JPS63236531A - Synthesis of diamond - Google Patents

Abstract

PURPOSE:To synthesize diamond having a particle size of 0.4mm or more, by interposing a metal having at least one hole communicating with the interfaces of a carbonaceous substance and a catalyst and inert to the synthesis of diamond between the carbonaceous substance and the catalyst to perform operation. CONSTITUTION:A carbonaceous substance bed 4 composed of amorphous carbon or pyrolitic graphite and a catalyst bed 3 composed of a substance containing 75wt.% or more of iron are arranged in opposed relation to each other and a metal 5 having at least one hole communicating with the interfaces of both beds and inert to the synthesis of diamond is interposed between the carbonaceous substance bed 4 and the catalyst bed 3. Then, diamond is synthesized at temp. adjusted to the eutectic temp. of the carbonaceous substance bed 4 and the catalyst bed 3 or more by a graphite heater 1 under pressure equal to or more than a diamond-graphite equilibrium curve. By this method, amorphous diamond having a large particle size of 0.4mm or more is obtained within a relatively short time wherein a high temp. and high pressure holding time is within 1hr.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for synthesizing diamond, and in particular to abrasive grains for tools used for grinding and cutting, cutting edges for cutting tools, or heat sinks in the semiconductor technology field. (cooling radiator)
The present invention relates to a method for synthesizing large diamond single crystals with a diameter of 0.4 mm or more, which are useful as materials for such materials.

[Prior Art] Due to its high hardness, diamond has been widely used in cutting tools in the past.

On the other hand, in recent years, attention has been focused on the high thermal conductivity and the possibility of using it as a semiconductor by doping with impurities. Applications to electronic technology fields such as semiconductor devices are being advanced. For this reason, there is an even stronger need to establish diamond synthesis technology, and various methods are being developed.

As a method for synthesizing diamonds, a gas phase synthesis method has recently been developed in which gaseous hydrocarbons are used as a carbon raw material and the process is carried out under low pressure conditions, but the diamonds synthesized by this method can only be obtained with small particle sizes. It is believed that when it is desired to synthesize diamond as a large single crystal, the conventional high temperature and high pressure method should be used.

[Problems to be Solved by the Invention] Various synthesis methods are known for the purpose of producing large diamond single crystals, and a representative example is that of Barbard M. Strong (H.M.).

Strong) is J, Phys, fhem, 75. (
One example is the so-called temperature difference method published in 1833 (1971).

This method is related to a technique for increasing the size of diamond particles using diamond obtained by a certain method as a raw material, and it involves placing a ready-made synthetic diamond on the high temperature side as a carbon source, and placing a metal catalyst on the low temperature side in contact with the carbon source. Place it so that
Furthermore, a diamond seed crystal is placed in the lowest temperature part of the metal catalyst to reduce the temperature difference between the highest temperature part and the lowest temperature part by approximately 5.
The temperature is maintained at 0° C., and due to this temperature difference, the carbon source diffuses through the metal catalyst and crystallizes as diamond on the seed crystal to grow as a large diamond single crystal. However, this method has the disadvantage that it takes a long time to obtain large diamond single crystals.
It took a long time of 10 to 30 hours to grow to this size.

On the other hand, methods for synthesizing diamond (however, small-diameter diamond as described later) in a relatively short period of time have already been developed prior to the above-mentioned technology.
There is a technology disclosed in the issue. This method, like the above-mentioned technique, is based on 8-Bird M. Strong, and uses elements belonging to group Ⅰ of the periodic table (iron group, platinum group) or C
r.

An element such as Ta, Mn, or an alloy containing these elements is used as a catalyst, and the catalyst and a carbon source (graphite) are made to coexist at a temperature higher than the eutectic temperature of both and higher than the diamond-graphite equilibrium line. It is synthesized by holding the diamond under pressure (conditions under which diamond is thermodynamically stable). By adopting such a configuration, we have succeeded in synthesizing diamond in a short time of 30 minutes or less, but since this method was originally used for the purpose of obtaining diamond powder, It is almost impossible to obtain a large diamond single crystal with a diameter of m+++ or more.

The present invention has been made to solve the above-mentioned technical problems, and its purpose is to provide a relatively short holding time of less than 1 hour at high temperature and high pressure, and to provide a 0.
The object of the present invention is to provide a method for synthesizing diamond that can yield large diamond single crystals of 4 mm or more.

[Means for Solving the Problems] The present invention, which has achieved the above object, has a carbon material layer and a catalyst layer that are disposed facing each other, and a temperature that is higher than the eutectic temperature of both and higher than the diamond-graphite equilibrium line. In the method of synthesizing diamond under pressure, amorphous carbon or pyrolytic graphite is used as the carbon material, a substance containing 75% by weight or more of iron is used as the catalyst, and between the carbon material and the catalyst, This method of synthesizing diamond is characterized in that it has at least one hole communicating with the interface between the two, and that it is operated while interposing a metal that is inert to diamond synthesis.

[Function] The present invention is constructed as described above, but the key point is that it is based on a high temperature and high pressure method, and it has been discovered that by limiting the types of carbon materials and catalysts, diamond crystals can grow in a shorter time than conventional methods. This is based on the fact that That is, amorphous carbon or pyrolytic graphite is used as the carbon material, a material containing 75% by weight or more of iron is used as the catalyst, and the carbon material and the catalyst are placed opposite each other so that the eutectic point or higher of the two is achieved. It was discovered that diamond crystals can grow in a short time if diamond is synthesized at a temperature of 100 mL and under a pressure above the diamond-graphite equilibrium line. The theoretical background behind the promotion of diamond crystal growth will be discussed later, but with the above configuration alone, the effect of shortening the diamond crystal growth time was limited, and only elongated diamonds were obtained.

In other words, if no special measures are taken to limit the number of nuclei generated in the above configuration method, a large number of generated nuclei will try to grow individually in the length and width directions, but in the width direction, adjacent ones will collide with each other and the width will increase. inhibit growth in the direction. Therefore, an elongated diamond crystal extending in the length direction is obtained.

Therefore, the present inventors conducted further intensive research based on the idea that it was necessary to take some means to control nucleation, and as a result, they discovered that at least one bond between the carbon material and the catalyst communicates with the interface between the two. The present inventors have discovered that the desired large-grain diamond single crystal can be obtained by intervening a metal that has pores and is inert to diamond synthesis, and has completed the present invention.

The amorphous carbon used in the present invention is also called amorphous carbon, and its crystal structure is almost the same as that of graphite, but the crystals are 1/J~ and the aggregation state is irregular. It differs from normal graphite in one respect.

Pyrolytic graphite is a carbon material that can be industrially produced by vapor phase carbonization, and is generally produced by bringing hydrocarbons such as methane, propane, benzene, acetylene, etc. into contact with artificial graphite heated to high temperature. It can be obtained by

Although pure iron is most suitable as the catalyst used in the present invention, the object of the present invention can be achieved even when a substance containing 75% by weight or more of iron (hereinafter referred to as ``car'') or more is used. The substances mentioned here are Fe-based alloys (e.g. Fe-Ni, Fa-Co,
Fe-Co-Ni, etc.), i.e. the iron content is 75%
If less than 100% of the substance is used as a catalyst, even if crystals are obtained, they will be fine (see Example 4 below).

On the other hand, metals inactive for diamond synthesis used in the present invention include, for example, Pt, Ti, Nb, and Cu.

Examples include Hf, V, Ta, Mo, W, Au, Ag, etc.
Examples of methods for interposing these inert metals between the carbon material and the catalyst include plating methods, vacuum evaporation methods, powder coating methods, and methods of sandwiching metal foils. These inert metals are interposed between the carbon material and the catalyst to suppress the reaction between the carbon material and the catalyst, thereby suppressing diamond nucleation. Note that this inert metal ensures chemical communication between the carbon material and the iron catalyst and is required to have at least one penetrating hole communicating with the two to perform nucleation.

As is clear from the above gist, the object of the present invention cannot be achieved even if any of the requirements for carbon material, catalyst, and inert metal are missing. For example, if Co, Ni, etc., which have been conventionally used as a catalyst, are used, a single crystal of diamond can be obtained, but it will be a fine crystal (see Example 4 below). Furthermore, when ordinary graphite, which has been conventionally used as a carbon material, is used, a large diamond single crystal cannot be obtained (see Comparative Example 2 described later).

In addition, in the present invention, "large diamond" means long sleeves of 0.
The goal is to have a diameter of 5 mm or more, a short axis of 0.3 mm or more, and an aspect ratio (major axis length to short axis length) of about 1 to 2, but of course these are Although the details of the reason why large-grain diamond single crystals can be obtained by the present invention are not known, this is not a factor that limits the invention, but it is probably because the amorphous carbon or pyrolytic graphite as the carbon material is dense and has a continuous structure. Therefore, together with the effect of iron catalyst, diamond growth progresses continuously and rapidly, and furthermore, by limiting the number of nucleation by the action of inert metal, large diamonds are formed while preventing the growth of elongated diamonds. It is thought to be a single crystal.

In the present invention, a preferred embodiment is to arrange diamond seed crystals in the pores of the inert metal (see Example 2 below). If such a configuration is adopted, the placed seed crystals will quickly grow to take in newly generated nucleation portions, thereby suppressing new nucleation. Therefore, the seed crystal (100
If the seed crystal is arranged so that the ) plane is parallel to the interface between the carbon material and the catalyst, the growth of the seed crystal will be faster and more excellent effects will be obtained.

[Example] Example 1 Figure 1 is a schematic explanatory diagram showing the configuration for carrying out the method of the present invention, in which 1 is a graphite heater, 2 is sodium chloride as an insulating member, 3 is a catalyst, and 4 is a 5 represents a carbon material, and 5 represents an inert metal having pores.

In the configuration shown in FIG. 1, the carbon material 4 has a diameter of 8
pyrolytic graphite with a diameter of 8 mm and a thickness of 2.5 mm as the catalyst 3, pure iron with a diameter of 8 mm and a thickness of 1y1 as the inert metal 5, and a thickness of 0.02 mm with holes of 0.6 mm in diameter at 21 intervals as the inert metal 5. Diamond synthesis was performed using each of the Zr foils. and 15 at 60 kbar and 1460°C
After processing for minutes, the long axis was approximately 1.5 mm.

A large diamond single crystal with a short axis of about 0.8 mm (aspect ratio 1.138) was obtained.

Although FIG. 1 shows a structure in which the carbon material layer and the catalyst layer are stacked and arranged facing each other, the structure for carrying out the method of the present invention is not limited to that shown in the figure, and for example, a columnar or cylindrical structure may be used. It is also possible to have a structure in which the parts are combined and arranged facing each other in a so-called concentric circle.

Comparative Example 1 Diamond was synthesized in the same manner as in Example 1 except that the inert metal 5 was not used, and the major axis was approximately 1.50111.
1. An elongated diamond crystal with a minor axis of 0.2 mm (aspect ratio 30) or less was obtained.

Example 2 Diamond was synthesized using the same configuration as Example 1, and further arranging a seed crystal in the hole of the Zr foil so that its (100) plane was parallel to the interface between the carbon material 4 and the catalyst 3. . When treated at 60 kbar and 1450°C for 20 minutes, a large diamond wheel crystal with a long sleeve direction of (100), a length of about 1.5 mm, and a short axis of about 1.0 mm (aspect ratio 1.5) was obtained. Obtained.

Example 3 In the configuration shown in FIG. 1, the carbon material 4 was prepared by adding 0.1% HNO to furfuryl alcohol and subjecting it to dehydration condensation, carbonizing it in nitrogen using aoo'e, and further carbonizing it in vacuum (
Diamond synthesis was performed using amorphous carbon treated at 1900° C. for 1 hour at 1×10 −’ Torr and using pure iron as a catalyst. and 60 kbar,
When treated at 1450'C for 15 minutes, the diameter was approximately 1.5 m.
A large diamond single crystal of m was obtained.

Comparative Example 2 Diamond was synthesized in the same manner as in Example 3 except that commercially available carbon material graphite or highly crystalline graphite was used as the carbon material, and in all cases only fine diamond particles of 0.3 mm or less were obtained.

Example 4 In the configuration shown in FIG. 1, the amorphous carbon shown in Example 3 was used as the carbon material 4, and the type of catalyst was changed.
When treated at kilobar and 1460° C. for 15 minutes, the results shown in Table 1 below were obtained.

Table 1 [Effects of the Invention] As described above, according to the present invention, large single-crystal diamonds were obtained in a short period of time by employing and operating the above-described configuration.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing a configuration for implementing the method of the present invention. 1...Graphite heater 2...Sodium chloride 3.
...Catalyst 4...Carbon substance 5...Inert metal

Claims (2)

[Claims] (1) In a method in which a carbon material layer and a catalyst layer are disposed facing each other and diamond is synthesized at a temperature higher than the eutectic temperature of the two and under a pressure higher than the diamond-graphite equilibrium line, the carbon material is amorphous carbon or Uses pyrolitic graphite, uses a substance containing 75% by weight or more of iron as a catalyst, has at least one pore communicating with the interface between the carbon material and the catalyst, and is incompatible with diamond synthesis. A method for synthesizing diamond, which is characterized in that it is operated in the presence of an active metal. (2) A method for synthesizing diamond according to claim 1, in which diamond seed crystals are placed in the pores of an inert metal.