TEOS-coated silicon nitride ceramic powder, and preparation method and application thereof

Abstract

This invention belongs to the field of silicon nitride ceramic technology, specifically relating to a TEOS-coated silicon nitride ceramic powder, its preparation method, and its application. The TEOS-coated silicon nitride ceramic powder comprises a core layer and a coating layer; the core layer comprises silicon nitride; the coating layer is mainly prepared from tetraethoxysilane; based on the mass of SiO2, the mass of the coating layer is 0.5–15 wt% of the mass of the core layer. The TEOS-coated silicon nitride ceramic powder prepared by this invention can achieve a better refractive index match with photosensitive resin and a more uniform interface in photocurable ceramic forming processes, reducing light scattering and absorption unevenness problems, and significantly increasing the curing depth under the same exposure conditions. When used as a sintering aid, the TEOS-coated silicon nitride ceramic powder prepared by this invention can lower the densification temperature of silicon nitride ceramics while improving relative density and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of silicon nitride ceramic technology, specifically relating to a TEOS-coated silicon nitride ceramic powder, its preparation method, and its application. Background Technology

[0002] Silicon nitride (Si3N4) ceramics possess excellent properties such as high strength, high toughness, thermal shock resistance, and wear resistance, making them promising for applications in bearings, cutting tools, engine components, and high-temperature structural parts. However, due to the low sintering activity of silicon nitride, high sintering temperatures (e.g., ≥1700℃) and complex sintering aid systems are typically required to obtain high-density sintered bodies, resulting in a narrow process window and high energy consumption.

[0003] With the development of near-net-shape forming technologies such as photopolymer additive manufacturing, binder spraying, and gel casting, higher requirements are being placed on silicon nitride powders. Therefore, the powder not only needs to have good dispersibility and interfacial wettability in photosensitive resin or organic binder systems to ensure the rheological stability and anti-settling properties of the slurry, but also should have a microstructure favorable for light transmission to achieve sufficient curing depth and forming efficiency. The formed green body still needs sintering aids to achieve densification during the sintering process; otherwise, problems such as high sintering temperature, uneven shrinkage, and insufficient density are likely to occur. In existing technologies, sintering aids such as Y₂O₃ and Al₂O₃ or pre-coating oxides are often added directly to improve the sintering performance of silicon nitride. However, some aids have limited contribution to the early photopolymerization or organic curing process, and may even worsen the rheological properties of the slurry and reduce the curing depth. Furthermore, the uniformity of the coating and the interfacial bonding state with the substrate are difficult to control precisely, thus affecting the stability of the microstructure and properties after sintering.

[0004] Therefore, there is an urgent need for a novel silicon nitride powder modification technology that simultaneously takes into account both the curing behavior during the photocuring stage and the densification behavior during the sintering stage. Summary of the Invention

[0005] This invention aims to provide a silicon nitride ceramic powder, its preparation method, and its applications. The TEOS-coated silicon nitride ceramic powder prepared by this invention exhibits better refractive index matching and more uniform interface with photosensitive resin in photocurable ceramic forming processes, reducing light scattering and absorption unevenness, and significantly increasing the curing depth under the same exposure conditions. When used as a sintering aid, the TEOS-coated silicon nitride ceramic powder prepared by this invention can lower the densification temperature of silicon nitride ceramics while simultaneously improving their relative density and mechanical properties.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a TEOS-coated silicon nitride ceramic powder, wherein the TEOS-coated silicon nitride ceramic powder comprises a core layer and a coating layer; the core layer comprises silicon nitride; and the coating layer is mainly prepared by a hydrolysis-condensation reaction of tetraethoxysilane. The mass of the coating layer is 0.5 to 15 wt% of the mass of the core layer, based on the mass of SiO2.

[0007] As one embodiment of the TEOS-coated silicon nitride ceramic powder of the present invention, the silicon nitride is silicon nitride particles or silicon nitride powder.

[0008] As one embodiment of the TEOS-coated silicon nitride ceramic powder of the present invention, the median particle size D of the silicon nitride particles is... 50 The particle size is 0.1–5 μm. In this invention, if the particle size of the silicon nitride particles used is unsuitable, the coating effect of tetraethoxysilane will significantly deteriorate, resulting in a decrease in the performance of the final ceramic product.

[0009] As one embodiment of the TEOS-coated silicon nitride ceramic powder of the present invention, the thickness of the coating layer is 5~300nm.

[0010] In this invention, when the coating layer of TEOS-coated silicon nitride ceramic powder is too thin, uneven ultraviolet light scattering and absorption are likely to occur; while when the coating layer is too thick, too much silicon dioxide sintering aid will be formed, which is not conducive to the performance of the ceramic after sintering.

[0011] As one embodiment of the TEOS-coated silicon nitride ceramic powder of the present invention, the thickness of the coating layer is 50-100 nm.

[0012] This invention also claims protection for a method for preparing the TEOS-coated silicon nitride ceramic powder, comprising the following steps: S1. Dissolve tetraethoxysilane, add water and acidic catalyst, adjust pH to form a sol; S2. Add silicon nitride to the sol obtained in step S1, disperse, react, separate solid and liquid, dry, and obtain crude product. S3. The crude product obtained in step S2 is subjected to heat treatment to obtain the TEOS-coated silicon nitride ceramic powder.

[0013] In one embodiment of the preparation method described in this invention, the solvent used for dissolution in step S1 is an alcohol solvent; the alcohol solvent includes at least one of ethanol and isopropanol.

[0014] In one embodiment of the preparation method described in this invention, the molar ratio of water to tetraethoxysilane in step S1 is (1-10):1.

[0015] As one embodiment of the preparation method described in this invention, the acidic catalyst in step S1 includes at least one of dilute hydrochloric acid, dilute nitric acid, and acetic acid.

[0016] In one embodiment of the preparation method described in this invention, the pH adjustment in step S1 is to make the pH of the solution 1 to 5.

[0017] As one embodiment of the preparation method described in this invention, the dispersion in step S2 is carried out by stirring and / or ultrasonication for a dispersion time of 50-80 min.

[0018] In one embodiment of the preparation method described in this invention, the reaction temperature in step S2 is 20~60℃ and the reaction time is 0.5~24h.

[0019] As one embodiment of the preparation method described in this invention, the solid-liquid separation in step S2 is performed by vacuum filtration or centrifugation.

[0020] As one embodiment of the preparation method described in this invention, the drying temperature in step S2 is 40~120℃ and the drying time is 2~24h.

[0021] As one embodiment of the preparation method described in this invention, the heat treatment in step S3 involves heating the crude product at 300–900°C in air or an inert atmosphere for 0.5–4 hours.

[0022] The inert atmosphere described in this invention can be nitrogen or other conventional inert gases in the art.

[0023] The TEOS-coated silicon nitride ceramic powder prepared by this invention through specific process steps can effectively improve the interfacial compatibility and refractive index matching between the powder and photosensitive resin / organic binder, increase the effective curing depth of photocuring or chemical curing, and improve the density and dimensional accuracy of the green body. Simultaneously, due to its specific structural composition, the TEOS-coated silicon nitride ceramic powder of this invention can be used as a sintering aid in ceramic sintering processes, participating in liquid-phase sintering, lowering the densification temperature of silicon nitride ceramics, thereby effectively improving the relative density and mechanical properties of the sintered body.

[0024] This invention also claims protection for the application of the TEOS-coated silicon nitride ceramic powder, or the TEOS-coated silicon nitride ceramic powder prepared by the method of preparing the TEOS-coated silicon nitride ceramic powder, in photocurable ceramic forming processes and silicon nitride ceramic sintering processes.

[0025] As one embodiment of the application described in this invention, the photocurable ceramic forming process includes the following steps: dispersing the TEOS-coated silicon nitride ceramic powder in a photosensitive resin to prepare a ceramic photosensitive slurry, and then performing layer-by-layer curing and forming by stereolithography (SLA) or digital light processing (DLP). Compared with using uncoated silicon nitride powder, the curing depth is increased by at least 10% under the same exposure conditions.

[0026] This invention also claims protection for the application of the TEOS-coated silicon nitride ceramic powder, or the TEOS-coated silicon nitride ceramic powder prepared by the method of preparing the TEOS-coated silicon nitride ceramic powder, in binder spray molding, gel casting, tape casting or slip casting processes.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses tetraethoxysilane (TEOS) to coat silicon nitride to obtain TEOS-coated silicon nitride ceramic powder, which not only improves the curing depth and the quality of the green body, but also functions as a sintering aid. In the photocurable ceramic forming process, it can better match the refractive index of the photosensitive resin and the interface is more uniform, reducing the problems of light scattering and uneven absorption. Under the same exposure conditions, the curing depth is significantly increased. When the TEOS-coated silicon nitride ceramic powder obtained by the present invention is used as a sintering aid, it can lower the densification temperature of silicon nitride ceramics, while improving the relative density and mechanical properties.

[0028] (2) The preparation process of the TEOS-coated silicon nitride ceramic powder of the present invention is simple, easy to operate, and has low cost, which is conducive to large-scale industrial production. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the experimental methods used in the examples and comparative examples are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0031] Example 1: A TEOS-coated silicon nitride ceramic powder Components: Core layer: Silicon nitride particles, D 50 It has a diameter of 0.8 μm and a specific surface area of ​​3-10 m². 2 ·g -1 ; Coating layer: prepared by hydrolysis-condensation reaction of tetraethoxysilane; Based on the mass of SiO2, the mass of the coating layer is 5 wt% of the mass of the core layer; The thickness of the coating layer is 100 nm.

[0032] Preparation method: S1. Dissolve tetraethoxysilane in anhydrous ethanol and stir under magnetic stirring for 30 min to ensure complete dissolution. Slowly add deionized water and simultaneously add 1 wt% dilute hydrochloric acid to adjust the pH to 2-3. Continue stirring for 60 min to form a sol. The molar ratio of water to tetraethoxysilane is 2:1. S2. Add silicon nitride particles to the gel obtained in step S1, pre-disperse using mechanical stirring (500 rpm) for 20 min, then ultrasonically disperse for 30 min, react at 30℃ for 4 h, filter, wash the filter cake twice with anhydrous ethanol to remove free oligomers, and dry the obtained solid at 80℃ for 12 h to obtain the crude product. S3. Place the crude product obtained in step S2 into a muffle furnace and heat it at 5 °C·min in an air atmosphere. -1 The temperature was increased to 600 °C at a heating rate, held for 2 h, and then naturally cooled to obtain the TEOS-coated silicon nitride ceramic powder.

[0033] Example 2: A TEOS-coated silicon nitride ceramic powder Components: Core layer: Silicon nitride particles, D 50 Its thickness is 0.1 μm, and its specific surface area is 3-10 m². 2 ·g -1 ; Coating layer: prepared by hydrolysis-condensation reaction of tetraethoxysilane; The mass of the coating layer, based on the mass of SiO2, is 0.5 wt% of the mass of the core layer. The thickness of the coating layer is 5 nm.

[0034] Preparation method: S1. Dissolve tetraethoxysilane in anhydrous ethanol and stir under magnetic stirring for 30 min to ensure complete dissolution. Slowly add deionized water and simultaneously add 1 wt% dilute nitric acid to adjust the pH to 1-5. Continue stirring for 60 min to form a sol. The molar ratio of water to tetraethoxysilane is 10:1. S2. Add silicon nitride particles to the gel obtained in step S1, stir mechanically (500 rpm) for 80 min, react at 20°C for 24 h, filter, and dry the obtained solid at 40°C for 24 h to obtain the crude product. S3. Place the crude product obtained in step S2 into a muffle furnace and heat it at 5 °C·min in an air atmosphere. -1 The temperature was increased to 300 °C at a heating rate, held for 4 h, and then naturally cooled to obtain the TEOS-coated silicon nitride ceramic powder.

[0035] Example 3: A TEOS-coated silicon nitride ceramic powder Components: Core layer: Silicon nitride particles, D 50 It has a diameter of 5 μm and a specific surface area of ​​3-10 m². 2 ·g -1 ; Coating layer: prepared by hydrolysis-condensation reaction of tetraethoxysilane; The mass of the coating layer, based on the mass of SiO2, is 15 wt% of the mass of the core layer. The thickness of the coating layer is 300 nm.

[0036] Preparation method: S1. Dissolve tetraethoxysilane in isopropanol and stir under magnetic stirring for 30 min to ensure complete dissolution. Slowly add deionized water and simultaneously add acetic acid with a mass fraction of 1 wt% to adjust the pH to 2-3. Continue stirring for 60 min to form a sol. The molar ratio of water to tetraethoxysilane is 1:1. S2. Add silicon nitride particles to the gel obtained in step S1, disperse ultrasonically for 50 min, react at 60℃ for 1 h, centrifuge, and dry the obtained solid at 120℃ for 2 h to obtain the crude product. S3. Place the crude product obtained in step S2 in a muffle furnace and heat it at 5 °C·min under an inert atmosphere (nitrogen). -1 The temperature was increased to 900 °C at a heating rate, held for 1 h, and then naturally cooled to obtain the TEOS-coated silicon nitride ceramic powder.

[0037] Example 4: A TEOS-coated silicon nitride ceramic powder Components: Core layer: Silicon nitride powder; Coating layer: prepared by hydrolysis-condensation reaction of tetraethoxysilane; The mass of the coating layer, based on the mass of SiO2, is 5 wt% of the mass of the core layer. The thickness of the coating layer is 100 nm.

[0038] Preparation method: S1. Dissolve tetraethoxysilane in anhydrous ethanol and stir under magnetic stirring for 30 min to ensure complete dissolution. Slowly add deionized water and simultaneously add 1 wt% dilute hydrochloric acid to adjust the pH to 2-3. Continue stirring for 60 min to form a sol. The molar ratio of water to tetraethoxysilane is 2:1. S2. Add silicon nitride powder to the gel obtained in step S1, pre-disperse it for 20 min by mechanical stirring (500 rpm), then ultrasonically disperse it for 30 min, react it at 30℃ for 4 h, filter it, wash the filter cake twice with anhydrous ethanol to remove free oligomers, and dry the obtained solid at 80℃ for 12 h to obtain the crude product. S3. Place the crude product obtained in step S2 into a muffle furnace and heat it at 5 °C·min in an air atmosphere. -1 The temperature was increased to 600 °C at a heating rate, held for 2 h, and then naturally cooled to obtain the TEOS-coated silicon nitride ceramic powder.

[0039] Example 5: A TEOS-coated silicon nitride ceramic powder Components: Core layer: Silicon nitride particles, D 50 It has a diameter of 0.8 μm and a specific surface area of ​​3-10 m². 2 ·g -1 ; Coating layer: prepared by hydrolysis-condensation reaction of tetraethoxysilane; Based on the mass of SiO2, the mass of the coating layer is 5 wt% of the mass of the core layer; The thickness of the coating layer is 100 nm.

[0040] Preparation method: S1. Dissolve tetraethoxysilane in anhydrous ethanol and stir under magnetic stirring for 30 min to ensure complete dissolution. Slowly add deionized water and simultaneously add 1 wt% dilute hydrochloric acid to adjust the pH to 2-3. Continue stirring for 60 min to form a sol. The molar ratio of water to tetraethoxysilane is 12:1. S2. Add silicon nitride particles to the gel obtained in step S1, pre-disperse using mechanical stirring (500 rpm) for 20 min, then ultrasonically disperse for 30 min, react at 30℃ for 4 h, filter, wash the filter cake twice with anhydrous ethanol to remove free oligomers, and dry the obtained solid at 80℃ for 12 h to obtain the crude product. S3. Place the crude product obtained in step S2 into a muffle furnace and heat it at 5 °C·min in an air atmosphere. -1 The temperature was increased to 600 °C at a heating rate, held for 2 h, and then naturally cooled to obtain the TEOS-coated silicon nitride ceramic powder.

[0041] Example 6: A TEOS-coated silicon nitride ceramic powder Components: Core layer: Silicon nitride particles, D 50 It has a diameter of 0.8 μm and a specific surface area of ​​3-10 m². 2 ·g -1 ; Coating layer: prepared by hydrolysis-condensation reaction of tetraethoxysilane; Based on the mass of SiO2, the mass of the coating layer is 5 wt% of the mass of the core layer; The thickness of the coating layer is 100 nm.

[0042] Preparation method: S1. Dissolve tetraethoxysilane in anhydrous ethanol and stir under magnetic stirring for 30 min to ensure complete dissolution. Slowly add deionized water and simultaneously add 1 wt% dilute hydrochloric acid to adjust the pH to 2-3. Continue stirring for 60 min to form a sol. The molar ratio of water to tetraethoxysilane is 2:1. S2. Add silicon nitride particles to the gel obtained in step S1, pre-disperse using mechanical stirring (500 rpm) for 20 min, then ultrasonically disperse for 30 min, react at 30℃ for 4 h, filter, wash the filter cake twice with anhydrous ethanol to remove free oligomers, and dry the obtained solid at 80℃ for 12 h to obtain the crude product. S3. Place the crude product obtained in step S2 into a muffle furnace and heat it at 5 °C·min in an air atmosphere. -1 The temperature was increased to 1000 °C at a heating rate, held for 2 h, and then naturally cooled to obtain the TEOS-coated silicon nitride ceramic powder.

[0043] Example 7: A TEOS-coated silicon nitride ceramic powder Components: Core layer: Silicon nitride particles, D 50 It has a diameter of 0.8 μm and a specific surface area of ​​3-10 m². 2 ·g -1 ; Coating layer: prepared by hydrolysis-condensation reaction of tetraethoxysilane; Based on the mass of SiO2, the mass of the coating layer is 5 wt% of the mass of the core layer; The thickness of the coating layer is 100 nm.

[0044] Preparation method: S1. Dissolve tetraethoxysilane in anhydrous ethanol and stir under magnetic stirring for 30 min to ensure complete dissolution. Slowly add deionized water and simultaneously add 1 wt% dilute hydrochloric acid to adjust the pH to 2-3. Continue stirring for 60 min to form a sol. The molar ratio of water to tetraethoxysilane is 2:1. S2. Add silicon nitride particles to the gel obtained in step S1, pre-disperse using mechanical stirring (500 rpm) for 20 min, then ultrasonically disperse for 30 min, react at 80℃ for 4 h, filter, wash the filter cake twice with anhydrous ethanol to remove free oligomers, and dry the obtained solid at 80℃ for 12 h to obtain crude product. S3. Place the crude product obtained in step S2 into a muffle furnace and heat it at 5 °C·min in an air atmosphere. -1 The temperature was increased to 600 °C at a heating rate, held for 2 h, and then naturally cooled to obtain the TEOS-coated silicon nitride ceramic powder.

[0045] Comparative Example 1 Components: Silicon nitride particles, D 50 It has a diameter of 0.8 μm and a specific surface area of ​​3-10 m². 2 ·g -1 .

[0046] Preparation method: Silicon nitride particles were placed in a muffle furnace and heated at 5 °C / min in an air atmosphere. -1 The temperature was increased to 600℃ at a heating rate, held for 2 hours, and then naturally cooled to obtain silicon nitride ceramic powder.

[0047] The only difference between this comparative example and Example 1 is that the silicon nitride particles are not coated.

[0048] Comparative Example 2 Components: Core layer: Silicon nitride particles, D 50 It has a diameter of 0.8 μm and a specific surface area of ​​3-10 m². 2 ·g -1 ; Coating layer: prepared by hydrolysis-condensation reaction of tetraethoxysilane; Based on the mass of SiO2, the mass of the coating layer is 5 wt% of the mass of the core layer; The thickness of the coating layer is 100 nm.

[0049] Preparation method: S1. Dissolve tetraethoxysilane in anhydrous ethanol and stir under magnetic stirring for 30 min to ensure complete dissolution. Slowly add deionized water and simultaneously add 1 wt% dilute hydrochloric acid to adjust the pH to 2-3. Continue stirring for 60 min to form a sol. The molar ratio of water to tetraethoxysilane is 2:1. S2. Add silicon nitride particles to the gel obtained in step S1, pre-disperse using mechanical stirring (500 rpm) for 20 min, then ultrasonically disperse for 30 min, react at 30℃ for 4 h, filter, wash the filter cake twice with anhydrous ethanol to remove free oligomers, and dry the obtained solid at 80℃ for 12 h to obtain silicon nitride ceramic powder.

[0050] The only difference between this comparative example and Example 1 is that step S3 is omitted.

[0051] Comparative Example 3 Components: Core layer: Silicon nitride particles, D 50 It has a diameter of 0.8 μm and a specific surface area of ​​3-10 m². 2 ·g -1 ; Coating layer: prepared by hydrolysis-condensation reaction of tetraethoxysilane; Based on the mass of SiO2, the mass of the coating layer is 16 wt% of the mass of the core layer; The thickness of the coating layer is 100 nm.

[0052] Preparation method: S1. Dissolve tetraethoxysilane in anhydrous ethanol and stir under magnetic stirring for 30 min to ensure complete dissolution. Slowly add deionized water and simultaneously add 1 wt% dilute hydrochloric acid to adjust the pH to 2-3. Continue stirring for 60 min to form a sol. The molar ratio of water to tetraethoxysilane is 2:1. S2. Add silicon nitride particles to the gel obtained in step S1, pre-disperse using mechanical stirring (500 rpm) for 20 min, then ultrasonically disperse for 30 min, react at 30℃ for 4 h, filter, wash the filter cake twice with anhydrous ethanol to remove free oligomers, and dry the obtained solid at 80℃ for 12 h to obtain the crude product. S3. Place the crude product obtained in step S2 into a muffle furnace and heat it at 5 °C·min in an air atmosphere. -1 The temperature was increased to 600 °C at a heating rate, held for 2 h, and then naturally cooled to obtain the silicon nitride ceramic powder.

[0053] The only difference between this comparative example and Example 1 is that, based on the mass of SiO2, the mass of the coating layer is 16 wt% of the mass of the core layer.

[0054] Comparative Example 4 Components: Core layer: Silicon nitride particles, D 50 It has a diameter of 0.8 μm and a specific surface area of ​​3-10 m². 2 ·g -1 ; Coating layer: Coating is performed using silane coupling agent KH560; The mass of the coating layer, based on the mass of SiO2, is 5 wt% of the mass of the core layer. The thickness of the coating layer is 100 nm.

[0055] Preparation method: S1. Dissolve KH560 in anhydrous ethanol and stir under magnetic stirring for 30 min to ensure complete dissolution. Slowly add deionized water and simultaneously add 1 wt% dilute hydrochloric acid to adjust the pH to 2-3. Continue stirring for 60 min to form a sol. The molar ratio of water to KH560 is 2:1. S2. Add silicon nitride particles to the gel obtained in step S1, pre-disperse using mechanical stirring (500 rpm) for 20 min, then ultrasonically disperse for 30 min, react at 30℃ for 4 h, filter, wash the filter cake twice with anhydrous ethanol to remove free oligomers, and dry the obtained solid at 80℃ for 12 h to obtain the crude product. S3. Place the crude product obtained in step S2 into a muffle furnace and heat it at 5 °C·min in an air atmosphere. -1 The temperature was increased to 600 °C at a heating rate, held for 2 h, and then naturally cooled to obtain the silicon nitride ceramic powder.

[0056] The only difference between this comparative example and Example 1 is that the silane coupling agent KH560 is used for coating.

[0057] Experimental Example 1: Photocuring Performance I. Sample Preparation (1) Preparation of photosensitive resin matrix Formula: (percentage by weight) Multifunctional acrylate prepolymer (U600, PPTTA): 60 wt% Reactive diluent (HDDA): 25 wt% Photoinitiator (TPO): 3 wt% Additive (BYK-110 dispersant): 2 wt%.

[0058] Preparation method: Mix all the above components to obtain a photosensitive resin matrix.

[0059] (2) Preparation of ceramic slurry Weigh 40 g of the photosensitive resin matrix prepared above, add dispersant (Lubrizol 17000, Lubrizol 41000, BYK-110) and pre-stir for 10 min; Add 60 g (volume fraction of approximately 50 vol%) of silicon nitride ceramic powder prepared in Examples 1-7 and Comparative Examples 1-4, and stir at 300 rpm for 30 min using a planetary vacuum mixer; The slurry is then ground 2-3 times with a three-roll mill to remove any obvious agglomerated particles, thus obtaining a ceramic slurry.

[0060] II. Experimental Methods Apparent viscosity (Pa·s): at 25℃ and a shear rate of 100 s⁻¹ -1 The apparent viscosity of different groups of slurry was tested.

[0061] Curing performance: The slurry was coated onto a transparent substrate using the same wavelength (405nm) and the same exposure energy (129.24mJ·cm⁻¹). 2 Perform spot curing tests and measure the corresponding curing depth.

[0062] III. Experimental Results The experimental results are shown in Table 1.

[0063] Table 1. Test results of photocuring performance for each group As can be seen from the experimental data in Table 1, the TEOS-coated silicon nitride ceramic powder prepared in the embodiments of the present invention effectively reduces the viscosity of the slurry, inhibits agglomeration and sedimentation after being prepared into ceramic slurry, and significantly improves the particle dispersion state and light transmission uniformity, thereby significantly increasing the effective curing depth. It is suitable for use in photocurable additive manufacturing processes such as SLA / DLP.

[0064] In Comparative Example 1, the silicon nitride particles were not coated, resulting in a ceramic slurry with poor photocuring properties. In Comparative Example 2, the ceramic powder lacked a heat treatment step, which failed to effectively reduce the viscosity of the ceramic slurry and also affected the photocuring properties. In Comparative Example 3, the mass ratio of the coating layer in the ceramic powder was inappropriate. In Comparative Example 4, KH560 was used to replace the TEOS component, resulting in a ceramic slurry with higher viscosity and poorer photocuring properties than in Example 1.

[0065] Experimental Example 2: Sintering Densification Properties and Mechanical Properties I. Experimental Samples The ceramic slurries prepared in each group of Experiment 1 were used to print standard specimens (long, curved specimens) using a DLP device. The layer thickness was 50 μm, and the exposure parameters were set according to the recommended values ​​of the device (129.24 mJ·cm). 2 After photocuring and thermal degreasing (800 degrees, 2 hours), a degreased preform is obtained.

[0066] The degreased green body was placed in a nitrogen atmosphere furnace at 5 °C·min. -1 The temperature was raised to 1650 ℃, held for 2 h, and then cooled to obtain the sintered sample.

[0067] Experimental methods Sintering densification properties: The relative density of sintered samples prepared in each group was measured using the Archimedes method (GB / T 25995-2010); Mechanical properties: The test method is carried out in accordance with GB / T 6569-86 standard. The test environment conditions are: room temperature; sample surface: polished to 1μm diamond suspension, surface roughness Ra<0.2μm; statistics: n≥6 for each item, report the mean ± standard deviation.

[0068] III. Experimental Results The experimental results are shown in Table 2.

[0069] Table 2 Performance test results for each group As can be seen from the experimental results in Table 2, the TEOS-coated ceramic powder prepared in the embodiments of the present invention can effectively improve the densification performance of ceramic slurry, enabling the sintered product to maintain a high relative density range, while also effectively improving its mechanical properties.

[0070] Compared with Example 1, the silicon nitride particles in the ceramic powder of Comparative Example 1 were not coated, resulting in a lower relative density and significantly worse mechanical properties in the sintered product. The ceramic powder in Comparative Example 2 lacked a heat treatment step, the mass ratio of the coating layer in the ceramic powder of Comparative Example 3 was inappropriate, and KH560 was used to replace the TEOS component in Comparative Example 4. The relative density and mechanical properties of the final sintered product were all worse than those in Example 1.

[0071] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A TEOS-coated silicon nitride ceramic powder, characterized in that, The TEOS-coated silicon nitride ceramic powder comprises a core layer and a coating layer; the core layer comprises silicon nitride; the coating layer is mainly made of tetraethoxysilane. The mass of the coating layer is 0.5 to 15 wt% of the mass of the core layer, based on the mass of SiO2.

2. The TEOS-coated silicon nitride ceramic powder as described in claim 1, characterized in that, The silicon nitride is silicon nitride particles or silicon nitride powder.

3. The TEOS-coated silicon nitride ceramic powder as described in claim 2, characterized in that, The median particle size D of the silicon nitride particles 50 The range is 0.1–5 μm.

4. The TEOS-coated silicon nitride ceramic powder as described in claim 1, characterized in that, The thickness of the coating layer is 5~300nm.

5. A method for preparing TEOS-coated silicon nitride ceramic powder as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Dissolve tetraethoxysilane, add water and acidic catalyst, adjust pH to form a sol; S2. Add silicon nitride to the sol obtained in step S1, disperse, react, separate solid and liquid, dry, and obtain crude product. S3. The crude product obtained in step S2 is subjected to heat treatment to obtain the TEOS-coated silicon nitride ceramic powder.

6. The method for preparing TEOS-coated silicon nitride ceramic powder as described in claim 5, characterized in that, The solvent used for dissolution in step S1 is an alcohol solvent; the alcohol solvent includes at least one of ethanol and isopropanol; The molar ratio of water to tetraethoxysilane in step S1 is (1-10):1; The acidic catalyst mentioned in step S1 includes at least one of dilute hydrochloric acid, dilute nitric acid, and acetic acid; The pH adjustment in step S1 is to make the pH of the solution between 1 and 5.

7. The method for preparing TEOS-coated silicon nitride ceramic powder as described in claim 5, characterized in that, The dispersion described in step S2 is carried out by stirring and / or ultrasonication, and the dispersion time is 50-80 min; The reaction temperature in step S2 is 20~60℃, and the reaction time is 0.5~24h; The solid-liquid separation in step S2 is performed by vacuum filtration or centrifugation. The drying temperature in step S2 is 40~120℃, and the drying time is 2~24h.

8. The method for preparing TEOS-coated silicon nitride ceramic powder as described in claim 5, characterized in that, The heat treatment described in step S3 involves heating the crude product in air or an inert atmosphere at 300–900°C for 0.5–4 hours.

9. The application of TEOS-coated silicon nitride ceramic powder as described in any one of claims 1 to 4, or TEOS-coated silicon nitride ceramic powder prepared by any one of claims 5 to 8, in photocurable ceramic forming processes and silicon nitride ceramic sintering processes.

10. The TEOS-coated silicon nitride ceramic powder prepared by any of the methods described in claims 1 to 4, or any of the methods described in claims 5 to 8, is used in binder spray molding, gel casting, tape casting, or slip casting processes.

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