Si3N4 in-situ modified carbon-based composite material as well as preparation method and application thereof

Abstract

The invention relates to a Si3N4 in-situ modified carbon-based composite material and a preparation method and application thereof.The method specifically comprises the steps that coke powder and graphite or carbon black are mixed, then the mixture and nano SiO2 are mixed and dried to obtain mixed powder, then asphalt is added, mixing and kneading are conducted at the temperature of 280-320 DEG C to form paste, finally, the paste is rolled, segmented and crushed, and a fine particle mixture is obtained; performing cold isostatic pressing on the fine particle mixture to obtain a sintered blank, and then roasting to obtain a carbon-based composite material; and heating the carbon-based composite material in a nitrogen atmosphere, carrying out low-temperature graphitization, and carrying out an in-situ reaction on the carbon-based composite material and Si3N4, so as to obtain the Si3N4 modified carbon-based composite material after the reaction is finished. According to the invention, the Si3N4 in-situ modified carbon-based composite material is prepared by introducing Si-C inert bonds and vacuum lubrication Si3N4 and adopting an in-situ reaction introduction method, so that the vacuum lubrication performance of the pure carbon sliding current collection material is improved on the basis of not reducing the wear resistance of the pure carbon sliding current collection material.

Description

Technical Field

[0001] This invention belongs to the field of carbon-based composite material preparation technology, specifically relating to an in-situ modified Si3N4 carbon-based composite material, its preparation method, and its application. Background Technology

[0002] Carbon-based composite materials have excellent friction-reducing properties and high conductivity under unlubricated conditions. As sliding current collectors, they are widely used in rail transportation, aerospace, thermal power and wind power generation, such as the application of pure carbon sliding current collectors in railway pantograph carbon slide plates and generator brushes.

[0003] Under standard atmospheric pressure and air conditions, when the pure carbon sliding plate current collector material and the contact wire pair are made of copper, the coefficient of friction is about 0.15-0.25. The friction makes it easy for a smooth carbon film to form on the friction surface of the pair. However, when the friction environment is changed to vacuum or dry air conditions, the carbon film between the pure carbon sliding plate current collector material and the copper friction pair gradually disappears, the coefficient of friction increases to 0.5-0.6, and the wear rate is hundreds or thousands of times that of normal wear.

[0004] The lubrication performance of pure carbon sliding current collectors is limited in vacuum or dry environments. This is primarily because graphite's lubricity is due to the weak van der Waals forces between carbon atoms in the layers. In normal friction environments, gas molecules such as water vapor and oxygen can adsorb onto the graphite surface, forming inert bonds like HC, OC, and XC between carbon atom layers, which helps reduce interlayer friction and facilitates sliding between graphite layers. However, in dry or vacuum environments, the adsorption of these gas molecules is absent, increasing interlayer friction and rapidly reducing lubrication performance. To address the severe wear of carbon-based sliding current collectors in vacuum or dry environments, researchers have employed methods such as impregnation with organic lubricants (barium fluoride or grease as lubricants), deposition of diamond-like carbon (DLC) films (DLC is deposited on the surface of pure carbon sliding plates or copper friction pairs), and replacing graphite with MoS2 (MoS2 layers interact through van der Waals forces, while sulfur and molybdenum atoms within the layers are tightly bonded by covalent bonds. This structure makes MoS2 prone to relative sliding between layers during friction). While impregnation with lubricants and coating methods effectively reduce the coefficient of friction of carbon-based sliding current collectors in a vacuum environment, their service life and stability are limited. Sliding current collectors using MoS2 instead of graphite also have superior vacuum lubrication performance, but their electrical and thermal conductivity and mechanical properties are far inferior to those of carbon-based sliding current collectors. Summary of the Invention

[0005] To address the problems of poor lubrication performance and severe abnormal wear of pure carbon current collectors under vacuum or dry air conditions, this invention proposes a method for preparing Si3N4 in-situ modified carbon-based composite materials. Starting with the introduction of Si-C inert bonds and vacuum-lubricating nano-Si3N4, an in-situ reaction introduction method is used to prepare nano-Si3N4 in-situ modified carbon-based composite materials, thereby improving the vacuum lubrication performance of pure carbon sliding current collectors without reducing their wear resistance.

[0006] To solve the above problems, the technical solution of the present invention is: In a first aspect, the present invention provides a method for preparing Si3N4 in-situ modified carbon-based composite materials, comprising the following steps: Step 1: Mixing and dispersing raw materials: Coke powder is mixed with graphite or carbon black to obtain mixed carbon powder; then the mixed carbon powder and nano-SiO2 are mixed and dried to obtain mixed powder; the mixed powder is then kneaded with pitch at 280-320℃ for 2 h to form a paste; finally, the paste is rolled, divided, and crushed to obtain a fine particle mixture with a particle size of 25-100 μm; the mixed powder obtained by mixing and drying carbon powder and nano-SiO2 in this invention is conducive to the subsequent reaction of nano-SiO2 with carbon at high temperature, creating conditions for the formation of Si3N4.

[0007] Step 2: Cold isostatic pressing: The fine particle mixture obtained in Step 1 is cold isostatically pressed under a pressure of 200 MPa to obtain a sintered blank.

[0008] Step 3: Calcination and carbonization: The sintered embryo obtained in step 2 is calcined. After calcination, it is cooled to obtain a carbon-based composite material. The calcination process is as follows: first, the temperature is increased from room temperature to 300℃ at a rate of 15℃ / h; then, the temperature is increased from 300℃ to 550℃ at a rate of 0.65℃ / h; then, the temperature is increased from 550℃ to 950℃ at a rate of 2℃ / h; finally, the temperature is held at 950℃ for 8 hours. The calcination process mainly decomposes and carbonizes the organic components (such as organic matter in binders like asphalt) in the sintered embryo.

[0009] Step 4: Low-temperature graphitization and in-situ reaction: The carbon-based composite material obtained in step 3 was subjected to low-temperature graphitization and in-situ reaction with Si3N4 under a nitrogen atmosphere. After the reaction was completed, Si3N4 modified carbon-based composite material was obtained. The heating process is as follows: First, raise the temperature from room temperature to 1000℃ at a rate of 500℃ / h, and then hold at 1000℃ for 5 minutes. Next, the temperature was increased from 1000℃ to 1550℃ at a rate of 400℃ / h, and then held at 1550℃ for 20 minutes. Then, the temperature was increased from 1550℃ to 2300℃ at a rate of 400℃ / h, and held at 2300℃ for 90 min.

[0010] The chemical reactions that occur during the low-temperature graphitization process are shown in formula (1) and formula (2), where formula (1) is the reaction formula for the formation of Si3N4 in the carbon-based composite material, and formula (2) is the chemical reaction formula for the graphitization of the carbon-based composite material.

[0011] (1) (2) In this invention, nano-SiO2 is introduced as a graphitization catalyst, which can effectively improve the graphitization degree of carbon-based composite materials through low-temperature heat treatment, thereby improving the lubrication performance of carbon-based composite materials without reducing their mechanical properties and wear resistance. On the other hand, pure carbon sliding current collectors are modified in situ with Si3N4. The Si3N4-modified carbon-based composite materials have excellent interfacial bonding properties (interfacial bonding between SiC / Si3N4 and the carbon matrix), which is beneficial for Si3N4 to improve the lubrication performance of pure carbon sliding current collectors without reducing their mechanical properties and wear resistance.

[0012] Further, the coke powder mentioned in step 1 is at least one of petroleum coke and pitch coke, and the coke powder accounts for 52 wt%-64 wt% of the total mass of the fine particulate mixture, with a particle size of 1-25 μm. The proportion of coke powder in the total mass of the fine particulate mixture can also be 52 wt%, 62 wt%, 64 wt%, or any range between the above two values. When the coke powder is both petroleum coke and pitch coke, the petroleum coke and pitch coke each account for 31 wt%-32 wt% of the total mass of the fine particulate mixture.

[0013] Furthermore, the graphite or carbon black mentioned in step 1 accounts for 3 wt% of the total mass of the fine particulate mixture.

[0014] Further, the nano-SiO2 accounts for 3 wt%-15 wt% of the total mass of the fine particulate mixture, and the particle size is 10 nm-100 nm. The amount of nano-SiO2 added in this invention can ensure the generation of an appropriate amount of Si3N4 particles in the carbon-based composite material. The proportion of nano-SiO2 in the total mass of the fine particulate mixture can also be 3 wt%, 5 wt%, 15 wt%, or any range between two of the above values; preferably, the mass fraction of nano-SiO2 in the total mass of the fine particulate mixture is 5 wt%.

[0015] Furthermore, the asphalt constitutes 22-35 wt% of the total mass of the fine-particle mixture, preferably 30 wt%. The asphalt provides sufficient binding force to enable the mixture to form a processable paste.

[0016] Furthermore, the nitrogen gas flow rate is 1.0-3.0 L / min.

[0017] In a second aspect, the present invention provides an in-situ modified carbon-based composite material of Si3N4 prepared according to the above preparation method.

[0018] In a third aspect, the present invention provides the application of the above-mentioned Si3N4 modified carbon-based composite material as a sliding current collector material.

[0019] Furthermore, the sliding current collector material is applied to the pantograph sliding plate.

[0020] The beneficial effects of the present invention through the above technical solution are as follows: (1) Innovative design concept for improving vacuum lubrication: Si3N4 addition and the introduction of C-Si inert bonds in the graphite layer. On the one hand, Si3N4 in the Si3N4 modified carbon-based composite material has excellent vacuum lubrication performance, which directly improves the vacuum lubrication performance of pure carbon sliding current collectors; on the other hand, during the vacuum sliding friction process, SiC / Si in the Si3N4 modified carbon-based composite material enters between the graphite layers and forms Si-C inert bonds with C atoms, which improves the vacuum lubrication performance of pure carbon sliding current collectors.

[0021] (2) Innovative preparation method: Low-temperature graphitization and in-situ reaction of Si3N4. On the one hand, nano-SiO2 is introduced as a graphitization catalyst, and the graphitization degree of carbon-based composite materials can be effectively improved through low-temperature heat treatment, thereby improving the lubrication performance of carbon-based composite materials without reducing their mechanical properties and wear resistance. On the other hand, pure carbon sliding current collectors are modified in-situ with Si3N4. The Si3N4-modified carbon-based composite materials have excellent interfacial bonding performance (interfacial bonding between SiC / Si3N4 and the carbon matrix), which is beneficial for Si3N4 to improve the lubrication performance of pure carbon sliding current collectors without reducing their mechanical properties and wear resistance.

[0022] (3) Si3N4 modified carbon-based composite materials are prepared by kneading, isostatic pressing and low-temperature graphitization. This method has a simple and easy-to-control process and does not require high-end equipment. Low-temperature graphitization shortens the preparation cycle and reduces the preparation cost of carbon-based composite materials. In addition, the one-time molding process of cold isostatic pressing + low-temperature graphitization is used instead of the traditional molding + multiple impregnation carbonization process, which improves the comprehensive performance and production efficiency of pure carbon current collector materials. Attached Figure Description

[0023] Figure 1 This is a flowchart of the preparation process of in-situ modified carbon-based composite materials using Si3N4. Figure 2These are XRD diffraction patterns of the pure carbon material prepared in Example 1 and the Si3N4 modified carbon-based composite materials prepared in Examples 2-6; Figure 3 These are the instantaneous and average friction coefficients of the pure carbon material in Example 1; Figure 4 The instantaneous friction coefficient and average friction coefficient of the Si3N4 modified carbon-based composite material in Example 2; Figure 5 The instantaneous friction coefficient and average friction coefficient of the Si3N4 modified carbon-based composite material in Example 3; Figure 6 The instantaneous friction coefficient and average friction coefficient of the Si3N4 modified carbon-based composite material in Example 4; Figure 7 The instantaneous friction coefficient and average friction coefficient of the Si3N4 modified carbon-based composite material in Example 5; Figure 8 These are the instantaneous friction coefficient and average friction coefficient of the Si3N4 modified carbon-based composite material in Example 6. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The present invention will be described in detail below with specific embodiments. Unless otherwise specified, all conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Raw materials and reagents whose manufacturers are not specified are all commercially available products. The preparation flow chart of Si3N4 in-situ modified carbon-based composite materials is shown below. Figure 1 .

[0026] Example 1 (without silicon dioxide) Step 1: Mixing and dispersing raw materials: 5.7 kg of pitch coke was crushed to approximately 2 mm, and then further pulverized to a particle size of 15 μm using an air jet mill to obtain coke powder; then, the above coke powder was mixed with 0.3 kg of natural graphite to obtain mixed carbon powder; the above mixed carbon powder was placed in a kneader, and 3 kg of high-temperature pitch (softening point 220℃) was added, and kneaded at 300℃ for 2 h. After kneading, the paste was quickly rolled into sheets, with the sheet thickness controlled at 1-2 mm; then, the rolled sheets were crushed to 2 mm, and further pulverized to a particle size of 30 μm using an impact air jet mill to obtain a fine particle mixture; the fine particle mixture contained 57 wt% pitch coke, 3 wt% natural graphite, 0 wt% nano-SiO2, and 30 wt% pitch. Step 2: Cold isostatic pressing: The mixed powder is placed in a rubber bag, vibrated and compacted, and then cold isostatically pressed under a pressure of 200 MPa to obtain a sintered blank with a sample diameter of 400 mm. Step 3: Calcination and carbonization: The sintered blank is transferred into a carbonization furnace for calcination. After calcination, it is cooled to obtain pure carbon material. The specific calcination process is as follows: First, the temperature is increased from room temperature to 300℃ at a rate of 15℃ / h; then, the temperature is increased from 300℃ to 550℃ at a rate of 0.65℃ / h; then, the temperature is increased from 550℃ to 950℃ at a rate of 2℃ / h; finally, the temperature is held at 950℃ for 8 hours. Step 4: Low-temperature graphitization: The carbon-based material is transferred to a graphitization furnace, and then heated to perform low-temperature graphitization. After the reaction is complete, graphitized pure carbon material is obtained, which can be directly used as a sliding current collector, i.e., pure carbon sliding current collector. The low-temperature graphitization heating process is as follows: First, the temperature is increased from room temperature to 1000℃ at a rate of 500℃ / h, and held at 1000℃ for 5 minutes; then, the temperature is increased from 1000℃ to 1550℃ at a rate of 400℃ / h, and held at 1550℃ for 20 minutes; then, the temperature is increased from 1550℃ to 2300℃ at a rate of 400℃ / h, and held at 2300℃ for 90 minutes.

[0027] The comprehensive properties of pure carbon materials (pure carbon sliding current collectors) were tested according to national standards GB / T 34572-2017 and TB / T 1842.3-2016. The relevant results are as follows: the graphitization degree of the pure carbon material is 3%. The flexural strength and compressive strength of the pure carbon material are 79 MPa and 163.77 MPa, respectively, the hardness is 93.5 HS, and the resistivity is 11.7 μΩ·m. The sliding friction test conditions of the pure carbon material and the copper friction pair are as follows: under vacuum, 10 A, speed 30 km / h, and load 15 N, the friction coefficient of the material is 0.55, and the wear rate is 750 mm / 10000 km. The sliding friction condition of the pure carbon material and the copper friction pair is unstable, and the friction surfaces of the pure carbon sliding current collector and the copper friction pair have deep wear tracks, indicating severe wear on both. Figure 3 The graph shows the instantaneous friction coefficient and average friction coefficient of the pure carbon material in Example 1.

[0028] Example 2 Step 1: Mixing and dispersing raw materials: 5.2 kg of pitch coke was crushed to about 2 mm, and then pulverized to a particle size of 15 μm using an air jet mill to obtain coke powder; then the coke powder was mixed with 0.3 kg of natural graphite to obtain mixed carbon powder; 1.5 kg of nano-SiO2 (particle size of 80 nm) and mixed carbon powder were placed in a V-type mixer, alcohol was added, and the mixture was wet-mixed for 8 hours, then dried for later use; then the mixture of nano-SiO2 and mixed carbon powder was placed in a kneader, 3 kg of high-temperature pitch (softening point 220℃) was added, and kneaded at 300℃ for 2 hours to obtain a paste; then the paste was rapidly rolled into sheets, with the sheet thickness controlled at 1-2 mm; then the sheets were crushed to 2 mm, and pulverized to a particle size of 30 μm using an impact air jet mill to obtain a fine particle mixture; the fine particle mixture contained 52 wt% pitch coke, 3 wt% natural graphite, 15 wt% nano-SiO2, and 30 wt% pitch. Step 2: Cold isostatic pressing: The fine particle mixture powder is placed in a rubber bag, vibrated and then cold isostatically pressed under a pressure of 200 MPa to obtain a sintered blank with a sample diameter of 400 mm. Step 3: Calcination and carbonization: The sintered blank is transferred into a carbonization furnace for calcination. After calcination, it is cooled to obtain a carbon-based composite material. The calcination process is as follows: First, the temperature is increased from room temperature to 300℃ at a rate of 15℃ / h; then, the temperature is increased from 300℃ to 550℃ at a rate of 0.65℃ / h; then, the temperature is increased from 550℃ to 950℃ at a rate of 2℃ / h; finally, the temperature is held at 950℃ for 8 hours. Step 4: Low-temperature graphitization and in-situ reaction: The carbon-based composite material is transferred into a graphitization furnace. After evacuation, nitrogen gas is introduced to a slightly positive pressure at a flow rate of 1.5 L / min. Then, the temperature is raised to carry out low-temperature graphitization and in-situ reaction with Si3N4. After the reaction, Si3N4-modified carbon-based composite material is obtained, which can be directly used as a sliding current collector material, i.e., Si3N4-modified carbon-based composite sliding current collector material. The heating process is as follows: First, the temperature is raised from room temperature to 1000℃ at a rate of 500℃ / h, and held at 1000℃ for 5 min; then, the temperature is raised from 1000℃ to 1550℃ at a rate of 400℃ / h, and held at 1550℃ for 20 min; then, the temperature is raised from 1550℃ to 2300℃ at a rate of 400℃ / h, and held at 2300℃ for 90 min.

[0029] The comprehensive properties of Si3N4 modified carbon-based composite materials (Si3N4 modified carbon-based composite sliding current collectors) were tested according to national standards GB / T 34572-2017 and TB / T 1842.3-2016. The relevant results are as follows: The graphitization degree of the Si3N4 modified carbon-based composite material is 55%. The flexural strength and compressive strength of the composite material are 94 MPa and 188.45 MPa, respectively, the hardness is 131.5HS, and the resistivity is 100.3 μΩ·m. The sliding friction test conditions of the Si3N4 modified carbon-based composite material and the copper friction pair are as follows: under vacuum, 10A, speed 30 km / h, and load 15 N, the friction coefficient of the composite material is 0.43, and the wear rate is 1.0 mm / 10000 km. The sliding friction condition of the Si3N4 modified carbon-based composite material and the copper friction pair is relatively stable. The Si3N4 modified carbon-based composite material has good wear resistance, but the friction surface of the copper friction pair has more grooves and severe wear. A continuous carbon film is formed on the friction surface of both the Si3N4 modified carbon-based composite material and the copper friction pair. Figure 4 The instantaneous friction coefficient and average friction coefficient of the Si3N4 modified carbon-based composite material prepared in Example 2 are shown.

[0030] Example 3 Step 1: Mixing and dispersing raw materials: 6.2 kg of pitch coke was crushed to approximately 2 mm, and then further pulverized to a particle size of 15 μm using an air jet mill to obtain coke powder; then, the coke powder was mixed with 0.3 kg of natural graphite to obtain mixed carbon powder; 0.5 kg of nano-SiO2 (particle size 50 nm) and the mixed carbon powder were placed in a V-type mixer, and after adding alcohol, they were wet-mixed for 8 hours, and then dried for later use; the mixture of nano-SiO2 and mixed carbon powder was placed in a kneader, and 3 kg of high-temperature pitch (softening point 220℃) was added, and kneaded at 300℃ for 2 hours to obtain a paste; then, the paste was rapidly rolled into sheets, with the sheet thickness controlled at 1-2 mm. The rolled sheets were then crushed to 2 mm and further pulverized to a particle size of 30 μm using an impact air jet mill to obtain a fine particle mixture; the fine particle mixture contained 62 wt% pitch coke, 3 wt% natural graphite, 5 wt% nano-SiO2, and 30 wt% pitch. Step 2: Cold isostatic pressing: The fine particle mixture powder is placed in a rubber bag, vibrated and then cold isostatically pressed under a pressure of 200 MPa to obtain a sintered blank with a sample diameter of 400 mm. Step 3: Calcination and carbonization: The sintered blank is transferred into a carbonization furnace for calcination. After calcination, it is cooled to obtain a carbon-based composite material. The calcination process is as follows: First, the temperature is increased from room temperature to 300℃ at a rate of 15℃ / h; then, the temperature is increased from 300℃ to 550℃ at a rate of 0.65℃ / h; then, the temperature is increased from 550℃ to 950℃ at a rate of 2℃ / h; finally, the temperature is held at 950℃ for 8 hours. Step 4: Low-temperature graphitization and in-situ reaction: The carbon-based composite material is transferred to a graphitization furnace. After evacuation, nitrogen gas is introduced to a slightly positive pressure at a flow rate of 1.5 L / min. Then, the temperature is raised to carry out low-temperature graphitization and in-situ reaction with Si3N4. After the reaction, Si3N4-modified carbon-based composite material is obtained, which can be directly used as a sliding current collector material, i.e., Si3N4-modified carbon-based composite sliding current collector material. The heating process is as follows: First, the temperature is raised from room temperature to 1000℃ at a rate of 500℃ / h, and held at 1000℃ for 5 min. Then, the temperature is raised from 1000℃ to 1550℃ at a rate of 400℃ / h, and held at 1550℃ for 20 min. After that, the temperature is raised from 1550℃ to 2300℃ at a rate of 400℃ / h, and held at 2300℃ for 90 min.

[0031] The comprehensive properties of Si3N4 modified carbon-based composite materials (Si3N4 modified carbon-based composite sliding current collectors) were tested according to national standards GB / T 34572-2017 and TB / T 1842.3-2016. The relevant results are as follows: The graphitization degree of the Si3N4 modified carbon-based composite material is 36%. The flexural strength and compressive strength of the composite material are 81 MPa and 171.6 MPa, respectively, the hardness is 96.1 HS, and the resistivity is 21.88 μΩ·m. The sliding friction test conditions of the Si3N4 modified carbon-based composite material with copper friction pair are as follows: under vacuum, 10 A, speed 30 km / h, and load 15 N, the friction coefficient of the composite material is 0.29, and the wear rate is 4.6 mm / 10000 km. The sliding friction condition of the Si3N4 modified carbon-based composite material and the copper friction pair is relatively stable. In addition, a continuous and stable carbon film is formed on the friction surface of both the Si3N4 modified carbon-based composite material and the copper friction pair. Both friction pairs have good wear resistance. The Si3N4 modified carbon-based composite material meets the comprehensive performance requirements of the pantograph sliding plate. Figure 5 The instantaneous friction coefficient and average friction coefficient of the Si3N4 modified carbon-based composite material prepared in Example 3 are shown.

[0032] Example 4 Step 1: Mixing and dispersing raw materials: 6.2 kg of petroleum coke was crushed to approximately 2 mm, and then further pulverized to a particle size of 15 μm using an air jet mill to obtain coke powder. The coke powder was then mixed with 0.3 kg of natural graphite to obtain mixed carbon powder. 0.5 kg of nano-SiO2 (50 nm particle size) and the mixed carbon powder were placed in a V-type mixer, and alcohol was added for 8 hours of wet mixing. The mixture was then dried and set aside. Next, the nano-SiO2 and mixed carbon powder mixture was placed in a kneader, and 3 kg of high-temperature asphalt (softening point 220℃) was added. The mixture was kneaded at 300℃ for 2 hours to obtain a paste. The paste was then rapidly rolled into sheets, with the sheet thickness controlled at 1-2 mm. The rolled sheets were then crushed to 2 mm and further pulverized to a particle size of 30 μm using an impact air jet mill to obtain a fine particle mixture. The fine particle mixture contained 52 wt% petroleum coke, 3 wt% natural graphite, 5 wt% nano-SiO2, and 30 wt% asphalt. Step 2: Cold isostatic pressing: The fine particle mixture powder is placed in a rubber bag, vibrated and then cold isostatically pressed under a pressure of 200 MPa to obtain a sintered blank with a sample diameter of 400 mm. Step 3: Calcination and carbonization: The sintered blank is transferred into a carbonization furnace for calcination. After calcination, it is cooled to obtain a carbon-based composite material. The calcination process is as follows: First, the temperature is increased from room temperature to 300℃ at a rate of 15℃ / h; then, the temperature is increased from 300℃ to 550℃ at a rate of 0.65℃ / h; then, the temperature is increased from 550℃ to 950℃ at a rate of 2℃ / h; finally, the temperature is held at 950℃ for 8 hours. Step 4: Low-temperature graphitization and in-situ reaction: The carbon-based composite material is transferred to a graphitization furnace. After evacuation, nitrogen gas is introduced to a slightly positive pressure at a flow rate of 1.5 L / min. Then, the temperature is raised to carry out low-temperature graphitization and in-situ reaction with Si3N4. After the reaction, Si3N4-modified carbon-based composite material is obtained, which can be directly used as a sliding current collector material, i.e., Si3N4-modified carbon-based composite sliding current collector material. The heating process is as follows: First, the temperature is raised from room temperature to 1000℃ at a rate of 500℃ / h, and held at 1000℃ for 5 min. Then, the temperature is raised from 1000℃ to 1550℃ at a rate of 400℃ / h, and held at 1550℃ for 20 min. After that, the temperature is raised from 1550℃ to 2300℃ at a rate of 400℃ / h, and held at 2300℃ for 90 min.

[0033] The comprehensive properties of Si3N4 modified carbon-based composite materials (Si3N4 modified carbon-based composite sliding current collectors) were tested according to national standards GB / T 34572-2017 and TB / T 1842.3-2016. The relevant results are as follows: the graphitization degree of the Si3N4 modified carbon-based composite material is 44%, the flexural strength and compressive strength of the composite material are 68 MPa and 128.8 MPa, respectively, the hardness is 74HS, and the resistivity is 15.88 μΩ·m. The sliding friction test conditions of the Si3N4 modified carbon-based composite material as a sliding current collector with a copper friction pair are as follows: under vacuum, 10A, speed 30 km / h, and load 15 N, the friction coefficient of the Si3N4 modified carbon-based composite material is 0.26, and the wear rate is 7.0 mm / 10000 km. Compared with other embodiments, the friction coefficient of Embodiment 4 has the smallest fluctuation and the wear rate of the copper friction pair is the lowest; the sliding friction condition of the Si3N4 modified carbon-based composite material and the copper friction pair is stable, and a continuous and stable carbon film is formed on the friction surfaces of the Si3N4 modified carbon-based composite material and the copper friction pair. Figure 6 The instantaneous friction coefficient and average friction coefficient of the Si3N4 modified carbon-based composite material prepared in Example 4 are shown.

[0034] Example 5 Step 1: Mixing and dispersing raw materials: Crush 3.1 kg of petroleum coke and 3.1 kg of pitch coke to about 2 mm, then pulverize them to a particle size of 8 μm using an air jet mill to obtain coke powder; then mix the coke powder with 0.3 kg of natural graphite to obtain mixed carbon powder. Put 0.5 kg of nano-SiO2 (particle size of 50 nm) and mixed carbon powder into a V-type mixer, add alcohol and wet mix for 8 hours, then dry for later use; put the mixture of nano-SiO2 and mixed carbon powder into a kneader, add 3 kg of high-temperature pitch (softening point 220℃), and knead at 300℃ for 2 hours to obtain a paste; then quickly roll the paste into sheets, controlling the sheet thickness to 1-2 mm. The rolled sheets were then crushed to 2 mm and further pulverized to a particle size of 30 μm using an impact jet mill to obtain a fine particle mixture. The fine particle mixture contained 31 wt% asphalt coke, 31 wt% petroleum coke, 3 wt% natural graphite, 5 wt% nano-SiO2, and 30 wt% asphalt. Step 2: Cold isostatic pressing: The fine particle mixture powder is placed into a rubber bag, vibrated, and then cold isostatically pressed under a pressure of 200 MPa to obtain a sintered preform; Step 3: Calcination and carbonization: The sintered blank is transferred into a carbonization furnace for calcination. After calcination, it is cooled to obtain a carbon-based composite material. The calcination process is as follows: First, the temperature is increased from room temperature to 300℃ at a rate of 15℃ / h; then, the temperature is increased from 300℃ to 550℃ at a rate of 0.65℃ / h; then, the temperature is increased from 550℃ to 950℃ at a rate of 2℃ / h; finally, the temperature is held at 950℃ for 8 hours. Step 4: Low-temperature graphitization and in-situ reaction: The carbon-based composite material is transferred to a graphitization furnace. After evacuation, nitrogen gas is introduced to a slightly positive pressure at a flow rate of 1.5 L / min. Then, the temperature is raised to carry out low-temperature graphitization and in-situ reaction with Si3N4. After the reaction, Si3N4-modified carbon-based composite material is obtained, which can be directly used as a sliding current collector material, i.e., Si3N4-modified carbon-based composite sliding current collector material. The heating process is as follows: First, the temperature is raised from room temperature to 1000℃ at a rate of 500℃ / h, and held at 1000℃ for 5 min. Then, the temperature is raised from 1000℃ to 1550℃ at a rate of 400℃ / h, and held at 1550℃ for 20 min. After that, the temperature is raised from 1550℃ to 2300℃ at a rate of 400℃ / h, and held at 2300℃ for 90 min.

[0035] The comprehensive properties of Si3N4 modified carbon-based composite materials (Si3N4 modified carbon-based composite sliding current collectors) were tested according to national standards GB / T 34572-2017 and TB / T 1842.3-2016. The relevant results are as follows: The graphitization degree of the Si3N4 modified carbon-based composite material is 37%. The flexural strength and compressive strength of the composite material are 78 MPa and 155.9 MPa, respectively, the hardness is 89HS, and the resistivity is 19.14 μΩ·m. The sliding friction test conditions of the Si3N4 modified carbon-based composite material and the copper friction pair are as follows: under vacuum, 10 A, speed 30 km / h, and load 15 N, the friction coefficient of the composite material is 0.27, and the wear rate is 5.11 mm / 10000 km. The sliding friction condition of the Si3N4 modified carbon-based composite material and the copper friction pair is relatively stable. A continuous and stable carbon film is formed on the friction surface of both the Si3N4 modified carbon-based composite material and the copper friction pair. Both friction pairs have good wear resistance. The Si3N4 modified carbon-based composite material meets the comprehensive performance requirements of the pantograph sliding plate. Figure 7 The instantaneous friction coefficient and average friction coefficient of the Si3N4 modified carbon-based composite material prepared in Example 5 are shown.

[0036] Example 6 Step 1: Mixing and dispersing raw materials: Crush 3.2 kg of petroleum coke and 3.2 kg of pitch coke to about 2 mm, then pulverize them to a particle size of 8 μm using an air jet mill to obtain coke powder; then mix the coke powder with 0.3 kg of natural graphite to obtain mixed carbon powder. Put 0.3 kg of nano-SiO2 (particle size of 50 nm) and mixed carbon powder into a V-type mixer, add alcohol and wet mix for 8 hours, then dry for later use; put the mixture of nano-SiO2 and mixed carbon powder into a kneader, add 3 kg of high-temperature pitch (softening point 220℃), and knead at 300℃ for 2 hours to obtain a paste; then quickly roll the paste into sheets, controlling the sheet thickness to 1-2 mm. The rolled sheets were then crushed to 2 mm and further pulverized to a particle size of 30 μm using an impact jet mill to obtain a fine particle mixture. The fine particle mixture contained 32 wt% asphalt coke, 32 wt% petroleum coke, 3 wt% natural graphite, 3 wt% nano-SiO2, and 30 wt% asphalt. Step 2: Cold isostatic pressing: The fine particle mixture powder is placed in a rubber bag, vibrated and then cold isostatically pressed under a pressure of 200 MPa to obtain a sintered blank with a sample diameter of 400 mm. Step 3: Calcination and carbonization: The sintered blank is transferred into a carbonization furnace for calcination. After calcination, it is cooled to obtain a carbon-based composite material. The calcination process is as follows: First, the temperature is increased from room temperature to 300℃ at a rate of 15℃ / h; then, the temperature is increased from 300℃ to 550℃ at a rate of 0.65℃ / h; then, the temperature is increased from 550℃ to 950℃ at a rate of 2℃ / h; finally, the temperature is held at 950℃ for 8 hours. Step 4: Low-temperature graphitization and in-situ reaction: The carbon-based composite material is transferred to a graphitization furnace. After evacuation, nitrogen gas is introduced to a slightly positive pressure at a flow rate of 1.5 L / min. Then, the temperature is raised to carry out low-temperature graphitization and in-situ reaction with Si3N4. After the reaction, Si3N4-modified carbon-based composite material is obtained, which can be directly used as a sliding current collector material, i.e., Si3N4-modified carbon-based composite sliding current collector material. The heating process is as follows: First, the temperature is raised from room temperature to 1000℃ at a rate of 500℃ / h, and held at 1000℃ for 5 min. Then, the temperature is raised from 1000℃ to 1550℃ at a rate of 400℃ / h, and held at 1550℃ for 20 min. After that, the temperature is raised from 1550℃ to 2300℃ at a rate of 400℃ / h, and held at 2300℃ for 90 min.

[0037] The comprehensive properties of Si3N4 modified carbon-based composite materials (Si3N4 modified carbon-based composite sliding current collectors) were tested according to national standards GB / T 34572-2017 and TB / T 1842.3-2016. The relevant results are as follows: The graphitization degree of the Si3N4 modified carbon-based composite material is 28%. The flexural strength and compressive strength of the composite material are 85 MPa and 171.4 MPa, respectively, the hardness is 95.6HS, and the resistivity is 30.3 μΩ·m. The sliding friction test conditions of the Si3N4 modified carbon-based composite material with copper friction pair are as follows: under vacuum, 10 A, speed 30 km / h, and load 15 N, the friction coefficient of the composite material is 0.39, and the wear rate is 15.74 mm / 10000 km. The Si3N4 modified carbon-based composite material exhibits good stability under sliding friction conditions with the copper friction pair. However, an incompletely continuous carbon film exists on the friction surface of the Si3N4 modified carbon-based composite material and the copper friction pair, and the wear rate of both friction pairs remains relatively high. Figure 8 The instantaneous friction coefficient and average friction coefficient of the Si3N4 modified carbon-based composite material prepared in Example 6.

[0038] Figure 2 The XRD diffraction patterns of the pure carbon material prepared in Example 1 and the Si3N4 modified carbon-based composite materials prepared in Examples 2-6 show that the carbon-based composite materials prepared in Examples 2-6 are doped with SiC / Si3N4.

[0039] The embodiments described above are merely preferred embodiments of the present invention and are only used to explain the present invention. They are not intended to limit the scope of the present invention. For those skilled in the art, other implementation methods can be easily made by substitution or modification based on the technical content disclosed in this specification. Therefore, all changes and improvements made on the principle of the present invention should be included within the scope of the patent application of the present invention.

Claims

1. A method for preparing Si3N4 in-situ modified carbon-based composite materials, characterized in that, Includes the following steps: Step 1: Mixing and dispersing raw materials: Mix coke powder with graphite or carbon black to obtain mixed carbon powder; Then, the mixed carbon powder and nano SiO2 are mixed and dried to obtain a mixed powder. The mixed powder is then kneaded with asphalt at 280-320℃ for 2 hours to form a paste. Finally, the paste is rolled, divided, and crushed to obtain a fine particle mixture with a particle size of 25-100 μm. Step 2: Cold isostatic pressing: The fine particle mixture obtained in Step 1 is cold isostatically pressed under a pressure of 200 MPa to obtain a sintered blank; Step 3: Calcination and carbonization: The sintered embryo obtained in step 2 is calcined. After calcination, it is cooled to obtain a carbon-based composite material. Step 4: Low-temperature graphitization and in-situ reaction: The carbon-based composite material obtained in step 3 was subjected to low-temperature graphitization and in-situ reaction with Si3N4 under a nitrogen atmosphere. After the reaction was completed, Si3N4 modified carbon-based composite material was obtained. The heating process is as follows: First, raise the temperature from room temperature to 1000℃ at a rate of 500℃ / h, and then hold at 1000℃ for 5 minutes. Next, the temperature was increased from 1000℃ to 1550℃ at a rate of 400℃ / h, and then held at 1550℃ for 20 minutes. Then, the temperature was increased from 1550℃ to 2300℃ at a rate of 400℃ / h, and held at 2300℃ for 90 min.

2. The method for preparing an in-situ modified Si3N4 carbon-based composite material according to claim 1, characterized in that, The coke powder mentioned in step 1 is at least one of petroleum coke and pitch coke, and the coke powder accounts for 52 wt%-64 wt% of the total mass of the fine particle mixture, with a particle size of 1-25 μm.

3. The method for preparing an in-situ modified Si3N4 carbon-based composite material according to claim 1, characterized in that, The graphite or carbon black mentioned in step 1 accounts for 3 wt% of the total mass of the fine particle mixture.

4. The method for preparing an in-situ modified Si3N4 carbon-based composite material according to claim 1, characterized in that, The nano-SiO2 accounts for 3 wt%-15 wt% of the total mass of the fine particle mixture, and the particle size is 10 nm-100 nm.

5. The method for preparing an in-situ modified Si3N4 carbon-based composite material according to claim 1, characterized in that, The asphalt accounts for 22-35 wt% of the total mass of the fine-particle mixture.

6. The method for preparing an in-situ modified Si3N4 carbon-based composite material according to claim 1, characterized in that, The roasting process is as follows: first, the temperature is increased from room temperature to 300℃ at a rate of 15℃ / h; then, the temperature is increased from 300℃ to 550℃ at a rate of 0.65℃ / h; then, the temperature is increased from 550℃ to 950℃ at a rate of 2℃ / h; finally, the temperature is maintained at 950℃ for 8 hours.

7. The method for preparing an in-situ modified Si3N4 carbon-based composite material according to claim 1, characterized in that, The nitrogen gas flow rate is 1.0-3.0 L / min.

8. The Si3N4 in-situ modified carbon-based composite material obtained by the preparation method according to any one of claims 1-7.

9. The application of the Si3N4 modified carbon-based composite material according to claim 8 as a sliding current collector material.

10. The application according to claim 9, characterized in that, The sliding current collector material is applied to the pantograph sliding plate.

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