of using the conventional solvent metal having no gradient composition.

Comparative Example 1 A solvent metal containing 40% by weight of nickel and 60% by weight of iron as a solvent metal and having no gradient composition was used, except that the synthesis temperature was changed to 1500 ° C. Diamond was synthesized in the same manner as in.

As a result, the diamond obtained is
Only small-sized diamond crystals having a particle size of 210 to 400 μm could be obtained. Moreover, in these diamond crystals, there were many particles in which the automorphic plane did not appear clearly.

(Embodiment 2) As shown in FIG. 3, a capsule having a space for accommodating a synthetic sample therein and a portion filled with water around it and a metal electrode has a width of 10 mm and a thickness. Is 2 mm, and both ends thereof are solvent metal plates having contact surfaces with the carbonaceous substance and graphite plates having a width of 10 mm and a thickness of 1 mm, which are alternately stacked and accommodated.

As the solvent metal, cobalt is 15% by weight and iron is 85% by weight at the contact surface with the carbonaceous substance.
Content of 50% by weight of cobalt and 50% by weight of iron at the position farthest from the contact surface with the carbonaceous substance.
Cobalt having a graded composition as well as containing
An iron solvent metal was used. The solvent metal includes iron powder and nickel powder having particle diameters of 10 μm and 20 μm, respectively.
It was prepared by adjusting the supply amount of each powder by plasma spraying.

The capsule containing the laminate of the graphite and the solvent metal was placed in an ultrahigh pressure / high temperature apparatus, and a synthesis reaction was carried out for 30 minutes under the conditions of a pressure of 55,000 Kg / cm ² and a temperature of 1500 ° C. I did.

As a result, the particle size is 420 to 550 μm.
The diamond particles are obtained. The crystal structure of this diamond was a 6-8 octahedron, which was suitable for abrasive grains. The amount of impurities mixed in the diamond crystal could be reduced by 35 to 40% by weight as compared with the case of using a conventional solvent metal having no gradient composition. (Comparative Example 2) Instead of the solvent metal in Example 2, 45 wt% cobalt was added to a 0.1 mm thick solvent metal plate containing 15 wt% cobalt and 85 wt% iron and having no gradient composition. A diamond was synthesized in the same manner as in Example 2 except that a solvent metal containing 55% by weight of iron and having a thickness of 1 mm and having no gradient composition was laminated.

As a result, the obtained diamond is
Only small-sized diamond crystals having a particle size of 250 to 425 μm could be obtained. Moreover, in these diamond crystals, there were many particles in which the automorphic plane did not appear clearly.

[0054]

EFFECTS OF THE INVENTION According to the present invention, it can be suitably used in a wide range of fields such as cutting abrasive grains, grinding abrasive grains, and diamond sintered bodies. The crystal form is good and the content of impurities is small. It is possible to provide a method for synthesizing diamond, which allows diamond particles having a large diameter to be obtained in high yield and economically.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a composition in a solvent metal having a graded composition.

FIG. 2 is a schematic explanatory diagram showing the growth of diamond crystals.

FIG. 3 is a schematic explanatory view showing an example of a capsule.

FIG. 4 is a schematic explanatory diagram of a gradient composition of a solvent metal having a first metal selected from cobalt, nickel and chromium in a solvent metal and a second metal selected from iron and manganese. is there.

[Explanation of sign]

 1 Graphite Plate 2 Solvent Metal Plate 3 Diamond 4 Graphite Heater 5 Pressure Medium 6 Metal Electrode 7 Copper Ring

[Procedure amendment]

[Submission date] February 23, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

[Figure 3]

[Figure 4]

Claims (1)

[Claims] 1. A first metal selected from cobalt, nickel and chromium, and a second metal selected from iron and manganese, wherein the second metal is provided near a contact surface with a carbonaceous material. In a solvent metal having a graded composition in which the content of the second metal continuously decreases as the distance from the contact surface increases, the carbonaceous material is contacted with diamond A method for synthesizing diamond, which comprises reacting under pressure and temperature conditions in a stable region.