RU2556763C2 - Method of synthesising ultradispersed diamonds - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to synthesis of diamond nanoparticles, which can be used in various fields of technology. Claimed method of synthesis of ultradispersed diamonds includes generation of carbon plasma from carbon-containing substance and its condensation with cooling liquid under conditions of cavitation. As plasma-generating substance any hydrocarbon gas or organic carbon-containing liquid, including one which additionally contains substances, containing heteroatoms, as well as dispersions of carbon particles of non-diamond allotropic shape in organic fluids or water, can be used. Flow of liquid inside flow cavitation apparatus, providing additional cavitation impact on cooling liquid, is used as cooling liquid.

EFFECT: invention makes it possible to increase energy efficiency of realised synthesis of nanodiamonds and provides possibility of managing properties of synthesised nanodiamonds.

3 dwg, 1 tbl

Description

The invention relates to the synthesis of diamond nanoparticles (or, according to the more traditional name in domestic literature, ultrafine diamonds), which can be used in materials science to create various kinds of nanocomposites, in catalysts, as anti-wear additives for oils, in cosmetology and pharmacology.

The conversion of various forms of carbon into diamond is known at a pressure of the order of 100,000 kg / cm ² [1]. The essence of the method is the 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. The disadvantage of this method is that the process can be carried out only in batch mode and requires quite cumbersome equipment. In addition, the resulting synthesis product, along with particles of nanodiamonds, contains particles of amorphous carbon (soot) and requires a purification and enrichment operation.

A known method and device for plasma-chemical synthesis of nano-objects [2]. The method consists in creating a plasma by passing a plasma-forming gas through an electric arc with the exit of the plasma through a nozzle into which the source dispersed material is introduced. In this case, the plasma is exposed to a high-frequency field, while a flow of a cooling inert gas is supplied to the region between the reaction zone and the water-cooled chamber. In addition, a catalyst is additionally introduced into the plasma by evaporation of the cathode, which is transferred as it evaporates.

The disadvantage of the analogue is the complexity of the equipment for its implementation, and the need to use catalysts.

A known method for producing carbon-containing nanoparticles [3], including the formation of a plasma jet (gaseous hydrocarbons are used as a plasma-forming substance) using a plasma torch and introducing the jet into the volume of liquid hydrocarbons. The disadvantage of this method is the fire hazard due to the combined use of plasma and hydrocarbons in combination with an ill-conceived method of introducing a plasma jet into the volume of hydrocarbons that do not completely exclude mixing with oxygen, or requiring the implementation of expensive technological measures aimed at preventing accidental fire.

The known method [4], which is closest to the patented one, is based on introducing a plasma jet into water with a velocity of its outflow from a nozzle of the order of 100 m / s. Ethyl alcohol or its aqueous solution is used as a plasma-forming substance. Due to the large gradients of velocities and temperatures, explosive vapor and vortex formation in the water volume in the zone of contact with the plasma, cavitation bubbles form, inside which the carbon atoms contained in the plasma fall as a product of the decomposition of alcohol molecules. When the bubbles collapse at a pressure of more than 10,000 kg / cm ² , nanodiamonds are formed in accordance with the phase diagram of carbon, which are concentrated in water in the form of a suspension.

The disadvantage of the method [4] is that as a plasma-forming substance, it is assumed to use alcohol in which the content of carbon atoms is low, thereby the synthesis process is less efficient than if raw materials were used in which the percentage of carbon atoms in the molecule is higher. In addition, the process does not allow changing the synthesis conditions, thereby changing the characteristics of the resulting nanoparticles, optimizing their properties for a particular area of their application.

The technical result of the claimed invention is the ability to increase the energy efficiency of the realized plasma-chemical synthesis of nanodiamonds and the ability to control the properties of the synthesized nanoparticles, changing the technological parameters of the synthesis process.

Figure 1 shows a photograph of a laboratory installation that implements this invention. Figure 2 shows a typical result of determining the size of nanoparticles by dynamic light scattering. Figure 3 shows a typical X-ray diffraction pattern (X-ray diffraction analysis) for one of the obtained nanodiamond samples.

The technical result is achieved due to the fact that in the proposed method it is possible to use any carbon-containing substance as a plasma-forming substance. As such a substance can be hydrocarbon gases, organic liquids, including additionally containing substances having heteroatoms, dispersions of amorphous carbon particles (soot) in organic liquids or water, and at the same time, cooling and condensation of the carbon plasma by the flow of the cooling liquid inside the jet cavitation apparatus of the hydrodynamic type, providing additional cavitation effect on the cooling liquid, is provided.

The synthesis of ultrafine (nano-) diamonds is as follows. Plasma-forming carbon-containing substance, which can be any hydrocarbon gas or organic liquid, as well as dispersions of carbon black particles in organic liquids or water, is passed through a plasmatron, with the formation of a plasma with a high content of carbon atoms.

The plasma jet is carried away by the flow of coolant inside the jet cavitation apparatus of the hydrodynamic type, which provides additional cavitation effect on the coolant.

Upon contact of a carbon-containing plasma, the condensation of carbon atoms into individual clusters occurs. Diamond is a metastable form of carbon. The transition of other allotropic modifications of carbon to diamond is possible under shock wave loading of its particles along the characteristic fracture of the shock adiabat of graphite. Such loading is possible if plasma condensation is accompanied by cavitation phenomena, which is described in detail in [4]. The cavitation phenomenon arises both in the case when the plasma jet is directed into the stationary volume of the liquid and in the case when there is no additional effect on the liquid causing the cavitation. However, in addition, the cavitation effect on the flow of coolant can significantly minimize the size of the installation, to conduct the process in a closed system without the use of a protective atmosphere. Also, changing the intensity of cavitation exposure (for flowing jet devices), it is enough to change the volume of coolant supply.

The choice of a plasma-forming substance from the point of view of the possibility of diamond formation is not fundamental and is based on ensuring the maximum energy efficiency of the process, the availability of one or another raw material, or taking into account the need to obtain diamond nanoparticles with certain properties. The higher the percentage of carbon atoms in the plasma-forming substance, the greater the number of nanodiamonds can be obtained by spending the same amount of energy. In addition, if it becomes necessary to synthesize nanodiamonds containing heteroatoms, it is possible to use mixtures of, for example, hydrocarbons with substances containing heteroatoms as a plasma-forming liquid. In particular, for diamonds containing nitrogen heteroatoms, it is advisable to use acetonitrile as an additive, and in the case of silicon atoms, tetraethoxysilane. In General, the choice of plasma-forming substances is not fundamental in terms of the possibility of obtaining nanodiamonds according to the claimed method and does not limit the invention. The choice of coolant, which is determined either by economic feasibility (water) or by imparting certain properties to the surface of diamond nanoparticles, is also not fundamental.

The use of one type or another of a plasmatron or a cavitation flow apparatus is unprincipled from the point of view of the invention, since it does not matter how the plasma will be obtained and how the cavitation effect on the fluid flow will be created.

To confirm the claimed technical result, a simple laboratory setup was constructed and a number of syntheses were carried out. The setup included an arc plasmatron and flow-through cavitation apparatus of a hydrodynamic type. Particle size was determined by dynamic light scattering, and the content of heteroatoms in the composition of the nanoparticles was confirmed by elemental analysis. The primary identification of diamonds was carried out by irradiating the dispersion with ultraviolet light (diamonds fluoresce, in contrast to other allotropic forms of carbon). For more accurate identification, the method of x-ray diffraction analysis was used. Data on a series of experiments are presented in table 1.

Table 1 No. Plasma-forming substance Coolant The yield ^{* of} diamond product, g / hour The average particle size, nm one Methane water 36.1 5 2 Propane-butane fraction water 38.5 7 3 Diesel oil fraction water 43,4 eleven four Diesel oil fraction diesel oil fraction ^** 47.2 fourteen 5 Diesel oil fraction + 12% carbon black water 45.8 16 6 Water + 62% carbon particles (finely divided activated carbon powder) water 43.6 12 7 Ethanol water 39.9 6

8 Ethyl alcohol + 2.3% tetraethoxysilane water 38.4 ^*** 8 9 Acetone + 1.5% acetonitrile water 37.1 ^**** 12 ^* yield of dry powder after evaporation of the dispersion of particles in the coolant; ^{** the} surface of the isolated particles had pronounced lyophilic properties and was easily dispersed in organic solvents; in Example 3, the particles showed more hydrophilic properties; ^{*** the} content of silicon atoms is 0.98%; ^{**** The} content of nitrogen atoms is 0.54%.

An experiment was also carried out that implements the method [4]. The cost of electricity for the power of the plasmatron, referred to the productivity of the plant for nanodiamonds, for the proposed method amounted to 0.87 (according to example 7 of table 1) compared with the prototype [4].

Thus, the above data confirm the reliability of the claimed technical result.

Information sources

1. RU 2359902, C01B 31/06.

2. RU 2371381, 2009.

3. B11283 C01B 31/00, 2008.

4. RU 2484014 C2 (prototype).

Claims (1)

A method for the synthesis of ultrafine diamonds, including the formation of a carbon plasma from a carbon-containing substance and its condensation by a cooling liquid under cavitation conditions, characterized in that any hydrocarbon gas or organic carbon-containing liquid can be used as a plasma-forming substance, including additionally containing substances containing heteroatoms, as well as dispersions of non-diamond allotropic carbon particles in organic liquids or water, and a fluid stream inside a flowing cavitation apparatus that provides additional cavitation action on the cooling fluid is used as a cooling fluid.

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