RU2627767C1 - Method for producing carbon-fluorocarbon nanocomposite material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method for producing a carbon-fluorocarbon nanocomposite material is proposed, which includes the thermal degradation of solid polytetrafluoroethylene, which is carried out in a plasma medium formed as a result of the preliminary destruction of a similar sample of polytetrafluoroethylene in a pulsed high-voltage electric discharge in air at a pulse amplitude of 2-10 kV, followed by the collection of degradation products in the form of an ash-like product containing individual nanoparticles of the elements that make up the electrodes. The product obtained is subjected to heat treatment by heating with an external source before the appearance of electrical conductivity, accompanied by self-heating of the product, when electric current is passed therethrough. As a result of heat treatment, a carbon-fluorocarbon material containing nanografen bands is produced and a powdered product consisting of composite nanoparticles containing carbon and fluorocarbon components.

EFFECT: producing high-yield carbon-fluorocarbon nanocomposite materials with a well-defined nanostructure providing their new properties and expanding the field of application.

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Description

The invention relates to the production of nanocomposite materials containing a matrix of partially profluorinated and oxidized amorphous carbon with inclusions of nanographite particles, additional carbon nanoparticles, metal-containing particles or nanographen to nanographite. These materials can find application directly as nanocatalysts, or in the form of a matrix for the introduction of catalytic nanoparticles; as sorbents; as well as interelectrode matrices for filling with electrolytes in chemical current sources; matrices for electrolytes in supercapacitors; materials for electric heating elements; hydrophobic coatings; radar absorbing coatings. The materials obtained by the proposed method exhibit magnetic properties of interest, in particular, the existence of a Josephson junction medium, paramagnetism and ferromagnetism of carbon nanoparticles.

A known method of producing a carbon material and carbon material (RU 2502668, publ. 2013.12.27), including the pyrolysis of solid polytetrafluoroethylene without air in a plasma pulsed high-voltage electric discharge at atmospheric pressure with a pulse amplitude of at least 9 kV to obtain a carbon material with an ordered nanostructure of defluorinated and partially graphitized supramolecular chain structures of PTFE with a thickness of 30-100 nm, formed by fibers with a diameter of 1-2 nm, randomly intertwined in a homogen hydrochloric porous body with a pore size of 1-2 nm. The disadvantages of the method include a low yield, difficult sample preparation, a limited set of nano-objects in the resulting material.

A known method of producing ultrafine organofluorine material (polytetrafluoroethylene), described in RF patent No. 2212418, publ. 2003.09.20, which includes the thermal degradation of polytetrafluoroethylene at 480-540 ° C in the environment of the released thermal degradation gases in the presence of oxygen-containing compounds thermodynamically suitable for the oxidation of polytetrafluoroethylene, selected from the group comprising air, oxygen, mixtures thereof, oxides or peroxide compounds of elements I, II, III, IV groups of the Periodic system, in the amount of 3-15 wt. % in terms of oxygen, followed by cooling and condensation of thermal degradation products. The disadvantages of this method include the fact that the particles of polytetrafluoroethylene obtained using it have an average size of about 1 micron (1.0 ± 0.5 μm), which in practice limits the possibilities of using the resulting material. In addition, the known method is complicated in hardware, and the product obtained with it needs to be washed from alkali and fluoride formed, or, when using the product together with a solvent that serves as a condensation medium, in almost all cases requires filtering off excess solvent, which leads to complication way

The closest to the claimed technical essence method for producing nanosized organofluorine material described in patent RU 2341536 (publ. 2008.12.20) is carried out by thermal decomposition of polytetrafluoroethylene in an air atmosphere in an electric discharge plasma in an alternating electric field with an alternating voltage amplitude of at least 2 kV s subsequent cooling of thermal decomposition products.

The known method does not provide reliable production with a sufficient yield of structured carbon-fluorocarbon nanocomposite material in an individual form, the resulting product contains its trace contents and, in addition, there are micro- and nanoparticles of fluorides and metal oxides forming conglomerates and leading to the composition of crystals, which defines the specifics and limits the possibilities of using the said product

The objective of the invention is to provide a method for producing a structured fluorocarbon nanocomposite material containing graphene nanoribbons with inclusions of foreign nanoparticles, while simultaneously providing a powdery carbon-fluorocarbon nanocomposite material and nanocomposite material, the structure of which is formed by amorphous nanofibrils.

The technical result of the method is to obtain a high yield of carbon-fluorocarbon nanocomposite materials with a clearly defined nanostructure, providing their new properties and expanding the scope.

The specified technical result is achieved by a method for producing a carbon-fluorocarbon nanocomposite material, including thermal decomposition of solid polytetrafluoroethylene in a high-voltage pulsed plasma followed by cooling and collection of degradation products, in which, unlike the known, thermal decomposition of solid polytetrafluoroethylene is carried out in a plasma medium formed as a result of preliminary degradation a similar sample of polytetrafluoroethylene in a high-voltage electric discharge in air, at the amplitude of the alternating voltage of 2-10 kV to obtain a soot-like product, which is subjected to heat treatment, including pre-heating using an external source, which provides the conductivity of the product, and its subsequent self-heating while passing an electric current.

Fluorocarbon nanocomposite material containing partially catalytic and magnetic properties, containing partially profluorinated and oxidized carbon, including individual (isolated from each other) nanoparticles of such carbon, is obtained by implementing a method with excitation of a high-voltage electric discharge between carbon electrodes.

In another embodiment of the method, a high voltage electric discharge plasma is excited between the metal electrodes, whereby a material is obtained containing partially profluorinated and oxidized carbon and isolated nanoparticles, which include metal elements from the electrodes. The composition of isolated non-carbon nanoparticles affects the properties of the material obtained and, accordingly, the scope of its application (nanocatalysis, chemical current sources, photocells, nanosensors, etc.).

The method is as follows.

To implement the method, a reactor is used, preferably made of a refractory material having insulating properties, which is equipped with built-in electrodes and a collector-receiver of the finished product, while the electrodes can be carbon or metal. When a high voltage is applied between the electrodes, an electric discharge occurs and a stable plasma is formed from ionized particles of the gaseous medium in which the discharge occurs.

A fluoroplastic material in the form of a monolithic rod is placed in the discharge gap, as a result of the destruction of which a fluoroplastic plasma is formed in the air gap between the electrodes under the influence of a high-voltage discharge, the appearance of which is noted by the appearance of a blue glow.

Use a voltage in the range of 2-10 kV, while choosing it so that there is no visible destruction of the electrodes, fixed by the exit of smoke from the plasma.

A working monolithic rod of similar fluoroplastic material is placed in the formed zone of the fluoroplastic plasma (without removing the first rod), while black smoke rises from the gap between the rods. The rods as they burn out are brought together so that the smoke output is kept constant. At this stage, a solid product is collected as a target, resulting from cooling of the smoke and settling on the collector substrate in the form of a black powder, which is collected from the substrate and sent for further processing.

A step-by-step scheme for producing the above-mentioned intermediate nanocomposite product is shown in FIG. 1 (1- initiation of air plasma, 1b - formation of a fluoroplastic plasma, 1c - obtaining a nanocomposite product), where 1 is a pulsed high voltage generator, 2, 3 are electrodes, 4 is an air plasma, 5 is an auxiliary fluoroplastic rod, 6 is a fluoroplastic plasma , 7 - working fluoroplastic rod, 8 - smoke generated as a result of destruction of the working fluoroplastic rod, 9 - substrate., 10 - nanocomposite product.

The characteristics of the obtained intermediate composite material are clearly shown in the pictures taken using transmission electron microscopy (TEM) at various magnifications. In FIG. 2a shows an image of the material obtained with carbon electrodes, 2b and 2c - with copper, 3 - with platinum, 4 - with titanium. The above images indicate that the material is formed by amorphous nanofibrils with inclusions of nanoparticles of the electrode material.

In FIG. 5 shows Raman spectra; FIG. 6 - data of x-ray phase analysis (XRD)).

The Raman spectra of samples obtained with carbon and copper electrodes (Figs. 5a and 5b) include the G and D lines characteristic of a number of carbon materials in terms of their relative intensities (J _D > J _G ) and widths (ΔJ _D > ΔJ _G ) corresponding to the content in the sample of nanoscale disordered graphite-like structures. The XRD spectra of these samples (FIGS. 6a and 6b) are characterized by the presence of lines corresponding to PTFE.

According to the data obtained using an energy dispersive spectrometer (EMF), nanofibrils contain C (more than 90 at.%), F (up to 6 at.%) And O (up to 5 at.%), While in the sample obtained with copper electrodes, contains copper (up to 1 at.%). The resistance of the samples decreases with increasing temperature from 2 megohms at T = 300 K to 50 kilo-ohms at T = 600 K, i.e. has a pronounced semiconductor nature.

Thus, the obtained samples are semiconductor nanocomposites formed by nanofibrils containing partially profluorinated and oxidized amorphous carbon with nanographite inclusions, and also include nanoparticles more dense with respect to electron beam transmission, which include carbon in the case of carbon electrodes, in the case of metal electrodes - appropriate metal.

This intermediate product is marketable and may find independent use.

Its subsequent heat treatment provides the production of carbon-fluorocarbon nanocomposite material of two modifications: a nanocomposite containing graphene nanoribbons (target product), and nanodispersed powder, consisting of composite nanoparticles.

The stepwise heat treatment of the obtained intermediate nanocomposite material together with the installation for its implementation are shown schematically in FIG. 7 (7a - pre-heating using an external heat source; 7b - heating by the current flowing through the sample), where 11 is the voltage source to power the heater; 12 - stabilized current source connected to the sample 13, 14 - electrodes; 15 - intermediate nanocomposite; 16 - heater; 17 - smoke leaving the sample when heated, 18 - substrate, 19 - nanocomposite deposited on the substrate.

A semiconductor-containing sample of an intermediate nanocomposite material to which a current source is connected is heated with an electric heater until a sufficient number of charge carriers appear in the sample and a current develops, the passage of which through the sample causes it to self-heat and light brown smoke to be released. The current is stabilized at a predetermined level (from 4 to 20 A), which is determined by the mass of the fluoroplastic and the heat treatment time, and heat treatment is continued, during which the structure of the heated sample changes with smoke emission.

As a result of heat treatment (at the end of smoke emission), a carbon-fluorocarbon nanocomposite material containing graphene nanoribbons is formed in place of the initial sample, and nanodispersed powder settles on the substrate.

The resulting powder consists of nanocomposite particles containing fluoroplastic and carbon components, which is confirmed by the analysis results.

Its TEM images at different magnifications for a material obtained from an intermediate nanocomposite synthesized using copper electrodes are shown in FIG. 8. The powder consists of spherical nanoparticles with transverse dimensions of 50-500 nm. In its Raman spectra shown in FIG. 9, a peak from fullerenes is observed, peaks D and G are present, as well as a set of wide weak peaks, which, presumably, can be attributed to fragments of fullerene structures.

The elemental composition of the particles of the obtained sample, determined by the method of local energy dispersive spectroscopy, includes 45 at. % F and 55 at. % C. From the obtained results it follows that the powder consists of nanoparticles being a nanocomposite of carbon and fluorocarbon components, with a certain content of fullerenes or their fragments. Particles in shape and size are similar to the well-known ultrafine polytetrafluoroethylene (UPTFE), but differ from it in the content of elements, because It is known that in UPTFE the fluorine content is more than twice the carbon content.

The resulting PTFE-carbon powder nanocomposite can be characterized by the presence of carbon nanoparticles packed in a matrix of nanodispersed PTFE and, according to its structure, must simultaneously possess the properties of ultrafine PTFE and nanodispersed carbon. It is also a marketable product.

TEM images of the target carbon-fluorocarbon nanocomposite material formed as a result of heat treatment on the substrate in place of the nanocomposite material of copper electrodes are shown in FIG. 10. The resulting material is characterized by a multi-chamber structure formed by tangles formed from graphene ribbons. The Raman spectrum of this product shown in FIG. 11 is characterized by the presence of a line corresponding to graphene structures and characteristic lines G and D from nanoscale disordered graphite-like structures. From these results it follows that the sample contains many swirling and curved nanographene ribbons and graphite-like nanosized regions.

Thus, the proposed method allows simultaneously with the main carbon-fluorocarbon nanocomposite material with a characteristic structure in the form of nests from graphene ribbons to obtain a powdery fluorocarbon nanocomposite material, and also makes it possible to use an intermediate nanocomposite material as a commodity.

Examples of specific implementation of the method

Example 1

A fluoroplastic rod with a 3 × 4 mm cross section weighing 25 g was held for 10 min in a previously created fluoroplastic plasma of a high voltage (10 kV) discharge between carbon electrodes. Received 0.31 grams of a soot-like product. The resulting product was heated with an electric heater until a current appeared in the circuit (for about 5 min), a current of 20 A was passed for 1 min, and a fluorocarbon nanocomposite material containing balls of graphene ribbons weighing 0.30 g was obtained. A TEM image of the obtained material is shown in FIG. 12. The nanocomposite powder in this case forms approximately 0.003 g.

Example 2

The method was carried out according to example 1, exciting a high voltage (2 kV) discharge between copper electrodes. After 15 minutes of plasma treatment from a fluoroplastic rod weighing 25 g, 0.24 grams of a carbon black product was obtained. The resulting product was heated for 5 min, a current of 4 A was passed, and approximately 0.23 g of a fluorocarbon nanocomposite material containing tangles of graphene ribbons was obtained (Fig. 8), and approximately 0.002 g of a nanocomposite powder.

Claims (3)

1. A method of producing a carbon-fluorocarbon nanocomposite material, comprising thermal decomposition of solid polytetrafluoroethylene in plasma with the collection of degradation products, characterized in that the thermal degradation of solid polytetrafluoroethylene is carried out in a plasma medium formed as a result of preliminary destruction of a similar sample of polytetrafluoroethylene in a pulsed high-voltage electric discharge plasma when the amplitude of the alternating voltage of 2-10 kV to obtain a soot-like product, which is subjected to oobrabotke comprising preheating by an external source, providing the appearance of a product of electric conductivity and its subsequent self-heating by passing an electric current therethrough. 2. The method according to p. 1, characterized in that the high-voltage electric discharge is excited between the carbon electrodes. 3. The method according to p. 1, characterized in that the high-voltage electric discharge is excited between the metal electrodes.

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