Glassy carbon mold and recrystallized silicon carbide article and method of making

Abstract

The application provides a glass carbon mold and a recrystallized silicon carbide product and a preparation method, and belongs to the technical field of ceramic material preparation. Microcrystalline cellulose is mixed with water, and the obtained mixture is formed to obtain a cellulose body; the cellulose body is subjected to a stabilization treatment in an oxygen-containing atmosphere to obtain a stabilized body; and the stabilized body is subjected to a carbonization treatment in a protective atmosphere to obtain the glass carbon mold. The glass carbon mold is used to prepare the recrystallized silicon carbide product, which is convenient for directly forming a complex green body and can be sintered together with the product, solves the problem that the green body is easily damaged and deformed in the transfer process, and is environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of ceramic material preparation technology, and in particular to glassy carbon molds and recrystallized silicon carbide products and their preparation methods. Background Technology

[0002] Recrystallized silicon carbide (R-SiC) materials are widely used in photovoltaics, semiconductors, aerospace, high-temperature kiln furniture, chemical metallurgy, and other fields due to their excellent high-temperature strength, high thermal conductivity, excellent thermal shock resistance, good wear resistance, and chemical stability. However, the sintering of R-SiC is usually achieved at high temperatures (>2400℃) through the evaporation-condensation mechanism of SiC materials. During this process, there is almost no volume shrinkage. This characteristic makes it difficult to use traditional ceramic forming processes that rely on sintering shrinkage for densification (such as dry pressing and isostatic pressing) to manufacture R-SiC products with complex shapes.

[0003] Currently, the main methods for preparing complex-shaped R-SiC products include processing sintering, slip casting, and gel casting. Processing sintering involves first preparing a simple-shaped R-SiC preform, then machining it with expensive diamond tools. This method results in significant material waste, high costs, and difficulty in machining complex internal channels or closed structures. Slip casting typically requires porous plaster molds, but these molds have low strength and are not heat-resistant, limiting their use to green body forming. After demolding, the green body has low strength and is prone to deformation and damage during subsequent handling and sintering, leading to a low yield. Gel casting also suffers from low green body strength and easy deformation after demolding. Furthermore, the gel casting process involves the polymerization of organic monomers, which poses health risks and has a significant environmental impact. Summary of the Invention

[0004] The purpose of this invention is to provide glassy carbon molds, recrystallized silicon carbide products, and preparation methods. Using the glassy carbon molds of this invention to prepare recrystallized silicon carbide products facilitates the direct molding of complex-shaped green bodies and enables sintering along with the finished product. This solves the problem of easy damage and deformation during the transfer of green bodies and is also environmentally friendly.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a glassy carbon mold, comprising the following steps:

[0007] Microcrystalline cellulose is mixed with water, and the resulting mixture is molded to obtain a cellulose preform.

[0008] The cellulose preform is stabilized in an oxygen-containing atmosphere to obtain a stabilized preform. The stabilization process includes: heating to 195-205°C at a heating rate of 1-2°C / min, continuing to heat to 295-305°C at a heating rate of 0.5-1°C / min, continuing to heat to 345-355°C at a heating rate of 0.2-0.5°C / min, and holding at the temperature for 1-2 hours.

[0009] In a protective atmosphere, the stabilized preform is carbonized to obtain the glass carbon mold; the carbonization process includes: heating to 595-605°C at a heating rate of 2-3°C / min, continuing to heat to 995-1005°C at a heating rate of 3-5°C / min, continuing to heat to 1395-1405°C at a heating rate of 1.5-2.5°C / min, and holding at the temperature for 1-2 hours.

[0010] Preferably, the density of the cellulose preform is 0.8~1.0 g / cm³. 3 The molding process is selected from 3D printing, compression molding, or coating molding.

[0011] When the 3D printing process is employed, the moisture content of the mixture is 78-82 wt%.

[0012] When compression molding is used, the moisture content of the mixture is ≤2wt%, and the compression molding pressure is 50~100MPa;

[0013] When a coating process is used, the moisture content of the mixture is 45-55 wt%.

[0014] This invention provides a glassy carbon mold, which is prepared by the preparation method described in the above technical solution.

[0015] This invention provides a method for preparing recrystallized silicon carbide products, comprising the following steps:

[0016] The silicon carbide raw material is shaped using the glass carbon mold described above to obtain a silicon carbide green body-glass carbon mold composite.

[0017] The silicon carbide green body-glass carbon mold composite is sintered in a vacuum or protective atmosphere to achieve silicon carbide recrystallization and glass carbon mold graphite phase pulverization, thereby obtaining the recrystallized silicon carbide product.

[0018] Preferably, the shaping method is selected from internal pressure shaping method, internal grouting shaping method, external grouting shaping method, or internal-external simultaneous grouting shaping method.

[0019] Preferably, the internal pressing and shaping method includes the following steps: a portion of the silicon carbide raw material is pressed in a first pressing to obtain a bottom blank; the glass carbon mold is placed on the surface of the bottom blank; the glass carbon mold is used as a core; the remaining silicon carbide raw material is pressed in a second pressing on the surface of the glass carbon mold to obtain a top blank; and the bottom blank, the glass carbon mold, and the top blank are pressed in a third pressing.

[0020] The internal grouting and shaping method includes the following steps: preparing silicon carbide slurry using the silicon carbide raw material; using the glass carbon mold as the core and the supporting mold as the shell; pouring the silicon carbide slurry into the gap between the core and the shell; and removing the shell after a first curing process; the supporting mold is selected from gypsum mold, graphite mold, polyurethane mold, polyethylene mold, PMMA mold, or paraffin wax mold.

[0021] The external grouting and shaping method includes the following steps: preparing silicon carbide slurry using the silicon carbide raw material; using the glass carbon mold as a shell, pouring the silicon carbide slurry into the cavity of the shell, and then performing a second curing;

[0022] The internal-external simultaneous grouting and shaping method includes the following steps: preparing silicon carbide slurry using the silicon carbide raw material; using two glass carbon molds as the core and shell respectively; pouring the silicon carbide slurry into the gap between the core and shell; and then performing a third curing.

[0023] Preferably, the first curing, second curing, and third curing independently include: standing for 15-25 minutes at a temperature of 20-25°C and a relative humidity of 50-70%; then pre-drying for 4-12 hours at a temperature of 20-25°C and a relative humidity of 60-75%; then low-temperature drying for 10-24 hours at a temperature of 40-50°C and a relative humidity of 40-50%; and then medium-temperature drying for 5-15 hours at a temperature of 60-80°C.

[0024] Preferably, the sintering temperature is 2250~2650℃, and the holding time is 1~4h.

[0025] Preferably, the sintering process further includes: high-pressure gas purging or low-temperature oxidation; the pressure of the high-pressure gas purging is 1~3 bar; the temperature of the low-temperature oxidation is 700~900℃.

[0026] This invention provides a recrystallized silicon carbide product, which is prepared by the preparation method described in the above technical solution. The recrystallized silicon carbide product is an irregularly shaped recrystallized silicon carbide product, and the recrystallized silicon carbide product is selected from filter membranes, precision screws, crystal boats or decorative crafts.

[0027] Beneficial Effects: This invention mixes microcrystalline cellulose with water, shapes the resulting mixture to obtain a cellulose preform, stabilizes the cellulose preform in an oxygen-containing atmosphere to obtain a stabilized preform, and then carbonizes the stabilized preform in a protective atmosphere to obtain the glassy carbon mold. In the stabilization process, this invention employs a slow heating rate, which helps the cellulose molecular chains to slowly crosslink, forming a stable network structure and avoiding rapid decomposition that could lead to cracking or pulverization of the preform. During the carbonization process, the stabilized preform is transformed into glassy carbon, and precise control of the heating program helps improve the strength of the glassy carbon, preventing breakage and pulverization. This invention creatively uses glassy carbon as a sacrificial mold material, mainly utilizing its four major characteristics: microcrystalline cellulose can be precisely shaped through the above treatment; it has sufficient support strength for silicon carbide green bodies; its coefficient of thermal expansion matches that of silicon carbide; and it can achieve self-pulverization and removal under the recrystallization silicon carbide sintering temperature.

[0028] This invention relates to the preparation of recrystallized silicon carbide products using a sacrificial glassy carbon mold. The glassy carbon mold is used to shape the silicon carbide raw material, resulting in a silicon carbide green body-glassy carbon mold composite. Then, the silicon carbide green body-glassy carbon mold composite is sintered in a vacuum or protective atmosphere to achieve silicon carbide recrystallization and the pulverization of the graphite phase in the glassy carbon mold, yielding the recrystallized silicon carbide product. The shaping method in this invention is flexible (e.g., internal pressing, internal slurry casting, external slurry casting, or simultaneous internal and external slurry casting), meeting the needs of products with different structural characteristics. This invention organically integrates the two key processes of shaping and sintering using a sacrificial glassy carbon mold, forming a complete, efficient, and reliable closed-loop process, solving the problem of easy damage and deformation during green body transfer, and is also environmentally friendly. Attached Figure Description

[0029] Figure 1 This is a process flow diagram for preparing glassy carbon molds and preparing recrystallized silicon carbide products based on sacrificial glassy carbon molds in this invention.

[0030] Figure 2 A photograph of a glass carbon mold used as a core.

[0031] Figure 3 A photograph of a glass carbon mold used as the outer shell;

[0032] Figure 4 A physical image of the silicon carbide green body-glass carbon mold composite;

[0033] Figure 5 A photograph of the recrystallized silicon carbide disc filter membrane with internal flow channels prepared in Example 1;

[0034] Figure 6The image shows a physical picture of the recrystallized silicon carbide ornament with embossed artistic patterns on the outside, prepared in Example 2. Detailed Implementation

[0035] This invention provides a method for preparing a glassy carbon mold, comprising the following steps:

[0036] Microcrystalline cellulose is mixed with water, and the resulting mixture is molded to obtain a cellulose preform.

[0037] The cellulose preform is stabilized in an oxygen-containing atmosphere to obtain a stabilized preform. The stabilization process includes: heating to 195-205°C at a heating rate of 1-2°C / min, continuing to heat to 295-305°C at a heating rate of 0.5-1°C / min, continuing to heat to 345-355°C at a heating rate of 0.2-0.5°C / min, and holding at the temperature for 1-2 hours.

[0038] In a protective atmosphere, the stabilized preform is carbonized to obtain the glass carbon mold; the carbonization process includes: heating to 595-605°C at a heating rate of 2-3°C / min, continuing to heat to 995-1005°C at a heating rate of 3-5°C / min, continuing to heat to 1395-1405°C at a heating rate of 1.5-2.5°C / min, and holding at the temperature for 1-2 hours.

[0039] In this invention, unless otherwise specified, all raw materials used are commercially available products well known to those skilled in the art or prepared using methods well known to those skilled in the art.

[0040] This invention involves mixing microcrystalline cellulose with water, and then molding the resulting mixture to obtain a cellulose preform. In one embodiment of this invention, the microcrystalline cellulose (MCC) has the following specifications: average particle size (D50) of 100 μm; Karl Fischer index of 16-20%; sulfate ash content ≤0.1 wt%; and heavy metal content ≤10 ppm. Preferably, the moisture content of the mixture is determined according to the molding method. In one embodiment of this invention, the molding process can be selected from 3D printing, compression molding, or coating molding. In one embodiment of this invention, when using 3D printing, the moisture content of the mixture can be 78-82 wt%, specifically 80 wt%. In one embodiment of this invention, when using compression molding, the moisture content of the mixture is ≤2 wt%, specifically 1-2 wt%; the compression molding pressure can be 50-100 MPa, specifically 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, or 100 MPa.In one embodiment of the present invention, when a coating film is used, the moisture content of the mixture can be 45-55 wt%, specifically 50 wt%; the coating film forming includes sequentially performing coating, a first curing treatment, a second curing treatment, a third curing treatment, and firing; the coating method can be a casting method or a smearing method; the first curing treatment includes: in an air atmosphere, heating from room temperature to 75-85°C at a heating rate of <2°C / min and holding at that temperature for 2.5-3.5 hours, specifically heating from room temperature to 80°C at a heating rate of 1°C / min and holding at that temperature for 3 hours. The present invention uses slow heating to avoid rapid evaporation of moisture leading to blistering or cracking of the film layer; the second curing treatment includes: in an air atmosphere, heating from the holding temperature of the first curing treatment to 195-205°C at a heating rate of <2°C / min and holding at that temperature for 50-70 minutes, specifically heating from 80°C to 200°C at a heating rate of 1°C / min and holding at that temperature for 1 hour. This stage is the core stage of pre-oxidation. The above conditions are conducive to the full and stable progress of the subsequent oxidation reaction; the third curing treatment includes: in an air atmosphere, heating from the holding temperature of the second curing treatment to 295~305℃ at a heating rate of <5℃ / min and holding at that temperature for 50~70min, specifically from 200℃ to 300℃ at a heating rate of 4℃ / min and holding at that temperature for 1h; the firing includes: in a protective atmosphere (such as nitrogen), heating from the holding temperature of the third curing treatment to... The firing process can be performed as follows: In a nitrogen atmosphere, the temperature is increased from 300°C to 600°C at a rate of 2°C / min and held for 30 minutes, then increased to 1000°C at a rate of 5°C / min and held for 2 hours, and then cooled to room temperature in the furnace while maintaining a protective atmosphere.

[0041] In one embodiment of the present invention, the density of the cellulose preform can be 0.8~1.0 g / cm³. 3 Specifically, it can be 0.8 g / cm³. 3 0.9g / cm 3 Or 1.0g / cm 3 The shape of the cellulose preform can be determined as needed. Specifically, the cellulose preform can be a male mold preform or a female mold preform, or it can be a preform with the required precision structure inside and an overall block shape on the outside.

[0042] After obtaining the cellulose preform, the present invention stabilizes the cellulose preform in an oxygen-containing atmosphere to obtain a stabilized preform. In one embodiment of the present invention, the oxygen-containing atmosphere can be an air atmosphere or an oxygen atmosphere. In the present invention, the stabilization treatment includes: heating to 195-205°C at a heating rate of 1-2°C / min, continuing to heat to 295-305°C at a heating rate of 0.5-1°C / min, continuing to heat to 345-355°C at a heating rate of 0.2-0.5°C / min, and holding at this temperature for 1-2 hours. In an embodiment of the present invention, specifically, the temperature is increased from room temperature to 200°C at a heating rate of 1.5°C / min (without holding), continued to heat to 300°C at a heating rate of 0.8°C / min (without holding), and continued to heat to 350°C at a heating rate of 0.3°C / min, and held at this temperature for 1.5 hours; after the holding period, the temperature is cooled in the furnace. The stabilization process described in this invention is a pre-carbonization process. The temperature range of 200~400℃ is the temperature range in which cellulose mainly decomposes and loses weight. In the stabilization process, this invention adopts a slow heating rate, which helps the cellulose molecular chains to crosslink slowly, forming a stable network structure and avoiding rapid decomposition that could lead to cracking or pulverization of the green body.

[0043] After obtaining the stabilized green body, the present invention performs carbonization treatment on the stabilized green body in a protective atmosphere to obtain the glass carbon mold. In one embodiment of the present invention, the protective atmosphere may include a nitrogen atmosphere or an argon atmosphere. In the present invention, the carbonization treatment includes: heating to 595-605°C at a heating rate of 2-3°C / min, continuing to heat to 995-1005°C at a heating rate of 3-5°C / min, continuing to heat to 1395-1405°C at a heating rate of 1.5-2.5°C / min, and holding at this temperature for 1-2 hours. In an embodiment of the present invention, specifically, the temperature is increased from room temperature to 600°C at a heating rate of 2.5°C / min (without holding), continued to heat to 1000°C at a heating rate of 4°C / min (without holding), and continued to heat to 1400°C at a heating rate of 2°C / min, and held at this temperature for 1.5 hours; after the holding period, the furnace is cooled. In the carbonization process described in this invention, the stabilized green body is transformed into glassy carbon. By precisely controlling the heating program, the strength of the glassy carbon is improved, and cracking and pulverization are avoided. During the heat preservation stage of the carbonization process, controlling the heat preservation time to 1-2 hours helps ensure the completion of the pyrolysis reaction and the homogenization of the structure.

[0044] As one embodiment of the present invention, after the carbonization treatment, laser cutting or computer numerical control processing can be performed according to actual needs to obtain a glass carbon mold with the required precision structure.

[0045] This invention provides a glassy carbon mold, prepared by the method described in the above technical solution. The glassy carbon mold obtained by the preparation method provided by this invention has high strength and a coefficient of thermal expansion that matches that of silicon carbide, enabling it to form complex-shaped silicon carbide green bodies. During the sintering process of the silicon carbide green body, the glassy carbon mold can decompose to pulverize the graphite phase and remove it.

[0046] This invention provides a method for preparing recrystallized silicon carbide products, comprising the following steps:

[0047] The silicon carbide raw material is shaped using the glass carbon mold described above to obtain a silicon carbide green body-glass carbon mold composite.

[0048] The silicon carbide green body-glass carbon mold composite is sintered in a vacuum or protective atmosphere to achieve silicon carbide recrystallization and glass carbon mold graphite phase pulverization, thereby obtaining the recrystallized silicon carbide product.

[0049] This invention uses the glassy carbon mold to shape silicon carbide raw materials, obtaining a silicon carbide green body-glassy carbon mold composite. As one embodiment of this invention, the shaping method can be selected from internal pressure shaping, internal grouting shaping, external grouting shaping, or simultaneous internal and external grouting shaping. These will be described below.

[0050] In one embodiment of the present invention, the internal pressing and shaping method includes the following steps: a portion of the silicon carbide raw material is pressed in a first pressing to obtain a bottom blank; a glassy carbon mold is placed on the surface of the bottom blank, the glassy carbon mold is used as a core; the remaining silicon carbide raw material is pressed in a second pressing on the surface of the glassy carbon mold to obtain a top blank; the bottom blank, the glassy carbon mold, and the top blank are pressed in a third pressing to obtain the silicon carbide green blank-glassy carbon mold composite. In another embodiment of the present invention, the silicon carbide raw material includes coarse silicon carbide particles, fine silicon carbide particles, microcrystalline cellulose, and water. The particle size of the coarse silicon carbide particles can be 7~10 μm, and the particle size of the fine silicon carbide particles can be 0.7~1.2 μm. The mass ratio of the coarse silicon carbide particles to the fine silicon carbide particles can be 6.5~7.5:2.5~3.5, specifically 7:3. The content of microcrystalline cellulose in the silicon carbide raw material can be 0.5~1 wt%, and the content of water can be 1.5~2 wt%. In one embodiment of the present invention, the conditions for the first pressing include: room temperature and an applied pressure of 70-100 MPa, specifically 75 MPa, 80 MPa, 85 MPa, or 90 MPa; the conditions for the second pressing include: room temperature and an applied pressure of 50-80 MPa, specifically 55 MPa, 60 MPa, 65 MPa, 70 MPa, or 75 MPa; the conditions for the third pressing include: room temperature and an applied pressure of 75-85 MPa, specifically 78 MPa, 80 MPa, or 82 MPa. Specifically, in this embodiment of the present invention, the silicon carbide green body-glass carbon mold composite is prepared using an internal pressing and shaping method in a stamping press.

[0051] In one embodiment of the present invention, the internal grouting and shaping method includes the following steps: preparing a silicon carbide slurry using the silicon carbide raw material; using the glass carbon mold as the core and the supporting mold as the shell; pouring the silicon carbide slurry into the gap between the core and the shell; and removing the shell after a first curing process to obtain the silicon carbide green body-glass carbon mold composite. In one embodiment of the present invention, the water content of the silicon carbide slurry can be 75-80 wt%. In one embodiment of the present invention, the supporting mold can be selected from gypsum molds, graphite molds, polyurethane molds, polyethylene molds, PMMA molds, or paraffin molds, preferably gypsum molds; the present invention uses gypsum molds as supporting molds, which have water absorption properties and can absorb some of the water in the silicon carbide slurry, thus promoting the curing of the silicon carbide slurry. In one embodiment of the present invention, the first curing includes: standing for 15-25 minutes at a temperature of 20-25°C and a relative humidity of 50-70%; then pre-drying for 4-12 hours at a temperature of 20-25°C and a relative humidity of 60-75%; then low-temperature drying for 10-24 hours at a temperature of 40-50°C and a relative humidity of 40-50%; and finally medium-temperature drying for 5-15 hours at a temperature of 60-80°C. In another embodiment of the present invention, humidification is preferably achieved using a humidifier during the standing and pre-drying processes to ensure the relative humidity remains within the aforementioned ranges; relative ventilation is preferably used during the low-temperature drying process; and natural ventilation is preferably used during the medium-temperature drying process. In this embodiment of the invention, the process involves: standing for 20 minutes at 20°C and 60% relative humidity (using a humidifier); pre-drying for 6 hours at 25°C and 65% relative humidity (using a humidifier); low-temperature drying for 15 hours at 45°C and 45% relative humidity (with relative ventilation); and medium-temperature drying for 10 hours at 70°C (with natural ventilation). Maintaining relative ventilation during the low-temperature drying process facilitates moisture removal and promotes curing. During the medium-temperature drying process, humidity is not the primary controlling factor; natural ventilation promotes curing.

[0052] In one embodiment of the present invention, the external grouting and shaping method includes the following steps: preparing a silicon carbide slurry using the silicon carbide raw material; using the glass carbon mold as a shell, pouring the silicon carbide slurry into the cavity of the shell, and then performing a second curing to obtain the silicon carbide green body-glass carbon mold composite. In one embodiment of the present invention, the moisture content of the silicon carbide slurry can be 80~85wt%. In one embodiment of the present invention, the steps and conditions of the second curing can be the same as those of the first curing.

[0053] In one embodiment of the present invention, the simultaneous internal-external grouting and shaping method includes the following steps: preparing a silicon carbide slurry using the silicon carbide raw material; using two glassy carbon molds as the core and shell respectively, pouring the silicon carbide slurry into the gap between the core and shell, and then performing a third curing to obtain the silicon carbide green body-glassy carbon mold composite. In one embodiment of the present invention, the moisture content of the silicon carbide slurry can be 80~85wt%. In one embodiment of the present invention, the third curing step and conditions can be the same as the first curing step.

[0054] After obtaining the silicon carbide green body-glassy carbon mold composite, the present invention sintersects the silicon carbide green body-glassy carbon mold composite in a vacuum or protective atmosphere to achieve silicon carbide recrystallization and glassy carbon mold graphite phase pulverization, thereby obtaining the recrystallized silicon carbide product. As one embodiment of the present invention, the sintering temperature can be 2250~2650℃, specifically 2250℃, 2300℃, 2350℃, 2400℃, 2450℃, 2500℃, 2550℃, 2600℃, or 2650℃; the holding time can be 1~4h, specifically 1h, 2h, 3h, or 4h; the heating rate to the sintering temperature can be 5~10℃ / min, specifically 8℃ / min; no pressure is applied during the sintering process of the present invention. As one embodiment of the present invention, when the sintering is performed under vacuum conditions, it is preferable to evacuate to 10... -2 The sintering is carried out below Pa. In this embodiment of the invention, the sintering is specifically carried out in a graphite induction furnace. During the sintering process of this invention, silicon carbide particles achieve recrystallization sintering through an evaporation-condensation mechanism to form a dense R-SiC network structure; at the same time, the glassy carbon mold, as a sacrificial material, begins to transform into the graphite phase above 2000°C, with a linear shrinkage rate of about 5~10% (isotropic shrinkage) and a volume shrinkage rate of about 15~20% (due to a density increase of more than 40%). Since no pressure is applied during the sintering process, the heating rate is high, such as close to 500°C / h in this embodiment, which causes the transformed graphite phase to pulverize, thereby achieving its separation from the recrystallized silicon carbide product.

[0055] In one embodiment of the present invention, the sintering process further includes: high-pressure gas purging or low-temperature oxidation, which facilitates further removal of residual graphite powder and ultimately yields a recrystallized silicon carbide product with complex shapes, high precision, and high surface quality. In one embodiment of the present invention, the pressure of the high-pressure gas purging can be 1~3 bar, specifically 1 bar, 2 bar, or 3 bar; the gas used can be air or nitrogen; and the purging time can be 10~20 s / cm, based on the area of ​​the recrystallized silicon carbide product. 2 Specifically, it can be 10 s / cm2 15s / cm 2 Or 20s / cm 2 In one embodiment of the present invention, the temperature of the low-temperature oxidation can be 700~900℃, specifically 700℃, 750℃, 800℃, 850℃ or 900℃; the time can be 30~60min, specifically 30min, 35min, 40min, 50min or 60min; the low-temperature oxidation can be carried out in an air atmosphere.

[0056] This invention provides a recrystallized silicon carbide product, prepared by the method described in the above technical solution. The recrystallized silicon carbide product is an irregularly shaped recrystallized silicon carbide product, selected from filter membranes, precision screws, crystal boats, or decorative artifacts. In this invention, the filter membrane can be a disc filter membrane, specifically a disc filter membrane with internal flow channels. In the embodiments, the disc filter membrane with internal flow channels has a complete structure, smooth surface, clear internal flow channels, an open porosity greater than 45%, an average pore size of 19.3 μm, and excellent mechanical properties, thermal properties, and chemical stability, meeting the usage requirements. The decorative artifact can be a decorative artifact with embossed artistic patterns on the outside.

[0057] Compared with the prior art, the present invention has at least the following beneficial effects:

[0058] 1. High precision and complex molding capability: Glass carbon molds can be replicated through high-precision 3D printing of master molds (volume shrinkage must be considered in the cellulose preform stage), enabling the preparation of recrystallized silicon carbide products with extremely complex internal flow channels, fine patterns or irregular structures, with high dimensional accuracy and good surface finish.

[0059] 2. Perfect green body support: The glass carbon mold provides rigid support for the fragile silicon carbide green body during the silicon carbide green body stage, which completely solves the industry problem of easy breakage and deformation of complex-shaped silicon carbide green bodies during demolding, transfer and furnace loading, and can greatly improve the yield.

[0060] 3. Integrated sintering and self-removal: The glass carbon mold and silicon carbide green body are sintered together, which can achieve the removal of the glass carbon mold in situ while the silicon carbide is sintering, eliminating the complicated mechanical demolding steps, simplifying the process, and achieving "near-net-shape forming".

[0061] 4. No pollution: The components of the glass carbon mold are transformed into graphite during the sintering process and gradually pulverize during the high-temperature heating process. This avoids the problem of introducing metal ion impurities that may occur when using gypsum molds or certain binders, ensuring that recrystallized silicon carbide products have high purity and excellent high-temperature performance.

[0062] 5. Good thermal compatibility: The thermal expansion coefficient of glassy carbon is similar to that of silicon carbide. During the heating process, it can effectively reduce the internal stress caused by the thermal expansion mismatch between the two and prevent the silicon carbide green blank from cracking.

[0063] Figure 1 This is a process flow diagram for preparing glassy carbon molds and preparing recrystallized silicon carbide products based on sacrificial glassy carbon molds in this invention. Figure 2 A photograph of a glass carbon mold used as a core. Figure 3 The image shows a glass carbon mold used as the outer shell. Figure 4 This is a physical image of the silicon carbide green body-glass carbon mold composite. The technical solutions of this invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0064] The specifications of the microcrystalline cellulose used in the following experiments include: average particle size (D50) of 100 μm, Karl Fischer index of 16-20%, sulfate ash content ≤0.1 wt%, and heavy metal content ≤10 ppm; purchased from Shandong Landu New Materials Co., Ltd., model ME4M.

[0065] Example 1

[0066] The preparation of a recrystallized silicon carbide disc filter membrane with internal flow channels includes the following steps:

[0067] Microcrystalline cellulose was mixed with water to obtain a mixture with a moisture content of 2 wt%; the mixture was then pressed and molded under a pressure of 80 MPa to obtain a cellulose preform (density 1.0 g / cm³). 3 );

[0068] The cellulose preform is stabilized in an air atmosphere to obtain a stabilized preform. The stabilization process includes: heating from room temperature to 200°C at a heating rate of 1.5°C / min (without holding), heating to 300°C at a heating rate of 0.8°C / min (without holding), heating to 350°C at a heating rate of 0.3°C / min, and holding for 1.5 hours; cooling with the furnace after the holding period.

[0069] In a nitrogen atmosphere, the stabilized preform is carbonized to obtain a glass carbon plate. The carbonization process includes: heating from room temperature to 600°C at a heating rate of 2.5°C / min (without holding), continuing to heat to 1000°C at a heating rate of 4°C / min (without holding), and continuing to heat to 1400°C at a heating rate of 2°C / min, holding for 1.5 hours; cooling with the furnace after holding; the glass carbon plate has a thickness of 2 mm, and the glass carbon plate is laser-cut to obtain a glass carbon mold with flow channels.

[0070] Silicon carbide coarse particles (7-10 μm in diameter), silicon carbide fine particles (0.7-1.2 μm in diameter), microcrystalline cellulose, and water are mixed to obtain silicon carbide raw material. The mass ratio of coarse to fine silicon carbide particles is 7:3. The content of microcrystalline cellulose in the silicon carbide raw material is 1 wt%, and the content of water is 2 wt%. The silicon carbide raw material is spread using a stamping press and pressed at room temperature and pressure of 80 MPa to obtain a bottom blank. The glass carbon mold is placed on the surface of the bottom blank as a core. Then, the silicon carbide raw material is spread on the surface of the glass carbon mold again using a stamping press and pressed at room temperature and pressure of 65 MPa to obtain a top blank. The bottom blank, glass carbon mold, and top blank are pressed at room temperature and pressure of 80 MPa to obtain a silicon carbide green blank-glass carbon mold composite.

[0071] The silicon carbide green body-glass carbon mold composite was placed in a graphite induction furnace and evacuated to 10°C. -2 The temperature was increased from room temperature to 2250℃ at a rate of 8℃ / min and held for 2 hours (without pressure). During this process, silicon carbide particles recrystallized and sintered, while the glassy carbon mold transformed into the graphite phase and pulverized. After the holding period, the furnace was cooled, followed by high-pressure gas purging to further remove residual graphite powder. The high-pressure gas purging pressure was 2 bar, the gas used was air, and the purging time was 15 s / cm. 2 After high-pressure gas purging, a recrystallized silicon carbide disc filter membrane with internal flow channels is obtained, which has a complete structure, smooth surface and clear internal flow channels.

[0072] Figure 5 The image shows a physical photograph of the recrystallized silicon carbide disc filter membrane with internal flow channels prepared in Example 1. The left side shows a photograph of the half-sheet structure, and the right side shows a photograph of the overall structure.

[0073] The performance of the recrystallized silicon carbide disc filter membrane with internal flow channels prepared in Example 1 was tested, and the results are shown in Table 1. The results show that the recrystallized silicon carbide disc filter membrane with internal flow channels prepared in Example 1 has high porosity and excellent mechanical properties, thermal properties, surface and chemical properties.

[0074] Table 1 Performance test results of the recrystallized silicon carbide disc filter membrane with internal flow channels in Example 1

[0075]

[0076] Example 2

[0077] The preparation of a recrystallized silicon carbide decorative piece with embossed artistic patterns on the exterior includes the following steps:

[0078] Microcrystalline cellulose was mixed with water to obtain a mixture with a water content of 50 wt%; the mixture was then coated to obtain a cellulose preform (density 0.8 g / cm³). 3 The coating process includes sequentially applying a coating, a first curing treatment, a second curing treatment, a third curing treatment, and firing. The coating method is a casting method. The first curing treatment is as follows: in an air atmosphere, the temperature is increased from room temperature to 80°C at a heating rate of 1°C / min and held for 3 hours. The second curing treatment is as follows: in an air atmosphere, the temperature is increased from 80°C to 200°C at a heating rate of 1°C / min and held for 1 hour. The third curing treatment is as follows: in an air atmosphere, the temperature is increased from 200°C to 300°C at a heating rate of 4°C / min and held for 1 hour. The firing process includes: in a nitrogen atmosphere, the temperature is increased from 300°C to 600°C at a heating rate of 2°C / min and held for 30 minutes, then increased to 1000°C at a heating rate of 5°C / min and held for 2 hours, and then the nitrogen atmosphere is maintained while the furnace cools to room temperature.

[0079] The cellulose preform is stabilized in an air atmosphere to obtain a stabilized preform. The stabilization process includes: heating from room temperature to 200°C at a heating rate of 1.5°C / min (without holding), heating to 300°C at a heating rate of 0.8°C / min (without holding), heating to 350°C at a heating rate of 0.3°C / min, and holding for 1.5 hours; cooling with the furnace after the holding period.

[0080] In a nitrogen atmosphere, the stabilized preform is carbonized to obtain a glass carbon plate. The carbonization process includes: heating from room temperature to 600°C at a heating rate of 2.5°C / min (without holding), heating to 1000°C at a heating rate of 4°C / min (without holding), heating to 1400°C at a heating rate of 2°C / min, and holding for 1.5 hours; cooling with the furnace after holding; the glass carbon plate has a thickness of 10 mm. The glass carbon plate is then machined by computer numerical control (CNC) to obtain a glass carbon mold with a pattern corresponding to the target relief art pattern.

[0081] Coarse silicon carbide particles (7-10 μm in diameter), fine silicon carbide particles (0.7-1.2 μm in diameter), and microcrystalline cellulose are mixed to obtain a silicon carbide raw material, wherein the mass ratio of coarse to fine silicon carbide particles is 7:3, and the content of microcrystalline cellulose in the silicon carbide raw material is 0.5 wt%. The silicon carbide raw material is mixed with water to obtain a silicon carbide slurry with a water content of 80 wt%. The glassy carbon mold is used as a shell, and the silicon carbide slurry is poured into the cavity of the shell. The process involves curing to obtain a silicon carbide green body-glass carbon mold composite. The curing process includes: standing for 20 minutes at 20°C and 60% relative humidity (using a humidifier); pre-drying for 6 hours at 25°C and 65% relative humidity (using a humidifier); low-temperature drying for 15 hours at 45°C and 45% relative humidity (with relative ventilation); and medium-temperature drying for 10 hours at 70°C (with natural ventilation).

[0082] The silicon carbide green body-glass carbon mold composite was placed in a graphite induction furnace and evacuated to 10°C. -2 Pa, heated from room temperature to 2250℃ at a rate of 8℃ / min, and held at this temperature for 2 hours (without pressure). During this process, silicon carbide particles recrystallize and sinter, while the glassy carbon mold transforms into the graphite phase and pulverizes. After the holding period, the furnace is cooled, followed by low-temperature oxidation to further remove residual graphite powder. The low-temperature oxidation is carried out in an air atmosphere at a temperature of 800℃ for 35 minutes. After the low-temperature oxidation is completed, a recrystallized silicon carbide craft ornament with embossed artistic patterns on the outside is obtained (see actual image). Figure 6 (As shown).

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing recrystallized silicon carbide products, characterized in that, Includes the following steps: Silicon carbide raw materials are shaped using glass carbon molds to obtain a silicon carbide green body-glass carbon mold composite. The preparation method of the glassy carbon mold includes the following steps: mixing microcrystalline cellulose with water, molding the resulting mixture to obtain a cellulose preform; stabilizing the cellulose preform in an oxygen-containing atmosphere to obtain a stabilized preform; the stabilization treatment includes: heating to 195-205℃ at a heating rate of 1-2℃ / min, continuing to heat to 295-305℃ at a heating rate of 0.5-1℃ / min, and then heating again at a heating rate of 0.2-0.5℃ / min. The temperature is further increased to 345~355℃ and held for 1~2 hours. The stabilized preform is then carbonized in a protective atmosphere to obtain the glass carbon mold. The carbonization process includes: increasing the temperature at a rate of 2~3℃ / min to 595~605℃, continuing to increase the temperature at a rate of 3~5℃ / min to 995~1005℃, and continuing to increase the temperature at a rate of 1.5~2.5℃ / min to 1395~1405℃, holding for 1~2 hours. The silicon carbide green body-glass carbon mold composite is sintered in a vacuum or protective atmosphere to achieve silicon carbide recrystallization and glass carbon mold graphite phase pulverization, thereby obtaining the recrystallized silicon carbide product.

2. The preparation method according to claim 1, characterized in that, The density of the cellulose preform is 0.8~1.0 g / cm³. 3 The molding process is selected from 3D printing, compression molding, or coating molding. When the 3D printing process is employed, the moisture content of the mixture is 78-82 wt%. When compression molding is used, the moisture content of the mixture is ≤2wt%, and the compression molding pressure is 50~100MPa; When a coating process is used, the moisture content of the mixture is 45-55 wt%.

3. The preparation method according to claim 1, characterized in that, The shaping method is selected from internal pressure shaping method, internal grouting shaping method, external grouting shaping method, or simultaneous internal and external grouting shaping method.

4. The preparation method according to claim 3, characterized in that, The internal pressing and shaping method includes the following steps: a portion of the silicon carbide raw material is pressed in a first pressing to obtain a bottom blank; the glass carbon mold is placed on the surface of the bottom blank; the glass carbon mold is used as a core; the remaining silicon carbide raw material is pressed in a second pressing on the surface of the glass carbon mold to obtain a top blank; and the bottom blank, the glass carbon mold, and the top blank are pressed in a third pressing. The internal grouting and shaping method includes the following steps: preparing silicon carbide slurry using the silicon carbide raw material; using the glass carbon mold as the core and the supporting mold as the shell; pouring the silicon carbide slurry into the gap between the core and the shell; and removing the shell after a first curing process; the supporting mold is selected from gypsum mold, graphite mold, polyurethane mold, polyethylene mold, PMMA mold, or paraffin wax mold. The external grouting and shaping method includes the following steps: preparing silicon carbide slurry using the silicon carbide raw material; using the glass carbon mold as a shell, pouring the silicon carbide slurry into the cavity of the shell, and then performing a second curing; The internal-external simultaneous grouting and shaping method includes the following steps: preparing silicon carbide slurry using the silicon carbide raw material; using two glass carbon molds as the core and shell respectively; pouring the silicon carbide slurry into the gap between the core and shell; and then performing a third curing.

5. The preparation method according to claim 4, characterized in that, The first curing, second curing, and third curing independently include: standing for 15-25 minutes at a temperature of 20-25°C and a relative humidity of 50-70%; then pre-drying for 4-12 hours at a temperature of 20-25°C and a relative humidity of 60-75%; then low-temperature drying for 10-24 hours at a temperature of 40-50°C and a relative humidity of 40-50%; and finally medium-temperature drying for 5-15 hours at a temperature of 60-80°C.

6. The preparation method according to claim 1, characterized in that, The sintering temperature is 2250~2650℃, and the holding time is 1~4h.

7. The preparation method according to claim 1, characterized in that, The process after sintering further includes: high-pressure gas purging or low-temperature oxidation; the pressure of the high-pressure gas purging is 1~3 bar; the temperature of the low-temperature oxidation is 700~900℃.

8. A recrystallized silicon carbide product, characterized in that, The recrystallized silicon carbide product is prepared by the preparation method according to any one of claims 1 to 7. The recrystallized silicon carbide product is an irregularly shaped recrystallized silicon carbide product, and the recrystallized silicon carbide product is selected from filter membranes, precision screws, crystal boats or decorative crafts.

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