Method for preparing multi-particle-size high-purity silicon carbide powder composite isostatic pressing ceramic barrel

Abstract

The application relates to the technical field of special ceramic preparation, and discloses a preparation method of a multi-particle-size high-purity silicon carbide powder composite isostatic pressing ceramic barrel, which comprises the following steps: grinding and dispersing multi-particle-size silicon carbide powder, boron carbide and tannic acid, adding fructose, polyethylene glycol and ammonium p-toluenesulfonate, and obtaining spherical granulation powder coated with an organic phase through spray drying; then, large-size thick-wall ceramic blanks are obtained through cold isostatic pressing; the blanks are heated in a glue-removing furnace; the decomposition characteristics of a latent catalyst are utilized; the first-order time derivative of the ammonia concentration in tail gas is monitored in real time; the heating state of the furnace body and the tail gas pneumatic butterfly valve are closed-loop controlled according to the first-order time derivative; in-situ cross-linking and solidification are completed; finally, the finished product is obtained through resin pyrolysis and pressureless solid-phase sintering. The application relieves the problems of gas accumulation and thermal stress during cross-linking and solidification of the thick-wall blanks, reduces the blank cracking probability, and improves the density and size stability of the ceramic product.

Description

Technical Field

[0001] This invention relates to the field of special ceramics preparation technology, specifically a method for preparing a composite isostatic pressure ceramic barrel using multi-particle-size high-purity silicon carbide powder. Background Technology

[0002] Silicon carbide ceramics are widely used in semiconductor manufacturing, chemical equipment and other fields due to their excellent mechanical properties, corrosion resistance and thermal stability. The industrial demand for large-size thick-walled silicon carbide ceramic barrels is increasing. At present, cold isostatic pressing is a common process for preparing such large-size components. In actual production, it is usually necessary to add organic binders or carbon source precursors to silicon carbide powder to assist powder forming and give the green body the necessary mechanical strength.

[0003] However, with the increase in the thickness of ceramic barrel walls and the enlargement of size, the existing molding and cross-linking debinding processes have revealed obvious technical limitations. In the molding stage, conventional powder gradation often fails to achieve extremely high density packing, resulting in more pores inside the green body. This directly increases the volume shrinkage rate during sintering, making it difficult to control the dimensional accuracy of large-sized products. A more prominent problem occurs in the heating, curing, and debinding stages of the green body. When the organic phase inside the green body undergoes cross-linking and polycondensation reactions under heat, it is usually accompanied by significant exothermic phenomena. Due to the long heat transfer path of thick-walled green bodies and the limited thermal conductivity of ceramic powder at low temperatures, the heat generated inside is difficult to dissipate quickly to the outside, easily leading to a higher temperature in the central region of the green body than the surface. This local temperature rise, in turn, accelerates the cross-linking reaction of the organic phase, causing it to release a large amount of water vapor and other small molecule byproducts in a short period of time.

[0004] Due to the obstruction of the thick-walled structure, these gaseous byproducts cannot diffuse to the outside through the dense powder gaps in time, thus forming a high local gas pressure inside the green blank. The expansion force generated by the gas accumulation and the thermal stress caused by the cross-linking reaction are superimposed, which can easily induce microcracks inside the green blank. In severe cases, it can lead to macroscopic delamination or expansion cracking of the entire component, resulting in scrap. Traditional solutions often rely on setting extremely slow fixed heating curves or relying on experience to extend the holding time. However, this static open-loop control method cannot detect the intensity of real-time chemical reactions inside the green blank. When local thermal runaway occurs, it cannot actively intervene. This not only significantly extends the production cycle, but also has limited effectiveness in completely solving the cracking problem of large-size thick-walled components. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing a composite isostatic pressure ceramic barrel using multi-particle-size high-purity silicon carbide powder, which solves the problem that existing large-size, thick-walled silicon carbide ceramic blanks are prone to cracking due to internal heat release and gas accumulation during molding and cross-linking curing.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a composite isostatic pressure ceramic barrel using multi-particle-size high-purity silicon carbide powder, the method comprising the following steps: Multi-size silicon carbide powder, boron carbide, tannic acid and deionized water are added to a lined stirred ball mill and wet milling is carried out under controlled temperature to obtain a dispersion slurry. The dispersion slurry was cooled, and fructose, polyethylene glycol and ammonium p-toluenesulfonate were added sequentially under continuous stirring. The mixture was then homogenized and stirred, and filtered to obtain the precursor slurry. The precursor slurry is fed into a centrifugal spray drying tower, where water is flashed in a hot air medium, and the spherical granulated powder with an amorphous organic phase coated on the surface is collected and screened. The spherical granulated powder with an amorphous organic phase on its surface is filled into a flexible mold, placed in a cold isostatic press and pressed, and then the pressure is released and the mold is demolded to obtain a large-sized thick-walled ceramic blank. The large-sized thick-walled ceramic blank is placed in a debinding furnace for heating. The ammonia concentration in the exhaust gas of the debinding furnace is monitored in real time by an online analyzer. The first time derivative of the ammonia concentration is calculated. Based on the first time derivative, the heating state of the debinding furnace and the pneumatic butterfly valve of the exhaust gas pipeline are controlled in a closed loop by a programmable logic controller until the in-situ crosslinking is completed, and a cured blank is obtained. The solidified green blank is heated and kept at a high temperature to complete resin pyrolysis, and then transferred to a sintering furnace for pressureless solid-phase sintering. After cooling, a multi-particle-size high-purity silicon carbide powder composite isostatic ceramic bucket is obtained.

[0007] By adopting the above technical solution, this invention improves the forming and curing process of large-size thick-walled ceramics based on the inorganic powder stacking principle and the in-situ chemical crosslinking mechanism of organic phase. Specifically, in the slurry preparation stage, the polyphenolic hydroxyl groups in the tannic acid molecular structure tend to form hydrogen bonds with the hydroxyl groups on the surface of silicon carbide particles, which reduces the surface energy of the powder to a certain extent, enabling multi-size powders to be dispersed in the aqueous medium by means of steric hindrance.

[0008] The fructose introduced into the system serves as an amorphous carbon source precursor. Combined with polyethylene glycol plasticizer and ammonium p-toluenesulfonate, a latent acid catalyst, it is miscible and relatively stable at low temperatures. In the subsequent spray flash drying stage, the outward capillary force generated by the rapid vaporization of water promotes the precipitation of fructose, polyethylene glycol, and ammonium p-toluenesulfonate, forming a coating layer on the surface of silicon carbide particles, resulting in spherical granulated powder with a certain degree of flowability.

[0009] When entering the cold isostatic pressing process, the high pressure transmission causes the surface-coated organic phase to undergo plastic deformation, filling the gaps between particles. Multi-sized powders thus achieve high-density packing. During the subsequent heating and debinding process, the latent catalyst ammonium toluenesulfonate decomposes upon heating. The decomposition product, p-toluenesulfonic acid, lowers the local pH value of the system.

[0010] In this acidic environment, fructose molecules dehydrate to form hydroxymethylfurfural, which then undergoes condensation and crosslinking to form a polymeric resin phase with a three-dimensional network structure, anchoring the free silicon carbide particles in situ. Considering that this crosslinking process is an exothermic reaction accompanied by the release of water vapor, there is a risk of accumulated thermal stress and microcracks inside the thick-walled blank.

[0011] Given that the release rate of ammonia, a byproduct of the above decomposition reaction, is roughly stoichiometrically related to the crosslinking reaction rate, this application indirectly assesses the crosslinking process inside the green blank by monitoring the first time derivative of the ammonia concentration in the tail gas. Based on this derivative, closed-loop control of the furnace temperature and pressure can limit the crosslinking reaction rate, assist in the discharge of residual gas inside, and thus reduce the probability of cracking of thick-walled green blanks during the curing stage.

[0012] During the high-temperature processing stage, the resin phase generated in situ is decomposed and transformed into highly active amorphous carbon under argon protection. When the temperature rises above 2100℃, the added boron carbide, together with the amorphous carbon, participates in the reduction of the oxide film on the surface of silicon carbide. This helps to reduce the grain boundary energy and promotes solid-phase volume diffusion of silicon carbide particles to complete the densification sintering.

[0013] Preferably, the multi-particle-size silicon carbide powder comprises coarse silicon carbide powder, medium silicon carbide powder, and fine silicon carbide powder, wherein the median particle size distribution D50 of the coarse silicon carbide powder is 45-55 μm, the median particle size distribution D50 of the medium silicon carbide powder is 8-12 μm, and the median particle size distribution D50 of the fine silicon carbide powder is 0.3-0.6 μm.

[0014] By adopting the above technical solution, and setting the median of the three powder particle sizes according to the Apollonius gasket packing theory, fine powder can more easily enter the pores created by the packing of medium powder, while medium powder fills the gaps between coarse powder.

[0015] This three-peaked particle size distribution system is beneficial for increasing the relative density of the green body after cold isostatic pressing, compressing the free space between particles, and thus reducing the volume shrinkage during the sintering stage to a certain extent, maintaining the dimensional stability of large-size ceramic barrels.

[0016] Preferably, in the steps of preparing the dispersion slurry and the precursor slurry, the addition ratio of each raw material is as follows: 55-65 parts by weight of coarse silicon carbide powder, 25-35 parts by weight of medium silicon carbide powder, 10 parts by weight of fine silicon carbide powder, 0.4-0.8 parts by weight of boron carbide, 1.5-2.5 parts by weight of tannic acid, 35-45 parts by weight of deionized water, 3.0-5.0 parts by weight of fructose, 1.0-2.0 parts by weight of polyethylene glycol, and 0.1-0.3 parts by weight of ammonium p-toluenesulfonate.

[0017] By adopting the above technical solution, the ratio of fructose to ammonium p-toluenesulfonate in the system usually affects the network structure density of the cross-linked resin and the amount of residual carbon after final pyrolysis. When the amount added is too high, carbon-rich phase is easily retained at the grain boundaries, which usually has an adverse effect on the overall density of the ceramic tank. Controlling the amount of ammonium p-toluenesulfonate to 0.1-0.3 parts by weight can provide a more suitable hydrogen ion concentration and guide the cross-linking reaction to proceed relatively smoothly within the preset temperature range.

[0018] Preferably, the step of controlling the temperature for wet grinding includes: adding 250-300 parts by weight of high-purity silicon carbide grinding balls to a stirred ball mill with a polyurethane liner, controlling the cooling water circulation to maintain the slurry temperature at 20-30°C, and performing wet grinding at a speed of 150-250 rpm for 4-6 hours.

[0019] By adopting the above technical solution, using silicon carbide grinding balls of the same material can reduce the mixing of foreign metal impurities and control the grinding temperature in the range of 20-30℃. The main purpose is to alleviate the oxidative degradation of tannic acid under continuous mechanical shearing and heat generation, thereby maintaining the structural stability and suitable rheological properties of the dispersion slurry.

[0020] Preferably, the step of obtaining the precursor slurry includes: forcibly lowering the temperature of the dispersion slurry to 15-22°C, adding fructose, polyethylene glycol and ammonium p-toluenesulfonate under continuous stirring at 30-60 rpm, continuing low-speed homogenization stirring for 30-60 minutes, and filtering to obtain the precursor slurry.

[0021] By adopting the above technical solution, the system is forcibly cooled to below 22°C before the introduction of ammonium p-toluenesulfonate, which can suppress the tendency of the catalyst to dissociate trace amounts of water in the aqueous environment and reduce the probability of the slurry's rheological properties deteriorating due to unintended crosslinking before entering the granulation tower. At the same time, the relatively low stirring speed helps to reduce the mechanical shear damage to the large molecular polyethylene glycol segments and retain their plasticizing function in subsequent compression molding.

[0022] Preferably, the step of feeding the precursor slurry into a centrifugal spray drying tower, flash evaporating moisture in a hot air medium, and collecting and sieving to obtain spherical granulated powder with an amorphous organic phase on the surface includes: feeding the precursor slurry into a centrifugal spray drying tower by a diaphragm pump, introducing hot air as the drying medium, setting the inlet air temperature to 180-210℃, the outlet air temperature to 80-95℃, and the atomizing disc rotation speed to 8000-12000 rpm, collecting the granulated powder during the moisture flash evaporation process, and sieving to obtain spherical granulated powder with an amorphous organic phase on the surface and a particle size between 80-150 μm.

[0023] By adopting the above technical solution, after the micron-sized droplets formed by centrifugal atomization enter the hot air environment at 180-210℃, the surface moisture of the droplets rapidly undergoes flash vaporization. The material migration accompanying this vaporization process drives components such as fructose and polyethylene glycol to accumulate on the outer layer of silicon carbide particles. Controlling the outlet air temperature at 80-95℃, which is usually below the threshold for severe fructose cross-linking, helps to preserve the amorphous state of the organic phase, enabling it to provide the necessary lubrication and physical bonding in subsequent molding steps.

[0024] Preferably, the step of filling the spherical granulated powder with the amorphous organic phase on the surface into a flexible mold, placing it in a cold isostatic press for pressing and molding, and then releasing the pressure to obtain a large-size thick-walled ceramic blank includes: filling the spherical granulated powder with the amorphous organic phase on the surface into a cylindrical polyurethane flexible mold, vibrating and compacting it, sealing it, placing it in a cold isostatic press, pressing it to 150-200MPa at a pressurization rate of 2-5MPa / min, holding the pressure for 5-15 minutes, and slowly releasing the pressure to obtain a large-size thick-walled ceramic blank.

[0025] By adopting the above technical solution, the set pressurization rate of 2-5 MPa / min provides a time window for the residual gas in the granulated powder to escape outward, reducing the probability of the formation of closed pores inside the thick wall. Under the high pressure of 150-200 MPa, the granulated powder particles undergo displacement and local plastic rheology, forming a relatively tight physical interlocking structure. The slow pressure relief operation performed after molding suppresses the rebound amplitude of the mold and the stress release rate inside the powder.

[0026] Preferably, the step of obtaining the cured green body includes: placing the large-sized thick-walled ceramic green body in a debinding furnace, raising it from room temperature to 80°C, and then raising it to the range of 130-140°C at a rate of 0.2-0.5°C / min; When the temperature rises above 110℃, the programmable logic controller (PLC) calculates the first time derivative of the ammonia concentration in real time: if the first time derivative of the ammonia concentration is less than 15 ppm / min, the degassing furnace maintains the heating rate of 0.2-0.5℃ / min; if the first time derivative of the ammonia concentration is greater than or equal to 15 ppm / min and less than or equal to 35 ppm / min, the PLC triggers the degassing furnace to stop heating and enter a constant temperature state, and at the same time starts the pulse exhaust program, opening the pneumatic butterfly valve 100% for 20-40 seconds every 2-3 minutes to create a negative pressure in the furnace chamber and then restore a slightly positive pressure.

[0027] By adopting the above technical solution, when the furnace temperature rise triggers catalyst decomposition and in-situ crosslinking, if the first time derivative of ammonia concentration is in the range of 15-35 ppm / min, it usually means that the amount of condensation water vapor and ammonia released by crosslinking inside the green blank is approaching the gas permeation load of the material itself. At this time, pausing the heating aims to reduce the continuous input of external heat, while the periodic full opening operation of the pneumatic butterfly valve can induce a small-amplitude alternating airflow pulsation in the furnace cavity, which helps the internal gas to diffuse to the surface and alleviates the local expansion and cracking that is easily caused by the accumulation of volatiles in the micropores.

[0028] Preferably, the step of obtaining the cured green blank further includes: Under the constant temperature pulse exhaust state, when the first time derivative of the ammonia concentration is below 10 ppm / min for 5 consecutive minutes, the programmable logic controller stops the pulse exhaust program and resumes the heating rate of 0.2-0.5℃ / min. If the first time derivative of the ammonia concentration is greater than 35 ppm / min, the programmable logic controller triggers an alarm, cuts off the heating element, and turns on the furnace circulation fan to introduce room temperature cold air at a speed of 3-5 m / s for forced cooling until the first time derivative of the ammonia concentration drops below 10 ppm / min, then the heating rate of 0.2-0.5℃ / min is restored. When the furnace temperature reaches 130-140℃ and the absolute concentration of ammonia in the exhaust gas is below 30ppm for 30 consecutive minutes, the in-situ crosslinking is considered complete, and a cured green body is obtained.

[0029] If the first time derivative exceeds 35 ppm / min by adopting the above technical solution, it indicates that the dehydration and polycondensation reaction inside the system has entered a self-accelerating stage where the exothermic reaction is greater than the heat dissipation reaction. The core of the green body is facing a rapid temperature rise. Due to the high thermal inertia of thick-walled ceramics, simply cutting off the heating element often makes it difficult to quickly suppress the reaction trend.

[0030] By introducing room temperature cold air to form forced convection, the surface temperature of the green blank can be lowered relatively quickly, establishing a temperature gradient that is high inside and low outside. This suppresses the intensity of the internal cross-linking reaction. When the ammonia concentration returns to and stabilizes at a low value, it can be inferred that the network cross-linking of the organic precursor has been basically formed. At this point, the green blank has acquired the basic mechanical strength to withstand subsequent high-temperature treatment.

[0031] Preferably, the step of subjecting the cured green blank to a heating and heat-holding treatment to complete resin pyrolysis, then transferring it to a sintering furnace for pressureless solid-phase sintering, and finally cooling to obtain a multi-particle-size high-purity silicon carbide powder composite isostatic pressing ceramic bucket includes: The closed-loop control system is deactivated, and the solidified preform is heated from 130-140℃ to 600-650℃ at a rate of 1.0-2.0℃ / min under an argon atmosphere, and held at that temperature for 1-3 hours to complete resin pyrolysis. Then it is transferred to a graphite tube sintering furnace, and heated to 2100-2150℃ at a rate of 5-10℃ / min under an argon atmosphere or a vacuum degree <10Pa, and held at that temperature for 1-2 hours to carry out pressureless solid-state sintering. The preform is then naturally cooled to room temperature with the furnace to obtain a multi-particle-size high-purity silicon carbide powder composite isostatic ceramic barrel.

[0032] By adopting the above technical solution, during the slow heating stage of 1.0-2.0℃ / min, the pyrolysis chain breaking of the resin skeleton and the release of small molecule gases are relatively gradual, so as to avoid the problem of loosening of the green body structure caused by instantaneous gas impact. Subsequently, during the high-temperature treatment stage at 2100-2150℃, free carbon participates in the carbothermic reduction reaction to clean the grain boundaries. The exposed highly active silicon carbide crystal surfaces undergo mass transport and grain boundary interconnection under the drive of surface energy, which promotes the closure of micro-voids and overall shrinkage, thereby obtaining a densified multi-particle-size composite silicon carbide ceramic component.

[0033] This invention provides a method for preparing a composite isostatically pressed ceramic barrel using high-purity silicon carbide powder with multiple particle sizes. It has the following beneficial effects: 1. This invention utilizes a three-peak particle size distribution system of coarse, medium and fine silicon carbide powder, combined with cold isostatic pressing, to improve the initial packing density of ceramic green bodies. The multi-size powder fills each other under pressure, reducing the void volume between particles. This not only limits the density gradient during the forming process, but also reduces the overall volume shrinkage rate during subsequent high-temperature sintering, which helps maintain the dimensional stability of large-size thick-walled ceramic components and improves the density after sintering.

[0034] 2. This invention introduces an organic coating system composed of fructose, polyethylene glycol, and ammonium p-toluenesulfonate, which takes into account the process requirements of powder forming and subsequent sintering. The system precipitates coating during the spray granulation stage, providing the powder with the plastic deformation capacity required for compression molding; in the early stage of heating, it crosslinks into a network resin through acid catalysis in situ dehydration, giving the thick-walled blank the mechanical strength required for demolding and handling; and in the high-temperature stage, it decomposes in situ into uniformly distributed amorphous carbon, which participates in the reduction of the oxide film on the surface of silicon carbide, promoting the pressureless solid-phase sintering.

[0035] 3. This invention establishes a closed-loop control mechanism for adhesive removal based on ammonia release rate to address the thermal stress problem during the crosslinking and curing of thick-walled green blanks. Since the ammonia rate generated by the decomposition of the latent catalyst is stoichiometrically related to the intensity of exothermic crosslinking inside the green blank, by calculating the first time derivative of the ammonia concentration in real time and coordinating the temperature rise and fall of the furnace body and the pulse opening and closing of the tail gas valve, it can actively intervene in the heat conduction and gas diffusion process when the crosslinking reaction is too fast, alleviate the accumulation of volatiles such as water vapor inside the material, and reduce the probability of expansion cracking of large-size ceramic green blanks during the curing stage. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the infrared spectral test results of the initial green blank and the cured green blank of the present invention; Figure 2 This is a schematic diagram of the thermogravimetric-differential thermal-mass spectrometry (TGA) analysis curves of the green body during the heating and curing process of the present invention, wherein, Figure 2 Part a of the diagram shows the curve of thermogravimetric residual mass changing with temperature. Figure 2 Part b is a schematic diagram of the DSC heat flow rate versus temperature curve. Figure 2 Part c is a schematic diagram of the curve of ion current intensity of gas phase product mass spectrometry as a function of temperature; Figure 3 This is a schematic diagram showing the apparent viscosity stability of the precursor slurry and the compressive stress-strain test results of the granulated powder of the present invention. Figure 3 Part a is a schematic diagram of the apparent viscosity of the precursor slurry as a function of standing time. Figure 3 Part b is a schematic diagram of the stress-strain curve during the granulation powder compression molding process; Figure 4 This is a schematic diagram comparing the physical and mechanical properties of silicon carbide ceramics after sintering in various embodiments and comparative examples of the present invention. Figure 4 Part a of the diagram shows a comparison of the bulk density and apparent porosity distribution of each group of sintered bodies. Figure 4 Part b is a schematic diagram comparing the room temperature flexural strength distribution of each group of sintered bodies. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0039] The silicon carbide used is commercially available micro powder with a purity of ≥99.5wt%, CAS number 409-21-2. This powder is compounded from coarse powder, medium powder and fine powder in a set mass ratio. In this invention, the median particle size distribution D50 of the coarse powder is 45-55μm, the median particle size distribution D50 of the medium powder is 8-12μm, and the median particle size distribution D50 of the fine powder is 0.3-0.8μm.

[0040] Boron carbide is a commercially available ultrafine powder with a purity of ≥99.0wt%, CAS number 12069-32-8, and its median particle size distribution D50 is controlled to be ≤1.0μm. In this invention, it is used as a solid-phase pressureless sintering aid.

[0041] The tannic acid used is a commercially available product with a purity of ≥95wt%, CAS number 1401-55-4. In this invention, it is used as a dispersant for the aqueous multi-particle-size system and a precursor monomer for the in-situ crosslinking polycondensation reaction.

[0042] D-fructose, using a commercially available solid crystalline product with a purity ≥98wt% and CAS number 57-48-7, is used in this invention as a non-volatile carbon source monomer for the in-situ generation of 5-hydroxymethylfurfural precursor in the latent reaction system inside ceramic forming.

[0043] Ammonium p-toluenesulfonate is a commercially available product with a purity of ≥98wt%, CAS number 4124-42-9. Its pH value of a 10wt% aqueous solution at 20℃ is 6.0-7.0. It undergoes thermal decomposition and releases ammonia gas when heated to above 110℃. In this invention, it serves as a latent catalyst for triggering the in-situ dehydration polycondensation crosslinking system and a concentration characteristic gas release probe.

[0044] Polyethylene glycol 400, a commercially available product with CAS number 25322-68-3, is used in this invention as a plasticizer to improve the toughness of amorphous syrup films.

[0045] Examples 1-5: Example 1: This embodiment provides a method for preparing a composite isostatic pressure ceramic barrel using multi-particle-size high-purity silicon carbide powder, including the following steps: S1. Add 60 parts by weight of coarse silicon carbide powder with a median particle size distribution of 50 μm, 30 parts by weight of medium silicon carbide powder with a median particle size distribution of 10 μm, 10 parts by weight of fine silicon carbide powder with a median particle size distribution of 0.5 μm, 0.6 parts by weight of boron carbide, 2.0 parts by weight of tannic acid, and 40 parts by weight of deionized water to a stirred ball mill with a polyurethane liner. Add 280 parts by weight of high-purity silicon carbide grinding balls, control the cooling water circulation to keep the slurry temperature at 25°C, and perform wet grinding at 200 rpm for 5 hours to obtain a dispersed slurry. S2. Adjust the jacket cooling water to force the temperature of the above dispersion slurry to drop to 20°C. Under continuous stirring at 45 rpm, add 4.0 parts by weight of fructose, 1.5 parts by weight of polyethylene glycol and 0.2 parts by weight of ammonium p-toluenesulfonate in sequence. Continue to homogenize and stir at low speed for 45 minutes. Filter to separate the high-purity silicon carbide grinding balls to obtain the precursor slurry. S3. The above precursor slurry is pumped into a centrifugal spray drying tower by a diaphragm pump. Hot air is introduced as the drying medium. The inlet air temperature is set to 195°C, the outlet air temperature is set to 85°C, and the atomizing disc speed is set to 10000 rpm. During the flash evaporation of water, the granulated powder is collected and sieved to obtain spherical granulated powder with a surface coated with an amorphous organic phase and a particle size between 80-150 μm. S4. The spherical granulated powder with the amorphous organic phase on the surface is filled into a cylindrical polyurethane flexible mold, vibrated and compacted, then sealed and placed in a cold isostatic press. The pressure is increased to 180MPa at a rate of 3MPa / min, and the pressure is held for 10 minutes. The pressure is then slowly released and the mold is demolded to obtain a large-size thick-walled ceramic blank. S5. Place the above-mentioned large-size thick-walled ceramic blank in a glue removal furnace. The exhaust gas pipeline of the glue removal furnace is equipped with a pneumatic butterfly valve and an online ammonia concentration analyzer. The end of the exhaust gas pipeline is connected to a variable frequency induced draft device to form a short-term negative pressure exhaust state when the pneumatic butterfly valve is opened. The sensor data is connected to the programmable logic controller. After the temperature rises from room temperature to 80°C, the temperature is increased to the 135°C range at a rate of 0.3°C / min. When the temperature rises above 110℃, the programmable logic controller calculates the first time derivative of the ammonia concentration in real time. If the first time derivative of the ammonia concentration is less than 15ppm / min, the debinding furnace maintains a heating rate of 0.3℃ / min. If the first time derivative of the ammonia concentration is greater than or equal to 15 ppm / min and less than or equal to 35 ppm / min, the programmable logic controller triggers the degassing furnace to stop heating and enter a constant temperature state. At the same time, the pulse exhaust program is started, and the pneumatic butterfly valve is fully opened to 100% for 30 seconds every 2 minutes, so that a negative pressure is formed in the furnace and then restored to a slightly positive pressure. Under constant temperature pulse exhaust mode, when the first time derivative of ammonia concentration is below 10 ppm / min for 5 consecutive minutes, the programmable logic controller (PLC) stops the pulse exhaust program and resumes the heating rate of 0.3℃ / min; if the first time derivative of ammonia concentration is greater than 35 ppm / min, the PLC triggers an alarm, cuts off the heating element, and turns on the furnace circulation fan to introduce room temperature cold air at a speed of 4 m / s for forced cooling until the first time derivative of ammonia concentration drops below 10 ppm / min, then resumes the heating rate of 0.3℃ / min. When the furnace temperature reaches 135℃ and the absolute concentration of ammonia in the tail gas is below 30ppm for 30 minutes, the in-situ crosslinking is considered complete, and a cured green body is obtained. S6. Deactivate the closed-loop control system and, under an argon atmosphere, heat the solidified preform from 135°C to 620°C at a rate of 1.5°C / min, and hold for 2 hours to complete resin pyrolysis. Then transfer it to a graphite tube sintering furnace and heat it to 2120°C at a rate of 8°C / min under an argon atmosphere, hold for 1.5 hours for pressureless solid-state sintering, and allow it to cool naturally to room temperature with the furnace to obtain a multi-particle-size high-purity silicon carbide powder composite isostatic ceramic bucket.

[0046] Example 2: This embodiment provides a method for preparing a composite isostatic pressure ceramic barrel using multi-particle-size high-purity silicon carbide powder, including the following steps: S1. Add 55 parts by weight of coarse silicon carbide powder with a median particle size distribution of 45 μm, 35 parts by weight of medium silicon carbide powder with a median particle size distribution of 8 μm, 10 parts by weight of fine silicon carbide powder with a median particle size distribution of 0.3 μm, 0.4 parts by weight of boron carbide, 1.5 parts by weight of tannic acid, and 35 parts by weight of deionized water to a stirred ball mill with a polyurethane liner. Add 250 parts by weight of high-purity silicon carbide grinding balls, control the cooling water circulation to keep the slurry temperature at 20°C, and perform wet grinding at 150 rpm for 4 hours to obtain a dispersed slurry. S2. Adjust the jacket cooling water to force the temperature of the above dispersion slurry to drop to 15°C. Under continuous stirring at 30 rpm, add 3.0 parts by weight of fructose, 1.0 parts by weight of polyethylene glycol and 0.1 parts by weight of ammonium p-toluenesulfonate in sequence. Continue to homogenize and stir at low speed for 30 minutes. Filter to separate the high-purity silicon carbide grinding balls to obtain the precursor slurry. S3. The above precursor slurry is pumped into a centrifugal spray drying tower by a diaphragm pump. Hot air is introduced as the drying medium. The inlet air temperature is set to 180°C, the outlet air temperature is set to 80°C, and the atomizing disc speed is set to 8000 rpm. During the flash evaporation of water, the granulated powder is collected and sieved to obtain spherical granulated powder with a surface coated with an amorphous organic phase and a particle size between 80-150 μm. S4. The spherical granulated powder with the amorphous organic phase on the surface is filled into a cylindrical polyurethane flexible mold, vibrated and compacted, then sealed and placed in a cold isostatic press. The pressure is increased to 150 MPa at a pressurization rate of 2 MPa / min, and the pressure is held for 5 minutes. The pressure is then slowly released and the mold is demolded to obtain a large-size thick-walled ceramic blank. S5. Place the above-mentioned large-size thick-walled ceramic blank in a debinding furnace. The exhaust gas pipeline of the debinding furnace is equipped with a pneumatic butterfly valve and an online ammonia concentration analyzer. The end of the exhaust gas pipeline is connected to a variable frequency induced draft device to form a short-term negative pressure exhaust state when the pneumatic butterfly valve is opened. The sensor data is connected to the programmable logic controller. After the temperature rises from room temperature to 80°C, the temperature is increased to the 130°C range at a rate of 0.2°C / min. When the temperature rises above 110℃, the programmable logic controller calculates the first time derivative of the ammonia concentration in real time. If the first time derivative of the ammonia concentration is less than 15ppm / min, the debinding furnace maintains a heating rate of 0.2℃ / min. If the first time derivative of the ammonia concentration is greater than or equal to 15 ppm / min and less than or equal to 35 ppm / min, the programmable logic controller triggers the glue removal furnace to stop heating and enter a constant temperature state. At the same time, the pulse exhaust program is started, and the pneumatic butterfly valve is fully opened to 100% for 20 seconds every 3 minutes, so that a negative pressure is formed in the furnace and then restored to a slightly positive pressure. Under constant temperature pulse exhaust mode, when the first time derivative of ammonia concentration is below 10 ppm / min for 5 consecutive minutes, the programmable logic controller (PLC) stops the pulse exhaust program and resumes the heating rate of 0.2℃ / min; if the first time derivative of ammonia concentration is greater than 35 ppm / min, the PLC triggers an alarm, cuts off the heating element, and turns on the furnace circulation fan to introduce room temperature cold air at a speed of 3 m / s for forced cooling until the first time derivative of ammonia concentration drops below 10 ppm / min, then resumes the heating rate of 0.2℃ / min. When the furnace temperature reaches 130℃ and the absolute concentration of ammonia in the tail gas is below 30ppm for 30 minutes, the in-situ crosslinking is considered complete, and a cured green body is obtained. S6. Deactivate the closed-loop control system and, under an argon atmosphere, heat the solidified preform from 130°C to 600°C at a rate of 1.0°C / min, and hold for 1 hour to complete resin pyrolysis. Then, transfer it to a graphite tube sintering furnace and heat it to 2100°C at a rate of 5°C / min under a vacuum of <10Pa, hold for 1 hour for pressureless solid-phase sintering, and allow it to cool naturally to room temperature with the furnace to obtain a multi-particle-size high-purity silicon carbide powder composite isostatic ceramic bucket.

[0047] Example 3: This embodiment provides a method for preparing a composite isostatic pressure ceramic barrel using multi-particle-size high-purity silicon carbide powder, including the following steps: S1. Add 65 parts by weight of coarse silicon carbide powder with a median particle size distribution of 55 μm, 25 parts by weight of medium silicon carbide powder with a median particle size distribution of 12 μm, 10 parts by weight of fine silicon carbide powder with a median particle size distribution of 0.8 μm, 0.8 parts by weight of boron carbide, 2.5 parts by weight of tannic acid, and 45 parts by weight of deionized water to a stirred ball mill with a polyurethane liner. Add 300 parts by weight of high-purity silicon carbide grinding balls, control the cooling water circulation to keep the slurry temperature at 30°C, and perform wet grinding at 250 rpm for 6 hours to obtain a dispersed slurry. S2. Adjust the jacket cooling water to force the temperature of the above dispersion slurry to drop to 22°C. Under continuous stirring at 60 rpm, add 5.0 parts by weight of fructose, 2.0 parts by weight of polyethylene glycol and 0.3 parts by weight of ammonium p-toluenesulfonate in sequence. Continue to homogenize and stir at low speed for 60 minutes. Filter to separate the high-purity silicon carbide grinding balls to obtain the precursor slurry. S3. The above precursor slurry is pumped into a centrifugal spray drying tower by a diaphragm pump. Hot air is introduced as the drying medium. The inlet air temperature is set to 210°C, the outlet air temperature is set to 95°C, and the atomizing disc speed is set to 12000 rpm. During the flash evaporation of water, the granulated powder is collected and sieved to obtain spherical granulated powder with a surface coated with an amorphous organic phase and a particle size between 80-150 μm. S4. The spherical granulated powder with the amorphous organic phase on the surface is filled into a cylindrical polyurethane flexible mold, vibrated and compacted, then sealed and placed in a cold isostatic press. The pressure is increased to 200 MPa at a pressurization rate of 5 MPa / min, and the pressure is held for 15 minutes. The pressure is then slowly released and the mold is demolded to obtain a large-size thick-walled ceramic blank. S5. Place the above-mentioned large-size thick-walled ceramic blank in a glue removal furnace. The exhaust gas pipeline of the glue removal furnace is equipped with a pneumatic butterfly valve and an online ammonia concentration analyzer. The end of the exhaust gas pipeline is connected to a variable frequency induced draft device to form a short-term negative pressure exhaust state when the pneumatic butterfly valve is opened. The sensor data is connected to the programmable logic controller. After the temperature rises from room temperature to 80°C, the temperature is increased to the 140°C range at a rate of 0.5°C / min. When the temperature rises above 110℃, the programmable logic controller calculates the first time derivative of the ammonia concentration in real time. If the first time derivative of the ammonia concentration is less than 15ppm / min, the debinding furnace maintains a heating rate of 0.5℃ / min. If the first time derivative of the ammonia concentration is greater than or equal to 15 ppm / min and less than or equal to 35 ppm / min, the programmable logic controller triggers the degassing furnace to stop heating and enter a constant temperature state. At the same time, the pulse exhaust program is started, and the pneumatic butterfly valve is fully opened to 100% for 40 seconds every 2 minutes, so that a negative pressure is formed in the furnace and then restored to a slightly positive pressure. Under constant temperature pulse exhaust mode, when the first time derivative of ammonia concentration is below 10 ppm / min for 5 consecutive minutes, the programmable logic controller (PLC) stops the pulse exhaust program and resumes the heating rate of 0.5℃ / min; if the first time derivative of ammonia concentration is greater than 35 ppm / min, the PLC triggers an alarm, cuts off the heating element, and turns on the furnace circulation fan to introduce room temperature cold air at a speed of 5 m / s for forced cooling until the first time derivative of ammonia concentration drops below 10 ppm / min, then resumes the heating rate of 0.5℃ / min. When the furnace temperature reaches 140℃ and the absolute concentration of ammonia in the tail gas is below 30ppm for 30 minutes, the in-situ crosslinking is considered complete, and a cured green body is obtained. S6. Deactivate the closed-loop control system and, under an argon atmosphere, heat the solidified preform from 140°C to 650°C at a rate of 2.0°C / min, and hold for 3 hours to complete resin pyrolysis. Then, transfer it to a graphite tube sintering furnace and heat it to 2150°C at a rate of 10°C / min under a vacuum of <10Pa, hold for 2 hours for pressureless solid-state sintering, and allow it to cool naturally to room temperature with the furnace to obtain a multi-particle-size high-purity silicon carbide powder composite isostatic ceramic bucket.

[0048] Example 4: This embodiment provides a method for preparing a composite isostatic pressure ceramic barrel using multi-particle-size high-purity silicon carbide powder, including the following steps: S1. Add 58 parts by weight of coarse silicon carbide powder with a median particle size distribution of 52 μm, 32 parts by weight of medium silicon carbide powder with a median particle size distribution of 9 μm, 10 parts by weight of fine silicon carbide powder with a median particle size distribution of 0.4 μm, 0.5 parts by weight of boron carbide, 1.8 parts by weight of tannic acid, and 38 parts by weight of deionized water to a stirred ball mill with a polyurethane liner. Add 260 parts by weight of high-purity silicon carbide grinding balls, control the cooling water circulation to keep the slurry temperature at 22℃, and perform wet grinding at a speed of 180 rpm for 4.5 hours to obtain a dispersed slurry. S2. Adjust the jacket cooling water to force the temperature of the above dispersion slurry to drop to 18°C. Under continuous stirring at 40 rpm, add 3.5 parts by weight of fructose, 1.2 parts by weight of polyethylene glycol and 0.15 parts by weight of ammonium p-toluenesulfonate in sequence. Continue to homogenize and stir at low speed for 40 minutes. Filter to separate the high-purity silicon carbide grinding balls to obtain the precursor slurry. S3. The above precursor slurry is pumped into a centrifugal spray drying tower by a diaphragm pump. Hot air is introduced as the drying medium. The inlet air temperature is set to 190°C, the outlet air temperature is set to 88°C, and the atomizing disc speed is set to 9000 rpm. During the flash evaporation of water, the granulated powder is collected and sieved to obtain spherical granulated powder with a surface coated with an amorphous organic phase and a particle size between 80-150 μm. S4. The spherical granulated powder with the amorphous organic phase on the surface is filled into a cylindrical polyurethane flexible mold, vibrated and compacted, then sealed and placed in a cold isostatic press. The pressure is increased to 160 MPa at a rate of 4 MPa / min, and the pressure is held for 8 minutes. The pressure is then slowly released and the mold is demolded to obtain a large-size thick-walled ceramic blank. S5. Place the above-mentioned large-size thick-walled ceramic blank in a glue removal furnace. The exhaust gas pipeline of the glue removal furnace is equipped with a pneumatic butterfly valve and an online ammonia concentration analyzer. The end of the exhaust gas pipeline is connected to a variable frequency induced draft device to form a short-term negative pressure exhaust state when the pneumatic butterfly valve is opened. The sensor data is connected to the programmable logic controller. After the temperature rises from room temperature to 80°C, the temperature is increased to the 132°C range at a rate of 0.4°C / min. When the temperature rises above 110℃, the programmable logic controller calculates the first time derivative of the ammonia concentration in real time. If the first time derivative of the ammonia concentration is less than 15ppm / min, the debinding furnace maintains a heating rate of 0.4℃ / min. If the first time derivative of the ammonia concentration is greater than or equal to 15 ppm / min and less than or equal to 35 ppm / min, the programmable logic controller triggers the degassing furnace to stop heating and enter a constant temperature state. At the same time, the pulse exhaust program is started, and the pneumatic butterfly valve is fully opened to 100% for 25 seconds every 2.5 minutes to create a negative pressure in the furnace and then restore a slight positive pressure. Under constant temperature pulse exhaust mode, when the first time derivative of ammonia concentration is below 10 ppm / min for 5 consecutive minutes, the programmable logic controller (PLC) stops the pulse exhaust program and resumes the heating rate of 0.4℃ / min; if the first time derivative of ammonia concentration is greater than 35 ppm / min, the PLC triggers an alarm, cuts off the heating element, and turns on the furnace circulation fan to introduce room temperature cold air at a speed of 4 m / s for forced cooling until the first time derivative of ammonia concentration drops below 10 ppm / min, then resumes the heating rate of 0.4℃ / min. When the furnace temperature reaches 132℃ and the absolute concentration of ammonia in the tail gas is below 30ppm for 30 minutes, the in-situ crosslinking is considered complete, and a cured green body is obtained. S6. Deactivate the closed-loop control system and, under an argon atmosphere, heat the solidified preform from 132°C to 630°C at a rate of 1.2°C / min, and hold for 1.5 hours to complete resin pyrolysis. Then transfer it to a graphite tube sintering furnace and heat it to 2110°C at a rate of 6°C / min under an argon atmosphere, hold for 1.2 hours for pressureless solid-state sintering, and allow it to cool naturally to room temperature with the furnace to obtain a multi-particle-size high-purity silicon carbide powder composite isostatic ceramic bucket.

[0049] Example 5: This embodiment provides a method for preparing a composite isostatic pressure ceramic barrel using multi-particle-size high-purity silicon carbide powder, including the following steps: S1. Add 62 parts by weight of coarse silicon carbide powder with a median particle size distribution of 52 μm, 28 parts by weight of medium silicon carbide powder with a median particle size distribution of 11 μm, 10 parts by weight of fine silicon carbide powder with a median particle size distribution of 0.6 μm, 0.7 parts by weight of boron carbide, 2.2 parts by weight of tannic acid, and 42 parts by weight of deionized water to a stirred ball mill with a polyurethane liner. Add 290 parts by weight of high-purity silicon carbide grinding balls, control the cooling water circulation to keep the slurry temperature at 28℃, and perform wet grinding at a speed of 220 rpm for 5.5 hours to obtain a dispersed slurry. S2. Adjust the jacket cooling water to force the temperature of the above dispersion slurry to drop to 21°C. Under continuous stirring at 50 rpm, add 4.5 parts by weight of fructose, 1.8 parts by weight of polyethylene glycol and 0.25 parts by weight of ammonium p-toluenesulfonate in sequence. Continue to homogenize and stir at low speed for 50 minutes. Filter to separate the high-purity silicon carbide grinding balls to obtain the precursor slurry. S3. The above precursor slurry is pumped into a centrifugal spray drying tower by a diaphragm pump. Hot air is introduced as the drying medium. The inlet air temperature is set to 200℃, the outlet air temperature is set to 92℃, and the atomizing disc speed is set to 11000rpm. During the flash evaporation of water, the granulated powder is collected and sieved to obtain spherical granulated powder with a surface coated with an amorphous organic phase and a particle size between 80-150μm. S4. The spherical granulated powder with the amorphous organic phase on the surface is filled into a cylindrical polyurethane flexible mold, vibrated and compacted, then sealed and placed in a cold isostatic press. The pressure is increased to 190 MPa at a rate of 3.5 MPa / min, and the pressure is held for 12 minutes. The pressure is then slowly released and the mold is demolded to obtain a large-size thick-walled ceramic blank. S5. Place the above-mentioned large-size thick-walled ceramic blank in a glue removal furnace. The exhaust gas pipeline of the glue removal furnace is equipped with a pneumatic butterfly valve and an online ammonia concentration analyzer. The end of the exhaust gas pipeline is connected to a variable frequency induced draft device to form a short-term negative pressure exhaust state when the pneumatic butterfly valve is opened. The sensor data is connected to the programmable logic controller. After the temperature rises from room temperature to 80°C, the temperature is increased to the 138°C range at a rate of 0.3°C / min. When the temperature rises above 110℃, the programmable logic controller calculates the first time derivative of the ammonia concentration in real time. If the first time derivative of the ammonia concentration is less than 15ppm / min, the debinding furnace maintains a heating rate of 0.3℃ / min. If the first time derivative of the ammonia concentration is greater than or equal to 15 ppm / min and less than or equal to 35 ppm / min, the programmable logic controller triggers the degassing furnace to stop heating and enter a constant temperature state. At the same time, the pulse exhaust program is started, and the pneumatic butterfly valve is fully opened to 100% for 35 seconds every 2 minutes, so that a negative pressure is formed in the furnace and then restored to a slightly positive pressure. Under constant temperature pulse exhaust mode, when the first time derivative of ammonia concentration is below 10 ppm / min for 5 consecutive minutes, the programmable logic controller (PLC) stops the pulse exhaust program and resumes the heating rate of 0.3℃ / min; if the first time derivative of ammonia concentration is greater than 35 ppm / min, the PLC triggers an alarm, cuts off the heating element, and turns on the furnace circulation fan to introduce room temperature cold air at a speed of 4.5 m / s for forced cooling until the first time derivative of ammonia concentration drops below 10 ppm / min, then resumes the heating rate of 0.3℃ / min. When the furnace temperature reaches 138℃ and the absolute concentration of ammonia in the tail gas is below 30ppm for 30 minutes, the in-situ crosslinking is considered complete, and a cured green body is obtained. S6. Deactivate the closed-loop control system and, under an argon atmosphere, heat the solidified preform from 138°C to 640°C at a rate of 1.8°C / min, and hold for 2.5 hours to complete resin pyrolysis. Then, transfer it to a graphite tube sintering furnace and heat it to 2140°C at a rate of 9°C / min under a vacuum of <10Pa, and hold for 1.8 hours for pressureless solid-state sintering. Allow it to cool naturally to room temperature with the furnace to obtain a multi-particle-size high-purity silicon carbide powder composite isostatic ceramic bucket.

[0050] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference is that tannic acid is not added in step S1 and fructose is not added in step S2. Instead, water-soluble phenolic resin and polyvinyl alcohol with equal carbon equivalents are added. All other aspects are the same.

[0051] Comparative Example 2: Compared with Example 1, the difference is that in step S2, solid fructose is replaced with liquid furfural of equal carbon equivalent, while the rest are the same.

[0052] Comparative Example 3: Compared with Example 1, the difference is that in step S2, ammonium p-toluenesulfonate is replaced with an equimolar amount of p-toluenesulfonic acid, while the rest are the same.

[0053] Comparative Example 4: Compared with Example 1, the difference is that in step S5, the closed-loop predictive control system of the programmable logic controller based on the first time derivative of the ammonia concentration is turned off, and the conventional constant heating rate of 0.3℃ / min is used to continuously heat to 135℃ and hold the temperature, and the pulse exhaust program is not started throughout the process. All other steps are the same.

[0054] Comparative Example 5: Compared with Example 1, the difference is that in step S1, tannic acid is not added and only pure water is used for grinding; in step S2, fructose of equal carbon equivalent is added; otherwise, they are the same.

[0055] Test Case 1-Test Case 4: Test Example 1: Take the initial blanks from Example 1 after cold isostatic pressing and before curing and crosslinking in step S5, and the cured blanks from Example 1 after crosslinking in step S5. Use a steel file to take samples from the core of each blank, grind them in an agate mortar and pass them through a 200-mesh sieve, and put them into sample bottles for later use.

[0056] Weigh 2.2 mg of initial preform powder and cured preform powder respectively, add 208 mg of spectrally pure potassium bromide powder that has been dried and dehydrated at 120℃ to each, mix and grind evenly in an agate mortar, transfer to an infrared tableting mold, and maintain a pressure of 15 MPa for 1.5 minutes to make a test tablet with a thickness of 0.5 mm.

[0057] Background spectra were collected in an air environment without samples using a Fourier transform infrared spectrometer. The prepared pellet was then fixed in the sample chamber, and the scanning wavenumber range was set to 400 cm⁻¹. -1 Up to 4000cm -1 The resolution is set to 4cm. -1 A total of 32 scans were performed, and the background spectrum was subtracted.

[0058] Read and record the wavenumber and transmittance values ​​corresponding to specific characteristic absorption peaks. The test results are shown in Table 1.

[0059] ; From Table 1 and Appendix Figure 1 We can obtain: At 3392.4cm -1 The wavenumber position corresponds to the stretching vibration peak of the hydroxyl group (-OH). The transmittance of the initial green preform at this position is 31.36%, while that of the cured green preform is 76.78%, showing an increase in transmittance value at 1618.7 cm⁻¹. -1 The wavenumber position corresponds to the vibrational peak of the furan ring C=C double bond skeleton, at 1146.2 cm⁻¹. -1 The wavenumber position corresponds to the vibrational peak of the COC crosslinked ether bond, at 1018.5 cm⁻¹. -1 The wavenumber position corresponds to the vibration peak of the CO bond within the furan ring.

[0060] At these three wavenumber positions, the transmittance of the cured green preform was 42.27%, 45.14%, and 38.89%, respectively, while the transmittance of the initial green preform was 88.15%, 92.51%, and 85.62%, respectively, showing a decrease in transmittance values.

[0061] The changes in infrared transmittance and absorption peak intensity indicate that, after heat treatment, the free hydroxyl functional groups in the original mixed system participated in the reaction and were consumed, while a furan ring skeleton structure and new COC crosslinked ether bonds were generated in the product.

[0062] The evolution of this bonding relationship indicates and corroborates that the thermal decomposition of ammonium p-toluenesulfonate in the system releases corresponding acidic substances, causing fructose molecules to undergo a dehydration reaction to generate an intermediate containing a furan ring structure. Furthermore, this furan ring-containing intermediate undergoes a dehydration condensation cross-linking reaction with tannic acid in the system, thereby forming a cross-linked organic network structure in the gaps between the raw silicon carbide powder particles.

[0063] Test Example 2: Extract the spherical granulated powder with surface-coated amorphous organic phase prepared in step S3 of Example 1, weigh 8.4 mg and put it into an alumina standard crucible, and place it in the sample chamber of a thermogravimetric-differential scanning calorimetry-mass spectrometry instrument.

[0064] The heating furnace was sealed, and high-purity argon gas was introduced. The carrier gas flow rate was set to 50 mL / min. The heating program was set as follows: the temperature was increased from room temperature to 80°C at a rate of 10°C / min, and then increased uniformly to 135°C at a rate of 0.3°C / min.

[0065] Within the temperature range of 80℃ to 135℃, the weight loss rate, heat flow rate, and mass spectrometry ion current intensity data of the powder sample were collected simultaneously. The mass spectrometry monitoring channels were set to m / z=17 and m / z=18, and the data values ​​at different temperature nodes were extracted and recorded.

[0066] The test results are shown in Table 2.

[0067] ; From Table 2 and Appendix Figure 2 We can obtain: Within the temperature range of 80.5℃ to 108.6℃, the mass spectrometry ion current intensities at m / z=17 and m / z=18 remained stable, while the differential scanning calorimetry heat flux was negative, indicating that the system was in an endothermic state with no gaseous products precipitating. When the temperature rose to 112.4℃, the ion current intensity corresponding to ammonia at m / z=17 increased from 0.28 × 10⁻⁶. -10 A rose to 3.42 × 10 -10 A, and this upward process is earlier than the significant enhancement process of the water molecule channel at m / z=18. Combined with the thermal decomposition characteristics of ammonium toluenesulfonate, it can be determined that this stage mainly deals with the process of producing ammonia gas through the thermal decomposition of ammonium toluenesulfonate.

[0068] Within the temperature range of 116.8℃ to 134.1℃, the DSC heat flux rate changed from negative to positive, reaching a peak exothermic value of 3.412 mW / mg at 123.5℃. Within this exothermic range, the ion current intensity of the monitoring channel corresponding to m / z=18 for water molecules increased to 38.92 × 10⁻⁶. -10 The peak value of A and the thermogravimetric residual mass simultaneously decreased to 97.28%. The aforementioned data changes showed a sequential relationship in the temperature process, with the precipitation of ammonia preceding the release of water molecules and the exothermic process of the system.

[0069] This test process reflects the process by which ammonium p-toluenesulfonate decomposes upon heating, releasing ammonia and acidic substances, and then the acidic substances catalyze the dehydration of fructose and the condensation and cross-linking of tannic acid. The generation rate of gaseous products corresponds to the trend of the exothermic curve, providing a physical parameter basis for estimating the progress of the cross-linking reaction and the exothermic state of the system by monitoring the change in ammonia concentration in the exhaust gas.

[0070] Test Example 3: The precursor slurries from Example 1, Comparative Example 3, and Comparative Example 5 after step S2 were extracted respectively. Each group of precursor slurries was placed into a stoppered glass graduated cylinder with a volume of 500 mL and sealed. The cylinders were then placed in a constant temperature water bath at 25°C and allowed to stand.

[0071] Using a coaxial cylindrical rotational viscometer, the apparent viscosity of the slurry in each graduated cylinder was measured at 0, 8, 16, and 24 hours of settling. After 24 hours of settling, 10 mL of slurry was taken from each graduated cylinder at a distance of 2 cm from the liquid surface and 2 cm from the bottom of the graduated cylinder. After centrifugation, washing, and ultrasonic dispersion, the median particle size distribution (D50) of the powder was tested using a laser particle size analyzer, and the corresponding data were recorded.

[0072] 20g of spherical granulated powder with amorphous organic phase coating prepared in step S3 of Example 1 and Comparative Example 3 were weighed and placed into a cylindrical alloy steel mold with an inner diameter of 30mm. The powder in the mold was subjected to axial load by a microcomputer-controlled electronic universal testing machine for cold pressing molding test. The displacement rate of the pressure head was set to 1 mm / min. During the application of the displacement load, the engineering strain data and corresponding axial compressive stress data of the powder were recorded simultaneously, and the data values ​​of typical strain nodes were extracted and recorded.

[0073] The test results are shown in Tables 3 and 4.

[0074] ; ; From Tables 3 and 4 and Figure 3 We can obtain: In the slurry settling test, the apparent viscosity of the precursor slurry in Example 1 was between 451.2 mPa·s and 472.5 mPa·s during the 24-hour settling period. The median D50 of the particle size distribution of the upper and lower extracted powders were 18.23 μm and 19.64 μm, respectively, and no particle sedimentation or stratification was observed.

[0075] In Comparative Example 5, without the addition of tannic acid, the apparent viscosity of the slurry decreased to 285.7 mPa·s after 24 hours of standing. The D50 of the upper extracted powder was 3.12 μm, and the D50 of the lower extracted powder was 48.75 μm. The system showed particle sedimentation and separation of coarse and fine powders. In Comparative Example 3, with p-toluenesulfonic acid replacing ammonium p-toluenesulfonate, the apparent viscosity of the slurry increased to 7621.8 mPa·s after 16 hours, and the slurry changed to a gel-agglomerate state after 24 hours.

[0076] In the granulated powder compression test, the granulated powder of Example 1 had a compressive stress of 9.42 MPa under a strain of 0.3, and its test curve showed a non-linear and gradual upward trend with the increase of strain. The granulated powder of Comparative Example 3 had a compressive stress of 118.74 MPa under a strain of 0.3, and brittle fracture occurred with the increase of compression displacement.

[0077] The data comparison above shows that the mixed system containing tannic acid and ammonium p-toluenesulfonate in Example 1 maintained the suspended dispersion state of multi-size silicon carbide powder in the aqueous phase; during the room temperature standing and pressing stages, no chemical cross-linking reaction was triggered inside the system, and the powder particles maintained their plastic deformation characteristics.

[0078] The introduction of strong acid in the control group triggered the early crosslinking reaction at room temperature and the curing of the slurry matrix; the control group without tannic acid lost the physical resistance to maintain the suspension of particles. The test results confirmed the physical state and chemical reaction triggering conditions of each material component and ratio corresponding to the process stage.

[0079] Test Example 4: Twenty thick-walled ceramic blanks were taken from each of Examples 1 to 5, Comparative Examples 1, 2 and 4 after the curing and debinding process was completed. The appearance of each group of blanks was inspected and the macroscopic integrity rate was recorded. An ultrasonic flaw detector was used to measure the longitudinal wave velocity of the central area of ​​the blank wall thickness at a frequency of 5 MHz and the data was recorded.

[0080] The intact blanks in each group were placed in a graphite tube sintering furnace or a vacuum / inert atmosphere sintering furnace, and resin pyrolysis carbonization and pressureless solid phase sintering were carried out according to the S6 process conditions of the corresponding group. Among them, only the sample fragments that were not completely broken were selected for observation in Comparative Example 4. However, due to their insufficient dimensional integrity and internal continuity, it was impossible to obtain standard test strips that met the size requirements of 3mm×4mm×36mm after sintering. Except for Comparative Example 4, the sintered ceramic parts of each group were processed into test strips of 3mm×4mm×36mm using a diamond cutter, and the surfaces were ground, polished and chamfered. 15 test strips were prepared for each group.

[0081] Using a universal testing machine, the room temperature bending strength of each group of specimens was tested using the three-point bending method under the conditions of a span of 30 mm and a loading rate of 0.5 mm / min. The bulk density and apparent porosity of each specimen were measured using the Archimedes displacement method. The data output by each testing instrument were read. Each group was tested at least 3 times. The average value of each group was calculated and recorded.

[0082] The test results are shown in Table 5.

[0083] ; From Table 5 and Appendix Figure 4 We can obtain: In the non-destructive testing of the billet, the macroscopic integrity rate of Examples 1 to 5 was 100%, and the ultrasonic longitudinal wave velocity of the billet was in the range of 3498 m / s to 3542 m / s. In Comparative Example 4, without the execution of the closed-loop pulse exhaust procedure, the billet integrity rate was 15%, most samples experienced macroscopic expansion cracks, and the ultrasonic velocity of the incompletely broken samples dropped to 1248 m / s.

[0084] The longitudinal wave velocity of ultrasound is positively correlated with the continuity of the internal medium of the material. The data of Comparative Example 4 shows that its internal continuity is reduced, suggesting the existence of cracks, pores, delamination or other defect structures that disrupt the continuity of sound wave propagation. This test reflects that in the early stage of curing and adhesive removal, the reaction exothermic and water vapor expansion accumulated inside the thick-walled medium changes the physical bonding state between powder particles.

[0085] In the sintered body performance testing phase, the bulk density of Examples 1 to 5 was 3.136 g / cm³. 3 Up to 3.147 g / cm 3 The apparent porosity ranges from 0.15% to 0.22%, and the average flexural strength at room temperature ranges from 459.8 MPa to 471.2 MPa.

[0086] Comparative Example 1, using a polymer binder to replace fructose and tannic acid, showed an apparent porosity of 4.87% and a bulk density of 2.943 g / cm³ in the sintered body.3 Its flexural strength at room temperature is 312.6 MPa.

[0087] Comparative Example 2, using liquid furfural instead of solid fructose, showed an apparent porosity of 2.54% and a bulk density of 3.018 g / cm³ in the sintered body. 3 Its flexural strength at room temperature is 345.3 MPa.

[0088] The data from Comparative Example 1 show that when a polymer system such as water-soluble phenolic resin and polyvinyl alcohol is used to replace the tannic acid and fructose small molecule blend system in this invention, the macromolecular chains tend to migrate to the powder surface during the granulation stage to form a hard shell structure, which affects the compression and reorganization of the powder in the cold isostatic pressing process, and retains mesoscopic pores inside the molded body, resulting in a decrease in the density and strength parameters of the sintered body.

[0089] The data from Comparative Example 2 show that when liquid furfural is used to replace solid fructose, the liquid carbon source is more prone to volatilization loss in the high-temperature environment of spray drying, which can easily lead to a reduction in the carbon equivalent inside the solid system and change the driving force for the sintering densification of silicon carbide grains. The test parameters of the Example Group confirm the mechanism of action of the process steps of using water-soluble small molecule blends for shell-less granulation and in-situ polymerization in the green body in controlling the porosity defects of the final product and maintaining the uniformity of carbon source distribution.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite isostatically pressed ceramic barrel using multi-particle-size high-purity silicon carbide powder, characterized in that, The method includes the following steps: Multi-size silicon carbide powder, boron carbide, tannic acid and deionized water are added to a lined stirred ball mill and wet milling is carried out under controlled temperature to obtain a dispersion slurry. The dispersion slurry was cooled, and fructose, polyethylene glycol and ammonium p-toluenesulfonate were added sequentially under continuous stirring. The mixture was then homogenized and stirred, and filtered to obtain the precursor slurry. The precursor slurry is fed into a centrifugal spray drying tower, where water is flashed in a hot air medium, and the spherical granulated powder with an amorphous organic phase coated on the surface is collected and screened. The spherical granulated powder with an amorphous organic phase on its surface is filled into a flexible mold, placed in a cold isostatic press and pressed, and then the pressure is released and the mold is demolded to obtain a large-sized thick-walled ceramic blank. The large-sized thick-walled ceramic blank is placed in a debinding furnace for heating. The ammonia concentration in the exhaust gas of the debinding furnace is monitored in real time by an online analyzer. The first time derivative of the ammonia concentration is calculated. Based on the first time derivative, the heating state of the debinding furnace and the pneumatic butterfly valve of the exhaust gas pipeline are controlled in a closed loop by a programmable logic controller until the in-situ crosslinking is completed, and a cured blank is obtained. The solidified green blank is heated and kept at a high temperature to complete resin pyrolysis, and then transferred to a sintering furnace for pressureless solid-phase sintering. After cooling, a multi-particle-size high-purity silicon carbide powder composite isostatic ceramic bucket is obtained.

2. The preparation method of the multi-particle-size high-purity silicon carbide powder composite isostatic pressing ceramic barrel according to claim 1, characterized in that, The multi-particle-size silicon carbide powder includes coarse silicon carbide powder, medium silicon carbide powder, and fine silicon carbide powder. The median particle size distribution (D50) of the coarse silicon carbide powder is 45-55 μm, the median particle size distribution (D50) of the medium silicon carbide powder is 8-12 μm, and the median particle size distribution (D50) of the fine silicon carbide powder is 0.3-0.8 μm.

3. The preparation method of the multi-particle-size high-purity silicon carbide powder composite isostatic pressing ceramic barrel according to claim 1, characterized in that, In the steps of preparing the dispersion slurry and the precursor slurry, the addition ratio of each raw material is as follows: The composition includes 55-65 parts by weight of coarse silicon carbide powder, 25-35 parts by weight of medium silicon carbide powder, 10 parts by weight of fine silicon carbide powder, 0.4-0.8 parts by weight of boron carbide, 1.5-2.5 parts by weight of tannic acid, 35-45 parts by weight of deionized water, 3.0-5.0 parts by weight of fructose, 1.0-2.0 parts by weight of polyethylene glycol, and 0.1-0.3 parts by weight of ammonium p-toluenesulfonate.

4. The method for preparing a multi-particle-size high-purity silicon carbide powder composite isostatic pressure ceramic barrel according to claim 1, characterized in that, The step of controlling the temperature during wet milling includes: Add 250-300 parts by weight of high-purity silicon carbide grinding balls to a stirred ball mill with a polyurethane liner, control the cooling water circulation to keep the slurry temperature at 20-30℃, and perform wet grinding at a speed of 150-250 rpm for 4-6 hours.

5. The method for preparing a multi-particle-size high-purity silicon carbide powder composite isostatic pressure ceramic barrel according to claim 1, characterized in that, The step of obtaining the precursor slurry includes: The temperature of the dispersed slurry is forcibly reduced to 15-22℃. Fructose, polyethylene glycol and ammonium p-toluenesulfonate are added under continuous stirring at 30-60 rpm. The mixture is then stirred at low speed for 30-60 minutes to homogenize it. After filtration, the precursor slurry is obtained.

6. The method for preparing a multi-particle-size high-purity silicon carbide powder composite isostatic pressure ceramic barrel according to claim 1, characterized in that, The steps of feeding the precursor slurry into a centrifugal spray drying tower, flash evaporating moisture in a hot air medium, and collecting and sieving to obtain spherical granulated powder with an amorphous organic phase coated on the surface include: The precursor slurry is pumped into a centrifugal spray drying tower by a diaphragm pump, and hot air is introduced as the drying medium. The inlet air temperature is set to 180-210℃, the outlet air temperature is set to 80-95℃, and the atomizing disc speed is set to 8000-12000 rpm. During the flash evaporation of water, the granulated powder is collected and sieved to obtain spherical granulated powder with a surface coated with an amorphous organic phase and a particle size between 80-150μm.

7. The method for preparing a multi-particle-size high-purity silicon carbide powder composite isostatic pressure ceramic barrel according to claim 1, characterized in that, The steps of filling the spherical granulated powder with the amorphous organic phase on the surface into a flexible mold, placing it in a cold isostatic press for pressing, and then releasing the pressure to obtain a large-size thick-walled ceramic green body include: The spherical granulated powder with the amorphous organic phase on the surface is filled into a cylindrical polyurethane flexible mold, vibrated to settle, sealed, and placed in a cold isostatic press. The pressure is increased to 150-200 MPa at a rate of 2-5 MPa / min, held for 5-15 minutes, and then slowly depressurized to obtain a large-sized thick-walled ceramic blank.

8. The method for preparing a multi-particle-size high-purity silicon carbide powder composite isostatic pressure ceramic barrel according to claim 1, characterized in that, The step of obtaining the cured green preform includes: The large-sized, thick-walled ceramic blank was placed in a debinding furnace and heated from room temperature to 80°C, then increased to 130-140°C at a rate of 0.2-0.5°C / min. When the temperature reached above 110°C, the programmable logic controller (PLC) calculated the first-order time derivative of the ammonia concentration in real time. If the first time derivative of the ammonia concentration is less than 15 ppm / min, the debinding furnace should maintain the heating rate of 0.2-0.5℃ / min. If the first time derivative of the ammonia concentration is greater than or equal to 15 ppm / min and less than or equal to 35 ppm / min, the programmable logic controller triggers the degassing furnace to stop heating and enter a constant temperature state. At the same time, the pulse exhaust program is started, and the pneumatic butterfly valve is fully opened to 100% for 20-40 seconds every 2-3 minutes to create a negative pressure in the furnace and then restore a slight positive pressure.

9. The method for preparing a multi-particle-size high-purity silicon carbide powder composite isostatic pressure ceramic barrel according to claim 8, characterized in that, The step of obtaining the cured green preform further includes: Under the constant temperature pulse exhaust state, when the first time derivative of the ammonia concentration is below 10 ppm / min for 5 consecutive minutes, the programmable logic controller stops the pulse exhaust program and resumes the heating rate of 0.2-0.5℃ / min. If the first time derivative of the ammonia concentration is greater than 35 ppm / min, the programmable logic controller triggers an alarm, cuts off the heating element, and turns on the furnace circulation fan to introduce room temperature cold air at a speed of 3-5 m / s for forced cooling until the first time derivative of the ammonia concentration drops below 10 ppm / min, then the heating rate of 0.2-0.5℃ / min is restored. When the furnace temperature reaches 130-140℃ and the absolute concentration of ammonia in the exhaust gas is below 30ppm for 30 consecutive minutes, the in-situ crosslinking is considered complete, and a cured green body is obtained.

10. The method for preparing a multi-particle-size high-purity silicon carbide powder composite isostatic pressure ceramic barrel according to claim 1, characterized in that, The steps of heating and holding the cured green blank to complete resin pyrolysis, then transferring it to a sintering furnace for pressureless solid-state sintering, and finally cooling it to obtain a multi-particle-size high-purity silicon carbide powder composite isostatically pressed ceramic barrel include: The closed-loop control system is deactivated, and the solidified preform is heated from 130-140℃ to 600-650℃ at a rate of 1.0-2.0℃ / min under an argon atmosphere, and held at that temperature for 1-3 hours to complete resin pyrolysis. Then it is transferred to a graphite tube sintering furnace, and heated to 2100-2150℃ at a rate of 5-10℃ / min under an argon atmosphere or a vacuum degree <10Pa, and held at that temperature for 1-2 hours to carry out pressureless solid-state sintering. The preform is then naturally cooled to room temperature with the furnace to obtain a multi-particle-size high-purity silicon carbide powder composite isostatic ceramic barrel.

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