Gas-phase process of manufacturing diamond nanoparticles

FIELD: carbon materials.

SUBSTANCE: weighed quantity of diamonds with average particle size 4 nm are placed into press mold and compacted into tablet. Tablet is then placed into vacuum chamber as target. The latter is evacuated and after introduction of cushion gas, target is cooled to -100оС and kept until its mass increases by a factor of 2-4. Direct voltage is then applied to electrodes of vacuum chamber and target is exposed to pulse laser emission with power providing heating of particles not higher than 900оС. Atomized target material form microfibers between electrodes. In order to reduce fragility of microfibers, vapors of nonionic-type polymer, e.g. polyvinyl alcohol, polyvinylbutyral or polyacrylamide, are added into chamber to pressure 10-2 to 10-4 gauge atm immediately after laser irradiation. Resulting microfibers have diamond structure and content of non-diamond phase therein does not exceed 6.22%.

EFFECT: increased proportion of diamond structure in product and increased its storage stability.

2 cl

 

The invention relates to the field of materials science, and in particular to methods of producing filamentary and fibrous materials. More specifically it relates to methods for filamentous structures of solids, in particular diamond, nanometer size in the gas phase.

It is known that almatadema threads micron diameter are prepared by the methods of chemical synthesis of microcrystalline diamond films (so-called methods of chemical vapor deposition) on the surface of the solid filaments (wires) of other material (Rmow et al. CVD diamond-coated fibres. Diam. Relat. Mater., v. 4, no. 5-6, pp. 794-797, 1995). The method does not allow to obtain filaments with diameter less than 10 microns and is characterized by low efficiency and high cost associated with using the procedure of synthesis of diamond coating. Obtained in this way threads are chemically heterogeneous structures consisting of diamond shell with a core of foreign material. In some cases (for example, a metal basis) of the core can be removed by chemical etching (.G.Partridge et al. Chemical vapour deposited diamond fibres: manufacture and potential properties. Mater. Sci. Technolog., v.10, no. 3, pp.177-189, 1994), receiving hollow chemically homogeneous diamond thread, but this process is very slow and getting long diamond fibers with a small diameter is difficult.

A known method of producing filaments of solid particles is the first material, based on the phenomenon of the growth of one-dimensional structures in the gas phase by laser ablation (vaporization) of solids in the presence of a constant electric field (..Lushnikov et al. Aerosol-aerogel transition. J. Aereosol Sci., v. 22, Suppl. 1, pp. S191-S194, 1991), selected as a prototype. In this method, the target of Ti, Fe or Ag is affected by the laser pulse with a capacity of 70 J and a duration of 1 MS (the density of radiation is 106-107W/cm2(A. A. Lushnikov et al. Aerosol-aerogel transition. J. Aereosol Sci., v. 22, Suppl. 1, pp.S191-S194, 1991)) in the cell filled with buffer gas. Near the target using two electrodes form an electric field 100-200/see laser vaporization of the target material, the formation of aerosol nanoparticles and their subsequent aggregation in the form of threadlike structures and fibers oriented along the electric field in the space between the electrodes. The particle size is ~20 nm, the diameter of the fibers to 30 μm, fiber length ~1 cm, the formation of the fibers of ~102(A.A.Lushnikov et al. Aerosol-aerogel transition. J.Aereosol Sci., v. 22, Suppl. 1, pp.S191-S194, 1991). As targets can be used in a variety of materials, however the method is based on the evaporation of a substance (education ionized nonequilibrium plasma) and the crystalline structure of the particles threads may not correspond to the structure of the target. In particular, the method is not applicable to diamond, because it produces is presented in this case, the threads are composed of particles of amorphous carbon or graphite.

The technical task of the present invention is to provide a method of producing filaments of solid nanoparticles, making use of the diamond material, as well as increasing the mechanical strength of the threads.

These goals are achieved by the preparation of the target by pressing a powder of nano-diamond particles (Patent RF 2051093, BI No 36, 1995, Ametuer, Aiyin, Nwholesale, Ehapter. The way to obtain diamonds. Auth. mon. The USSR, N 1165007 (01.07.82)) on the air, cooling the target in the chamber to a temperature below the condensation temperature, but above the melting temperature of the buffer gas by keeping to the increased weight of the target to 2.0 to 4.0 from the start prior to exposure to laser irradiation, and the effect on the target by laser radiation with power, causing heating of the nanodiamond particles is not more than 900°that provides a sputtering target in the form of the original diamond nanoparticles without changing their crystal structure, as well as an overlap in the vapor chamber of polyvinyl alcohol to a pressure of 10-2-10-4ATM immediately after exposure to laser irradiation, which increases the mechanical strength of the fibers by increasing the strength of the interparticle interactions.

As a diamond-like substance used powder ultradispersed diamond (UDD) [6], resulting from the detonation of an explosive mixture trochilus RDX in a 1:1 ratio in an explosion chamber, filled with carbon dioxide. Powders UDA was extracted from the condensed carbon products of the explosion sequential chemical treatment in concentrated and dilute acid to remove non-diamond forms of carbon and metallic impurities. Physico-chemical properties of UDD characterized by a set of analytical techniques, including x-ray structural analysis, spectroscopy Raman scattering, mass spectrometry and electron microprobe elemental analysis, infrared spectroscopy. The samples represent carbon dielectric material with a crystalline structure of diamond. The average crystallite size of ~4 nm. The specific surface of the powder 280 m2/g part UDA includes: oxygen - up to 10%, the nitrogen and hydrogen to 1%, other impurities - a total of up to 2%.

The invention is illustrated by the following examples.

Example 1.

A portion of the UDD powder (0.1 g) with an average size of diamond particles of 4 nm were loaded in the press form and was preparing a tablet with a diameter of 0.6 cm and a thickness of 0.15 cm by pressing under a load of 800 ATM. The obtained target was placed in a vacuum chamber equipped with optical Windows for the input laser beam and monitoring the growth of the threads using the external optical microscope. The target was mounted on the holder, equipped with a system of cooling to cryogenic temperatures. In ka is este radiation source used He-Ne laser at a wavelength of 0,69 µm with a capacity of 10-100 J, pulse duration of 1 MS and a beam diameter of ~1 mm of the Axis of the laser beam was perpendicular to the target surface. At a distance of 2 cm from the target in the camera had two metal electrodes on both sides of the axis of the laser beam and parallel to it to create the electric field intensity 100-1000/see the Distance between the electrodes was 1 cm After evacuation of the chamber were filled with carbon dioxide to a pressure of 0.5 ATM. As the buffer gas can be any gas that is not an oxidizer (such as oxygen, water vapor) carbon, nitrogen, inert gases, etc. the Use of hydrocarbons is also undesirable due to the potential for uncontrolled laser-stimulated reactions. The target was cooled to a temperature of -100°that is less than the condensation temperature of carbon dioxide, and maintained during the time required to raise a weight target of 2.0-4.0 times. Such extracts, depending on the type of gas and the temperature of the target, determine independently in the adsorption experiments using thermogravimetry. In this case it was 20 min and was increased target mass 3.2 times. The electrodes Podwale constant voltage of 300 V and irradiated the target with a laser pulse with a power beam 20 J. beam Power is set such that it is, on the one hand, provided abrazilian, as in the prototype, on the other hand, did not lead to the heating of the particles nd more than 900° (beginning-of-change of the crystal structure of nanodiamonds (Aposhian, Spivakov. The electrophoretic method of obtaining filaments of solid nanoparticles. The application for an invention patent of the Russian Federation No. 2001135443/12, prior. 28.12.01, Paul. Resch. 24.10.02). In various specific conditions of the method, the upper limit power estimate based on the maximum temperature of heating the sprayed particles from a laser beam power. This dependence, in turn, is determined experimentally using calibration measurements based on comparative mass spectrometric study of the properties of nanodiamonds (the surface composition of the particles) after heating to various temperatures and after exposure to laser radiation with different capacity. Under these conditions, the method estimated the maximum temperature of heating was 650°C.

The formation of filaments between the electrodes in several minutes and their growth rate is controlled using an optical microscope. After the formation of the filaments were removed from the chamber and examined their properties using scanning electron microscope and structure-sensitive methods.

When the target temperature above the condensing temperature b the atmospheric gas is unable to achieve the desired increase in weight of the sample by adsorption of gas in the pores between the nanoparticles. If the mass of the condensed gas is less than 2.0 from a target mass of the spray pattern is achieved only at high power of the laser beam, resulting in heating of the particles over 900°With the destruction of the diamond patterns and even to the evaporation material particles. With a weight of more than 4.0 thread is not formed, since the outer surface of the target condenses a thick layer of molecules, preventing the dispersion in the form of separate particles of nd. For sputtering the target material is necessary in this case large beam power, which in turn leads to the destruction of the diamond structure of particles. When the power of the laser beam, causing heating of the particles of nanodiamond over 900°With formed threads consist of carbon particles, the surface layers which have a non-diamond crystal structure and the proportion of the diamond faction in the threads is reduced. In particular, when heating to 900°crystal structure of the sprayed particles corresponds to the diamond structure of the particles of the target, when heated to temperatures of 1000, 1200 and 1400°With the share of non-diamond phase in the sprayed material is increased to 6, 22 and 58%, respectively.

Example 2.

Operations are performed as in example 1, but immediately after laser irradiation on the target in the camera putting a pair of polyvinyl alcohol (or other non-ionic polymer type butyral, poly is Grilamid) to a pressure of 10 -2-10-4ATM. Adsorption of polymer molecules on nanomatrix particles leads to the strengthening of ties between the particles during the growth of the threads (including due to the increased reactivity “svezheubrannyh” diamond nanoparticles. Polymer molecule in this case act as a cohesive environment. Thus obtained filament stable after one month of storage. At a pressure of less than 10-4ATM thread is still fragile, because not all particles have time to adsorb molecules during formation of filaments (seconds to minutes). At pressures above 10-2ATM the share of diamond phase in the threads becomes less than 50% by increasing the amount of polymer used.

1. The method of producing microfibers of solid particles in the gas phase, is the impact of pulsed laser radiation on solid target in the cell with a buffer gas in the laser power, sufficient for thermal sputtering of the target material, and creating a constant electric field near the target using two electrodes to aggregation sprayable material into filaments, characterized in that as a target using compressed air nanodiamond powder, prior to exposure to laser irradiation, the target is cooled to a temperature below the condensation temperature of the buffer gas and withstand what about the weight gain target to 2.0 to 4.0 from the start, and impact on the target of laser radiation with power, causing heating of the nanodiamond particles is not more than 900°C.

2. The method according to claim 1, characterized in that immediately after exposure to laser training at the camera putting a pair of polyvinyl alcohol to a pressure of 10-2-10-4bar.



 

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SUBSTANCE: weighed quantity of diamonds with average particle size 4 nm are placed into press mold and compacted into tablet. Tablet is then placed into vacuum chamber as target. The latter is evacuated and after introduction of cushion gas, target is cooled to -100оС and kept until its mass increases by a factor of 2-4. Direct voltage is then applied to electrodes of vacuum chamber and target is exposed to pulse laser emission with power providing heating of particles not higher than 900оС. Atomized target material form microfibers between electrodes. In order to reduce fragility of microfibers, vapors of nonionic-type polymer, e.g. polyvinyl alcohol, polyvinylbutyral or polyacrylamide, are added into chamber to pressure 10-2 to 10-4 gauge atm immediately after laser irradiation. Resulting microfibers have diamond structure and content of non-diamond phase therein does not exceed 6.22%.

EFFECT: increased proportion of diamond structure in product and increased its storage stability.

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