JPS59203717A - Manufacture of diamond crystal - Google Patents

Abstract

PURPOSE:To manufacture easily diamond while inhibiting the spontaneous formation of diamond nuclei by mixing a carbonaceous substance with a metal for synthesizing diamond and diamond particles for seeds and by bringing the mixture into a reaction at a specified high temp. under a specified high pressure. CONSTITUTION:Artificial graphite as a starting material for diamond and a metal such as Fe, Co, Ni, Rh, Ru, Pd, Os, Ir, Pt, Cr, Ta or Mn as a flux for dissolving the graphite are laminated, and plural diamond particles of about 500mum size for seeds are arranged at the boundary part. A vessel contg. them is put in a superhigh temp. and pressure apparatus, and it is heated to a temp. above the temp. at which graphite reacts with said metal to cause recrystallization while applying a pressure below the minimum pressure required to cause spontaneous formation of diamond nuclei from recrystallized graphite. The artificial graphite is first recrystallized, and the diamond for seeds is grown while inhibiting the spontaneous formation of diamond nuclei. Thus, diamond particles are easily manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing diamond crystals from a carbonaceous material, a metal material for diamond synthesis, and diamond particles for seeds, and in particular, a method for directly suppressing the spontaneous nucleation of diamond from the carbonaceous material. The present invention relates to a method for producing diamond crystals for growing diamond grains for seeds.

Many methods for producing diamond crystals have been proposed in recent years, and generally artificial graphite, which is a polycrystalline material without additives, is used as a starting material, and the conversion of this artificial graphite to diamond can be carried out at economical temperatures and pressures. It is necessary to coexist with a metal substance for diamond synthesis in order to proceed under the conditions.

This metal material for diamond synthesis is iron group or platinum group metal (
It is understood that elements in group A of the periodic table and alloys containing them are widely used, and that this metal material for diamond synthesis melts in the coexistence of carbon and acts as a solvent for carbon under extremely high temperature and high pressure. has been done.

In order to control the particle size and crystal quality of diamond produced by this method, the formation process of diamond crystal nuclei is controlled and the density of diamond crystal nuclei that spontaneously form from graphite is suppressed to an appropriate value. It is essential that

Since the density of nuclei resulting from spontaneous nucleation is extremely sensitive to reaction pressure, strict reaction pressure control is required. Therefore, producing high-quality diamond particles (tough particles suitable for metal bond tools) consisting of single crystals isolated from each other with euhedral surfaces requires extremely advanced pressure control technology, which is not easy to achieve. There is a problem.

Regarding these, for example, Nippon Kagaku Yoshin, Japanese Patent Application Publication No. 59-203717 (2) Edition Center Publishing (1979), "Ultra High Pressure and Chemistry 124
It is described on pages 5 and below.

In order to grow a particularly large, high-quality single crystal, the raw material is diamond itself, and a reaction material is prepared in which a metal substance is interposed between this and the seed diamond particles, and the temperature and pressure within the diamond safe range are prepared. There is also a method of growing seed diamonds by providing an appropriate temperature difference between the seed diamonds and the raw diamond (temperature difference method). Although it is possible to grow multiple seed diamonds using this method, the respective temperatures and temperatures of the seed diamond and other starting materials must be adjusted to suppress the formation of spontaneously nucleated diamonds other than the seed diamond. The problem is that the direction in which gravity acts plays an important role in dividing the membrane, and only a very limited portion of the reaction vessel can be used.

The present invention was made in consideration of the above-mentioned problems in the conventional method, and involves growing diamond grains for seeds as a starting material under conditions where spontaneous nucleation of diamond is completely or almost completely suppressed. This is a method for manufacturing diamond crystals, which makes it possible to control the quality of manufactured crystals using manufacturing techniques that are easier to control than conventional methods.

In the method for producing diamond crystals of the present invention, a container in which a metallic flux, a carbonaceous substance, and seed diamond particles are inserted is placed in an ultra-high temperature and high pressure apparatus, and the metallic flux and the carbonaceous substance are mixed together. At a temperature higher than the lower limit of the temperature at which this carbonaceous material is recrystallized by reaction, at a pressure that does not exceed the lowest pressure at which diamond can spontaneously nucleate from this recrystallized carbonaceous material, and at a graphite-diamond equilibrium line. In this method, diamond crystals are manufactured by applying and maintaining a higher pressure than the above-mentioned method to grow the seed diamond particles. The holding temperature maintained under high temperature and high pressure in the method of the present invention is a temperature sufficient for the action of the metallic flux, and its lower limit is the eutectic point (eutectic point) of the metallic flux and the carbonaceous material. ), and the holding pressure must be set within the range defined by the following two limit pressures. That is, the lower limit of the holding pressure is the equilibrium pressure of the graphite-dykimo under the action of the metallic flux at the holding temperature, while the upper limit of the reaction force is the equilibrium pressure between the metallic flux and the recrystallized carbonaceous material. is the lower limit of the pressure required for spontaneous nucleation of diamond to occur under

The metallic flux used in the method of the present invention is not a special one, and any metal flux may be used as long as it can synthesize diamond from a carbonaceous material under appropriate temperature and pressure. Such metallic fluxes include iron,
There are cobalt, nickel, rhodium, ruthenium, palladium, osmium, iridium, platinum, chromium, and manganese. Among these, iron group elements and alloys thereof are preferable, and their working temperature is preferably about 1200'C or higher. The carbonaceous materials used in the method of the present invention include graphite, coal containing carbon in addition to amorphous carbon, and rehydrated sugar.

There are coke, charcoal, paper, wood, etc. Among these, graphite is the best.

In the method for producing diamond crystals of the present invention, a recrystallized carbonaceous material is prepared in advance and used as a starting material, and the recrystallized carbonaceous material, a metallic solvent, and diamond particles for seeds are placed in a container 7. Insert this page, place this container in an ultra-high-temperature, high-pressure device, and at a temperature higher than the lower limit of the temperature at which the metallic solvent acts,
Moreover, at a pressure that does not exceed the lowest pressure at which diamond can spontaneously nucleate from the recrystallized carbonaceous material, 11.
It is also possible to produce diamond crystals by applying and maintaining a pressure higher than the graphite-diamond equilibrium line to grow the seed diamond particles. The metallic solvent used here and the aforementioned metallic flux, which acts as a solvent and recrystallizes the carbonaceous material in the ultra-high temperature and high pressure equipment, may have the same composition or may have different compositions. There may be. Further, as one of the typical embodiments, a step of crystallizing the recrystallized carbonaceous material in an extremely high temperature and high pressure device is provided, and then all the steps are performed in the same device so that the constitutional conditions of the present invention are satisfied. You may also set a process. For example, a starting material in which pure artificial graphite and a metallic flux are brought into contact with each other in a container, and seed diamond particles are placed at the boundary between these materials is held under a sufficiently low pressure so that diamonds cannot form. Then, it is heated to the working temperature of a metallic flux to crystallize recrystallized graphite on the surface of the artificial graphite. This recrystallization process takes approximately 2 minutes or more. Next, at the recrystallization treatment temperature, the pressure is increased to be higher than the graphite-diamond equilibrium line and maintained at a pressure that does not exceed the lower limit of the pressure at which spontaneous nucleation of diamond occurs, so that the seed diamond particles placed in advance grow. .

The graphite-diamond equilibrium pressure, which is the lower limit of the reaction pressure for growing seed diamonds by the method of the present invention, is a function of the reaction temperature, and is generally P1 = 7 + 0.027 (T +
273) It is said that it can be approximated by the following relationship: Ki14+0.027T. However, Pl is kilo/<-) Kb
), T is the temperature in degrees Celsius. Experimentally, the method involves bringing pure ordinary crystalline artificial graphite into contact with a metallic flux, pressurizing it to a constant temperature under constant pressure, holding it for several minutes, lowering the temperature and pressure, and collecting the generated diamond. If the pressure at that time is varied, the lowest pressure at which diamond formation can be confirmed can be determined. - Although a theory for quantitatively determining the upper limit of the 9-page pressure of the invention method for strength wood has not yet been established, it has been experimentally demonstrated that graphite or recrystallized graphite and metallic flux under a metallic flux for diamond synthesis It can be determined experimentally as the pressure at which the yield of diamond produced suddenly begins to increase as a function of the reaction pressure by applying a constant pressure and heating the reactants in contact with a constant temperature. It is currently impossible to quantitatively determine this upper limit pressure, and since it seems to depend on the metallic flux used as the starting material, it must be determined experimentally. According to the inventor's experiments, C
The graphite-diamond equilibrium pressure is estimated to be about 3 kilobar higher than the graphite-diamond equilibrium pressure when carbon dioxide or Fe-Ni-Co alloy is used as the flux.

In the method of the present invention, there is a sufficient width of at least 2 to 3 kilobars between the lower limit pressure and the upper limit pressure, so that pressure control during the reaction step is easy. That is, by supplying the seed diamond nucleus in advance, it is not necessary to control the nucleation process, which is the most difficult process of pressure control. Furthermore, the number or density of nuclei can be set arbitrarily. Regarding the field of products to which this invention can be applied, it can be used not only to produce abrasive grains for simultaneously synthesizing a large number of high quality diamond particles, but also to grow a small number of large single crystal diamonds.

The reactants used in the method of the present invention may contain substances that do not inhibit the growth of high-quality diamond crystals. For example, the reaction material, which is a uniform mixture of pre-prepared coarse recrystallized powder, carbonaceous material, metallic flux, or metallic solvent powder, and an appropriate amount of seed diamond powder, is heated at a temperature suitable for the configuration of the present invention. It is possible to recover the reaction product containing particles from the growth of this seed diamond by holding the pressure at 1, but even if the reaction material is further mixed with a substance forming the container, such as magnesia powder, the same result can be obtained. Reaction products are collected. Magnesia does not significantly promote the generation of new nuclei under a metallic flux or metallic solvent and does not inhibit the effects of the present invention, and does not affect the diamond growth process and is particularly defective. It also does not show the effect of generating particles. Furthermore, the reaction product containing magnesia powder has the advantage that the metallic flux or metallic solvent and the residual carbonaceous material can be removed and only the produced diamond can be recovered more quickly.

In carrying out the method of the present invention, it is not necessary to maintain the temperature and pressure at constant values as long as they are within the range that satisfies the constituent requirements already mentioned, but they may be regulated according to the temperature at each moment during the reaction. If the reaction pressure is maintained between the equilibrium pressure of effect occurs.

In the method of the present invention, new diamond crystal nuclei are difficult to form from graphite recrystallized in a metallic flux, and the formation of diamond crystal nuclei is significantly inhibited at pressures that are at least about 3 kilobar higher than the graphite-diamond equilibrium pressure. This was realized by discovering the fact that the seed diamond crystals can be effectively grown under pressure within this range, and if the seed diamond crystals exist under pressure within this range. However, the reason and mechanism by which spontaneous nucleation of diamond is suppressed in the presence of recrystallized graphite are still unknown.

Next, the method of the present invention will be specifically explained according to Examples.

Example 1 Plate graphite made from graphite for emission spectroscopy and Fe-Ni-Co alloy (weight ratio 55:29 = 16) in a Magnesia container
A container made of Magnesia is laminated with a plate-shaped metallic flux made from the above, and five seed diamond particles of about 500 μm each are inserted and set in the boundary between the plate-shaped graphite and the plate-shaped metallic flux. was placed in an ultra-high temperature and high pressure apparatus and first pressurized to 52 kbar, and only the force was increased to 57.3 kbar and held for 10 minutes. (Growing process of diamond for seeds) When the metallic flux of the collected sample was dissolved and removed, it was confirmed that the diamond particles for seeds had grown to a size of 1.2 to 1.8 mm.

The same results were obtained even when artificial graphite for crucibles was used instead of graphite for emission spectroscopy, which was used as the starting material. Similar results were also obtained when a Co plate was used as the metallic flux used as the starting material.

Example 2 A container made of artificial graphite was filled with a mixed powder of equal amounts of Fe and Ni and placed in an electric furnace in a situation where the temperature at the top was lower than at the bottom.
A metallic flux consisting of Fe and Ni was melted at 500 to 1700°C to produce recrystallized graphite. After cooling, the metallic flux was dissolved and removed with acid to recover recrystallized graphite particles. The recrystallized graphite particles prepared in advance in this manner were
Based on the weight part, 5 parts by weight of Fe powder, 3 parts by weight of Ni powder, Co
2 parts by weight of powder and 0.2 parts by weight of diamond powder for seeds of 88 to 105 μm were mixed, packed in a Magnesia container, set in an ultra-high temperature and high pressure device, and heated to about 1400°C under a pressure of 55.5 kilobars for 10 minutes. After holding for a minute, the product was dissolved and separated to recover diamonds. The recovered diamonds were single-crystal diamonds with a diameter ranging from approximately 150 μm to a maximum of 400 μm and well-developed euhedral surfaces.

The yield of 14-page diamonds was about 6 times that of the mixed seed diamonds. In addition, as a comparative experiment, when diamond powder for seeds was excluded from the above starting materials, approximately 57
Only cluster diamonds above kilobar could be recovered.

Claims (4)

[Claims] (1) A container containing a metallic flux, a carbonaceous substance, and a seed diamond particle is placed in an ultra-high temperature and high pressure device, and the carbonaceous substance is removed by a reaction between the metallic flux and the carbonaceous substance. At a temperature below the lower limit of the recrystallization temperature, at a pressure that does not exceed the lowest pressure at which diamond can spontaneously nucleate from this recrystallized carbonaceous material, and at a pressure that is higher than the graphite-diamond equilibrium line. A method for producing diamond crystals, which comprises growing the seed diamond particles by applying and maintaining pressure. (2) The method for producing a diamond crystal according to claim 1, wherein the carbonaceous material is graphite. (3) The container containing the metallic solvent, the recrystallized carbonaceous material, and the seed diamond particles is placed in an ultra-high temperature and high pressure device, and the temperature at which the metallic solvent acts is at least the lower limit of 2 degrees, Furthermore, the seed diamond particles are grown by applying and maintaining a pressure that does not exceed the lowest pressure at which diamond can spontaneously nucleate from the recrystallized carbonaceous material and which is higher than the graphite-diamond equilibrium line. A method for producing a diamond crystal, characterized by: (4) The method for producing diamond crystals according to claim 3, wherein the recrystallized carbonaceous material is recrystallized graphite.