RU2397950C2 - Multilayer carbon nanoparticles of fulleroid type and toroidal shape - Google Patents

Abstract

FIELD: nanotechnologies.

SUBSTANCE: invention relates to nanotechnologies and may find application in construction, electronic and optical industry. Cathode deposit is produced by electroarc erosion of anode graphite rod. Tight crust of cathode deposit is separated from loose core, ground and placed into rotary quartz tube arranged in microwave field. After gas-cycle oxidation produced powder is cooled and placed into vacuum volume onto negative electrode into interelectrode space between cathode and anode. Then difference of potentials is increased between cathode and anode until field emission current appears, as a result of which some multilayer carbon nanoparticles move to positive electrode. On completion of the process they are gathered from surface of anode. Produced multilayer carbon nanoparticles have toroidal shape, average size of which is 15-100 nm. Ratio of external diametre to thickness of tore body thickness makes (10-3):1.

EFFECT: invention makes it possible to achieve high values of power interaction in interelectrode space during field emission.

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Description

The invention relates to the chemistry of non-metallic compounds, namely to the chemistry of carbon, and, in particular, to the production of multilayer carbon nanoparticles of the fulleroid type. These nanoparticles can be used in construction, in the production of structural materials, plasticizers of concrete mixtures, as well as in the electronic and optical industries, for example, in the production of field emission cathodes with the effect of force interaction.

Known multilayer carbon nanoparticles of the fulleroid type - multilayer carbon nanotubes (application JP No. 07-165406, M.cl. C01B 31/00, B 31/02, 1995), which are tubular nanoparticles having a fairly wide range of sizes: length 10-100000 nm; outer diameter 1-500 nm; wall thickness 0.1-200 nm. Nanotubes are obtained by isolation from a cathode deposit obtained by arc evaporation of a graphite anode.

The disadvantage of multilayer carbon nanotubes is the almost complete absence of the effect of force interaction in the interelectrode gaps during field emission from cathodes containing such nanoparticles, as well as the relatively low values of the electric field gain realized on their surface (up to 28 times), which makes it impossible to obtain a high level of dispersion interactions at the borders of various environments.

Closest to the claimed technical solution are polyhedral multilayer carbon nanoparticles of the fulleroid type (RF patent No. 2196731, M.cl. C01B 31/02, 2003), having an interlayer distance of 0.34-0.35 nm and an average particle size of 60- 200 nm.

Polyhedral multilayer carbon nanoparticles are 4-7-sided polyhedra with an internal slit-like capillary. They can also have a branched appearance and do not contain an internal capillary, or have the appearance of a flattened polyhedron, the outer diameter of which exceeds the length of the nanoparticle.

Polyhedral multilayer carbon nanoparticles of the fulleroid type are isolated from the crust of the cathode deposit obtained by the arc process of evaporation of a graphite anode. The production method includes gas-phase oxidation of the crust of the cathode deposit and subsequent liquid-phase oxidation of the carbon powder in the melt of a mixture of potassium hydroxide and potassium nitrate, as shown in RU 2196731.

The disadvantage of polyhedral multilayer carbon nanoparticles is the random nature of their size and shape distribution, which does not allow to realize the effect of force interaction in the interelectrode gap during field emission from cathodes made of such nanoparticles and to achieve high values of the electric field gain on their surface, which ensured would be the highest level of dispersion interaction at the phase boundaries in various media.

The technical result achieved in the claimed invention is to obtain multilayer carbon nanoparticles of the fulleroid type, giving high values of force interaction in the interelectrode gap during field emission from a cathode made of these nanoparticles.

The specified technical result is achieved in that the multilayer carbon nanoparticles of the fulleroid type with an interlayer distance of 0.34-0.36 nm have a toroidal shape with a ratio of the outer diameter to the thickness of the multilayer torus body equal to (10-3): 1, and the average size of the nanoparticles is 15 -100 nm.

Fulleroid-type toroidal multilayer carbon nanoparticles were obtained by selecting the sizes and shapes of multilayer carbon nanoparticles by separating them in an electric field, as described in the work of A. N. Brozdnichenko and others. in. "Surface. X-ray, Synchrotron and Neutron studies "No. 2, 2007, p.69-73. To obtain nanoparticles of this shape, a cathode plate is placed in a vacuum volume on which multilayer carbon nanoparticles obtained by oxidation as a result of previous operations are placed and, parallel to it, an anode plate made of a non-magnetic material, for example tantalum. After connecting the anode and cathode to a high voltage source, power is supplied and the potential difference acting in the interelectrode gap is gradually increased. Upon reaching a field strength of 800-1000 V / mm, field emission current begins to appear. When the field emission current increases, the anode attracts the cathode, which is fixed by a vacuum dynamometer on which the anode plate is fixed. Starting from a certain value of the field emission current, part of the multilayer carbon nanoparticles moves from the cathode to the anode, while the force acting in the interelectrode gap ceases to grow. Then, the voltage applied to the cathode and the anode is removed, the vacuum volume is filled with an inert gas, and carbon multilayer nanoparticles accumulated on the anode plate are collected.

The multilayer carbon nanoparticles thus isolated have a toroidal shape with a ratio of the outer diameter to the thickness of the torus body equal to (10-3): 1, as shown by studies using a transmission electron microscope such as JEM-100C.

Microphotographs of the obtained nanoparticles are presented in Fig.1-2.

Figure 1 presents the image of multilayer carbon nanoparticles of the fulleroid type, agglomerated in the form of a bundle of tori.

Figure 2 presents the image of the toroidal multilayer carbon nanoparticles of the fullerene type at a higher magnification, which allows to determine the ratio of the outer diameter of the torus to the thickness of its body.

The claimed invention is illustrated by examples, but not limited to.

Example 1

By electric arc erosion of an anode graphite rod with a cross section of 30-160 mm ² at a current density of 80-200 A / cm ² and a voltage drop on an arc of 20-28 V in a helium atmosphere at a pressure of 40-100 torr, a cathode deposit is obtained. The dense crust of the cathode deposit is separated from the loose core, crushed and placed in a rotating quartz tube placed in a microwave field with a frequency of 2.5 GHz and a power of 500-1500 watts. After 100-150 min of gas-phase oxidation under the indicated conditions, the resulting powder is cooled and placed in a vacuum volume on a negative electrode in the interelectrode space between the cathode and anode. Then, the potential difference between the cathode and the anode is increased until the field emission current appears. With increasing field emission current, part of the multilayer carbon nanoparticles moves to the positive electrode. After the end of the process, they are collected from the surface of the anode and transferred to a dispersion in an organic solvent, for example in dimethylformamide.

Example 2

The product is obtained as in example 1, but the gas-phase oxidation is carried out in a medium containing an increased amount of oxygen, for example from 20 to 60%.

Example 3

The product is obtained as in example 1, but after gas-phase oxidation, multilayer carbon nanoparticles are additionally oxidized electrochemically in an aqueous electrolyte containing solutions of chlorine compounds.

Example 4

The product is obtained, as in example 1, but the selection of toroidal multilayer carbon nanoparticles is produced in an electric field in a dielectric medium with a high dielectric constant (for example, in white spirit).

Example 5

The product is obtained as in example 1, but after gas-phase oxidation, the multilayer carbon nanoparticles are additionally cooled by placing liquid gas (nitrogen, helium) in the medium, bubbling and separating the precipitate with the liquid phase, followed by evaporation of the liquid gas and obtaining two types of carbon powder, which are further processed as shown in example 1.

To determine the electrophysical parameters, the product is separated from the solvent and examined according to the following parameters:

- X-ray determine the interlayer distance in multilayer carbon nanoparticles, which is equal to 0.34-0.36 nm, which is typical for carbon compounds of the fulleroid type;

- using an electron transmission microscope, for example JEM-100C, and standard samples of latex balls, determine the size, shape and ratio of the external diameters of the toroidal nanoparticles and the thickness of their multilayer body.

A field emission cathode was made from the obtained toroidal nanoparticles by depositing them on an electrically conductive substrate. In a similar way, field emission cathodes with multilayer nanotubes and with polyhedral multilayer carbon nanoparticles according to RU 2196731 were manufactured.

For these field emission cathodes, the force interaction in the interelectrode gap was determined. The indicators are shown in the table.

Table Indicators of force interaction for electrodes of multilayer carbon nanoparticles of fulleroid type according to the claimed technical solution No. p / p Name and composition of negative electrode material Electric field strength, V / mm Field emission current, μA The value of the force acting in the interelectrode gap, N one 2 3 four one. Multilayer carbon
nanotubes 800 500 0.001 2. Polyhedral multilayer carbon nanoparticles 1000 200 0.01 3. fulleroid type
Fulleroid type toroidal multilayer carbon nanoparticles with an average particle size of 15-100 nm and a ratio of the outer diameter of the toroidal nanoparticle and the thickness of the multilayer torus body (10-3): 1 1000 one hundred 0.1

The table shows that the force acting in the interelectrode gap in the case of a negative electrode made of toroidal multilayer carbon nanoparticles of the fulleroid type sharply differs from the values of such forces for electrodes of multilayer nanotubes and polyhedral multilayer carbon nanoparticles of the fulleroid type obtained in accordance with RU 2196731 .

Due to the high value of the electric field gain on the surface of such toroidal multilayer carbon nanoparticles of the fulleroid type, the obtained product can be used in electronic devices using the effect of force interaction in the interelectrode gap during field emission (sensors of dynamic parameters), as a component of nonlinear optical media, as amplifying additive to structural composite materials and as a plasticizing additive to concrete mixtures in construction ve.

Claims (1)

Multilayer carbon nanoparticles of fulleroid type with an interlayer distance of 0.34-0.36 nm, characterized in that they have a toroidal shape with a ratio of the outer diameter to the thickness of the multilayer torus body equal to (10-3): 1, and the average size is 15-100 nm

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