Particles of ceramic filter membrane and preparation method of ceramic filter membrane

Abstract

The invention relates to particles of a ceramic filter membrane and a preparation method of the ceramic filter membrane. Particles of the ceramic filter membrane are prepared from the following raw materials in parts by mass through mixing and extrusion molding: 60-99 parts of high-purity aluminum oxide powder; 8-20 parts of an organic binder; 3-15 parts of a pore forming agent; and 5-20 parts of a diluent. The particles can adapt to various ceramic membrane forming modes. Various ceramic membranes can be prepared only through simple heating extrusion molding, hot press molding or injection molding and sintering processes. The particle preparation process is simple, the equipment investment is low, the production efficiency is high, a complete and uniformly distributed membrane material can be prepared by optimizing a forming formula and process parameters, and the performance quality is controllable; the hollow fiber ceramic membrane and the honeycomb tube type ceramic membrane which are prepared by directly extruding and molding the particles are high in blank strength, straightness in appearance and good in flatness, do not need to be dried and shaped, and can be directly sintered in a kiln. Disc ceramic membranes and plate ceramic membranes prepared from the particles through hot press molding or injection molding have the advantages of small deformation, high mechanical strength, good thermal stability and good chemical stability.

Description

Technical Field

[0001] The present invention relates to a filter membrane, in particular to particles of a ceramic filter membrane and a preparation method thereof. Background Art

[0002] In the field of preparation of porous filter materials, ceramic membranes have attracted much attention due to their high mechanical strength, chemical resistance, thermal stability, and durability. The existing porous ceramic membrane technology mainly relies on specific raw material ratios and forming processes. For example, clay, alumina, calcium carbonate, silica, etc. are used as the main raw materials, and ceramic membranes are prepared through processes such as extrusion forming, drying, and sintering. The porous ceramic membranes in the existing technology are widely used in fields such as water treatment, gas separation, and biopharmaceuticals.

[0003] Although certain progress has been made in the preparation of porous ceramic membranes in the existing technology, there are still the following deficiencies:

[0004] 1. Unable to adapt to multiple forming methods: The raw materials of traditional wet extrusion-formed ceramic membranes are extruded after being kneaded by vacuum pugging. The moisture content of the clay blank is high and the fluidity is poor, which is not suitable for other forming methods, such as pressing forming, injection molding, etc.

[0005] 2. Balance between porosity and strength: Ceramic membranes with higher porosity often sacrifice mechanical strength, while membranes with higher strength often have lower porosity.

[0006] 3. Difficult to shape: The ceramic membranes formed by wet extrusion are very sensitive to moisture control during the extrusion and shaping process. The wet and soft clay blank may easily lead to deformation, structural collapse, or uneven pore distribution during the long-term drying and shaping process, resulting in a low yield rate.

[0007] 4. Energy-saving problem: The preparation cost of ceramic membranes formed by wet extrusion is relatively high, and high-power dehydration, shaping, and drying equipment need to be invested, which increases the equipment investment cost. At the same time, the traditional production drying temperature is high and the energy consumption is large, which does not meet the current requirements of energy conservation and emission reduction. This limits its popularization in large-scale industrial applications. Summary of the Invention

[0008] To solve the above problems, the present invention provides particles of a ceramic filter membrane, and the specific technical solution is as follows:

[0009] A kind of particles of a ceramic filter membrane, which are granulated after heating, mixing, and extruding the following raw materials according to mass parts: 60-99 parts of high-purity alumina powder; 8-20 parts of organic binder; 3-15 parts of pore-forming agent; 5-20 parts of diluent.

[0010] Preferably, the purity of the high-purity alumina powder is ≥99.9%, and the average particle size is 0.5-20 μm.

[0011] Preferably, the organic binder comprises the following raw materials in parts by mass: 5-15 parts of epoxy resin; 20-60 parts of polyethersulfone plastic; 2-4 parts of polyethylene wax; 20-60 parts of high-density polyethylene; 0-10 parts of liquid rubber; 1-2 parts of polyethylene glycol plasticizer; 2-4 parts of polyvinylpyrrolidone dispersant; 1-2 parts of magnesium stearate.

[0012] Preferably, the pore-forming agent comprises the following raw materials in parts by mass: 10-30 parts of corn starch; 10-20 parts of phenolic resin powder; 30-60 parts of synthetic carbon powder; 0-30 parts of graphene; 0-30 parts of carbon nanotubes; 0-30 parts of polymethyl methacrylate powder.

[0013] Preferably, the diluent comprises the following raw materials in parts by mass: 50-80 parts of ethylene glycol; 4-20 parts of paraffin wax; 4-20 parts of liquid paraffin; 5-10 parts of dioctyl phthalate.

[0014] Preferably, the temperature of the mixing is 150-240 °C, and the mixing time is 1-4 hours.

[0015] A method for preparing a ceramic filter membrane, using particles of a ceramic filter membrane, comprising the following steps:

[0016] Forming, preparing the particles of the ceramic filter membrane into a desired shape;

[0017] Debinding, removing the organic binder and the pore-forming agent;

[0018] Sintering, the sintering temperature is 1300-1750 °C.

[0019] Preferably, the forming includes: thermoplastic extrusion forming using a screw extruder, hot pressing forming using a hydraulic press, and injection molding.

[0020] Preferably, the debinding includes: debinding in a debinding furnace, supercritical carbon dioxide debinding, or superheated saturated steam debinding.

[0021] Furthermore, the sintering includes: a low-temperature stage, room temperature to 300 °C, a heating rate of 0.5-1 °C / min; a medium-temperature stage, 300 °C to 750 °C, a heating rate of 1-2 °C / min; a high-temperature stage, 750 °C to the sintering temperature, a heating rate of 3-5 °C / min; a holding stage, holding for 1-3 hours.

[0022] The particles of a ceramic filter membrane provided by the present invention can be adapted to a variety of ceramic membrane forming methods. Only through simple heating and extrusion molding, hot pressing molding or injection molding and sintering process can various ceramic membranes be prepared. The particle preparation process is simple, with low equipment investment and high production efficiency. By optimizing the forming formula and process parameters, a complete and uniformly distributed membrane material can be prepared, and the quality of the membrane layer is controllable; the hollow fiber ceramic membrane and tubular ceramic membrane blank prepared by direct extrusion molding of the particles have high strength, good straightness and flatness of the appearance, and do not require drying and shaping, and can be directly sintered in a kiln. It can meet the actual production application requirements. Brief Description of the Drawings

[0023] Figure 1 Figure 1 is the first SEM image of the finished ceramic membrane prepared with these particles;

[0024] Figure 2 Figure 2 is the second SEM image of the finished ceramic membrane prepared with these particles;

[0025] Figure 3 Figure 3 is a photo of the granulated particles of the mixing raw materials of the ceramic filter membrane;

[0026] Figure 4 Figure 4 is a photo of the hollow ceramic filter membrane extruded with these particles. Detailed Embodiments

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] For the particles of a ceramic filter membrane, high-purity alumina powder is mixed with an organic binder, a pore-forming agent and a diluent according to a mass ratio, and kneaded at 150-240°C for 1-4 hours to obtain ceramic granulated particles.

[0029] 60-99 parts of high-purity alumina powder (purity ≥ 99.9%, average particle size 0.5-20 μm); 8-20 parts of organic binder; 3-15 parts of pore-forming agent; 5-20 parts of diluent.

[0030] The purity of the high-purity alumina powder is ≥ 99.9%, and the average particle size is 0.5-20 μm.

[0031] The organic binder includes the following raw materials according to mass parts: 5-15 parts of epoxy resin; 20-60 parts of polyethersulfone plastic; 2-4 parts of polyethylene wax; 20-60 parts of high-density polyethylene; 0-10 parts of liquid rubber; 1-2 parts of polyethylene glycol plasticizer; 2-4 parts of polyvinylpyrrolidone dispersant; 1-2 parts of magnesium stearate.

[0032] Epoxy resin: increases the strength, toughness, adhesiveness and durability of the material.

[0033] Polyethersulfone (PES) plastic: As the base material for injection molding, it can improve the impact strength, weather resistance, and moldability of the matrix material.

[0034] Polyethylene wax: Used as a lubricant, it can reduce the friction during the extrusion process, thereby improving production efficiency and product quality.

[0035] High-density polyethylene (HDPE): As the base material for extrusion molding, it is used to improve the properties of the material.

[0036] Liquid rubber: It increases flexibility and impact resistance, and its high elasticity can prevent the embryo from cracking.

[0037] Polyethylene glycol plasticizer (PEG): It is used to soften the plastic and make it more flexible.

[0038] Polyvinylpyrrolidone dispersant (PVP): It improves dispersibility, prevents particle aggregation, and ensures uniformity.

[0039] Magnesium stearate: Lubricant, anti-adhesive agent, glidant. It improves the fluidity and compressibility of particles.

[0040] The pore-forming agent comprises the following raw materials by mass parts: 10 - 30 parts of corn starch; 10 - 20 parts of phenolic resin powder; 30 - 60 parts of synthetic carbon powder; 0 - 30 parts of graphene; 0 - 30 parts of carbon nanotubes; 0 - 30 parts of polymethyl methacrylate powder.

[0041] Corn starch: While acting as a pore-forming agent, it can also increase the viscosity of the raw materials at high temperatures.

[0042] Phenolic resin powder: It provides structural support and heat resistance, and reduces the thermal deformation during the debinding process.

[0043] Synthetic carbon powder: By changing the mixing ratio, the friction characteristics of the material surface can be adjusted.

[0044] Graphene: An extremely thin carbon layer structure, it improves the mechanical strength of particles and embryos. A small amount of addition can significantly enhance the overall performance of the material.

[0045] Carbon nanotubes: Similar to graphene, it is mainly used for pore formation in nanofiltration membranes and ultrafiltration membranes.

[0046] Polymethyl methacrylate powder: It has the functions of pore formation, improving moldability, assisting in adjusting mechanical properties, and optimizing surface properties in the pore-forming agent.

[0047] The diluent comprises the following raw materials by mass parts: 50 - 80 parts of ethylene glycol; 4 - 20 parts of paraffin wax; 4 - 20 parts of liquid paraffin; 5 - 10 parts of dioctyl phthalate.

[0048] Ethylene glycol: Reduces the melt viscosity, improves the processing fluidity, flexibility and plasticity, lowers the processing temperature, and is used for modifying existing formulations at low concentrations.

[0049] Paraffin wax: Also acts as a lubricant, helps control the viscosity, and makes the mixture easier to pass through the die.

[0050] Liquid paraffin: Similar to solid paraffin, but more fluid, used to adjust the fluidity of the system.

[0051] Dioctyl phthalate: Can reduce the viscosity of the pore-forming agent system, improve its fluidity and dispersibility, make the components mix more evenly, and facilitate the uniform formation of the pore structure during the pore-forming process.

[0052] The temperature of the mixing is 150 - 240 °C, and the mixing time is 1 - 4 hours.

[0053] A method for preparing a ceramic filter membrane, using particles of a ceramic filter membrane, comprising the following steps:

[0054] Forming, preparing the particles of the ceramic filter membrane into the required shape;

[0055] Debinding, removing the organic binder and the pore-forming agent;

[0056] Sintering, the sintering temperature is 1300 - 1750 °C.

[0057] Preferably, the forming includes: thermoplastic extrusion forming using a screw extruder, hot pressing forming using a hydraulic press, and injection molding.

[0058] Preferably, the debinding includes: debinding in a debinding furnace, supercritical carbon dioxide debinding, or superheated saturated steam debinding.

[0059] Furthermore, the sintering includes: a low-temperature stage, room temperature - 300 °C, heating rate 0.5 - 1 °C / min; a medium-temperature stage, 300 °C - 750 °C, heating rate 1 - 2 °C / min; a high-temperature stage, 750 °C - sintering temperature, heating rate 3 - 5 °C / min; a holding stage, holding for 1 - 3 hours.

[0060] Pelletizing is carried out by mixing and pelletizing with a parallel twin-screw extruder. The temperature in the feeding section is generally relatively low. Because in this stage, the main tasks are to convey the raw materials and stir the powder materials to prevent premature plasticization of the raw materials. The temperature is set at about 50 - 100 °C. If the temperature is too high, the raw materials may adhere near the feeding port, resulting in poor feeding. The key area for plasticization. The temperature needs to be determined according to the composition and characteristics of the ceramic raw materials. The temperature is set between 140 - 200 °C. If the ceramic raw materials contain more additives such as binders, the temperature may need to be appropriately increased to ensure that the binder can play its full role and make the ceramic particles have good formability. The homogenization section is mainly to further uniformly mix and knead the materials, and the temperature can be slightly higher than that in the plasticization section. The temperature is set at 150 - 240 °C. The high temperature in this stage helps to eliminate the internal stress of the materials and make the internal structure of the pelletized ceramic particles more uniform. The die temperature has an important impact on the appearance and quality of the ceramic particles. The temperature is set at 140 - 180 °C. An appropriate die temperature can make the particle surface smooth and prevent defects such as cracks. At the same time, the die temperature also affects the discharging speed and shape retention of the particles. During the operation, the temperature parameters can be fine-tuned by trial extrusion and observing the quality of the particles (such as shape, strength, density, etc.).

[0061] Forming: After granulation, the ceramic particles are used to prepare the required ceramic membrane form by heating extrusion forming, hot pressing forming, injection molding or injection molding. Generally, there are hollow fiber ceramic membranes, tubular ceramic membranes, disk ceramic membranes and flat ceramic membranes. Taking the extrusion forming of honeycomb ceramic membranes as an example, the temperature of the heating extrusion barrel: According to the characteristics of the ceramic particles and the binder, generally, the temperature of the front section of the barrel is 180 - 220°C, the middle section is 200 - 240°C, and the rear section is 160 - 190°C. For the system containing HDPE binder, the front section can be appropriately reduced to 170 - 200°C to prevent premature curing. Die temperature: Usually 10 - 20°C higher than the temperature of the front section of the barrel, between 190 - 240°C, which helps the ceramic particles to be smoothly extruded after remelting and maintain a certain shape. Extrusion pressure: Generally between 5 - 20 MPa, specifically depending on the particle size distribution of the ceramic particles, the binder content, and the screw design of the extruder, etc. For systems with finer ceramic particles and a high binder content, the pressure can be appropriately reduced to 3 - 15 MPa. Back pressure: The back pressure is usually controlled between 0.5 - 2 MPa. Appropriate back pressure helps to improve the density and uniformity of the ceramic particles. Screw speed: Generally between 10 - 60 r / min. Too fast a speed may cause uneven mixing of the ceramic particles and the binder or generate too much heat to decompose the binder. For ceramic particle systems with high viscosity, the speed can be 10 - 30 r / min. Extrusion speed: According to the size and shape of the product, the extrusion speed is generally between 0.5 - 5 m / min. For ceramic membrane forms with complex shapes, the extrusion speed should be slow, between 0.5 - 2 m / min. Taking the injection molding of disk ceramic membranes as an example, the barrel temperature: Generally divided into three sections for control, the front section is 160 - 190°C, the middle section is 180 - 210°C, and the rear section is 150 - 170°C. If a paraffin-based binder is used, the temperature can be appropriately reduced by 10 - 20°C. Mold temperature: The mold temperature is usually between 30 - 80°C. For some ceramic membrane forms with complex shapes and high precision requirements, the mold temperature can be controlled between 50 - 80°C to ensure the filling effect and demolding performance. Injection pressure: Generally between 50 - 150 MPa. For ceramic particle systems with high filling amounts or thin-walled products, the injection pressure may need to be increased to 100 - 200 MPa. Holding pressure: The holding pressure is usually 60% - 80% of the injection pressure, that is, 30 - 120 MPa, and the holding time is generally 5 - 30 s. Injection speed: The injection speed is generally between 5 - 30 cm 3 / s. For small-sized and thin-walled ceramic membrane forms, the injection speed can be increased to 15 - 30 cm 3 / s; For large-sized and thick-walled products, the injection speed should be between 5 - 15 cm 3 / s.

[0062] Degreasing: Degreasing can be carried out in a degreasing furnace or by using supercritical carbon dioxide. When degreasing in a degreasing furnace, the degreasing temperature is 580 - 620 °C, and the degreasing time is 1 - 3 hours. When using supercritical carbon dioxide for degreasing, the temperature and pressure need to be precisely controlled above the critical values of carbon dioxide. Generally, the temperature is controlled at 32 - 50 °C, the pressure is 7.5 - 10 MPa, and the flow rate is generally 1 - 5 L / min. Excessive temperature may cause defects such as cracks in the green body, and too low pressure will cause carbon dioxide not to reach the supercritical state, affecting the degreasing effect. The degreasing time is determined according to factors such as the size, shape, and organic content of the green body. Usually, for small ceramic green bodies, the degreasing time is 1 - 3 hours; for large or high-organic-content green bodies, the degreasing time may be extended to 5 - 10 hours. Controlling the flow rate of supercritical carbon dioxide is also very important. An appropriate flow rate can ensure the degreasing efficiency and avoid physical damage to the green body due to excessive flow rate.

[0063] Sintering: The final sintering temperature is 1300 - 1750 °C.

[0064] Low-temperature stage (room temperature - 300 °C): The heating rate should be slow, generally controlled at 0.5 - 1 °C / min. This stage is mainly the evaporation period of water in the green body. Too fast heating may cause internal vapor pressure in the green body, resulting in cracking of the green body.

[0065] Medium-temperature stage (300 °C - 750 °C): This is the peak period for the decomposition and volatilization of organic matter. The heating rate still needs to be controlled at 1 - 2 °C / min. Slow heating can prevent the high gas pressure formed by the decomposed gas in the green body from cracking the green body. The degreasing temperature is 580 - 620 °C, and the degreasing time is 1 - 3 hours.

[0066] High-temperature stage (750 °C - sintering temperature): After 750 °C, the heating rate can be appropriately increased, but different heating rates should be adopted according to the size of the workpiece, considering the internal temperature gradient and heat conduction rate of the green body. Generally, the heating rate is 3 - 5 °C / min. For larger workpieces or easily deformed green bodies, the heating rate should be further slowed down.

[0067] Insulation stage: After reaching the sintering temperature, according to factors such as the thickness, size, and required properties of the green body, insulate for about 1 - 3 hours to fully sinter the green body and obtain good densification and properties.

[0068] Example 1

[0069] A particle of a ceramic filter membrane, characterized in that it is kneaded and extruded into shape from the following raw materials by mass fraction: 60 parts of high-purity alumina powder; 8 parts of organic binder; 12 parts of pore-forming agent; 20 parts of diluent.

[0070] The purity of the high-purity alumina powder is ≥99.9%, and the average particle size is 0.5 μm.

[0071] The organic binder includes the following raw materials by mass fraction: 5 parts of epoxy resin; 20 parts of polyethersulfone plastic; 2 parts of polyethylene wax; 60 parts of high-density polyethylene; 9 parts of liquid rubber; 1 part of polyethylene glycol plasticizer; 2 parts of polyvinylpyrrolidone dispersant; 1 part of magnesium stearate.

[0072] The pore former includes the following raw materials by mass fraction: 10 parts of corn starch; 10 parts of phenolic resin powder; 50 parts of synthetic carbon powder; 10 parts of graphene; 10 parts of carbon nanotubes; 10 parts of polymethyl methacrylate powder.

[0073] The diluent includes the following raw materials by mass fraction: 80 parts of ethylene glycol; 10 parts of paraffin wax; 5 parts of liquid paraffin; 5 parts of dioctyl phthalate.

[0074] The temperature of the mixing is 150 °C and the mixing time is 4 hours.

[0075] Example 2

[0076] A particle of a ceramic filter membrane, characterized in that it is mixed and extruded into shape according to the following raw materials by mass fraction: 72 parts of high-purity alumina powder; 20 parts of organic binder; 3 parts of pore former; 5 parts of diluent.

[0077] The purity of the high-purity alumina powder is ≥99.9% and the average particle size is 20 μm.

[0078] The organic binder includes the following raw materials by mass fraction: 8 parts of epoxy resin; 60 parts of polyethersulfone plastic; 4 parts of polyethylene wax; 20 parts of high-density polyethylene; 2 parts of polyethylene glycol plasticizer; 4 parts of polyvinylpyrrolidone dispersant; 2 parts of magnesium stearate.

[0079] The pore former includes the following raw materials by mass fraction: 30 parts of corn starch; 10 parts of phenolic resin powder; 30 parts of synthetic carbon powder; 30 parts of graphene.

[0080] The diluent includes the following raw materials by mass fraction: 60 parts of ethylene glycol; 20 parts of paraffin wax; 10 parts of liquid paraffin; 10 parts of dioctyl phthalate.

[0081] The temperature of the mixing is 260 °C and the mixing time is 2 hours.

[0082] Example 3

[0083] A particle of a ceramic filter membrane, characterized in that it is mixed and extruded into shape according to the following raw materials by mass fraction: 65 parts of high-purity alumina powder; 15 parts of organic binder; 15 parts of pore former; 5 parts of diluent.

[0084] The purity of the high-purity alumina powder is ≥99.9% and the average particle size is 5 μm.

[0085] The organic binder comprises the following raw materials by mass parts: 15 parts of epoxy resin; 30 parts of polyethersulfone plastic; 4 parts of polyethylene wax; 37 parts of high-density polyethylene; 10 parts of liquid rubber; 1 part of polyethylene glycol plasticizer; 2 parts of polyvinylpyrrolidone dispersant; 1 part of magnesium stearate.

[0086] The pore former comprises the following raw materials by mass parts: 20 parts of corn starch; 20 parts of phenolic resin powder; 30 parts of synthetic carbon powder; 30 parts of polymethyl methacrylate powder.

[0087] The diluent comprises the following raw materials by mass parts: 80 parts of ethylene glycol; 10 parts of paraffin wax; 5 parts of liquid paraffin; 5 parts of dioctyl phthalate.

[0088] The temperature of the mixing is 190 °C and the mixing time is 1 hour.

[0089] The technical principle of the present invention has been described with reference to specific embodiments. These descriptions are only for explaining the principle of the present invention and should not be construed in any way as a limitation on the protection scope of the present invention. Based on the explanations herein, those skilled in the art can readily conceive of other specific embodiments of the present invention without creative efforts, and these embodiments will fall within the protection scope of the claims of the present invention.

Claims

1. A particle of a ceramic filter membrane, characterized in that, Mix and extrude into shape according to the following raw materials by mass parts: 60 - 99 parts of high-purity alumina powder; 8 - 20 parts of organic binder; 3 - 15 parts of pore former; 5 - 20 parts of diluent.

2. The particles of a ceramic filter membrane according to claim 1, wherein the purity of the high-purity alumina powder is ≥99.9%, and the average particle size is 0.5 - 20 μm.

3. The particles of a ceramic filter membrane according to claim 1, wherein the organic binder comprises the following raw materials by mass parts: the organic binder comprises the following raw materials by mass parts: 5 - 15 parts of epoxy resin; 20 - 60 parts of polyethersulfone plastic; 2 - 4 parts of polyethylene wax; 20 - 60 parts of high-density polyethylene; 0 - 10 parts of liquid rubber; 1 - 2 parts of polyethylene glycol plasticizer; 2 - 4 parts of polyvinylpyrrolidone dispersant; 1 - 2 parts of magnesium stearate.

4. The particles of a ceramic filter membrane according to claim 1, wherein the pore former comprises the following raw materials by mass parts: 10 - 30 parts of corn starch; 10 - 20 parts of phenolic resin powder; 30 - 60 parts of synthetic carbon powder; 0 - 30 parts of graphene; 0 - 30 parts of carbon nanotubes; 0 - 30 parts of polymethyl methacrylate powder.

5. The particles of a ceramic filter membrane according to claim 1, wherein the diluent comprises the following raw materials by mass parts: 50 - 80 parts of ethylene glycol; 4 - 20 parts of paraffin wax; 4 - 20 parts of liquid paraffin; 5 - 10 parts of dioctyl phthalate.

6. The particles of a ceramic filter membrane according to claim 1, wherein the temperature of the mixing is 150 - 240 °C, and the mixing time is 1 - 4 hours.

7. A method for preparing a ceramic filter membrane, using the particles of a ceramic filter membrane described in claim 1, characterized in that, It includes the following steps: Forming, preparing the particles of the ceramic filter membrane into the required shape; Debinding, removing the organic binder and pore former; Sintering, the sintering temperature is 1300 - 1750 °C.

8. The forming method of a ceramic filter membrane according to claim 7, wherein the forming includes: thermoplastic extrusion forming using a screw extruder, hot pressing forming using a hydraulic press, and injection molding.

9. The debinding method of a ceramic filter membrane according to claim 7, wherein the debinding includes: debinding in a debinding furnace, supercritical carbon dioxide debinding, or superheated saturated steam debinding.

10. The preparation method of a ceramic filter membrane according to claim 7, wherein the sintering process curve of the sintering includes: Low-temperature stage, room temperature - 300 °C, heating rate 0.5 - 1 °C / min; Medium-temperature stage, 300 °C - 750 °C, heating rate 1 - 2 °C / min; High-temperature stage, 750 °C - sintering temperature, heating rate 3 - 5 °C / min; Insulation stage, insulating for 1 - 3 hours.

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