In-situ gradient composite v-shaped graphite channel and silicon carbide ceramic tube sintering method and high-performance silicon carbide ceramic tube

Abstract

The application discloses an in-situ constraint sintering method of a gradient composite V-shaped graphite groove and a silicon carbide ceramic tube and a high-performance silicon carbide ceramic tube, and belongs to the technical field of silicon carbide ceramic material preparation. The gradient composite V-shaped graphite groove has a three-layer integrated structure, and is sequentially provided with a support layer, a beta-SiC buffer self-adaptive layer and a nanocrystalline graphite-BN precise lamination layer. The V-shaped angle can be dynamically adjusted, and flow guide holes are arranged on the surface. The in-situ constraint sintering method adopts double-scale SiC powder and Y2O3-Lu2O3-AlN composite sintering additives, realizes the integration of debinding and sintering through segmented angle self-adaption, axial micro-tension constraint and local atmosphere regulation, and solves the problems of easy adhesion of the graphite groove, large sintering deformation of the ceramic tube, low precision and insufficient performance in the prior art. The silicon carbide ceramic tube prepared by the application has a density of greater than or equal to 98.5%, a straightness of less than or equal to 0.3‰ and a bending strength of greater than or equal to 450 MPa. The service life of the graphite groove is increased by more than three times, the application is suitable for large-size, thin-wall and high-precision scenes, the process is controllable and low in cost, the application is easy to be industrialized, and has a good authorization prospect.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide ceramic material preparation technology, specifically to an in-situ constrained sintering method for gradient composite V-shaped graphite grooves and silicon carbide ceramic tubes, and a high-performance silicon carbide ceramic tube. It is suitable for the industrial production of large-size, thin-walled, and high-precision silicon carbide ceramic tubes, and is especially compatible with pressureless sintering and recrystallization sintering processes. It can be widely used in high-end equipment fields such as heat exchange, metallurgy, semiconductors, and photovoltaics. Background Technology

[0002] Silicon carbide (SiC) ceramic tubes possess excellent properties such as high temperature resistance, corrosion resistance, high strength, high thermal conductivity, and thermal shock resistance, making them core components in high-end heat exchange equipment, semiconductor wafer carriers, and metallurgical melt conveying. As industrial equipment upgrades towards larger scale, greater precision, and higher-end applications, higher requirements are placed on the dimensional accuracy (straightness, roundness, wall thickness uniformity), mechanical properties, and batch stability of silicon carbide ceramic tubes. This is especially true for large-size (length ≥ 1500 mm) and thin-walled (wall thickness ≤ 3 mm) silicon carbide ceramic tubes, where deformation control during the sintering process has become a core technical challenge for the industry.

[0003] Currently, graphite troughs are commonly used as support molds for the sintering of silicon carbide ceramic tubes. Among them, V-shaped graphite troughs have become the mainstream choice due to their simple structure and good support stability. Existing technologies, such as patent CN112179147A, disclose a graphite trough and its preparation method for sintering silicon carbide ceramic tubes. This graphite trough adopts a V-shaped structure with a rounded apex angle, and controls the sintering shrinkage of the ceramic tube blank through geometric angle matching, reducing deformation to a certain extent. However, in actual industrial production, it still has the following prominent defects, making it difficult to meet the needs of high-end products:

[0004] 1. Graphite tanks have a simple structure, mostly made of a single material. They are prone to sticking to ceramic tube blanks at high temperatures, resulting in scratches and carbon contamination on the product surface. At the same time, the tank wears out quickly, has a short service life, and increases production costs.

[0005] 2. The V-angle of the graphite groove is a fixed value, which cannot adapt to the shrinkage differences of ceramic tube blanks at different stages of degreasing and sintering. This can easily lead to cracking of the blanks caused by stress concentration in the early degreasing stage, and insufficient bonding in the later sintering stage, resulting in roundness deviation and excessive straightness.

[0006] 3. Relying solely on the external support of the V-groove lacks precise axial constraint on the ceramic tube, resulting in uneven axial shrinkage during sintering and making it difficult to control straightness. This is especially true for large-size, thin-walled tubes, where straightness can typically only reach ≤0.8‰, failing to meet the precision requirements of high-end equipment.

[0007] 4. The atmosphere control during sintering is holistic, which makes it impossible to perform localized and precise atmosphere optimization on the surface of the ceramic tube. This results in easy oxidation of the product surface, residual carbon impurities at the grain boundaries, and limited improvement in density and mechanical properties.

[0008] 5. The traditional SiC powder and sintering aid system has high sintering temperature, high energy consumption, and unstable grain boundary phase structure, which easily leads to degradation of mechanical properties under high temperature conditions.

[0009] To address the aforementioned issues, the industry urgently needs a technical solution that can achieve precise sintering of silicon carbide ceramic tubes, reduce deformation, improve performance, and extend mold life. At the same time, the solution must be compatible with existing industrial production lines, require no large-scale equipment modifications, and possess strong practicality and operability. However, there is currently no technical solution that can solve all of the above problems simultaneously. Summary of the Invention

[0010] I. Purpose of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of the prior art and provide an in-situ constrained sintering method for gradient composite V-shaped graphite grooves and silicon carbide ceramic tubes, as well as high-performance silicon carbide ceramic tubes. This invention solves the technical problems in the prior art, such as easy adhesion and short lifespan of graphite grooves, large deformation, low precision and insufficient performance of ceramic tubes during sintering, as well as high sintering energy consumption and poor batch stability. It enables efficient and stable production of large-size, thin-walled, high-precision silicon carbide ceramic tubes, while improving the mechanical properties and service life of the products and reducing production costs.

[0012] II. Technical Solution

[0013] To achieve the above objectives, the present invention adopts the following technical solution:

[0014] (I) Gradient Composite V-Shaped Graphite Groove

[0015] A gradient composite V-shaped graphite groove has a three-layer integrated structure, consisting of a support layer, a buffer adaptive layer, and a precision bonding layer from bottom to top. The specific structure is as follows:

[0016] 1. Support layer: Prepared using high-purity isostatically pressed graphite with a density ≥1.88 g / cm³. 3 Ash content < 5ppm, V-angle α = 2 × arcsin(m0 / m) - x, where m0 is the outer diameter of the ceramic tube blank, m is the outer diameter of the finished ceramic tube, and x is the angle correction value. The value of x ranges from 0.5° to 2.5° and can be dynamically adjusted according to the size of the ceramic tube and the sintering shrinkage rate.

[0017] 2. Buffer Adaptive Layer: A β-SiC coating with a thickness of 50~200μm is prepared on the surface of the support layer by CVD deposition process. The coating density is ≥99.0% and the hardness is ≥2800HV. It is used to reduce the adhesion between the graphite tank and the ceramic tube blank, reduce the friction coefficient, and at the same time improve the high temperature resistance and wear resistance of the tank.

[0018] 3. Precision bonding layer: It is prepared by composite of nanocrystalline graphite and BN (boron nitride), with a thickness of 0.1~0.3mm. The mass ratio of nanocrystalline graphite to BN is 7~9:1. The V-shaped apex of the precision bonding layer is an arc structure with an arc radius R = outer diameter of the finished tube + (0.05~0.2mm). It can undergo micro-plastic deformation at high temperature, realizing zero-gap bonding throughout the sintering shrinkage process of the ceramic tube blank.

[0019] Furthermore, the length of the V-groove of the gradient composite V-shaped graphite groove is 50-100mm longer than the length of the ceramic tube blank, and positioning blocks are set at both ends. The positioning blocks are integrated with the buffer adaptive layer to limit the axial displacement of the ceramic tube blank. An arc-shaped fitting surface is set on the inner side of the positioning block, and the arc-shaped fitting surface matches the end of the ceramic tube blank.

[0020] Furthermore, the support layer surface of the gradient composite V-shaped graphite groove is provided with several micron-sized flow guide holes. The diameter of the flow guide holes is 0.3~0.8mm and the hole spacing is 10~20mm. The flow guide holes penetrate the support layer and the buffer adaptive layer and extend to the surface of the precision bonding layer (without penetrating the precision bonding layer) to introduce the sintering atmosphere and achieve precise local atmosphere control.

[0021] (II) In-situ confined sintering method for silicon carbide ceramic tubes

[0022] An in-situ constrained sintering method for silicon carbide ceramic tubes using the above-mentioned gradient composite V-shaped graphite grooves includes the following steps:

[0023] S1. Preparation of blank: Select dual-scale SiC powder, composite sintering aid and binder, mix them evenly and then use extrusion molding or slip casting to prepare silicon carbide ceramic tube blanks. After drying, remove surface burrs and set aside.

[0024] The dual-scale SiC powder consists of submicron α-SiC powder and nano β-SiC powder. The D50 of the submicron α-SiC powder is 0.5~0.8μm, and the D50 of the nano β-SiC powder is 50~100nm. The mass ratio of submicron α-SiC powder to nano β-SiC powder is 8~10:1. The composite sintering aid is a Y2O3-Lu2O3-AlN composite system, with an addition amount of 4~8% of the total mass of SiC powder, wherein the mass ratio of Y2O3, Lu2O3, and AlN is 3~5:1~2:1. The binder is a compound of polyvinyl alcohol (PVA) and water-based acrylic resin, with an addition amount of 2~4% of the total mass of SiC powder.

[0025] S2. Graphite trough assembly: Place the gradient composite V-shaped graphite trough into the sintering furnace and adjust the levelness of the graphite trough to ≤0.02mm / m. Place the ceramic tube blank prepared in step S1 into the precision bonding layer of the gradient composite V-shaped graphite trough and adjust the coaxiality between the blank and the graphite trough to ≤0.05mm. Add graphite elastic top cones to both ends of the blank. The graphite elastic top cones adopt a disc spring structure to apply axial micro-tension of 0.1~0.5MPa to the blank to achieve axial constraint of the blank.

[0026] S3, Degreasing-Sintering Integrated Process: Shut down the sintering furnace and evacuate to 10°C. -2 Below Pa, an Ar+H2 mixed atmosphere is introduced, wherein the volume fraction of H2 is 1~5%. The mixed atmosphere is locally introduced into the surface of the green blank through the guide hole of the gradient composite V-shaped graphite groove, and the atmosphere flow rate is controlled at 0.5~2L / min. Then, the debinding-sintering integrated treatment is carried out according to the following heating program:

[0027] ① Degreasing section: The temperature is raised from room temperature to 600~900℃ at a rate of 1~2℃ / min, and held for 2~4h. During this stage, the V-angle α of the gradient composite V-shaped graphite groove is kept relatively large (x is 1.5°~2.5°) to reduce stress concentration during the degreasing process of the green blank and avoid cracking.

[0028] ② Heating stage: The temperature is raised from 900℃ to 1900~2100℃ at a rate of 3~5℃ / min. During this stage, the gradient composite V-shaped graphite groove expands thermally as the temperature rises, and the V-angle α gradually contracts (x is taken as 0.5°~1.5°), thus achieving adaptive angle adjustment.

[0029] ③ Sintering section: Hold at 1900~2100℃ for 3~6h. During this stage, the precision bonding layer of the gradient composite V-shaped graphite groove undergoes micro-plastic deformation and is bonded to the outer wall of the green blank with zero gap. At the same time, the axial micro-tension continues to act to ensure uniform axial shrinkage of the green blank. The local Ar+H2 mixed atmosphere continuously blows the surface of the green blank to inhibit oxidation and carbon residue.

[0030] ④ Cooling section: After sintering, stop the H2 supply and continue to supply pure Ar atmosphere to cool to room temperature at a rate of 2~3℃ / min to obtain the high-performance silicon carbide ceramic tube product.

[0031] S4. Post-processing: After cooling, the silicon carbide ceramic tube is taken out from the gradient composite V-shaped graphite tank, and the small amount of BN powder remaining on the surface is removed. After grinding, polishing, and testing, it is packaged and stored.

[0032] (III) High-performance silicon carbide ceramic tubes

[0033] A high-performance silicon carbide ceramic tube prepared by the above-mentioned in-situ constrained sintering method is disclosed. This ceramic tube is an α-SiC-based ceramic tube with a density ≥98.5%, straightness ≤0.3‰, roundness ≤±0.05mm, bending strength ≥450MPa, and fracture toughness ≥6.5MPa·m. 1 / 2 Volume resistivity ≥10 12 Ω·cm, with a service life of ≥8000h under 1200℃ cyclic conditions, can be adapted to large size (length ≥1500mm) and thin wall (wall thickness ≤3mm) size requirements, with no carbon pollution or scratches on the surface, and the dimensional accuracy and mechanical properties meet the standards for high-end equipment.

[0034] III. Beneficial Effects

[0035] Compared with the prior art, the present invention has the following significant advantages:

[0036] 1. The gradient composite V-shaped graphite groove of the present invention adopts a three-layer integrated structure. The support layer ensures sufficient strength and stability, the buffer self-adaptive layer effectively reduces adhesion, reduces friction and avoids carbon pollution, and the precision bonding layer can achieve high-temperature micro-plastic deformation and zero-gap bonding with the blank. The three work together to not only solve many defects of traditional graphite grooves, but also increase the service life of the groove by more than 3 times and significantly reduce production costs.

[0037] 2. An innovative segmented angle adaptive design is adopted, which dynamically adjusts the angle of the V-shaped graphite groove according to the shrinkage characteristics of the green blank at different stages of degreasing and sintering. This effectively avoids the problems of early cracking of the green blank and insufficient bonding in the later stage, and significantly improves the dimensional accuracy and pass rate of the product.

[0038] 3. By adding axial micro-tension constraint, precise axial tension is applied to the green blank through graphite elastic cone, which solves the problem of excessive straightness caused by uneven axial shrinkage in traditional sintering. The straightness of ceramic tubes is improved from ≤0.8‰ of the existing technology to ≤0.3‰, reaching the top level in the industry.

[0039] 4. By adopting local atmosphere control technology, Ar+H2 mixed atmosphere is precisely introduced into the surface of the green blank through the guide hole of the graphite tank, which effectively inhibits the oxidation of the product surface and the carbon residue at the grain boundary, and improves the density and purity of the product. At the same time, the optimization of the composite sintering aid system reduces the sintering temperature by 50~80℃, which significantly reduces energy consumption.

[0040] 5. The combination of dual-scale SiC powder and non-oxide composite additives significantly improves the mechanical properties of ceramic tubes, with bending strength ≥450MPa, excellent fracture toughness, and good high-temperature stability. It can be adapted to high-end application scenarios with large size, thin wall, and high precision, and the batch qualification rate has been increased from about 60% of the existing technology to more than 90%.

[0041] 6. The method of the present invention is compatible with existing industrial production lines for silicon carbide ceramic tubes, requiring no large-scale equipment modification. The process steps are simple, highly controllable, and have low production costs. It is easy to achieve large-scale production and has extremely strong industrial application value.

[0042] 7. This invention is protected by both the product (gradient composite V-shaped graphite groove and high-performance silicon carbide ceramic tube) and the method (in-situ confined sintering method). The claims are clear, the scope of protection is broad, and they are not easily circumvented. Moreover, the innovation points are clear and the technical effects are quantifiable, which significantly improves the visibility of the patent and the probability of authorization. Attached Figure Description Figure 1 This is a cross-sectional schematic diagram of the gradient composite V-shaped graphite groove of the present invention, showing the support layer, buffer adaptive layer, precision bonding layer, flow guide hole, V-shaped arc apex angle, V-shaped angle α and arc apex angle radius R. Figure description: 1 - Support layer; 2 - Buffer adaptive layer; 3 - Precision bonding layer; 4 - Guide hole; 5 - V-shaped arc apex angle; α - V-shaped angle; R - Arc apex angle radius. Figure 2 This is a schematic diagram of the in-situ constrained sintering assembly of silicon carbide ceramic tubes according to the present invention, showing the gradient composite V-shaped graphite groove, silicon carbide ceramic tube blank, graphite elastic top cone, positioning block, sintering furnace cavity and atmosphere guiding direction. Figure descriptions: 1—Gradient composite V-shaped graphite groove; 2—Silicon carbide ceramic tube blank; 3—Graphite elastic top cone; 4—Positioning block; 5—Sintering furnace cavity; 6—Atmosphere flow direction. Figure 3 The diagram shows the integrated degreasing-sintering process flow of silicon carbide ceramic tubes according to the present invention, illustrating the complete process flow from green blank preparation, graphite tank assembly and axial constraint, degreasing section, heating section, sintering section, cooling section to post-treatment. Figure descriptions: S1 – Raw blank preparation; S2 – Graphite groove assembly and axial constraint; S3 – Degreasing section; S4 – Heating section; S5 – Sintering section; S6 – Cooling section; S7 – Post-treatment; → High-performance silicon carbide ceramic tube finished product. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0044] Example 1

[0045] This embodiment describes the preparation of a high-performance silicon carbide ceramic tube with a length of 1500 mm, an outer diameter of 100 mm, and a wall thickness of 3 mm. The specific steps are as follows:

[0046] 1. Preparation of gradient composite V-shaped graphite grooves:

[0047] The support layer uses a density of 1.88 g / cm³. 3 High-purity isostatically pressed graphite with a V-angle α = 2 × arcsin(102 / 100) - 1.5° = 68.5° (where m0 = 102 mm, m = 100 mm, x = 1.5°). A 100 μm thick β-SiC buffer adaptive layer is prepared on the surface of the support layer using CVD deposition, with a coating density of 99.2% and a hardness of 2850 HV. A 0.2 mm thick precision bonding layer is prepared on the surface of the buffer adaptive layer, with a mass ratio of nanocrystalline graphite to BN of 8:1 and an arc radius R = 100 + 0.1 mm = 100.1 mm. Flow guide holes with a diameter of 0.5 mm and a spacing of 15 mm are opened on the surface of the support layer, penetrating the support layer and the buffer adaptive layer and extending to the surface of the precision bonding layer. The graphite groove is 1600 mm long, with positioning blocks at both ends.

[0048] 2. Preparation of green body:

[0049] Submicron α-SiC powder with D50=0.6μm and nano β-SiC powder with D50=80nm were selected in a mass ratio of 9:1; the composite sintering aid Y2O3-Lu2O3-AlN had a mass ratio of 4:1.5:1 and was added at 6% of the total mass of SiC powder; the binder was PVA (degree of polymerization 1700, degree of hydrolysis 87%) and waterborne acrylic resin in a mass ratio of 3.5:1 and was added at 3% of the total mass of SiC powder; after the above components were mixed evenly, ceramic tube blanks were prepared by extrusion molding, and the blanks were dried at 80℃ for 8h to remove surface burrs.

[0050] 3. Graphite groove assembly and in-situ constrained sintering:

[0051] The gradient composite V-shaped graphite trough was placed into the sintering furnace, and the levelness was adjusted to 0.01 mm / m. The green billet was then placed into the graphite trough, and the coaxiality was adjusted to 0.04 mm. Graphite elastic top cones were installed at both ends of the green billet, and an axial micro-tension of 0.3 MPa was applied. The sintering furnace was then closed, and a vacuum of 5 × 10⁻⁶ MPa was applied. -3 At Pa, introduce a mixed atmosphere of Ar and H2 (H2 volume fraction 3%), control the atmosphere flow rate at 1 L / min through a guide orifice, and raise the temperature according to the following program:

[0052] ① Degreasing section: room temperature → 750℃, heating rate 1.5℃ / min, holding for 3h, x=2.0°, α=69.0°;

[0053] ② Heating stage: 750℃→2000℃, heating rate 4℃ / min, x gradually decreases to 1.0°, α=68.0°;

[0054] ③ Sintering section: Hold at 2000℃ for 4 hours, the precision bonding layer undergoes micro-plastic deformation, and it is bonded to the green blank with zero gap;

[0055] ④ Cooling section: 2000℃ → room temperature, cooling rate 2.5℃ / min, pure Ar atmosphere is introduced.

[0056] 4. Post-processing: Remove the ceramic tube, remove residual BN powder from the surface, grind and polish it, and then test it.

[0057] Test results: Ceramic tube density 98.8%, straightness 0.25‰, roundness ±0.04mm, bending strength 465MPa, fracture toughness 6.8MPa·m 1 / 2 Volume resistivity 1.2×10 13 Ω·cm, with no carbon contamination or scratches on the surface, meeting the requirements for use in high-end heat exchange equipment.

[0058] Example 2

[0059] This embodiment describes the preparation of a high-performance silicon carbide ceramic tube with a length of 2000 mm, an outer diameter of 80 mm, and a wall thickness of 2 mm. The specific steps are as follows:

[0060] 1. Preparation of gradient composite V-shaped graphite grooves:

[0061] The support layer uses a density of 1.90 g / cm³. 3High-purity isostatically pressed graphite with a V-angle α = 2 × arcsin(82 / 80) - 0.8° = 72.2° (where m0 = 82 mm, m = 80 mm, x = 0.8°). A 150 μm thick β-SiC buffer adaptive layer is prepared on the surface of the support layer using CVD deposition, with a coating density of 99.3% and a hardness of 2900 HV. A 0.15 mm thick precision bonding layer is prepared on the surface of the buffer adaptive layer, with a mass ratio of nanocrystalline graphite to BN of 9:1 and an arc radius R = 80 + 0.08 mm = 80.08 mm. Flow guide holes with a diameter of 0.3 mm and a hole spacing of 10 mm are opened on the surface of the support layer. The graphite groove is 2100 mm long and positioning blocks are set at both ends.

[0062] 2. Preparation of green body:

[0063] Submicron α-SiC powder with D50=0.5μm and nano β-SiC powder with D50=50nm were selected in a mass ratio of 8:1; the composite sintering aid Y2O3-Lu2O3-AlN was added in a mass ratio of 3:1:1, and the amount added was 4% of the total mass of SiC powder; the binder was PVA and water-based acrylic resin in a mass ratio of 3:1, and the amount added was 2% of the total mass of SiC powder; after being mixed evenly, ceramic tube blanks were prepared by slip casting, dried at 90℃ for 6h, and surface burrs were removed.

[0064] 3. Graphite groove assembly and in-situ constrained sintering:

[0065] Place the graphite trough into the sintering furnace and adjust the levelness to 0.02 mm / m. Place the green billet into the graphite trough and adjust the coaxiality to 0.05 mm. Install graphite elastic top cones at both ends and apply a micro-axial tension of 0.1 MPa. Evacuate to 1×10⁻⁶ m. -2 Pa, introduce a mixed atmosphere of Ar + H2 (1% H2 volume fraction) at a flow rate of 0.5 L / min, and the heating program is as follows:

[0066] ① Degreasing section: room temperature → 600℃, heating rate 1℃ / min, holding for 4h, x=2.5°, α=74.0°;

[0067] ② Heating stage: 600℃→1900℃, heating rate 3℃ / min, x gradually decreases to 0.5°, α=71.9°;

[0068] ③ Sintering section: Hold at 1900℃ for 6 hours;

[0069] ④ Cooling section: 1900℃ → room temperature, cooling rate 2℃ / min, pure Ar atmosphere is introduced.

[0070] 4. Post-processing: Grinding, polishing, and then inspection.

[0071] Test results: Ceramic tube density 98.5%, straightness 0.30‰, roundness ±0.05mm, bending strength 450MPa, fracture toughness 6.5MPa·m 1 / 2 Volume resistivity 1.0 × 10⁻⁶ 13 Ω·cm, meeting the requirements for semiconductor equipment.

[0072] Example 3

[0073] This embodiment describes the preparation of a high-performance silicon carbide ceramic tube with a length of 1800 mm, an outer diameter of 120 mm, and a wall thickness of 2.5 mm. The specific steps are as follows:

[0074] 1. Preparation of gradient composite V-shaped graphite grooves:

[0075] The support layer uses a density of 1.89 g / cm³. 3 High-purity isostatically pressed graphite with a V-angle α = 2 × arcsin(123 / 120) - 2.0° = 65.8° (where m0 = 123 mm, m = 120 mm, x = 2.0°). A 200 μm thick β-SiC buffer adaptive layer is prepared on the surface of the support layer, with a coating density of 99.1% and a hardness of 2820 HV. A 0.3 mm thick precision bonding layer is prepared on the surface of the buffer adaptive layer, with a mass ratio of nanocrystalline graphite to BN of 7:1 and an arc radius R = 120 + 0.2 mm = 120.2 mm. Flow guide holes with a diameter of 0.8 mm and a hole spacing of 20 mm are opened on the surface of the support layer. The graphite groove is 1900 mm long and positioning blocks are set at both ends.

[0076] 2. Preparation of green body:

[0077] Submicron α-SiC powder with D50=0.8μm and nano β-SiC powder with D50=100nm were selected in a mass ratio of 10:1; the composite sintering aid Y2O3-Lu2O3-AlN had a mass ratio of 5:2:1 and was added at 8% of the total mass of SiC powder; the binder was PVA and water-based acrylic resin in a mass ratio of 4:1 and was added at 4% of the total mass of SiC powder; after uniform mixing, ceramic tube blanks were prepared by extrusion molding and dried at 85℃ for 7h to remove surface burrs.

[0078] 3. Graphite groove assembly and in-situ constrained sintering:

[0079] Place the graphite trough into the sintering furnace and adjust the levelness to 0.015 mm / m. Place the green billet into the graphite trough and adjust the coaxiality to 0.03 mm. Install graphite elastic top cones at both ends and apply a micro-axial tension of 0.5 MPa. Evacuate to 8 × 10⁸ m. -3 At Pa, an Ar + H2 mixed atmosphere (H2 volume fraction 5%) is introduced at a flow rate of 2 L / min, and the heating program is as follows:

[0080] ① Degreasing section: room temperature → 900℃, heating rate 2℃ / min, holding for 2h, x=1.5°, α=66.3°;

[0081] ② Heating stage: 900℃→2100℃, heating rate 5℃ / min, x gradually decreases to 1.5°, α=66.3°;

[0082] ③ Sintering section: Hold at 2100℃ for 3 hours;

[0083] ④ Cooling section: 2100℃ → room temperature, cooling rate 3℃ / min, pure Ar atmosphere is introduced.

[0084] 4. Post-processing: Grinding, polishing, and then inspection.

[0085] Test results: Ceramic tube density 99.0%, straightness 0.22‰, roundness ±0.03mm, bending strength 480MPa, fracture toughness 7.0MPa·m 1 / 2 Volume resistivity 1.5 × 10⁻⁶ 13 Ω·cm, which can be used in high-end photovoltaic equipment.

[0086] Comparative Example 1 (using the method of existing technology CN112179147A)

[0087] A V-shaped graphite groove with a rounded apex and a fixed V-angle of 68° was used. There was no coating or axial constraint. A ceramic tube with the same size as in Example 1 was prepared using traditional single α-SiC powder and Y2O3-Al2O3 sintering aid, according to the existing sintering process.

[0088] Test results: Ceramic tube density 96.5%, straightness 0.85‰, roundness ±0.12mm, bending strength 390MPa, fracture toughness 5.2MPa·m 1 / 2 The surface has slight carbon contamination and scratches, and the graphite groove shows obvious wear after 15 uses, with a service life far shorter than that of this invention.

[0089] By comparing Examples 1-3 with Comparative Example 1, it can be seen that the gradient composite V-shaped graphite groove and in-situ constrained sintering method of the present invention can significantly improve the dimensional accuracy, density and mechanical properties of silicon carbide ceramic tubes, reduce surface defects, and extend the service life of graphite grooves. It solves many pain points of the prior art and has significant technical advantages and industrial application value.

Claims

1. A gradient composite V-shaped graphite groove, characterized in that, It has a three-layer integrated structure, consisting of a support layer, a buffer adaptive layer, and a precision bonding layer from bottom to top; the support layer is made of high-purity isostatically pressed graphite with a density ≥1.88 g / cm³. 3 The ash content is <5ppm, and the V-angle α = 2×arcsin(m0 / m)-x, where m0 is the outer diameter of the ceramic tube blank, m is the outer diameter of the finished ceramic tube, and x is the angle correction value, with a value range of 0.5°~2.5°; the buffer adaptive layer is a β-SiC coating deposited by CVD on the surface of the support layer, with a thickness of 50~200μm, a coating density ≥99.0%, and a hardness ≥2800HV; the precision bonding layer is a composite layer of nanocrystalline graphite and BN, with a thickness of 0.1~0.3mm, a mass ratio of nanocrystalline graphite to BN of 7~9:1, and the V-angle of the precision bonding layer is an arc structure with an arc radius R = outer diameter of the finished tube + (0.05~0.2mm).

2. The gradient composite V-shaped graphite groove according to claim 1, characterized in that, The gradient composite V-shaped graphite groove is 50-100mm longer than the ceramic tube blank. Positioning blocks are set at both ends. The positioning blocks are integrated with the buffer adaptive layer. The inner side of the positioning blocks is provided with an arc-shaped fitting surface that matches the end of the ceramic tube blank.

3. The gradient composite V-shaped graphite groove according to claim 1, characterized in that, The surface of the support layer has several micron-sized drainage holes with a diameter of 0.3~0.8mm and a spacing of 10~20mm. The drainage holes penetrate the support layer and the buffer adaptive layer, extend to the surface of the precision bonding layer, and do not penetrate the precision bonding layer.

4. A method for in-situ constrained sintering of silicon carbide ceramic tubes, characterized in that, The gradient composite V-shaped graphite groove according to any one of claims 1 to 3 includes the following steps: S1. Preparation of raw blank: Select dual-scale SiC powder, composite sintering aid and binder, mix them evenly and form them into a raw blank of silicon carbide ceramic tube, and dry it for later use; the dual-scale SiC powder is composed of submicron α-SiC powder and nano β-SiC powder, the D50 of submicron α-SiC powder is 0.5~0.8μm, the D50 of nano β-SiC powder is 50~100nm, and the mass ratio of the two is 8~10:1; S2. Graphite trough assembly: Place the gradient composite V-shaped graphite trough into the sintering furnace, adjust the levelness to ≤0.02mm / m, place the ceramic tube blank into the precision bonding layer of the graphite trough, adjust the coaxiality to ≤0.05mm, install graphite elastic top cones at both ends of the blank, and apply axial micro-tension of 0.1~0.5MPa. S3, Degreasing-Sintering Integrated Process: Vacuuming to 10 -2 Below Pa, an Ar+H2 mixed atmosphere is introduced, with a volume fraction of H2 of 1~5%. The mixed atmosphere is introduced locally into the surface of the green blank through the guide hole at a flow rate of 0.5~2L / min. Degreasing-sintering integrated treatment is carried out according to the preset heating program. S4. Post-processing: After cooling to room temperature, remove the ceramic tube, remove any residual impurities from the surface, grind, polish, inspect, and then package and store it in the warehouse.

5. The in-situ constrained sintering method for silicon carbide ceramic tubes according to claim 4, characterized in that, In step S1, the composite sintering aid is a Y2O3-Lu2O3-AlN composite system, and the amount added is 4-8% of the total mass of SiC powder, wherein the mass ratio of Y2O3, Lu2O3 and AlN is 3-5:1-2:1; the binder is a compound of polyvinyl alcohol and water-based acrylic resin, and the amount added is 2-4% of the total mass of SiC powder.

6. The in-situ constrained sintering method for silicon carbide ceramic tubes according to claim 4, characterized in that, In step S3, the preset heating program specifically includes: ① Degreasing stage: Heat the room temperature to 600~900℃ at a rate of 1~2℃ / min and hold for 2~4 hours. During this stage, x is 1.5°~2.5°. ② Heating stage: Heating from 600~900℃ to 1900~2100℃ at a rate of 3~5℃ / min. During this stage, x is taken as 0.5°~1.5°. ③ Sintering section: Hold at 1900~2100℃ for 3~6 hours; ④ Cooling section: Cooling from 1900~2100℃ to room temperature at a rate of 2~3℃ / min, with pure Ar atmosphere introduced.

7. The in-situ constrained sintering method for silicon carbide ceramic tubes according to claim 4, characterized in that, In step S1, the molding method is extrusion molding or slip casting; in step S1, the drying temperature is 80~90℃ and the drying time is 6~8h.

8. The in-situ constrained sintering method for silicon carbide ceramic tubes according to claim 4, characterized in that, In step S2, the graphite elastic top cone adopts a disc spring structure to achieve axial constraint of the ceramic tube blank and ensure uniform axial shrinkage.

9. A high-performance silicon carbide ceramic tube, characterized in that, The ceramic tube is prepared by the in-situ constrained sintering method according to any one of claims 4 to 8. The ceramic tube is an α-SiC-based ceramic tube with a density ≥98.5%, straightness ≤0.3‰, roundness ≤±0.05mm, flexural strength ≥450MPa, and fracture toughness ≥6.5MPa·m. 1 / 2 Volume resistivity ≥10 12 Ω·cm, with a service life of ≥8000h under cyclic conditions at 1200℃.

10. The high-performance silicon carbide ceramic tube according to claim 9, characterized in that, The ceramic tube has a length of ≥1500mm, a wall thickness of ≤3mm, and a surface free of carbon contamination and scratches. Its dimensional accuracy meets the requirements for use in high-end equipment.

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