Carbon-ceramic heating body material with gradient SiC structure and preparation method of carbon-ceramic heating body material

Abstract

The invention discloses a carbon ceramic heating body material with a gradient SiC structure and a preparation method thereof, and belongs to the technical field of high-performance composite materials. The preparation method comprises the following steps: preparing a carbon fiber preform with density gradient; carrying out CVI densification to obtain a gradient C / C porous body; then forming a SiC / C / SiC composite matrix with a gradient SiC structure through an RMI process; and finally, preparing the SiC protective coating on the surface of the SiC / C / SiC composite matrix through CVD (Chemical Vapor Deposition). According to the invention, by constructing the gradient structure with the interior rich in C and the exterior rich in SiC, the resistance of the heating element is mainly controlled by an internal C / C main body, and excellent resistance stability is ensured; and meanwhile, the gradient SiC layer effectively relieves thermal stress, the surface coating is prevented from cracking and falling off, the thermal shock resistance and the oxidation resistance of the material are remarkably improved, the service life of the material is remarkably prolonged, and unification of long service life, high corrosion resistance and stable resistance is achieved.

Description

Technical Field

[0001] This application belongs to the field of high-performance composite material technology. Specifically, it relates to a high-temperature heating element for use in harsh conditions such as semiconductor and photovoltaic material processing and high-end vacuum furnaces, and in particular to a carbon ceramic heating element material with a gradient SiC structure and its preparation method. Background Technology

[0002] Carbon-ceramic (C / SiC) composite heating elements, combining the excellent electrical conductivity and thermal shock resistance of carbon with the high-temperature strength, oxidation resistance, and corrosion resistance of silicon carbide (SiC), have become core components of high-temperature equipment in advanced manufacturing fields such as semiconductors and photovoltaics. However, existing technologies still have significant shortcomings in meeting the stringent requirements of long lifespan and high stability.

[0003] Currently, existing technologies are mainly divided into three categories, but all of them have insurmountable defects: 1. Traditional graphite or carbon-carbon (C / C) heating elements: These heating elements use carbon as the matrix and, while possessing good electrical conductivity and basic thermal shock resistance (C / C is superior to graphite), their fundamental drawback lies in their poor chemical corrosion resistance. In high-temperature oxidizing or corrosive atmospheres, the carbon matrix is ​​easily corroded, leading to rapid strength decay and severely limited service life, failing to meet the long-cycle requirements of high-end applications.

[0004] 2. Traditional carbon-ceramic (C / SiC) heating elements: To address corrosion issues, existing technologies have introduced the SiC phase, but this has introduced new technical bottlenecks. One approach involves introducing a large amount of SiC into the matrix, which significantly affects the overall resistivity of the material, causing orders-of-magnitude jumps between high and low temperatures, severely interfering with the precise temperature control of the power supply system. Another approach involves preparing a SiC protective coating on the carbon matrix surface; however, due to the significant differences in physical properties (such as the coefficient of thermal expansion) between the coating and the matrix, it is prone to cracking and peeling under thermal cycling due to thermal stress mismatch, ultimately losing its protective function.

[0005] In summary, existing technologies cannot simultaneously meet the three core requirements of long lifespan and high corrosion resistance, excellent electrical stability, and reliable structural integrity when producing carbon-ceramic heating element materials. Summary of the Invention

[0006] The purpose of this application is to provide a carbon ceramic heating element material with a gradient SiC structure and its preparation method, which can simultaneously meet the requirements of long life, high corrosion resistance, excellent electrical stability and reliable structural integrity, thereby achieving the goal of comprehensive and balanced performance of carbon ceramic heating elements.

[0007] To achieve the above objectives, this application provides a method for preparing a carbon ceramic heating element material with a gradient SiC structure, comprising the following steps: A carbon fiber preform with a density / porosity gradient was prepared, wherein the density of the carbon fiber preform gradually decreased and the porosity gradually increased from the center region to the edge region in the thickness direction. Chemical vapor infiltration densification treatment is performed on carbon fiber preforms to obtain C / C porous bodies with gradient density, and the C / C porous bodies maintain the density / porosity gradient structure of the carbon fiber preforms. By contacting C / C porous materials with a silicon source and carrying out a melt infiltration reaction under high temperature and vacuum conditions, a SiC / C / SiC composite material with a gradient SiC structure is formed. Chemical vapor deposition was performed on SiC / C / SiC composite materials to prepare a SiC protective coating on their surface, thus obtaining a carbon ceramic heating element material with a gradient SiC structure.

[0008] Furthermore, the carbon fiber preform includes, in the thickness direction, a central region, a middle region, and an edge region; wherein, The density of the central region is 0.5 g / cm³. 3 ~0.6g / cm 3 The porosity is 66%~72%, and the central region accounts for 75%~80% of the total volume of the carbon fiber preform. The density of the middle region is 0.3 g / cm³. 3 ~0.4g / cm 3 The porosity is 77%~83%, and the middle region accounts for 12%~15% of the total volume of the carbon fiber preform; The density of the edge region is 0.1 g / cm³. 3 ~0.2g / cm 3 The porosity is 89%~95%, and the edge region accounts for 5%~8% of the total volume of the carbon fiber preform.

[0009] Furthermore, the central and intermediate areas are prepared using a 2.5D needle-punching process with carbon cloth composite mesh, while the edge areas are prepared using a pure mesh needle-punching process. The central area uses a surface density of 400 g / m³. 2 ~450g / m 2 carbon cloth with 30g / m 2 ~35g / m 2 The mesh is laid in alternating layers at a density of 25 stitches / cm. 2 ~30 stitches / cm 2 The needle-punching density was obtained by needle-punching preparation; The middle area uses an area density of 250 g / m³ 2 ~350g / m 2 carbon cloth with 30g / m 2 ~35g / m 2 The mesh is laid in alternating layers at a density of 25 stitches / cm. 2~30 stitches / cm 2 The needle-punching density was obtained by needle-punching preparation; The edge area uses 30g / m 2 ~35g / m 2 The mesh tire has 15 stitches / cm. 2 ~30 stitches / cm 2 The needle density was obtained by needle acupuncture preparation.

[0010] Furthermore, the temperature for chemical vapor infiltration (CVI) densification treatment is 950℃~1080℃, the deposition pressure is 1kPa~3kPa, and the deposition time is 500h~700h; the reaction gas is a mixture of natural gas, low molecular weight hydrocarbon gas, and carrier gas, and the gas flow rate is 40m³. 3 / h~50m 3 / h.

[0011] Furthermore, the density of the central region of the C / C porous body is 1.5 g / cm³. 3 ~1.6g / cm 3 The open porosity is 4%~10%; the density in the middle region is 1.35g / cm³. 3 ~1.45g / cm 3 The open porosity is 15%~20%; the density in the edge region is 1.15 g / cm³. 3 ~1.25g / cm 3 The porosity is 27%~33%.

[0012] Furthermore, the silicon source is a mixed powder of solid silicon powder and silicon carbide powder mixed in a mass ratio of 1:1, with the solid silicon powder having a mesh size of 200-400 mesh and the silicon carbide powder having a mesh size of 100-300 mesh.

[0013] Furthermore, the heating procedure for the melt infiltration reaction is as follows: Evacuate to ≤100Pa, heat to 1200℃ at a rate of ≤5℃ / min, and hold for 1 hour; Heat to 1400℃ at a rate of ≤3℃ / min and hold for 1 hour; Heat to 1550℃ at a rate of ≤5℃ / min and hold for 1 hour; Heat to 1650℃ at a rate of ≤5℃ / min, hold for 0.5h~1h, and then cool to room temperature in a protective atmosphere.

[0014] Furthermore, the process parameters for chemical vapor deposition are: temperature 900℃~1300℃, pressure 1kPa~5kPa, time 15h~24h, the reaction gas is a mixture of CH3SiCl3 and H2 (carrier gas) and H2 (dilution gas), or a mixture of SiCl4 and H2 (carrier gas) and H2 (dilution gas), and the flow rate of the mixed gas is 5mL / min·mm. 2 ~10mL / min·mm 2 ; The thickness of the SiC protective coating prepared by chemical vapor deposition is 30μm~200μm.

[0015] This application also provides a carbon ceramic heating element material with a gradient SiC structure. The overall structure of the carbon ceramic heating element material has a density / porosity gradient in the thickness direction, with the density gradually decreasing and the porosity gradually increasing from the central region to the edge region.

[0016] Furthermore, the carbon-ceramic heating element material includes: A SiC / C / SiC composite matrix with a gradient SiC structure is formed inside the SiC / C / SiC composite matrix. The central region has low SiC content and low porosity, while the edge region has high SiC content and high porosity. A SiC protective coating located on the surface of a SiC / C / SiC composite substrate.

[0017] In summary, this application has the following advantages: This application provides a carbon-ceramic heating element material with a gradient SiC structure and its preparation method. By constructing a carbon fiber preform with a density gradient, and through key steps such as CVI densification, RMI melt infiltration, and CVD coating, a robust composite structure with an internally stable carbon / carbon matrix, an externally formed gradient transition layer enriched with silicon carbide, and a dense protective layer is prepared. Specifically, the preparation process first uses a needle-punching process to prepare a carbon fiber preform with a high density at the center and a low density at the edges. Then, CVI is used to form a gradient C / C porous body. Subsequently, RMI is used to allow molten silicon to preferentially infiltrate the high-porosity edge region, forming a gradient matrix with decreasing SiC content from the outside to the inside. Finally, a pure SiC protective layer is deposited on the surface using CVD. In the carbon-ceramic heating element material with a gradient SiC structure prepared in this application, the heating element resistance is mainly controlled by the internal C / C matrix, ensuring excellent resistance stability and thermal shock resistance. The gradient SiC structure effectively alleviates thermal stress, prevents surface coating cracking and peeling, and endows the material with excellent oxidation and corrosion resistance. Therefore, the carbon ceramic heating element material of this application has comprehensive advantages such as long life, high corrosion resistance, stable resistance and reliable structure. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a simplified flowchart of the preparation method of the carbon ceramic heating element material proposed in this application.

[0020] Figure 2 This is a density distribution diagram of the carbon fiber preform proposed in this application.

[0021] Figure 3 This is a cross-sectional structural diagram of the carbon ceramic heating element material proposed in this application.

[0022] Figure 4 This is a comparison chart of the percentage change in electrical resistance between the conventional carbon ceramic material proposed in this application and the carbon ceramic material of Example 1.

[0023] Figure 5 This is a photograph of the finished carbon ceramic heating element material obtained in Example 1 of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] Carbon-ceramic (C / SiC) composite heating elements, combining the excellent electrical conductivity and thermal shock resistance of carbon with the high-temperature strength, oxidation resistance, and corrosion resistance of silicon carbide (SiC), have become indispensable core heating elements in harsh environments such as semiconductors, photovoltaic material processing, and high-end vacuum furnaces. In these fields, heating elements not only need to operate stably at extremely high temperatures but also must resist corrosive atmospheres and withstand frequent heating and cooling cycles. Therefore, extremely stringent requirements are placed on the overall performance of the heating element. However, existing heating elements either sacrifice corrosion resistance (graphite / C / C), electrical resistance stability (integral siliconized carbon-ceramic), or structural integrity (coated carbon-ceramic), making it impossible to achieve a balance. Based on this, the heating element material prepared in this application forms a smooth transition structure with an internal C-rich interior and an external SiC-rich exterior. This gradient design offers three major advantages: First, the internal core remains a high-density C / C material, ensuring excellent electrical stability; second, a dense SiC protective layer forms on the outside, providing superior corrosion resistance; and most importantly, the intermediate gradient transition layer acts as a buffer, effectively alleviating thermal stress and fundamentally solving the coating peeling problem, ensuring structural integrity and an ultra-long service life. Therefore, this application achieves for the first time a perfect integration of long lifespan, high corrosion resistance, and excellent electrical stability in a single carbon-ceramic heating element.

[0026] Specifically, in the first aspect, this application provides a method for preparing a carbon ceramic heating element material with a gradient SiC structure, such as... Figure 1As shown, the process includes preparing carbon fiber preforms through needle punching, preparing C / C heating element blanks through CVI densification technology, machining grooves according to the product shape, obtaining a SiC / C / SiC composite matrix through RMI SiC ceramization, and obtaining a SiC coating through surface CVD. The CVI densification technology in this application refers to chemical vapor infiltration densification, a technique that achieves densification by depositing matrix materials into the pores of materials through gas-phase reactions. The core principle of this process is to place the carbon fiber preform in a deposition furnace, introduce hydrocarbon gases (such as methane, propane, etc.) as precursors, and pyrolyze the gases at high temperatures to deposit carbon atoms, gradually filling the pores of the preform. The RMI melt infiltration in this application refers to reactive melt infiltration (RMI), an advanced material preparation technology that achieves densification by infiltrating molten metal or alloy into a porous preform and undergoing a chemical reaction at high temperatures to generate a ceramic phase. The core principle of this method is to utilize molten metal, driven by capillary force, to penetrate into the pores of a preform, subsequently reacting with the carbon matrix in the preform to generate ceramic phases such as carbides and borides, thereby obtaining a high-density composite material. The CVD SiC coating in this application is a silicon carbide coating prepared using chemical vapor deposition (CVD) technology. It possesses high uniformity and purity and is widely used in the fields of wear-resistant and corrosion-resistant surface coatings and the preparation of high-temperature ceramic materials. This process deposits a vapor-phase precursor on a heated substrate to form a solid material, making it suitable for the manufacture of ceramic matrix composites in aerospace and other fields.

[0027] Specifically, it includes the following steps: S1. Prepare a carbon fiber preform with a density / porosity gradient, wherein the density of the carbon fiber preform gradually decreases and the porosity gradually increases from the center region to the edge region in the thickness direction.

[0028] In a specific embodiment, the carbon fiber preform includes, in the thickness direction, a central region, a middle region, and an edge region; wherein, the density of the central region is 0.5 g / cm³. 3 ~0.6g / cm 3 The porosity is 66%~72%, and the central region accounts for 75%~80% of the total volume of the carbon fiber preform; the density of the central region is 0.3 g / cm³. 3 ~0.4g / cm 3 The porosity is 77%~83%, with the central region accounting for 12%~15% of the total volume of the carbon fiber preform; the density of the edge region is 0.1 g / cm³. 3 ~0.2g / cm 3The porosity is 89%–95%, with the edge region accounting for 5%–8% of the total volume of the carbon fiber preform. The controlled density and porosity of this application allow the central high-density region to form a conductive core with stable electrical resistance and excellent mechanical properties after subsequent densification, while the high-porosity edge region guides the preferential penetration and reaction of molten silicon, thus naturally forming a gradient SiC structure with a smooth transition in composition and properties. This gradient design from the inside out fundamentally solves key problems such as thermal stress mismatch, easy coating peeling, and unstable electrical resistance caused by abrupt performance changes in traditional homogeneous structures or simple coatings, ultimately resulting in a heating element structure that combines long lifespan, high reliability, and excellent electrical performance.

[0029] In a specific embodiment, the central and intermediate regions are prepared using a 2.5D needle-punching process with carbon cloth composite mesh, while the edge regions are prepared using a pure mesh needle-punching process; wherein, the central region has an areal density of 400 g / m². 2 ~450g / m 2 carbon cloth with 30g / m 2 ~35g / m 2 The mesh is laid in alternating layers at a density of 25 stitches / cm. 2 ~30 stitches / cm 2 The needle-punching method was used to prepare the needle-punching material; the middle region used a surface density of 250 g / m². 2 ~350g / m 2 carbon cloth with 30g / m 2 ~35g / m 2 The mesh is laid in alternating layers at a density of 25 stitches / cm. 2 ~30 stitches / cm 2 The needle was prepared by needle punching at a needle density of 30 g / m². 2 ~35g / m 2 The mesh tire has 15 stitches / cm. 2 ~30 stitches / cm 2 The core structure was prepared by needle punching at a specific needle punching density. This application ensures high strength, high density, and low porosity in the core area by using a high-area-density carbon cloth composite with a mesh core and performing high-density needle punching, laying a solid foundation for the subsequent formation of a stable conductive substrate and mechanical support. A medium-area-density carbon cloth is used in the middle area to achieve a smooth performance transition. In contrast, the clever use of a pure mesh core and a relatively low needle punching density in the edge area directly creates high-porosity channels. This differentiated design not only precisely shapes the required density gradient but also actively guides the subsequent penetration path of molten silicon, thereby efficiently forming an ideal gradient SiC structure.

[0030] S2. Chemical vapor infiltration densification treatment is performed on the carbon fiber preform to obtain a C / C porous body with gradient density. The C / C porous body maintains the density / porosity gradient structure of the carbon fiber preform.

[0031] In a specific embodiment, the temperature for chemical vapor infiltration densification is 950℃~1080℃, the deposition pressure is 1kPa~3kPa, and the deposition time is 500h~700h; the reaction gas is a mixture of natural gas, low molecular weight hydrocarbon gas, and carrier gas, and the gas flow rate is 40m³. 3 / h~50m 3 / h. Natural gas (fuel) is a mixture of gases with methane as the main component, primarily composed of methane (approximately 85 vol%) and small amounts of ethane (approximately 9 vol%), propane (approximately 3 vol%), etc. Low molecular weight hydrocarbon gases include at least one of ethylene, propylene, and ethane, and the carrier gas includes nitrogen and / or argon.

[0032] This application utilizes a relatively low temperature environment of 950℃~1080℃ and a low pressure environment of 1kPa~3kPa, enabling the reactive gas to penetrate into every pore of the preform at a slower rate and more uniformly, preferentially depositing on the fiber surface. This effectively avoids premature sealing at the surface or in large pores, ensuring that even after 500h~700h of deposition, the original density / porosity gradient structure from the center to the edge of the preform is well preserved and inherited. This results in a highly uniform C / C porous body with a unique internal structure, providing an ideal and predictable reaction precursor for subsequent reactive melting and infiltration, thus achieving the gradient structure and excellent performance of the final product.

[0033] In a specific embodiment, the density of the central region of the C / C porous body is 1.5 g / cm³. 3 ~1.6g / cm 3 The open porosity is 4%~10%; the density in the middle region is 1.35g / cm³. 3 ~1.45g / cm 3 The open porosity is 15%~20%; the density in the edge region is 1.15 g / cm³. 3 ~1.25g / cm 3 The open porosity is 27%~33%. The central region of the C / C porous body in this application has a porosity as high as 1.5 g / cm³. 3 ~1.6g / cm 3 Its high density and low porosity of 4%~10% ensure excellent mechanical strength and stable electrical resistance when used as the core of a heating element; while the edge region has a porosity of 1.15 g / cm³. 3 ~1.25g / cm 3The high density and porosity of 27%–33% create a highly efficient permeation channel that actively guides and accommodates the reaction of molten silicon, thus naturally forming a gradient structure with a smooth decrease in SiC content from the outside to the inside during the subsequent RMI process. This application successfully fabricated a heating element that combines stable resistance, structural integrity, and high corrosion resistance through precise control of the density and porosity of each region of the C / C porous body.

[0034] As an optional implementation of this application, such as Figure 1 As shown, after preparing the C / C porous body, the process also includes corresponding processing according to the heater structure requirements to obtain the final product structure. The processing method mainly involves designing the structure based on the material resistivity and processing the shape using processing equipment, including thickness, number and depth of grooves, etc., to obtain a heating element with the required resistance.

[0035] S3. The C / C porous body is brought into contact with a silicon source and subjected to a melt infiltration reaction under high temperature and vacuum conditions to form a SiC / C / SiC composite material with a gradient SiC structure.

[0036] In this specific embodiment, the silicon source is a mixture of solid silicon powder and silicon carbide powder in a 1:1 mass ratio. The solid silicon powder has a mesh size of 200-400 mesh, and the silicon carbide powder has a mesh size of 100-300 mesh. Using a 1:1 mixture of silicon powder and SiC powder ensures sufficient active silicon source for reaction with carbon, while utilizing SiC powder as an inert filler to regulate melt flowability and reaction rate, preventing over-reaction that could lead to material embrittlement.

[0037] In the specific implementation method, the heating procedure for the melt infiltration reaction is as follows: S301. Evacuate to ≤100Pa, heat to 1200℃ at a rate of ≤5℃ / min, and hold for 1 hour; S302. Heat to 1400℃ at a rate of ≤3℃ / min and hold for 1 hour; S303. Heat to 1550℃ at a rate of ≤5℃ / min and hold for 1 hour; S304. Heat to 1650℃ at a rate of ≤5℃ / min and hold for 0.5h~1h; S305. Cooling to room temperature. This application ensures uniform temperature transfer and slow discharge of residual gas through stepped heat treatment at 1200℃, 1400℃, and 1550℃, effectively preventing cracking caused by violent reactions or thermal shock, and finally completing the reaction at a peak temperature of 1650℃. Precise process control ensures that molten silicon can smoothly and controllably penetrate and react along the porosity gradient of the preform from the outside to the inside, ultimately forming a high-performance gradient SiC / C / SiC composite material with a smooth transition in composition and structure and no internal defects.

[0038] S4. Chemical vapor deposition is performed on the SiC / C / SiC composite material to prepare a SiC protective coating on its surface, thereby obtaining a carbon ceramic heating element material with a gradient SiC structure.

[0039] In a specific embodiment, the process parameters for chemical vapor deposition are: temperature 900℃~1300℃, pressure 1kPa~5kPa, time 15h~24h, the reaction gas is a mixture of CH3SiCl3 or SiCl4 with H2 (carrier gas) and diluted H2, and the flow rate of the mixed gas is 5mL / min·mm. 2 ~10mL / min·mm 2 The SiC protective coating prepared by chemical vapor deposition has a thickness of 30μm to 200μm. Temperatures of 900℃ to 1300℃ and low pressure conditions of 1kPa to 5kPa, combined with precursors such as CH3SiCl3 (or SiCl4), can deposit a high-purity, dense SiC coating, effectively blocking the intrusion of external corrosive media. A deposition time of 15h to 24h precisely controls the deposition of the 30μm to 200μm coating, providing sufficient protection while avoiding new internal stresses caused by excessive thickness. Most importantly, because the coating is deposited directly on a subsurface layer with a gradient composition, rather than directly on the C / C substrate, the performance difference between the two is significantly reduced, ensuring excellent bonding strength between the coating and the substrate. This fundamentally eliminates the risk of traditional coatings easily detaching, providing the ultimate guarantee for the ultra-long service life of the heating element. During deposition, hydrogen is first introduced into the liquid CH3SiCl3 or SiCl4 to carry the saturated vapor of CH3SiCl3 or SiCl4 to the rear end of the deposition furnace. Then, an appropriate amount of hydrogen (dilution gas) is mixed into the rear end of the deposition furnace to control the amount of CH3SiCl3 or SiCl4 introduced. Therefore, the H2 introduced later is called dilution gas.

[0040] Secondly, based on a general inventive concept, this application also provides a carbon ceramic heating element material with a gradient SiC structure. The overall structure of the carbon ceramic heating element material has a density / porosity gradient in the thickness direction, with the density gradually decreasing and the porosity gradually increasing from the central region to the edge region.

[0041] In specific implementation methods, such as Figure 3 As shown, the carbon-ceramic heating element material includes: a SiC / C / SiC composite matrix with a gradient SiC structure, wherein a gradient SiC structure is formed inside the SiC / C / SiC composite matrix, with low SiC content and low porosity in the central region and high SiC content and high porosity in the edge region; and a SiC protective coating on the surface of the SiC / C / SiC composite matrix. Figure 2As can be seen, the carbon-ceramic heating element material of this application has a C / C preform at its center, with SiC content gradually increasing outwards from the central region, and finally a pure SiC protective coating deposited on the surface. The central region of the carbon-ceramic heating element material retains a low-SiC content, low-porosity C / C structure, serving as a stable conductive substrate and mechanical support, ensuring excellent resistance stability and thermal shock resistance. From the center outwards, the SiC content increases in a gradient, forming a buffer layer with a smooth performance transition, effectively alleviating thermal stress. The outermost layer is covered with a dense pure SiC protective coating, providing excellent oxidation and corrosion resistance. This ingenious multi-layered gradient synergistic design allows the heating element to combine the advantages of long lifespan, high corrosion resistance, stable resistance, and reliable structure, achieving a perfect balance and unity of various performance indicators.

[0042] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments.

[0043] Example 1 This embodiment provides a method for preparing a carbon ceramic heating element material with a gradient SiC structure, including the following steps: (1) By adjusting the needle punching density, the number of fiber cloth layers, and introducing fiber blankets of different densities, a carbon fiber preform was designed, specifically: The carbon fiber preform includes, in the thickness direction, a central region (e.g., Figure 2 Area A in the middle area (e.g.) Figure 2 Region B in the middle) and edge regions (such as Figure 2 (Region C in the text); where the density of the central region is 0.55 g / cm³. 3 The porosity is 68%, and the central region accounts for 75%~80% of the total volume of the carbon fiber preform; the density of the central region is 0.35 g / cm³. 3 The porosity is 77%, with the central region accounting for 12%–15% of the total volume of the carbon fiber preform; the density of the edge region is 0.15 g / cm³. 3 The porosity is 91%, and the edge region accounts for 5% of the total volume of the carbon fiber preform.

[0044] The central and intermediate areas are fabricated using a 2.5D needle-punching process with carbon cloth composite mesh, while the edge areas are fabricated using a pure mesh needle-punching process; the central area has an areal density of 410 g / m². 2 carbon cloth with 32g / m 2 The mesh is laid in alternating layers at a density of 25 stitches / cm. 2 The needle-punching method was used to prepare the needle-punching material; the middle region used a surface density of 270 g / m². 2 carbon cloth with 32g / m 2 The mesh is laid in alternating layers with a stitch density of 27 stitches / cm.2 The needle was prepared by needle punching at a needle density of 32 g / m². 2 The mesh tire has 17 stitches / cm. 2 The needle density was obtained by needle acupuncture preparation.

[0045] (2) Densification treatment of carbon fiber preforms by chemical vapor infiltration process, specifically: the carbon fiber preforms are placed in a deposition furnace, nitrogen is introduced and the temperature is gradually raised to 970°C, and then a mixture of natural gas, ethylene and nitrogen (the volume ratio of the three in the mixture is 80:20:100 respectively) is introduced, and the flow rate of the mixture is controlled at 42m³. 3 The deposition pressure was set to 1.2 kPa, and deposition was carried out for 550 h to obtain a C / C porous body with gradient density. This resulted in a carbon fiber preform with high density and low porosity at the center and low density and high porosity at the edges.

[0046] The density of the central region of the C / C porous body is 1.55 g / cm³. 3 The open porosity is 5%; the density in the middle region is 1.4 g / cm³. 3 The open porosity is 17%; the density in the edge region is 1.2 g / cm³. 3 The porosity is 29%.

[0047] (3) According to the structural requirements of the heater, the C / C porous body is processed to obtain an annular blank with a finished structure. The processing is to adjust the thickness, number of grooves and depth of the blank to obtain a heating element with the required resistance.

[0048] (4) The processed annular blank was brought into contact with the silicon source and placed in a melting infiltration furnace. The melting infiltration reaction was carried out under high temperature and vacuum. The average density of the product after melting infiltration was 1.65±0.5g, and the silicon density of different regions was shown in Table 2. The silicon source for the melting infiltration reaction was a mixed powder of solid silicon powder and silicon carbide powder mixed at a mass ratio of 1:1. The mesh size of the solid silicon powder was 220 mesh, and the mesh size of the silicon carbide powder was 120 mesh.

[0049] The heating procedure for the melt infiltration reaction is as follows: Evacuate to ≤100Pa, heat to 1200℃ at a rate of ≤5℃ / min, and hold for 1 hour; Heat to 1400℃ at a rate of ≤3℃ / min and hold for 1 hour; Heat to 1550℃ at a rate of ≤5℃ / min and hold for 1 hour; Heat to 1650℃ at a rate of ≤5℃ / min and hold for 0.5h~1h; The furnace was cooled to room temperature under argon protection.

[0050] (5) The material obtained from the melt infiltration reaction is placed in a deposition furnace, and a mixture of CH3SiCl3, H2 (carrier gas), and H2 (dilution gas) is introduced as the reaction gas (flow rate of 5 mL / min·mm). 2 The gas purity was ≥99%. The flow rate of the reactant gas was controlled by the flow rate of H2 (carrier gas) and the water bath temperature, which was 42℃. The volume ratio of carrier gas to H2 (dilution gas) was maintained at 1:3. Then, the temperature was raised to 950℃, and the pressure was controlled at 2kPa for deposition for 19h. The density after deposition is shown in Table 2. A carbon ceramic heating element material with a gradient SiC structure was obtained. The finished product is shown in Table 2. Figure 5 As shown, its cross-sectional structure is as follows Figure 3 As shown in the diagram, hydrogen is first introduced into the liquid CH3SiCl3 to carry the saturated vapor of CH3SiCl3 to the rear end, where an appropriate amount of hydrogen (dilution gas) is then mixed in to control the amount of CH3SiCl3 introduced; therefore, the H2 introduced later is called the dilution gas (the same applies below).

[0051] Example 2 This embodiment provides a method for preparing a carbon ceramic heating element material with a gradient SiC structure, including the following steps: (1) By adjusting the needle punching density, the number of fiber cloth layers, and introducing fiber blankets of different densities, a carbon fiber preform was designed, specifically: The carbon fiber preform includes, in the thickness direction, a central region (e.g., Figure 2 Area A in the middle area (e.g.) Figure 2 Region B in the middle) and edge regions (such as Figure 2 (Region C in the text); where the density of the central region is 0.55 g / cm³. 3 The porosity is 69%, and the central region accounts for 75% of the total volume of the carbon fiber preform; the density of the central region is 0.35 g / cm³. 3 The porosity is 77%, with the central region accounting for 13% of the total volume of the carbon fiber preform; the density of the edge region is 0.15 g / cm³. 3 The porosity is 91%, and the edge region accounts for 7% of the total volume of the carbon fiber preform.

[0052] The central and intermediate areas are fabricated using a 2.5D needle-punching process with carbon cloth composite mesh, while the edge areas are fabricated using a pure mesh needle-punching process; the central area has an areal density of 420 g / m². 2 carbon cloth with 32g / m 2 The mesh is laid in alternating layers at a density of 25 stitches / cm. 2 The needle-punching method was used to prepare the needle-punching material; the middle region used a surface density of 270 g / m². 2 carbon cloth with 30g / m 2 The mesh is laid in alternating layers at a density of 25 stitches / cm.2 The needled material was prepared by needle punching at a needle punching density of 33 g / m². 2 The mesh tire has 19 stitches / cm. 2 The needle density was obtained by needle acupuncture preparation.

[0053] (2) Densification treatment of carbon fiber preforms by chemical vapor infiltration process, specifically: the carbon fiber preforms are placed in a deposition furnace, nitrogen is introduced and the temperature is gradually raised to 1010℃, and then a mixture of natural gas, ethane and carrier gas (nitrogen) is introduced (the volume ratio of the three in the mixture is 80:20:100 respectively), and the flow rate of the mixture is controlled at 45m³. 3 At a deposition rate of 2 kPa, a deposition pressure of 2 kPa was set for 600 h to obtain a C / C porous body with gradient density. This resulted in a carbon fiber preform exhibiting a structure characterized by high density and low porosity at the center, and low density and high porosity at the edges.

[0054] The density of the central region of the C / C porous body is 1.55 g / cm³. 3 The open porosity is 4%~10%; the density in the middle region is 1.4 g / cm³. 3 The open porosity is 17%; the density in the edge region is 1.2 g / cm³. 3 The porosity is 30%.

[0055] (3) According to the structural requirements of the heater, the C / C porous body is processed to obtain an annular blank with a finished structure. The processing is to adjust the thickness, number of grooves and depth of the blank to obtain a heating element with the required resistance.

[0056] (4) The processed annular billet is brought into contact with the silicon source and placed in a melting infiltration furnace for melting infiltration reaction under high temperature and vacuum. The average density of the product after melting infiltration is 1.65±0.5g. The silicon source for melting infiltration reaction is a mixed powder of solid silicon powder and silicon carbide powder mixed in a mass ratio of 1:1. The mesh size of the solid silicon powder is 300 mesh and the mesh size of the silicon carbide powder is 200 mesh.

[0057] The heating procedure for the melt infiltration reaction is as follows: Evacuate to ≤100Pa, heat to 1200℃ at a rate of ≤5℃ / min, and hold for 1 hour; Heat to 1400℃ at a rate of ≤3℃ / min and hold for 1 hour; Heat to 1550℃ at a rate of ≤5℃ / min and hold for 1 hour; Heat to 1650℃ at a rate of ≤5℃ / min and hold for 1 hour; Cool down to room temperature.

[0058] (5) The material obtained from the melt infiltration reaction is placed in a deposition furnace, and a mixture of CH3SiCl3, H2 (carrier gas), and H2 (dilution gas) is introduced as the reaction gas (flow rate of 9 mL / min·mm). 2 The gas purity was ≥99%. The flow rate of the reactant gas was controlled by the flow rate of H2 (carrier gas) and the water bath temperature, which was 46℃. The ratio of carrier gas to diluted H2 was maintained at 1:5. Then, the temperature was raised to 1100℃ and the pressure was controlled at 3.5 kPa for deposition for 21 h to obtain a carbon ceramic heating element material with a gradient SiC structure.

[0059] Example 3 This embodiment provides a method for preparing a carbon ceramic heating element material with a gradient SiC structure, including the following steps: (1) By adjusting the needle punching density, the number of fiber cloth layers, and introducing fiber blankets of different densities, a carbon fiber preform was designed, specifically: The carbon fiber preform includes, in the thickness direction, a central region (e.g., Figure 2 Area A in the middle area (e.g.) Figure 2 Region B in the middle) and edge regions (such as Figure 2 (Region C in the text); where the density of the central region is 0.55 g / cm³. 3 The porosity is 70%, and the central region accounts for 79% of the total volume of the carbon fiber preform; the density of the central region is 0.35 g / cm³. 3 The porosity is 80%, with the central region accounting for 14% of the total volume of the carbon fiber preform; the density of the edge region is 0.15 g / cm³. 3 The porosity is 92%, and the edge region accounts for 7% of the total volume of the carbon fiber preform.

[0060] The central and intermediate areas are fabricated using a 2.5D needle-punching process with carbon cloth composite mesh, while the edge areas are fabricated using a pure mesh needle-punching process; the central area has an areal density of 430 g / m². 2 carbon cloth with 35g / m 2 The mesh is laid in alternating layers with a stitch density of 28 stitches / cm. 2 The needle-punching method was used to prepare the needle-punching material; the middle region used a surface density of 320 g / m². 2 carbon cloth with 34g / m 2 The mesh is laid in alternating layers with a stitch density of 28 stitches / cm. 2 The needled material was prepared by needle punching at a needle punching density of 33 g / m². 2 The mesh tire has 25 stitches / cm. 2 The needle density was obtained by needle acupuncture preparation.

[0061] (2) Densification treatment of carbon fiber preforms by chemical vapor infiltration process, specifically: the carbon fiber preforms are placed in a deposition furnace, nitrogen is introduced and the temperature is gradually raised to 1040℃, and then a mixture of natural gas, low molecular weight hydrocarbon gas (propane) and carrier gas (nitrogen) is introduced (the volume ratio of the three in the mixture is 80:20:100 respectively), and the gas flow rate of the mixture is controlled at 48m³. 3 At a deposition rate of 2.5 kPa, deposition was carried out for approximately 700 h to obtain a C / C porous body with a gradient density. This resulted in a carbon fiber preform exhibiting a structure characterized by high density and low porosity at the center, and low density and high porosity at the edges.

[0062] The density of the central region of the C / C porous body is 1.55 g / cm³. 3 The open porosity is 9%; the density in the middle region is 1.4 g / cm³. 3 The open porosity is 18%; the density in the edge region is 1.2 g / cm³. 3 The porosity is 30%.

[0063] (3) According to the structural requirements of the heater, the C / C porous body is processed to obtain an annular blank with a finished structure. The processing is to adjust the thickness, number of grooves and depth of the blank to obtain a heating element with the required resistance.

[0064] (4) The processed annular billet is brought into contact with the silicon source and placed in a melting infiltration furnace for melting infiltration reaction under high temperature and vacuum. The average density of the product after melting infiltration is 1.65±0.5g. The silicon source for melting infiltration reaction is a mixed powder of solid silicon powder and silicon carbide powder mixed in a mass ratio of 1:1. The mesh size of the solid silicon powder is 400 mesh and the mesh size of the silicon carbide powder is 300 mesh.

[0065] The heating procedure for the melt infiltration reaction is as follows: Evacuate to ≤100Pa, heat to 1200℃ at a rate of ≤5℃ / min, and hold for 1 hour; Heat to 1400℃ at a rate of ≤3℃ / min and hold for 1 hour; Heat to 1550℃ at a rate of ≤5℃ / min and hold for 1 hour; Heat to 1650℃ at a rate of ≤5℃ / min and hold for ~1h; Cool down to room temperature.

[0066] (5) The material obtained from the melt infiltration reaction is placed in a deposition furnace, and a mixture of CH3SiCl3, H2 (carrier gas), and H2 (dilution gas) is introduced as the reaction gas (flow rate of 10 mL / min·mm). 2The gas purity was ≥99%. The flow rate of the reactant gas was controlled by the flow rate of H2 (carrier gas) and the water bath temperature, which was 50℃. The ratio of carrier gas to diluted H2 was maintained at 1:10. Then, the temperature was raised to 1200℃ and the pressure was controlled at 3.5kPa for deposition for 21h to obtain a carbon ceramic heating element material with a gradient SiC structure.

[0067] Comparative Example 1 The difference between this comparative example and Example 1 is that a SiC protective coating is prepared on the surface of the SiC / C / SiC composite material by brushing, and the thickness of the brush coating is the same as in Example 1.

[0068] Comparative Example 2 The difference between this comparative example and Example 1 is that the density of the carbon fiber preform is 0.45 g / cm³ in the central, middle, and edge regions. 3 .

[0069] Comparative Example 3 The difference between this comparative example and Example 1 is that the density of the carbon fiber preform is 0.15 g / cm³ in the central region, middle region, and edge region. 3 0.45g / cm 3 and 0.55g / cm 3 .

[0070] The carbon-ceramic heating elements obtained in Example 1 and Comparative Example 1 were subjected to thermal cycling tests at 25℃~1600℃. The samples were heated to 1600℃ at a rate of 5℃ / min, held at that temperature for 10min, and then cooled to 25℃ at a rate of 10℃ / min, and the cycle was repeated. The results are shown in Table 1. The structural characteristics of the carbon-ceramic heating elements obtained in Example 1 and Comparative Examples 2-3 are shown in Table 2.

[0071] Table 1 Results of thermal cycling experiments

[0072] Table 2 Structural Feature Data

[0073] As shown in Table 1, the CVD SiC coating of Example 1 remained intact after 50 severe thermal cycles, while Comparative Example 1, which used a conventional brush coating process, experienced severe coating peeling under the same conditions (25% peeling area after 50 cycles). This directly proves that the gradient structure design of this application fundamentally solves the industry problem of coating peeling. The reason is that the SiC coating of Example 1 is grown in situ on the substrate surface through CVD, forming a strong chemical bond with the substrate. In contrast, the brush-coated coating of Comparative Example 1 is merely physically attached, with extremely low bonding strength. Furthermore, the substrate of Example 1 itself has a gradient structure with continuously increasing SiC content from the center to the surface, and its coefficient of thermal expansion is also smoothly transitioned. This greatly alleviates the thermal stress between the coating and the substrate, avoiding cracking and peeling caused by thermal mismatch. In contrast, there is a huge difference in the coefficient of thermal expansion between the homogeneous substrate and the coating of Comparative Example 1, and the thermal stress cannot be effectively released, causing the coating to fail rapidly during thermal cycling.

[0074] As shown in Table 2, this application successfully achieved precise and differentiated control of the density of each region of the final carbon-ceramic heating element material (after CVD coating) by accurately setting a density gradient with a high center and low edge during the preform stage, thus constructing an ideal gradient structure. In Example 1, the preform was designed with a high density at the center and a low density at the edge. This initial gradient structure was perfectly inherited and strengthened after chemical vapor infiltration (CVI) densification and reactive infiltration (RMI). The final CVD-coated material exhibited a gradient distribution with a low center and a high edge. This gradient structure is the core physical basis for the excellent performance (such as resistance stability and coating adhesion) of this application. In Comparative Example 2, the preform had a uniform density, resulting in all subsequent process steps (CVI, RMI) acting on a homogeneous precursor. Ultimately, the density after CVD coating was also uniform, with minimal density differences between regions. This homogeneous structure cannot form a functional gradient, which is the root cause of the drastic resistance changes and easy coating detachment problems in traditional carbon-ceramic materials. Comparative Example 3 preforms were designed with low density at the center and high density at the edges, which is the opposite of the ideal gradient direction. This resulted in the final CVD coating exhibiting a reverse gradient with high density at the center and low density at the edges, which not only failed to form an effective protective layer but may also have damaged the overall performance of the material.

[0075] A comparison of the percentage change in resistance of a traditional carbon-ceramic sample (patent CN117923939A) and the carbon-ceramic heating element obtained in Example 1 with temperature (resistance change values ​​were collected in real time as the sample was gradually heated to 1600℃ using a high-temperature four-probe resistance test method). Figure 4As shown, the conductive path of the heating element mainly consists of an internal, almost unreacted, and resistively stable C / C network. The outer SiC layer acts as a protective shell and contributes little to the overall resistance. Therefore, during the heating and cooling process, the resistance of the carbon-ceramic heating element prepared in this application decreases by approximately 50%, which is far lower than the >90% decrease of traditional carbon-ceramic materials, making it more compatible with power supply systems.

[0076] In summary, the carbon ceramic heating element material with a gradient SiC structure of this application has at least the following advantages: (1) In terms of structural design, this application successfully prepared a C / C porous body with a specific density gradient by constructing a gradient carbon fiber preform with high density at the center and high porosity at the edges and by precisely controlling the chemical vapor infiltration (CVI) process. This gradient structure is a key prerequisite for the subsequent formation of an ideal SiC gradient distribution, ensuring the continuous transition of the internal properties of the material.

[0077] (2) In terms of material formation, this application innovatively utilizes gradient C / C porous bodies as precursors and uses reactive infiltration (RMI) process to enable molten silicon to smoothly and controllably infiltrate and react along the porosity gradient from the outside to the inside. This process naturally guides the formation of a gradient structure with continuously decreasing SiC content from the surface to the core, avoiding the problem of drastic resistance changes caused by traditional integral siliconization.

[0078] (3) In terms of product performance, the carbon ceramic heating element finally obtained in this application has unique microstructure characteristics: from the surface to the core, the volume content of SiC continuously decreases from 100% to 0% (the internal porosity is low, which makes it almost impossible for silicon carbide to penetrate into the interior during the RMI process, so the internal silicon carbide volume content is close to zero or 0%), the thickness of the silicon carbide layer is <25%, and the core is mainly composed of C / C composite material with stable resistance. This gradient structure, characterized by internal toughness and external strength, delivers three major superior performance characteristics: First, the pure SiC coating on the surface (CVD coatings also only deposit on the surface and cannot penetrate the interior through tiny pores to quickly form a dense coating) provides superior corrosion resistance, enabling stable operation for over 10,000 hours in harsh environments containing SiO vapor; Second, the conductive pathway is mainly composed of a stable internal C / C network, resulting in a resistance decrease of only about 50% during temperature rise and fall, far superior to the >90% decrease of traditional carbon ceramic materials, making it extremely friendly to power systems; Third, because the SiC layer is chemically bonded to the substrate and has a continuously transitioning coefficient of thermal expansion, thermal stress is perfectly resolved, and cracking or peeling will not occur under repeated thermal cycling, fundamentally solving the problem of coating detachment.

[0079] (4) In terms of application value, the resistance of the carbon ceramic heating element of this application is adjustable. In the range of ≤1800℃, the resistance is mainly controlled by the C / C of the main body and there is no fluctuation of more than a multiple. It provides a stable and reliable heating solution for fields such as semiconductors and photovoltaics that require precise temperature control.

[0080] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of this application.

[0081] Finally, it should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes the element.

[0082] This application uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a carbon ceramic heating element material with a gradient SiC structure, characterized in that, Includes the following steps: A carbon fiber preform with a density / porosity gradient is prepared, wherein the density of the carbon fiber preform gradually decreases and the porosity gradually increases from the center region to the edge region in the thickness direction; The carbon fiber preform is subjected to chemical vapor infiltration densification treatment to obtain a C / C porous body with gradient density, wherein the C / C porous body maintains the density / porosity gradient structure of the carbon fiber preform. The C / C porous body is brought into contact with a silicon source and a melt infiltration reaction is carried out under high temperature and vacuum conditions to form a SiC / C / SiC composite material with a gradient SiC structure. Chemical vapor deposition was performed on the SiC / C / SiC composite material to prepare a SiC protective coating on its surface, thereby obtaining a carbon ceramic heating element material with a gradient SiC structure.

2. The preparation method according to claim 1, characterized in that, The carbon fiber preform includes, in the thickness direction, a central region, a middle region, and an edge region; wherein... The density of the central region is 0.5 g / cm³. 3 ~0.6g / cm 3 The porosity is 66%~72%, and the central region accounts for 75%~80% of the total volume of the carbon fiber preform. The density of the intermediate region is 0.3 g / cm³. 3 ~0.4g / cm 3 The porosity is 77%~83%, and the intermediate region accounts for 12%~15% of the total volume of the carbon fiber preform. The density of the edge region is 0.1 g / cm³. 3 ~0.2g / cm 3 The porosity is 89%~95%, and the edge region accounts for 5%~8% of the total volume of the carbon fiber preform.

3. The preparation method according to claim 2, characterized in that, The central and intermediate areas are prepared using a 2.5D needle-punching process with carbon cloth composite mesh, while the edge areas are prepared using a pure mesh needle-punching process. The central region has a surface density of 400 g / m³. 2 ~450g / m 2 carbon cloth with 30g / m 2 ~35g / m 2 The mesh is laid in alternating layers at a density of 25 stitches / cm. 2 ~30 stitches / cm 2 The needle-punching density was obtained by needle-punching preparation; The intermediate region has a surface density of 250 g / m³. 2 ~350g / m 2 carbon cloth with 30g / m 2 ~35g / m 2 The mesh is laid in alternating layers at a density of 25 stitches / cm. 2 ~30 stitches / cm 2 The needle-punching density was obtained by needle-punching preparation; The edge area uses 30g / m 2 ~35g / m 2 The mesh tire has 15 stitches / cm. 2 ~30 stitches / cm 2 The needle density was obtained by needle acupuncture preparation.

4. The preparation method according to claim 1, characterized in that, The chemical vapor infiltration (CVI) densification treatment is performed at a temperature of 950℃ to 1080℃, with a deposition pressure of 1 kPa to 3 kPa and a deposition time of 500 h to 700 h. The reaction gas is a mixture of natural gas, low molecular weight hydrocarbon gas, and carrier gas, with a flow rate of 40 m³ / h. 3 / h~50m 3 / h.

5. The preparation method according to claim 1, characterized in that, The density of the central region of the C / C porous body is 1.5 g / cm³. 3 ~1.6g / cm 3 The open porosity is 4%~10%; the density in the middle region is 1.35g / cm³. 3 ~1.45g / cm 3 The open porosity is 15%~20%; the density in the edge region is 1.15 g / cm³. 3 ~1.25g / cm 3 The porosity is 27%~33%.

6. The preparation method according to claim 1, characterized in that, The silicon source is a mixed powder of solid silicon powder and silicon carbide powder mixed at a mass ratio of 1:1, wherein the solid silicon powder has a mesh size of 200-400 mesh and the silicon carbide powder has a mesh size of 100-300 mesh.

7. The preparation method according to claim 1, characterized in that, The heating procedure for the melting and infiltration reaction is as follows: Evacuate to ≤100Pa, heat to 1200℃ at a rate of ≤5℃ / min, and hold for 1 hour; Heat to 1400℃ at a rate of ≤3℃ / min and hold for 1 hour; Heat to 1550℃ at a rate of ≤5℃ / min and hold for 1 hour; Heat to 1650℃ at a rate of ≤5℃ / min, hold for 0.5h~1h, then cool to room temperature.

8. The preparation method according to claim 1, characterized in that, The process parameters for chemical vapor deposition are: temperature 900℃~1300℃, pressure 1kPa~5kPa, and time 15h~24h. The thickness of the SiC protective coating prepared by chemical vapor deposition is 30 μm to 200 μm.

9. A carbon ceramic heating element material with a gradient SiC structure, obtained by the preparation method according to any one of claims 1-8, characterized in that, The overall structure of the carbon-ceramic heating element material has a density / porosity gradient in the thickness direction, with the density gradually decreasing and the porosity gradually increasing from the central region to the edge region.

10. The carbon ceramic heating element material with a gradient SiC structure according to claim 9, characterized in that, The carbon-ceramic heating element material includes: A SiC / C / SiC composite matrix with a gradient SiC structure, wherein a gradient SiC structure is formed inside the SiC / C / SiC composite matrix, with low SiC content and low porosity in the central region and high SiC content and high porosity in the edge region; A SiC protective coating located on the surface of the SiC / C / SiC composite matrix.

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