JP2002210350A - Method of synthesizing diamond powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method for synthesizing diamond by a process similar to the natural diamond formation process. SOLUTION: A method for synthesizing a diamond powder comprising reducing a carbonate melt with Si or SiC by using a high-temperature high-pressure apparatus. The carbonate melt is desirably a melt of dolomite. It is also possible to add diamond powder seed crystals to the starting material. The pressure in the apparatus is 6.0-8.0 GPa, and the heating temperature is 1,500-1,800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for synthesizing diamond powder by reducing a carbonate melt.

[0002]

2. Description of the Related Art Artificial diamond powder is synthesized by using graphite as a carbon material and using a metal catalyst such as Ni or an inorganic solvent such as carbonate, silicate or sulfate in an ultra-high pressure apparatus. Are known. In addition, carbonates such as magnesium carbonate, iron carbonate, and zinc carbonate are used as carbon sources, and iron, aluminum,
A reducing metal powder such as magnesium is mixed at a ratio of 67 mol% or more and molded by pressure.
There is also known a method of synthesizing diamond powder by using a high temperature and a high pressure instantaneously generated by a shock wave by performing a shock compression of 0 kbar (Japanese Patent Publication No. 4-7673).
No. 3).

[0003]

In the conventional synthesis method, diamond is not generated from all graphite, and a part of graphite is usually mixed with diamond without reacting even after completion of the synthesis reaction. Therefore, it was difficult to control the amount of synthesized diamond.

[0004]

The carbon in the mantle may be a solid such as diamond, carbonate mineral, silicon carbide, or carbonatite magma (carbonate melt), C-H-O.
Is considered to exist as a system supercritical fluid phase,
The origin of these carbons and their production processes are important in clarifying the global carbon cycle.

[0005] The environment of diamond production, such as temperature and pressure conditions, has been studied from the combination of the minerals contained therein. It is considered that the carbon concentration of the mantle is up to several tens of ppm, and it is considered that carbon is required to move and concentrate in the mantle in order to form diamond, and carbonatite magma or C—H—O based supercritical A model of diamond formation by the movement and concentration of carbon in the mantle by fluid and its oxidation and reduction has been proposed.

However, the conventional method of synthesizing diamond under high-temperature and high-pressure conditions uses graphite as a raw material, which is very different from the natural diamond production process. Thus, no experimental verification of diamond crystallization by the reduction reaction of carbonate melt (carbonatite magma) under high-temperature and high-pressure conditions in the Earth's mantle has been performed, and diamond is produced by a method similar to the natural diamond production process. No synthesis method has been realized so far.

By using Si or SiC, which is known as an inclusion crystal of natural diamond, as a reducing agent, the present inventors artificially produce diamond by a process similar to that of producing natural diamond from a carbonate melt. The powder was successfully synthesized.

That is, according to the present invention, a pressure of 6.0 to 8.0 GPa and a heating temperature of 1500 to 18
A method for synthesizing diamond powder, comprising reducing a carbonate melt with Si or SiC at 00 ° C. Further, the present invention is the above method for synthesizing diamond powder, wherein the high-temperature high-pressure device is any one of a belt-type high-pressure generator, a multi-anvil-type high-pressure generator, and a Bridgman-type high-pressure generator. Further, the present invention is the above method for synthesizing diamond powder, wherein the molten carbonate is dolomite. Further, the present invention is the above-described method for synthesizing diamond powder, wherein a diamond powder seed crystal is contained in a starting material for forming a carbonate melt.

The present invention is a method of synthesizing diamond powder using high-temperature and high-pressure means without using graphite as a carbon raw material. In the present invention, the high-temperature heating under high pressure causes all of the reducing agent to react with the carbonate melt, as shown by the following chemical formula, to produce diamond corresponding to the molar amount of the reducing agent present in the starting material. CaMg (CO
₃ ) ₂ + 2Si → CaMgSi ₂ O ₆ + 2CCaMg (C
O ₃ ) ₂ + 2SiC → CaMgSi ₂ O ₆ + 4C In other words, when Si is used as a reducing agent, the diamond equivalent to the molar amount of Si is used, and when SiC is used as a reducing agent, the molar amount is twice as large as that of SiC. Is produced. For this reason, it is possible to easily control the diamond synthesis amount by the mixing amount of the reducing agent.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a carbonate melt from a starting material contained in a capsule made of a high melting point metal such as Pt, Mo or Ta in a high temperature and high pressure apparatus, Wherein the diamond powder is directly crystallized from the carbonate melt by a reduction reaction with Si or SiC.

As a carbon source in a starting material for forming a carbonate melt, calcite (CaCO ₃ ), magnesite (MgCO ₃ ), Siderite (FeCO ₃ ), Mn
CO ₃ , Na ₂ CO ₃ , dolomite (CaMg (C
O ₃ ) ₂ ), but it is preferable to use dolomite, which has the lowest melting point among the carbonate melts existing in the earth's mantle, or a mixture of calcite and magnesite forming dolomite.

The reducing agent in the starting material is Si or S
Although any of iC may be used, the crystallization reaction rate of diamond is faster when Si is used as the reducing agent than when SiC is used as the reducing agent. The mixing ratio of Si in the starting material is about 12 to 24 mol%, and the mixing ratio of SiC is 25 m
ol% is sufficient.

The high-temperature / high-pressure apparatus may be any apparatus capable of maintaining the high-pressure / high-temperature condition in the present invention for a long time. Any of generators may be used. The pressure during synthesis is 6.0 to 8.0 GPa, and the heating temperature is 1500 to 1800 ° C. If it is less than 6.0 GPa, the temperature condition (1500 ° C. or higher) where the reaction time is short is close to the stable region of graphite, and it is difficult to form diamond. At a low temperature of less than 6.0 GPa and less than 1500 ° C., the reaction rate is low, so that diamond synthesis becomes difficult. 8.
At a high pressure exceeding 0 GPa and / or a high temperature exceeding 1800 ° C., there is a technical difficulty for stably generating pressure and temperature conditions for a long time.

The time required for crystallization of diamond differs depending on the heating temperature and pressure conditions. If the temperature is lower than 1500 ° C., a long time exceeding 24 hours is required for producing diamond powder, which is not efficient. For example, when Si is used as a reducing agent, 60 minutes at 1800 ° C., 240 minutes at 1600 ° C., and when SiC is used as a reducing agent, 180 minutes.
60 minutes at 0 ° C, 480 minutes at 1600 ° C, 1500 ° C
In this case, a reaction time of 1440 minutes (24 hours) is required.

The spontaneously growing nucleation diamond powder is
Exists in the aggregate of diopside and carbonate (these are quenched phases that crystallize from the liquid phase formed as the temperature drops at the end of the reduction reaction) and crystallize directly from the carbonate melt It is thought that it was done. Diobide and carbonate minerals (calcite, dolomite) in the product
The presence of a quenched phase was confirmed, but no silicon or moisanite was found.

[0016] A diamond powder seed can also be placed at the center of the starting material. The shape and size of the seed crystal are not particularly limited, but those having a size of about 1 to 3 mm are preferable. When a seed crystal is used, many growth hills develop on the {111} plane of the seed crystal diamond powder. The growth hill shows a triangular shape, a hexagonal shape, or an irregular shape in both positive and negative positions with respect to the orientation of the {111} plane of the seed crystal.
The growth hill has a diameter of about 10 μm to 50 μm.

On the ridge of the {111} plane of the seed crystal, a frost columnar growth hill develops in a direction perpendicular to the ridge. The length of the frost columnar growth hill is up to about 20 μm. The ridges and vertices of the seed crystal become very sharp due to the development of the frost columnar growth hill.

[0018]

EXAMPLES Examples 1 to 5 and Comparative Example 1 FIG. 1 is a schematic sectional view showing a state in which a capsule filled with a starting material is incorporated in an ultrahigh-pressure synthesis apparatus. As the ultra-high pressure synthesizing apparatus, a flat belt type high-pressure apparatus (FB30H of Inorganic Materials Laboratory Ultra High Pressure Station) was used.

Calcite and magnesite powders were mixed at a molar ratio of 1: 1 and mixed with silicon (Si) or moisanite (SiC) powder was used as a starting material.

As shown in FIG. 1, about 250 mg of starting material
A Pt capsule 3 filled with NaCl is surrounded by a NaCl block 2, and a NaCl-20 wt% ZrO ₂ molded body 7
A structure in which a NaCl-10 wt% ZrO ₂ molded body 6 is disposed on the side surface as a pressure medium, the periphery thereof is fixed with a steel ring 5, covered with pyrophyllite 1, and heated by a graphite heater 4.

Table 1 shows the starting material composition, the heating temperature, the heating time, and the maximum particle size of the spontaneously growing diamond powder in each of Examples and Comparative Examples. The pressure was 7.7 GPa.
The obtained product was analyzed by an optical microscope, a differential interference microscope, XR
D, evaluated by SEM-EDS.

[0022]

[Table 1]

In the dolomite-Si system of Examples 1 and 2, and the dolomite-SiC (25 mol%) of Examples 3, 4, and 5, a large number of spontaneously grown diamond powders were formed, and Pt was produced.
It concentrated at the bottom of the capsule. The spontaneously growing diamond powder has a maximum diameter of about 90 μm. However, in Comparative Example 1 in which only dolomite not mixed with silicon or moisanite was used as a starting material, generation of spontaneously growing diamond powder was not observed.

FIG. 3 is an electron micrograph of the spontaneously growing diamond powder present in the quenched phase matrix crystallized from the liquid phase formed as the temperature decreased in Example 2. FIG. 4 is an electron micrograph of the spontaneous nucleus growth diamond powder obtained in Example 2 with a magnification larger than that of FIG. The spontaneously growing diamond powder is an octahedral crystal with {111} planes developed, but in rare cases, {100} planes were also confirmed. Many spontaneously growing diamond powders exhibited spinel twinning.

[0025]

As described above, the present invention is a method in which graphite is not used as a carbon material in a diamond powder synthesizing method using high-temperature and high-pressure means, and it is possible to easily control the carbon material. Further, it is possible to easily control the synthesis amount of diamond powder by controlling the mixing amount of the reducing agent, and to provide a new industrial production method of diamond powder.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a state in which a capsule filled with a starting material is incorporated in a high-temperature and high-pressure apparatus.

FIG. 2 is a graph showing a Raman spectrum of a product obtained in Example 1.

FIG. 3 is an electron micrograph of a spontaneous nucleation growth diamond powder present in a quenched phase matrix crystallized from a liquid phase formed with a decrease in temperature in Example 2;

4 is an electron micrograph instead of a drawing, in which the magnification of the spontaneously growing diamond powder obtained in Example 2 is larger than that of FIG.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yusuke Furugi 1634 Imajuku Higashicho, Asahi-ku, Yokohama-shi, Kanagawa Prefecture 2-221 Imajuku Mallside F-term (reference) 4G046 GA03

Claims (4)

[Claims] 1. A pressure of 6.0 to 8.0 using a high-temperature and high-pressure apparatus.
A method for synthesizing diamond powder, comprising reducing a carbonate melt with Si or SiC at 0 GPa and a heating temperature of 1500 to 1800 ° C. 2. The high-temperature and high-pressure apparatus is one of a belt-type high-pressure generator, a multi-anvil-type high-pressure generator, and a Bridgman-type high-pressure generator.
A method for synthesizing the described diamond powder. 3. The method for synthesizing diamond powder according to claim 1, wherein the molten carbonate is dolomite. 4. The method for synthesizing diamond powder according to claim 1, wherein a seed crystal of diamond powder is contained in a starting material forming a carbonate melt.