RU2501815C1 - Method of producing nanodispersed fluoroplastic - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing nanodispersed fluoroplastic is realised via thermal decomposition of solid polytetrafluoroethylene in an air atmosphere using high-voltage electric discharge in an alternating electric field. Thermal decomposition is initiated by placing the starting material into the plasma of the high-voltage electric discharge between completely or partially platinum electrodes and holding in the plasma area until inflammation thereof. The material is then removed from the plasma area and transferred into a chamber with access to air to allow thermal composition thereof under the action of spontaneously continuing smouldering. The nanodispersed thermal decomposition product is then collected.

EFFECT: improved tribological properties of the obtained material by forming a separate chemical compound which corresponds to the polytetrafluoroethylene formula, the structure of which is homogeneous and includes spherical nanoparticles.

2 cl, 6 dwg, 1 ex

Description

The invention relates to the chemistry of organofluorine compounds, in particular, to a technology for producing nanodispersed organofluorine material, which can be used as a solid lubricant, as well as in antiwear, antifriction water-repellent, electret, insulating coatings and compositions for devices, devices, machines and mechanisms, including oil compositions for engines and transmissions of automobiles.

A known method of producing fluoropolymer fine powder (US Pat. RF No. 1818328, publ. 1993.05.30), including heating the fluoroplastic material to a temperature of 480-540 ° C, followed by evaporation in an inert gas stream during a residence time of the reaction products in the heating zone of 0.2 0.3 seconds with further condensation of a fine powder of polytetrafluoroethylene on the walls of the reactor, cooled to 0-100 ° C. The fluoropolymer powder obtained in a known manner when used in the composition of antifriction additives due to the insufficient size of its particles requires the use of special additives to prevent their agglomeration. In addition, the known method is quite complicated in hardware design, which is associated with the need to conduct the reaction in a stream of dry inert gas.

A known method of producing a monofractional fine powder of polytetrafluoroethylene, described in RF patent No. 2100376, publ. 1997.12.27, including thermal degradation of fluoroplastic at 480-540 ° C in a stream of circulating gaseous thermal degradation products containing 0.05-1.0 vol.% Oxygen unsaturated with water or 0.1-5.0 vol.% Air saturated with water, which in terms of oxygen is 0.015-0.4 wt.%. A disadvantage of the known method is the relatively large particle size of the material obtained with its use (about 1 μm) and, as a consequence, the insufficient resistance to sedimentation of the oil dispersions containing it, which in some cases impedes successful practical use.

There is also a method of producing ultrafine polytetrafluoroethylene described in the patent of the Russian Federation No. 2212418, publ. September 2003, 20, including 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 consisting of air, oxygen, mixtures thereof, oxides or peroxide compounds of elements I, II, III , IV groups of the periodic system, in an amount of 3-15 wt.% In terms of oxygen, and subsequent simultaneous cooling and condensation of thermal decomposition products by passing them to a solvent. A disadvantage of the known method is the insufficiently small size of the fluoroplastic particles obtained with its help, as well as the need to isolate the resulting ultrafine fluoroplastic from the solvent, for example, by filtration or centrifugation, and washing it off from the organic solvent, which negatively affects the purity of the resulting material and complicates the known method .

Closest to the claimed is a method for producing nanosized organofluorine material (US Pat. RF No. 2341536, publ. 2008.12.20), by thermal decomposition of polytetrafluoroethylene in an electric discharge plasma in an alternating electric field with an alternating voltage amplitude of at least 2 kV in air atmosphere, followed by cooling.

The nanodispersed organofluorine material obtained in a known manner is not an individual chemical compound, since in addition to the organofluorine compounds corresponding to polytetrafluoroethylene, it also contains other organofluorine compounds. In addition, it consists of either particles of irregular shape, which are agglomerates of smaller formations, or of crystals. Thus, the chemical composition and structure of the organofluorine material obtained in a known manner do not provide the required tribological properties when used directly as a lubricant, as well as as an ingredient in lubricant compositions.

The objective of the invention is to develop a method for producing nanosized organofluorine material corresponding to the individual formula of polytetrafluoroethylene, exhibiting high tribological properties.

The technical result of the method is to improve the tribological properties of the obtained nanodispersed organofluorine material by forming an individual chemical compound corresponding to the formula of polytetrafluoroethylene, the structure of which is homogeneous and includes particles of a spherical shape.

The indicated technical result is provided by a method for producing nanodispersed fluoroplastic by thermal decomposition of solid polytetrafluoroethylene in an air atmosphere using a high-voltage electric discharge in an alternating electric field, in which, unlike the known one, the onset of thermal destruction is initiated by placing the starting material in a high-voltage electric discharge plasma between fully or partially platinum electrodes and holding in the plasma zone until it ignites with the flame, This material is removed from the plasma zone and transferred to a chamber with air access for its thermal destruction under the influence of spontaneously continuing smoldering and the subsequent collection of the nanodispersed thermal destruction product.

Optimal for initiating the process of thermal destruction is the amplitude of an alternating voltage of 8-10 kV.

The method is as follows.

Solid polytetrafluoroethylene (PTFE), otherwise fluoroplastic (common technical name), is placed as a feedstock in a reactor made of refractory material equipped with built-in electrodes made of platinum or copper with platinum tips. To prevent breakdown of the electric discharge, the electrodes are reliably isolated from the reactor vessel and are designed in such a way that the electric discharge is carried out far enough from its walls. The reactor is provided with constant access of air.

A high-voltage electric discharge with alternating (pulse, sinusoidal) voltage with an amplitude of 8-10 kV is excited between the electrodes. The initial fluoroplastic sample is placed in the plasma zone of this discharge.

After a short period of time in the region located in the plasma zone, the fluoroplastic begins to burn with a red flame with the emission of black smoke, while the areas of the fluoroplastic surface between the electrodes also become black.

After the appearance of flame and black smoke, the moment of occurrence of which is strictly controlled, the fluoroplastic sample is removed from the plasma zone and transferred from the reactor to an adjacent closed chamber with air access. At the same time, the process of its thermal degradation continues, since the burning of the fluoroplastic does not stop completely, but continues in the form of decay, as evidenced by the disappearance of the flame and the appearance of a red glow visible through the surface of the fluoroplastic blackened as a result of burning in the plasma zone. Smoldering of ftoroplast with the evolution of white smoke continues for several seconds.

The white smoke emitted during the decay of the fluoroplastic, cooling, settles on the walls of the chamber or on a specially designed product receiver, for example, in the form of a plate, in the form of a white nanodispersed powder, which is the target product.

According to electron microscopy, the resulting product is formed by spherical particles (figure 1) with a diameter of 0.1-0.4 μm, which have a layered structure (figure 2).

According to X-ray spectroscopy, the settled substance by its chemical composition is pure fluoroplastic (PTFE). This is indicated by the ratio of the fluorine and carbon contents and the bond energy of fluorine atoms (Fls) and carbon (Cls) (Fig. 3), characteristic of fluoroplastic (Moulder JF, SticKle WF, Sobol PE, Bomben KD Handbook of X-ray Photoelectron Spectroscopy. Published by Perkin-Elmer Corp., 1992, Eden Prairie, USA).

According to x-ray phase analysis (XRD) (Fig. 4), the spectrum of the obtained substance practically coincides with the XRD spectrum of the known ultrafine PTFE described in RF patent No. 2212418.

Established according to pyrolytic mass chromatography, the distribution of molecular weights of the molecules obtained by the proposed method of nanodispersed fluoroplastic is shown in Fig. 5 in comparison with the distribution of molecular weights of the molecules of the aforementioned well-known ultrafine PTFE grade FORUM described in (A.D. Pavlov, S.V. Sukhoverkhov, AK Tsvetnikov. Use of pyrolytic chromato-mass spectrometry to determine the composition of FORUM and its fractions. Vestnik FEB RAS., 2011, No. 5, P.72-75). These data are presented in FIG. 5 as follows: 1 — the known ultrafine fluoroplastic powder of the FORUM brand, 2 — the proposed nanodispersed fluoroplastic powder. Peaks corresponding to the number of carbon atoms in the molecule 5, 6, 7, 8, 9 are marked on the spectrum, the remaining peaks are located in the direction of increasing retention time, while each subsequent one contains one carbon atom in the molecules more than the previous one.

In the composition of the proposed nanodispersed fluoroplastic, in contrast to the known ultrafine, there are practically no extreme low molecular weight or extreme high molecular weight components. The known ultrafine PTFE contains perfluorocarbon molecules with 5-70 carbon atoms, while the proposed nanodispersed fluoroplastic mainly includes molecules with 13-48 atoms. The absence or insignificant amount of low molecular weight components is preferable from an environmental point of view mainly due to the fact that they are released into the atmosphere from the lubricant during friction due to heating of the rubbing surfaces. The shortening of the molecular chain of the fluoroplastic leads to its easier rubbing between the rubbing surfaces, thereby increasing its tribological properties.

The practically spherical shape and small particle size of the nanodispersed fluoroplast obtained using the proposed method ensure their effective penetration into micro- and nanopores and easy grinding between friction surfaces, giving the material high tribological properties. In addition, improving the tribological properties of the proposed material is associated with the possibility of applying a thinner layer of lubricant on the surface of various materials and products with its high quality. This ensures high stability containing the proposed nanodispersed fluoroplastic dispersions approaching colloidal solutions.

Along with high tribological properties, the proposed material exhibits water-repellent, dielectric, electret and heat-insulating properties, has high climatic resistance, does not age, has biocompatibility and non-toxicity.

Examples of specific implementation of the method

A fluoroplastic rod with dimensions of 3 mm × 3 mm × 100 mm is placed in a reactor made of refractory glass with mounted copper electrodes equipped with platinum tips. The fluoroplastic rod is held by a standard fixture such as a clamp.

The current source is an alternating current generator, the voltage at the electrodes changes in a pulsed mode with an amplitude of 10 kV.

Schematically, the device is shown in Fig.6 (a block diagram of a two-chamber installation, where a is the stage of ignition of the fluoroplastic in the plasma, 6 is the stage of decay of the fluoroplastic outside the plasma region and the collection of the product.). The installation includes: 1 - a chamber where combustion occurs in a plasma discharge, 2 - a chamber where the target product is obtained, 3, 4 - copper electrodes with platinum tips, 5 - a fluoroplastic rod, 6 - a plate for collecting the product, 7, 8 - openings for air access, 9 - smoke product.

With the appearance of the plasma cord, the fluoroplastic rod 5 placed in the chamber 1 between the electrodes 3 and 4 begins to burn with a red flame with the release of black smoke in the region located in the plasma zone.

Immediately after the appearance of flame and smoke (this moment is clearly controlled), the fluoroplastic rod is removed from the plasma zone and moved to adjacent chamber 2. This is due to the fact that the delay of the fluoroplastic in the plasma zone leads to the loss of its mass without the release of nanodispersed PTFE, since with its further During combustion, fluorinated soot is formed, mixed with platinum nanoparticles. The same phenomenon is observed with values of the voltage amplitude above the claimed.

After removing the fluoroplastic rod from the plasma zone and moving to an adjacent chamber, the flame disappears, but the rod continues to smolder in the blackened central region for about 8 seconds, emitting white smoke that settles as it cools on plate 6 and on the walls of chamber 2.

After the cessation of white smoke and the final cooling of the fluoroplastic rod 5 by scraping from the plate 6 and partially from the walls of the chamber 2 the precipitate formed as a result of cooling of this smoke, a white nanoparticle fluoroplastic powder is obtained with a yield of about 10% with respect to the total fluoroplastic mass loss at its thermal degradation.

Similar results were obtained with an amplitude of an alternating voltage of 8 kV.

At lower values of the voltage amplitude, the ignition of the fluoroplastic slows down; at large, the formation of a large amount of fluorinated soot with platinum nanoparticles is observed.

X-ray electron spectroscopy (RES) of the obtained product was carried out using a complex of SPECS to study the surface using a 150-mm hemispherical electrostatic analyzer. To excite the spectra, MgKα radiation was used. Calibration of the binding energies was carried out along the Cls line of hydrocarbons, for which Ecb = 285.0 eV was adopted. In the interpretation, a well-known literary source was used (Moulder J.F., SticKle W.F., Sobol P.E., Bomben K.D. Handbook of X-ray Photoelectron Spectroscopy. Published by Perkin-Elmer Corp., 1992, Eden Prairie, USA).

The morphology of the samples was studied by electron scanning microscopy (ESM) using a Hitachi S5500 high resolution scanning electron microscope.

X-ray phase analysis (XRD) was performed on a D8 ADVANCE diffractometer according to the Bragg-Brentano method without sample rotation in Cu Kα radiation using an PDF-2 powder data bank for interpretation of the EVA search program.

Chromatographic analysis was performed on a Shimadzu GCMS-QP2010 mass spectrometer equipped with a PY-2020iD pyrolyzer.

Claims (2)

1. The method of producing nanodispersed fluoroplastic by thermal decomposition of solid polytetrafluoroethylene in an atmosphere of air using a high voltage electric discharge in an alternating electric field, characterized in that the onset of thermal destruction is initiated by placing the source material in a high voltage electric discharge plasma between fully or partially platinum electrodes and holding in the plasma zone until it ignites with the appearance of a flame, then this material is removed from the plasma zone and transferred to the chamber with the access of air for the course of its thermal destruction under the influence of spontaneously continuing smoldering and the subsequent collection of the nanodispersed thermal destruction product. 2. The method according to claim 1, characterized in that the onset of thermal decomposition of solid polytetrafluoroethylene is initiated in an electric discharge plasma at an alternating voltage amplitude of 8-10 kV.

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