A carbon / carbon composite crucible having a silicon carbonitride oxygen-free coating and a method of making the same

Abstract

The application provides a carbon / carbon composite material crucible with a silicon carbon nitrogen oxygen-free coating and a preparation method thereof, and relates to the technical field of crucible preparation. The carbon / carbon composite material crucible is densified by phenolic resin, the PIP process is adopted, the high-density carbon / carbon composite material crucible is impregnated more than twice by a PIP impregnating solution containing polycarbosilane, polyazidosilane and a binder, the high-density carbon / carbon composite material crucible is fully impregnated with the PIP impregnating solution, and the uniformity and the density of the silicon carbon nitrogen oxygen-free coating are improved, the PIP impregnating solution on the surface of the crucible is in-situ reacted to form the silicon carbon nitrogen oxygen-free coating after heat treatment, and the interlayer bonding force is strong. The silicon carbon nitrogen oxygen-free coating effectively seals the holes of the carbon / carbon composite material crucible, improves the density, prevents the silicon liquid from penetrating, effectively prevents the carbon / carbon composite material crucible from being corroded and damaged, improves the high-temperature mechanical properties and the silicon corrosion resistance, and significantly prolongs the service life of the carbon / carbon composite material crucible.

Description

Technical Field

[0001] This invention relates to the field of crucible preparation technology, specifically to a carbon / carbon composite material crucible with a silicon-carbon-nitrogen oxygen-free coating and its preparation method. Background Technology

[0002] Currently, quartz crucibles are commonly used in monocrystalline silicon pulling furnaces. However, in recent years, there has been a shortage of high-purity quartz sand raw materials, and imports have been restricted. Furthermore, quartz crucibles have a short service life of only about 15 days, requiring frequent replacement, which significantly increases the production cost of monocrystalline silicon. As the size of monocrystalline silicon continues to increase, the size requirements for hot zone components are also becoming larger. Carbon-carbon composite materials have become the preferred material for hot zone materials in monocrystalline silicon due to their excellent dimensional stability and mechanical properties.

[0003] During the Czochralski (CZ) process of growing single-crystal silicon, the melting of silicon material generates silicon vapor and molten silicon splashes, causing silicide erosion of the carbon-carbon thermal field material. This severely affects the mechanical properties and service life of the carbon-carbon thermal field material. Therefore, how to reduce silicide erosion of carbon-carbon thermal field materials and improve their service life has become a common concern for both single-crystal silicon manufacturers and carbon-carbon thermal field material manufacturers.

[0004] Chinese patent CN112374917A discloses a method for preparing a high-temperature ceramic coating. First, a mixture of polycarbosilane and polysilazane is used as a precursor to prepare a ceramic phase coating with SiC-SiCN as the main component on the surface of a C / C composite material. Then, a second coating is prepared by high-temperature sintering of SiC powder as the main component on the C / C composite material surface. Finally, a BN coating is deposited on the surface. Using this method, a ceramic coating is obtained for the protection of C / C composite materials, which can improve the tensile properties by more than 8% at room temperature and has good high-temperature resistance and oxidation resistance. However, single-crystal silicon is extremely sensitive to boron. Modifying the carbon-carbon thermal field material using the above method easily causes boron contamination, leading to the fracture of the silicon single crystal during the pulling process.

[0005] Chinese patent CN113277867A discloses a method for preparing a carbon / carbon / silicon carbide composite crucible, comprising the following steps: A) alternately stacking carbon fiber plain weave fabric and carbon fiber mesh on a mandrel, and when a predetermined thickness is reached, forming a crucible preform through a needle-punching and stitching process; B) using propylene as the carbon source gas and argon as the carrier gas, performing chemical vapor deposition to deposit and densify the preform, followed by repeated impregnation-high-temperature pyrolysis operations to prepare a crucible blank of a predetermined density; C) machining the crucible blank to produce a crucible product; D) performing vapor-phase silicon infiltration on the crucible product to form a dense silicon carbide coating, thus obtaining the finished crucible. This method does not introduce boron contamination, fully utilizes the advantages of each process in filling the internal pores of the preform, and forms a dense silicon carbide coating on the surface of the crucible product, which can effectively inhibit oxidation and corrosion, and significantly improve the service life of the crucible. However, the dense silicon carbide coating prepared by the above method using the vapor phase silicon diffusion method has poor uniformity, resulting in poor silicon diffusion effect and thus affecting the service life of the crucible products. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a carbon / carbon composite material crucible with a silicon-carbon-nitrogen oxygen-free coating and a method for preparing the same. The silicon-carbon-nitrogen oxygen-free coating obtained by the method of the present invention has high uniformity and excellent silicon infiltration effect, and the carbon / carbon composite material crucible with the silicon-carbon-nitrogen oxygen-free coating has a long service life.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing a carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating, comprising the following steps:

[0009] A carbon / carbon composite crucible is mixed with phenolic resin and subjected to a first impregnation, cross-linking curing, and pyrolysis carbonization process to obtain a high-density carbon / carbon composite crucible; the density of the high-density carbon / carbon composite crucible is 1.65–1.85 g / cm³. 3 ;

[0010] The high-density carbon / carbon composite crucible is mixed with PIP impregnation solution and subjected to a second impregnation followed by heat treatment to obtain a carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating. The PIP impregnation solution includes a polycarbosilane solution, a polynitrosilane solution, and a binder. The solid content of the polycarbosilane solution and the polynitrosilane solution is independently ≥60%. The mass ratio of the polycarbosilane solution and the polynitrosilane solution is 1 to 1.5:1. The mass ratio of the total mass of the polycarbosilane solution and the polynitrosilane solution to the mass of the binder is 1:0.005 to 0.05. The temperature of the second impregnation is 25 to 40°C, the time of a single impregnation is 6 to 12 hours, and the pressure is 0 to 1 kPa. The number of second impregnations is ≥2.

[0011] Preferably, the first impregnation includes sequential vacuum impregnation and pressure impregnation, wherein the vacuum degree of the vacuum impregnation is -0.1 to 0 MPa and the time is 1 to 6 hours; and the pressure of the pressure impregnation is 1 to 2 MPa and the time is 1 to 3 hours.

[0012] Preferably, the cross-linking curing temperature is 100-200℃, the pressure is 1-3MPa, and the time is 2-4h.

[0013] Preferably, the pyrolysis and carbonization temperature is 600–1200°C, and the time is 10–36 h.

[0014] Preferably, the heat treatment temperature is 1400–1800°C and the time is 8–12 hours.

[0015] Preferably, the method for preparing the carbon / carbon composite crucible includes the following steps:

[0016] Carbon fibers are woven into a shape to obtain a carbon fiber crucible preform;

[0017] The carbon fiber crucible preform is subjected to a first high-temperature heat treatment, vapor deposition densification, a second high-temperature heat treatment, and machining in sequence to obtain a carbon / carbon composite material crucible.

[0018] Preferably, the temperature of the first high-temperature heat treatment and the second high-temperature heat treatment are independently 1800-2300°C, and the time is independently 1-4 hours;

[0019] The vapor deposition densification is chemical vapor deposition densification, and the conditions for vapor deposition densification include: a deposition temperature of 1000–1200℃, a deposition time of 100–300 h, a deposition pressure of 2–10 kPa, a temperature rise rate from room temperature to the deposition temperature of 40–80℃ / h, and a carbon source gas flow rate of 2–20 m³ / h. 3 / h.

[0020] Preferably, the density of the carbon fiber crucible preform is 1.3–1.5 g / cm³. 3 .

[0021] The present invention provides a carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating prepared by the preparation method described above, comprising a high-density carbon / carbon composite crucible and a silicon-carbon-nitrogen oxygen-free coating loaded on the inner surface of the high-density carbon / carbon composite crucible.

[0022] This invention utilizes phenolic resin to densify carbon / carbon composite crucibles, increasing their density. Employing a PIP (Polypropylene Infusion) process, the high-density carbon / carbon composite crucible is repeatedly impregnated (more than twice) with a PIP impregnation solution containing polycarbosilane, polynitrogen silane, and a binder. This ensures thorough impregnation of the raw materials for a silicon-carbon-nitrogen oxygen-free coating, thereby improving the uniformity and density of the coating. After heat treatment, the PIP impregnation solution on the crucible surface reacts in situ to form the silicon-carbon-nitrogen oxygen-free coating, resulting in a stronger interlayer bond. The silicon-carbon-nitrogen oxygen-free coating effectively seals the pores of the carbon / carbon composite crucible, making its surface denser, preventing silicon melt penetration, and inhibiting chemical reactions between silicon vapor and the crucible. This effectively prevents corrosion and damage, significantly improving the high-temperature mechanical properties and resistance to siliconization corrosion, protecting the crucible, and extending its service life. As shown in the test results of the examples, the carbon / carbon composite material crucible with silicon-carbon-nitrogen oxygen-free coating prepared by the present invention has a service life of 6 to 12 months for pulling single crystal silicon. The long service life can meet the requirements of the core structural part of the carbon / carbon composite material crucible for single crystal silicon Czochralski furnace in photovoltaic thermal field.

[0023] This invention replaces traditional quartz crucibles with carbon / carbon composite crucibles coated with a silicon-carbon-nitrogen oxygen-free coating, alleviating the domestic shortage of quartz sand and extending the service life of single-crystal silicon pulling crucibles while reducing production costs for enterprises. Furthermore, the preparation method provided by this invention has the advantages of simple process, convenient operation, short preparation cycle, and low production cost, offering a practical and effective method for the large-scale industrial production of carbon / carbon composite crucibles with silicon-carbon-nitrogen oxygen-free coatings.

[0024] Furthermore, the present invention employs chemical vapor deposition to initially densify the carbon fiber crucible preform after the first heat treatment, which can maximize the connectivity of the pores, shorten the subsequent resin carbon densification cycle, quickly reach the predetermined volume density, greatly shorten the crucible preparation cycle, and reduce production costs.

[0025] This invention provides a carbon / carbon composite material crucible with a silicon-carbon-nitrogen oxygen-free coating prepared by the method described above. The crucible comprises a high-density carbon / carbon composite material crucible and a silicon-carbon-nitrogen oxygen-free coating loaded on the inner surface of the high-density carbon / carbon composite material crucible. The carbon / carbon composite material crucible with a silicon-carbon-nitrogen oxygen-free coating provided by this invention exhibits strong corrosion resistance, excellent mechanical properties, and strong interlayer bonding between the silicon-carbon-nitrogen oxygen-free coating and the high-density carbon / carbon composite material crucible. Detailed Implementation

[0026] This invention provides a method for preparing a carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating, comprising the following steps:

[0027] A carbon / carbon composite crucible is mixed with phenolic resin and subjected to a first impregnation, cross-linking curing, and pyrolysis carbonization process to obtain a high-density carbon / carbon composite crucible; the density of the high-density carbon / carbon composite crucible is 1.65–1.85 g / cm³. 3 ;

[0028] The high-density carbon / carbon composite crucible is mixed with PIP impregnation solution and subjected to a second impregnation 3 to 5 times, followed by heat treatment to obtain a carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating. The PIP impregnation solution includes polycarbosilane solution, polynitrosilane solution, and binder. The solid content of the polycarbosilane solution and the polynitrosilane solution is independently ≥60%. The mass ratio of the polycarbosilane solution and the polynitrosilane solution is 1 to 1.5:1. The mass ratio of the total mass of the polycarbosilane solution and the polynitrosilane solution to the mass of the binder is 1:0.005 to 0.05. The temperature of the second impregnation is 25 to 40°C, the time of a single impregnation is 6 to 12 hours, and the pressure is 0 to 1 kPa. The number of second impregnations is ≥2.

[0029] Unless otherwise specified, all raw materials used in this invention are commercially available products.

[0030] This invention involves mixing a carbon / carbon composite crucible with phenolic resin, followed by a first impregnation, cross-linking curing, and pyrolysis carbonization to obtain a high-density carbon / carbon composite crucible; the density of the high-density carbon / carbon composite crucible is 1.65–1.85 g / cm³. 3 .

[0031] In this invention, the method for preparing the carbon / carbon composite crucible preferably includes the following steps:

[0032] Carbon fibers are woven into a shape to obtain a carbon fiber crucible preform;

[0033] The carbon fiber crucible preform is subjected to a first high-temperature heat treatment, vapor deposition densification, a second high-temperature heat treatment, and machining in sequence to obtain a carbon / carbon composite material crucible.

[0034] This invention involves weaving carbon fiber to obtain a carbon fiber crucible preform. In this invention, the weaving structure of the carbon fiber crucible preform is preferably a needle-punched structure. The weaving process is preferably achieved by alternating layers of non-woven fabric and ultra-thin mesh needle-punching, with Z-direction fibers bidirectionally penetrating the mesh. The thickness of the ultra-thin mesh is preferably 1–5 mm, more preferably 1–2 mm. In this invention, the density of the carbon fiber crucible preform is preferably 1.3–1.5 g / cm³. 3 More preferably, it is 1.35–1.45 g / cm³.3 Further preferred value is 1.4 g / cm³. 3 .

[0035] After obtaining the carbon fiber crucible preform, the present invention sequentially performs a first high-temperature heat treatment, vapor deposition densification, a second high-temperature heat treatment, and machining on the carbon fiber crucible preform to obtain a carbon / carbon composite material crucible. In this invention, the temperatures of the first and second high-temperature heat treatments are independently preferably 1800–2300°C, more preferably 1900–2200°C, and even more preferably 2000–2100°C; the times of the first and second high-temperature heat treatments are independently preferably 1–4 hours, more preferably 1.5–3.5 hours, and even more preferably 2–3 hours; the first and second high-temperature heat treatments are preferably performed under a protective atmosphere, preferably high-purity helium or high-purity argon; the purity of the protective atmosphere is preferably ≥99.99%. In this invention, the vapor deposition densification is preferably chemical vapor deposition densification, preferably performed in a CVD vapor deposition furnace; the conditions for vapor deposition densification include: a deposition temperature preferably of 1000–1200°C, more preferably 1050–1150°C, and even more preferably 1100°C; a deposition time preferably of 100–300 h, more preferably 150–240 h, and even more preferably 200 h; a deposition pressure preferably of 2–10 kPa, more preferably 4–8 kPa, and even more preferably 5–6 kPa; a temperature rise rate from room temperature to the deposition temperature preferably of 40–80°C / h, more preferably 50–70°C / h, and even more preferably 60°C / h; and a carbon source gas flow rate preferably of 2–20 m³ / h. 3 / h, more preferably 5-15m 3 / h, further preferably 10m 3 / h, wherein the carbon source gas is preferably methane and / or propylene; during the vapor deposition densification process, graphite is preferably used as a small piece of material for assembling the prefabricated carbon fiber crucible assembly after the first high-temperature heat treatment; the graphite is reusable. In this invention, the graphite is preferably subjected to high-temperature treatment before use, the temperature of which is preferably 1800-2200℃, more preferably 1900-2100℃; the time of which is preferably 1-4h, more preferably 2-3h; the pressure of which is preferably 1-10kPa, more preferably 4-8kPa, and even more preferably 5-6kPa. In this invention, the purpose of machining is to maximize the exposure of the internal pores of the material on the inner and outer surfaces, which is beneficial to the subsequent first impregnation; this invention does not have special limitations on the machining, as long as the outer surface is polished to be smooth and free of slag and a carbon / carbon composite crucible of a predetermined size can be obtained.

[0036] In this invention, the phenolic resin is preferably used in the form of a phenolic resin solution, wherein the solid content of the phenolic resin solution is preferably 60-85%, more preferably 70-75%; and the solvent in the phenolic resin solution is preferably xylene and / or styrene.

[0037] In this invention, the first impregnation preferably includes sequential vacuum impregnation and pressure impregnation. The vacuum degree of the vacuum impregnation is preferably -0.1 to 0 MPa, more preferably -0.1 to -0.05 MPa, and the vacuum impregnation time is preferably 1 to 6 hours, more preferably 2 to 4 hours. The pressure of the pressure impregnation is preferably 1 to 2 MPa, more preferably 1.2 to 2 MPa, and even more preferably 1.5 to 2 MPa. The pressure impregnation time is preferably 1 to 3 hours, more preferably 1.5 to 3 hours, and even more preferably 2 to 3 hours. The temperature of the first impregnation is preferably 25 to 40°C, more preferably 25 to 30°C.

[0038] In this invention, the crosslinking curing temperature is preferably 100-200℃, more preferably 120-200℃, and even more preferably 150-200℃; the crosslinking curing pressure is preferably 1-3 MPa, more preferably 1.5-3 MPa, and even more preferably 2-3 MPa; the crosslinking curing time is preferably 2-4 h, more preferably 2.5-4 h, and even more preferably 3-4 h.

[0039] In this invention, the temperature of the pyrolysis carbonization is preferably 600-1200℃, more preferably 800-1200℃, and even more preferably 1000-1200℃; the time of the pyrolysis carbonization is preferably 10-36h, more preferably 10-20h, and even more preferably 10-15h; the pyrolysis carbonization is preferably carried out in a carbonization furnace.

[0040] In this invention, the density of the carbon / carbon composite crucible is preferably 1.65–1.85 g / cm³. 3 More preferably, it is 1.7–1.85 g / cm³. 3 More preferably, it is 1.75–1.8 g / cm³. 3 .

[0041] After obtaining the high-density carbon / carbon composite material crucible, the present invention mixes the high-density carbon / carbon composite material crucible with PIP impregnation liquid, performs a second impregnation and then heat treatment to obtain a carbon / carbon composite material crucible with a silicon-carbon-nitrogen oxygen-free coating.

[0042] In this invention, the PIP impregnation solution comprises a polycarbosilane solution, a polynitrosilane solution, and a binder; the solid content of the polycarbosilane solution and the polynitrosilane solution is independently ≥60%, preferably 60-100%; the mass ratio of the polycarbosilane solution and the polynitrosilane solution is 1-1.5:1, preferably 1-1.4:1, more preferably 1-1.2:1; in the polycarbosilane solution, the molecular weight of the polycarbosilane is preferably 5000-20000, more preferably 10000-15000, and the solvent is preferably xylene; in the polynitrosilane solution, the molecular weight of the polynitrosilane is preferably 5000-20000, more preferably 10000-15000, and the solvent is preferably xylene. In this invention, the adhesive preferably comprises silica sol, wherein the silica sol preferably contains 20-45 wt% silica, more preferably 30-40 wt% silica; and in the PIP impregnation solution, the mass ratio of the total mass of the polycarbosilane solution and the polynitrosilane solution to the mass of the adhesive is 1:0.005-0.05, preferably 1:0.01-0.04, more preferably 1:0.02-0.03.

[0043] In this invention, the temperature of the second impregnation is 25–40°C, preferably 25–30°C; the single impregnation time of the second impregnation is 6–12 hours, preferably 8–10 hours; the pressure of the second impregnation is 0–1 kPa, preferably 0.2–0.5 kPa; the number of second impregnations is ≥2, preferably 3–5 times, more preferably 4 times. The cyclic impregnation of this invention ensures that the high-density carbon / carbon composite material crucible is fully impregnated with the raw material of the silicon-carbon-nitrogen oxygen-free coating, thereby improving the uniformity and density of the silicon-carbon-nitrogen oxygen-free coating. In this invention, drying is preferably included after each second impregnation. The drying temperature is preferably 150–300°C, more preferably 180–250°C; the drying time is not particularly limited in this invention, drying to constant weight is sufficient.

[0044] In this invention, the heat treatment temperature is preferably 1400–1800℃, more preferably 1500–1800℃, and even more preferably 1600–1800℃; the heat treatment time is preferably 8–12 h, more preferably 9–11 h, and even more preferably 10 h. In this invention, during the heat treatment process, polycarbosilane and polynitrosilane undergo an in-situ reaction to generate a silicon-carbon-nitrogen oxygen-free coating, thereby improving the carbon / carbon crucible's resistance to siliconization corrosion and its surface mechanical properties.

[0045] This invention provides a carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating prepared by the method described above, comprising a high-density carbon / carbon composite crucible and a silicon-carbon-nitrogen oxygen-free coating loaded on the inner surface of the high-density carbon / carbon composite crucible. In this invention, the thickness of the silicon-carbon-nitrogen oxygen-free coating is preferably 100–500 μm, and the porosity of the silicon-carbon-nitrogen oxygen-free coating is preferably 1–5%, more preferably 1–2%.

[0046] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0047] The specific graphite used in the following examples is graphite that has undergone high-temperature treatment. The high-temperature treatment temperature is 2200℃, the time is 4h, and the pressure is 1kPa.

[0048] Example 1

[0049] The fabric is made by alternating layers of non-woven fabric and ultra-thin mesh needle punching, and then woven using Z-direction fibers in both directions to achieve a density of 1.4 g / cm³. 3 A carbon fiber crucible preform was prepared. The preform was subjected to high-temperature treatment at 2000℃ for 3 hours. Then, a three-layer, six-piece tooling was constructed using a specific graphite kit. Rapid vapor deposition densification was performed in a CVD (Chemical Vapor Deposition) furnace, followed by high-temperature treatment at 2000℃ for 2 hours. The surface was then machined and polished until smooth and free of residue. Surface residue was removed to obtain a carbon / carbon composite material crucible. The vapor deposition conditions were as follows: methane was used as the carbon source gas, and the methane flow rate was 10 m³ / s. 3 The deposition temperature was 1200℃, the deposition time was 200h, and the deposition pressure was 5kPa.

[0050] The carbon / carbon composite crucible was placed in a phenolic resin solution (75% solids content, xylene solvent), and vacuum impregnated for 4 hours at room temperature and a vacuum degree of -0.09 MPa, followed by pressure impregnation for 3 hours at room temperature and 2 MPa, then crosslinking and curing for 4 hours at 200°C and 3 MPa, and finally pyrolyzing and carbonizing in a carbonization furnace at 1200°C for 12 hours to obtain a product with a density of 1.8 g / cm³. 3 High-density carbon / carbon composite crucible.

[0051] The xylene solution of polynitrosilane (60 wt% solid content), the xylene solution of polycarbosilane (60 wt% solid content), and the silica sol binder (35 wt% silica content) were mixed evenly in a mass ratio of 1:1:0.05 to obtain the PIP impregnation solution.

[0052] The high-density carbon / carbon composite crucible was immersed in PIP impregnation solution three times, with each immersion lasting 8 hours. After each immersion, it was dried at 180°C. The resulting impregnated high-density carbon / carbon composite crucible was then placed in a high-temperature furnace and heat-treated at 1800°C to obtain a carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating. The thickness of the silicon-carbon-nitrogen oxygen-free coating was 100 μm, and the coating uniformly and densely covered the inner surface of the high-density carbon / carbon composite crucible.

[0053] Example 2

[0054] A carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating was prepared according to the method of Example 1, the only difference from Example 1 being that the thickness of the silicon-carbon-nitrogen oxygen-free coating was 300 μm.

[0055] In the PIP impregnation solution, the solid content of the xylene solution of polynitrosilane is 80 wt%, and the solid content of polycarbosilane is 80 wt%.

[0056] Example 3

[0057] A carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating was prepared according to the method of Example 1, the only difference from Example 1 being that the thickness of the silicon-carbon-nitrogen oxygen-free coating was 500 μm.

[0058] The solid content of the xylene solution of polynitrosilane and the solid content of the xylene solution of polycarbosilane in the PIP impregnation solution are both 99 wt%.

[0059] Comparative Example 1

[0060] The sample prepared in Example CN112374917A had a density of 2.24 g / cm³. 3 Carbon / carbon / silicon carbide composite crucible.

[0061] Test Example 1

[0062] (1) The density and open porosity results of the carbon / carbon composite crucible (denoted as C / C crucible), high-density carbon / carbon composite crucible (denoted as HC / C crucible) prepared in Example 1 and the carbon / carbon composite crucible with silicon-carbon-nitrogen oxygen-free coating (denoted as SiCN / HC / C crucible) prepared in Examples 1 to 3 are shown in Table 1:

[0063] Table 1. Density and porosity results of carbon / carbon composite crucibles, high-density carbon / carbon composite crucibles, and carbon / carbon composite crucibles with silicon-carbon-nitrogen oxygen-free coatings.

[0064] crucible <![CDATA[Density (g / cm 3 )]]> Open area ratio (%) C / C crucible 1.4 12.45 HC / C crucible 1.7 9.78 SiCN / HC / C crucible prepared in Example 1 1.78 4.32 SiCN / HC / C crucible prepared in Example 2 1.83 2.97 SiCN / HC / C crucible prepared in Example 3 1.92 0.34

[0065] As shown in Table 1, the carbon / carbon / silicon carbide composite crucible coated with a silicon-carbon-nitrogen oxygen-free coating has the characteristics of low porosity and high surface density, which can better isolate molten silicon, protect silicon material, and prevent contamination.

[0066] (2) Carbon / carbon composite crucibles with silicon-carbon-nitrogen oxygen-free coatings prepared in Examples 1-3 and uncoated quartz crucibles were used to pull single-crystal silicon under the same conditions. Among them, the Czochralski method was used to pull single-crystal silicon, and a 4-meter-long single-crystal silicon rod was stably pulled in a high temperature environment of 1420-1460℃ for 40 hours. The carbon / carbon composite crucibles with silicon-carbon-nitrogen oxygen-free coatings prepared in Examples 1-3 showed no crystal breakage during single-crystal silicon pulling, no silicon melt leakage, and no deformation. This indicates that the carbon / carbon composite crucibles with silicon-carbon-nitrogen oxygen-free coatings prepared in this invention can better support the silicon melt and reduce the risk of crystal breakage. The service life of the carbon / carbon composite crucibles with silicon-carbon-nitrogen oxygen-free coatings prepared in Examples 1-3 were 189 days, 256 days, and 341 days, respectively. The service life of the uncoated quartz crucibles was only 15-30 days. This shows that the carbon / carbon composite crucibles with silicon-carbon-nitrogen oxygen-free coatings prepared in this invention have a long service life for single-crystal silicon pulling and can meet the requirements of the core structural part of the carbon / carbon composite material crucible for single-crystal silicon Czochralski furnaces used in photovoltaic thermal fields.

[0067] (3) Corrosion resistance test: Molten pure silicon liquid was directly brought into contact with the carbon / carbon composite crucibles with silicon-carbon-nitrogen oxygen-free coatings prepared in Examples 1-3 and the carbon / carbon / silicon carbide composite crucible prepared in Comparative Example 1, respectively. The carbon / carbon / silicon carbide composite crucible prepared in Comparative Example 1 reacted with the silicon liquid to form silicon carbide, which in turn caused corrosion of the carbon-carbon crucible. However, the carbon / carbon composite crucibles with silicon-carbon-nitrogen oxygen-free coatings prepared in the examples were coated with a silicon-carbon-nitrogen coating, which could isolate the silicon liquid and prevent corrosion of the crucible.

[0068] (4) Mechanical property testing

[0069] The mechanical properties of the impregnated high-density carbon / carbon composite crucibles (before heat treatment) and the carbon / carbon composite crucibles with silicon-carbon-nitrogen oxygen-free coatings (after heat treatment) prepared in Examples 1-3 are shown in Table 2. The compressive strength and flexural strength were tested using the three-point bending method.

[0070] Table 2 Mechanical properties of the crucible before and after heat treatment

[0071]

[0072] As shown in Table 2, the preparation method provided by this invention can effectively improve the compressive and flexural strength of the carbon-carbon crucible, thereby enhancing its ability to withstand molten silicon. Furthermore, the density of the carbon-carbon crucible is increased by 25-35%, reflecting a decrease in porosity, effective pore sealing by the coating, and improved resistance to silicon melt corrosion. This indicates that the carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating prepared by this invention exhibits excellent resistance to silicon melt corrosion, thus significantly extending the crucible's service life.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating, comprising the following steps: A carbon / carbon composite crucible is mixed with phenolic resin and subjected to a first impregnation, cross-linking curing, and pyrolysis carbonization process to obtain a high-density carbon / carbon composite crucible; the density of the high-density carbon / carbon composite crucible is 1.65~1.85 g / cm³. 3 ; The high-density carbon / carbon composite crucible is mixed with PIP impregnation liquid and subjected to a second impregnation followed by heat treatment to obtain a carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating. The PIP impregnation solution comprises a polycarbosilane solution, a polynitrosilane solution, and a binder; the solid content of the polycarbosilane solution and the polynitrosilane solution is independently 60-100%; the binder is silica sol, and the silica content in the silica sol is 20-45 wt%; the mass ratio of the polycarbosilane solution to the polynitrosilane solution is 1-1.5:1; the mass ratio of the total mass of the polycarbosilane solution and the polynitrosilane solution to the mass of the binder is 1:0.005-0.05; the second impregnation temperature is 25-40℃, the single impregnation time is 6-12 h, and the pressure is 0-1 kPa; the number of second impregnations is ≥2.

2. The preparation method according to claim 1, characterized in that, The first impregnation includes sequential vacuum impregnation and pressure impregnation; the vacuum degree of the vacuum impregnation is -0.1~0MPa, and the time is 1~6h; the pressure of the pressure impregnation is 1~2MPa, and the time is 1~3h.

3. The preparation method according to claim 1, characterized in that, The cross-linking curing temperature is 100~200℃, the pressure is 1~3MPa, and the time is 2~4h.

4. The preparation method according to claim 1, characterized in that, The pyrolysis and carbonization temperature is 600~1200℃, and the time is 10~36h.

5. The preparation method according to claim 1, characterized in that, The heat treatment is performed at a temperature of 1400~1800℃ for 8~12 hours.

6. The preparation method according to claim 1, characterized in that, The preparation method of the carbon / carbon composite material crucible includes the following steps: Carbon fibers are woven into a shape to obtain a carbon fiber crucible preform; The carbon fiber crucible preform is subjected to a first high-temperature heat treatment, vapor deposition densification, a second high-temperature heat treatment, and machining in sequence to obtain a carbon / carbon composite material crucible.

7. The preparation method according to claim 6, characterized in that, The temperature of the first high-temperature heat treatment and the second high-temperature heat treatment are independently 1800~2300℃, and the time is independently 1~4h; The vapor deposition densification is chemical vapor deposition densification, and the conditions for vapor deposition densification include: deposition temperature of 1000~1200℃, deposition time of 100~300h, deposition pressure of 2~10kPa, temperature rise rate from room temperature to the deposition temperature of 40~80℃ / h, and carbon source gas flow rate of 2~20m³ / h. 3 / h.

8. The preparation method according to claim 6, characterized in that, The density of the carbon fiber crucible preform is 1.3~1.5 g / cm³. 3 .

9. A carbon / carbon composite crucible with a silicon-carbon-nitrogen oxygen-free coating prepared by the preparation method according to any one of claims 1 to 8, comprising a high-density carbon / carbon composite crucible and a silicon-carbon-nitrogen oxygen-free coating loaded on the inner surface of the high-density carbon / carbon composite crucible.

Images