RU2740933C1 - Method of producing powders of highly-purified diamond - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to diamond synthesis, which can be used to produce conductive and superconducting composites. For this purpose, carbon source is nano-globular carbon with particle size of 20–70 nm, and as boron source X-ray amorphous boron with particle size of less than 2 µmol in atomic ratio of boron/carbon from 1/10 to 1/20, is mixed using ethyl alcohol with superposition of ultrasound, air-dried at 100 °C for 1 hour, treated at pressure 3–6 hPa and temperature 1400–1700 °C for 60 s, then treated at pressure of 8 hPa and temperature of 1600–1800 °C for 60 s.EFFECT: method enables to obtain powders of high hardness diamonds doped with boron in concentration higher than 1021atom/cm-3and having micron diameters of about 1–10 µmol, and submicron, about 0.1–1 µmol, particle size.1 cl, 4 dwg, 3 ex

Description

The invention relates to the field of diamond synthesis, and, in particular, to methods for the synthesis of diamond powders doped with boron at a concentration above 10 ²¹ atom / cm ^-3 . A distinctive feature of this material is the metallic type of conductivity and the presence of superconductivity at low temperatures, which determines its demand in such areas as electrochemistry, biochemistry, electroanalysis, electronic and electromechanical devices. The need for micron and submicron powders of highly boron-doped diamond is due to the fact that they can be used to obtain conductive and superconducting composites with exceptional hardness.

At present, there are two main technological approaches to obtain highly borated diamond powders. The first is based on the decomposition of gaseous substances containing boron and carbon, followed by the reaction deposition of borated diamonds on a substrate, while the pressure of the gaseous medium most often does not exceed 10 atmospheres. The second is based on carrying out the reaction of substances containing boron and carbon under conditions of high pressures of at least 4 GPa and temperatures of at least 1200 ° C, that is, in the area of the thermodynamic stability of diamond.

There is a known method (US patent US 7144753, publ. 26.05.2005, IPC H01L 21/00 (2006.01)) for obtaining boron-doped nanocrystalline diamond from a gas mixture of a boron, methane, hydrogen and argon compound on a substrate, and B ₂ is taken as a boron compound H ₆ , and the ratio CH ₄ / H ₂ / Ar is (1% / 5% / 95%). The resulting diamond grains have a size of about 10-15 nm, the thickness of the nanodiamond film is about 4 μm, and the doping level is 10 ¹⁹ atom / cm ³ .

The main disadvantages of methods based on the decomposition of substances from the gas phase and deposition on a substrate include: long duration of the process; low yield of the final material from a single synthesis cycle; the difficulty of obtaining individual micron-sized single crystals, since the growing crystals coalesce, forming polycrystals. A group of methods based on the decomposition and deposition of substances from the gas phase on a substrate is used mainly for the synthesis of films of borated diamond and diamond-like materials.

Known methods of obtaining borated diamond powders by crushing with subsequent separation into fractions of a certain grain size of films of borated diamond obtained by deposition from the gas phase. However, this approach does not eliminate the disadvantages of gas phase synthesis methods, but adds additional operations.

There is a known method of obtaining a diamond powder doped with boron (Chinese patent CN 106119807, publ. 16.11.2016, IPC С23С 16/27, С23С 16/56 (2006.01), С23С 16/02 (2006.01), С01В 32/26 (2006.01)) by growing a diamond layer on particles of a boron-containing compound (pure boron, boron nitride, titanium boride) by the HFCVD method (chemical vapor deposition using a hot filament) using a gas mixture containing 0.5% -2% methane at a temperature of 2000-2200 ° C , and the temperature of the substrate 650-950 ° C for 1-6 hours, and subsequent vacuum annealing of the particles with the increased diamond layer at 1100-1600 ° C for 3-6 hours.

The disadvantages of this method include the complexity and duration of the process, the difficulty of controlling the degree of doping with boron, and the presence of impurities in the final material (nitrogen, titanium).

There is a known method of producing boron-doped diamond nanoparticles (Japanese patent JP 6241943 B2, publ. 05.10.2015, IPC S01B 31/06 (2006.01)), including the stage of preparing a mixture of boron or its compound and diamond nanoparticles, heating the mixture in a hydrogen atmosphere preferably at temperature 700-1000 ° C.

The disadvantages of this method include the fact that in this way it is impossible to obtain diamonds with a high level of doping, that is, more than 10 ²¹ atom / cm ^-3 .

A known method of obtaining nanocrystalline diamond material doped with boron (Chinese patent CN 110256078, publ. 09/20/2019, IPC С04В 35/52 (2006.01), С04В 35/622 (2006.01), С04В 35/626 (2006.01), by mixing diamond powder 50-100 nm with a boron source, the volume fraction of which is 0.05-1%, which is one of: boron, B ₂ O ₃ , BO, B ₂ O, B ₆ O, as well as boric acid; and subsequent processing the resulting mixture at a pressure of 10-15 GPa and a temperature of 1800-2300 ° C.

The disadvantages of this method include relatively high processing parameters at pressure and temperature and the impossibility of obtaining micron and submicron powders of boron-doped diamond by this method.

There is a known method (international application WO 2004035197 A1, publ. 04/29/2004, IPC B01J 3/06) for obtaining boron-doped blue diamonds from a homogeneous mixture of graphite, a catalyst-solvent, a boron source and optionally diamond seed crystals exposed to high pressures and temperatures. The boron source is taken from the list: B ₄ C, FeB alloy, metallic boron, amorphous boron powder; moreover, the total boron content in the mixture is 0.1-0.5% by weight; exposure pressure is selected in the range of 5-10 GPa, and the temperature in the range of 1300-2000 ° C.

The disadvantages of this method include the need to use a catalyst-solvent, usually a metal of the iron group, or an alloy of such metals, which deteriorates the performance of the resulting diamond, and, in particular, temperature stability. In addition, this method does not allow achieving a high degree of alloying.

параметр элементарной ячейки и концентрацию легирующей добавки бора в решетке алмаза до ~2-3% (3.5-5.2*10²¹ см^-3).The closest to the claimed method is described in (Zibrov IP, Filonenko VP. Heavily boron doped diamond powder: synthesis and rietveld refinement. Crystals. 2018, Vol. 8, pages 297-7, DOI: 10.3390 / Cryst8070297). The method consists in processing at a pressure of 8 GPa and a temperature of 1700 ° C a mixture of amorphous globular carbon with C ₄ B ₁₀ H ₁₆ O ₂ (1,7-di (hydroxymethyl) -M-carborane). The obtained microcrystals of diamond had a particle size of up to 5 μm, increased to

the unit cell parameter and the concentration of boron dopant in the diamond lattice up to ~ 2-3% (3.5-5.2 * 10 ²¹ cm ^-3 ).

The disadvantages of the method include the need to use a hydrogen-containing compound, which at a pressure of 8 GPa and a temperature of 1700 ° C increases the likelihood of depressurization and explosions of the working chamber, and limits the volume of the final material obtained in one processing cycle. In addition, the method does not allow varying the parameters of thermobaric treatment, so as to obtain micron and submicron diamond powders.

The task of the proposed technical solution is to eliminate these disadvantages, and in particular to eliminate the use of a hydrogen-containing substance, and to obtain diamond powders of micron about 1-10 microns and submicron 0.1-1 microns sizes containing a boron alloying additive in a concentration of at least 10 ²¹ atom / cm ^-3 ... In addition, the problem of obtaining diamond powders of a given grain size in the micron and submicron ranges is being solved.

The study of the proposed solution made it possible to establish that the fineness and level of doping with boron of the obtained diamond powders is determined by the state of the initial carbon material, and, in particular, by its fineness and level of doping with boron. It was found that the starting carbon material can be borated graphite, which can be obtained from a mixture of nanoglobular carbon and X-ray amorphous boron by exposure to high pressure and temperature, while the pressure should be lower than the pressure required to synthesize diamond. It was found that varying the atomic ratio of boron to carbon in a mixture of nanoglobular carbon and X-ray amorphous boron, as well as varying the parameters of thermobaric treatment, makes it possible to obtain boron-doped graphite powders of various grain sizes and crystal perfection. At the same time, the difference in grain size and crystal perfection of such graphite powders makes it possible, with appropriate further thermobaric treatment, to obtain diamond powders with micron sizes of about 1-10 microns and submicron sizes of 0.1-1 microns, containing a boron dopant at a concentration of at least 10 ²¹ atom / cm ^-3 .

The goal is achieved by the fact that nanoglobular carbon and X-ray amorphous boron are taken in an atomic ratio of boron / carbon from 1/10 to 1/20, mixed and treated with a pressure in the range of 3-6 GPa with a temperature in the range of 1400-1700 ° C, and powders of borated graphite are obtained, which are then processed at a pressure of 8 GPa and a temperature of 1600-1800 ° C.

The technical solution is confirmed by figures 1-4. FIG. 1 shows an image of the starting boron powder obtained using a scanning electron microscope. It is seen that the particle size is 0.02–2 μm. FIG. 2 shows an image of nanoglobular carbon obtained using a transmission electron microscope. FIG. 3 is a transmission electron microscope image of a highly borated diamond powder obtained according to Example 1. FIG. 4 shows an image obtained using a scanning electron microscope, highly borated diamond powder obtained in example 2.

Example 1

Take X-ray amorphous boron with a particle size of up to 2 microns (Fig. 1) and globular nanocarbon with a particle size of 20-70 nm (Fig. 2) in a ratio of 1/10, mixed in an agate mortar in ethyl alcohol with the imposition of ultrasound; dried in air at 100 ° C for 1 hour; placed in a high pressure container; processed at a pressure of 3 GPa, a temperature of 1400 ° C for 60 seconds; the temperature is reduced to room temperature, the pressure is reduced to atmospheric; disassemble the container; the substance is placed in a high pressure container; processed at a pressure of 8 GPa, a temperature of 1600 ° C for 60 seconds; the temperature is reduced to room temperature, the pressure is reduced to atmospheric; disassemble the container.

The resulting substance contains diamonds with a particle size of up to 1 micron and a boron concentration of at least 10 ²¹ atoms / cm ^-3 in an amount of at least 70 wt. %.

Example 2

Take X-ray amorphous boron with a particle size of up to 2 microns (Fig. 1) and globular nanocarbon with a particle size of 20-70 nm (Fig. 2) in a ratio of 1/15, mixed in an agate mortar in ethyl alcohol with the imposition of ultrasound; dried in air at 100 ° C for 1 hour; placed in a high pressure container; processed at a pressure of 3 GPa, a temperature of 1550 ° C for 60 seconds; the temperature is reduced to room temperature, the pressure is reduced to atmospheric; disassemble the container; the substance is placed in a high pressure container; processed at a pressure of 8 GPa, a temperature of 1700 ° C for 60 seconds; the temperature is reduced to room temperature, the pressure is reduced to atmospheric; disassemble the container.

The resulting substance contains diamonds with an average particle size of about 4 microns and a boron concentration of at least 10 ²¹ atom / cm ^-3 in an amount of at least 70 wt. %.

Example 3

Take X-ray amorphous boron with a particle size of up to 2 microns (Fig. 1) and globular nanocarbon with a particle size of 20-70 nm (Fig. 2) in a ratio of 1/20, mixed in an agate mortar in ethyl alcohol with the imposition of ultrasound; dried in air at 100 ° C for 1 hour; placed in a high pressure container; processed at a pressure of 6 GPa, a temperature of 1700 ° C for 60 seconds; the temperature is reduced to room temperature, the pressure is reduced to atmospheric; disassemble the container; the substance is placed in a high pressure container; processed at a pressure of 8 GPa, a temperature of 1800 ° C for 60 seconds; the temperature is reduced to room temperature, the pressure is reduced to atmospheric; disassemble the container.

The resulting substance contains diamonds with an average particle size of about 12 microns and a boron concentration of at least 10 ²¹ atom / cm ^-3 in an amount of at least 70 wt. %.

The method makes it possible to obtain diamond powders having a particle size of about 1-10 micron microns and 0.1-1 micron submicron sizes, doped with boron at a concentration of at least 10 ²¹ atom / cm ^-3 .

Claims (1)

A method of obtaining powders of highly borated diamond, including processing by high pressure and temperature of a homogeneous mixture of a carbon source and boron, characterized in that nanoglobular carbon with a particle size of 20-70 nm is taken as a carbon source, and X-ray amorphous boron with a particle size of less than 2 is taken as a boron source μm in an atomic ratio of boron / carbon from 1/10 to 1/20, mixed using ethyl alcohol with the imposition of ultrasound, dried in air at 100 ° C for 1 hour, processed at a pressure of 3-6 GPa and a temperature of 1400-1700 ° C for 60 s, then treated at a pressure of 8 GPa and a temperature of 1600-1800 ° C for 60 s.

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