WO2021034215A1 - Article fait de graphite avec couche de surface modifiée et procédé de modification de la surface d'un article ayant une base en graphite - Google Patents

Article fait de graphite avec couche de surface modifiée et procédé de modification de la surface d'un article ayant une base en graphite Download PDF

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Publication number
WO2021034215A1
WO2021034215A1 PCT/RU2019/000584 RU2019000584W WO2021034215A1 WO 2021034215 A1 WO2021034215 A1 WO 2021034215A1 RU 2019000584 W RU2019000584 W RU 2019000584W WO 2021034215 A1 WO2021034215 A1 WO 2021034215A1
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WIPO (PCT)
Prior art keywords
base
graphite
silicon
article
silicon carbide
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PCT/RU2019/000584
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English (en)
Russian (ru)
Inventor
Александр Сергеевич ГРАЩЕНКО
Сергей Арсеньевич КУКУШКИН
Андрей Викторович ОСИПОВ
Алексей Викторович РЕДЬКОВ
Николай Александрович ФЕОКТИСТОВ
Original Assignee
СВЯТЕЦ, Генадий Викторович
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by СВЯТЕЦ, Генадий Викторович filed Critical СВЯТЕЦ, Генадий Викторович
Priority to PCT/RU2019/000584 priority Critical patent/WO2021034215A1/fr
Publication of WO2021034215A1 publication Critical patent/WO2021034215A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
    • C23C16/42—Silicides
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating

Definitions

  • the group of inventions relates to the field of thermal protective and antioxidant coatings and can be used to increase the chemical inertness and operating temperature of materials used in the aerospace industry, the fuel and energy complex, in the chemical industry, etc. More precisely, the invention makes it possible to modify the surface of a graphite product by forming in its near-surface layer of a layer of silicon carbide embedded in graphite.
  • the invention allows to combine the advantages of both materials: graphite and silicon carbide.
  • the term "product” is understood in the broadest sense. It can be: a three-dimensional indivisible structure (part); flat plate; profiled or bent sheet, including as part of a shaped shell or casing; tubular product; thread for forming a carbon-carbon composite material (CCCM), etc.
  • the term "subsurface layer” is understood as the layer immediately below the outer surface of the article.
  • the near-surface layer in contrast to the surface (covering) layer, is buried inside the material the base of the product and practically does not go beyond the original (before modification) dimensions of the base.
  • the subsurface layer can be formed on one or several surfaces of the product, including completely covering the base material.
  • the subsurface layer can be continuous or fragmentary, that is, it can be located only under a part of the outer surface, and is made using masking of the surface that is not subject to processing.
  • the known methods of obtaining silicon carbide coatings on various materials can be conditionally divided into two groups.
  • the methods of the first group use physicochemical processes in which silicon and carbon for the formation of silicon carbide are fed into the synthesis zone in the form of chemical compounds or steam: hydrides, halides, etc. [see, for example, USSR Author's certificate No. 145106]. That is, they use "external" sources of matter.
  • SiC coatings on various products is widely used in the manufacture of microelectronic products. These are mainly methods of chemical deposition.
  • US Pat. No. 3,520,740 proposes the use of a gas mixture: silane (S1H4 propane (C3H 8 ) and hydrogen H2) , in which silicon carbide is formed, which is deposited on the surface of the substrate.
  • silane S1H4 propane (C3H 8 ) and hydrogen H2
  • SiC3H 8 propane
  • hydrogen H2 hydrogen
  • the source of the silicon carbide-forming substance is the material itself (base), on which silicon carbide is grown.
  • base the material itself
  • silicon carbide is grown.
  • a silicon substrate is used as a source of silicon, on which a silicon carbide layer is applied by annealing in an atmosphere of CO or CO2 gas or their mixture.
  • a thin SiC film grows on the substrate surface.
  • a method of obtaining a film of silicon carbide on silicon [Haq KE, Khan I. N. Surface Characteristics and Electrical Conduction of b-SiC Films Formed by Chemical Conversion. Journal of Vacuum Science and Technology, (1970) 7 (4), 490-493.
  • a known method of applying a gas-tight coating of silicon carbide described in patent RU 2601049, aimed at increasing the thermal-oxidative strength of coated parts from various materials, including graphite.
  • the method includes the following stages: placing an article made of a high-temperature material in the thermal zone of the furnace; supplying a gaseous silicon-containing component and gaseous hydrocarbons to the surface of the article.
  • a silicon-containing component a silicon melt is used, placed in a crucible in the thermal zone of the furnace.
  • an article is obtained covered with a layer of silicon carbide.
  • the method makes it possible to obtain nano- and microcrystalline gas-tight coatings with different structures, controlled polytypic composition and size of silicon carbide particles from 50 nm to hundreds of microns.
  • a graphite plate described in the same patent RU 2601049, on which a protective surface layer of silicon carbide is applied, is adopted as a prototype of the claimed product.
  • a SiC layer is formed on the surface of the graphite base of the product, which is carried out from the reagents in the furnace.
  • the presence of any coating (surface layer) increases the geometric dimensions of the product itself, which is not always acceptable, especially for products of complex configuration with a given dimensional accuracy.
  • obtaining a coating that is uniform in thickness is very problematic.
  • the coating is held on the substrate by adhesive forces. Under shear loads, coating delamination is possible due to the presence of a clear boundary between silicon carbide and the surface of the product base. Coating delamination is also possible under thermal cyclic loads due to differences in thermal expansion coefficients. This is especially negative in the presence of protrusions and depressions on the surface of the product, causing the occurrence of zones of thermal stress and during the formation of thick layers of coatings.
  • a protective layer is possible not only by applying coatings to the substrate.
  • Another direction of changing the properties of the base material is chemical-thermal treatment, during which the surface of the base material is enriched with certain elements, for example, such processes as carburizing, siliconizing, carbonization.
  • the present invention relates to this direction, however, sources of information that disclose methods for modifying the surface of graphite silicon carbide, not identified.
  • the basis of the invention is the task of expanding the arsenal of tools and creating a new product with a base of graphite and a corresponding method for modifying the surface layer of this product.
  • the achieved technical result is to increase the thickness of the protective layer and the strength characteristics of the product by transforming the structure of the surface layer of the product base and without changing the geometric dimensions of the product itself.
  • the problem posed in the first object of the invention - an article - is solved by the fact that it is characterized by the presence of a base of graphite and a surface modified layer consisting of a base graphite and silicon carbide.
  • the surface layer is obtained by replacing part of the base graphite with silicon carbide, with the formation of a branched dendritic crystal structure of silicon carbide inside the graphite.
  • a silicon carbide surface layer can be additionally formed on the surface layer of the product.
  • this additional coating was applied not to the graphite base, but to a modified layer, including silicon carbide, the concentration of which is maximum at the surface.
  • the problem posed in the second object of the invention - the method - is solved by the fact that the modification of the surface of the product is carried out in a vacuum furnace by forming a surface modified layer, which is carried out by providing a thermochemical heterogeneous reaction of the base graphite with the silicon melt in contact with the base surface and carbon monoxide, which is fed into the vacuum furnace.
  • the above reaction is accompanied by the replacement of a part of the base graphite with silicon carbide with the formation of a branched dendritic crystal structure of silicon carbide inside the graphite.
  • the contact of the silicon melt with the surface of the base can be obtained in various ways, for example, it is formed: - when melting silicon, previously deposited in the form of a powder on the surface of the base, during the melting of a silicon film previously formed on the surface of the base,
  • Fig. 2 is a schematic representation of the implementation of the method in which silicon powder is preliminarily applied to the surface of the base;
  • Fig. 4. implementation of the method in which a silicon plate (monocrystalline or amorphous) is placed on the base surface (top).
  • a silicon plate monocrystalline or amorphous
  • FIG. 1-Fig. 4 it is indicated: 1 - vacuum furnace (walls of the body), 2 - inlet pipe for supplying CO, 3 - outlet pipe for removing gaseous reaction products, 4 - product made of graphite (initial state), 5 - thermal zone furnaces, 6 - silicon film previously deposited on a graphite base, 7 - silicon powder, 8 - crucible with silicon melt, 9 - movable product holder, 10 - silicon plate.
  • FIG. 5 SEM image of the surface of the article made according to Example 1, obtained by a scanning electron microscope, FIG. 6. SEM image of a cross-section of a product with a fragmentary modified surface layer,
  • FIG. 7. SEM image of SiC microcrystals on cross section of the modified subsurface layer
  • FIG. 8. Micro-Raman spectrum of the original surface of the product (graphite), and the surface of the product, after the implementation of the method.
  • FIG. 9. Micro-Raman spectra of individual crystallites
  • SiC found in the volume of the modified near-surface layer.
  • the base (a flat plate of graphite grade MPG-7 measuring 30 * 30 * 5 mm) of the product with a silicon film with a thickness of 1 mm, previously applied to the surface, is placed in furnace 1.
  • the internal volume of the furnace is heated in a vacuum of 10 2 - 10 3 Pa to temperature of about 950 ° C.
  • CO gas is fed into the inner volume of the furnace through the inlet 2 into the internal volume of the furnace (CO can be supplied in a mixture with an inert gas - argon or xenon, the reagent remains CO) while maintaining a pressure of 5 - 20 Pa and the furnace chamber is heated to melting silicon (1410 ° C).
  • the temperature is lowered to a temperature below the melting point of silicon (up to 1350 ° C) while maintaining the CO flow and pressure in the furnace.
  • the product is kept at this temperature for 20 minutes, after which the gas is evacuated, the furnace is cooled, and the product with a modified surface layer of about 950 microns or more is removed, which depends on the thickness of the applied silicon layer.
  • the inventive method in the presence of CO gas in a vacuum furnace, the surface layer is modified. This is due to a different process taking place in the furnace.
  • the formation of the near-surface modified layer is carried out due to the thermochemical heterogeneous reaction of the reagents with the base graphite as follows.
  • the reaction product is SiO gas - leaves the reaction zone much slower than CO. This is due to the fact that the SiO molecule is larger, as well as to the fact that during the passage of CO during heating to the melting temperature, the initial channels in Si “overgrown” with the SiC reaction product to a greater depth, changing their diameter. As a result, the SiO gas cannot completely escape outside and the rate of chemical reaction (1) slows down and equilibrium is established.
  • Reaction (2) occurs at the interface between the melt and graphite, resulting in the following processes.
  • reaction (2) Part of the reaction product (1) is consumed in reaction (2), which leads to a shift in the equilibrium of reaction (1) towards the formation of SiC.
  • reaction (2) one of the carbon atoms is removed from the graphite base, forming vacancies that can merge into nanopores and microchannels, while liquid silicon saturated with SiO gas “breaks out” from under the SiC film layer and penetrates into graphite, filling nanopores, microchannels and other voids in graphite.
  • CO gas easily penetrates deep into the base, since the removed atoms of both silicon, according to reaction (1) and carbon according to reaction (2), form voids in graphite, greatly facilitating the process of penetration of gases and silicon into it.
  • the synthesis lasts 20 minutes. During this time, all of the silicon is converted to silicon carbide.
  • the final structure is lacunae with a branched dendritic crystal structure, filled with SiC, inside the graphite base with an increase in the concentration of SiC on the surface of the product to almost 100% (see Fig. 5 and Fig. 8).
  • reactions (1) and (2) must necessarily proceed simultaneously. They simultaneously ensure the flow of two processes, namely the initial creation of a SiC surface crust, which protects against Si evaporation, and plays the role of a “cover” that holds SiO in the melt until the required concentration is created in it for the reaction (2), which prepares the base graphite for rapid penetration of silicon carbide melt into it.
  • reactions (1) and (2) complete the transformation of the residues of graphite and silicon into SiC.
  • the silicon atom is attached to carbon, which increases the molecular volume and does not allow the formation of SiC inside the graphite, but only on its surface.
  • both the silicon atom according to reaction (1) and the carbon atom according to reaction (2) are removed from the system, which reduces the atomic volume and leads to the formation of vacancies and voids for filling them with silicon carbide.
  • silicon is brought to melting, which leads to reaction (2), the flow of which is not possible if SiO gas is released onto the SiC surface and does not create the required pressure inside the molten silicon.
  • a SiC film is created in a furnace, silicon melts under a SiC film on the base surface, a thermochemical heterogeneous reaction (1) with carbon monoxide and a thermochemical heterogeneous reaction of graphite with silicon melt and silicon monoxide and the formation of a surface modified layer.
  • the article with a modified surface layer was examined by optical microscopy, scanning scanning electron microscopy, and Raman spectroscopy.
  • the structure of the modified near-surface layer is shown in the images of scanning electron microscopy (Fig. 5. Fig. 6).
  • the characteristic size of crystals on the surface is on the order of several microns, which is an order of magnitude less than in the prototype method. From FIG. 6 that the thickness of the SiC layer was about 950 ⁇ m.
  • FIG. 7 shows a SEM image of individual crystallites on a cross section of a sample. Their size is also on the order of a few microns.
  • FIG. 8 shows the micro-Raman spectra of the product surface before (dashed line) and after modification (solid line).
  • the micro-Raman spectrum of the initial surface corresponds to graphite, while the modified surface consists mainly of silicon carbide - the SiC line of the cubic polytype (796 sample cm) dominates in the spectrum. It should be noted that the spectrum shows averaging over an area of 50 * 50 ⁇ m.
  • the graphite base is fixed on a movable holder 9 (Fig. 3), under which a crucible with silicon 8 is installed.
  • a crucible with silicon 8 is installed.
  • the furnace is heated above the melting point of silicon, silicon in the crucible forms a melt.
  • the product is immersed in the melt using the holder silicon and then slowly drawn in the presence of CO gas.
  • the furnace is cooled to a temperature below the melting point of silicon and kept at a temperature in the range of 800-1380 ° C.
  • the CO gas supply is stopped and the furnace is cooled to room temperature. After the furnace has cooled, the product is removed with a modified subsurface layer over the entire surface of the product.
  • the surface of the product can be subjected to additional etching and heat treatment operations, for example, in air at 500-800 ° C to remove unwanted contaminants.
  • Acids such as nitric or perchloric acids can be used as liquid etchants. Boiling treatment in these acids allows the silicon carbide surfaces to be cleaned from technological contaminants. It is also possible to carry out additional heat treatment of the product at temperatures up to 1400 ° C (vacuum annealing) to influence the structural features of the silicon carbide film.
  • a new product was obtained from graphite with a near-surface protective layer formed by replacing part of the base graphite with silicon carbide, with the formation of a branched dendritic crystal structure of silicon carbide inside the graphite.
  • This inner (extending deep into the product) layer increases the strength properties of the product, its chemical and thermal resistance.
  • the inventive method allows to form a near-surface protective layer up to 1 mm thick.
  • the near-surface layer formed according to the claimed method is inside the base and forms a branched dendritic embedding of silicon carbide inside the base graphite.

Abstract

Cet article comprend une base en graphite, la couche de surface modifiée de l'article se compose du graphite de la base et de carbure de silicium, et possède une structure cristalline dendritique ramifiée de carbure de silicium dans le graphite. Le procédé de modification de la surface de l'article consiste à modifier la surface de l'article dans un four à vide, ceci en assurant un écoulement de la réaction hétérogène du graphite de la base avec du silicium en fusion entrant en contact avec la surface de la base, et du monoxyde de carbone. La réaction s'accompagne d'un remplacement d'une partie du graphite de la base par du carbure de silicium de manière à former une structure cristalline dendritique ramifiée de carbure de silicium dans le graphite. On assure ainsi une augmentation de l'épaisseur de la couche de protection et de la résistance des caractéristiques de l'article du fait de la conversion de la structure de la couche de surface de la base de l'article, sans modifier les dimensions géométriques de l'article proprement dit.
PCT/RU2019/000584 2019-08-19 2019-08-19 Article fait de graphite avec couche de surface modifiée et procédé de modification de la surface d'un article ayant une base en graphite WO2021034215A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3925577A (en) * 1972-11-24 1975-12-09 Westinghouse Electric Corp Silicon carbide coated graphite members and process for producing the same
RU2601049C1 (ru) * 2015-04-29 2016-10-27 Федеральное государственное бюджетное учреждение науки Институт физики твердого тела Российской академии наук (ИФТТ РАН) Способ нанесения газоплотного покрытия из карбида кремния
RU2684128C1 (ru) * 2018-04-06 2019-04-04 Общество с ограниченной ответственностью "Научно технический центр "Новые технологии" Изделие с покрытием из карбида кремния и способ изготовления изделия с покрытием из карбида кремния

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3925577A (en) * 1972-11-24 1975-12-09 Westinghouse Electric Corp Silicon carbide coated graphite members and process for producing the same
RU2601049C1 (ru) * 2015-04-29 2016-10-27 Федеральное государственное бюджетное учреждение науки Институт физики твердого тела Российской академии наук (ИФТТ РАН) Способ нанесения газоплотного покрытия из карбида кремния
RU2684128C1 (ru) * 2018-04-06 2019-04-04 Общество с ограниченной ответственностью "Научно технический центр "Новые технологии" Изделие с покрытием из карбида кремния и способ изготовления изделия с покрытием из карбида кремния

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