A method for preparing a bottom heater for a single crystal silicon furnace

Abstract

The present application discloses a preparation method for a bottom heater for a single crystal silicon furnace, which relates to the technical field of material preparation. The method comprises: adding graphite powder, petroleum coke, asphalt powder, adhesive, fiber and dispersant to water in proportion, and mixing them evenly to obtain a premix; molding the premix once in a bottom heater mold, and then drying it in the shade to form a blank; molding the blank in the bottom heater mold at high temperature for a second time to obtain a preform; carbonizing the preform to obtain a carbonized blank; and heat-treating the carbonized blank at high temperature to obtain a bottom heater. The present application replaces the traditional needling method with a two-molding process, thereby avoiding the problem of gas leakage caused by excessive use of adhesives. The combination of shade drying and staged molding shortens the blank molding cycle, eliminates internal stress concentration points, and the fiber realizes a three-dimensional reinforcement effect of the material. The carbonization and high-temperature treatment improve the thermal conductivity stability of the final product, thereby increasing the service life of the bottom heater.

Description

Technical Field

[0001] The present application relates to the technical field of material preparation, and in particular to a method for preparing a bottom heater for a single crystal silicon furnace. Background Art

[0002] The bottom heater is an important thermal field component in the single crystal silicon pulling furnace. It is used in conjunction with the heater to adjust the temperature in the furnace by changing the power to melt the silicon material and provide a suitable thermal field environment for the growth of single crystal silicon. During the single crystal silicon production process, the bottom heater needs to withstand extremely high temperatures and intense thermal cycles. Its performance directly affects the growth quality and production efficiency of single crystal silicon.

[0003] At present, most bottom heaters are made of graphite materials, but traditional graphite has the defects of low strength and poor thermal shock resistance. It is easy to crack and deform under long-term high-temperature working environment, resulting in a short service life of the bottom heater. In the existing technology, the preparation method of the bottom heater mainly adopts the needle punching method to make a preform, and then repeatedly impregnates and carbonizes it with resin for densification treatment, and finally obtains the finished bottom heater through high-temperature graphitization. The above method has many defects: the multiple impregnation processes require the consumption of a large amount of resin material, which increases the production cost; secondly, the resin produces a large amount of gas during carbonization and decomposition, which easily causes cracks and peeling on the surface of the bottom heater, seriously affecting the appearance and performance of the product; at the same time, the production cycle of this process is usually more than 60 days, which is inefficient; finally, due to uneven impregnation, the prepared product is prone to uneven density distribution and even internal stratification, which reduces the service life of the bottom heater. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a method for preparing a bottom heater for a single crystal silicon furnace, aiming to improve the production efficiency and service life of the bottom heater.

[0005] A method for preparing a bottom heater for a single crystal silicon furnace comprises the following steps:

[0006] Add graphite powder, petroleum coke, asphalt powder, adhesive, fiber and dispersant into water in proportion and mix well to obtain a premix;

[0007] The premix is ​​molded once in a bottom heater mold, and then air-dried to form a blank;

[0008] The blank is subjected to secondary high-temperature molding in a bottom heater mold to obtain a preform;

[0009] performing carbonization treatment on the prefabricated body to obtain a carbonized body;

[0010] The carbonized body is subjected to high-temperature heat treatment to obtain a bottom heater.

[0011] The components in the premix are evenly distributed in the system through dispersants, and the fibers are formed into a multi-level gradient distribution through two moldings, which effectively improves the ligand's bending strength; among them, the first molding constructs the basic skeleton structure of the material, and the shade drying process can avoid the stress concentration problem caused by rapid volatilization of water; the second molding combined with thermal curing allows the adhesive to fully penetrate into the gaps between the particles to form a three-dimensional grid structure; carbonization treatment converts the adhesive into a carbonaceous connector, and high-temperature heat treatment promotes the ordering of the material's crystal structure, and finally a high-density, low-porosity bottom heater is obtained, which effectively solves the problems of uneven density and surface cracking of the bottom heater, and the production cycle is significantly shortened.

[0012] Optionally, the premix is ​​made of the following raw materials in parts by weight: 40-70 parts of graphite powder, 5-20 parts of petroleum coke, 5-10 parts of asphalt powder, 22-50 parts of adhesive, 5-25 parts of fiber, 1.1-10 parts of dispersant and 30-60 parts of deionized water.

[0013] By limiting the mass ratio of each component in the premix, the mechanical strength and thermal shock resistance of the bottom heater are guaranteed, while shortening the production cycle and avoiding surface cracking. The improvement of the uniformity of the premix dispersion reduces the internal defects of the blank. The continuous bonding carbon network formed during the carbonization process improves the density of the material. The final bottom heater has a more uniform microstructure and a longer service life. Graphite powder ensures the carbon content of the material, petroleum coke supplements the carbon source ratio to optimize the pore structure of the material during the carbonization process, asphalt powder is converted into a bonding carbon phase at high temperature to improve the integrity of the blank, the adhesive ratio ensures that the blank has sufficient molding strength during the molding stage, the fiber realizes the three-dimensional reinforcement effect of the material, the dispersant ensures the uniform dispersion of each component and reduces particle sedimentation, and deionized water balances the rheological properties of the slurry with the molding efficiency. This ratio reduces the density unevenness or stratification defects caused by the imbalance of component ratios during the molding and carbonization process of the premix, while avoiding the problem of thermal decomposition gas escape caused by excessive resin impregnation.

[0014] Optionally, the adhesive comprises phenolic resin and industrial ethanol;

[0015] The mass ratio of the phenolic resin to industrial ethanol is 2-20:1.

[0016] Phenolic resin and industrial ethanol are mixed in proportion to form an adhesive system, which evenly coats solid particles such as graphite powder in the premix. During the curing process, the industrial ethanol gradually evaporates, and the phenolic resin undergoes a cross-linking reaction under heating conditions to form a continuous adhesive network. The mass ratio is controlled within the range of 2-20:1, which not only ensures that the adhesive fully wets the powder and avoids local stress concentration caused by uneven mixing, but also prevents excessive solvent residue from affecting the curing effect, ensuring that the preform has sufficient initial strength before carbonization. If there is too much phenolic resin, the viscosity of the premix is ​​too high and it is difficult to disperse evenly. If there is too little phenolic resin, the material strength will be insufficient. By optimizing the ratio of the two, the bonding strength is guaranteed while the mixing uniformity is improved, effectively avoiding the expansion of microcracks caused by solvent residue during the carbonization process.

[0017] Optionally, the dispersant includes carboxymethyl cellulose and sodium dodecylbenzene sulfonate;

[0018] The mass ratio of the carboxymethyl cellulose to sodium dodecylbenzenesulfonate is 1-80:1.

[0019] Carboxymethyl cellulose delays particle settling by increasing the viscosity of the aqueous phase, while sodium dodecylbenzene sulfonate reduces its tendency to agglomerate by adsorbing on the surfaces of graphite powder and petroleum coke. When the two are properly combined, they achieve uniform distribution of high-solids materials such as graphite powder and petroleum coke under low-shear mixing conditions, avoiding stress concentration or density differences within the subsequent molded green body due to uneven dispersion. This effectively prevents crack propagation caused by localized stress release during carbonization, while also shortening mixing time and reducing equipment energy consumption, thereby improving the production efficiency of the bottom heater.

[0020] Optionally, the particle size of the graphite powder is 200-1000 mesh, the particle size of the petroleum coke is 500-800 mesh, and the particle size of the asphalt powder is 200-500 mesh; the fiber is carbon fiber, and the length of the carbon fiber is 5-50 mm;

[0021] The mixing time of the premix is ​​2-5 hours.

[0022] By limiting the particle size range of graphite powder, petroleum coke and asphalt powder, and combining the mixing time of the premix, a stable dispersion system can be formed in the raw material mixing stage. The fine-grained petroleum coke and asphalt powder mentioned above help fill the gaps between large particles, and sufficient mixing time can avoid local component segregation; in the subsequent molding and curing process, the uniformity of the internal structure of the material is improved, thereby reducing the risk of cracking caused by uneven density during the carbonization and high-temperature treatment stages. A mixing time of 2-5h can ensure that the components are fully dispersed and form a uniform slurry system, thereby improving the production efficiency and service life of the bottom heater.

[0023] Optionally, the carbon fibers include 30-50% carbon fibers with a length of 5-15 mm, 30-40% carbon fibers with a length of 16-35 mm, and 10-30% carbon fibers with a length of 36-50 mm.

[0024] During the compression molding process, short fibers fill gaps in the material, reducing porosity. Medium and long fibers enhance the toughness of the preform through their staggered arrangement. Long fibers form a continuous skeleton along the compression direction. Carbon fibers of varying lengths form a gradient transition interface during the heat curing phase, preventing crack propagation caused by stress concentration. By adjusting the ratio of length intervals, the material's density and flexural strength are balanced. The synergistic effect of fibers of varying lengths ensures the preform maintains its integrity during carbonization and high-temperature treatment, reducing the risk of internal stress cracking and shortening the preform molding cycle.

[0025] Optionally, the primary molding is performed at room temperature;

[0026] The pressure of the primary molding is 0.05-0.5 MPa, and the time of the primary molding is 10-20 minutes.

[0027] Pressing at room temperature can avoid the difference in thermal expansion of materials caused by high temperature, which helps to maintain the shape stability of the blank. The combination of pressure and time allows the graphite powder and fibers to be evenly arranged with the help of moisture, which not only avoids the fiber damage caused by traditional needle punching, but also reduces the internal stress concentration of the blank through uniform pressure distribution, providing a structurally stable blank foundation for subsequent carbonization treatment.

[0028] Optionally, the pressing temperature of the secondary molding is between 120-250°C;

[0029] The secondary molding pressure is 10-15 MPa, and the molding time is 20-120 min.

[0030] By adjusting the temperature of the secondary molding, the adhesive in the prefabricated body is softened but not completely decomposed, thereby promoting material flow and enhancing density; the pressure range can effectively eliminate the pores inside the body and increase the density of the material; the time range ensures that the material fully flows to fill the mold cavity and complete the structural shaping. In this process, the remaining pores inside the body are compressed and eliminated, and the various component materials are densified and arranged under the joint action of heat and force. This operation completes the final shaping of the body structure through a single process. This application effectively solves the problems of long production cycle, uneven product density and surface cracking caused by multiple impregnation and carbonization in the traditional process. By optimizing the secondary molding process parameters, the forming efficiency is significantly improved while ensuring the body density, and structural damage caused by gas escape inside the material is avoided.

[0031] Optionally, the temperature of the carbonization treatment is 850-1050° C., and the time of the carbonization treatment is 5-8 hours.

[0032] The prefabricated body is heated to the target temperature range in a closed environment, and the temperature inside the body is evenly distributed through gradient heating. The gas generated during the carbonization process is directed out through the negative pressure exhaust system. The carbonized body forms a carbon matrix with a three-dimensional network structure, which effectively reduces the gas aggregation phenomenon during the carbonization process and improves the surface integrity of the bottom heater body.

[0033] Optionally, the temperature of the high-temperature heat treatment is 1800-2300° C., and the time of the high-temperature heat treatment is 1-2 hours.

[0034] During the high-temperature heat treatment process, carbon atoms are arranged in an orderly manner through diffusion to form a three-dimensional network graphite structure, which inhibits abnormal grain growth while ensuring the density of the material, thereby obtaining a bottom heater with high thermal stability.

[0035] The beneficial effects of the present invention are: the traditional needling and repeated dipping steps are replaced by a two-step molding process, thereby avoiding the problem of gas escape caused by excessive use of adhesives; the combination of shade drying and staged molding shortens the blank molding cycle, while eliminating internal stress concentration points; the directional arrangement and multi-level gradient distribution of fibers enhance the material's thermal shock resistance; the synergistic effect of carbonization and high-temperature treatment improves the thermal conductivity stability of the final product and increases the service life of the bottom heater. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of a method for preparing a bottom heater for a single crystal silicon furnace provided in an embodiment of the present application. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] Figure 1 This is a flow chart of a method for preparing a bottom heater for a single crystal silicon furnace provided in an embodiment of the present application, such as Figure 1 As shown, the method includes the following steps:

[0039] S10, adding graphite powder, petroleum coke, asphalt powder, adhesive, fiber and dispersant to water in proportion, and mixing them uniformly to obtain a premix;

[0040] S20, molding the premix once at room temperature, and then drying in the shade to form a blank;

[0041] S30, performing secondary high-temperature molding on the blank in a bottom heater mold to obtain a preform;

[0042] S40, carbonizing the prefabricated body to obtain a carbonized body;

[0043] S50, performing high-temperature heat treatment on the carbonized body to obtain a bottom heater.

[0044] In the technical solution provided in the present application, each component in the premix is ​​evenly distributed in the system through a dispersant, and the fibers are formed into a multi-level gradient distribution through two moldings, which effectively improves the flexural strength of the ligand; wherein, the one-time molding refers to the preliminary densification of the premix under normal temperature conditions, and the hydraulically activated mechanical press is used to apply pressure to make the material initially formed, and the green body after the one-time molding is placed in a humidity-controlled environment for slow dehydration to prevent cracking caused by rapid drying, and the one-time molding constructs the basic skeleton structure of the material, and the shade drying process avoids stress concentration caused by rapid volatilization of water; the heating and curing treatment makes the adhesive A cross-linking reaction occurs; higher pressure is applied to the green body through secondary molding to further eliminate the internal pores of the green body and enhance the structural density. The secondary molding combined with thermal curing allows the adhesive to fully penetrate into the gaps between the particles to form a three-dimensional grid structure; carbonization treatment converts the adhesive into a carbonaceous connector, and high-temperature heat treatment promotes the ordering of the material's crystal structure, ultimately obtaining a high-density, low-porosity bottom heater. The carbonized green body is graphitized at high temperature through high-temperature heat treatment to improve the thermal stability of the material, effectively solving the problems of uneven density and surface cracking of the bottom heater, and significantly shortening the production cycle.

[0045] Optionally, the premix is ​​made of the following raw materials in the following mass ratio: 40-70 parts of graphite powder, 5-20 parts of petroleum coke, 5-10 parts of asphalt powder, 22-50 parts of adhesive, 5-25 parts of fiber, 1.1-10 parts of dispersant and 30-60 parts of deionized water.

[0046] Graphite powder can specifically use artificial graphite powder as the matrix material to ensure the material's high-temperature resistance; petroleum coke can be used as a recarburizer, specifically needle coke, which can increase the carbon content of the green body after high-temperature treatment; asphalt powder forms a bonding carbon network during the carbonization process to enhance the green body's strength; the adhesive plays a temporary bonding role during the green body forming stage; the fibers are distributed inside the green body to achieve stress dispersion; the dispersant prevents solid particles from agglomerating and improves the fluidity of the slurry. By controlling the proportion of the premix components, a uniform carbon skeleton structure can be directly constructed during the green body forming stage, reducing subsequent process steps. While ensuring the mechanical strength and thermal shock resistance of the bottom heater, the production cycle can be shortened and surface cracking problems can be avoided. The improvement in the uniformity of the slurry dispersion reduces internal defects in the green body, and the continuous bonding carbon network formed during the carbonization process increases the material density. The resulting bottom heater has a more uniform microstructure and a longer service life.

[0047] Optionally, the adhesive includes phenolic resin and industrial ethanol; the mass ratio of the phenolic resin to the industrial ethanol is 2-20:1.

[0048] Phenolic resin has thermosetting characteristics and forms a three-dimensional network structure through curing reaction to ensure bonding strength; industrial ethanol is used to adjust the viscosity and fluidity of the phenolic resin system. When the mass ratio of phenolic resin to industrial ethanol is within the range of 2-20:1, it can balance the wettability of the adhesive in the premix to the powder material and the stability of the product structure. When the amount of phenolic resin added is small, the viscosity of the adhesive is small, which is not conducive to the displacement filling of the powder particles in the subsequent molding process, affecting the strength of the blank before carbonization treatment; when the amount of phenolic resin added is large, the viscosity of the premix is ​​too high and the remaining components are difficult to disperse; this ratio achieves uniform mixing and distribution of the adhesive in the premix, reduces internal defects caused by concentrated volatilization of the solvent in subsequent processing, improves the structural density of the bottom heater, shortens the time required for the adhesive to cure, and further improves the production efficiency of the bottom heater.

[0049] Optionally, the dispersants are carboxymethyl cellulose and sodium dodecylbenzene sulfonate; the mass ratio of carboxymethyl cellulose to sodium dodecylbenzene sulfonate is 1-80:1.

[0050] Carboxymethyl cellulose is a substance with thickening and stabilizing effects. Specifically, powdered sodium carboxymethyl cellulose can be used. It forms a steric hindrance effect by adsorbing on the surface of the system particles, reducing the phenomenon of particle agglomeration in the premix; sodium dodecylbenzene sulfonate promotes the wetting and dispersion of solid particles by reducing the surface tension of the liquid.

[0051] Carboxymethyl cellulose slows particle settling by increasing aqueous viscosity, while sodium dodecylbenzene sulfonate reduces agglomeration by adsorbing on the surfaces of graphite powder and petroleum coke. When these two ingredients are properly combined, they achieve uniform distribution of high-solids materials like graphite powder and petroleum coke under low-shear mixing conditions. This prevents stress concentration or density differences within the subsequent molded green body caused by uneven dispersion, effectively preventing crack propagation caused by localized stress release during carbonization, and simultaneously shortens mixing time and reduces equipment energy consumption.

[0052] Optionally, the fiber is carbon fiber, the length of the carbon fiber is 5-50 mm and is distributed in a multi-level length gradient, the carbon fiber including 30-50% carbon fiber with a length of 5-15 mm, 30-40% carbon fiber with a length of 16-35 mm and 10-30% carbon fiber with a length of 36-50 mm.

[0053] Carbon fiber is an inorganic polymer fiber material composed of carbon elements. It has high strength and heat resistance at high temperatures. By mixing carbon fibers of different lengths in different proportions, the 5-15mm carbon fibers in the blank can fill the material gaps and reduce porosity. The 16-35mm carbon fibers are staggered to enhance the toughness of the blank. The 36-50mm carbon fibers form a continuous skeleton structure, improving the overall strength of the blank. By adjusting the ratio of the length intervals, the density and flexural strength of the blank can be balanced. Carbon fibers of different lengths form a gradient transition interface during the thermal curing stage, which can avoid crack propagation caused by stress concentration. By precisely controlling the multi-level length gradient distribution, the fibers are complementary reinforced in different directions, which not only avoids the carbonization cracking problem caused by excessive impregnation of adhesives in traditional processes, but also improves the dimensional stability of the blank during the high-temperature treatment stage.

[0054] Optionally, the particle size of the graphite powder is 200-1000 mesh, the particle size of the petroleum coke is 500-800 mesh, and the particle size of the asphalt powder is 200-500 mesh; and the mixing time of the premix is ​​2-5 hours.

[0055] The particle size of graphite powder is in the range of 200-1000 mesh, which is beneficial to improving the uniformity of the premix and the density of the bottom heater; the particle size of petroleum coke is in the range of 500-800 mesh, which helps to improve the thermal conductivity of the material during high-temperature treatment; the particle size of asphalt powder is in the range of 200-500 mesh, which can promote the dispersion of the adhesive during the mixing process, and ensure that the components are fully dispersed and form a uniform premix system through stirring for 2-5 hours. By precisely controlling the particle size of raw materials and mixing parameters, the structural uniformity of the premix is ​​optimized, avoiding the problem of extended production cycle caused by repeated impregnation in traditional processes, and reducing surface defects caused by the escape of resin decomposition gas; effectively reducing the internal stress concentration of the bottom heater blank during the molding and heat treatment stages, reducing the risk of product cracking, while shortening the mixing process time and improving batch consistency, thereby improving the production efficiency of the bottom heater and the stability of finished product quality.

[0056] Optionally, the primary molding is performed at room temperature; the primary molding pressure is 0.05-0.5 MPa, and the primary molding time is 10-20 min.

[0057] Specifically, after the premix is ​​loaded into the mold, it is molded once at room temperature, which effectively avoids the thermal expansion difference of the material caused by high temperature and helps to maintain the shape stability of the blank. The molding pressure range is 0.05-0.5MPa, which can not only ensure the initial compactness of the blank, but also prevent excessive pressure from causing fiber breakage inside the blank. The pressing time is 10-20min to ensure that the premix particles fully fill the mold cavity, while avoiding excessive moisture precipitation caused by long-term pressing. The coordination of molding pressure and time allows the graphite powder and fibers to form a uniform arrangement with the assistance of moisture, which not only avoids fiber damage caused by traditional needle punching, but also reduces stress concentration inside the blank through uniform pressure distribution, providing a structurally stable blank foundation for subsequent carbonization treatment.

[0058] Optionally, the pressing temperature of the secondary molding is between 120-250° C.; the pressure of the secondary molding is 10-15 MPa; and the time of the secondary molding is 20-120 min.

[0059] Specifically, the blank is subjected to secondary molding on a press, and the temperature of the secondary molding is controlled within the range of 120-250°C, which can soften the adhesive in the blank but not completely decompose it, thereby promoting material flow and increasing the density of the material; the pressure of the secondary molding is within the range of 10-15MPa, which can effectively discharge the internal pores of the blank and increase the density of the material, and fill the mold cavity and complete the structural shaping within 20-120min. The traditional method relies on repeated impregnation of resin and carbonization to increase the density. Each carbonization process takes several hours and is prone to gas generation, which causes cracks. The present application achieves material densification and structural forming simultaneously in a single hot pressing process by precisely controlling the temperature, pressure and time parameters of the secondary molding, which not only shortens the production cycle, but also avoids surface defects caused by the release of resin decomposition gas.

[0060] Optionally, the temperature of the carbonization treatment is 850-1050° C., and the time of the carbonization treatment is 5-8 hours.

[0061] The temperature range of the carbonization treatment is 850-1050℃. This temperature range can effectively control the decomposition rate of organic matter and avoid violent gas overflow that causes cracking of the green body. The carbonization time is 5-8h, ensuring that the organic matter is fully decomposed and avoiding excessive energy consumption. In the early stage of carbonization, the temperature is raised to 600℃ at a rate of 50-80℃ per hour to complete the coking of the adhesive, and then raised to the target temperature at a rate of 20-30℃ per hour to complete the carbonization of the asphalt. The gas generated during the carbonization process is directed out through the negative pressure exhaust system. The carbonized green body forms a carbon matrix with a three-dimensional network structure. The temperature of the existing technology is about 1200℃, which causes the green body to carbonize rapidly and the resin to decompose rapidly to produce a large amount of gas. However, the present application reduces the carbonization temperature and adjusts the carbonization time, so that the gas is slowly released through the pores of the material, and the stress distribution inside the green body is more uniform. At the same time, the carbonization temperature forms a gradient connection with the subsequent high-temperature heat treatment to avoid structural damage to the material due to excessive temperature difference.

[0062] Optionally, the temperature of the high-temperature heat treatment is 1800-2300° C., and the time of the high-temperature heat treatment is 1-2 hours.

[0063] High-temperature heat treatment promotes the rearrangement of carbon atoms to form a graphite crystal structure. The temperature of 1800-2300°C helps to eliminate the residual stress of the carbonized body during the carbonization process and promotes the transformation of the carbon material into high-crystallinity graphite. The high-temperature heat treatment of 1-2 hours can ensure that the material completes the graphitization transformation while avoiding excessive energy consumption. By precisely controlling the upper temperature limit and the holding time, the abnormal grain growth can be suppressed while ensuring the density of the material, thereby obtaining a bottom heater with uniform conductivity and high thermal stability, and shortening the total production cycle to less than 1 / 4 of the original process.

[0064] The preparation method of the bottom heater involved in this application is described in detail below with reference to specific examples and comparative examples:

[0065] Example 1

[0066] A method for preparing a bottom heater for a single crystal silicon furnace comprises the following steps:

[0067] 40 g of 200-mesh graphite powder, 5 g of 500-mesh petroleum coke, 5 g of 200-mesh asphalt powder, 20 g of phenolic resin, 2 g of industrial ethanol, 5 g of fiber, 1 g of sodium carboxymethyl cellulose, and 0.1 g of sodium dodecylbenzene sulfonate were added to 30 g of deionized water and stirred at 200 r / min for 2 h to obtain a premix, wherein the fiber consisted of 30% carbon fibers with a length of 5-15 mm, 30% carbon fibers with a length of 16-35 mm, and 40% carbon fibers with a length of 36-50 mm;

[0068] The premix is ​​added into the bottom heater mold and molded once at room temperature and 0.05 MPa, and then the mold is dried in the shade after holding the pressure for 10 minutes to form a blank;

[0069] The blank was heated to 120°C and 10 MPa in a bottom heater mold for secondary molding. The heating and molding time was 20 minutes to obtain a preform.

[0070] The preform was placed in a carbonization furnace and carbonized at 850°C for 5 h to obtain a carbonized body;

[0071] The carbonized body was heated at 1800°C for 1 hour, processed into a desired size, and the surface was ground and polished to obtain a bottom heater.

[0072] Example 2

[0073] A method for preparing a bottom heater for a single crystal silicon furnace comprises the following steps:

[0074] 70 g of 200-mesh graphite powder, 20 g of 500-mesh petroleum coke, 10 g of 200-mesh asphalt powder, 40 g of phenolic resin, 10 g of industrial ethanol, 25 g of fiber, 9 g of sodium carboxymethyl cellulose, and 1 g of sodium dodecylbenzene sulfonate were added to 60 g of deionized water and stirred at 200 r / min for 5 h to obtain a premix, wherein the fiber consisted of carbon fibers with a length of 5-15 mm (50%), a length of 16-35 mm (40%), and a length of 36-50 mm (10%).

[0075] The premix is ​​added into the bottom heater mold and molded once at room temperature and 0.5 MPa, and then dried in the shade after holding the pressure for 20 minutes to form a blank;

[0076] The blank was heated in a bottom heater mold to 250°C and 15 MPa for secondary molding. The heating and molding time was 120 min to obtain a preform.

[0077] The preform was placed in a carbonization furnace and carbonized at 1050°C for 8 h to obtain a carbonized body;

[0078] The carbonized body was heated at 2300°C for 2 hours, processed into the required size and the surface was ground and polished to obtain a bottom heater.

[0079] Example 3

[0080] A method for preparing a bottom heater for a single crystal silicon furnace comprises the following steps:

[0081] 60 g of 200-mesh graphite powder, 10 g of 500-mesh petroleum coke, 8 g of 200-mesh asphalt powder, 30 g of phenolic resin, 10 g of industrial ethanol, 15 g of fiber, 5 g of sodium carboxymethyl cellulose, and 0.6 g of sodium dodecylbenzene sulfonate were added to 50 g of deionized water and stirred at 200 r / min for 2 h to obtain a premix, wherein the fiber consisted of 40% carbon fibers with a length of 5-15 mm, 35% carbon fibers with a length of 16-35 mm, and 25% carbon fibers with a length of 36-50 mm;

[0082] The premix is ​​added into the bottom heater mold and molded once at room temperature and 0.3 MPa, and then the mold is dried in the shade after holding the pressure for 15 minutes to form a blank;

[0083] The blank was heated to 180°C and 12 MPa in a bottom heater mold for secondary molding. The heating and molding time was 70 min to obtain a preform.

[0084] The preform was placed in a carbonization furnace and carbonized at 950°C for 6 h to obtain a carbonized body;

[0085] The carbonized body was heated at 2000°C for 1.5 hours, processed into a desired size, and the surface was ground and polished to obtain a bottom heater.

[0086] Example 4

[0087] A method for preparing a bottom heater for a single crystal silicon furnace comprises the following steps:

[0088] 58 g of 500-mesh graphite powder, 15 g of 600-mesh petroleum coke, 7 g of 300-mesh asphalt powder, 30 g of phenolic resin, 6 g of industrial ethanol, 20 g of fiber, 6 g of sodium carboxymethyl cellulose, and 0.6 g of sodium dodecylbenzene sulfonate were added to 53 g of deionized water and stirred at 200 rpm for 3 h to obtain a premix, wherein the fiber consisted of 40% carbon fibers with a length of 5-15 mm, 35% carbon fibers with a length of 16-35 mm, and 25% carbon fibers with a length of 36-50 mm;

[0089] The premix is ​​added into the bottom heater mold and molded once at room temperature and 0.5 MPa, and then the mold is dried in the shade after holding the pressure for 15 minutes to form a blank;

[0090] The blank was heated to 200°C and 13 MPa in a bottom heater mold for secondary molding. The heating and molding time was 100 min to obtain a preform.

[0091] The preform was placed in a carbonization furnace and carbonized at 1000°C for 6 h to obtain a carbonized body;

[0092] The carbonized body was heated at 2100° C. for 1.5 h, processed into a desired size, and the surface was ground and polished to obtain a bottom heater.

[0093] Example 5

[0094] A method for preparing a bottom heater for a single crystal silicon furnace is different from that of Example 4 in that the amount of phenolic resin added is 20 g.

[0095] Example 6

[0096] A method for preparing a bottom heater for a single crystal silicon furnace is different from Example 4 in that the amount of phenolic resin added is 40 g.

[0097] Example 7

[0098] A method for preparing a bottom heater for a single crystal silicon furnace is different from that of Example 4 in that the amount of carboxymethyl cellulose added is 1 g.

[0099] Example 8

[0100] A method for preparing a bottom heater for a single crystal silicon furnace is different from that of Example 4 in that the amount of carboxymethyl cellulose added is 8 g.

[0101] Comparative Example 1

[0102] A method for preparing a bottom heater for a single crystal silicon furnace comprises the following steps: preparing a 2.5D carbon fiber preform by needle puncture, and heating the carbon fiber preform at 1000°C for 1 hour to obtain a preform, adding 150g of water to the premix prepared in Example 3 to prepare a slurry, placing the heated preform into the slurry and drying it at 100°C for 16 hours, repeating this process five times, curing the impregnated preform at 200°C for 80 minutes, and then performing the carbonization treatment, high-temperature heat treatment, and subsequent treatments in Example 3.

[0103] Comparative Example 2

[0104] A method for preparing a bottom heater for a single crystal silicon furnace is different from that of Example 3 in that the heating temperature of the first molding is 500°C.

[0105] Comparative Example 3

[0106] A method for preparing a bottom heater for a single crystal silicon furnace is different from Example 3 in that the molding time is 2 hours.

[0107] Comparative Example 4

[0108] A method for preparing a bottom heater for a single crystal silicon furnace is different from Example 3 in that the secondary molding time is 5 hours.

[0109] Comparative Example 5

[0110] A method for preparing a bottom heater for a single crystal silicon furnace is different from that of Example 3 in that the secondary molding temperature is 500°C.

[0111] Comparative Example 6

[0112] A method for preparing a bottom heater for a single crystal silicon furnace is different from that of Example 3 in that the carbonization treatment temperature is 1200°C.

[0113] The preparation methods of the bottom heaters of Examples 2-8 and Comparative Example 1 are the same as that of Example 1.

[0114] The following performance tests were conducted on the bottom heaters provided in Examples 1-8 of the present invention and Comparative Examples 1-6. Table 1 shows the performance test results.

[0115] Density: Take 1cm*1cm*1cm cube samples of the bottom heaters of Examples 1-8 and Comparative Example 1, weigh them and record their weights as m1. Immerse the samples in water for more than 30 minutes, take out the saturated samples, wipe off the surface droplets, and weigh them as m2. Hang the saturated samples in water and weigh them as m3. The density calculation formula is as follows:

[0116]

[0117] Density CV value: Take 5 samples in each of Examples 1-8 and Comparative Example 1 to measure 5 density values, calculate the average value and standard deviation of the 5 density values, and calculate the density CV value using the following formula:

[0118]

[0119] Bending strength: The bottom heater samples of Examples 1-8 and Comparative Example 1 were taken respectively, and the bending strength of the samples was tested according to GB / T 33501-2017 “Test method for flexural properties of carbon-carbon composite materials”.

[0120] Bending strength CV value: Take 5 samples in each of Examples 1-8 and Comparative Example 1 to measure 5 bending strengths, calculate the average value and standard deviation of the 5 bending strengths, and calculate the bending strength CV value using the following formula:

[0121]

[0122] Resistivity: The bottom heater samples of Examples 1-8 and Comparative Example 1 were taken respectively, and the room temperature resistivity of the samples was tested according to GB / T24525-2009 "Determination of Resistivity of Carbon Materials".

[0123] Resistivity CV value: Take 5 samples in each of Examples 1-8 and Comparative Example 1 to measure 5 resistivities, calculate the average value and standard deviation of the 5 resistivities, and calculate the resistivity CV value using the following formula:

[0124]

[0125] Porosity: Take the m1, m2 and m3 of each sample in Examples 1-8 and Comparative Example 1 in the density measurement respectively, and calculate the porosity of the bottom heater sample by the following formula:

[0126]

[0127] Three samples were taken for each example and comparative example, and the test results were averaged. The specific test results are shown in Table 1.

[0128] Table 1 Performance results

[0129]

[0130] This application replaces the traditional needling and repeated dipping steps with a two-step molding process, avoiding the problem of gas escape caused by excessive use of adhesives. The combination of shade drying and staged molding shortens the blank molding cycle and eliminates internal stress concentration points. The directional arrangement and multi-level gradient distribution of fibers enhance the material's thermal shock resistance. The synergistic effect of carbonization and high-temperature treatment improves the thermal conductivity stability of the final product and increases the service life of the bottom heater.

[0131] The bottom heater prepared by the preparation method of the present application has an internal porosity of less than 8%. The carbonization time is shortened to 1 / 4 of that of the traditional process, and the production cycle is compressed from 60-90 days to 10-15 days. Specifically, the production cycle of Comparative Example 1 is 90 days, and the production cycle of Examples 1-8 and Comparative Examples 2-6 is 10-15 days. In addition, the product density uniformity of the bottom heater prepared according to the preparation method of the present application reaches more than 97%, effectively improving the service life and production efficiency of the bottom heater.

[0132] Finally, it should be noted that the above descriptions are merely optional examples of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a bottom heater for a single crystal silicon furnace, characterized in that: The steps include: 40-70 parts of graphite powder, 5-20 parts of petroleum coke, 5-10 parts of asphalt powder, 22-50 parts of adhesive, 5-25 parts of fiber, 1.1-10 parts of dispersant and 30-60 parts of deionized water are uniformly mixed to obtain a premix; wherein the adhesive comprises phenolic resin and industrial ethanol; the mass ratio of the phenolic resin to the industrial ethanol is 2-20:1; the dispersant comprises carboxymethyl cellulose and sodium dodecylbenzene sulfonate; the mass ratio of the carboxymethyl cellulose to the sodium dodecylbenzene sulfonate is 1-80:1; the fiber is carbon fiber, and the carbon fiber comprises 30-50% carbon fiber with a length of 5-15 mm, 30-40% carbon fiber with a length of 16-35 mm and 10-40% carbon fiber with a length of 36-50 mm; The premix is ​​molded once in a bottom heater mold, and then air-dried to form a blank; wherein the once molding is performed at room temperature and the time of the once molding is 10-20 minutes; The blank is subjected to high-temperature secondary molding in a bottom heater mold to obtain a preform; wherein the pressing temperature of the secondary molding is between 120-250° C. and the time of the secondary molding is 20-120 minutes; Carrying out a carbonization treatment on the prefabricated body to obtain a carbonized body; wherein the temperature of the carbonization treatment is 850-1050° C.; The carbonized body is subjected to high-temperature heat treatment to obtain a bottom heater.

2. The preparation method according to claim 1, characterized in that The particle size of the graphite powder is 200-1000 meshes, the particle size of the petroleum coke is 500-800 meshes, and the particle size of the asphalt powder is 200-500 meshes; and the mixing time of the premix is ​​2-5 hours.

3. The preparation method according to claim 1, characterized in that The pressure of the primary molding is 0.05-0.5 MPa.

4. The preparation method according to claim 1, characterized in that The secondary molding pressure is 10-15 MPa.

5. The preparation method according to claim 1, characterized in that The carbonization treatment time is 5-8 hours.

6. The preparation method according to claim 1, characterized in that The temperature of the high-temperature heat treatment is 1800-2300° C., and the time of the high-temperature heat treatment is 1-2 hours.

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