Method for producing a carbon film

Abstract

Method for producing a carbon film comprising the steps a. Providing a graphene dispersion comprising graphene oxide flakes and a dispersing agent, b. Providing a filter designed as a surface filter, c. Applying the graphene dispersion to the filter in such a way that the graphene oxide flakes remain on the filter as a filter cake and the dispersion medium passes at least partially through the filter, d. Drying the filter cake so that a carbon film is formed from the filter cake, e. Thermal treatment of the carbon film in an inert atmosphere, in particular in an Ar atmosphere, for at least partial reduction of the graphene oxide present in the carbon film, characterized in that, - in step a) the graphene dispersion at least one carbide precursor compound selected from the group of sodium tungstate (Na2WO4), sodium molybdate (Na2MoO4), vanadium(IV) oxide sulfate (VOSO4), zirconium(IV) nitrate (Zr(NO3)4), molybdenum disulfide (MoS2), tungsten disulfide (WS2) is added and - in step e) electrically conductive metal carbide, in particular tungsten carbide (WC), dimolybdenum carbide (Mo2C), vanadium carbide (VC), zirconium carbide (ZrC), is formed in particle form in the carbon film.

Description

State of the art

[0001] The invention is based on a method for producing a carbon film according to the preamble of the main claim.

[0002] A method for producing a carbon film is already known from DE 102020206563 A1. This known method comprises, in a first step, providing a graphene dispersion containing graphene oxide flakes and a dispersant. Subsequently, in a second step, providing a filter configured as a surface filter is provided. In a third step, the graphene dispersion is applied to the filter in such a way that the graphene oxide flakes remain on the filter as a filter cake, in particular without penetrating the filter, and the dispersant at least partially passes through the filter. In a fourth step, the filter cake is dried, so that a carbon film for use as an electrical graphene conductor is formed from the filter cake.In a fifth step, the carbon film is thermally treated in an inert atmosphere at a specific treatment temperature to reduce the graphene oxide present in the carbon film.

[0003] In carbon films produced with graphene oxide flakes, the electrical conductivity is limited by the contact resistance between the individual graphene oxide flakes. This effect is more pronounced the smaller the average flake size. When producing graphene oxide flakes, the average size varies depending on the batch, causing the electrical conductivity of the finished film to vary depending on the graphene oxide batch. This problem also exists when adding boric acid or glucose. Advantages of the invention

[0004] The method according to the invention for producing a carbon film with the characterizing features of the main claim has the advantage that the electrical conductivity of the carbon film is increased.

[0005] According to the invention, a suitable additive is added to the graphene dispersion, which reacts with the carbon and electrically crosslinks the graphene flakes formed from the graphene oxide flakes, thereby compensating for the size variation of the graphene oxide flakes. This is achieved according to the invention by admixing at least one carbide precursor compound selected from the group consisting of sodium tungstate (Na2WO4), sodium molybdate (Na2MoO4), vanadium(IV) oxide sulfate (VOSO4), zirconium(IV) nitrate (Zr(NO3)4), molybdenum disulfide (MoS2), and tungsten disulfide (WS2) in step a) to the graphene dispersion, and by forming electrically conductive metal carbide, in particular tungsten carbide (WC), dimolybdenum carbide (Mo2C), vanadium carbide (VC), or zirconium carbide (ZrC), in step e) in the carbon film, particularly in particle form.

[0006] The carbon film produced by the process according to the invention is temperature-stable up to at least 250 °C and insensitive to moisture.

[0007] The measures listed in the subclaims enable advantageous further developments and improvements of the method for producing a carbon film specified in the main claim.

[0008] It is particularly advantageous that in step e), the carbide precursor compound reacts with the carbon of the graphene oxide flakes to form the metal carbide by setting a suitable treatment temperature. In this way, a carbide-decorated or carbide-doped carbon film with high electrical conductivity is formed.

[0009] It is very advantageous if the treatment temperature in step e) is selected and maintained such that the formed metal carbide at least partially melts and is distributed throughout the carbon film. This achieves a high electrical conductivity of the carbon film.

[0010] It is further advantageous if the carbon film is thermally pretreated between step d) and step e) to remove volatile by-products, particularly in a temperature range of 300°C-500°C, especially at 400°C. In this way, volatile by-products are removed from the carbon film.

[0011] It is very advantageous if the carbon film is compacted in step f) to remove gas bubbles, in particular with a force of 250-375 MPa and / or in particular at a temperature of 20°C-150°C. In this way, gas bubbles formed in step e) by gaseous reaction products during the reaction of the carbide precursor compound with the carbon of the graphene oxide flakes in the carbon film are removed from the carbon film.

[0012] It is further advantageous if at least one Lewis acid, for example AlCl3, AlF3, ZrF4, FeF3, MgF2, TiF4, CuCl2, MoCl5, is intercalated into the carbon film in step g). In this way, the electrical conductivity of the carbon film can be further increased.

[0013] It is also advantageous that the carbon film is removed from the filter after drying in step d). This allows the carbon film to be placed in an inert atmosphere as a separate element in step e).

[0014] The invention further relates to an electrically conductive carbon film with a lattice structure, in which, according to the invention, metal carbide is incorporated into the lattice structure of the carbon film via a covalent and ionic bond. The metal carbide can be incorporated into the lattice structure of the carbon film, for example, in the form of nano- or microparticles. Description of the embodiment

[0015] The method according to the invention is a method for producing a carbon film which is an electrical conductor and as such is to be used in an electrical application, for example as an electrical conductor of an electrical winding of an electrical machine or in electronics, in particular in power electronics.

[0016] The method according to the invention comprises the following steps: In a first step a), a graphene dispersion is provided, comprising graphene oxide flakes and a dispersant, in particular water, ethanol, or 2-propanol. The graphene dispersion can also be referred to as graphene oxide dispersion.

[0017] In a second step b), a filter designed as a surface filter is provided.

[0018] In a third step c), the graphene dispersion is applied to the filter and filtered in such a way that the graphene oxide flakes of the graphene dispersion remain on the filter as, for example, a film-like, membrane-like, or ribbon-like filter cake, in particular without penetrating the filter, and the dispersant passes at least partially through the filter. The filter cake has, for example, a longitudinal extension to form the carbon film or can also be membrane-like.

[0019] In a fourth step (d), the resulting filter cake is dried to form a solid carbon film. After drying, the carbon film is removed from the filter.

[0020] In a fifth step e), the carbon film is thermally treated in an inert atmosphere, in particular in an Ar atmosphere, to at least partially reduce the graphene oxide present in the carbon film, in particular at a treatment temperature in the range of 1800°C-3000°C, especially at 2000°C. The graphene oxide flakes are thereby reduced to graphene flakes.

[0021] According to the invention, in the first step a) at least one carbide precursor compound selected from the group of sodium tungstate (Na2WO4), sodium molybdate (Na2MoO4), vanadium(IV) oxide sulfate (VOSO4), zirconium(IV) nitrate (Zr(NO3)4), molybdenum disulfide (MoS2), tungsten disulfide (WS2) is added to the graphene dispersion.

[0022] Furthermore, according to the invention, in the fifth step e), electrically conductive metal carbide, in particular tungsten carbide (WC), dimolybdenum carbide (Mo2C), vanadium carbide (VC), zirconium carbide (ZrC), is formed in the carbon film, in particular metal carbide in particle form.

[0023] The formation of the electrically conductive metal carbide in the carbon film is achieved in step e) by setting a suitable treatment temperature to react the carbide precursor compound with the carbon of the graphene oxide flakes to form a metal carbide.

[0024] Particularly reactive are the so-called terminal carbon atoms located at the edge of the graphene oxide flakes. The reaction of the carbide precursor compound with the carbon of the graphene oxide flakes forms a metal carbide that is covalently bonded to two graphene oxide flakes, forming a conductive bridge. The resulting metal carbides must themselves be electrically conductive to increase the electrical conductivity in the carbon film.

[0025] Depending on the selected carbide precursor compound, one of the following reactions occurs: 1.Conversion of sodium tungstate to tungsten carbide and carbon dioxide, the sodium evaporates at the treatment temperature: Na2WO4 + 3C → WC + 2Na + 2CO2 2. Conversion of sodium molybdate to dimolybdenum carbide and carbon dioxide. The sodium evaporates at the treatment temperature: 2Na2MoO4 + 5C → Mo2C + 4Na + 4CO2 3. Reaction of vanadium(IV) oxide sulfate with carbon to form vanadium carbide, sulfur dioxide, carbon dioxide and carbon monoxide: VOSO4 + 3C → VC + SO2+ CO2+ CO 4. Conversion of zirconium(IV) nitrate with carbon to zirconium carbide, nitrogen and carbon dioxide: Zr(NO3)4 + 7C → ZrC + 2N2 + 6CO2 5. Conversion of molybdenum disulfide with carbon to dimolybdenum carbide and carbon disulfide: 2MoS2 + 3C → Mo2C + 2CS2 6. Conversion of tungsten disulfide with carbon to tungsten carbide and carbon disulfide: WS2 + 2C → WC + CS2

[0026] In step e), the treatment temperature is selected and maintained such that the metal carbide formed melts at least partially and is finely distributed in the carbon film.

[0027] The carbon film may be thermally pretreated between step d) and step e) to remove volatile by-products, in particular in a temperature range of 300°C-500°C, especially at 400°C.

[0028] In a sixth step f), the carbon film is compressed to remove gas bubbles from the carbon film, in particular with a force of 250 - 375 MPa and / or in particular at a temperature of 20°C - 150°C.

[0029] In a seventh step g), at least one Lewis acid can be intercalated into the material of the carbon film according to the invention, for example AlCl3, AlF3, ZrF4, FeF3, MgF2, TiF4, CuCl2, MoCl5.

[0030] Through the steps of the process according to the invention, the metal carbide formed in the carbon film is incorporated into the lattice structure of the carbon film, for example in the form of nano- or microparticles.

[0031] A possible embodiment of the method according to the invention is described below: The graphene dispersion can be a 0.5 wt.% graphene oxide dispersion. The carbide precursor (Na2WO4, Na2MoO4, VOSO4, Zr(NO3)4, MoS2, WS2) is added to the solution to achieve a concentration of 6 mM to 300 mM and 30 mg of graphene oxide in the solution. The solution is then stirred for at least 60 minutes and then vacuum filtered through a filter paper (pore size 0.45 µm). In the case of MoS2 and WS2, an additional ultrasonic treatment of 10–20 minutes is performed prior to filtration to obtain a homogeneous graphene oxide dispersion. Once the solvent has permeated, the filter cake is dried on the filter paper. This can be done at room temperature or in an oven at up to 60°C. Once the filter cake is dry, it can be removed from the filter paper. The dried filter cake is then weighted down with a plate, for example, and thermally treated.During the thermal treatment, the material is first heated to 400°C at a rate of 100°C / h in an Ar atmosphere (flow rate of 424 l / h) to remove volatile byproducts during the treatment. This is followed by heating to 1200°C at 800°C / h and then to 2000°C at 900°C / h. The temperature is maintained for 2 hours and then cooled to room temperature at 1000°C. During this treatment, the graphene oxide is reduced and the metals of the carbide precursors react with the carbon. The carbon film is then densified for 15-30 minutes at 250-375 MPa and 20-150°C. This removes gas bubbles created during the treatment and makes the carbon film flexible. The material is then heated again in an Ar atmosphere at a rate of 100 °C / h to 400 °C, and then at a rate of 900 °C / h to 2850 °C - 3000 °C. The target temperature is maintained for 30 minutes.The metal carbides partially melt and can be finely distributed in the carbon film without producing gaseous byproducts. Cooling takes place in an Ar atmosphere at 1000°C / h. Since the resulting carbon film expands slightly during treatment, it can be re-densified for 15-30 minutes at 250-375 MPa and 20-150°C. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 102020206563 A1

[0002]

Claims

[1] A method for producing a carbon film, in particular graphene film or graphite film, comprising the steps a. Providing a graphene dispersion comprising graphene oxide flakes and a dispersant, in particular water, ethanol or 2-propanol, b. Providing a filter designed as a surface filter, c. applying the graphene dispersion to the filter in such a way that the graphene oxide flakes remain as a filter cake on the filter, in particular without penetrating the filter, and the dispersant passes at least partially through the filter, d. Drying the filter cake to form a carbon film for use as an electrical graphene conductor, e. Thermally treating the carbon film in an inert atmosphere, in particular in an Ar atmosphere, to at least partially reduce the graphene oxide present in the carbon film, in particular at a treatment temperature in the range of 1800°C-3000°C, characterized by that, - in step a) at least one carbide precursor compound selected from the group of sodium tungstate (Na2WO4), sodium molybdate (Na2MoO4), vanadium(IV) oxide sulfate (VOSO4), zirconium(IV) nitrate (Zr(NO3)4), molybdenum disulfide (MoS2), tungsten disulfide (WS2) is added to the graphene dispersion and - in step e) electrically conductive metal carbide, in particular tungsten carbide (WC), dimolybdenum carbide (Mo2C), vanadium carbide (VC), zirconium carbide (ZrC), is formed in the carbon film, in particular in particle form. [2] Method according to claim 1, characterized bythat in step e) the carbide precursor compound reacts with the carbon of the graphene oxide flakes to form a metal carbide by setting a suitable treatment temperature. [3] Method according to one of the preceding claims, characterized by that the treatment temperature in step e) is selected and maintained such that the metal carbide formed melts at least partially and is distributed in the carbon film. [4] Method according to one of the preceding claims, characterized by that the carbon film is thermally pretreated between step d) and step e) to remove volatile by-products, in particular in a temperature range of 300°C-500°C, especially at 400°C. [5] Method according to one of the preceding claims, characterized bythat the carbon film is compacted in a step f) to remove gas bubbles, in particular with a force of 250 - 375 MPa and / or in particular at a temperature of 20°C - 150°C. [6] Method according to one of the preceding claims, characterized by that at least one Lewis acid, in particular AlCl3, AlF3, ZrF4, FeF3, MgF2, TiF4, CuCl2, MoCl5, is intercalated into the carbon film in a step g). [7] Method according to one of the preceding claims, characterized by that the carbon film is detached from the filter after drying in step d). [8] Electrically conductive carbon film with a lattice structure, characterized by that metal carbide is incorporated into the lattice structure of the carbon film, particularly in the form of nano- or microparticles.