A pyrolytic porous graphite coating for SiC crystal surface and preparation method thereof

Abstract

The invention discloses a pyrolytic porous graphite coating for SiC crystal surface and a preparation method thereof, belonging to the technical field of carbon material preparation, and the preparation method comprises the following steps: mixing cleaned silicon carbide crystal, nickel salt and composite precursor, carbonizing at high temperature to obtain modified SiC crystal; placing the modified SiC crystal in a pyrolysis furnace, introducing methane and argon, performing pyrolysis deposition reaction, cooling to obtain pyrolyzed modified SiC crystal; polishing, grinding and cleaning the pyrolyzed modified SiC crystal to obtain a pyrolytic porous graphite coating. The metal carbide nickel carbide formed by nano-iron-nickel particles has a high melting temperature, and forms a uniform and orderly step-like structure with a height of about nanometers on the surface of the silicon carbide crystal, showing good roughness; the mesh carbon layer acts as a buffer layer, plays a transition role between the silicon carbide substrate and the surface pyrolytic porous graphite, and improves the lattice matching between the pyrolytic porous graphite and the silicon carbide crystal.

Description

Technical Field

[0001] The invention relates to the technical field of carbon material preparation, in particular to a pyrolytic porous graphite coating for SiC crystal surface and a preparation method thereof. Background Art

[0002] Pyrolytic graphite is a carbon material that is deposited on the surface of a hot solid (SiC crystal) by thermal decomposition of hydrocarbon gases. It is not real graphite but a carbon material. Carbon deposited at temperatures above 1800°C is called pyrolytic graphite, and carbon deposited at temperatures below 1800°C is called pyrolytic carbon. Pyrolytic graphite is a new type of carbon material with high-temperature chemical stability, good high-temperature corrosion resistance, and a dense structure and good airtightness. Pyrolytic porous graphite coating is a carbon material that is deposited on the surface of a SiC crystal by thermal decomposition of hydrocarbon gases. Pyrolytic porous graphite is formed on the surface of a silicon carbide crystal, which can effectively improve the service life and stability of the silicon carbide crystal.

[0003] The lattice matching degree between pyrolytic porous graphite and silicon carbide crystals is not high, which causes the CC bonds in the pyrolytic porous graphite lattice to stretch to match the underlying substrate silicon carbide crystals, resulting in large stress on the surface of the pyrolytic porous graphite, thereby producing a defective pyrolytic porous graphite coating with poor stability; synthesizing metal nanoparticles such as iron and nickel on the surface of silicon carbide crystals can promote the crystallization and growth of the pyrolytic graphite coating, but the interaction force between metal nanoparticles such as iron and nickel and silicon carbide crystals is small and easy to slip, and the distribution of metal nanoparticles such as iron and nickel is uneven, affecting the stability and distribution state of the pyrolytic graphite coating. Summary of the invention

[0004] The present invention aims to provide a pyrolytic porous graphite coating for SiC crystal surface and a preparation method thereof: nickel chloride hexahydrate, ferrous sulfate heptahydrate and polyethylene glycol are mixed to prepare nano iron-nickel particles with a core-shell structure, wherein the nickel and iron metal elements can promote the growth of carbon atoms generated by methane pyrolysis into pyrolytic graphite and can attach the carbon atoms to the surface of silicon carbide crystal; a composite precursor formed by nano iron-nickel particles and phenolic resin is coated on the surface of the cleaned silicon carbide crystal, and after high-temperature carbonization, the phenolic resin in the composite precursor is thermally decomposed to form a network carbon layer, and a nano iron-nickel doped carbon layer is formed on the surface of the cleaned silicon carbide crystal. The formed network carbon layer acts as a buffer layer, plays a transition role between the silicon carbide substrate and the surface pyrolytic porous graphite, and improves the lattice matching between the pyrolytic porous graphite and the silicon carbide crystal; the nano-iron-nickel particles can form metal carbides nickel carbide and iron carbide with the carbon element in the carbon layer through chemical bonds, so that the nickel carbide and iron carbide are evenly distributed on the surface of the carbon layer, serving as adsorption sites for pyrolytic carbon; nickel carbide has a high melting point and is not easy to melt during the pyrolysis deposition reaction process, and can form a uniform and orderly step-like structure with a height of about nanometers on the surface of the silicon carbide crystal, showing good roughness.

[0005] The technical problems to be solved by the present invention are as follows: the lattice matching degree between pyrolytic porous graphite and silicon carbide crystal is not high, which causes the C-C bonds in the pyrolytic porous graphite lattice to stretch to match the underlying substrate silicon carbide crystal, resulting in great stress on the surface of the pyrolytic porous graphite, thereby producing a defective pyrolytic porous graphite coating with poor stability; synthesizing metal nanoparticles such as iron and nickel on the surface of silicon carbide crystal can promote the crystallization and growth of the pyrolytic graphite coating, but the interaction force between the metal nanoparticles such as iron and nickel and the silicon carbide crystal is small and easy to slip, and the metal nanoparticles such as iron and nickel are unevenly distributed, affecting the stability and distribution state of the pyrolytic graphite coating.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a pyrolytic porous graphite coating for a SiC crystal surface comprises the following steps:

[0008] S1. The silicon carbide crystal is washed with acetone and then treated with a hydrofluoric acid solution to obtain a cleaned silicon carbide crystal.

[0009] S2. The cleaned silicon carbide crystal, nickel salt and composite precursor are mixed and carbonized at high temperature to obtain modified SiC crystal.

[0010] S3. placing the modified SiC crystal in a pyrolysis furnace, introducing methane and argon to carry out pyrolysis deposition reaction, cooling, and obtaining a pyrolyzed modified SiC crystal.

[0011] S4. The modified SiC crystal after pyrolysis is polished, ground and cleaned to obtain a pyrolytic porous graphite coating.

[0012] Furthermore, in step S1, the concentration of the acetone solution is 0.2-0.4 mol / L; the hydrofluoric acid solution is analytically pure with a mass fraction of 50-60%.

[0013] Furthermore, in step S2, the high temperature carbonization temperature is 800-1200°C, and the time is 2-4 hours; the nickel salt is selected from nickel nitrate.

[0014] Furthermore, in step S3, the pyrolysis deposition temperature is 2100-2300°C, the pyrolysis deposition time is 5-6h; the pyrolysis furnace pressure is 3-3.2kPa; the argon gas flow rate is 8-12m 3 / h, methane ventilation is 13-17m 3 / h.

[0015] Furthermore, in step S4, the thickness of the pyrolytic porous graphite coating is 25-35 μm.

[0016] Furthermore, the cleaned silicon carbide crystal in step S1 is specifically prepared by the following steps:

[0017] The silicon carbide crystal was placed in an acetone solution with a concentration of 0.2-0.4 mol / L, and ultrasonically cleaned for 5-10 minutes to remove grease on the substrate surface. The substrate was filtered, washed with anhydrous ethanol for 3 times, washed with deionized water for 3 times, placed in 30 mL of hydrofluoric acid solution, stirred and cleaned for 2 minutes, filtered, washed, and dried to obtain the cleaned silicon carbide crystal.

[0018] Among them, the silicon carbide crystal is placed in an acetone solution, and the acetone interacts with the grease, organic pollutants, etc. on the surface of the silicon carbide crystal, dissolving them in the acetone, thereby removing the surface grease, particles and various pollutants; the silicon carbide crystal after acetone cleaning is mixed with a hydrofluoric acid solution, and the fluoride ions in the hydrofluoric acid solution react with the silicon atoms on the surface to form silicon fluoride, which dissolves in the hydrofluoric acid solution to remove surface scratches and defects.

[0019] Furthermore, the amount ratio of silicon carbide crystal, acetone solution and hydrofluoric acid solution is (2.2-2.6) g: (15-25) mL: (25-35) mL.

[0020] Furthermore, the modified SiC crystal in step S2 is specifically prepared by the following steps:

[0021] Add nickel salt and composite precursor to ethanol, stir evenly, add cleaned silicon carbide crystals, continue stirring at 80°C until the ethanol solvent evaporates and forms a gel, place the gel in a carbonization furnace, carbonize at 1000°C for 3h, cool to room temperature, and obtain modified SiC crystals.

[0022] Among them, the cleaned silicon carbide crystals are mixed with a composite precursor, and the oxygen-containing functional groups contained in the composite precursor can combine with the hydroxyl groups carried by the cleaned silicon carbide crystals to form a gel, so that the composite precursor is coated on the surface of the cleaned silicon carbide crystals. After high-temperature carbonization, the phenolic resin in the composite precursor is thermally decomposed to form a network carbon layer. Nickel nitrate is used as a catalyst here to catalyze the carbonization rate of the phenolic resin in the composite precursor, so that the network carbon layer is coated on the surface of the silicon carbide crystal, thereby forming a nano-iron-nickel doped network carbon layer on the surface of the cleaned silicon carbide crystal.

[0023] Furthermore, the usage ratio of nickel salt, composite precursor, ethanol, and cleaned silicon carbide crystal is (0.1-0.3) g:(10-11) g:(45-55) mL:(1-2) g.

[0024] Furthermore, the composite precursor is prepared by mixing a nickel source, an iron source and polyethylene glycol to prepare nano-iron-nickel particles, and then mixing them with a carbon precursor.

[0025] Further, the nickel source is selected from nickel nitrate or nickel chloride hexahydrate.

[0026] Furthermore, the iron source is selected from ferrous sulfate heptahydrate or ferrous chloride.

[0027] Furthermore, the carbon precursor is selected from phenolic resin or polystyrene resin.

[0028] Furthermore, the polyethylene glycol is selected from polyethylene glycol 4000.

[0029] Further, the composite precursor is specifically prepared by the following steps:

[0030] A1. Add iron source and polyethylene glycol to ethanol and deionized water, stir evenly, introduce argon, add potassium borohydride for redox reaction, stir for 40 minutes, filter, wash 3 times with deionized water, place in ethanol, stir evenly, add nickel source and deionized water, stir for 20 minutes, filter, wash 3 times with deionized water, and dry in an oven at 60°C for 10 minutes to obtain nano iron-nickel particles.

[0031] Among them, polyethylene glycol, as a stabilizer, can combine with ferrous ions in the iron source to form a stable complex. Under argon atmosphere, potassium borohydride, as a reducing agent, reduces the ferrous ions in the iron source to form iron atoms. As the reaction proceeds, the iron atoms nucleate and grow to form stable nano-iron ions. The polyethylene glycol contained on the surface of the nano-iron ions can inhibit the agglomeration of nano-iron.

[0032] Furthermore, nickel ions in the nickel source nickel chloride hexahydrate are adsorbed onto the surface of nano-iron through the action of polyethylene glycol, and under the reduction action of potassium borohydride, the nickel ions are transformed into nickel atoms, forming nano-nickel on the surface of nano-iron, forming nano-nickel-iron particles with a core-shell structure.

[0033] Furthermore, the usage ratio of iron source, polyethylene glycol, ethanol, deionized water, potassium borohydride and nickel source is (0.7-0.8) g:(0.3-0.34) g:(10-20) mL:(70-80) mL:(0.4-0.5) g:(0.02-0.04) g.

[0034] A2. Add nano-iron-nickel particles and carbon precursor into ethanol and stir evenly to obtain a composite precursor.

[0035] Among them, nano-iron-nickel particles are dispersed in the carbon precursor and coated on the surface of the silicon carbide crystal as a carbon source, thereby realizing a carbon layer on the surface of the silicon carbide crystal. As a buffer layer, it plays a transition role between the silicon carbide substrate and the surface pyrolytic porous graphite, thereby improving the lattice matching between the pyrolytic porous graphite and the silicon carbide crystal.

[0036] Furthermore, the dosage ratio of nano-iron-nickel particles, carbon precursor phenolic resin, and ethanol is (0.3-0.7) g: (8-12) g: (25-35) mL.

[0037] Furthermore, compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) In the technical solution of the present invention, the silicon carbide crystal is surface treated with acetone and hydrofluoric acid solution to remove surface grease, particles and various pollutants. The surface treatment of the silicon carbide crystal with hydrofluoric acid solution can remove scratches and defects on the surface of the silicon carbide crystal, exposing a purer silicon carbide surface, which is helpful for subsequent treatment and processing. Nickel chloride hexahydrate, ferrous sulfate heptahydrate and polyethylene glycol are mixed to prepare nano-iron-nickel particles with a core-shell structure. The nickel and iron metal elements can promote the growth of carbon atoms produced by methane pyrolysis into pyrolytic graphite, and can attach carbon atoms to the surface of the silicon carbide crystal.

[0039] (2) In the technical solution of the present invention, a composite precursor formed by nano-iron-nickel particles and phenolic resin is coated on the surface of the cleaned silicon carbide crystal. After high-temperature carbonization, the phenolic resin in the composite precursor is thermally decomposed to form a network carbon layer, so that the network carbon layer is coated on the surface of the silicon carbide crystal, thereby forming a nano-iron-nickel doped network carbon layer on the surface of the cleaned silicon carbide crystal. The formed network carbon layer serves as a buffer layer, plays a transition role between the silicon carbide substrate and the surface pyrolytic porous graphite, improves the lattice matching between the pyrolytic porous graphite and the silicon carbide crystal, avoids the stretching of the CC bonds in the pyrolytic porous graphite lattice, and causes a large stress on the surface of the pyrolytic porous graphite, thereby producing a defective pyrolytic porous graphite coating, thereby improving the stability of the pyrolytic porous graphite.

[0040] (4) In the technical solution of the present invention, during the pyrolysis deposition reaction, the nano-iron-nickel particles can form metal carbides such as nickel carbide and iron carbide with the carbon elements in the carbon layer through chemical bonds, so that the nickel carbide and iron carbide are evenly distributed on the surface of the carbon layer, avoiding the small interaction force between the metal nanoparticles such as iron and nickel and the silicon carbide crystals, which is easy to slip, resulting in the instability of the formed pyrolytic porous graphite coating. In addition, nickel carbide and iron carbide both serve as adsorption sites for pyrolytic carbon, which can promote the deposition of carbon elements produced by methane pyrolysis on the surface of the silicon carbide crystals and accelerate and promote the formation of the pyrolytic porous graphite coating. In addition, nickel carbide has a high melting point. During the pyrolysis deposition reaction, it is not easy to melt. It can form a uniform and orderly step-like structure with a height of about nanometers on the surface of the silicon carbide crystal, showing good roughness, thereby increasing the bonding force with the pyrolytic porous graphite.

[0041] (5) In the technical solution of the present invention, during the pyrolysis deposition reaction, the metal carbide iron carbide is formed and melts into liquid at 2200°C. It exists inside the pyrolytic graphite on the surface of the silicon carbide crystal and acts as an activator to increase the porosity of the pyrolytic graphite, thereby forming a pyrolytic porous graphite coating on the surface of the silicon carbide crystal and improving the performance of the silicon carbide crystal. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] The raw materials used in the embodiments of the present invention are as follows: ferrous sulfate heptahydrate (effective ingredient content 99.8%, Shanghai Aladdin Reagent Co., Ltd.); polyethylene glycol 4000 (analytical grade, Tianjin Xiensi Biochemical Technology Co., Ltd.); potassium borohydride (effective ingredient content 98.6%, Shanghai Aladdin Reagent Co., Ltd.); nickel chloride hexahydrate (effective ingredient content 98.9%, Tianjin Yuanli Chemical Co., Ltd.); ethanol (analytical grade, Tianjin Concord Reagent Co., Ltd.); phenolic resin (effective ingredient content 99%, Green Union (Jining) Chemical Technology Co., Ltd.); acetone (model HZ67-64-1, Shanghai Huzhen Industrial Co., Ltd.); hydrofluoric acid solution (analytical grade, mass fraction 55%, Zibo Qingxu Chemical Sales Co., Ltd.); nickel nitrate (AR, Zhejiang Jindi Biochemical Co., Ltd.); argon (effective ingredient content 99.999%, Xi'an Teheng Gas Chemical Co., Ltd.); methane (Oriental Chemical Glass (Beijing) Technology Co., Ltd., model BB59-CH4).

[0044] Silicon carbide crystal: Beijing Tianke Heda Semiconductor Co., Ltd., β-type silicon carbide crystal, particle size is 2-5mm.

[0045] Example 1

[0046] The composite precursor is specifically prepared by the following steps:

[0047] A1. Add 0.75 g of ferrous sulfate heptahydrate and 0.32 g of polyethylene glycol 4000 to 15 mL of ethanol and 75 mL of deionized water, stir evenly, introduce argon, add 0.45 g of potassium borohydride for redox reaction, stir for 40 min, filter, wash 3 times with deionized water, place in 30 mL of ethanol, stir evenly, add 0.03 g of nickel chloride hexahydrate and 5 mL of deionized water, stir for 20 min, filter, wash 3 times with deionized water, and dry in an oven at 60°C for 10 min to obtain nano iron-nickel particles.

[0048] A2. Add 0.5 g of nano-iron-nickel particles and 10 g of phenolic resin into 30 mL of ethanol and stir evenly to obtain a composite precursor.

[0049] Comparative Example 1

[0050] The difference between this comparative example and Example 1 is that the nano-iron-nickel particles are replaced by nano-iron particles, and the remaining steps and raw materials are the same as those of Example 1.

[0051] A1. Add 0.75 g of ferrous sulfate heptahydrate and 0.32 g of polyethylene glycol 4000 to 15 mL of ethanol and 75 mL of deionized water, stir evenly, introduce argon gas, add 0.45 g of potassium borohydride for redox reaction, stir for 40 min, filter, and wash with deionized water 3 times to obtain nano iron particles.

[0052] A2. Add 0.5 g of nano-iron particles and 10 g of phenolic resin into 30 mL of ethanol and stir evenly to obtain a composite precursor.

[0053] Comparative Example 2

[0054] The difference between this comparative example and Example 1 is that nano-iron-nickel particles are not added, and the remaining steps and raw materials are the same as those of Example 1.

[0055] Example 2

[0056] The modified SiC crystal is specifically prepared by the following steps:

[0057] B1. Place 2.4 g of silicon carbide crystal in 20 mL of 0.3 mol / L acetone solution, and perform ultrasonic cleaning for 5-10 min to remove grease from the substrate surface. Filter, wash with anhydrous ethanol 3 times, and wash with deionized water 3 times. Place in 30 mL of hydrofluoric acid solution, stir and wash for 2 min, filter, wash, and dry to obtain the cleaned silicon carbide crystal.

[0058] B2. Add 0.2 g of nickel nitrate and 10.5 g of the composite precursor prepared in Example 1 to 50 mL of ethanol, stir evenly, add 1.5 g of the cleaned silicon carbide crystal, continue stirring at 80°C until the ethanol solvent evaporates to form a gel, place the gel in a carbonization furnace, carbonize at 1000°C for 3 hours, cool to room temperature, and obtain modified SiC crystals.

[0059] Comparative Example 3

[0060] The difference between this comparative example and Example 2 is that the composite precursor is replaced by the material prepared in Comparative Example 1, and the remaining steps are synchronized with Example 2.

[0061] Comparative Example 4

[0062] The difference between this comparative example and Example 2 is that the composite precursor is replaced by the material prepared in Comparative Example 2, and the remaining steps are synchronized with Example 2.

[0063] Comparative Example 5

[0064] The difference between this comparative example and Example 2 is that the cleaned silicon carbide crystal is replaced with an uncleaned silicon carbide crystal, and the remaining steps are synchronized with Example 2.

[0065] 0.2 g of nickel nitrate and 10.5 g of the composite precursor prepared in Example 1 were added to 50 mL of ethanol and stirred evenly. 1.5 g of unwashed silicon carbide crystals were added and stirring was continued at 80° C. until the ethanol solvent evaporated to form a gel. The gel was placed in a carbonization furnace and carbonized at 1000° C. for 3 h. The mixture was cooled to room temperature to obtain a modified SiC crystal.

[0066] Comparative Example 6

[0067] The difference between this comparative example and Example 2 is that no composite precursor is added, and the remaining steps are synchronized with Example 2.

[0068] 2.4 g of silicon carbide crystal was placed in 20 mL of 0.3 mol / L acetone solution, and ultrasonically cleaned for 5-10 min to remove grease on the substrate surface. The substrate was filtered, washed with anhydrous ethanol for 3 times, washed with deionized water for 3 times, placed in 30 mL of hydrofluoric acid solution, stirred and cleaned for 2 min, filtered, washed, and dried to obtain a modified SiC crystal.

[0069] Example 3

[0070] A method for preparing a pyrolytic porous graphite coating for a SiC crystal surface comprises the following steps:

[0071] S1. The modified SiC crystal prepared in Example 2 was placed in a pyrolysis furnace with a furnace pressure of 3 kPa, argon was introduced, and the temperature was kept at 2250°C for 1 hour, then the temperature was lowered to 2100°C, methane was introduced, and the pyrolysis deposition reaction was carried out for 5 hours, and then cooled to room temperature and taken out to obtain the modified SiC crystal after pyrolysis, wherein the argon ventilation rate was 8m 3 / h, methane ventilation is 13m 3 / h.

[0072] S2. Polishing, grinding and cleaning the pyrolyzed modified SiC crystal prepared in step S1 to obtain a pyrolyzed porous graphite coating.

[0073] Example 4

[0074] A method for preparing a pyrolytic porous graphite coating for a SiC crystal surface comprises the following steps:

[0075] S1. The modified SiC crystal prepared in Example 2 was placed in a pyrolysis furnace with a furnace pressure of 3.1 kPa, argon was introduced, and the temperature was kept at 2250°C for 1 hour, then the temperature was lowered to 2200°C, methane was introduced, and the pyrolysis deposition reaction was carried out for 5.5 hours, and then the modified SiC crystal was obtained after pyrolysis. The argon gas flow rate was 10m 3 / h, methane ventilation is 15m 3 / h.

[0076] S2. Polishing, grinding and cleaning the pyrolyzed modified SiC crystal prepared in step S1 to obtain a pyrolyzed porous graphite coating.

[0077] Example 5

[0078] A method for preparing a pyrolytic porous graphite coating for a SiC crystal surface comprises the following steps:

[0079] S1. The modified SiC crystal prepared in Example 2 was placed in a pyrolysis furnace with a furnace pressure of 3.2 kPa, argon was introduced, and the temperature was kept at 2250°C for 1 hour, then the temperature was lowered to 2200°C, methane was introduced, and the pyrolysis deposition reaction was carried out for 6 hours, then cooled to room temperature, and taken out to obtain the modified SiC crystal after pyrolysis, wherein the argon ventilation rate was 12m 3 / h, methane ventilation is 17m 3 / h.

[0080] S2. Polishing, grinding and cleaning the pyrolyzed modified SiC crystal prepared in step S1 to obtain a pyrolyzed porous graphite coating.

[0081] Comparative Example 7

[0082] The difference between this comparative example and Example 4 is that the modified SiC crystal is replaced by the material prepared in Comparative Example 3, and the remaining steps are synchronized with Example 4.

[0083] Comparative Example 8

[0084] The difference between this comparative example and Example 4 is that the modified SiC crystal is replaced by the material prepared in Comparative Example 4, and the remaining steps are synchronized with Example 4.

[0085] Comparative Example 9

[0086] The difference between this comparative example and Example 4 is that the modified SiC crystal is replaced by the material prepared in Comparative Example 5, and the remaining steps are synchronized with Example 4.

[0087] Comparative Example 10

[0088] The difference between this comparative example and Example 4 is that the modified SiC crystal is replaced by the material prepared in Comparative Example 6, and the remaining steps are synchronized with Example 4.

[0089] The performance of the pyrolytic porous graphite coatings prepared in Examples 3-5 and Comparative Examples 7-10 is now tested;

[0090] Appearance inspection: Surface observation of the pyrolytic porous graphite coating.

[0091] Volume density: The volume density of the pyrolytic porous graphite coating is measured by referring to GB / T24528-2009 standard to test the volume density performance of the pyrolytic porous graphite coating prepared above.

[0092] Adhesion test: According to GB / T9286-1998 standard, the adhesion performance of the pyrolytic porous graphite coating prepared above was tested and graded into 0-6 levels, with 0 being better and 6 being worse.

[0093] Shore hardness test: The Shore hardness of the pyrolytic porous graphite coating prepared above was tested using the JB / T6624-1993 standard.

[0094] Impact strength test: The impact strength of the pyrolytic porous graphite coating prepared above was tested according to GB / T13465.4-2014 standard.

[0095] The test results are shown in Table 1 below.

[0096] Table 1: Test results

[0097] project <![CDATA[Volume density g / cm 3 > Adhesion / Grade Shore hardness / HS Impact strength / MPa Appearance inspection Example 3 2.15 0 74.2 95.6 Gray black, smooth surface Example 4 2.18 0 75.6 96.8 Gray black, smooth surface Example 5 2.16 0 75.4 96.2 Gray black, smooth surface Comparative Example 7 2.12 4 72.2 93.5 Grayish black, slightly rough surface Comparative Example 8 2.09 4 56.3 78.6 Gray black, rough surface Comparative Example 9 2.11 2 70.2 90.1 Gray black, smooth surface Comparative Example 10 2.01 5 55.2 76.3 Gray black, rough surface

[0098] It can be seen from the test results in Table 1 that in Comparative Example 7, the nano-iron-nickel particles are replaced with a composite precursor prepared by nano-iron particles, which is coated on the surface of the silicon carbide crystal to prepare the pyrolytic porous graphite coating, and its adhesion decreases. This may be because the nano-iron-nickel particles can form metal carbides with the carbon elements in the carbon layer through chemical bonds. Nickel carbide has a higher melting point and is not easy to melt during the pyrolysis deposition reaction. It can form a uniform and orderly step-like structure with a height of about nanometers on the surface of the silicon carbide crystal, showing good roughness. Roughness, increase the bonding force with pyrolytic porous graphite, while the nano iron particles lack nickel and cannot achieve this effect, so the adhesion is reduced; Comparative Example 8 does not add the composite precursor prepared by nano iron nickel particles, which is coated on the surface of silicon carbide crystals to prepare pyrolytic porous graphite coatings, and its adhesion and mechanical properties are reduced. This may be because the nano iron nickel particles, nickel, and iron metal elements can promote the growth of carbon atoms produced by methane pyrolysis into pyrolytic graphite, and can attach carbon atoms to the surface of silicon carbide crystals to form a stable pyrolytic graphite coating with good mechanical properties;

[0099] In Comparative Example 9, the cleaned silicon carbide crystals were replaced with uncleaned silicon carbide crystals to prepare modified SiC crystals, which were then used to prepare pyrolytic porous graphite coatings. The mechanical properties of the modified SiC crystals were reduced. This may be because the silicon carbide crystals were surface treated with acetone and hydrofluoric acid solution to remove surface grease, particles and various pollutants. The surface treatment of the silicon carbide crystals with hydrofluoric acid solution can remove scratches and defects on the surface of the silicon carbide crystals, exposing a purer silicon carbide surface, which is helpful for subsequent treatment and processing. In Comparative Example 10, the modified SiC crystals prepared without adding the composite precursor were used to prepare The appearance stability, adhesion and mechanical properties of the prepared pyrolytic porous graphite coating are reduced. This may be because a nano-iron-nickel doped network carbon layer is formed on the surface of the silicon carbide crystal after cleaning. The formed network carbon layer acts as a buffer layer, which plays a transition role between the silicon carbide substrate and the surface pyrolytic porous graphite, improves the lattice matching between the pyrolytic porous graphite and the silicon carbide crystal, avoids the stretching of the CC bonds in the formed pyrolytic porous graphite lattice, and causes a large stress on the surface of the pyrolytic porous graphite, thereby producing a defective pyrolytic porous graphite coating, thereby improving the stability of the pyrolytic porous graphite.

[0100] The data in Table 1 show that the pyrolytic porous graphite coatings prepared in Examples 3-5 not only have high mechanical strength and stability, but also have high adhesion. The silicon carbide crystals are washed with acetone and then treated with a hydrofluoric acid solution to obtain cleaned silicon carbide crystals; the cleaned silicon carbide crystals are mixed with a composite precursor and carbonized at high temperature to obtain modified SiC crystals; the modified SiC crystals are placed in a pyrolysis furnace, methane and argon are introduced, a pyrolysis deposition reaction is carried out, and the reaction is cooled to obtain pyrolyzed modified SiC crystals; the pyrolyzed modified SiC crystals are polished, ground, and cleaned to obtain pyrolytic porous graphite coatings that meet the test performance requirements, while the pyrolytic porous graphite coatings prepared in Comparative Examples 7-10 do not meet the performance requirements, indicating that the pyrolytic porous graphite coatings prepared by the present invention not only have high mechanical strength and stability, but also have high adhesion.

[0101] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0102] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for preparing a pyrolytic porous graphite coating on a SiC crystal surface, characterized in that: The following steps are involved: S1. The silicon carbide crystal is washed with acetone and then treated with a hydrofluoric acid solution to obtain a cleaned silicon carbide crystal; S2. The cleaned silicon carbide crystal, the nickel salt and the composite precursor are mixed and carbonized at high temperature to obtain a modified SiC crystal; The composite precursor is prepared by mixing a nickel source, an iron source and polyethylene glycol to prepare nano-iron-nickel particles, and then mixing with a carbon precursor; The carbon precursor is selected from phenolic resin or polystyrene resin; The nickel source is selected from nickel nitrate or nickel chloride hexahydrate; the iron source is selected from ferrous sulfate heptahydrate or ferrous chloride; the polyethylene glycol is selected from polyethylene glycol 4000; The nano-iron-nickel particles are specifically prepared by the following steps: The iron source and polyethylene glycol are added to ethanol and deionized water, stirred evenly, argon gas is introduced, potassium borohydride is added, stirred for reaction, filtered and washed, placed in ethanol, stirred evenly, a nickel source and deionized water are added, stirred for reaction, filtered, washed and dried to obtain nano iron-nickel particles; S3. Placing the modified SiC crystal in a pyrolysis furnace, introducing methane and argon, performing a pyrolysis deposition reaction, and cooling to obtain a pyrolyzed modified SiC crystal; S4. The modified SiC crystal after pyrolysis is polished, ground and cleaned to obtain a pyrolytic porous graphite coating.

2. The method for preparing a pyrolytic porous graphite coating for SiC crystal surface according to claim 1, characterized in that: The cleaned silicon carbide crystal is specifically prepared by the following steps: The silicon carbide crystal is placed in an acetone solution with a concentration of 0.2-0.4 mol / L, and ultrasonically cleaned for 5-10 minutes to remove grease on the substrate surface. After filtering and washing, the silicon carbide crystal is placed in a hydrofluoric acid solution, stirred and cleaned, filtered, washed, and dried to obtain the cleaned silicon carbide crystal.

3. The method for preparing a pyrolytic porous graphite coating for SiC crystal surface according to claim 2, characterized in that: The amount ratio of the silicon carbide crystal, acetone solution and hydrofluoric acid solution is (2.2-2.6) g: (15-25) mL: (25-35) mL.

4. The method for preparing a pyrolytic porous graphite coating for a SiC crystal surface according to claim 1, characterized in that: The high temperature carbonization temperature is 800-1200° C., and the time is 2-4 hours; the nickel salt is selected from nickel nitrate.

5. The method for preparing a pyrolytic porous graphite coating for SiC crystal surface according to claim 1, characterized in that: The pyrolysis deposition temperature is 2100-2300° C., and the pyrolysis deposition time is 5-6 hours.

6. The method for preparing a pyrolytic porous graphite coating for a SiC crystal surface according to claim 1, characterized in that: The pyrolysis furnace pressure is 3-3.2 kPa; the argon gas flow rate is 8-12 m 3 / h, methane ventilation is 13-17m 3 / h; the thickness of the pyrolytic porous graphite coating is 25-35μm.

7. The pyrolytic porous graphite coating prepared according to the preparation method according to any one of claims 1 to 6.