A method for manufacturing a silicon carbide boat

Abstract

The present application relates to the technical field of silicon carbide as base material crystal boat preparation, disclose a kind of preparation method of silicon carbide crystal boat, including sequentially following steps: preparation silicon carbide granulation powder, powder raw material uses multiple particle size section silicon carbide powder mixing, adjuvant includes polyethylene glycol, polyvinyl alcohol, carbon black and graphite;Silicon carbide granulation powder die forming green body unit;Green body unit drying forms blank body unit;Blank body unit isostatic pressing treatment;Each blank body unit is processed according to assembly design requirement;Blank body unit is reacted and sintered, uses ladder heating;Blank body unit after reaction sintering is polished and sand blasted and is bonded;After the crystal boat combination of bonding assembly is sintered second time, uses ladder heating, obtains silicon carbide crystal boat.Adopting twice sintering, greatly improve the performance of the prepared crystal boat, to solve the technical problems, such as insufficient structural strength and complex process of existing silicon carbide crystal boat preparation method.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide-based crystal boat preparation technology, and in particular, to a method for preparing a silicon carbide crystal boat. Background Technology

[0002] Reaction sintering has become an important process for preparing ceramic composite materials due to its advantages such as low sintering temperature, simple process, and low manufacturing cost. Reaction-sintered silicon carbide ceramic materials have excellent properties such as low density, high temperature resistance, impact resistance, high strength, corrosion resistance, strong oxidation resistance, and good thermal shock resistance, and are widely used in fields such as safety protection, chemical industry, aerospace, machinery, metallurgy, and electronics.

[0003] The traditional process for preparing reactive sintered silicon carbide ceramics is as follows: fine-particle SiC and additives are pressed, extruded or slurry-cast to form a green body, which is then brought into contact with liquid silicon at high temperature. The plasticizer is pyrolyzed to form a porous carbon skeleton. The carbon in the green body reacts with the infiltrated liquid / gas silicon to generate SiC. The SiC generated by the reaction combines with the original SiC particles, and excess silicon fills the pores, ultimately obtaining a dense, non-porous ceramic material.

[0004] Currently, for silicon carbide boats with complex structures, a common manufacturing process involves disassembling the components and then assembling them. However, this method has significant drawbacks: the bonding strength at the assembled parts is only about 30% of the strength of the component body, becoming a weak point in the overall structure and limiting the application of the boat in high-stress or harsh environments.

[0005] Therefore, there is an urgent need to develop a new method that can achieve integral molding of silicon carbide crystal boats and take into account both high strength and high efficiency in preparation, so as to solve the problems of insufficient strength of the assembled structure and complex process in the existing technology. Summary of the Invention

[0006] This invention provides a method for preparing a silicon carbide crystal boat, which employs a two-stage sintering process. The first sintering process prepares reaction-sintered products of pillars, top plates, bottom plates, and side wings. The second sintering process effectively bonds the components into a whole using an adhesive slurry. Simultaneously, the top and bottom plates are subjected to a second reaction sintering, which greatly improves the performance of the prepared crystal boat and solves the technical problems of insufficient structural strength and complex processes in existing silicon carbide crystal boat preparation methods.

[0007] This invention provides a method for preparing a silicon carbide boat, comprising the following steps in sequence:

[0008] S100. Prepare silicon carbide granulated powder. The powder raw material is a mixture of silicon carbide powder with multiple particle size ranges. The auxiliary materials include polyethylene glycol, polyvinyl alcohol, carbon black and graphite. After mixing the powder raw material and auxiliary materials, the mixture is ball-milled and then spray-granulated to obtain silicon carbide granulated powder. The moisture content of the silicon carbide granulated powder is 1%-2%.

[0009] S200 silicon carbide granulated powder molding green body unit: Column molding pressure 60-65 tons, holding pressure 10-15s; Top plate, bottom plate, and side wings molding pressure 80-85 tons, holding pressure time 15-20s; Green body density ≥1.91g / cm³. 3 ;

[0010] S300, the green body unit is dried to form a green body unit, dried at 40℃ for 3 hours, and dried at 70-80℃ for 2-3 hours, with a green body moisture content ≤0.1%;

[0011] S400, isostatic pressing of the billet unit, isostatic pressing pressure 150-160MPa, holding pressure 15-20s, the density of the treated billet ≥2.05g / cm³ 3 ;

[0012] S500, each blank unit is processed according to the assembly design requirements;

[0013] S600: The green body units are subjected to reaction sintering using a stepped heating method. The density of the green body units after sintering is ≥3.03 g / cm³. 3 Straightness ≤ 0.25;

[0014] S700: Grinding, sandblasting and bonding of the reaction-sintered green body units.

[0015] S800, the bonded and assembled crystal boat assembly is sintered a second time using a stepped heating method to obtain a silicon carbide crystal boat.

[0016] Furthermore, the powder raw materials in step S100 are high-purity silicon carbide with four particle size ranges: 1-3μm, 5-8μm, 10-15μm, and 20-25μm. The purity of the high-purity silicon carbide is ≥98%, and they are mixed in a mass ratio of (1-3μm):(5-8μm):(10-15μm):(20-25μm)=2:3:2:3.

[0017] By mixing silicon carbide powders of different particle sizes, the bulk density of the powder is optimized, reducing sintering shrinkage stress. After the silicon carbide granulated powder is prepared, compression molding is used to ensure the initial shape stability of the green body, reduce subsequent processing, improve dimensional accuracy, and reduce process costs. After compression molding, drying is performed to remove moisture and volatile organic compounds from the green body, avoiding cracking or porosity defects caused by gas escape during sintering. After drying, isostatic pressing is applied to increase the density of the green body through uniform pressure, reduce internal porosity, enhance the mechanical strength of the green body, and provide a more uniform microstructure foundation for subsequent sintering. After isostatic pressing, green body unit processing is performed, and the green body units are precisely processed before sintering. The process ensures precise assembly and reduces gaps at subsequent bonding surfaces, improving the stability of the assembled structure. After processing, the preform units undergo reaction sintering. Staged temperature control prevents localized overheating or thermal stress concentration caused by exothermic reactions, promoting uniform silicon penetration and reaction, and improving the density and mechanical properties of the sintered body. Following reaction sintering, the sintered preform units are surface-treated with grinding and sandblasting to enhance the roughness and bonding force of the bonding surfaces, improving the mechanical strength of the assembled parts. A second sintering process is performed after bonding, using stepped heating to further react the adhesive with the preform units, strengthening the bonding strength at the assembly interface, ultimately resulting in a silicon carbide boat with overall performance approaching that of a single sintered body. This method, by optimizing powder composition, adhesive slurry composition, preform forming, and sintering processes, combined with staged processing and secondary sintering, effectively solves the problem of low bonding strength in traditional assembled boats, achieving efficient preparation of high-strength silicon carbide boats.

[0018] Further, in step S100, the auxiliary materials—carbon black with an average particle size of 0.01–1 μm—contain polyethylene glycol at 3 wt%–5 wt% of the powder raw material weight, polyvinyl alcohol at 1 wt%–3 wt% of the powder raw material weight, carbon black at 15 wt%–20 wt% of the powder raw material weight, and graphite at 5 wt%–10 wt% of the powder raw material weight. Polyethylene glycol and polyvinyl alcohol act as organic binders (forming agents), jointly improving the plasticity of the powder, enhancing the molding strength of the green body, and preventing demolding cracking. Polyethylene glycol decomposes and volatilizes at low temperatures, forming porous channels that promote subsequent liquid silicon infiltration. Polyvinyl alcohol carbonizes at high temperatures, providing some carbon source to participate in the reaction and sintering. Carbon black has a high specific surface area and, as the main carbon source, reacts with silicon infiltration to generate SiC. Its nanoscale particle size can significantly improve the reaction activity and promote the rapid formation of SiC network structures at low temperatures. The layered structure of graphite is partially retained during sintering, giving the material certain self-lubricating and thermal shock resistance; its carbon source characteristics replenish the reaction consumption of carbon black, ensuring that the silanization reaction proceeds fully and avoiding excessive residue of free silicon.

[0019] Furthermore, before the reaction sintering of the blank unit in step S600, the following steps are also included: spraying boron nitride coating onto the graphite boat and drying it; placing the column blank unit, top plate blank unit, bottom plate blank unit and side wing blank unit onto the graphite boat; and covering the upper and lower surfaces of each blank unit with silicon particles, the weight of which is 78-82% of the total weight of all blank units, and the particle size of the silicon particles is (0.5-1mm):(3-5mm)=1:2.

[0020] Further, in step S600, under a vacuum environment with a vacuum degree ≤65MPa, the green body unit is subjected to reaction sintering using a stepped heating method, specifically: room temperature - 200℃, 50min-60min; 200℃-400℃, 80min-90min; 400℃-800℃, 110min-120min; 800℃-1000℃, 110min-120min; 1000℃-1250℃, 80min-90min; 1250℃-1650℃, 190min-200min; and holding at 1650℃ for 110min-120min. A vacuum environment is used to eliminate oxygen and prevent high-temperature oxidation of the carbon source (carbon black, graphite) and SiC powder. The stepped temperature design slowly removes residual moisture and organic binders (polyvinyl alcohol) from room temperature to 200℃, preventing rapid escape of volatile components that could cause cracking of the green body. From 200℃ to 500℃, the organic matter (polyethylene glycol) is further decomposed and carbonized, forming a porous carbon skeleton that provides channels for subsequent silicon infiltration. From 1000℃ to 1250℃, silicon particles begin to melt and infiltrate into the carbon skeleton, initiating a localized SiC reaction. From 1250℃ to 1650℃, highly active carbon sources such as carbon black react fully with silicon to generate nano-SiC, filling the pores and achieving overall densification. Holding at 1650℃ ensures complete reaction, uniform distribution of residual silicon, and the formation of a dense structure, improving the material's high-temperature stability. By controlling the temperature in stages to match the removal of volatile components, silicon melting and infiltration, SiC formation, and densification processes, thermal stress concentration or reaction runaway is avoided, ensuring the efficiency and uniformity of the silicon-carbon reaction. Ultimately, low-porosity, highly dense silicon carbide ceramic components with consistent mechanical properties are obtained.

[0021] Furthermore, before the reaction sintering of the blank unit in step S800, the following steps are also included: spraying boron nitride coating onto the graphite boat and drying it; placing the bonded crystal boat horizontally on the graphite boat; supporting the side wings of the crystal boat assembly with graphite pillars to prevent deformation during sintering; and placing two portions of silicon grains weighing 250-270g on the upper surface of the top and bottom plates of each crystal boat, with a particle size of 0.1-0.4mm. Spraying boron nitride (BN) as a high-temperature inert coating can effectively prevent the graphite boat from reacting with the preform unit or molten silicon at high temperatures, avoiding carbon contamination or adhesion, and ensuring the purity of the surface composition of the crystal boat after sintering. The lubricity of the BN coating helps the preform unit to be demolded smoothly after sintering, reducing the risk of mechanical damage. Silicon particles are evenly laid on the upper and lower surfaces of the preform unit, allowing liquid silicon to penetrate simultaneously from multiple directions, improving the uniformity of the reaction and reducing density gradients or deformation caused by unidirectional silicon penetration. After the silicon particles melt, they penetrate into the pores of the preform through capillary action, reacting with carbon sources such as carbon black and graphite to generate SiC, filling the pores and connecting the initially added SiC particles, thus achieving overall structural densification.

[0022] Further, step S800 involves a secondary sintering of the bonded and assembled crystal boat assembly. Specifically, this is performed in an argon or vacuum environment using a stepped heating sintering process, followed by cooling at a rate of ≤10℃ / min to reduce thermal stress cracking. The stepped heating sintering process is as follows: heating at 50℃ / h to 200℃ for pre-curing for 1 hour, heating to 800℃ and holding for 1 hour, then heating at 100℃ / h to 1450℃-1550℃ and holding for 2 hours, and finally holding at 1650℃ for 2 hours. Secondary sintering in an argon / vacuum environment suppresses the oxidation reactions of silicon carbide, free silicon, and the binder at high temperatures, preventing material performance degradation; it also reduces gas thermal convection interference, ensures temperature field uniformity, and prevents localized overheating that could lead to deformation or cracking. The stepped heating design involves a 50℃ / h heating rate to 200℃ for 1 hour of pre-curing, where the phenolic resin cures and connects the various units of the crystal boat into a unified structure. A 1-hour holding at 800℃ is the debonding stage, during which the phenolic resin carbonizes. A 2-hour holding at 1450℃-1550℃ allows the molten silicon to fully penetrate the bonding interface, reacting with the carbon source to generate SiC, repairing assembly gaps and enhancing interfacial bonding strength. A 2-hour holding at 1650℃ is the high-temperature densification stage, where the newly generated silicon carbide bridges with the silicon carbide in the raw materials. After sintering, cooling is performed at a rate of ≤10℃ / min to reduce the thermal shrinkage differences between the components of the crystal boat (substrate and bonding layer), minimizing the risk of thermal stress concentration and preventing cooling cracks. Through inert atmosphere protection, staged temperature control, and the synergistic effect of slow cooling, high-strength bonding at the bonding interface is achieved, while ensuring the dimensional stability and thermal shock resistance of the overall crystal boat structure, ultimately resulting in a defect-free, highly reliable monolithic silicon carbide crystal boat.

[0023] Further, in step S700, the green body units after reaction sintering are bonded together using an adhesive slurry. The adhesive slurry comprises, by mass percentage: 55%-60% high-purity silicon carbide, 8%-12% phenolic resin, 15%-20% high-purity silicon powder, 3%-5% polycarbosilane, 3%-5% sodium silicate, 1%-2% silicon carbide whiskers, 0.5%-1.5% boron nitride, and 0.5%-1.5% Y2O3-Al2O3, with the ratio of boron nitride to Y2O3-Al2O3 being 1:1. The high-purity silicon carbide has a purity ≥98% and is mixed in a mass ratio of (1-3μm):(5-8μm) = 1:1. The high-purity silicon powder has a particle size of 0.5-5μm.

[0024] Further, the preparation method of the adhesive slurry is as follows: S701, pre-dispersion: silicon carbide, silicon powder, silicon carbide whiskers, boron nitride and Y2O3-Al2O3 are mixed and first ball-milled with 0.5%-1% polyvinylpyrrolidone solution for 4h-6h at 300rpm to break up agglomerates and obtain a powder mixture; S702, phenolic resin is diluted with 70% ethanol to a solid content of 30%; S703, the materials prepared in steps S701 and S702 are mixed, and polycarbosilane and sodium silicate are added in sequence to adjust the pH value of the slurry to 9-10 to form an alkaline environment of sodium silicate and enhance dispersion stability; the mixture is stirred and dried simultaneously to promote the viscosity of the slurry, and carboxymethyl cellulose is added as a thickener to control the viscosity at 500-800mPa·s to obtain the adhesive slurry.

[0025] The present invention has the following beneficial effects:

[0026] 1. By mixing silicon carbide powders of different particle sizes, the bulk density of the powder is optimized, and sintering shrinkage stress is reduced. By using silicon particles of different sizes, coarse silicon particles are used to fill large pores, while fine silicon particles are used to improve reaction uniformity. The combination of coarse and fine silicon particles can increase the bulk density of the green body, so that the relative density of the final sintered body reaches 90-95%. Stepped temperature sintering is adopted. By controlling the temperature in stages, local overheating or thermal stress concentration caused by exothermic reaction is avoided, promoting uniform silicon penetration and reaction, and improving the density and mechanical properties of the sintered body.

[0027] 2. By designing an adhesive slurry different from existing technologies, the strength of the bond is improved. High-purity silicon carbide in the slurry acts as a basic framework, connecting with silicon carbide in the preform unit to ensure a matching coefficient of thermal expansion and reduce interfacial stress at high temperatures. Phenolic resin acts as an adhesive and decomposes at high temperatures to form a porous carbon framework, providing channels for subsequent silicon melt penetration (containing approximately 80-85% carbon) and providing a carbon source for SiC synthesis. The porous structure promotes silicon melt penetration. High-purity silicon powder reacts with carbon to generate silicon carbide, which connects with the silicon carbide framework to further enhance the bond strength. Polycarbosilane decomposes at high temperatures to generate silicon carbide and a small amount of free silicon. The free silicon reacts with the carbon from the decomposition of phenolic resin to generate carbon. Silicon carbide; sodium silicate acts as an inorganic binder at low temperatures, providing initial bond strength through hydrolysis and gelation. After complete melting, it acts as a flux, reacting with other oxides (Al2O3) in the system to form a eutectic liquid phase. This process promotes sintering densification and reduces material porosity. Silicon carbide whiskers inhibit crack propagation through a fiber toughening mechanism, improving the fracture toughness of the adhesive layer. As a reinforcing phase, they enhance the strength of the bond and improve material toughness through bridging, strengthening interfacial bonding. Boron nitride inhibits oxidation reactions, preventing silicon powder from oxidizing to SiO2, while reducing sintering shrinkage stress and preventing interfacial delamination. Y2O3-Al2O3 forms YAG (Y3Al5O3) above 1700℃. 12 The liquid phase lowers the sintering densification temperature, inhibits abnormal growth of silicon carbide grains, and promotes bridging and densification of silicon carbide grains.

[0028] The various components of the adhesive slurry work synergistically to achieve a gradient strengthening of the adhesive layer through "low-temperature bonding - medium-temperature carbonization - high-temperature reaction densification". In the low-temperature stage, sodium silicate and phenolic resin provide adhesive strength. In the medium-temperature stage, the carbonization of phenolic resin forms a porous carbon network, which provides pre-lay channels for silicon penetration. In the high-temperature stage, the reaction generates a dense SiC phase that connects with the green body unit to form a whole. During the secondary sintering, high-density silicon carbide is generated. The silicon carbide in the green body unit and the silicon carbide skeleton / newly generated silicon carbide in the adhesive slurry are bridged to further improve the strength of the bond. The silicon carbide whiskers and Y2O3-Al2O3 optimize the microstructure, ultimately making the strength of the adhesive layer greater than 70% of the strength of the matrix, which is significantly better than the existing technology.

[0029] 3. After bonding, secondary sintering is carried out. On the one hand, high-strength silicon carbide is generated at the bonding point and the adjacent blank unit, so that each unit forms a whole. On the other hand, each crystal boat is equipped with silicon grains and placed on the upper surface of the top and bottom plates. Secondary reaction silicon infiltration is achieved through secondary sintering by step heating, which minimizes the carbon residue of the crystal boat and further improves the overall strength of the crystal boat.

[0030] 4. This method effectively solves the problem of low bonding strength in traditional assembled silicon carbide crystal boats by optimizing the composition of raw material powders, the composition of the bonding slurry, and the green body forming and sintering processes, combined with staged processing and secondary sintering. This achieves efficient preparation of high-strength silicon carbide crystal boats. The silicon carbide crystal boat prepared by this invention has a density of 3.05 g / cm³. 3 -3.15g / cm 3 With a porosity of less than 1%, the room temperature bending strength is 310MPa-360MPa, and the room temperature bending strength of the joint is increased to 215Pa-260MPa. The room temperature bending strength of the joint is about 70%-75% of that of other parts, which is more than 30% higher than the strength of the adhesive joint in the prior art.

[0031] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0032] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0033] Figure 1 This is a schematic diagram of the main structure of a silicon carbide boat according to a preferred embodiment of the present invention;

[0034] Figure 2 This is a top view of a silicon carbide crystal boat according to a preferred embodiment of the present invention;

[0035] Figure 3 This is a side view of a silicon carbide boat according to a preferred embodiment of the present invention;

[0036] Figure 4 This is a cross-sectional view of a silicon carbide boat after being cut in the middle according to a preferred embodiment of the present invention.

[0037] Legend:

[0038] 1. Top plate; 2. Side wings; 3. Columns; 4. Base plate. Detailed Implementation

[0039] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available or can be prepared by known methods.

[0040] Example 1:

[0041] The preparation method in this embodiment is as shown in the attached figure. Figure 1 - Appendix Figure 4The silicon carbide boat shown specifically includes the following steps:

[0042] S100, Granulation Powder Preparation:

[0043] 10 kg of 98% pure silicon carbide powder is mixed according to particle size as follows: (1μm-3μm): (5μm-8μm): (10μm-15μm): (20μm-25μm) = 2:3:2:3;

[0044] Polyethylene glycol accounts for 3% of the weight of silicon carbide powder, polyvinyl alcohol accounts for 1% of the weight of silicon carbide powder, carbon black accounts for 15% of the weight of silicon carbide powder, and graphite accounts for 5% of the weight of silicon carbide powder.

[0045] The prepared powder raw materials and other auxiliary materials are mixed together and then ball-milled, followed by spray granulation to obtain granulated powder with a moisture content of 1.5%.

[0046] S200, Compression Molding:

[0047] The density of the pressed green body is 1.92 g / cm³. 3 ;

[0048] The molding pressure of the columns is 60 tons, and the pressure holding time is 15 seconds; the molding pressure of the top plate, bottom plate and side wings is 80 tons, and the pressure holding time is 20 seconds.

[0049] S300, Drying: Dry at 40℃ for 3 hours, then at 70℃ for 3 hours, with a green body moisture content ≤0.1%.

[0050] S400, isostatic pressing treatment: isostatic pressing pressure 150MPa, holding pressure 20s, the density of the treated green body is 2.06g / cm³. 3 .

[0051] S500, Machining: Make connection holes on the top and bottom plates at the locations where they connect to the columns;

[0052] S600, Reaction Sintering: Boron nitride coating is sprayed onto a graphite boat and dried. The billet with columns, top plate, bottom plate and side wings is placed on the graphite boat. The upper and lower surfaces of the billet are covered with silicon particles. The weight of silicon particles is 79% of the total weight of the billet. The particle size of silicon particles is (0.5-1mm):(3-5mm)=1:2.

[0053] The sintering process is as follows: heating time from room temperature to 200℃ for 60 minutes, heating time from 200℃ to 500℃ for 90 minutes, heating time from 500℃ to 800℃ for 120 minutes, heating time from 800℃ to 1000℃ for 120 minutes, heating time from 1000℃ to 1250℃ for 90 minutes, heating time from 1250℃ to 1650℃ for 180 minutes, holding at 1650℃ for 120 minutes, and vacuum degree ≤65MPa.

[0054] The density of the green body unit after one sintering is 3.03 g / cm³. 3 Straightness ≤ 0.25.

[0055] S700, Grinding, Sandblasting and Bonding: The sintered blank units are sandblasted and ground, adhesive slurry is applied to the joints, the blank units are bonded together and pressure of 0.5MPa is applied for curing and maintained for 25 minutes.

[0056] Preparation method of adhesive slurry: 60% of the slurry is silicon carbide micro powder with a purity of 98%, wherein the mass ratio of silicon carbide with different particle sizes (1-3μm):(5-8μm) is 1:1, 18% is high-purity silicon powder (particle size of 0.5-5μm), 5% is polycarbosilane, 3% is sodium silicate, 12% is phenolic resin, 1% is silicon carbide whiskers, 0.5% is boron nitride (BN), and 0.5% is Y2O3-Al2O3.

[0057] S701, Pre-dispersion: Silicon carbide, silicon powder, silicon carbide whiskers, boron nitride and Y2O3-Al2O3 are mixed and first ball-milled with 0.5% polyvinylpyrrolidone (PVP) solution for 4 hours at 300 rpm to break up agglomerates and obtain a powder mixture.

[0058] S702, phenolic resin is diluted with 70% ethanol to a solid content of 30%;

[0059] S703. Mix the materials prepared in steps S701 and S702, add polycarbosilane and sodium silicate in sequence, adjust the pH of the slurry to 9-10 to form an alkaline environment of sodium silicate and enhance dispersion stability; stir the mixture and dry it at the same time to promote the viscosity of the slurry, add carboxymethyl cellulose as a thickener, control the viscosity at 500-550 mmPa·s, and obtain the adhesive slurry.

[0060] S800, Secondary Sintering: The bonded crystal boat is placed on a graphite boat (pre-sprayed with boron nitride). Each crystal boat is equipped with 250g of silicon particles, divided into two portions and laid flat on the upper surface of the top and bottom plates. The particle size of the silicon particles is 0.1-0.4mm. The side wings are supported by graphite pillars to prevent deformation during sintering.

[0061] The stepped temperature sintering process is as follows: heat up to 200℃ at 50℃ / h for 1 hour of pre-curing, heat up to 800℃ and hold for 1 hour, then heat up to 1450℃-1550℃ at 100℃ / h and hold for 2 hours, then heat up to 1650℃ and hold for 2 hours, and sinter in an argon or vacuum environment to suppress oxidation reaction and accelerate silicon melt penetration. After sintering, cool at a rate of ≤10℃ / min to reduce thermal stress cracks.

[0062] S900, grinding, sandblasting, cleaning and inspection, all bonding joints are ground smooth, product surface is flat, straightness ≤0.1.

[0063] The prepared silicon carbide boat has a density of 3.11 g / cm³. 3 The porosity is 0.90%, the bending strength at room temperature is 325 MPa, the bending strength at room temperature at the joint is 236 MPa, and the bending strength at room temperature at the joint is about 72% of that of other parts.

[0064] Example 2

[0065] The preparation of the silicon carbide boat in this embodiment specifically includes the following steps:

[0066] S100, Granulation Powder Preparation:

[0067] 10 kg of high-purity (≥98%) silicon carbide powder, with particle size distribution (1μm-3μm): (5μm-8μm): (10μm-15μm): (20μm-25μm) = 2:3:2:3;

[0068] Polyethylene glycol accounts for 5% of the weight of silicon carbide powder, polyvinyl alcohol accounts for 3% of the weight of silicon carbide powder, carbon black accounts for 20% of the weight of silicon carbide powder, and graphite accounts for 10% of the weight of silicon carbide powder.

[0069] The prepared powder raw materials and other auxiliary materials are mixed together and then ball-milled, followed by spray granulation to obtain granulated powder with a moisture content of 2%.

[0070] S200, Compression Molding:

[0071] The molding pressure of the uprights is 65 tons, with a holding time of 10 seconds; the molding pressure of the top plate, bottom plate, and side wings is 85 tons, with a holding time of 15 seconds, resulting in a green compact density of 1.93 g / cm³. 3 ;

[0072] S300, Drying: Dry at 40℃ for 3 hours, then at 80℃ for 2 hours, with a green body moisture content ≤0.1%.

[0073] S400, isostatic pressing: isostatic pressing pressure 160MPa, holding pressure 15s, the density of the treated green body is 2.06g / cm³. 3 .

[0074] S500, Machining: Make connection holes on the top and bottom plates at the locations where they connect to the columns;

[0075] S600, Reaction Sintering: Boron nitride coating is sprayed onto a graphite boat and dried. The billet with columns, top plate, bottom plate and side wings is placed on the graphite boat. The upper and lower surfaces of the billet are covered with silicon particles. The weight of silicon particles is 82% of the total weight of the billet. The particle size of silicon particles is (0.5-1mm):(3-5mm)=1:2.

[0076] The sintering process is as follows: heating time from room temperature to 200℃ for 60 minutes, heating time from 200℃ to 500℃ for 90 minutes, heating time from 500℃ to 800℃ for 120 minutes, heating time from 800℃ to 1000℃ for 120 minutes, heating time from 1000℃ to 1250℃ for 90 minutes, heating time from 1250℃ to 1650℃ for 180 minutes, holding at 1650℃ for 120 minutes, and vacuum degree ≤65MPa.

[0077] The density of the green body unit after one sintering is 3.04 g / cm³. 3 Straightness ≤ 0.25.

[0078] S700, Grinding, Sandblasting and Bonding: Sandblast and grind the sintered blank units, apply bonding slurry to the joints, bond the blank units together and apply 0.5MPa pressure to cure for 25 minutes.

[0079] Preparation method of adhesive slurry: 58% high-purity (≥98%) silicon carbide micro powder, wherein the mass ratio of silicon carbide with different particle sizes (1-3μm):(5-8μm) = 1:1, 18% high-purity silicon powder (particle size of 0.5-5μm), 5% polycarbosilane, 5% sodium silicate, 10% phenolic resin, 2% silicon carbide whiskers, 1% boron nitride (BN), and 1% Y2O3-Al2O3.

[0080] S701, Pre-dispersion: Silicon carbide micro powder and silicon carbide whiskers: Silicon carbide, silicon powder, silicon carbide whiskers, boron nitride and Y2O3-Al2O3 are mixed and first ball-milled with 0.5% polyvinylpyrrolidone (PVP) solution for 4 hours at 300 rpm to break up agglomerates and obtain a powder mixture.

[0081] S702, phenolic resin is diluted with 70% ethanol to a solid content of 30%;

[0082] S703. Mix the materials prepared in steps S701 and S702, add polycarbosilane and sodium silicate in sequence, adjust the pH of the slurry to 9-10 to form an alkaline environment of sodium silicate and enhance dispersion stability; stir the mixture and dry it at the same time to promote the viscosity of the slurry, add carboxymethyl cellulose as a thickener, control the viscosity at 600-650 mmPa·s, and obtain the adhesive slurry.

[0083] S800, Secondary Sintering: The bonded crystal boats are placed on graphite boats (pre-sprayed with boron nitride). Each crystal boat is equipped with two portions of silicon particles weighing 260g, which are laid flat on the upper surface of the top and bottom plates. The particle size of the silicon particles is 0.1-0.4mm. The side wings are supported by graphite pillars to prevent deformation during sintering. Stepped temperature rise sintering process: The temperature is raised to 200℃ at 50℃ / h for pre-curing for 1h, raised to 800℃ and held for 1h, then raised to 1450℃-1550℃ at 100℃ / h and held for 2h, and then held at 1650℃ for 2h. Sintering is carried out in an argon or vacuum environment to suppress oxidation reaction and accelerate silicon melt penetration. After sintering, the temperature is cooled at a rate of ≤10℃ / min to reduce thermal stress cracks.

[0084] S900, grinding, sandblasting, cleaning and inspection, all bonding joints are ground smooth, product surface is flat, straightness ≤0.1.

[0085] The prepared silicon carbide boat has a density of 3.12 g / cm³. 3 The porosity is 0.89%, the bending strength at room temperature is 342 MPa, the bending strength at room temperature at the joint is 248 MPa, and the bending strength at room temperature at the joint is about 73% of that of other parts.

[0086] Comparative Example 1

[0087] Compared with Example 1, the following differences exist:

[0088] The adhesive slurry used in S700 is different. Specifically, it consists of 15% phenolic resin, 3% sodium carboxymethyl cellulose, 5% graphite, 10% carbon black, and 62% silicon carbide powder of different particle sizes. The mixture is stirred for 24 hours after being mixed with water. The purity of the silicon carbide is 98%. The mixture is prepared according to the mass ratio of (1-3μm):(5-8μm):(10-15μm):(20-25μm)=2:3:2:3.

[0089] Test results: The density of the prepared silicon carbide boat is 3.05 g / cm³. 3 The bending strength at room temperature is 314 MPa, and the bending strength at the joint at room temperature is 116 MPa. The bending strength at the joint at room temperature is about 37% of that of other parts.

[0090] Comparative Example 2

[0091] Compared with Example 1, the following differences exist:

[0092] The adhesive slurry used in S700 does not contain boron nitride or silicon carbide whiskers. The ratio of each raw material in the adhesive slurry is as follows: 61.5% of the raw material is silicon carbide micro powder with a purity of 98% and (1-3μm):(5-8μm) = 1:1. The remaining raw materials are the same as in Example 1.

[0093] Test results: The density of the prepared silicon carbide boat is 3.07 g / cm³. 3 The bending strength at room temperature is 319 MPa, and the bending strength at the joint at room temperature is 192 MPa. The bending strength at the joint at room temperature is about 60% of that of other parts.

[0094] Comparative Example 3

[0095] Compared with Example 1, the following differences exist:

[0096] The adhesive slurry used in step S700 does not contain sodium silicate or polycarbosilane. The raw materials include: 68% pure silicon carbide micro powder with a particle size of (1-3μm):(5-8μm) = 1:1 by mass, and the remaining raw materials are the same as in Example 1.

[0097] Test results: The density of the prepared silicon carbide crystal boat is 3.06 g / cm³. 3 The bending strength at room temperature is 321 MPa, and the bending strength at the joint at room temperature is 212 MPa. The bending strength at the joint at room temperature is about 66% of that of other parts.

[0098] Comparative Example 4

[0099] Compared with Example 1, the following differences exist:

[0100] In step S800, during the second sintering, no silicon particles are added to the upper surfaces of the top and bottom plates of the crystal boat; otherwise, it is the same as in Example 1.

[0101] Test results: The density of the prepared silicon carbide crystal boat is 3.02 g / cm³. 3 The bending strength at room temperature is 302 MPa, and the bending strength at the joint at room temperature is 215 MPa. The bending strength at the joint at room temperature is about 71% of that of other parts.

[0102] Comparative Example 5

[0103] Compared with Example 1, the following differences exist:

[0104] The silicon carbide used in steps S100 and S700 is non-graded, and the silicon particles used in step S600 are non-graded. The silicon carbide particle size is 1-3μm, and the silicon particle size is 3-5mm. The proportions of other raw materials and processes are the same as in Example 1.

[0105] Test results: The density of the prepared silicon carbide crystal boat is 2.98 g / cm³. 3 The bending strength at room temperature is 293 MPa, and the bending strength at the joint at room temperature is 191 MPa. The bending strength at the joint at room temperature is about 65% of that of other parts.

[0106] Comparing the data from Example 1 and Comparative Examples 1-5, it can be seen that...

[0107] 1. In Comparative Example 1, a common formula in the prior art was used to prepare the bonding slurry: silicon carbide powder, resin, graphite and carbon black. The bending strength of the joint at room temperature was about 37% of that of other parts. This shows that compared with the slurry in Comparative Example 1, the bonding slurry in Example 1 of the present invention increased the strength of the joint from 27% to 72%, which significantly improved the strength of the bonding joint of the crystal boat.

[0108] 2. The adhesive slurry in Comparative Example 2 did not contain boron nitride and silicon carbide whiskers. The overall density and strength of the prepared crystal boat were not significantly different from those in Example 1. However, the bending strength of the joint at room temperature in Comparative Example 2 was about 60% of that of other parts. The strength of the joint in Example 1 was more than 10% higher than that in Comparative Example 2. This indicates that the addition of boron nitride and silicon carbide whiskers to the adhesive slurry in Example 1 can significantly improve the strength of the joint.

[0109] 3. In Comparative Example 3, no sodium silicate and polycarbosilane were added to the adhesive slurry. The overall density and strength of the prepared crystal boat were not significantly different from those in Example 1. However, the bending strength of the joint at room temperature in Comparative Example 3 was about 66% of that of other parts, which was lower than the joint strength in Example 1. This indicates that adding sodium silicate and polycarbosilane to the adhesive slurry helps to improve the strength.

[0110] 4. In Comparative Example 4, no silicon particles were added to the upper surfaces of the top and bottom plates of the crystal boat during the second sintering in step S800. The room temperature bending strength of the silicon carbide crystal boat prepared by this example was significantly lower than that of Example 1. This indicates that adding silicon particles during the second sintering in step S800 helps to improve the overall bending strength of the crystal boat.

[0111] 5. In Comparative Example 5, the silicon carbide used in steps S100 and S700 is ungraded, and the silicon particles used in step S600 are ungraded. The density and strength of the prepared crystal boat are significantly lower than those in Example 1. This indicates that the silicon carbide used in steps S100 and S700 is graded, and the silicon particles used in step S600 are graded by size, which can significantly improve the density and overall bending strength of the crystal boat.

[0112] Matters not covered in this invention are common knowledge.

[0113] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0114] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

[0115] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon carbide crystal boat, characterized in that, This includes performing the following steps in sequence: S100. Preparation of silicon carbide granulated powder: The powder raw material is a mixture of silicon carbide powders of multiple particle size ranges. The auxiliary materials include polyethylene glycol, polyvinyl alcohol, carbon black and graphite. The mixed powder raw material and auxiliary materials are ball-milled and then spray-granulated to obtain silicon carbide granulated powder. The moisture content of the silicon carbide granulated powder is 1%-2%. S200, silicon carbide granulated powder compression molding green body unit; S300, the green body unit is dried to form a green body unit; S400, isostatic pressing of billet unit; S500, each blank unit is processed according to the assembly design requirements; S600, reaction sintering of the green body unit is carried out using stepped heating; S700, grinding and sandblasting the green body units after reaction sintering and bonding with adhesive slurry. The adhesive slurry comprises, by weight percentage: 55%-60% high-purity silicon carbide, 8%-12% phenolic resin, 15%-20% high-purity silica powder, 3%-5% polycarbosilane, 3%-5% sodium silicate, 1%-2% silicon carbide whiskers, 0.5%-1.5% boron nitride, and 0.5%-1.5% Y2O3-Al2O3, wherein the ratio of boron nitride to Y2O3-Al2O3 is 1:

1. The high-purity silicon carbide has a purity ≥98% and is mixed in a mass ratio of (1-3μm):(5-8μm)=1:

1. The particle size of the high-purity silica powder is 0.5-5μm. S800. The bonded and assembled crystal boat assembly is subjected to secondary sintering using a stepped heating method to obtain a silicon carbide crystal boat. The secondary sintering is specifically performed as follows: in an argon or vacuum environment, sintering is carried out using a stepped heating method. After sintering, the temperature is cooled at a rate of ≤10℃ / min to reduce thermal stress cracks. The stepped heating sintering process is as follows: heating at 50℃ / h to 200℃ for pre-curing for 1h, heating to 800℃ and holding for 1h, then heating at 100℃ / h to 1450℃-1550℃ and holding for 2h, and finally holding at 1650℃ for 2h.

2. The method for preparing a silicon carbide boat according to claim 1, characterized in that, The powder raw materials in step S100 are high-purity silicon carbide with four particle size ranges: 1-3μm, 5-8μm, 10-15μm, and 20-25μm. The purity of the high-purity silicon carbide is ≥98%, and they are mixed in a mass ratio of (1-3μm):(5-8μm):(10-15μm):(20-25μm)=2:3:2:

3.

3. The method for preparing a silicon carbide boat according to claim 2, characterized in that, The auxiliary materials in step S100: The average particle size of carbon black is 0.01-1 μm, of which polyethylene glycol accounts for 3 wt%-5 wt% of the weight of the powder raw material, polyvinyl alcohol accounts for 1 wt%-3 wt% of the weight of the powder raw material, carbon black accounts for 15 wt%-20 wt% of the weight of the powder raw material, and graphite accounts for 5 wt%-10 wt% of the weight of the powder raw material.

4. The method for preparing a silicon carbide boat according to claim 3, characterized in that, Before the reaction sintering of the blank unit in step S600, the following steps are also included: spraying boron nitride coating on the graphite boat and drying it; placing the column blank unit, top plate blank unit, bottom plate blank unit and side wing blank unit on the graphite boat; and covering the upper and lower surfaces of each blank unit with silicon particles. The weight of the silicon particles is 78-82% of the total weight of all blank units, and the particle size of the silicon particles is (0.5-1mm):(3-5mm)=1:

2.

5. The method for preparing a silicon carbide boat according to claim 4, characterized in that, In step S600, under a vacuum environment with a vacuum degree ≤65MPa, a stepped heating method is used to perform reaction sintering on the green body unit, specifically as follows: Room temperature-200℃, 50min-60min; 200℃-400℃, 80min-90min; 400℃-800℃, 110min-120min; 800℃-1000℃, 110min-120min; 1000℃-1250℃, 80min-90min; 1250℃-1650℃, 190min-200min; Hold at 1650℃ for 110-120 minutes.

6. The method for preparing a silicon carbide boat according to claim 1, characterized in that, Before the reaction sintering of the green body unit in step S800, the following steps are also included: Boron nitride coating is sprayed onto the graphite boat and dried. The bonded crystal boat is placed horizontally on the graphite boat. The side wings of the crystal boat assembly are supported by graphite pillars to prevent deformation during sintering. Each crystal boat is equipped with two portions of silicon grains weighing 250-270g, which are laid flat on the upper surface of the top and bottom plates. The particle size of the silicon grains is 0.1-0.4mm.

7. The method for preparing a silicon carbide boat according to any one of claims 1-6, characterized in that, The preparation method of the adhesive mortar is as follows: S701, Pre-dispersion: Silicon carbide, silicon powder, silicon carbide whiskers, boron nitride and Y2O3-Al2O3 are mixed and first ball-milled with 0.5%-1% polyvinylpyrrolidone solution for 4h-6h at 300rpm to break up agglomerates and obtain powder mixture. S702, phenolic resin is diluted with 70% ethanol to a solid content of 30%; S703. Mix the materials prepared in steps S701 and S702, add polycarbosilane and sodium silicate in sequence, adjust the pH of the slurry to 9-10 to form an alkaline environment of sodium silicate and enhance dispersion stability; stir the mixture and dry it at the same time to promote the viscosity of the slurry, add carboxymethyl cellulose as a thickener, and control the viscosity at 500-800 mmPa·s to obtain the adhesive slurry.

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