JPS637832A - Formation of diamond - Google Patents

Abstract

PURPOSE:To carry out formation of diamond and an integrated molding thereof simultaneously by generating a special behavior of a liberated spherical graphite, a preferable pressure and temperature gradient in a reaction progress by means of a special metallic catalyst and a vessel. CONSTITUTION:A pressure medium 1 on the extreme outer periphery is a vessel made of pyrophyllite, the inside of which is constituted with, from outside inwardly, molybdenum electrode 2, a carbon heating element 3, an insulating sleeve 4 made of hexagonal boron nitrate and an insulating disc 5, and in a reaction chamber constituted in its inside, a multi-layer is formed by piling up alternately metallic catalysts 6A, 6B, 6C,... and a carbon substance as a starting material. The hexagonal boron nitrate molded material constituting directly the reaction chamber is not mixed with the combination of carbon substance and catalyst even at a high temperature and under a high pressure for the diamond formation reaction. Also, the volume of the same has a flexibility to be reduced in compliance with the reduction of the raw material volume in the reaction chamber, and an adequate pressure gradient and a temperature gradient are maintained in the reaction chamber.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for artificially converting carbonaceous substances into diamond, and in particular, a method for producing strong and dense diamond dense aggregates directly from starting materials. be.

[Conventional technology] If it were possible to make a strong and dense diamond compact using cheap powder as a starting material instead of natural diamond, the disadvantage of natural diamonds that tend to cause phallus deformation would be corrected, and it would be possible to make cutting tools, wire drawing dies, etc. There are strong expectations that it will be found to be economically viable even when applied to many new applications, such as for tools such as dressers.

The methods of producing artificial diamond dense viscosity that are currently widely used include, for example, graphite and coal.

Suitable carbonaceous substances such as coke, sugar, charcoal, etc. and catalytic metals (mainly metals from Group II of the Periodic Table of Elements, such as chromium,
at least one of manganese and tantalum, or alloys of these and other metals) and treated under pressure (minimum 50,000 atmospheres) and temperature (minimum 1,200° C.) resulting in conversion to diamond; The diamond grains, which are usually synthesized as contained in a matrix, are extracted.

This reaction is called a film growth method because a metal film passes through a layer of carbonaceous material and creates more and more diamonds behind it, but since the metal film acts as a channel for carbon, the amount of diamond is limited. Only metal can penetrate.

Next, the diamond crystal grains are sintered to make them into a strong, dense, and dense viscous material, and to form them into a desired shape as a tool.

Usually, so-called liquid phase sintering is carried out under high temperature and pressure using Co, Cu, etc. as a binder.
C-Co alloy, carbide, r! In some cases where an i-ide is used as a binder, inclusions other than diamond remain in the sintered body.

In contrast to the current mainstream technology described above, if the synthesis (conversion) and dense atrophy of carbonaceous materials into diamonds can be performed in one step by 1q, it will not only be possible to simplify the process, but also to achieve the desired results. Complex shapes can also be obtained, killing two birds with one stone.

This research seems to have been carried out for a long time, and for example, there is a method for producing dense diamond aggregates
-17807 (Figures 8 to 10).

This technology is based on U.S. Patent No. 2941.
The high temperature and high pressure device shown in FIG. 8 shown in the specification of No. 248,
It includes a pair of pressing members 8, 8 made of a hard material, such as tangelyl carbide, and an intermediate bell 1 or die 9.9 made of the same material.

The compressed body is composed of a combination of several members surrounded by these four members, and the gasket structure 10 is arranged in order from the outside.
, 11, 12. Graphite tube 13. Alumina cylinder 14
The reaction sample 7a reaches the space filled with the reaction sample 7a.

Other plugs 15. Seal with cap 16.

Such an apparatus is filled with a combination of a carbonaceous material such as graphite or coal and a catalytic metal, and the pressing members are moved in a direction close to each other to apply pressure while passing an electric current through the graphite 1 to tube 13 to indirectly heat the mixture. This causes high temperature and high pressure conditions.

This favorable condition is detailed in U.S. Pat.
It is a single crystal taken out from the reaction vessel as a form contained in diamonds, and the lump made of the matrix is fragile and the diamond is only loosely bonded to the matrix, making it unusable as it is. It was unbearable.

This prior art reports that 1q of sufficiently high-strength diamond dense aggregates of a desired shape can be obtained by combining a specific growth method and a specific shell protection means.

In other words, as shown in Fig. 8, the external materials including the reactor forming materials decompose or melt under the high temperature and high pressure reaction conditions and get mixed into the carbonaceous material and catalyst combination, significantly inhibiting the conversion and growth of diamond. be.

Therefore, raw materials and catalyst are filled in a shell (capsule) as shown in Figure 9, and this shell is made of a metal that does not lose its original form even when subjected to significant compression and deformation during the reaction. For example, tantalum and nickel.

If made of a nickel-iron alloy, etc., the shell will be completely filled with dense polycrystalline diamond aggregates D-D (Fig. 10), which are extremely strong and resistant. ing.

[Problems to be Solved by the Invention] The prior art described here follows the known method of synthesizing diamond from starting materials, but confines the reaction within a strong shell to directly form dense diamond aggregates. Suppose you get it.

However, even after this invention was disclosed, up to the present day,
The mainstream manufacturing method for artificial diamonds remains the same as before, using a two-step process of synthesis and sintering, and although a number of technological developments have been made to improve the details of each step, the basics remain the same.

The details of why this highly advantageous manufacturing method has not become mainstream for diamond dense aggregates are unknown, but
I have not come across any information that it has been put into practical use.

To estimate the problem, if we confine the starting materials inside such a strong shell and proceed with the reaction, the pressure will be applied to the volume change (approximately 35% reduction) that occurs as the carbonaceous material is converted to diamond. Therefore, the synthesized diamond crystal group is thought to be porous and of low density.

In some cases, defects similar to internal defects (so-called crack holes) in cast products may occur.

This raises concerns that the ``containment'' (shell) that allows diamond synthesis and sintering to proceed at the same time may actually be a disadvantage.

Furthermore, regarding the Soviet Union, which is thought to be one of the most advanced countries in research in this field, there are no reports on its manufacturing method, so it is not clear, but it is thought that they probably use a method in which diamond is synthesized and sintered at the same time. Information is only sporadically added to 1q. (L, F, Ve
reschagain et al 5ovPhy D
OK15, 1065 ('71), etc.) Based on the conventional technology, the present invention obtains the target product from the starting material in one step by simultaneously proceeding with the conversion of carbonaceous material to diamond and dense viscosity. The purpose is to provide a method to meet the strong needs of industry.

Means for Solving Problem E] In the method for converting diamond according to the present invention, the metal catalyst is formed of ductile cast iron or niresist ductile cast iron in which free graphite is precipitated in a spherical shape in an iron base, and the capacity of the reaction chamber is solved the above problem by providing flexibility to follow the volume changes that occur as the conversion of the carbon material to diamond progresses.

[Operation] As is well known, the iron-carbon binary phase diagram teaches that when carbon is contained in an iron-based metal, its form changes depending on the amount of carbon.

Depending on the content and temperature, the carbon content may form a solid solution in the ferrite or austenite phase, may precipitate alone as a carbide, or form a pearlite structure.

When the carbon content exceeds 1.7%, it falls into a region called cast iron, and unless rapidly cooled, the molten material will precipitate graphite cores during solidification, and this molten metal will be treated with magnesium (explosive addition) to form the graphite cores. The r:A portion contained in the molten metal grows into a spherical shape and becomes a structure precipitated as spherical graphite.

The base of the structure after cooling to room temperature is ductile cast iron, which becomes pearlite and/or ferrite, as well as aluminum alloy, which has almost the same carbon content but has a large amount of chromium and nickel added to prevent transformation and carry the austenite phase to room temperature. Resist ductile cast iron is also available.

In order to accurately explain how an iron-based catalyst in which spherical free graphite is precipitated behaves in diamond conversion, additional experiments are still required, but the inventors focused their attention on this when starting the experiment. The reason is that the spheroidized graphite precipitated on the surface of the catalyst may become a nucleation point for diamonds.

That is, for ordinary metal catalysts, the theory of the film growth method described above is considered to be almost an established theory, but the unique effects when graphite is deposited on the catalyst surface require a different explanation.

When the diamond synthesis conditions of high temperature and high pressure are reached, the iron around the free graphite on the catalyst surface reacts preferentially, creating a low melting point liquid phase around the graphite, and the raw material graphite enters this liquid phase, raising the melting point. However, when the carbon content reaches a supersaturated state, this part first converts into diamond.

That is, free spheroidal graphite is preferentially converted into diamond nuclei, and iron around the spheroidal graphite is eluted toward the raw material graphite.

The raw material graphite wrapped in this eluted iron grows on the extension of the diamond nucleus that was formed first, and the film-like iron advances into the raw material graphite one after another and spreads the diamond crystal in one direction [1
00].

- direction Another feature of the present invention is that the reaction vessel is variable in accordance with the volume reduction of the raw material accompanying the diamond conversion, and therefore diamond is synthesized and continues to be consolidated even as it grows in the - direction. As the reaction progresses, the iron wraps the tip of the diamond-forming process in a film and moves forward as the reaction progresses, and is squeezed out from between the synthesized diamonds, becoming dense and forming -D bonds (diamond dense aggregates). Form.

Therefore, as a result, regarding the synthetic conversion of diamond, at the interface between the molten metal and carbonaceous material, the graphite in the molten cast iron becomes a nucleus and the diamond conversion reaction begins, and the raw material graphite is suppressed from nucleation and becomes exclusively diamond. It is thought that it is consumed only for the growth of .

In addition, regarding dense viscosity, rather than using liquid phase sintering with a binder, the diamond crystal grains are tightened to squeeze out impurities and form pure diamond bonds with N.
It is interpreted that this is due to the effect of compression molding in the [00] direction.

In other words, it would be more accurate to call it agglomeration rather than sintering.

The spherical shape of the free graphite on the surface of the catalyst is considered to be far more advantageous than flake-like free graphite when it becomes a diamond nucleus and is preferentially the point of development of diamond crystal grains. .

[Example] FIG. 1 shows a schematic diagram of a diamond conversion apparatus used in experiments of the present invention.

In the figure, the pressure medium 1 at the outermost periphery is a container made of pyrophyllite, and inside this container, from the outside, electrodes 2 and 3 made of molybdenum are placed. Carbon heating element 3° hexagonal boron nitride (h
BN), and a metal catalyst plate 6 is placed inside the reaction chamber.
A, 68.6C... and the carbonaceous material 7 as a starting material are alternately stacked to form a multilayer body.

The hexagonal boron nitride molded body that directly constitutes the reaction chamber in question is
Even under the high temperature and high pressure conditions of the diamond conversion reaction, there is no risk of decomposition, melting, or damage and getting mixed up with the carbonaceous material and catalyst combination. Since it has the flexibility to follow the temperature gradient, it is possible to maintain a favorable pressure gradient and temperature gradient in the reaction chamber at all times.

The following experiment was conducted using this device.

Example 1. Catalyst metal is ductile cast iron (FCD45) (1)
Ingredients Table 1 (2) Structure As shown in the micrograph (xlOO) shown in Figure 2, graphite is precipitated in a spheroidal form.

The base is mainly pearlite with some ferrite scattered.

(3) State of implementation The above-mentioned ductile cast iron is cut into a plate shape with a thickness of 2M and an outer diameter of 3.8rM1, and the catalyst plates 6A, 6B, 6c... are bound.The carbonaceous material 7 has a thickness of 2IrIM. , using graphite plates for spectroscopic analysis with an outer diameter of 368 m, which were arranged in a stacked manner and held at a temperature of 1600°C and a pressure of 65 Kb for 15 minutes,
Rapid cooling lowered the pressure.

After the reaction, unreacted graphite was heated to be released as an oxide, and the remaining catalyst was dissolved in aqua regia and released.

These post-treatments are known.

The third image shows the structure of the diamond dense aggregate thus obtained using a scanning electron microscope (x150).
When the yield and density were measured, it was possible to obtain an 85% yield and a 95% density, respectively.

Example 2. The catalyst metal is Niresist ductile cast iron (1) Ingredients Table 3 (2) Structure As shown in the micrograph (xloo) shown in Figure 4, graphite is precipitated in a spherical shape.

The base is austenite. (Some cementite is also visible in the - part.) (3) Condition of implementation The dimensions of the catalyst, the type of carbonaceous material, and the dimensions are the same as in Example 1. The temperature is 1550℃, the pressure is 62.5℃, and after holding for 15 minutes, the same condition is applied. Post-processing was performed.

Figure 5 shows the structure of the obtained diamond dense aggregates under a scanning electron microscope (x200).
%, a density of 93% was obtained.

Example 3. Example (1) In which the catalyst metal has voids that correspond to the shape of the desired final dense aggregate (1) Component 9 Structure The same material as the Niresist ductile cast iron shown in Example 2 was used.

(2) Status of implementation As shown in FIG. 6, the catalyst 6x has an outer diameter of 3.8 mφ.

It has a cylindrical shape with an inner diameter of 21M1φ, a height of 6.0m, and a conical top on the inner side.

The catalyst 6Y is a disk with an outer diameter of 3.8 m and a height of 2.0 m.

Graphite for spectroscopic analysis cut to the same dimensions as this void is inserted into the internal void created by combining the two, and the temperature is 16.
After holding at 00'C and a pressure of 65 Kb for 20 minutes, the product was rapidly cooled and the pressure was lowered, and the product was subjected to the same treatment as in Example 1.

The dense viscous material D-D obtained had a yield of 82% and a density of 97%, and its schematic diagram is shown in FIG.

As shown in the figure, the conical shape of D-D has a slight step at its root, and catalyst 6X undergoes elastic deformation under high pressure, compressing and promoting the conversion and synthesis of carbon to diamond. It is understood that this confirms the development.

Although the obtained diamond dense aggregate has a shape almost similar to that of the final product (tools, etc.), it is necessary to fill the remaining pores, albeit slightly, in order to provide rough reinforcement and impact resistance. It is also conceivable that better results can be achieved by press-in impregnation of substances (for example adhesives).

[Effects of the Invention] The method for converting diamond according to the present invention is based on the conventional technology, and utilizes a special metal catalyst and a container to achieve a special behavior of liberated spherical graphite, and a preferable pressure for the reaction to proceed. By creating a gradient and temperature gradient, we were able to complete diamond conversion and integrated molding simultaneously, reducing the number of steps by more than half compared to conventional technology.

In addition, the obtained diamond dense aggregates are consolidated while growing in the [100] direction, so that they have no virility and have extremely excellent cutting properties when used as a tool.

It is not clear how the shape and size of graphite crystallized in cast iron are related to the physical properties of converted diamonds, as there are still few examples, but the shape and size of graphite can be determined by the melting of cast iron, coagulation.

It can be controlled relatively easily by manipulating the cooling process, and if the above relationships can be understood, there is a possibility that the morphology of diamonds can be controlled.

These will be replenished at a later date.

In addition, the liquidus temperature is lower than that of conventional catalyst metals, and the correlation between temperature and components is well known, so it can be expected to have the effect of shifting the reaction initiation point to the lower temperature side, but this point will be addressed at a later date. .

Furthermore, the challenges faced by conventional diamond sintered bodies are:
The problem was how to shape the sintered body into a desired shape, such as a tool.

On the other hand, since a material with extremely good machinability is used as a catalyst for the interlocking of the converted product and the precipitation of free graphite, cast iron can be processed and cut into the desired shape in advance and reacted as a catalyst to form the final shape. You can get 1q of similar conversions.

That is, in this case, it can be said that the catalyst produces an effect unique to the embodiment in which it simultaneously functions as the sintering mold in the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view schematically showing the apparatus used in the examples of the present application, FIGS. 2 and 4 are micrographs showing the structures of the metal catalysts used in different examples, and FIGS.
Fig. 5 is an SE image taken by a scanning electron microscope showing the structure of the diamond converter given in Example 1 in each of the different examples above, Fig. 6 is a front sectional view showing the shape of the catalyst used in Example 3, and Fig. 7 The figure is a perspective view of a diamond compact formed by turning. 8 to 10 are front sectional views and perspective views showing the prior art. 1... Pressure medium 2... Electrode 3... Heating element 4, 5... Flexible insulator 6A,
6 B, 6 c, 6

Claims (1)

[Claims] 1. In a method for converting a carbonaceous substance into diamond by bringing a carbonaceous substance and a metal catalyst into contact with each other in a reaction chamber and placing them under high temperature and high pressure reaction conditions, the metal catalyst is placed in an iron base. The reaction chamber is made of a cast iron-based material in which free graphite is precipitated in a spherical form, and the reaction chamber is flexible enough to follow the volume change that occurs as the conversion of the carbonaceous material into diamond progresses. , a diamond conversion method characterized by directly obtaining a strong and dense diamond compact from a carbonaceous material. 2. The method for converting diamond according to claim 1, wherein the iron base of the metal catalyst is ductile cast iron in a ferrite and/or pearlite phase. 3. The method for converting diamond according to claim 1, wherein the iron base of the metal catalyst is austenitic phase Niresist ductile cast iron. 4. The interior of the metal catalyst has voids that match the shape of the desired final dense aggregate, and the voids are filled with a carbonaceous material to promote the reaction in a compressible manner. The method for converting diamonds according to item 3.