Low-cost, pollution-free water-soluble binder 3D printing silicon carbide ceramic and preparation method thereof

Abstract

The application belongs to the technical field of silicon carbide 3D printing, and particularly relates to a low-cost, pollution-free water-soluble binder 3D printed silicon carbide ceramic and a preparation method thereof. The preparation method comprises the following steps: 1) mixing polyvinyl alcohol and a first modifier, and then mixing the polyvinyl alcohol and the first modifier with a plasticizer to obtain plasticized modified polyvinyl alcohol; 2) mixing silicon carbide ceramic powder, a second modifier and carbon black to obtain modified silicon carbide and carbon black mixed powder; 3) uniformly mixing and crushing and granulating the obtained modified silicon carbide and carbon black mixed powder, the plasticized modified polyvinyl alcohol and an organic binder to obtain silicon carbide printing material; 4) 3D printing the obtained silicon carbide printing material to obtain a silicon carbide ceramic green body; 5) performing degreasing on the obtained silicon carbide ceramic green body to obtain a silicon carbide ceramic degreasing body; and 6) performing molten silicon infiltration reaction sintering on the silicon carbide ceramic degreasing body to obtain a 3D printed silicon carbide ceramic.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide 3D printing technology, specifically relating to a low-cost, pollution-free water-soluble binder for 3D printing silicon carbide ceramics and its preparation method. Background Technology

[0002] Silicon carbide (SiC) is widely used in aerospace, nuclear industry, and new energy fields due to its high mechanical strength, high temperature resistance, wear resistance, good thermal shock resistance, good oxidation resistance, corrosion resistance, low coefficient of thermal expansion, and high thermal conductivity. It also possesses excellent properties such as radiation resistance, radioactivity resistance, and microwave absorption. With technological advancements, the application of precision silicon carbide ceramic structural components requires increasingly larger sizes, more complex structures, higher precision, and better mechanical properties. However, because SiC is a covalent compound with very strong Si-C bonds, its hardness is second only to diamond, exhibiting extremely high hardness and significant brittleness, making precision machining difficult. Therefore, the fabrication of large-size, complex, irregularly shaped hollow precision SiC structural components is challenging, limiting the widespread application of SiC ceramics in high-end equipment manufacturing fields such as integrated circuits.

[0003] To address the aforementioned shortcomings, 3D printing technology can effectively solve this problem. Due to its unparalleled advantages over traditional molding methods in manufacturing complex, large-sized parts, as well as in terms of manufacturing cost and efficiency, the preparation technology of SiC ceramics and their composites using 3D printing has become a major research and application direction. Among these technologies, powder extrusion printing (PEP) is a very promising molding technology, as it uses a printing material made by mixing organic binders and silicon carbide powder to achieve complex-shaped silicon carbide ceramic 3D printing.

[0004] However, powder extrusion printing of SiC ceramic preforms typically requires debinding to remove organic matter from the preform. Numerous patents and literature indicate that the binder used in powder extrusion printing of silicon carbide ceramic preforms is a paraffin / HDPE / EVA system. To reduce debinding time and defects generated during the process, the debinding process involves first solvent debinding to remove paraffin, followed by thermal debinding to remove HDPE / EVA. Solvent debinding typically uses organic solvents such as n-heptane, n-hexane, and kerosene. However, organic solvents are not only highly toxic and expensive, but also present challenges in wastewater treatment. Summary of the Invention

[0005] To address the aforementioned issues, this application discloses a low-cost, pollution-free water-soluble binder powder extrusion printing method for silicon carbide ceramics and its preparation method.

[0006] In a first aspect, the present invention provides a low-cost, pollution-free method for preparing silicon carbide ceramics by extrusion printing using water-soluble binder powder, comprising:

[0007] (1) First, mix polyvinyl alcohol and the first modifier, and then mix with the plasticizer to obtain plasticized modified polyvinyl alcohol;

[0008] (2) A mixture of silicon carbide ceramic powder, a second modifier and carbon black is obtained to obtain a mixed powder of modified silicon carbide and carbon black.

[0009] (3) The obtained modified silicon carbide and carbon black mixed powder, plasticized modified polyvinyl alcohol and organic binder are mixed evenly and crushed and granulated to obtain silicon carbide printing material.

[0010] (4) The obtained silicon carbide printing material is 3D printed to obtain a silicon carbide ceramic blank;

[0011] (5) The obtained silicon carbide ceramic green body is degreased to obtain a degreased silicon carbide ceramic green body;

[0012] (6) The degreased silicon carbide ceramic preform is sintered by melt infiltration reaction to obtain 3D printed silicon carbide ceramic.

[0013] Preferably, in step (1), the polyvinyl alcohol is at least one of four types: 1788, 1799, 2088, and 2099.

[0014] Preferably, in step (1): the first modifier includes at least one of glycerol, ethylene glycol, butanediol, diethylene glycol, acetic acid, animal gelatin, polyamide, polyurethane, lactic acid, glycerol, mannitol, sorbitol, pentaerythritol, caprolactam, and polyethylene glycol (low molecular weight 200-600); the amount of the first modifier is 5-40 wt% of the total mass of polyvinyl alcohol.

[0015] Preferably, in step (1): the plasticizer includes at least one of the following: di-n-octyl phthalate (DNOP), di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), dimethyl phthalate (DMP), diethyl phthalate (DEP), diallyl phthalate (DAP), di(2-methoxy)ethyl phthalate (DMEP), dipentyl phthalate (DPP), dihexyl phthalate (DHXP), and dicyclohexyl phthalate (DCHP); the amount of plasticizer used is 5 to 40 wt% of the total mass of polyvinyl alcohol.

[0016] Preferably, in step (1): the mixing method is a constant temperature magnetic stirring method; the parameters of the constant temperature magnetic stirring method include: stirring temperature of 30-70℃ and stirring time of 1-4h.

[0017] Preferably, in step (2): the silicon carbide powder is D 50 =1~10μm and D 50 A mixture of silicon carbide particles with two particle size distributions of 10–70 μm; preferably, D is controlled. 50 =1~10μm and D 50 The mass ratio of silicon carbide with two particle size distributions of 10 to 70 μm is 1:(1 to 4).

[0018] Preferably, in step (2): the second modifier includes at least one of stearic acid, polyoxyethylene fatty acid ester, n-butanol, alkylphenol polyoxyethylene ether, hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS); the mass of the second modifier accounts for 0.5 to 1.5 wt% of the mass of silicon carbide powder.

[0019] Preferably, in step (2): the particle size of the carbon black is 10-100 nm; the carbon black accounts for 5-20 wt% of the silicon carbide powder.

[0020] Preferably, in step (3): the organic binder includes at least one of polycarbonate PC, polyoxymethylene POM, ethylene-vinyl acetate copolymer EVA, polystyrene PS, polyamide PA, and polymethyl methacrylate PMMA.

[0021] Preferably, in step (3): the mixed powder of modified silicon carbide and carbon black accounts for 50-80 wt% of the silicon carbide printing material, the plasticized modified polyvinyl alcohol accounts for 5-30 wt% of the silicon carbide printing material, and the organic binder accounts for 5-25 wt% of the silicon carbide printing material.

[0022] Preferably, in step (3), the particle size of the granulated silicon carbide printing material is 0.2 to 0.5 cm.

[0023] Preferably, in step (4): the parameters for 3D printing include: the nozzle temperature is set to 150-200℃, the stage temperature is set to 50-110℃, the cavity atmosphere temperature is set to 30-50℃, the printing speed is 20-50mm / s, the printing spacing is set to 0.05-0.15mm, and the single layer thickness is set to 0.05-0.2mm; preferably, the cavity atmosphere of the printer used for 3D printing is air.

[0024] Preferably, in step (5), the degreasing method involves first performing water-based degreasing, followed by thermal degreasing. This invention uses water instead of organic solvents for solvent degreasing, which can significantly reduce the cost of solvent degreasing for powder extrusion printing of SiC ceramic preforms, shorten degreasing time, and reduce pollutant emissions.

[0025] Furthermore, preferably, the water-based degreasing temperature is set to 30–90°C, the degreasing time is 2–12 hours, and the solvent is water; the water-based degreasing environment is an ultrasonic field with an ultrasonic frequency of 30–70 kHz.

[0026] The conditions for thermal degreasing are as follows: under argon or vacuum atmosphere, the silicon carbide ceramic green body is heated to 400-500°C at a heating rate of 0.2-1°C / min, and held at that temperature for 0.5-3 hours.

[0027] Preferably, in step (6): the degreased silicon carbide ceramic blank is mixed with silicon powder; the particle size of the silicon powder is 0.1 to 1 cm; the mass ratio of the degreased silicon carbide ceramic blank to the silicon powder is 1:(1 to 2).

[0028] Preferably, in step (6): the sintering regime of the molten silicon infiltration reaction sintering includes: a temperature of 1500-1750℃, a sintering time of 1-4h, and a sintering atmosphere of vacuum.

[0029] Secondly, the present invention provides a low-cost, pollution-free method for preparing silicon carbide ceramics by extrusion printing using water-soluble binder powder, comprising:

[0030] (1) First, mix polyvinyl alcohol and the first modifier, and then mix with the plasticizer to obtain plasticized modified polyvinyl alcohol;

[0031] (2) Silicon carbide ceramic powder and a second modifier are mixed to obtain modified silicon carbide powder;

[0032] (3) The obtained modified silicon carbide powder, plasticized modified polyvinyl alcohol and organic binder are mixed evenly and crushed and granulated to obtain silicon carbide printing material;

[0033] (4) The obtained silicon carbide printing material is 3D printed to obtain a silicon carbide ceramic blank;

[0034] (5) The obtained silicon carbide ceramic green body is degreased to obtain a degreased silicon carbide ceramic green body;

[0035] (6) The degreased silicon carbide ceramic green body is impregnated in a phenolic resin solution and then carbonized to obtain a C / SiC ceramic green body;

[0036] (7) The C / SiC ceramic blank is sintered by melt infiltration reaction to obtain 3D printed silicon carbide ceramic.

[0037] Preferably, in step (1), the polyvinyl alcohol is at least one of four types: 1788, 1799, 2088, and 2099.

[0038] Preferably, in step (1): the first modifier includes at least one of glycerol, ethylene glycol, butanediol, diethylene glycol, acetic acid, animal gelatin, polyamide, polyurethane, lactic acid, glycerol, mannitol, sorbitol, pentaerythritol, caprolactam, and polyethylene glycol (low molecular weight 200-600); the amount of the first modifier is 5-40 wt% of the total mass of polyvinyl alcohol.

[0039] Preferably, in step (1): the plasticizer includes at least one of the following: di-n-octyl phthalate (DNOP), di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), dimethyl phthalate (DMP), diethyl phthalate (DEP), diallyl phthalate (DAP), di(2-methoxy)ethyl phthalate (DMEP), dipentyl phthalate (DPP), dihexyl phthalate (DHXP), and dicyclohexyl phthalate (DCHP); the amount of plasticizer used is 5 to 40 wt% of the total mass of polyvinyl alcohol.

[0040] Preferably, in step (1): the mixing method is a constant temperature magnetic stirring method; the parameters of the constant temperature magnetic stirring method include: stirring temperature of 30 to 70°C and stirring time of 1 to 4 hours.

[0041] Preferably, in step (2): the silicon carbide powder is D 50 =1~10μm and D 50 A mixture of silicon carbide particles with two particle size distributions of 10–70 μm; preferably, D is controlled. 50 =1~10μm and D 50 The mass ratio of silicon carbide with two particle size distributions of 10 to 70 μm is 1:(1 to 4).

[0042] Preferably, in step (2): the second modifier includes at least one of stearic acid, polyoxyethylene fatty acid ester, n-butanol, alkylphenol polyoxyethylene ether, hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS); the mass of the second modifier accounts for 0.5 to 1.5 wt% of the mass of silicon carbide powder.

[0043] Preferably, in step (3): the modified silicon carbide powder accounts for 50-80 wt% of the silicon carbide printing material, the plasticized modified polyvinyl alcohol accounts for 5-30 wt% of the silicon carbide printing material, and the organic binder accounts for 5-25 wt% of the silicon carbide printing material.

[0044] Preferably, in step (3), the particle size of the granulated silicon carbide printing material is 0.2 to 0.5 cm.

[0045] Preferably, in step (4): the parameters for 3D printing include: the nozzle temperature is set to 150-200℃, the stage temperature is set to 50-110℃, the cavity atmosphere temperature is set to 30-50℃, the printing speed is 20-50mm / s, the printing spacing is set to 0.05-0.15mm, and the single layer thickness is set to 0.05-0.2mm; preferably, the cavity atmosphere of the printer used for 3D printing is air.

[0046] Preferably, in step (5), the degreasing method is to first perform water-based degreasing, followed by thermal degreasing. This invention uses water instead of organic solvents for solvent degreasing, which can significantly reduce the cost of solvent degreasing for powder extrusion printing of SiC ceramic green bodies, shorten the degreasing time, and reduce pollutant emissions. Preferably, the temperature for water-based degreasing is set to 30–90°C, the degreasing time is 2–12 hours, and the solvent is water; the water-based degreasing environment is an ultrasonic field with an ultrasonic frequency of 30–70 kHz; the thermal degreasing conditions are: heating the silicon carbide ceramic green body to 400–500°C at a heating rate of 0.2–1°C / min under argon or vacuum atmosphere, and holding for 0.5–3 hours.

[0047] Preferably, in step (6): the mass fraction of the phenolic resin solution is 30-50 wt%, preferably 50 wt%;

[0048] The impregnation environment is a vacuum, and the impregnation time is 20 to 30 minutes, preferably 30 minutes;

[0049] The carbonization parameters include: a vacuum atmosphere, a temperature of 600–800°C, and a time of 1–3 hours;

[0050] Impregnation and carbonization constitute one cycle, and the number of cycles is at least 2 times, preferably 3 times.

[0051] Preferably, in step (7): the degreased silicon carbide ceramic blank is mixed with silicon powder; the particle size of the silicon powder is 0.1 to 1 cm; the mass ratio of the degreased silicon carbide ceramic blank to the silicon powder is 1:(1 to 2).

[0052] Preferably, in step (7), the sintering regime of the molten silicon infiltration reaction sintering includes: a temperature of 1500-1750°C, a sintering time of 1-4 hours, and a sintering atmosphere of vacuum.

[0053] On the other hand, the present invention provides a 3D printed silicon carbide ceramic obtained according to the above preparation method.

[0054] The beneficial effects of this invention are:

[0055] In this invention, the obtained silicon carbide 3D printed blank has high forming accuracy and strength, and can be used to prepare silicon carbide ceramics with complex shapes. The obtained silicon carbide 3D printed blank can effectively remove soluble components by water-soluble degreasing, which, compared with organic solvent degreasing, achieves low-cost, pollution-free, and efficient water-soluble degreasing of silicon carbide 3D printed blank. The obtained reaction-sintered silicon carbide ceramic has almost no dimensional shrinkage, can maintain complex shapes, and has the characteristics of low free silicon content and high strength. Attached Figure Description

[0056] Figure 1 (a) is a photograph of the printing material obtained with insufficient binder, and (b) is a photograph of unmodified polyvinyl alcohol undergoing dehydration and etherification.

[0057] Figure 2 Adding plasticizer before modifier causes polyvinyl alcohol to be encapsulated, preventing the modification from being completed;

[0058] Figure 3 Photographs of silicon carbide ceramic green body samples obtained in the process, where (a) shows the addition of both plasticizer and modifier, and (b) shows the addition of only plasticizer without modifier;

[0059] Figure 4 The images show the surface morphology of ceramic green bodies after water solvent degreasing, where (a) is before degreasing, (b) is after degreasing for 2 hours, and (c) is after degreasing for 4 hours.

[0060] Figure 5 This is a surface morphology image of silicon carbide ceramic after reaction sintering following powder extrusion printing in Example 1.

[0061] Figure 6 This is a photograph of the ceramic blank obtained after hot degreasing. Detailed Implementation

[0062] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0063] This disclosure provides a method for preparing a powder extrusion printed silicon carbide preform that is easy to degrease, low-cost, pollution-free, and has good molding accuracy and strength.

[0064] Modification of polyvinyl alcohol. Polyvinyl alcohol and a first modifier are mixed uniformly to obtain low-melting-point modified polyvinyl alcohol. The polyvinyl alcohol is at least one of four types: 1788, 1799, 2088, and 2099. The particle size of the powder is 100-200 μm. If the particle size is too small, agglomeration easily occurs during stirring; if the particle size is too large, the polyvinyl alcohol in the center of the powder cannot contact the modifier, resulting in incomplete modification.

[0065] In an optional embodiment, the first modifier includes at least one of glycerol, ethylene glycol, butanediol, diethylene glycol, acetic acid, animal gelatin, polyamide, polyurethane, lactic acid, glycerol, mannitol, sorbitol, pentaerythritol, caprolactam, and polyethylene glycol (low molecular weight). Since pure polyvinyl alcohol is difficult to melt-process, the purpose of adding the modifier is to disrupt the hydrogen bonds within the polyvinyl alcohol molecule, reduce the regularity of the polyvinyl alcohol molecular structure, thereby lowering the melting point of polyvinyl alcohol and ensuring that it melts only during heating without decomposition, thus meeting subsequent processing requirements. The amount of the first modifier is 5-40 wt% of the total mass of polyvinyl alcohol. If the modifier content is too low, it will not effectively lower the melting point of polyvinyl alcohol; if the modifier content is too high, it will easily reduce the degree of cross-linking between polyvinyl alcohol molecules, affecting the mechanical properties of polyvinyl alcohol.

[0066] In an optional embodiment, the method for achieving uniform mixing is a constant-temperature water bath magnetic stirring method, with a water bath temperature of 30-70℃ and a stirring time of 1-4 hours. If the water bath temperature is too low, the modifying activity of the modifier on polyvinyl alcohol may decrease, thereby reducing the modification efficiency; if the temperature is too high, some modifiers may decompose. If the water bath stirring time is too short, incomplete modification and uneven mixing may occur; if the stirring time is too long, prolonged heating may cause some water within the polyvinyl alcohol molecules to evaporate, reducing the water solubility and binding properties of the polyvinyl alcohol.

[0067] Plasticization of polyvinyl alcohol. The modified polyvinyl alcohol described above is mixed uniformly with a plasticizer to obtain a plasticized modified polyvinyl alcohol with high plasticity and a low melting point. The plasticizer includes at least one of the following: di-n-octyl phthalate (DNOP), di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), dimethyl phthalate (DMP), diethyl phthalate (DEP), diallyl phthalate (DAP), di(2-methoxy)ethyl phthalate (DMEP), dipentyl phthalate (DPP), dihexyl phthalate (DHXP), and dicyclohexyl phthalate (DCHP). The plasticizer effectively optimizes the flexibility of silicon carbide ceramic filaments, thereby improving the precision and mechanical properties of silicon carbide ceramic printed products. The plasticizer accounts for 5-40% of the mass of polyvinyl alcohol. Insufficient plasticizer content reduces the plasticizing effect on the silicon carbide ceramic filaments, while excessive content leads to precipitation of low-molecular-weight plasticizers during heating and cooling, affecting subsequent preparation steps. The method for achieving uniform mixing is a constant-temperature water bath with magnetic stirring at 30-70℃ for 1-4 hours. The water bath temperature and stirring time must be maintained within a reasonable range; excessively low or high temperatures will lead to the same consequences as when adding the first modifier. During the modification and plasticizing of polyvinyl alcohol, the order of adding the modifier and plasticizer cannot be reversed. If the plasticizer is added first, followed by the first modifier, the plasticizer added first will mix with the polyvinyl alcohol and encapsulate the polyvinyl alcohol molecules, preventing the modifier added later from directly contacting the polyvinyl alcohol molecules and completing the modification.

[0068] Modification of silicon carbide powder. Silicon carbide ceramic powder is uniformly mixed with a second modifier and carbon black to obtain a well-dispersed mixed powder of modified silicon carbide and carbon black. Preferably, the mixing is ball milling. The mixture is first ball-milled to obtain a slurry, and then the slurry is dried to obtain a well-dispersed mixed powder of modified silicon carbide and carbon black.

[0069] In an optional embodiment, the silicon carbide powder is D. 50 =1-10μm and D 50 =A mixture of silicon carbide particles with two particle size distributions of 10-70μm, and D controlled 50 =1-10μm and D 50The mass ratio of silicon carbide with two particle size distributions of 10-70 μm is 1:(1-4). The second modifier is at least one selected from stearic acid, polyoxyethylene fatty acid ester, n-butanol, alkylphenol polyoxyethylene ether, hexadecyltrimethylammonium bromide (CTAB), and sodium dodecyl sulfate (SDS). The amount of the second modifier is 0.5%-1.5 wt% of the silicon carbide powder mass. If the second modifier is too small, the modification effect on the silicon carbide powder is poor; if the second modifier is too large, it will affect the viscosity and mechanical properties of the silicon carbide printing material. The carbon black has a particle size of 10-100 nm. The carbon black accounts for 5-20 wt% of the silicon carbide powder mass. If the carbon black particle size is too small, it will easily agglomerate. If the carbon black particle size is too large, in the subsequent reaction sintering, there will be incomplete reaction between the carbon near the center of the carbon black particles and silicon, thus affecting the mechanical properties of the silicon carbide ceramic.

[0070] Mixing. The modified silicon carbide and carbon black powder, plasticized modified polyvinyl alcohol, and organic binder are mixed evenly, then crushed and granulated to obtain silicon carbide printing material. The organic binder includes at least one of polycarbonate (PC), polyoxymethylene (POM), ethylene-vinyl acetate copolymer (EVA), polystyrene (PS), polyamide (PA), polymethyl methacrylate (PMMA), dibutyl phthalate (DBP), and polyurethane (PU). The resulting granulated particles have a particle size of 0.2-0.5 cm.

[0071] In an optional embodiment, the silicon carbide powder accounts for 50-90 wt% of the printing material, the organic binder accounts for 5-25 wt% of the printing material, and the plasticized modified polyvinyl alcohol accounts for 5-25 wt% of the printing material. The plasticized modified polyvinyl alcohol is controlled to account for 5-25 wt% of the printing material. This plasticized modified polyvinyl alcohol is removed during the water-soluble degreasing process, forming a porous structure inside the silicon carbide preform. This allows a large amount of binder to volatilize through these pores during subsequent thermal degreasing, further reducing cracking and bulging defects caused by excessive gas leakage. If the amount of plasticized modified polyvinyl alcohol added is too low, the pores formed after water-soluble degreasing of the silicon carbide preform will be very small or few, failing to provide channels for subsequent binder removal and easily leading to bulging. If the amount of plasticized modified polyvinyl alcohol added is too high, a large number of large-sized pores will appear after water-soluble degreasing, which are prone to shrinkage after drying, resulting in deformation of the preform shape.

[0072] Printing and shaping. The silicon carbide printing material is 3D printed, and the printing parameters are adjusted to obtain a silicon carbide ceramic blank. The 3D printing parameters are: printhead temperature set to 150-200℃, stage temperature set to 50-110℃, cavity atmosphere temperature set to 30-50℃, printing speed set to 20-50mm / s, printing spacing set to 0.05-0.15mm, and single-layer thickness set to 0.05-0.2mm. The printer cavity atmosphere is air.

[0073] Degreasing. The silicon carbide ceramic green body is degreased to obtain a degreased silicon carbide ceramic green body. The degreasing method involves first performing water-soluble degreasing, followed by thermal degreasing. The combination of solvent degreasing and thermal degreasing is used because the silicon carbide ceramic green body printed from powder extrusion contains some high-molecular-weight organic matter, which needs to be removed by thermal degreasing technology. However, direct thermal degreasing can easily lead to a large amount of organic matter not evaporating in time or evaporating too quickly, resulting in bulging and cracking. Therefore, water-soluble degreasing before thermal degreasing can remove some water-soluble organic matter, reducing the total amount of organic matter; secondly, it can remove pores formed inside the green body by removing soluble binders, providing evaporation channels for a large amount of binder during thermal degreasing, preventing bulging and cracking caused by excessive evaporation of organic matter. The temperature for water-soluble degreasing is set at 30-90℃, the degreasing time is 2-12 hours, and the solvent is water. The water-soluble degreasing environment is an ultrasonic field with an ultrasonic frequency of 30-70 kHz. The conditions for thermal degreasing are as follows: under argon or vacuum atmosphere, the silicon carbide ceramic green body is heated to 400-500℃ at a heating rate of 0.2℃-1℃ / min, and held at that temperature for 0.5-3h.

[0074] Densification. A degreased silicon carbide ceramic preform is mixed with Si particles at a mass ratio of 1:1-2 and subjected to reaction sintering to obtain the low-cost, pollution-free water-soluble binder for 3D printing silicon carbide ceramic. The silicon powder has a particle size of 0.1-1 cm, and the mass ratio of the SiC preform to the silicon powder is 1:1-2. The silicon infiltration sintering process is set at a temperature of 1500-1750℃, a sintering time of 1-4 hours, and a vacuum sintering atmosphere.

[0075] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0076] Example 1

[0077] (1) Modification and plasticization of polyvinyl alcohol: Polyvinyl alcohol and the first modifier were mixed in a constant temperature water bath magnetic stirrer at 60°C for 1 hour. Then, the plasticizer was added and the mixture was continued under the same conditions to obtain plasticized modified polyvinyl alcohol. The first modifier was a mixture of polyamide and glycerol in a mass ratio of 1:1, and the mass fraction of the first modifier accounted for 30 wt% of the mass of polyvinyl alcohol. The plasticizer was a mixture of diethyl phthalate and dibutyl phthalate in a mass ratio of 1:1, and the mass fraction of the plasticizer accounted for 30 wt% of the mass of polyvinyl alcohol.

[0078] (2) Modification of silicon carbide powder: A second modifier and carbon black powder were added to silicon carbide powder, and the mixture was ball-milled using deionized water or anhydrous ethanol as a solvent to obtain a modified silicon carbide and carbon black mixed powder. The second modifier was a mixture of polyoxyethylene fatty acid ester and alkylphenol polyoxyethylene ether in a 1:1 mass ratio, and the mass of the second modifier accounted for 1 wt% of the silicon carbide powder. The silicon carbide powder was D... 50 =1-10μm and D 50 =A mixture of silicon carbide particles with two particle size distributions of 10-70μm, and D controlled 50 =1-10μm and D 50 The mass ratio of silicon carbide with two particle size distributions of 10-70 μm is 1:2. The grinding balls used in the modification and mixing process are one or more of SiC ceramic balls, Si3N4 ceramic balls, ZrO2 ceramic balls, Al2O3 ceramic balls, and polyurethane balls, with SiC ceramic balls being preferred. The carbon black accounts for 15 wt% of the silicon carbide powder and has a particle size of 80-100 nm.

[0079] (3) Mixing: The above-mentioned mixed powder, plasticized modified polyvinyl alcohol, and binder are mixed evenly at 170°C for 30 minutes, and then crushed and granulated to obtain 3D printing material with a diameter of about 0.5 cm. The binder is a mixture of EVA and PMMA in a mass ratio of 1:1, the modified silicon carbide powder accounts for 60 wt% of the printing material, the binder accounts for 15 wt% of the printing material, and the plasticized modified polyvinyl alcohol accounts for 25 wt% of the printing material;

[0080] (4) 3D printing: The obtained silicon carbide printing material is printed by FDM. The printing parameters are set as follows: nozzle temperature is 170℃, platform temperature is 110℃, printing speed is 40mm / s, printing layer height is 0.2mm, nozzle diameter is 0.8mm, line angle is -45° and 45°, and infill density is 100% to obtain silicon carbide printing blank.

[0081] (5) Degreasing: The printed blank is placed in an ultrasonic cleaner filled with water for water-soluble degreasing to remove soluble components. The blank is then placed in a drying oven for 6 hours to remove moisture. After drying, the blank is thermally degreased in a vacuum sintering furnace to obtain the degreased silicon carbide blank. The ultrasonic cleaner frequency is 50 kHz, the water-soluble degreasing temperature is 60°C, and the water-soluble degreasing time is 0 h, 2 h, and 4 h (see [reference]). Figure 4 After degreasing with water solvent (4 hours), more than 80% of the soluble components can be removed. The thermal degreasing conditions are as follows: under an argon atmosphere, the silicon carbide ceramic green body is heated to 480°C at a heating rate of 0.5 g / min and held at that temperature for 3 hours.

[0082] (6) Densification: The preform is placed in a sintering furnace for melt infiltration reaction sintering. An appropriate amount of silicon powder is taken to ensure that the ratio of silicon powder mass to silicon carbide preform mass is 1.5:1. The sintering temperature is 1600℃ and the sintering time is 1h to obtain reaction sintered silicon carbide ceramic.

[0083] Example 2

[0084] (1) Modification and plasticization of polyvinyl alcohol: Polyvinyl alcohol and the first modifier were mixed in a constant temperature magnetic stirrer at 60°C for 1 hour. Then, the plasticizer was added and the mixture was continued under the same conditions to obtain plasticized modified polyvinyl alcohol. The first modifier was a mixture of ethylene glycol, lactic acid and polyurethane in a mass ratio of 1:1:1 and the mass fraction of the first modifier accounted for 30 wt% of the mass of polyvinyl alcohol. The plasticizer was a mixture of dibutyl phthalate and dicyclohexyl phthalate in a mass ratio of 1:1 and the mass fraction of the plasticizer accounted for 30 wt% of the mass of polyvinyl alcohol.

[0085] (2) Modification of silicon carbide powder: A second modifier and carbon black were added to silicon carbide powder, and the mixture was ball-milled using deionized water or anhydrous ethanol as a solvent to obtain a modified silicon carbide and carbon black mixed powder. The second modifier was a mixture of polyoxyethylene fatty acid ester and alkylphenol polyoxyethylene ether in a 1:1 mass ratio, and the mass of the second modifier accounted for 1 wt% of the silicon carbide powder. The carbon black was a powder with a particle size of approximately 50 nm, and its mass accounted for 10 wt% of the silicon carbide powder. The silicon carbide powder was D... 50 =1-10μm and D 50 =A mixture of silicon carbide particles with two particle size distributions of 10-70μm, and D controlled 50 =1-10μm and D 50The mass ratio of silicon carbide with two particle size distributions of 10-70 μm is 1:2. The grinding balls used in the modified mixing process are one or more of SiC ceramic balls, Si3N4 ceramic balls, ZrO2 ceramic balls, Al2O3 ceramic balls, and polyurethane balls, with SiC ceramic balls being preferred.

[0086] (3) Mixing: The above-mentioned mixed powder, plasticized modified polyvinyl alcohol, and binder are mixed evenly at 170°C for 30 minutes, and then crushed and granulated to obtain 3D printing material with a diameter of about 0.5 cm. The binder is a mixture of EVA and PMMA in a mass ratio of 1:1, the modified silicon carbide powder accounts for 65 wt% of the printing material, the binder accounts for 15 wt% of the printing material, and the plasticized modified polyvinyl alcohol accounts for 20 wt% of the printing material;

[0087] (4) 3D printing: The obtained silicon carbide printing material is printed by FDM. The printing parameters are set as follows: nozzle temperature is 170℃, platform temperature is 110℃, printing speed is 40mm / s, printing layer height is 0.2mm, nozzle diameter is 0.8mm, line angle is -45° and 45°, and infill density is 100% to obtain silicon carbide printing blank.

[0088] (5) Degreasing: The printed green blank is placed in an ultrasonic cleaner filled with water for water-soluble degreasing to remove soluble components. Then, the green blank is placed in a drying oven for 6 hours to remove moisture. The dried green blank is then subjected to thermal degreasing in a vacuum sintering furnace to obtain a degreased silicon carbide green blank. The ultrasonic cleaner frequency is 50 kHz, the water-soluble degreasing temperature is 60 ℃, and the water-soluble degreasing time is 4 hours. More than 80% of soluble components can be removed by water-soluble degreasing. The thermal degreasing conditions are as follows: under an argon atmosphere, the silicon carbide ceramic green blank is heated to 480 ℃ at a heating rate of 0.5 / min and held for 3 hours.

[0089] (6) Densification: The preform is placed in a sintering furnace for melt infiltration reaction sintering. An appropriate amount of silicon powder is taken to ensure that the ratio of silicon powder mass to silicon carbide preform mass is 1.5:1. The sintering temperature is 1600℃ and the sintering time is 1h to obtain reaction sintered silicon carbide ceramic.

[0090] Example 3

[0091] (1) Modification and plasticization of polyvinyl alcohol: Polyvinyl alcohol and the first modifier were mixed in a constant temperature magnetic stirrer at 60°C for 1 hour. Then, the plasticizer was added and the mixture was continued under the same conditions to obtain plasticized modified polyvinyl alcohol. The first modifier was a mixture of ethylene glycol and animal gelatin in a mass ratio of 1:1, and the mass fraction of the first modifier accounted for 30 wt% of the mass of polyvinyl alcohol. The plasticizer was a mixture of dibutyl phthalate and dicyclohexyl phthalate in a mass ratio of 1:1, and the mass fraction of the plasticizer accounted for 30 wt% of the mass of polyvinyl alcohol.

[0092] (2) Modification of silicon carbide powder: A second modifier and carbon black were added to silicon carbide powder, and the mixture was ball-milled using deionized water or anhydrous ethanol as a solvent to obtain a modified silicon carbide and carbon black mixed powder. The second modifier was a mixture of polyoxyethylene fatty acid ester and alkylphenol polyoxyethylene ether in a 1:1 mass ratio, and the mass of the second modifier accounted for 1 wt% of the silicon carbide powder. The silicon carbide powder was D... 50 =1-10μm and D 50 =A mixture of silicon carbide particles with two particle size distributions of 10-70μm, and D controlled 50 =1-10μm and D 50 The mass ratio of silicon carbide with two particle size distributions of 10-70 μm is 1:2. The grinding balls used in the modification and mixing process are one or more of SiC ceramic balls, Si3N4 ceramic balls, ZrO2 ceramic balls, Al2O3 ceramic balls, and polyurethane balls, with SiC ceramic balls being preferred. Carbon black accounts for 20 wt% of the silicon carbide powder, with a particle size of 80-100 nm.

[0093] (3) Mixing: The above-mentioned mixed powder, plasticized modified polyvinyl alcohol, and binder are mixed evenly at 170°C for 30 minutes, and then crushed and granulated to obtain 3D printing material with a diameter of about 0.5 cm. The binder is a mixture of EVA and PMMA in a mass ratio of 1:1, the modified silicon carbide powder accounts for 70 wt% of the printing material, the binder accounts for 15 wt% of the printing material, and the plasticized modified polyvinyl alcohol accounts for 15 wt% of the printing material.

[0094] (4) 3D printing: The obtained silicon carbide printing material is printed by FDM. The printing parameters are set as follows: nozzle temperature is 170℃, platform temperature is 110℃, printing speed is 40mm / s, printing layer height is 0.2mm, nozzle diameter is 0.8mm, line angle is -45° and 45°, and infill density is 100% to obtain silicon carbide printing blank.

[0095] (5) Degreasing: The printed green blank is placed in an ultrasonic cleaner filled with water for water-soluble degreasing to remove soluble components. Then, the green blank is placed in a drying oven for 6 hours to remove moisture. The dried green blank is then subjected to thermal degreasing in a vacuum sintering furnace to obtain a degreased silicon carbide green blank. The ultrasonic cleaner frequency is 50 kHz, the water-soluble degreasing temperature is 60 ℃, and the water-soluble degreasing time is 4 hours. More than 80% of soluble components can be removed by water-soluble degreasing. The thermal degreasing conditions are as follows: under an argon atmosphere, the silicon carbide ceramic green blank is heated to 480 ℃ at a heating rate of 0.5 / min and held for 3 hours.

[0096] (6) Densification: The preform is placed in a sintering furnace for melt infiltration reaction sintering. An appropriate amount of silicon powder is taken to ensure that the ratio of silicon powder mass to silicon carbide preform mass is 1.5:1. The sintering temperature is 1600℃ and the sintering time is 1h to obtain reaction sintered silicon carbide ceramic.

[0097] Example 4

[0098] The preparation process of 3D printed silicon carbide ceramics in this embodiment 4 is the same as that in embodiment 1, except that: in step (3), the modified silicon carbide powder accounts for 65 wt% of the printing material, the binder accounts for 15 wt% of the printing material, and the plasticized modified polyvinyl alcohol accounts for 20 wt% of the printing material.

[0099] Example 5

[0100] The preparation process of 3D printed silicon carbide ceramics in Example 5 is the same as in Example 1, except that: the modified silicon carbide powder accounts for 70 wt% of the printing material, the binder accounts for 15 wt% of the printing material, and the plasticized modified polyvinyl alcohol accounts for 15 wt% of the printing material.

[0101] Example 6

[0102] The preparation process of 3D printed silicon carbide ceramics in Example 6 is the same as in Example 1, except that: the modified silicon carbide powder accounts for 75 wt% of the printing material, the binder accounts for 15 wt% of the printing material, and the plasticized modified polyvinyl alcohol accounts for 10 wt% of the printing material.

[0103] Example 7

[0104] The preparation process of 3D printed silicon carbide ceramics in Example 7 is the same as in Example 1, except that: the modified silicon carbide powder accounts for 80 wt% of the printing material, the binder accounts for 15 wt% of the printing material, and the plasticized modified polyvinyl alcohol accounts for 5 wt% of the printing material.

[0105] Example 8

[0106] The preparation process of 3D printed silicon carbide ceramic in Example 8 is the same as in Example 1, except that the carbon source added is not the carbon black in step (3), but the carbon source formed by impregnation and carbonization of the green blank with phenolic resin solution after degreasing in step (5). The mass percentage of phenolic resin solution is 50 wt%, the impregnation environment is vacuum, the impregnation time is 30 min, and after impregnation, it is carbonized in a vacuum environment at 800℃ for 2 h. After three cycles of impregnation and carbonization with phenolic resin solution, a C / SiC ceramic green body is formed. Then, the densification process in Example 1 is performed to finally form reaction sintered silicon carbide ceramic.

[0107] Example 9

[0108] The preparation process of 3D printed silicon carbide ceramics in Example 9 is the same as in Example 1, except that in step (3), the modified silicon carbide powder accounts for 55 wt% of the printing material, the binder accounts for 15 wt% of the printing material, and the plasticized modified polyvinyl alcohol accounts for 30 wt% of the printing material. The resulting sample has good printing accuracy, such as... Figure 3 As shown in (a).

[0109] Comparative Example 1

[0110] The preparation process of the 3D printed silicon carbide ceramic in Comparative Example 1 is the same as in Example 1, except that: the modified silicon carbide powder accounts for 85 wt% of the printing material, the binder accounts for 15 wt% of the printing material, and the plasticized modified polyvinyl alcohol accounts for 0 wt% of the printing material. The results show that during the mixing process, due to insufficient binder, printing material cannot be formed. Figure 1 As shown in (a).

[0111] Comparative Example 2

[0112] The preparation process of the 3D printed silicon carbide ceramic in Comparative Example 2 is the same as in Example 1, except that in step (1), only a plasticizer is added and no first modifier is added. After mixing, brownish spherical agglomerates are formed, which cannot form printing material. Figure 1 As shown in (b).

[0113] Comparative Example 3

[0114] The preparation process of the 3D printed silicon carbide ceramic in Comparative Example 3 is the same as in Example 1, except that the order of adding the plasticizer and the first modifier in step (1) is reversed, i.e., the plasticizer is added first, followed by the first modifier. It was found that the first modifier could not directly contact polyvinyl alcohol, such as... Figure 2 As shown.

[0115] Comparative Example 4

[0116] The preparation process of the 3D printed silicon carbide ceramic in Comparative Example 4 is the same as that in Example 1, except that only the thermal degreasing process exists in step (5), and the resulting degreased green body shows bulging and delamination. Figure 6 The thermal degreasing conditions were as follows: the silicon carbide ceramic green body was heated to 480℃ at a heating rate of 0.5℃ / min under an argon atmosphere, and held at that temperature for 3 hours.

[0117] Comparative Example 5

[0118] The preparation process of the 3D printed silicon carbide ceramic in Comparative Example 5 is the same as in Example 1, except that in step (1), only a modifier is added without a plasticizer, resulting in poor forming accuracy in the subsequent powder extrusion printing process. Figure 3 As shown in (b).

[0119] Table 1:

[0120] Plasticized modified polyvinyl alcohol / wt% Shrinkage rate / % Free silicon / vol.% Flexural strength / MPa Example 1 25wt% 3.1％ 15.2 vol.% 351MPa Example 2 20wt% 2.8％ 14.5 vol.% 332MPa Example 3 15wt% 2.4％ 16.5 vol.% 314MPa Example 4 20wt% 2.9％ 13.2 vol.% 389MPa Example 5 15wt% 2.7％ 14.3 vol.% 384MPa Example 6 10wt% 1.9％ 18.8 vol.% 356MPa Example 7 5wt% 1.3％ 17.5 vol.% 298MPa Example 8 25wt% 2.9％ 15.8 vol.% 377MPa Example 9 30wt% 4.5％ 15.7 vol.% 339MPa .

[0121] Methods or instruments for testing shrinkage include: photographic testing;

[0122] Methods or instruments for testing flexural strength include: the three-point bending test and a universal testing machine for materials;

[0123] Test methods or instruments for free silicon include: theoretical calculation of carbon density.

Claims

1. A method for preparing silicon carbide ceramics for 3D printing using a water-soluble binder, characterized in that, include: (1) First, mix polyvinyl alcohol and the first modifier, and then mix with the plasticizer to obtain plasticized modified polyvinyl alcohol; The first modifier comprises at least one of the following: glycerol, ethylene glycol, butylene glycol, diethylene glycol, acetic acid, animal gelatin, polyamide, polyurethane, lactic acid, glycerol, mannitol, sorbitol, pentaerythritol, caprolactam, and polyethylene glycol; the amount of the first modifier is 5-40 wt% of the total mass of polyvinyl alcohol. (2) A second modifier is added to silicon carbide ceramic powder, and the mixture is ball-milled using deionized water or anhydrous ethanol as a solvent to obtain modified silicon carbide powder; the second modifier includes at least one of stearic acid, polyoxyethylene fatty acid ester, n-butanol, alkylphenol polyoxyethylene ether, hexadecyltrimethylammonium bromide, and sodium dodecyl sulfate; the mass of the second modifier accounts for 0.5 to 1.5 wt% of the mass of the silicon carbide powder; (3) The modified silicon carbide powder, the plasticized modified polyvinyl alcohol and the organic binder are mixed evenly and crushed and granulated to obtain silicon carbide printing material; (4) The obtained silicon carbide printing material is 3D printed to obtain a silicon carbide ceramic blank; (5) The obtained silicon carbide ceramic green body is first degreased with water solvent and then degreased with heat to obtain a degreased silicon carbide ceramic green body; (6) The degreased silicon carbide ceramic green body is impregnated in a phenolic resin solution and then carbonized to obtain a C / SiC ceramic green body; (7) The C / SiC ceramic blank is sintered by melt infiltration reaction to obtain 3D printed silicon carbide ceramic.

2. The preparation method according to claim 1, characterized in that, In step (1): the polyvinyl alcohol is at least one of the four types: 1788, 1799, 2088, and 2099.

3. The preparation method according to claim 1, characterized in that, In step (1): the plasticizer includes at least one of the following: di-n-octyl phthalate, di(2-ethylhexyl) phthalate, dibutyl phthalate, butyl benzyl phthalate, diisononyl phthalate, diisodecyl phthalate, dimethyl phthalate, diethyl phthalate, diallyl phthalate, di(2-methoxy)ethyl phthalate, dipentyl phthalate, dihexyl phthalate, and dicyclohexyl phthalate; the amount of plasticizer used is 5 to 40 wt% of the total mass of polyvinyl alcohol.

4. The preparation method according to claim 1, characterized in that, In step (1): the mixing method is constant temperature magnetic stirring method; the parameters of the constant temperature magnetic stirring method include: stirring temperature of 30 to 70°C and stirring time of 1 to 4 hours.

5. The preparation method according to claim 1, characterized in that, In step (2): the silicon carbide powder is D 50 =1~10μm and D 50 A mixture of silicon carbide particles with two particle size distributions of 10 to 70 μm.

6. The preparation method according to claim 5, characterized in that, Control D 50 =1~10μm and D 50 The mass ratio of silicon carbide with two particle size distributions of 10 to 70 μm is 1:(1 to 4).

7. The preparation method according to claim 1, characterized in that, In step (3): the organic binder includes at least one of polycarbonate, polyoxymethylene, ethylene-vinyl acetate copolymer, polystyrene, polyamide, and polymethyl methacrylate.

8. The preparation method according to claim 1, characterized in that, In step (3): the modified silicon carbide powder accounts for 50-80 wt% of the silicon carbide printing material, the plasticized modified polyvinyl alcohol accounts for 5-30 wt% of the silicon carbide printing material, and the organic binder accounts for 5-25 wt% of the silicon carbide printing material.

9. The preparation method according to claim 1, characterized in that, In step (3): the particle size of the granulated silicon carbide printing material is 0.2 to 0.5 cm.

10. The preparation method according to claim 1, characterized in that, In step (4): the parameters for 3D printing include: the nozzle temperature is set to 150-200℃, the stage temperature is set to 50-110℃, the cavity atmosphere temperature is set to 30-50℃, the printing speed is 20-50mm / s, the printing spacing is set to 0.05-0.15mm, and the single layer thickness is set to 0.05-0.2mm.

11. The preparation method according to claim 10, characterized in that, The printer cavity atmosphere used in the 3D printing process is air.

12. The preparation method according to claim 1, characterized in that, The water-based degreasing temperature is set to 30–90°C, the degreasing time is 2–12 hours, and the solvent is water; the water-based degreasing environment is an ultrasonic field with an ultrasonic frequency of 30–70 kHz. The conditions for thermal degreasing are as follows: under argon or vacuum atmosphere, the silicon carbide ceramic green body is heated to 400-500°C at a heating rate of 0.2-1°C / min, and held at that temperature for 0.5-3 hours.

13. The preparation method according to claim 1, characterized in that, In step (6): the mass fraction of the phenolic resin solution is 30-50 wt%; The impregnation environment is a vacuum, and the impregnation time is 20 to 30 minutes; The carbonization parameters include: a vacuum atmosphere, a temperature of 600–800°C, and a time of 1–4 hours; Impregnation and carbonization constitute one cycle, and the number of cycles is at least 2.

14. The preparation method according to claim 13, characterized in that, The phenolic resin solution has a mass fraction of 50 wt%; the impregnation time is 30 min; and the number of cycles is 3.

15. The preparation method according to claim 1, characterized in that, In step (7): the degreased silicon carbide ceramic blank is mixed with silicon powder; the particle size of the silicon powder is 0.1-1cm; the mass ratio of the degreased silicon carbide ceramic blank to the silicon powder is 1:(1-2).

16. The preparation method according to claim 1, characterized in that, In step (7): the sintering regime of the molten silicon infiltration reaction sintering includes: a temperature of 1500-1750℃, a sintering time of 1-4h, and a sintering atmosphere of vacuum.

17. A 3D-printed silicon carbide ceramic obtained by the preparation method according to any one of claims 1-16.

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