Chemical vapor deposition silicon infiltration modified isostatic pressing graphite and preparation method thereof

Abstract

This invention discloses a chemical vapor deposition (CVD) silicate-modified isostatic graphite and its preparation method, belonging to the field of graphite material modification technology. The CVD silicate-modified isostatic graphite includes an isostatic graphite matrix and a CVD silicate layer. The isostatic graphite matrix has a porosity of 12-20%. The CVD silicate layer includes a SiC coating and a SiC filler layer. The SiC coating is tightly adhered to the surface of the isostatic graphite matrix, and the SiC filler layer uniformly fills the internal pores of the isostatic graphite matrix. This invention optimizes the CVD silicate process parameters to achieve uniform and dense SiC deposition on the graphite surface and within its internal pores—forming a continuous SiC coating on the surface and uniformly filling the internal pores. This avoids both excessively rapid deposition clogging of pore channels and insufficient deposition due to excessively rapid diffusion, significantly improving the modification effect.

Description

Technical Field

[0001] This invention belongs to the field of graphite material modification technology, and particularly relates to a chemical vapor deposition silicate-modified isostatic graphite and its preparation method. Background Technology

[0002] Isostatic graphite, with its excellent isotropy, high thermal conductivity, good machinability and high temperature stability, is often used as a material for making graphite molds for 3D hot bending glass.

[0003] Currently, some common 3D glass hot bending graphite molds on the market directly use isostatic graphite as raw material, such as the 3D glass hot bending graphite mold products with announcement numbers CN107034405A and CN115403383A. However, isostatic graphite itself has obvious shortcomings: graphite is essentially a brittle material and easily reacts with oxygen in high-temperature environments to generate volatile CO or CO2, leading to surface oxidation and peeling, dimensional deformation, and seriously affecting its service life; at the same time, its surface hardness is low and its wear resistance is insufficient, making it prone to damage under friction and impact conditions.

[0004] In the application of heating plates and 3D hot bending molds in 3D glass hot bending machines, they are in a high-temperature working environment of 400~1000℃ for a long time and need to withstand the extrusion and friction during the glass hot bending process. The above-mentioned shortcomings will lead to uneven heating of the heating plate in the 3D glass hot bending machine and a decrease in the precision of the 3D hot bending mold, which will affect the forming quality and production efficiency of 3D glass and limit its application scope in the field of 3D glass hot bending. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a chemical vapor deposition silicon-modified isostatic graphite and its preparation method that can overcome or at least partially solve the above problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A chemical vapor deposition (CVD) silicon-modified isostatic graphite, characterized in that it comprises an isostatic graphite substrate (1) and a CVD silicon-infiltrating layer, wherein the porosity of the isostatic graphite substrate (1) is 12-20%; the CVD silicon-infiltrating layer comprises a SiC coating (2) and a SiC filling layer (4), wherein the SiC coating is tightly adhered to the surface of the isostatic graphite substrate (1), and the SiC filling layer (4) is uniformly filled in the internal pores (3) of the isostatic graphite substrate (1), and the porosity of the isostatic graphite substrate (1) after filling is 4-8%.

[0007] Preferably, the isostatically pressed graphite matrix (1) is made by mixing carbonaceous needle-shaped coke powder and binder, followed by isostatic pressing, calcination, and graphitization.

[0008] Furthermore, the carbonaceous needle-shaped coke powder comprises three particle size specifications: 0.5~1.0mm, 0.15~0.5mm, and D50=10~50μm, respectively, and the three particle sizes are mixed in a weight ratio of 1:0.5~2:2~10 to form carbonaceous needle-shaped coke powder.

[0009] Preferably, the binder is a medium-temperature coal tar pitch with a softening temperature of 80-95°C, and the mass ratio of carbonaceous needle-shaped coke powder to the binder is 70-85:15-30.

[0010] Furthermore, the SiC in the CVD silica layer is β-SiC, which is distributed in a spherical shape. The CVD silica layer and the isostatic graphite matrix (1) have no obvious interface, are tightly bonded, and have no cracking or peeling.

[0011] This invention also provides a method for preparing chemical vapor deposition-modified silica-infiltrated isostatic graphite, characterized by comprising the following steps: Step 1: Mix the carbonaceous needle-shaped coke powder of three different particle sizes evenly, add a binder to make a paste, and press it into a green body by isostatic pressing; place the green body in an inert gas environment for calcination and graphitization treatment in sequence to obtain an isostatic graphite matrix with a porosity of 12~20% (1). Step 2: The isostatic graphite substrate (1) prepared in Step 1 is polished and ultrasonically cleaned to remove surface oil and complete the pretreatment; Step 3: Place the pretreated isostatic graphite matrix (1) into the CVD reactor and keep it at 1150~1300℃ for 30~60min; introduce silicon source gas, carrier gas and dilution gas into the furnace to carry out CVD silicon infiltration reaction; Step 4: After the CVD silicon infiltration reaction is completed, stop the supply of silicon source gas and continue to supply inert gas for protection and cooling. After the reactor cools down to room temperature, take out the workpiece and polish its surface to remove excess SiC deposits to obtain the finished product.

[0012] Preferably, the surface roughness Ra of the isostatic graphite matrix (1) after polishing in step two is ≤0.8μm.

[0013] Preferably, in step three, the silicon source gas is methyltrichlorosilane with a purity ≥99.9%; the carrier gas is hydrogen with a purity ≥99.9%; the dilution gas is argon with a purity ≥99.9%; the volume ratio of silicon source gas to carrier gas is 1:5~10; and the flow rate of the dilution gas is 80~120L / h.

[0014] Preferably, the CVD silicon infiltration reaction process in step three adopts a segmented temperature control method: In the first stage, the temperature is raised to 1150~1200℃, and the deposition rate is controlled at 0.5~0.7μm / h; In the second stage, the temperature is raised to 1200~1300℃, and the deposition rate is controlled at 0.8~1.0μm / h.

[0015] Preferably, the inert gas in steps one and four is argon or nitrogen with a purity ≥99.9% and a flow rate of 50~80L / h.

[0016] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. This invention optimizes the CVD silicon infiltration process parameters for isostatic graphite with a porosity of 12-20%. By controlling the ratio of silicon source gas, carrier gas, and dilution gas, and adjusting the SiC deposition rate through segmented temperature control, uniform and dense SiC deposition on the graphite surface and internal pores is achieved. This results in a continuous SiC coating on the surface and uniform filling of internal pores. This approach avoids both excessively rapid deposition that could clog pore channels and insufficient deposition due to excessively rapid diffusion, significantly improving the modification effect.

[0017] 2. The modified isostatic graphite has a reduced porosity of 4-8%, an increased oxidation resistance temperature of over 1200℃, an increased Rockwell hardness of 80-90 HRC, an increased flexural strength of over 30%, and an increased wear resistance of over 50%. It also exhibits excellent thermal conductivity uniformity and dimensional stability, effectively solving the problems of poor oxidation resistance, insufficient wear resistance, and limited mechanical properties of the original isostatic graphite with a porosity of 12-20%. It can perfectly meet the usage requirements of heating plates for 3D glass hot bending machines (requiring high-temperature uniform thermal conductivity and oxidation resistance) and 3D hot bending molds (requiring wear resistance, high precision, and deformation resistance), significantly improving the quality and production efficiency of 3D glass forming, while expanding its application range in harsh environments such as high temperature, friction, and corrosion. 3. The CVD silicon infiltration process uses inert gas protection to avoid oxidation of the graphite matrix at high temperatures. The CVD silicon infiltrated layer is tightly bonded to the graphite matrix without cracking or peeling. The preparation process has no harmful gas emissions, which meets environmental protection requirements. At the same time, no additional modifiers are needed, the raw material cost is low, the process is highly stable, and it is suitable for large-scale production.

[0018] 4. The isostatically pressed graphite matrix is ​​prepared using carbonaceous needle-shaped coke fine powder with gradient particle size and medium-temperature coal tar pitch. By optimizing the particle size ratio and mixing and molding parameters, the porosity of the matrix is ​​precisely controlled at 12~20%, and the pores are mainly open pores, which provides a good channel for the infiltration of silicon source gas and the deposition of SiC during the CVD silicon infiltration process, further improving the uniformity and stability of CVD silicon infiltration modification. Attached Figure Description

[0019] Figure 1This is a photograph of a 3D glass hot bending machine heating plate made from a chemical vapor deposition silica-modified isostatic graphite, as proposed in this invention. Figure 2 In the method for preparing chemical vapor deposition-modified isostatic graphite proposed in this invention, the microstructure of the finished product prepared in Example 1 was locally acquired using a secondary electron detector (SED) at a magnification of 300x. Figure 1 ; Figure 3 To and Figure 1 Microscopic morphology of backscattered electrons (BSE) acquired using a backscattered electron detector (BED-C) at 300x magnification within the same local observation area. Figure 1 ; Figure 4 In the method for preparing chemical vapor deposition-modified isostatic graphite proposed in this invention, the microstructure of the finished product prepared in Example 1 is locally analyzed using SED at 1000x magnification. Figure 2 ; Figure 5 To and Figure 3 Microscopic morphology of BSE acquired using BED-C at 1000x magnification within the same local observation area. Figure 2 ; Figure 6 In the method for preparing chemical vapor deposition-modified isostatic graphite proposed in this invention, the microstructure of the finished product prepared in Example 1 is locally analyzed using SED at 1000x magnification. Figure 3 ; Figure 7 To and Figure 5 Microscopic morphology of BSE acquired using BED-C at 1000x magnification within the same local observation area. Figure 3 ; Figure 8 In the method for preparing chemical vapor deposition-modified isostatic graphite proposed in this invention, the microstructure of the finished product prepared in Example 1 was locally acquired using BED-C at 100x magnification. Figure 4 ; Figure 9 To and Figure 7 Energy dispersive spectral (EDS) distribution of carbon (C) in the same local observation area; Figure 10 To and Figure 7 EDS distribution map of silicon (Si) in the same local observation area; Figure 11 To and Figure 7 EDS elemental spectral density of the same local observation area Figure 1; Figure 12 In the method for preparing chemical vapor deposition-modified isostatic graphite proposed in this invention, the microstructure of the finished product prepared in Example 1 was locally acquired using BED-C at 150x magnification. Figure 5 ; Figure 13 To and Figure 11 Spectrum II of EDS energy distribution of C element in the same local observation area; Figure 14 To and Figure 11 EDS energy spectrum distribution of Si element in the same local observation area (II); Figure 15 To and Figure 11 EDS elemental spectral density of the same local observation area Figure 2 .

[0020] In the figure: 1. Isostatic graphite; 2. SiC coating; 3. Internal pores; 4. SiC filling layer. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] A chemical vapor deposition (CVD) silica-modified isostatic graphite comprises an isostatic graphite substrate 1 and a CVD silica layer. The isostatic graphite substrate 1 has a porosity of 12-20%. The CVD silica layer comprises a continuous SiC coating 2 on the surface of the graphite substrate and a SiC filling layer 4 in the internal pores 3. The SiC coating 2 has a thickness of 0.1-0.3 mm, and the SiC filling rate of the internal pores 3 is 60-80%. After filling, the isostatic graphite substrate 1 has a porosity of 4-8%.

[0023] The isostatically pressed graphite matrix 1 is made by mixing carbonaceous needle-shaped coke powder and binder, followed by isostatic pressing, calcination, and graphitization.

[0024] The carbonaceous needle-shaped coke powder contains three particle size specifications: 0.5~1.0mm, 0.15~0.5mm and D50=10~50μm. The three particle sizes are mixed in a weight ratio of 1:0.5~2:2~10 to form the carbonaceous needle-shaped coke powder.

[0025] The binder is a medium-temperature coal tar pitch with a softening temperature of 80~95℃, and the mass ratio of carbonaceous needle-shaped coke powder to binder is 70~85:15~30.

[0026] The SiC in the CVD silica-infiltrated layer is β-SiC, which is distributed in a spherical shape. There is no obvious interface between the CVD silica-infiltrated layer and the isostatic graphite matrix 1. The bonding is tight and there is no cracking or peeling.

[0027] This invention also provides a method for preparing chemical vapor deposition-modified silica-infiltrated isostatic graphite, comprising the following steps: Step 1: Mix the three types of carbonaceous needle-shaped coke powder evenly, add a binder, and knead at 180~220℃ for 1~4h to form a uniform paste; put the paste into an isostatic pressing mold and press it at 180~250MPa for 10~60min to form a green body; place the formed green body into a calcining furnace and heat it to 1000~1200℃ at a heating rate of 5~10℃ / h under inert gas protection, and hold it for 2~4h to complete the calcination; then place the calcined green body into a graphitization furnace and heat it to 2800~3000℃ under inert gas protection, and hold it for 1~2h to complete the graphitization, obtaining an isostatic graphite matrix 1 with a porosity of 12~20%; Step 2: The isostatic graphite substrate 1 prepared in Step 1 is mechanically polished to remove the surface oxide layer and impurities; then the isostatic graphite substrate 1 is placed in an ultrasonic cleaner and cleaned with anhydrous ethanol for 10-20 minutes to remove surface oil stains. After removal, it is dried at 80-100℃ for 1-2 hours to complete the pretreatment. Step 3: Place the pretreated isostatically pressed graphite matrix 1 into the CVD reactor, seal it, and then evacuate it to 10°C. -3 ~10 -2 Pa; Inert gas is introduced into the reactor, and the temperature inside the furnace is raised to 1150~1300℃ at a rate of 8~12℃ / h, held for 30~60min, and residual air inside the furnace is removed; then the pressure inside the furnace is adjusted to 10 Pa. -1 ~100Pa, silicon source gas, carrier gas and dilution gas are introduced to carry out CVD silicon infiltration reaction, and the reaction time is 24~48h; Step 4: After the CVD silicon infiltration reaction is completed, stop the supply of silicon source gas and continue to supply inert gas. Cool the reactor temperature down to room temperature at a rate of 5~8℃ / h to obtain a graphite sample. Take out the graphite sample and lightly polish the surface to remove excess SiC deposits and obtain the finished product.

[0028] The surface roughness Ra of the isostatically pressed graphite matrix 1 after grinding in step two is ≤0.8μm.

[0029] In step three, the silicon source gas is MTS with a purity ≥99.9%; the carrier gas is H2 with a purity ≥99.9%; the dilution gas is Ar with a purity ≥99.9%; the volume ratio of silicon source gas to carrier gas is 1:5~10; and the flow rate of the dilution gas is 80~120L / h.

[0030] In step three, the CVD silicon infiltration reaction process adopts a segmented temperature control method: In the first stage, the temperature is raised to 1150~1200℃, and the deposition rate is controlled at 0.5~0.7μm / h; the focus of this stage is to achieve the penetration of silicon source gas into the internal pores 3 of graphite. In the second stage, the temperature is raised to 1200~1300℃, and the deposition rate is controlled at 0.8~1.0μm / h. The focus of this stage is to achieve dense deposition of SiC on the surface and in the pores, so as to avoid pore channel blockage.

[0031] The inert gas used in steps one, three, and four is Ar or N2 with a purity ≥99.9% and a flow rate of 50~80 L / h.

[0032] Isostatic graphite, with its excellent isotropy, high thermal conductivity, good machinability, and high-temperature stability, is widely used in various high-end fields. Among them, isostatic graphite with a porosity of 12-20% balances the material's density and permeability, avoiding the problems of high processing difficulty and high cost of low porosity graphite, while overcoming the defects of poor mechanical properties and easy corrosion of high porosity graphite. It is one of the most widely used types of isostatic graphite.

[0033] However, this type of isostatically pressed graphite has significant drawbacks: graphite is inherently a brittle material and readily reacts with oxygen at high temperatures to generate volatile CO or CO2, leading to surface oxidation and dimensional deformation, severely impacting its service life. Simultaneously, its low surface hardness and insufficient wear resistance make it susceptible to damage under friction and impact conditions. This is particularly problematic in applications such as heating plates and 3D hot bending molds for 3D glass, which operate at temperatures of 400-800°C and withstand the pressure and friction during the glass hot bending process. These defects result in uneven heating of the heating plate and reduced mold precision, ultimately affecting the forming quality and production efficiency of 3D glass and limiting its application in the field of 3D glass hot bending.

[0034] To improve the aforementioned defects of isostatically pressed graphite, silica infiltration modification is one of the most effective techniques currently available. Silica infiltration modification can form SiC fillers on and within the graphite matrix. SiC possesses high hardness, high melting point, excellent oxidation resistance, and wear resistance, significantly enhancing the overall performance of graphite materials. Currently, commonly used silica infiltration methods include liquid silica infiltration, chemical vapor deposition (CVR), and chemical vapor deposition (CVD).

[0035] While liquid silicon infiltration is simple to operate and fast, it easily generates a large amount of free silicon during the process, leading to increased material brittleness. Furthermore, it is difficult to precisely control the thickness of the silicon-infiltrated layer, resulting in uneven silicon infiltration. CVR produces a SiC layer that bonds tightly to the graphite matrix, but this method still retains the porous structure of the graphite matrix. For applications such as sealing and high-temperature load-bearing, additional post-processing such as resin impregnation is required, making the process cumbersome and costly. CVD silicon infiltration can prepare dense and uniform SiC coatings and achieve precise filling of the internal pores of graphite. However, existing CVD silicon infiltration processes are mostly designed for graphite with low porosity (<12%) or high porosity (>20%). For graphite with a porosity of 12-20%, this method is less suitable. The existing process for isostatic graphite has problems such as insufficient silicon infiltration, weak bonding between the SiC layer and the substrate, and insignificant improvement in material performance after silicon infiltration. Low porosity graphite has narrow pore channels, making it difficult for silicon source gas to penetrate into the internal pores during CVD silicon infiltration, resulting in ineffective filling of the internal pores. High porosity graphite has too large pores, making it difficult for the SiC layer to form a continuous and dense protective layer, which is prone to cracking and peeling. Graphite with a porosity of 12-20% has a moderate pore size, and the existing process has not optimized the parameters for its pore characteristics, resulting in a mismatch between the silicon source gas diffusion rate and the deposition rate. Either the deposition is too fast and blocks the pore channels, or the diffusion is too fast and the SiC deposition is insufficient, which cannot give full play to the effect of silicon infiltration modification.

[0036] Therefore, for isostatic graphite with a porosity of 12-20%, this invention provides a chemical vapor deposition silicon-modified isostatic graphite and its preparation method, which realizes uniform and dense deposition of SiC on the surface and internal pores 3 of the isostatic graphite matrix 1, significantly improving the material's oxidation resistance, wear resistance and mechanical properties. At the same time, it leverages its advantages over metal and ceramic heating plates, such as low density, fast thermal conductivity, large thermal radiation and high overall thermal efficiency, making it suitable for the high temperature, wear resistance and high precision requirements of heating plates for 3D glass hot bending machines and 3D hot bending molds, while also taking into account the stability and economy of the process.

[0037] Example 1: A method for preparing chemical vapor deposition-modified silica-infiltrated isostatic graphite includes the following steps: Step 1: Crush and grind the needle coke, and screen out carbonaceous needle coke fine powders with three particle sizes: 0.5~1.0mm, 0.15~0.5mm, and D50=30μm. Mix them evenly in a weight ratio of 1:1:6. Add medium-temperature coal tar pitch (softening temperature 85℃) to the mixed carbonaceous needle coke fine powder. The mass ratio of carbonaceous needle coke fine powder to binder is 80:20. Knead at 200℃ for 2 hours to form a uniform paste. Place the paste into an isostatic pressing mold and press it under a pressure of 200MPa. The isostatic pressing was completed by holding the pressure for 30 minutes. The formed green body was then placed in a calcination furnace, Ar was introduced at a flow rate of 60 L / h, and the temperature was raised to 1100℃ at a heating rate of 8℃ / h. The temperature was held for 3 hours to complete the calcination. The calcined green body was then placed in a graphitization furnace, Ar was introduced at a flow rate of 60 L / h, and the temperature was raised to 2900℃. The temperature was held for 1.5 hours to complete the graphitization, resulting in an isostatic graphite matrix 1 with a porosity of 15%, a bulk density of 1.80 g / cm³, and a flexural strength of 28 MPa. Step 2: The isostatically pressed graphite substrate 1 is mechanically polished to remove the surface oxide layer and impurities. The surface roughness Ra after polishing is 0.6μm. Then, it is placed in an ultrasonic cleaner and cleaned with anhydrous ethanol for 15 minutes to remove surface oil. After removal, it is dried at 90℃ for 1.5 hours for later use. Step 3: Place the pretreated graphite substrate into the CVD reactor, seal it, and then evacuate it to a vacuum level of 5×10⁻⁶. -3 Pa; Ar was introduced into the reactor at a flow rate of 60 L / h, and the temperature was increased to 1200℃ at a heating rate of 10℃ / h, held for 45 min, and residual air in the furnace was removed; then the pressure in the furnace was adjusted to 10 Pa, and MTS, H2 and Ar were introduced, with the volume ratio of MTS to H2 controlled at 1:7 and the Ar flow rate at 100 L / h. The CVD silicon infiltration reaction was carried out using a segmented temperature control method: in the 1150~1200℃ stage, the deposition rate was controlled at 0.6 μm / h, and the reaction was carried out for 15 h; in the 1200~1250℃ stage, the deposition rate was controlled at 0.9 μm / h, and the reaction was carried out for 20 h, with a total reaction time of 35 h; Step 4: After the reaction is complete, stop the MTS flow and continue to flow Ar at a flow rate of 60 L / h, and cool down to room temperature at a rate of 6 °C / h; take out the graphite sample, lightly polish the surface to remove excess SiC deposits, and obtain the finished product.

[0038] Example 2: A method for preparing chemical vapor deposition-modified silica-infiltrated isostatic graphite includes the following steps: Step 1: Crush and grind the needle coke, and screen out carbonaceous needle coke fine powders with three particle sizes: 0.5~1.0mm, 0.15~0.5mm, and D50=10μm. Mix them evenly in a weight ratio of 1:0.5:2. Add medium-temperature coal tar pitch (softening temperature 80℃) to the mixed carbonaceous needle coke fine powder. The mass ratio of carbonaceous needle coke fine powder to binder is 85:15. Knead at 180℃ for 4 hours to form a uniform paste. Place the paste into an isostatic pressing mold and press at 250MPa. The green body was held under pressure for 10 minutes to complete isostatic pressing. The green body was then placed in a calcination furnace, and N2 was introduced at a flow rate of 50 L / h. The temperature was increased to 1000℃ at a rate of 5℃ / h and held for 4 hours to complete calcination. The calcined green body was then placed in a graphitization furnace, and N2 was introduced at a flow rate of 50 L / h. The temperature was increased to 2800℃ and held for 2 hours to complete graphitization, resulting in an isostatic graphite matrix 1 with a porosity of 12%, a bulk density of 1.85 g / cm³, and a flexural strength of 30 MPa. Step 2: The isostatically pressed graphite substrate 1 is mechanically polished to remove the surface oxide layer and impurities. After polishing, the surface roughness Ra=0.7μm. Then, it is placed in an ultrasonic cleaner and cleaned with anhydrous ethanol for 10 minutes to remove surface oil. After removal, it is dried at 80℃ for 2 hours for later use. Step 3: Place the pretreated graphite substrate into the CVD reactor, seal it, and then evacuate it to a vacuum level of 1×10⁻⁶. -2 Pa; introduce N2 into the reactor at a flow rate of 50 L / h, raise the temperature to 1150℃ at a rate of 8℃ / h, hold for 60 min, and remove residual air from the furnace; then adjust the pressure inside the furnace to 10 Pa. -1 Pa was used to introduce MTS, H2, and Ar, with the volume ratio of MTS to H2 controlled at 1:5 and the Ar flow rate at 80 L / h. The CVD silicon infiltration reaction was carried out using a segmented temperature control method: in the 1150~1200℃ stage, the deposition rate was controlled at 0.5 μm / h and the reaction was carried out for 12 h; in the 1200~1300℃ stage, the deposition rate was controlled at 0.8 μm / h and the reaction was carried out for 18 h, with a total reaction time of 30 h. Step 4: After the reaction is complete, stop the MTS flow and continue to flow N2 at a flow rate of 50 L / h, cooling the sample to room temperature at a rate of 5 °C / h; remove the graphite sample, lightly polish the surface to remove excess SiC deposits, and obtain the finished product.

[0039] Example 3: A method for preparing chemical vapor deposition-modified silica-infiltrated isostatic graphite includes the following steps: Step 1: Crush and grind the needle coke, and screen out carbonaceous needle coke fine powders with three particle sizes: 0.5~1.0mm, 0.15~0.5mm, and D50=50μm. Mix them evenly in a weight ratio of 1:2:10. Add medium-temperature coal tar pitch (softening temperature 95℃) to the mixed carbonaceous needle coke fine powder. The mass ratio of carbonaceous needle coke fine powder to binder is 70:30. Knead at 220℃ for 1 hour to form a uniform paste. Load the paste into an isostatic pressing mold and press at 180MPa. The green body was subjected to pressure for 60 minutes to complete isostatic pressing. The green body was then placed in a calcination furnace, Ar was introduced at a flow rate of 80 L / h, and the temperature was raised to 1200℃ at a heating rate of 10℃ / h. The temperature was held for 2 hours to complete calcination. The calcined green body was then placed in a graphitization furnace, Ar was introduced at a flow rate of 80 L / h, and the temperature was raised to 3000℃. The temperature was held for 1 hour to complete graphitization, resulting in an isostatic graphite matrix 1 with a porosity of 20%, a bulk density of 1.75 g / cm³, and a flexural strength of 25 MPa. Step 2: The isostatically pressed graphite substrate 1 is mechanically polished to remove the surface oxide layer and impurities. After polishing, the surface roughness Ra=0.8μm. Then, it is placed in an ultrasonic cleaner and cleaned with anhydrous ethanol for 20 minutes to remove surface oil. After removal, it is dried at 100℃ for 1 hour for later use. Step 3: Place the pretreated graphite substrate into the CVD reactor, seal it, and then evacuate it to a vacuum level of 1×10⁻⁶. -3 Pa; Ar was introduced into the reactor at a flow rate of 80 L / h, and the temperature was increased to 1300℃ at a heating rate of 12℃ / h, held for 30 min, and residual air in the furnace was removed; then the pressure in the furnace was adjusted to 100 Pa, and MTS, H2 and Ar were introduced, with the volume ratio of MTS to H2 controlled at 1:10 and the Ar flow rate at 120 L / h. The CVD silicon infiltration reaction was carried out using a segmented temperature control method: in the 1150~1200℃ stage, the deposition rate was controlled at 0.7 μm / h, and the reaction was carried out for 20 h; in the 1200~1300℃ stage, the deposition rate was controlled at 1.0 μm / h, and the reaction was carried out for 20 h, for a total reaction time of 40 h; Step 4: After the reaction is complete, stop the MTS flow and continue to flow Ar at a flow rate of 80 L / h, and cool down to room temperature at a cooling rate of 8℃ / h; take out the graphite sample, lightly polish the surface to remove excess SiC deposits, and obtain the finished product.

[0040] Comparative example: Based on Example 1, the difference is that: the isostatic graphite matrix 1 (porosity 15%) from Example 1 was modified using the existing conventional CVD silicon infiltration process: without optimization of gas ratio and deposition rate, reaction temperature 1200℃, reaction time 35h, MTS to H2 volume ratio 1:3, Ar flow rate 50L / h, to obtain the comparative sample.

[0041] The relevant performance of the finished products and comparative samples obtained in Examples 1, 2, 3 and the comparative examples was tested.

[0042] Test results: The chemical vapor deposition silicon-modified isostatic graphite prepared in Example 1 has a SiC coating thickness of 0.2 mm, an internal pore 3 SiC filling rate of 70%, a modified porosity of 6%, an oxidation resistance temperature of 1250℃, a Rockwell hardness of 85 HRC, a flexural strength of 37 MPa, and wear resistance improved by 55% compared with unmodified graphite.

[0043] Observed under a scanning electron microscope Figure 2 , Figure 4 and Figure 6 The image shows a partial SE microstructure of the finished product prepared in Example 1, acquired using SED. Figure 2 , Figure 4 and Figure 6 It can be seen that the CVD silicon infiltrated layer is tightly bonded to the graphite substrate, with no cracking or peeling, excellent thermal conductivity uniformity, and good dimensional stability. Figure 3 , Figure 5 and Figure 7 They are respectively with Figure 2 , Figure 4 and Figure 6 The BSE microstructure images of the same local observation area were acquired using BED-C. In the images, the dark areas represent the distribution areas of isostatically pressed graphite matrix 1, and the light areas represent the distribution areas of the CVD silica-infiltrated layer. Figure 3 , Figure 5 and Figure 7 It can be seen that the CVD silicon infiltration layer fully fills the surface and internal pores 3 of the isostatic graphite substrate 1; Figure 8 , Figure 12 The image shows a localized BSE microstructure of the finished product prepared in Example 1, captured using BED-C imaging. Figure 8 and Figure 12 The skeletal structure, pore morphology and overall microscopic features of the cross section of the isostatically pressed graphite matrix 1 can be clearly observed; Figure 9 and Figure 13 They are respectively with Figure 8 and Figure 12 Carbon elemental surface distribution map by EDS energy dispersive spectroscopy in the same local observation area. Figure 10 and Figure 14 They are respectively with Figure 8 and Figure 12 The elemental surface distribution map of silicon in the same local observation area by EDS energy dispersive spectroscopy, combined with Figure 9 , Figure 10 , Figure 13 and Figure 14It can be seen that carbon elements constitute the continuous framework of isostatically pressed graphite matrix 1, and silicon elements are uniformly penetrated and dispersed to fill the entire pore area of ​​the matrix. The two phases have a high degree of matching and no obvious interface delamination or local segregation defects. Figure 11 and Figure 15 They are respectively with Figure 8 and Figure 12 Energy-dispersive X-ray (EDS) elemental spectra of the same local observation area, from Figure 11 and Figure 15 As can be seen, in the finished product prepared in Example 1, only the characteristic peaks of two exclusive elements, carbon and silicon, exist, and the composition is pure with no obvious impurities. The intensity of the characteristic peak of silicon is significantly higher than that of carbon, indicating that the silicon component has been efficiently penetrated into the porous framework of isostatic graphite, and a composite phase structure of isostatic graphite matrix-CVD silicon-infiltrated layer has been successfully constructed. This fully verifies the excellent pore penetration and filling ability and composition controllability of the preparation method, and the material modification quality is stable and reliable.

[0044] When the chemical vapor deposition-modified isostatic graphite obtained in Example 1 is used to make a heating plate for a 3D glass hot bending machine, such as Figure 1 As shown, the density is 1.80 g / cm³, which is much lower than that of commonly used metal heating plates (7.5 g / cm³) and ceramic heating plates (3.0 g / cm³). The thermal conductivity of the heating plate of the 3D glass hot bending machine made in Example 1 reaches 180 W / (m·K), the heat radiation area is increased by 25% compared with the metal heating plate, and the comprehensive thermal efficiency reaches 88%, which is 32% higher than the metal heating plate and 55% higher than the ceramic heating plate.

[0045] When the chemical vapor deposition silicon-modified isostatic graphite obtained in Example 1 is used to make a hot bending mold, the heating deviation is ≤5℃ and the heat conduction is uniform, which can effectively avoid problems such as warping and breakage during the hot bending of glass. The supported hot bending mold has excellent wear resistance and its service life is more than 60% longer than that of the unmodified graphite mold, and the glass forming qualification rate is increased by 15%.

[0046] Example 2 prepared chemical vapor deposition silicon-infiltrated modified isostatic graphite with a SiC coating thickness of 0.1 mm, an internal pore 3 SiC filling rate of 60%, a modified porosity of 4%, an oxidation resistance temperature of 1200℃, a Rockwell hardness of 80 HRC, a flexural strength of 39 MPa, and a wear resistance performance improved by 50% compared to unmodified graphite. Under a scanning electron microscope, the CVD silicon-infiltrated layer was found to be tightly bonded to the graphite matrix without cracking or peeling, and exhibited high dimensional accuracy.

[0047] When the chemical vapor deposition-modified isostatic graphite obtained in Example 2 is used to make a heating plate for a 3D glass hot bending machine, its density is 1.85 g / cm³, its thermal conductivity is 190 W / (m·K), and its comprehensive thermal efficiency is 85%, which is 30% higher than that of metal heating plates and 52% higher than that of ceramic heating plates.

[0048] The hot bending die made from the chemical vapor deposition silicate modified isostatic graphite of Example 2 has the same excellent overall performance as that of Example 1.

[0049] The chemical vapor deposition (CVD) silica-modified isostatic graphite prepared in Example 3 has a SiC coating thickness of 0.3 mm, an internal pore 3 SiC filling rate of 80%, a modified porosity of 8%, an oxidation resistance temperature of 1300℃, a Rockwell hardness of 90 HRC, a flexural strength of 33 MPa, and wear resistance improved by 60% compared to unmodified graphite. Under a scanning electron microscope, the CVD silica layer is tightly bonded to the graphite matrix without cracking or peeling, and exhibits outstanding high-temperature resistance.

[0050] When the chemical vapor deposition-modified isostatic graphite obtained in Example 3 is used to make a heating plate for a 3D glass hot bending machine, its density is 1.75 g / cm³, which is about 1 / 4 of that of a metal heating plate and about 2 / 3 of that of a ceramic heating plate. Its thermal conductivity reaches 160 W / (m·K), and it has strong thermal radiation capability. Its comprehensive thermal efficiency reaches 90%, which is 35% higher than that of a metal heating plate and 58% higher than that of a ceramic heating plate.

[0051] The hot bending die made from the chemical vapor deposition silicate modified isostatic graphite of Example 3 has the same excellent overall performance as that of Example 1.

[0052] The comparative sample obtained in the comparison example showed that the SiC coating 2 had an uneven thickness (0.05~0.35mm), the SiC filling rate of the internal pores 3 was only 35%, the porosity after modification was 10%, the oxidation resistance temperature was 1000℃, the Rockwell hardness was 65HRC, the flexural strength was 29MPa, and the wear resistance was improved by 20% compared with the unmodified isostatic graphite. Under the scanning electron microscope, the SiC was not tightly bonded to the isostatic graphite matrix 1, and there were local cracks.

[0053] The comparative sample was used as a heating plate for a 3D glass hot bending machine. During actual use, the heating was uneven, with a deviation exceeding 15°C, and the overall thermal efficiency was only 65%, far lower than the 88% of Example 1 of this invention. When used in 3D hot bending molds, it was prone to wear and deformation, resulting in a low glass forming pass rate and failing to meet the requirements of the 3D glass hot bending field. Furthermore, although the comparative sample had a lower density compared to metal and ceramic heating plates, insufficient silicon infiltration meant that its thermal conductivity and heat radiation capabilities were not fully utilized, and its overall thermal efficiency did not show a significant advantage, failing to highlight the core characteristics of graphite materials.

[0054] In summary, compared with the comparative samples, the chemical vapor deposition silicate-modified isostatic graphite prepared in Examples 1, 2 and 3 of this invention has significantly improved in terms of CVD silicate layer uniformity, internal pore filling rate, oxidation resistance, wear resistance and mechanical properties. When used as a heating plate in a 3D glass hot bending machine, it exhibits uniform heat conduction and high temperature resistance. Compared with metal and ceramic heating plates, it has lower density, faster heat conduction, greater heat radiation and higher overall thermal efficiency. When used in 3D hot bending molds, it is wear-resistant and deformation-resistant, which can effectively improve the quality and production efficiency of 3D glass forming. This fully demonstrates the superiority of this invention and its adaptability in the field of 3D glass hot bending.

[0055] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A chemical vapor deposition-modified silica-infiltrated isostatic graphite, characterized in that, The isostatic graphite substrate (1) and the CVD silicon infiltrated layer are included. The porosity of the isostatic graphite substrate (1) is 12-20%. The CVD silicon infiltrated layer includes a SiC coating (2) and a SiC filling layer (4). The SiC coating is tightly attached to the surface of the isostatic graphite substrate (1). The SiC filling layer (4) is uniformly filled in the internal pores (3) of the isostatic graphite substrate (1). After filling, the porosity of the isostatic graphite substrate (1) is 4-8%.

2. The chemical vapor deposition silicate-modified isostatic graphite according to claim 1, characterized in that, The isostatically pressed graphite matrix (1) is made by mixing carbonaceous needle-shaped coke powder and binder, followed by isostatic pressing, calcination, and graphitization.

3. The chemical vapor deposition silicate-modified isostatic graphite according to claim 2, characterized in that, The carbonaceous needle-shaped coke powder comprises three particle size specifications: 0.5~1.0mm, 0.15~0.5mm and D50=10~50μm, respectively. The three particle sizes are mixed in a weight ratio of 1:0.5~2:2~10 to form carbonaceous needle-shaped coke powder.

4. The chemical vapor deposition silicate-modified isostatic graphite according to claim 2, characterized in that, The binder is a medium-temperature coal tar pitch with a softening temperature of 80~95℃, and the mass ratio of carbonaceous needle-shaped coke powder to binder is 70~85:15~30.

5. The chemical vapor deposition silicate-modified isostatic graphite according to claim 1, characterized in that, The SiC in the CVD silica layer is β-SiC, which is distributed in a spherical shape. The CVD silica layer and the isostatic graphite matrix (1) have no obvious interface, are tightly bonded, and have no cracking or peeling.

6. A method for preparing chemical vapor deposition-modified silica-infiltrated isostatic graphite, characterized in that, Includes the following steps: Step 1: Mix the carbonaceous needle-shaped coke powder of three different particle sizes evenly, add a binder to make a paste, and press it into a green body by isostatic pressing; place the green body in an inert gas environment for calcination and graphitization treatment in sequence to obtain an isostatic graphite matrix with a porosity of 12~20% (1). Step 2: The isostatic graphite substrate (1) prepared in Step 1 is polished and ultrasonically cleaned to remove surface oil and complete the pretreatment; Step 3: Place the pretreated isostatic graphite matrix (1) into the CVD reactor and keep it at 1150~1300℃ for 30~60min; introduce silicon source gas, carrier gas and dilution gas into the furnace to carry out CVD silicon infiltration reaction; Step 4: After the CVD silicon infiltration reaction is completed, stop the supply of silicon source gas and continue to supply inert gas for protection and cooling. After the reactor cools down to room temperature, take out the workpiece and polish its surface to remove excess SiC deposits to obtain the finished product.

7. The method for preparing chemical vapor deposition-modified silica-infiltrated isostatic graphite according to claim 6, characterized in that, The surface roughness Ra of the isostatic graphite matrix (1) after grinding in step 2 is ≤ 0.8 μm.

8. The method for preparing chemical vapor deposition-modified silica-infiltrated isostatic graphite according to claim 6, characterized in that, In step three, the silicon source gas is methyltrichlorosilane with a purity ≥99.9%; the carrier gas is hydrogen with a purity ≥99.9%; the dilution gas is argon with a purity ≥99.9%; the volume ratio of silicon source gas to carrier gas is 1:5~10; and the flow rate of the dilution gas is 80~120L / h.

9. The method for preparing chemical vapor deposition-modified silica-infiltrated isostatic graphite according to claim 8, characterized in that, In step three, the CVD silicon infiltration reaction process adopts a segmented temperature control method: In the first stage, the temperature is raised to 1150~1200℃, and the deposition rate is controlled at 0.5~0.7μm / h; In the second stage, the temperature is raised to 1200~1300℃, and the deposition rate is controlled at 0.8~1.0μm / h.

10. The method for preparing chemical vapor deposition-modified silica-infiltrated isostatic graphite according to claim 6, characterized in that, The inert gas used in steps one and four is argon or nitrogen with a purity ≥99.9% and a flow rate of 50~80L / h.

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