RU2348580C1 - Nanodiamond and method of its obtainment - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: carbon-containing explosive with negative oxygen balance is placed in a shell of condensed phase including reduction agent. Mass ratio of reduction agent to carbon-containing explosive is not less than 0.01:1. Detonation is performed in closed volume in gas medium inert to carbon. Detonation product is processed by 2-40% aqueous nitric acid together with oxygen of compressed air at 200-280°C and pressure of 5-15 MPa. Obtained nanodiamond includes carbon of cubic diamond modification and roentgen-amorphous phase at the ratio of (82-95):(18-5) wt % respectively. Element composition of nanodiamond, wt %: carbon 90.2-98.0; hydrogen 0.1-5.0; nitrogen 1.5-3.0; oxygen 0.1-4.5.

EFFECT: improved process safety, obtaining nanodiamond with predictable properties at industrial scale.

3 cl, 5 tbl

Description

The present invention relates to the field of inorganic chemistry of carbon, namely to diamond carbon modification — nanodiamonds having superhard material properties, and a method for their preparation, in particular, by detonation synthesis from carbon-containing explosive mixtures, followed by the separation of nanodiamonds using chemical methods.

State of the art

Various composite materials are known that are obtained by methods of detonation synthesis from carbon-containing explosives and containing carbon in various phases.

A nanodiamond is formed during the detonation of carbon-containing explosives with a negative oxygen balance in a special medium under conditions that allow it to survive.

Nanodiamonds are individual particles ranging in size from 2 to 20 nm, aggregated, as a rule, into larger ensembles of particles. Owing to its nanosize, the nanodiamond has a high dispersion, the presence of defects in the surface structures of the particle, and, as a consequence of the above, an active surface. These characteristics can vary within wide limits depending on the conditions for the production of nanodiamonds.

For more than 20 years, carbon nanocrystal composite material of classical elemental composition, mainly containing carbon in a cubic diamond phase with the following element content, wt.%: Carbon - 72-90; hydrogen 0.6-1.5; nitrogen - 1.0-4.5 and oxygen - 4-25; and methods for its preparation (Volkov K.V., Danilenko V.V., Elin V.I. Synthesis of diamond from carbon of detonation products of explosives. Physics of Combustion and Explosion. 1990, vol. 26, No. 3, pp. 123-125; Lyamkin A.I., Petrov E.A., Ershov A.P. et al. Obtaining diamonds from explosives, DAN SSSR, 1988, v. 302, p. 611-613; Greiner NR, Phillips DS. Johnson FJD Diamonds in detonation soot. Nature, 1988, vol. 333, p.440-442; Petrov BA, Sakovich G.V., Brylyakov P.M. Conditions for the conservation of diamonds in the process of detonation production, DAN SSSR, 1990, v. 313, No. 4, p. 862-864; V.Yu. Dolmatov, Ultrafine detonation synthesis diamonds: properties and applications, Uspekhi Khimii, 2001, vol. 70 (7), p.687-708; V.Yu. Dolmatov, Ultrafine detonation synthesis diamonds, St. Petersburg, SPbSPU, 2003, 344 p.).

The properties of a classical nanodiamond are quite fully described (V.Yu. Dolmatov. Ultrafine detonation synthesis diamonds: properties and application. Advances in Chemistry, 2001, vol. 70 (7), pp. 687-708; V.Yu. Dolmatov. Ultrafine detonation synthesis diamonds , St. Petersburg, SPbPU, 2003, 344 p .; EP, 1288162, A2,).

Condensed carbon (CG) is also known to specialists in the field of carbon chemistry, which is a composite carbon material containing carbon in various modifications and, depending on the detonation conditions of carbon-containing explosives, containing or not containing carbon in the cubic diamond phase.

Such a KU can be obtained by detonating carbon-containing explosives with a negative oxygen balance in a special medium under conditions that allow the condensed carbon products of the explosion to be preserved (Lyamkin A.I., Petrov E.A., Ershov A.P. et al. Obtaining diamonds from explosives, DAN SSSR, 1988, v. 302, pp. 611-613; Greiner NR, Phillips DS, Johnson FJD Diamonds in detonation soot. Nature, 1988, vol. 333, p. 440-442; Petrov V.A. , Sakovich GV, Brylyakov PM Conditions for the conservation of diamonds in the process of detonation production, DAN SSSR, 1990, vol. 313, No. 4, pp. 862-864; V.Yu. Dolmatov. The basics of detonation synthesis: properties and applications. Advances in Chemistry, 2001 vol. 70 (7), pp. 687-708; V. Yu. Dolmatov. Ultrafine detonation synthesis diamonds, St. Petersburg, St. Petersburg State Polytechnical University, 2003, 344 pp.).

It is known that the method of obtaining KU may include undermining the charge of a carbon-containing explosive in a different environment, for example:

- in a gas medium inert to carbon, for example, in an atmosphere of nitrogen, carbon dioxide, gaseous products of previous explosions (US, 5916955, C1);

- in water foam (Petrov V.A., Sakovich G.V., Brylyakov P.M. Conditions for the conservation of diamonds in the process of detonation production, DAN SSSR, 1990, vol. 313, No. 4, pp. 862-964);

- during charge irrigation with water (RU, 2036835, C1);

- in a water shell (US, 5353708, C1);

- in ice (RU, 2230702, C1).

Of the existing methods of detonating carbon-containing explosives, the most effective from the point of view of KU yield and the actual diamond modification is charge detonation in a water or ice shell (V.Yu. Dolmatov. Ultrafine detonation synthesis diamonds, St. Petersburg, SPbSPU, 2003, 344 pp .; RU, 2230702, C).

At the same time, the obtained KU is a nanosized carbon-containing powder with specific properties and structure. For example, KU is highly dispersed, has a large specific surface area, the presence of defective carbon structures formed, and increased reactivity.

Known synthetic diamond-carbon material (US, 5861349, A), consisting mainly of grouped round and irregularly shaped particles in a diameter range not exceeding 0.1 μ, in which:

a) elemental composition, wt.%: carbon from 75.0 to 90.0; hydrogen from 0.8 to 1.5; nitrogen from 0.8 to 4.5; oxygen - to balance;

b) phase composition, wt.%; amorphous carbon from 10 to 30, diamond of cubic modification - to balance;

c) the porous structure of the material having pores with a volume of 0.6-1.0 cm ³ / gram;

d) the surface of the material with 10-20% of the surface of methyl, nitrite, primary and secondary hydroxyl groups having different chemical shifts in the nuclear magnetic resonance spectrum region and one or more hydroxy carboxyl functional groups selected from the group consisting of carbonyl groups, carboxyl groups, guinone groups, hydroperoxide groups and lactone groups on 1-2% of the surface of the material associated with carbon atoms by uncompensated bonds; and

e) special surface from 200 to 450 gM ² / g.

Moreover, this material is obtained by the method of detonation synthesis in a closed volume of an explosive charge containing mainly a carbon-containing explosive or a mixture of such substances having a negative oxygen balance, while the detonation of the charge is initiated in the presence of carbon particles in a concentration of from 0.01 to 0.015 kg / m ³ in a medium consisting of oxygen from about 0.1 to 6% by volume and a gas inert to carbon, at a temperature of from 303 to 363 K. (US, 5861349, A). The method is carried out in a pressure chamber with a charge having a negative oxygen balance and consisting mainly of at least one carbon-containing solid explosive.

On 10-20% of the surface of the material there are methyl, nitrile, primary and secondary hydroxyl groups, as well as oxycarboxyl and functional groups of the general formula O.dbd.R, where R is this.dbd.COH, .dbd.COOH, .dbd .C. Regulation 6H. position 4 or other combinations thereof, in addition, 1-2% of the surface of the material is occupied by carbon atoms with uncompensated bonds.

Moreover, the parameter — the crystal lattice constant — is a ₀ = 0.3562 ± 0.0004 nm, the content of non-combustible impurities is from 0.1 to 5.0 wt.%.

Moreover, in the obtained material, the X-ray amorphous phase of the obtained material does not contain graphite.

Oxygen-containing functional groups, as a rule, are derivatives of more diverse surface carbon structures, including aliphatic, alicyclic and aromatic. On the surface of the obtained material, both lactone.dbd.COOCO ^- , quinone.O.dbd.C pol. 6H. Perol. 4H.dbd.O, and hydroperoxide.dbd.COOOH groups were identified. The total amount of oxygen-containing surface groups occupied from 10 to 20% of the sample surface.

However, the above method for producing diamond-carbon material has a low yield of diamond-carbon material - 3.1-5.1 wt.% And thus does not allow to obtain a material with high efficiency of high quality, because of the low content of the most important in diamond - carbon material of the element - carbon - the resulting product contains a large number of heteroatoms, mainly oxygen, present in the form of lactone, ether and aldehyde groups, which leads to too high chemical activity of the diamond-carbon material. This fact increases the likelihood of destructive processes in compositions using diamond-carbon material, for example, in polymer and oil compositions, especially at elevated operating temperatures.

The low (from 9.1 to 58.4 wt.%) Content in the resulting condensed carbon of the main component of the nanodiamond - cubic modification diamond - complicates the subsequent chemical purification of the nanodiamond. Moreover, the properties of nanodiamonds are deteriorated due to a significant, ~ 2.3 wt.%, Amount of non-combustible impurities in chemically refined nanodiamonds.

In addition, the aforementioned patent (US, 5861349, A) describes a method for producing material using only one explosive composition — a mixture of trotyl and gesscogen in a ratio of 60/40, respectively, which does not allow to evaluate all the advantages of the above-described method for producing diamond-carbon materials.

A known method of cleaning nanodiamonds obtained by the method of detonation synthesis followed by purification from impurities (RU, 2109683, A) by two-stage processing of detonation products with an aqueous solution of nitric acid: first, 50-99% nitric acid at 80-180 ° C, then 10- 40% nitric acid at 220-280 ° C. The liquid phase process is provided by pressure. However, the implementation of this method does not find wide application because of the high aggressiveness and corrosiveness of the used concentrated nitric acid, the large consumption of the latter, the complexity of the disposal and disposal of gas and liquid wastes.

The closest analogue of the proposed cleaning method is the method for cleaning nanodiamonds described in the literature (Gubarevich T.M., Dolmatov V.Yu. Chemical cleaning of ultrafine diamonds with hydrogen peroxide. Journal of Applied Chemistry, 1992, V. 65, No. 11, p. 2512-2516 ) The method consists in processing detonation products containing nanodiamonds with an oxidizing mixture comprising hydrogen peroxide, nitric acid or a metal salt of variable valency.

The disadvantage of this method is the use of a relatively expensive and scarce oxidizing agent - hydrogen peroxide, the danger of working with such an easily decomposable compound as hydrogen peroxide, which constantly releases too active oxidizing agent - atomic oxygen.

Disclosure of invention

The aim of the present invention is to develop a method for producing nanodiamonds, a safe, reliable method characterized by improved technical, economic and environmental parameters and making it possible to organize on its basis a large-scale production of nanodiamonds with predictable properties and predicted elemental composition at a high carbon content in the desired phase states.

When creating the invention, the task was to develop a method for producing a nanodiamond having a high carbon concentration of the desired modifications and the desired phase composition from a carbon-containing material using detonation synthesis under conditions that prevent oxidation of the surface of the nanodiamond and ensure the safety of the obtained diamond phase.

The problem was solved by obtaining a nanodiamond containing carbon, hydrogen, nitrogen and oxygen, characterized in that the material contains carbon in the form of a diamond cubic modification and in the X-ray amorphous phase in the ratio (82-95) :( 18-5) by weight of carbon, respectively, and it contains, wt.%:

Carbon 90.2-98.0 Hydrogen 0.1-5.0 Nitrogen 1.5-3.0 Oxygen 0.1-4.5.

The problem was also solved by the development of a method for producing nanodiamonds, including detonation of a carbon-containing explosive with a negative oxygen balance in a closed volume in a gas medium inert to carbon, surrounded by a condensed phase and subsequent chemical cleaning, characterized in that the carbon-containing explosive placed is detonated into a shell from a condensed phase containing a reducing agent with a quantitative ratio of the mass of the reducing agent to condensed phase to the mass of the carbon-containing explosive used is not less than 0.01: 1, chemical cleaning is carried out by treating the detonation products with 2-40% aqueous nitric acid together with compressed air oxygen at a temperature of 200-280 ° C and a pressure of 5-15 MPa and at the same time receive a nanodiamond containing, wt.%:

Carbon 90.2-98.0 Hydrogen 0.1-5.0 Nitrogen 1.5-3.0 Oxygen 0.1-4.5

and at the same time in the mass of carbon containing carbon of diamond cubic modification and carbon in the X-ray amorphous phase in the ratio (82-95) :( 18-5) wt.%, respectively.

Moreover, according to the invention, it is advisable to use an inorganic or organic compound, preferably not containing oxygen atoms and halogens, as a reducing agent.

Further, the present invention is illustrated by examples of its implementation, but not limiting the options for implementing the method and not beyond the scope of patent claims.

The best embodiment of the invention

The process of forming a nanodiamond by the method according to the invention, including detonation of a carbon-containing explosive with a negative oxygen balance, surrounded by a condensed phase containing a reducing agent, can be divided into four stages.

1. The first stage of the detonation transformation of a carbon-containing explosive during its explosion mainly occurs within the charge volume limited by its external surfaces, and the features of the environment surrounding the charge do not affect the conversion process.

Studies have shown that the choice of the composition of explosives with a negative oxygen balance leads to the formation of "excess" carbon, which remains in condensed form. Part of this "excess" carbon during the explosion turns into a diamond of cubic modification.

The placement of a charge in an environment in a liquid or solid state of aggregation, for example, during a blast in a pool filled with water or ice, which prevents the detonation products from flying apart, creates conditions for increasing the duration of existence of an ultrahigh pressure and high temperature complex formed upon detonation, which are the region of existence of liquid carbon and diamond.

The placement of a charge inside a shell containing a condensed phase in a liquid or solid state of aggregation, for example, in the form of water, ice, also allows for a longer time to hold the detonation products in the volume of the initial charge, which leads to a longer existence of a plasma containing detonation products, and contributes to more complete transition of "excess" carbon to the diamond phase.

2. In the second stage of the transformation, which occurs after the detonation process is completed, it is very important to ensure rapid gas-dynamic cooling of the detonation products to preserve cubic-modified diamonds formed in the zone of chemical transformations.

It is known that during an explosion in a vacuum, due to the high expansion velocities, the fastest gas-dynamic cooling of detonation products is observed. However, upon subsequent impact of the detonation products on the walls of the explosive chamber, their kinetic energy transforms into thermal energy and the temperature in the chamber rises rapidly, reaching very high values, and after the decay of all shock waves in the chamber cavity, a temperature is established - 3500K, close to the detonation temperature. And since the pressure in the chamber drops many times faster than the temperature, cubic-modified diamonds completely turn (pass) into graphite. Then, with prolonged exposure to high temperatures, the entire KU is gasified. That is why, when exploded in a vacuum, diamonds of cubic modification are not preserved.

The slowest gas-dynamic cooling is observed during the expansion of detonation products surrounded by massive water or ice shells. In this case, the maximum steady-state temperature of detonation products does not exceed 500-800K due to efficient energy extraction by water (RU, 2230702, C; V.A. Mazanov. Macrokinetics of conservation of condensed carbon and detonation nanodiamonds in a sealed explosive chamber. Solid State Physics, 2004, vol. 46, issue 4, p. 614-620).

An explosion in an inert gas medium in terms of gas-dynamic cooling takes an intermediate position between an explosion in a vacuum and an explosion in a shell from a condensed phase in the form of water or ice, since the rate of expansion of detonation products in a gas medium is lower than in vacuum, but more than in the presence of water shell or ice shell.

Since the existence of KU is largely determined by the residual temperature in the blast chamber — the lower the temperature, the higher the yield of diamond-carbon material — the optimal use of condensed shells around the charge, creating the greatest cooling.

3. The third stage of detonation synthesis of diamond-carbon material occurs after the reflection of shock waves from the chamber walls: shock waves propagating at a supersonic speed circulate, accompanied by processes of a sharp increase in matter density, pressure and temperature, and turbulent mixing of the detonation products with the medium in the chamber cavity .

The maximum steady-state temperature of the medium in the chamber cavity depends on the mass ratio of explosives and on the composition of the gaseous medium, i.e., the chemical activity of the medium and the heat capacity of the gases.

4. At the fourth stage of the detonation synthesis process, a medium heated by an explosion of a carbon-containing explosive and bounded by a cold shell is intensively cooled. After the explosion and the release of detonation products in the chamber, in addition to various types of gaseous products (СО ₂ , СО, O ₂ , Н ₂ , N ₂ , СН ₄ , NO, NO ₂ , NH ₃ , Н ₂ О), there is also a highly dispersed suspension of particles KU, which have a large emitting ability. Therefore, the cooling process of such a medium is characterized by the combined transfer of heat by convection and radiation.

It is known that using the method of measuring the conductivity profile in a detonation wave, it was found that the formation time of a diamond cubic modification does not exceed 0.2-0.5 μs, which corresponds to the width of the chemical reaction zone in mixed explosive compositions of trinitrotoluene-hexogen, as in injection molded and extruded (Staver A.M., Ershov A.P., Lyamkin A.I. Investigation of the detonation conversion of condensed explosives by the electrical conductivity method. Combustion and Explosion Physics, 1984, v. 20, No. 3, p. 79 -82).

Since part of the KU solid particles formed at the first stage of detonation is converted to gases under the influence of gaseous oxidizing agents formed during the explosion: СО ₂ , Н ₂ О, СО, O ₂ , N ₂ О ₃ , NO ₂ , we can speak of “preserved particles” of KU which did not have time to gasify, including due to a lack of quantities of these gaseous oxidizing agents.

Since any unreacted solid carbon particles of KU have a functional cover, the interaction of surface functional groups with gaseous oxidizing agents can change the primary functional groups, including those that do not contain oxygen, to oxygen-containing groups, since all oxidizing agents have oxygen in their composition.

In this case, the use of an important function of the reducing agent is to bind the oxidizing agent, preventing the oxidation of carbon, and creates conditions for preventing the oxidation of the surface of carbon particles. This creates the conditions for a substantial increase in the carbon content in the nanodiamond. This increase is achieved precisely due to a decrease in the oxygen content, since studies show that the content of hydrogen and nitrogen varies little.

It should be noted that the high oxygen content in the nanodiamonds prevents its effective use in a number of technologies. For example, when used as an additive to industrial oils, the presence of a large amount of oxygen increases the oxidizing ability of the material.

It is known that when a carbon-containing explosive is blown up in a gaseous medium under conditions of a temperature of 1500 ± 150 K established in the chamber cavity, the KU yield is maximum and equal to ~ 12%. With an increase in temperature in the chamber cavity to 3000-3500K, the KU yield decreases almost to zero (V.A. Mazanov. Macrokinetics of the conservation of condensed carbon and detonation nanodiamonds in a sealed explosive chamber. Solid State Physics, 2004, v. 46, issue 4, s .614-620).

The possibilities of preserving the obtained cubic-modified diamonds and the elemental composition of nanodiamonds depend on the intensity of heterophase endothermic gasification reactions of KU with carbon dioxide (1) and water vapor (2), which can be represented by a single gross reaction (3):

At high temperature, 2 competing processes occur in the chamber cavity: gasification of KU - primarily non-diamond carbon as more active and graphitization of the formed diamonds of cubic modification.

Therefore, the authors considered it appropriate to develop conditions for the synthesis, which would provide minimal possibilities for the influence of detonation products on the product obtained during detonation and the maximum possible rate of cooling of the product to exclude gasification.

According to the invention, the introduction of a reducing agent in the composition of the condensed shell surrounding the charge allows several effects to be achieved:

1. The reducing agent prevents the oxidation of the surface of carbon particles in the third stage of the detonation process, binding oxidizing agents as the most chemically active substances in the chamber cavity. At the same time, the content of the main heteroatom, oxygen, which interferes with the subsequent use of KU, decreases sharply to 0.1%, and its place is occupied by rather inert and non-disturbing hydrogen. The carbon content accordingly increases to 95.2%.

2. Due to the partial decomposition of the reducing agent at high temperatures, a temperature drop occurs in the chamber, which, in turn, reduces the gasification process (reactions 1-3) and “freezes” the phase transition of diamond into graphite.

Thus, the introduction of a reducing agent makes it possible to increase the yield of nanodiamonds by 1.7–2.6 times as compared with the yield of nanodiamonds 3.1–5.1% according to known technology (US, 5681459, A).

As the reducing agent, any inorganic or organic compounds having the properties of a reducing agent, mainly containing no oxygen and halogens and exhibiting pronounced reducing properties, can be used.

The intermediate product obtained as a result of detonation synthesis is a highly dispersed condensed carbon (hereinafter referred to as KU), containing not only nanodiamonds, but also non-diamond carbon in a highly reactive form, subjected to chemical treatment according to the invention.

In relation to non-diamond carbon, nitric acid is a rather active oxidizing agent.

The range of concentrations of nitric acid used for purification of 2-40 wt.% Was established experimentally based on technologically acceptable reaction rates. A decrease in concentration below 2% leads to a decrease in productivity. An increase in the concentration of nitric acid above 40% is impractical, since this increases the amount of acid waste and the corrosiveness of the medium.

If KU is treated only with nitric acid of a concentration of 2-40 wt.%, Subject to other conditions of the technology (t = 200-280 ° C and P = 5-15 MPa), the quality of treatment will be very low, and the purity of the obtained nanodiamond will not exceed 85% .

At a concentration of nitric acid of 2 wt.%, A temperature of 280 ° C should be maintained, a pressure of 12-15 MPa due to compressed air (intrinsic pressure of 2% nitric acid corresponds to 6.5 MPa). The exposure time is 1 hour. The purity of the obtained nanodiamond product is 98.7%.

At a concentration of nitric acid of 40 wt.%, It is sufficient to maintain a temperature of 200 ° C and a pressure of 5 MPa due to compressed air (the intrinsic pressure of 40% nitric acid corresponds to 2.9 MPa). Exposure time 40 min. The purity of the obtained product is 99.2%.

Compressed air provides overpressure and a super-equilibrium oxygen content in the system, as well as a high rate of nitric acid regeneration.

The amount of overpressure of 2-9 MPa created by compressed air provides both physical condition (liquid phase of the system) and a complex material balance between gaseous and condensed components of the system. The interval of the total pressure of the system 5-15 MPa is an experimentally established region of a stable process.

The introduction of compressed air oxygen into the oxidation system creates optimal conditions for the course of the oxidation process. The products of oxidation of non-diamond carbon - CO ₂ , NO ₂ and NO - are released into the gas phase. At the same time, with an excess of oxygen of compressed air in the solution and the gas phase, nitric acid regeneration processes occur according to the scheme:

2NO₂

N₂O₄ 2NO + O ₂

2NO ₂

N ₂ O ₄

4HNO₃ 4NO + 3O ₂ + 2H ₂ O

4HNO ₃

4HNO₃ 4NO ₂ + O ₂ + 2H ₂ O

4HNO ₃

The newly formed nitric acid reacts again with non-diamond carbon.

In addition to non-diamond carbon, the oxidizing system under consideration is able to oxidize and dissolve the main non-carbon impurities in carbon compounds - iron, copper, their oxides, and some carbides.

The present invention can be illustrated by examples of the method of producing nanodiamonds according to the invention, including the production of condensed carbon (CG) and its subsequent chemical processing to obtain nanodiamonds with improved properties.

Usually, mixed carbon-containing explosives are used to synthesize KUs, for example, a mixture of trinitrotoluene with hexogen or octogen with a trinitrotoluene content of 30 to 70%. It is possible to use trinitrotriaminobenzene in a mixture with octogen, hexogen or trinitrotoluene.

For testing as carbon-containing explosives were selected:

- charges from a mixture of trinitrotoluene with hexogen formed by pressing at a pressing pressure of 1500 kg / cm ² in the ratio of 50/50 (examples 1-18) and melting in the ratio of 65/35 (examples 19,20);

- charges from a mixture of trinitrotoluene and HMX, formed by pressing at a pressing pressure of 1500 kg / cm ² in a ratio of 60/40 (example 21);

- charges from a mixture of triaminotrinitrobenzene with octogen formed by pressing at a pressing pressure of 1500 kg / cm ² in a ratio of 50/50 (example 22).

In this case, the charge form was chosen traditional, in the form of a continuous cylinder, the diameter of the cylindrical checkers 48.5 mm, the charge length 167.1 mm.

The charge was detonated using an electric detonator placed at the end of the charge inside it.

A charge of a carbon-containing explosive was placed in the shell of their condensed phase, which is a solution of a reducing agent in water in a liquid aggregate state (examples 1-16, 18, 19, 21, 22) or in an ice state (example 20), or in a shell representing a charge reservation made from a pressed solid reducing agent (Example 17). The mass of the shell ranged from 4.0 to 6.0 kg, and the shells having a liquid state of aggregation of the condensed phase were cylindrical bags made of polyethylene filled with the condensed phase of a reducing agent solution, and the charge was suspended (placed) in the center of the bag. In the case of a solid state of aggregation of the shell using adamantane as a reducing agent, the shell had the appearance of an external charge reservation on all surfaces.

As reducing agents, dimethylhydrazine (examples 1-5, 19), urotropin (examples 6-10, 20-22), ammonia (examples 11-13), urea (examples 14-16), adamantane (example 17), acetonitrile were used (example 18) with various, in the range (0.01-10.0): 1.0, the mass ratios of the reducing agent used and the mass of the carbon-containing explosive used, respectively.

The tests were carried out as follows: the charge in the shell was placed through the upper hatch into an explosive chamber made of stainless steel with a volume of 1 m ³ filled with gaseous products of the previous explosion, the chamber was closed, and the charge was detonated.

3 minutes after the blasting, the resulting aqueous suspension of the product was unloaded through the bottom valve into the receiving tank. The aqueous suspension was then passed through a 200 μm sieve and dried. The dried product was crushed and sieved through a sieve with a mesh size of 80 μm. Then the resulting product was subjected to chemical purification according to the invention.

The resulting product was placed in a titanium autoclave containing 56% nitric acid based on 1 part by weight. The resulting product 20 parts by weight acids. The autoclave was heated to 513K and held at this temperature for 30 minutes. Then the autoclave was cooled, the gases were vented, a suspension of the product in spent weak nitric acid was recovered. Then, the nanodiamonds were washed with distilled water to a pH of 6-7 and dried in air at a temperature of 423K for 5 hours.

Samples of the obtained product were prepared by the preparation method according to the invention for subsequent studies of their elemental composition.

With the help of studies it was found that KU contains from 8 to 14 wt.% Volatile impurities (mainly water, nitrogen oxides and carbon). The removal of such impurities, firmly bound by the adsorption forces in micropores, by conventional heating in air at a temperature of 120-125 ° C is impossible. Raising the heating temperature to higher temperatures in air is dangerous due to decomposition, the possibility of ignition and ignition of non-diamond carbon particles.

To completely remove volatile impurities, a vacuum should be used at a residual pressure of 0.01-10.0 Pa. In this case, the temperature must be maintained in the range of 120-140 ° C.

At a vacuum of 0.01 Pa, it is sufficient to maintain a temperature of 120 ° C, and at a pressure of 10.0 Pa - 140 ° C. A pressure of less than 0.01 Pa is impractical to maintain for economic reasons, and above 10.0 Pa - because of the possible incomplete removal of volatile impurities. An increase in temperature above 140 ° C can cause the decomposition of part of unstable non-diamond carbon. A warm-up time of 3-5 hours also guarantees complete removal of volatile impurities. At a pressure of 0.01 Pa and 120 ° C, 3 hours of exposure is sufficient, and at 10.0 Pa and 140 ° C it is more appropriate to withstand 5 hours.

To determine the elemental composition of a nanodiamond, a standard method of organic chemistry is usually used: the heating temperature in an oxygen stream is 850-900 ° С for 5 s. However, the nanodiamond is very different in its oxidation resistance from any organic compounds. Therefore, the above conditions are not sufficient for the complete oxidation of the elements making up the nanodiamond. The temperature providing complete combustion (oxidation) of the nanodiamond is 1050-1200 ° C, while the warm-up time should be 40-50 seconds. These conditions are achievable, for example, on the device No. 185 of the company "Hewlett Packard" (USA).

The samples were kept at a temperature of 120-140 ° C under a vacuum of 0.01-10.0 Pa for 3-5 hours and then subjected to processing at a temperature of 1050-1200 ° C with a stream of oxygen at a speed that ensured its burning for 40-50 seconds .

Prepared by the method described above, samples of the products of synthesis were subjected to the following studies:

- research using the small-angle scattering method to determine the quantitative distribution of material particles by their size;

- research using polarographic titration to determine the presence and composition of surface oxygen-containing, amine and amide functional groups. In this case, hydroxyl, carboxyl, amine and amide groups are identified by the values of the corresponding reduction potentials, as well as by IR spectroscopy;

- a study using gas chromatographic analysis of the presence of surface methyl groups, identified by the composition of the released gases when heated at a temperature of 663-673K for 3 hours, by the amount of methane released. In this case, the products obtained before gas chromatographic analysis were heated at 473 K in vacuum (0.1 Pa) until a constant weight product was obtained (within 24 hours), while the volatile products, including gases, previously adsorbed on the surface of the obtained product, were removed, and the gases CH ₄ , H ₂ , CO ₂ , CO, O ₂ , N _2, and NH ₃ released during gas chromatographic analysis were gases formed upon the destruction of surface groups chemically bonded to KU;

- research using x-ray photoelectron spectroscopy (XPES) to analyze the distribution of carbon forms in the resulting product;

- research using the method of small-angle scattering (Svergun D.I., Feigin L.A. X-ray and neutron small-angle scattering. M: Nauka, 1986, 280 p.);

- research using the method of determining the specific surface of powders by low-temperature sorption of nitrogen (hereinafter BET) (Gerasimov Y.I. et al. Course in Physical Chemistry. T.1, 2nd edition, Moscow: Chemistry, 1969, p. 592 ) The test results are shown in the Table.

Table
Obtaining nanodiamonds according to the invention by the method according to the invention The components of the method of obtaining No. p / p Example No. Parameters one 2 A. Explosive t Structure Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50 extruded 2 Weight kg 0.5 0.5 3 Density, g / cm ³ 1,62 1,62 B. four Reducing agent dimethylhydrazine dimethylhydrazine Shell 5 The ratio of the mass of the reducing agent to the mass of the explosive 0.32: 1.00 0.01: 1.00 6 Solvent water water 7 Aggregate state of the shell liquid liquid 8 Weight kg 4.0 4.0 B. Received product 9 The output of nanodiamonds,% by weight of explosives 9.1 7.0 10 Elemental composition, wt.%:
[FROM]
[N]
[N]
[ABOUT]
fireproof impurities 96.1
1,0
2.2
0.4
0.3 90.2
5,0
1,5
3.2
0.1 eleven The phase composition of the nanodiamond, wt.%:
- a diamond of cubic modification,
- X-ray amorphous carbon phase 91 85 9 fifteen 12 The content of nanodiamonds in KU 60.0 58.0

Continuation of 1 table 3 four 5 6 BUT. one Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded 2 0.5 0.5 0.5 0.5 3 1,62 1,62 1,62 1,62 B. four dimethylhydrazine dimethylhydrazine dimethylhydrazine urotropin 5 0.16: 1.0 0.64: 1.00 10.0: 1.0 0.01: 1.00 6 water water Water Water 7 liquid liquid liquid Liquid 8 4.0 4.0 4.0 6.0 AT. 9 9.5 10.1 8.6 8.3 10 93.9 94.2 98.0 92.3 1.6 2.9 1,1 2.1 2.5 2.9 1.7 2,3 1,2 0.1 0.1 1.8 0.8 0.9 0.1 1,5 eleven 88 91 95 86 12 9 5 fourteen 12 68.0 63 61 66

Continuation of 2 tables No. 7 8 9 10 BUT. one Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded 2 0.5 0.5 0.5 0.5 3 1,62 1,62 1,62 1,62 B four urotropin urotropin urotropin urotropin 5 0.25: 1.0 0.50: 1.00 1.0: 1.0 10.0: 1.00 6 water water water water 7 liquid liquid liquid suspension 8 6.0 6.0 6.0 6.0 AT 9 10,4 11.5 12.0 11,2 10 94.9 95.2 96.0 97.0 1,1 1,0 0.4 0.7 2.5 2.2 2.6 2.0 1.4 1,5 0.7 0.1 0.1 0.1 0.3 0.2 eleven 90 92 91 95 10 8 9 5 12 71 74 75 69

Continuation of 3 tables No. eleven 12 13 fourteen BUT one Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded B 2 0.5 0.5 0.5 0.5 3 1,62 1,62 1,62 1,62 four ammonia ammonia ammonia urea 5 0.01: 1.0 0.50: 1.00 1.0: 1.0 10.0: 1.00 6 water water water water 7 liquid liquid liquid liquid 8 5,0 5,0 5,0 5,0 AT 9 6.0 6.8 6.4 7.5 10 91.4 92.7 92.1 92.8 2.9 2,4 2.9 1.8 2,8 2.9 3.0 2.2 2.0 1.3 1,2 2.1 0.9 0.7 0.8 1,1 eleven 86 89 91 88 fourteen eleven 9 12 12 52 51 49 58

Continuation of 4 tables No. fifteen 16 17 eighteen BUT one Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded Trinitrotoluene / RDX, 50/50, extruded 2 0.5 0.5 0.5 0.5 3 1,62 1,62 1,62 1,62 B four urea urea adamantane acetonitrile 5 0.4: 1.0 10.0: 1.00 1.4: 1.0 2.0: 1.00 6 water water - water 7 liquid liquid pressed solid liquid 8 5,0 5,0 charge reservation 5,0 AT 9 9.0 5,4 12.6 8.0 10 91.6 90.8 97.2 95.3 1.8 1.4 0.2 1,2 2.5 3,5 2.1 2.2 3.0 4,5 0.2 0.9 1,1 0.3 0.3 0.4 eleven 86 85 95 93 fourteen fifteen 5 7 12 61 40 80 56

Continuation of table 5 No. 19 twenty 21 22 BUT one Trinitrotoluene / RDX, 65/35, fused Trinitrotoluene / RDX, 65/35, fused Trinitrotoluene / Octogen, 60/40, pressed Triaminotrinitrobenzene / Octogen, 50/50, extruded 2 0.51 0.51 0.51 0.53 3 1,64 1,64 1.65 1.71 B dimethylhydrazine urotropin urotropin urotropin 5 0.64: 1.00 0.5: 1.0 0.5: 1.0 0.5: 1.0 6 water water water water 7 liquid ice liquid liquid 8 4.0 6.0 6.0 6.0 AT 9 11.7 12.9 13.3 6.8 10 94.8 95.2 95.9 92.0 1,2 1,1 0.2 2,3 2.9 2.0 2.1 2.6 0.2 1,1 0.8 2,3 0.9 0.6 1,0 0.8 eleven 92 94 93 86 8 6 7 fourteen 12 69 78 79 52

As a result of studies, it was found that the nanodiamond obtained by the method according to the present invention is a powder from light gray to gray.

According to polarographic, chromatographic and IR spectroscopic analysis, the composition of surface functional groups is as follows: hydroxyl, carbonyl, carboxyl, nitrile, amide and methyl groups were found in all samples obtained in the process carried out according to the method according to the invention.

In the X-ray diffraction patterns of the nanodiamond obtained in this way (Cu K _α ), broad symmetric diffraction maxima, well described by the Lorentz contours, were noted at angles 2θ = 43.9; 75.3 and 91.5 °, corresponding to (111) -, (220) - and (311) reflections from the diamond lattice of cubic modification with the lattice parameter a _о = 3.565 ± 0.002 Å. The average size of the obtained nanoparticles is 4.0-5.0 nm, which indicates that the broadening of diffraction peaks is mainly associated not with internal stresses, but with a small particle size.

In the range 2θ = 16 ° –37 °, a strong localized halo is observed, which is characteristic of diffraction by disordered amorphous structures, indicating the presence of an X-ray amorphous carbon phase. Estimation of the thickness of these structures by the half-width of the halo gives 2-4 Å, which is 5-18 wt.% Of the weight of the nanodiamond. In addition, the amount of the amorphous phase was determined from a decrease in the reflection intensity to 220 nanodiamonds of the present invention compared to a sample of pure cubic diamond of natural origin (Yakutia-Sakha, settlement Mirny, Russia). The estimated amount of X-ray amorphous phase is from 5 to 18 wt.%.

The presence of ~ 2.5 wt.% Nitrogen in the amorphous phase was determined as follows.

A portion of the nanodiamond obtained by the method according to the present invention was heated at a temperature of 473K for 20 hours under a vacuum of 0.1 Pa to constant weight. Then, various parts of this sample of the nanodiamond were subjected, in turn, to deep extraction with various solvents at temperatures of 473-573 K under pressure for 30 minutes. Used solvents: normal structure - heptane, dean; aromatic - benzene, toluene, and alicyclic - cyclohexane hydrocarbons, hydronaphthalenes - tetralin and decalin. After this treatment, the ratio of the diamond phase of carbon, which under these conditions does not change, and the amorphous phase, which decreased, has changed. The weight of the nanodiamond samples decreased by ~ 5 wt.%. Only nitrogen-containing heterocyclic aromatic compounds with the number of cycles from 1 to 4 and with the nitrogen content in the rings from 1 to 2 passed into the solution of the above solvents. No other heteroatoms in any form were found in the extracts. After extraction, the IR spectra in the nanodiamond showed the same surface oxygen, hydrogen, and nitrogen containing groups that were before the extraction. Thus, nitrogen in the form of heterocyclic compounds was almost certainly delivered from the intermediate layer — from the X-ray amorphous phase of carbon.

Moreover, the complexity of the structure of the X-ray amorphous phase of carbon in a nanodiamond is also demonstrated by the fact that when similarly prepared nanodiamond samples according to the invention (mode: 473K, 20 hours, 0.1 Pa) were subjected to thermal desorption under mild conditions (mode: 573K, 2 hours, 0.001 Pa), the composition of the desorption products was very diverse: acetonitrile, nitromethane, butanon-1-one and butanon-2-one, tetrahydrofuran, ethyl acetate, benzene and homologues, alkylbenzene (C ₉ and C ₁₀ ), alkanes (C ₇ -C ₁₁ ), alkenes (C ₇ - C ₁₀ ), terpen (C ₁₀ ) and naphthalene (C ₁₀ ).

At 573 K, partial destruction of the external functional groups occurs with the formation of nitromethane, butanones, tetrahydrofuran, ethyl acetate, presumably acetonitrile. However, the main number of identified compounds: benzene and homologs, alkanes, alkenes, terpene and naphthalene, which have a special nature of their structure, can be formed only upon destruction of the X-ray amorphous phase of carbon, which confirms the fact that the weight loss of the samples after thermal desorption amounted to ~ 8 wt.% .

The temperature of the onset of oxidation of nanodiamonds in air — the gasification temperature measured on a derivatograph at a heating rate of 10 deg / min — is 473 K, and a small exo effect continues until it is heated to 800 K. In this case, all non-diamond - X-ray amorphous - carbon is oxidized. The drop in sample weight in this case is 5-18 wt.%, Which corresponds to the amount of X-ray amorphous carbon in the nanodiamond.

After heating above 800K, a strong exoeffect begins, indicating the reaction of atmospheric oxygen with the actual diamond core of the nanodiamond, which ends at a temperature of 1050K with complete oxidation (burning) of the nanodiamond. The maximum heat release (maximum oxidation) occurs in the temperature range 930-990K.

For comparison, studies were carried out of crystalline crystals of static synthesis (hereinafter AFM), crushed to particles with a size of 2-100 nm (with an average diameter of 20 nm), placed in similar conditions. Studies have shown that the temperature at which oxidation of a diamond crystal begins is 785K, and the maximum oxidation temperature is 890K. The process of complete oxidation of the AFM is completed at a temperature of 1060K.

Thus, the oxidation stability of the actual diamond is practically the same for both the nanodiamonds of the present invention and classical synthetic diamonds.

In a nanodiamond obtained by the method according to the closest analogue, the oxidation of the diamond core begins already at a temperature of 703K.

Each HA particle according to this invention represents a complex structural formation, including, as the required constituent elements:

- a core of carbon atoms sp ³ hybridized, bonded into a cubic crystalline structure characteristic of diamonds; the nucleus covers 82-95% of carbon atoms and according to x-ray diffraction data has a size of 40-50 Å; the core has ~ 2.5 wt.% nitrogen, mainly in the form of substitution atoms;

- a transitional carbon shell around the nucleus, consisting of X-ray amorphous carbon structures 2-4 Å thick, which may include 5-18% of the carbon atoms of the particle. The shell consisting of carbon in sp ² hybridization is heterogeneous. The inner layer of this shell, directly adjacent to the core, consists of onion-like carbons continuous carbon layers (on top of them are fragmentary graphite-like monolayers (“aromatic clusters”).

This amorphous carbon shell has a porous structure, contains numerous defects, includes a small number of heteroatoms (primarily, ~ 2.5 wt.% Nitrogen), which entered the shell structure during detonation synthesis;

- surface layers, including, in addition to carbon atoms, and other heteroatoms that form the spectrum of different functional groups (hydroxyl-carbonyl, carboxyl, nitrile and methyl groups). The total number of heteroatoms in the particle - nitrogen, hydrogen and oxygen - is from 2.0 to 9.8 wt.%.

Thus, it was found that the nanodiamond particles are not a purely carbon material, and the carbon itself is in the product at the same time in several modifications, and only one of them corresponds to the structure of the diamond.

The outer shell of a nanodiamond particle determines its relationship with the environment. It is she who forms the phase boundary and participates in the interaction with it. The presence on the surface of highly polar and reactive groups concentrated in a small volume determines the sufficient activity of the impact of nanodiamond particles on the environment.

The nanodiamonds obtained according to this invention are a unique material due to their transitional nature from an inorganic product to an organic one, and this is what determines their special position among ultrafine materials.

Industrial applicability

The nanodiamond obtained by the method according to the invention allows it to be used as a nanoscale component of highly effective composite materials, in the form of additives that improve the performance properties of structures — wear resistance, strength, and resource — more than when using nanodiamonds known from the prior art described above.

The nanodiamonds according to the invention can find wide application in various technologies, for example, in polishing and finishing compositions, film coatings, as part of radiation-resistant materials.

Nanodiamonds according to the invention can be obtained by the method according to the invention, which can be carried out using existing processing equipment and known explosives.

Claims (3)

1. Nanodiamond containing carbon, hydrogen, nitrogen and oxygen, characterized in that it contains carbon in the form of a diamond cubic modification and carbon in the X-ray amorphous phase in the ratio (82-95): (18-5) wt.% By weight of carbon, respectively, and it contains, wt.%:
Carbon 90.2-98.0 Hydrogen 0.1-5.0 Nitrogen 1.5-3.0 Oxygen 0.1-4.5 2. A method of producing a nanodiamond, including detonation of a carbon-containing explosive with a negative oxygen balance in a closed volume in a gas medium inert to carbon, surrounded by a condensed phase and subsequent chemical purification, characterized in that the carbon-containing explosive placed in a shell of condensed is detonated the phase containing the reducing agent, with a quantitative ratio of the mass of the reducing agent in the condensed phase to the mass of the carbon-containing explosive is not less than 0.01: 1, chemical purification is carried out by treating detonation products with 2-40% aqueous nitric acid together with oxygen of compressed air at a temperature of 200-280 ° C and a pressure of 5-15 MPa, and nanodiamonds are obtained containing, wt.%:
Carbon 90.2-98.0 Hydrogen 0.1-5.0 Nitrogen 1.5-3.0 Oxygen 0.1-4.5
and at the same time in the mass of carbon containing carbon of diamond cubic modification and carbon in the X-ray amorphous phase in the ratio (82-95) :( 18-5) wt.%, respectively. 3. The method according to claim 2, characterized in that as the reducing agent use an inorganic or organic compound, preferably not containing oxygen atoms and halogens.