RU2569548C2 - Method of production of arrays of carbon nanotubes with controllable surface density - Google Patents

Abstract

FIELD: nanotechnology.

SUBSTANCE: invention can be used in the manufacture of sorbents and reinforcing additives. First, the growth substrate is prepared by applying on its surface of the nanodisperse particles of the catalyst with the condensation of the colloidal solution microdroplets under the influence of ultrasound. During condensation the growth substrate is additionally sonicated using the ultrasonic generator of 25-40 W. The prepared substrate is placed in a growth furnace, acetylene is fed to the reaction zone, and the arrays of carbon nanotubes are grown on the substrate, which surface density increases with the increase in power of ultrasonic generator influencing on the substrate.

EFFECT: increase in efficiency of the method.

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Description

The invention relates to a catalytic method for the production of carbon nanotubes from hydrocarbons, is intended for growing arrays of carbon nanotubes. It can be used in the production of sorbents, reinforcing additives, etc.

A known method of producing carbon nanotubes by thermocatalytic decomposition of acetylene with the participation of nanodispersed particles of iron and nickel placed on the surface of substrates of single-crystal silicon [1]. The disadvantage of this method is the impossibility of producing carbon nanotubes, as well as their large scatter in diameter and uneven distribution over the surface of the substrate.

A known method of producing carbon nanotubes by catalytic decomposition of acetylene with the deposition of carbon on cobalt-filled mesoporous substrates of anodized alumina [2]. The disadvantages of the method are the rather large scatter of the resulting nanotubes in diameter, the relatively low uniformity of the distribution of the tubes over the area of the substrate, the lack of reproducibility of the process in individual sections of the substrate.

The closest technical solution, selected as a prototype, is a method of applying anticorrosive coatings on the protected surfaces of metals by plasma spraying, vacuum evaporation or deposition from the gas phase with simultaneous ultrasonic action on the metal [3]. The disadvantage of this method is that the ultrasonic effect on the metal when applying anti-corrosion coatings on the surface to be protected leads to uncontrolled filling of surface irregularities, pores, cracks, which leads to an uneven distribution of the applied material over the surface. The unevenness of the protective coating is determined by the use of ultrasonic exposure in the frequency range corresponding to the frequencies of the natural vibrations of the metal and leading to the appearance of resonance. This method does not allow the controlled application of metal nanoparticles on the surface of the growth substrate without filling cracks, bumps, not a continuous layer. Using this method to obtain arrays of carbon nanotubes is impossible.

The invention is directed to obtaining arrays of carbon nanotubes on the surface of a growth substrate.

This is achieved by the fact that before placing the growth substrate in the furnace and growing arrays of carbon nanotubes, the catalyst is deposited on the substrate by condensation of microdrops of a colloidal solution upon exposure to ultrasound, while ultrasound additionally acts on the growth substrate during the condensation process, and the power of the ultrasonic generator is set ranging from 25 to 40 watts.

A method of obtaining arrays of carbon nanotubes is carried out in the following way. A growth substrate with a previously cleaned prepared surface is fixed above the free surface of a colloidal solution consisting of catalyst nanoparticles and a liquid solvent, the type of solvent and catalyst, as well as their quantitative ratio in the solution, being set in advance, taking into account the task. Under the influence of ultrasound, steam is formed above the surface of the colloidal solution, the microdroplets of which contain catalyst nanoparticles. Once in the colder zone above the substrate, the vapor condenses on the surface of the growth substrate in the form of microdrops. During the condensation process, the growth substrate is additionally exposed to ultrasound with the power of the ultrasonic generator in the specified limits. Then, the growth substrate is placed in a furnace, heated to the temperature of growing carbon nanotubes, and carbon nanotubes are grown.

The use of ultrasonic action on the growth substrate during the condensation process is determined by the fact that in the microdroplets of a colloidal solution condensing on the surface of the growth substrate, catalytic nanoparticles coagulate and sediment continuously, and the effect of ultrasound on the growth substrate minimizes the negative consequences associated with these processes. Those. the effect of ultrasound on the growth substrate allows catalytic nanoparticles to be placed on its surface with maximum uniformity by maintaining a uniform distribution of nanoparticles in the volume of deposited microdrops throughout the process, up to the complete evaporation of the solvent.

The power of the U3 generator, set in the range from 25 to 40 W, is determined by the fact that in this interval, by varying the specific power of the ultrasonic generator, it is possible to control the deposition of catalytic nanoparticles. At lower than 25 W power values, clusters of catalytic nanoparticles in the form of lumps and regions with different nanoparticle densities are formed on the surface of the growth substrate, i.e. the uniformity in the distribution of catalytic nanoparticles on the surface of the growth substrate is violated, and it is not possible to obtain the required surface density of the arrangement of particles on the substrate. At a power value greater than 40 W, a significant part of the catalytic nanoparticles detaches from the surface of the growth substrate and, as a result, the process of controlled deposition of nanoparticles becomes impossible.

Using the proposed method allows to obtain arrays of carbon nanotubes with controlled surface density.

Examples of the method

Example 1

As a growth substrate, plates of monocrystalline silicon of the {111} orientation of the ECBD type were used. Nickel nanopowder with a purity of 99.99% with average particle diameters of 20 to 80 nm was used as a source of metal catalyst catalyst nanoparticles.

An ultrasonic bath of the ULTRASONIC CLEANER CT-400D type was used to treat the colloidal solution with ultrasound. Distilled water was used as a solvent.

The deposition of nanosized particles of the metal catalyst on the growth substrate was carried out as follows. A growth substrate with a washed and degreased surface was fixed above the bath with a colloidal solution of the required concentration. Then the colloidal solution was subjected to ultrasound for 60 s with a generator power of 30 watts. The power of the ultrasonic generator that affects the growth substrate during the condensation process was set at 25 watts. Then the substrates were placed in an oven until the liquid was completely removed. Then, the prepared substrates were placed in a growth furnace, gaseous acetylene C ₂ H _{2 was} fed into the reaction zone, and CNTs were grown. The growing time ranged from 10 to 15 minutes, depending on the required length of carbon nanotubes. The surface density of the grown arrays of carbon nanotubes was 1.21 × 10 mm ^-2 . The resulting nanotubes had a diameter of 80 ± 1 nm and a length of ~ 800 nm to ~ 3 μm.

Example 2

The implementation of the invention was carried out analogously to example 1, but the power of the ultrasonic generator, which affects the growth substrate, was set at 30 watts. The surface density of the grown arrays of carbon nanotubes was 4.41 × 10 ⁶ mm ^-2 . The resulting nanotubes had a diameter of 60 ± 1 nm and a length of ~ 500 nm to ~ 3 μm.

Example 3

The implementation of the invention was carried out analogously to example 1, but the power of the ultrasonic generator, which affects the growth substrate, was set at 40 watts. The surface density of the grown arrays of carbon nanotubes was 2.21 × 10 ⁷ mm ^-2 . The obtained nanotubes had a diameter of 30 ± 1 nm and a length of ~ 250 nm to ~ 1 μm.

Information sources

1. RF patent No. 2301821 "Method for producing carbon nanofibers", IPC ⁶ C09C 1/44, B82B 3/00, C01B 31/00 / Peshnev B.V., Nikolaev A.I.

2. Suh J. S., Lee J. S. Highly ordered two-dimensional carbon nanotube arrays // Appl. Phys. Lett. 1999. V.75. P. 2047.

3. RF patent N 2026887 "Method for applying anti-corrosion coatings", cl. С23С 4/00, С23С 14/00, С23С 16/00, 1995 / Bakulin V.N., Bakulin A.V.

Claims (1)

A method of producing arrays of carbon nanotubes, including preparing a growth substrate by depositing nanodispersed catalyst particles on its surface by condensation of microdrops of a colloidal solution under the influence of ultrasound, and placing the prepared substrate in a growth furnace with subsequent growth of carbon nanotubes, characterized in that they produce additional exposure to ultrasound on growth substrate, and the power of the ultrasonic generator is set in the range from 25 to 40 watts.