Efficient silicon nitride slurry based on light-cured molding and ceramic low-temperature sintering molding method thereof

Abstract

The application discloses a kind of high-efficiency silicon nitride slurry based on light-cured forming and its ceramic low-temperature sintering forming method, comprising, beta phase silicon nitride powder, high-temperature binder, sintering aid is dispersed in ethanol solution by ball milling, ceramic mixed powder is obtained after drying and grinding;Add photo-initiator and oxygen barrier in photosensitive resin, stir uniformly to obtain premix liquid;Ceramic mixed powder and premix liquid are mixed, add dispersing agent, thixotropic agent, stir uniformly and vacuum defoaming to obtain silicon nitride ceramic slurry.The application effectively solves the technical defects of low single-layer curing thickness of traditional silicon nitride ceramic slurry light-cured forming, realizes high-precision, defect-free sample of 50 μm layer thickness printing of single layer, effectively improves the printing efficiency.High-temperature binder aluminum dihydrogen phosphate is introduced at the same time, and the problem of more and larger gaps between powders after debinding is solved by using metasilicate generated by its decomposition to bond silicon nitride particles, so as to realize the preparation of dense silicon nitride ceramics.

Description

Technical Field

[0001] This invention belongs to the field of ceramic additive manufacturing technology, specifically relating to a high-efficiency silicon nitride slurry based on photopolymerization molding and its low-temperature sintering molding method for ceramics. Background Technology

[0002] Silicon nitride ceramics, as an important structural ceramic, are widely used in aerospace, military, mechanical engineering, electronics, automotive, chemical, and biological fields due to their high temperature resistance, corrosion resistance, wear resistance, and unique dielectric properties. They are among the most promising advanced ceramic materials for extreme environment applications. However, their high hardness, excellent strength, and brittleness make it difficult to manufacture porous, irregularly shaped, and other complex Si3N4 parts using traditional forming methods, which limits the application and development of silicon nitride ceramics.

[0003] The development of moldless manufacturing technologies such as photopolymerization has made it possible to prepare ceramics with complex structures. However, existing photopolymerization technologies suffer from technical drawbacks such as low curing depth of single layers and poor mechanical properties after sintering. According to the Beer-Lambert model, scattering and absorption by powder are the main factors affecting the photopolymerization properties of ceramic slurries, as shown in the following formula:

[0004]

[0005] D p - Penetration depth, C d -Cure depth. E0 -Exposure energy, Equation (2)E c -Critical exposure energy, d 50 - Average particle size. S - Distance between ceramic particles. λ - Wavelength. p - The refractive index (RI) of the ceramic particles, n0 - the RI of the resin. Silicon nitride powder has the characteristics of high absorbance and high refractive index (n≈2.1), which is the main reason for the low curing depth of silicon nitride slurry.

[0006] Meanwhile, due to the layer-by-layer accumulation characteristic of the photopolymerization process, the ceramic powder is essentially embedded within the cross-linked structure of the photosensitive resin, and the two are tightly bonded. After degreasing and decarburization, the macromolecular resin is decomposed, resulting in numerous voids between the powder particles. This makes it difficult to obtain high-density ceramic products after pressureless sintering, hindering the printing of complex-shaped ceramics with good mechanical properties. Patent CN202210179265 uses a high-refractive-index resin to formulate the silicon nitride slurry, but this only slightly increases the curing depth of the slurry and results in relatively weak mechanical properties. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0008] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0009] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a high-efficiency silicon nitride slurry based on photocuring molding.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a high-efficiency silicon nitride slurry based on photocuring molding, characterized in that:

[0011] The high-efficiency silicon nitride slurry based on photocuring is composed of ceramic powder and photosensitive resin. The ceramic powder includes β-phase silicon nitride powder, sintering aid and high-temperature binder. The photosensitive resin includes resin, photoinitiator, oxygen barrier, dispersant and thixotropic agent.

[0012] The ceramic powder contains 86-94% β-phase silicon nitride powder, 4-8% sintering aid, and 5-12% high-temperature binder by mass fraction.

[0013] The photosensitive resin has a resin mass fraction of 90%–96%, a photoinitiator mass fraction of 1–3%, an oxygen barrier mass fraction of 1–3%, a dispersant mass fraction of 1–4%, and a thixotropic agent mass fraction of 1–5%.

[0014] As a preferred embodiment of the high-efficiency silicon nitride slurry based on photocuring molding described in this invention, the mass ratio of the ceramic powder to the photosensitive resin is 1:1.

[0015] As a preferred embodiment of the high-efficiency silicon nitride slurry based on photocuring according to the present invention, wherein: the particle size of the β-phase silicon nitride powder is 500nm to 5μm; the sintering aid is yttrium oxide powder with a particle size of 0.1 to 2μm; and the high-temperature binder is aluminum dihydrogen phosphate with a particle size of 0.1 to 2μm.

[0016] As a preferred embodiment of the high-efficiency silicon nitride slurry based on photocuring according to the present invention, the resin comprises a mixture of o-phenylphenoxyethyl acrylate and 1,6-hexanediol diacrylate, wherein the content of o-phenylphenoxyethyl acrylate is 60-80 wt% and the content of 1,6-hexanediol diacrylate is 20-40 wt%.

[0017] As a preferred embodiment of the high-efficiency silicon nitride slurry based on photocuring according to the present invention, the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and the oxygen inhibitor is diisopropylphenyldiphenylamine.

[0018] As a preferred embodiment of the high-efficiency silicon nitride slurry based on photocuring molding described in this invention, the dispersant is wetting and dispersing agent SP710, and the thixotropic agent is octamethylcyclotetrasiloxane.

[0019] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for low-temperature sintering of high-efficiency silicon nitride slurry based on photopolymerization molding, characterized by comprising:

[0020] Silicon nitride powder, sintering aid, and aluminum dihydrogen phosphate were mixed and ball-milled to obtain a ceramic mixed powder.

[0021] A premix of photosensitive resin monomer, photoinitiator, and oxygen barrier is formed;

[0022] The silicon nitride ceramic slurry is obtained by mixing ceramic mixed powder, premixed liquid, dispersant and thixotropic agent;

[0023] Silicon nitride ceramic slurry is printed using a photopolymer printer to form a silicon nitride printed blank. The printed blank is then cleaned, degreased and decarburized, and sintered.

[0024] In a preferred embodiment of the method described in this invention, the solid content of the silicon nitride ceramic slurry is 40–60 vol%.

[0025] In a preferred embodiment of the method described in this invention, the wavelength of the light source used for photocuring is 405 nm, and the light intensity during the curing process is controlled between 6.56 and 25.36 mw / cm². 2 The curing time is controlled between 4 and 15 seconds; the degreasing-decarburizing process involves heating to 950–1150°C under a nitrogen atmosphere to remove organic matter and water molecules from aluminum dihydrogen phosphate, followed by removing carbon elements under an air atmosphere at 500–700°C.

[0026] As a preferred embodiment of the method described in this invention, the sintering is pressureless sintering under a nitrogen atmosphere, the sintering temperature is 1600-1700℃, and the holding time is 2-5h.

[0027] Beneficial effects of this invention:

[0028] This invention employs a high-refractive-index photosensitive resin system. By reducing the refractive index difference between the resin and silicon nitride powder, the penetration depth of ultraviolet light is increased. Simultaneously, an oxygen barrier agent is used to deplete oxygen on the surface of the photosensitive resin, reducing active free radicals bound to oxygen and improving the curing depth of the silicon nitride slurry printing. This results in a silicon nitride ceramic slurry with high solid content, low viscosity, and excellent curing performance, effectively addressing the technical shortcomings of traditional silicon nitride ceramic slurry photocuring, which results in low single-layer curing thickness. This facilitates the printing of high-precision, defect-free silicon nitride preforms. Furthermore, this invention incorporates a high-temperature binder (aluminum dihydrogen phosphate) instead of a sintering aid to encapsulate and modify the silicon nitride powder. At high temperatures, the decomposition of aluminum dihydrogen phosphate produces type A aluminate, which binds the high-temperature resistant silicon nitride particles together, thereby improving the sample density. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0030] Figure 1 This is a schematic diagram of the overall process of the photocurable 3D printing dense silicon nitride ceramic slurry based on a high refractive index resin system and the printing method thereof, according to the present invention.

[0031] Figure 2 The effect of oxygen inhibitor content on the curing properties of silicon nitride slurry. The effect of 0–3 vol% KI oxygen inhibitor content on the curing properties of silicon nitride slurry in Examples 1-3 and Comparative Examples 1-3.

[0032] Figure 3 To improve interlayer bonding and printing efficiency for different printing layer thicknesses.

[0033] Figure 4 The silicon nitride slurry prepared for Example 1 was used to print a complex model preform with a single layer thickness of 50 μm, and the model accuracy was tested. Figure 4 (a) is the gyroid print model. Figure 4 (b) is a BCC printing model. Figure 4 (c) is a test of the model's accuracy.

[0034] Figure 5 XRD characterization of silicon nitride ceramics at different temperatures. Detailed Implementation

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0037] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0038] The correspondence between the English abbreviations and full names of the raw materials used in specific embodiments of this invention is shown in Table 1.

[0039] Table 1 lists the English abbreviations and full names of the raw materials used.

[0040]

[0041]

[0042] Unless otherwise specified, all raw materials used in this invention are commercially available in the field.

[0043] Among them, Si3N4 powder was purchased from Shandong Cixing New Materials Co., Ltd., photosensitive resin was purchased from Zhongshan Qianyou Chemical Materials Co., Ltd., SP710 dispersant was purchased from Xinbocheng Environmental Protection Materials Co., Ltd., and BAPO initiator was purchased from Fusman Technology (Beijing) Co., Ltd.

[0044] The 3D printer used in this invention is the CeraStation 1.0 ceramic 3D printer developed by QuickDemos Intelligent Manufacturing High-Tech Company, used for curing depth testing and model printing.

[0045] This invention uses a Brookfield-Rheocalc rheometer to test the viscosity change of the prepared ceramic slurry at shear rates of 0-400 s⁻¹.

[0046] This invention uses the CeraStation 1.0 ceramic 3D printer developed by QuickDemos Intelligent Manufacturing High-Tech Company to print precision models. The molding accuracy of the model is judged by observing the minimum side length and minimum hole size of the formed blank through a three-dimensional profilometer.

[0047] Example 1

[0048] This embodiment provides a photopolymerization 3D printing method for dense silicon nitride ceramics with excellent curing performance, specifically:

[0049] 1) Weigh the raw materials according to the following formula:

[0050] The total ceramic mixed powder is 300g: 270g of 90% Si3N4 powder (3-5μm β-Si3N4 powder), 15g of 5% high-temperature binder aluminum dihydrogen phosphate, and 15g of 5% sintering aid Y2O3.

[0051] Photosensitive resin premix:

[0052] Mixture: 105.77 g of OPPEOA and HDDA, with volume fractions of 65 vol% and 35 vol%, respectively;

[0053] The mixture contains 2.12 g of BAPO photoinitiator, which accounts for 2% of the total mass of the photosensitive resin mixture; and 1.59 g of KI oxygen inhibitor, which accounts for 1.5% of the total mass of the photosensitive resin mixture.

[0054] The volume ratio of ceramic mixed powder to photosensitive resin premix is ​​1:1;

[0055] The ceramic mixed powder contains 2% dispersant SP710 (6g) and 1% thixotropic agent D4 (3g).

[0056] 2) Preparation of silicon nitride ceramic slurry:

[0057] The ceramic mixed powder raw materials were placed in a ball mill jar, anhydrous ethanol and grinding balls were added, and the mixture was ball milled in a planetary ball mill for 4 hours. The mixture was then dried and sieved for later use.

[0058] After mixing photosensitive resins OPPEOA and HDDA at volume fractions of 65 vol% and 35 vol%, respectively, 2 vol% of photoinitiator BAPO and 1.5 vol% of oxygen inhibitor KI were added, and the mixture was stirred evenly with a magnetic stirrer to form a premixed solution of 109.48 g.

[0059] After mixing 300g of pretreated ceramic mixed powder and 109.58g of premixed liquid, 6g of dispersant and 3g of thixotropic agent D4 were added in sequence. The mixture was stirred evenly by a homogenizer and then degassed under vacuum to obtain silicon nitride ceramic slurry.

[0060] 3) Characterization of curing performance:

[0061] The CeraStation 1.0 ceramic 3D printer, developed by QuickDemos Intelligent Manufacturing High-Tech Co., Ltd., was used. The aforementioned photocurable silicon nitride ceramic slurry was placed in a photocuring molding device, and the single-layer curing depth was measured using the photocuring method. The light source wavelength for photocuring was 405nm, and the light intensity during curing was adjusted between 6.56 and 25.63 mW / cm². 2 The curing time is 3 to 15 seconds;

[0062] 4) Perform 3D printing:

[0063] Photopolymerization 3D printing of silicon nitride ceramic slurry was used to obtain silicon nitride preforms, and the interlayer bonding and printing accuracy of the preforms were examined. Simultaneously, a 3D profilometer was used to examine the shrinkage and deformation between the printed preform and the model.

[0064] 5) Degreasing-decarbonization:

[0065] After printing, the printed blank is ultrasonically cleaned. Following cleaning, a two-step degreasing method is used. First, under a nitrogen atmosphere, the temperature is increased from 5℃ / min to 200℃, then increased at 0.2℃ / min to 450℃ and held at this temperature for 2 hours. Next, the temperature is increased at 0.5℃ / min to 600℃ and held at this temperature for 1 hour. Finally, the temperature is increased at 1℃ / min to 950℃ and held at this temperature for 2 hours. After cooling, the temperature is increased to 600℃ under an air atmosphere at 1℃ / min and held for 2 hours.

[0066] 6) Sintering of silicon nitride ceramics:

[0067] After degreasing, sintering was performed under a pressureless nitrogen atmosphere, with the temperature increased to 1400℃ at a rate of 10℃ / min, then increased to 1650℃ at a rate of 5℃ / min, and held for 4 hours to obtain silicon nitride ceramics. The flexural strength and porosity were measured using a mechanical property testing instrument and Archimedes' drainage method.

[0068] Figure 1 This is an overall flow chart of a high-efficiency silicon nitride slurry based on photocuring and its ceramic low-temperature sintering molding method according to the present invention.

[0069] Example 2

[0070] The difference between this embodiment and Example 1 is that the oxygen barrier content is changed to 1 vol% with a mass of 1.06 g. All other process steps and parameters are the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared to Example 1, this embodiment shows a relatively lower curing performance of 119.17 μm under the same light incident intensity, but the molded surface is smooth and no overexposure phenomenon is observed.

[0071] Example 3

[0072] The difference between this embodiment and Example 1 is that the oxygen barrier content is changed to 2 vol% with a mass of 2.12 g. All other process steps and parameters are the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared to Example 1, this embodiment shows a relatively lower curing performance of 136.17 μm under the same light incident intensity, but a small amount of whisker-like material appears at the edge of the molded surface, indicating a slight overexposure.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that no oxygen inhibitor is added. Compared with Example 1, this example has a curing performance of 108.67 μm under the same light incident intensity, which is too low and not conducive to printing.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 1 is that the content of the oxygen inhibitor in Example 1 is changed to 2.5%. Compared with Example 1, this example has a curing performance of 144.33 μm and a higher curing depth under the same light incident intensity. However, a large number of whisker-like structures appear on the edge of the molded surface, indicating a serious overexposure phenomenon, and the printed blank shows obvious warping deformation.

[0077] Comparative Example 3

[0078] The difference between this comparative example and Example 1 is that the content of the oxygen inhibitor in Example 1 is changed to 3%. Compared with Example 1, this example has a curing performance of 148.33 μm and a higher curing depth under the same light incident intensity. However, excessive whisker-like substances appear on the edge of the molded surface, indicating a very serious overexposure phenomenon. The printed blank warps and deforms, making it difficult to form.

[0079] Figure 2 The addition of oxygen inhibitors effectively improves the curing performance of silicon nitride slurries, facilitating the formulation of slurries with high curing performance. Table 1 shows that, based on data from Example 1 and Comparative Example 1, the curing depth increases with increasing oxygen inhibitor content. However, excessive oxygen inhibitor content leads to significant overexposure during single-layer curing, causing edge curing. This results in stress concentration at the edges during printing, leading to model warping and significantly impacting the printing accuracy. Ideally, an oxygen inhibitor content of 1 vol% to 2 vol% provides superior slurry curing performance.

[0080] Table 2. Effect of different oxygen barrier KI contents on the curing properties of ceramic slurry

[0081] Different oxygen barrier agent contents 1％ 1.5％ 2％ 2.5％ 3％ <![CDATA[Optical incident dose (mJ / cm 2 )]]> 256.3 256.3 256.3 256.3 256.3 Curing depth (μm) 119.17 129.67 136.17 144.33 148.33

[0082] Figure 3The silicon nitride slurry prepared for Example 1 shows the interlayer bonding of the model preforms formed with different printing layer thicknesses. It is evident that after curing performance optimization, no obvious cracks are found in the interlayer bonding of the preforms obtained by printing with a single 25μm layer thickness and a single 50μm layer thickness. This indicates that the curing performance we obtained is sufficient for printing samples with a single 50μm layer thickness. We also listed the printing efficiency for different printing layer thicknesses, demonstrating that our silicon nitride slurry system can significantly reduce printing time and achieve a highly efficient printing process.

[0083] Figure 4 The silicon nitride slurry prepared for Example 1 was used to print a complex model preform using a single-layer printing process with a thickness of 50 μm, and the model accuracy was tested. Figure (a) shows the gyroid-printed model, (b) shows the BCC-printed model, and (c) shows the model accuracy test. It can be seen that the silicon nitride slurry preparation method of this invention can achieve the printing process of small-pore, complex-structure models, and can print circular holes with a minimum radius of 0.3 mm, and equilateral triangles, squares, and trapezoids with a minimum side length of 0.5 mm.

[0084] Comparative Example 4

[0085] The difference between this embodiment and Example 1 is that aluminum dihydrogen phosphate is replaced with 5 vol% phosphoric acid at a mass of 15 g. All other process steps and parameters are the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared to Example 1, this embodiment exhibits a curing performance of 127.12 μm under the same light incident intensity. The curing performance remains largely unchanged, with a flexural strength of 165 MPa after sintering at 1650℃ for 4 hours.

[0086] Comparative Example 5

[0087] The difference between this embodiment and Example 1 is that aluminum dihydrogen phosphate is replaced with 5 vol% magnesium hydrogen phosphate (15 g). All other process steps and parameters are the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared to Example 1, this embodiment exhibits a curing performance of 124.52 μm under the same light incident intensity. The curing performance remains largely unchanged, with a flexural strength of 192 MPa after sintering at 1650℃ for 4 hours.

[0088] Table 3. Effects of different high-temperature binders on mechanical properties

[0089] Types of high-temperature adhesives Phosphoric acid Magnesium hydrogen phosphate Aluminum dihydrogen phosphate Flexural strength (MPa) 165 192 253 Porosity (%) 17.02 12.18 9.31

[0090] As can be seen from Table 3, under the same temperature and content, the addition of aluminum dihydrogen phosphate in several high-temperature binders is more beneficial to improving the mechanical properties of silicon nitride ceramics after sintering.

[0091] Example 4

[0092] The difference between this embodiment and Example 1 is that the aluminum dihydrogen phosphate content is changed to 8 vol% and the mass is 24 g. All other process steps and parameters are the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared with Example 1, this embodiment has a curing performance of 126.83 μm under the same light incident intensity. The curing performance is not significantly different; the flexural strength after sintering at 1650℃ for 4 hours is 272 MPa.

[0093] Comparative Example 6

[0094] The difference between this embodiment and Example 1 is that the aluminum dihydrogen phosphate content is changed to 10 vol% and the mass is 30 g. All other process steps and parameters are the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared with Example 1, this embodiment has a curing performance of 123.17 μm under the same light incident intensity. The curing performance is not significantly different; the flexural strength after sintering at 1650℃ for 4 hours is 187 MPa. This is mainly due to the excessive aluminum dihydrogen phosphate content leading to decomposition and the generation of excessive gas, resulting in a decrease in overall density.

[0095] Comparative Example 7

[0096] The difference between this embodiment and Example 1 is that the aluminum dihydrogen phosphate content is changed to 15 vol% and the mass is 36 g. All other process steps and parameters are the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared with Example 1, this embodiment has a curing performance of 120.67 μm under the same light incident intensity. The curing performance is not significantly different; the flexural strength after sintering at 1650℃ for 4 hours is 43 MPa. This is mainly due to the excessively high aluminum dihydrogen phosphate content, which leads to decomposition and the generation of a large amount of gas, causing a sharp decrease in overall density and thus a reduction in overall mechanical properties.

[0097] Table 4. Effects of different aluminum dihydrogen phosphate contents on mechanical properties

[0098] Aluminum dihydrogen phosphate content 5％ 8％ 10％ 15％ Flexural strength (MPa) 253 272 187 43 Porosity (%) 9.31 8.43 16.56 54.32

[0099] With increasing aluminum dihydrogen phosphate content, the overall curing properties of the slurry did not change significantly. However, as shown in Table 4, the mechanical properties initially increased and then decreased with increasing aluminum dihydrogen phosphate content. After debinding at temperatures above 950℃, aluminum dihydrogen phosphate reacts to form type A aluminate, which forms strong physical bonds with silicon nitride powder, binding the silicon nitride powder and reducing the distance between the powder particles after debinding. Simultaneously, at a sintering temperature of 1400℃, aluminum dihydrogen phosphate decomposes to form alumina, which acts as a sintering aid, further improving the density of the sintered ceramic and thus increasing the mechanical properties of the silicon nitride ceramic. Therefore, when the aluminum dihydrogen phosphate content is high, at higher sintering temperatures, excessive aluminum dihydrogen phosphate decomposes, producing gas that is released, causing the overall powder to disperse, leading to decreased density and reduced mechanical properties.

[0100] Example 6

[0101] The difference between this embodiment and Example 1 is that the sintering temperature is changed to 1700℃, while the remaining process steps and parameters are the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared with Example 1, the flexural strength of this embodiment after sintering for 4 hours is 232 MPa, showing little difference after sintering.

[0102] Comparative Example 8

[0103] The difference between this comparative example and Example 1 is that the sintering temperature was changed to 1600℃, while the remaining process steps and parameters were the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared with Example 1, the flexural strength of this example after sintering for 4 hours was 170 MPa. This is mainly due to the lower sintering temperature, which led to incomplete solid-phase reaction of the ceramic powder, incomplete grain growth and pore shrinkage, resulting in higher porosity and decreased flexural strength.

[0104] Comparative Example 9

[0105] The difference between this comparative example and Example 1 is that the sintering temperature was changed to 1750℃, while the remaining process steps and parameters were the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared with Example 1, the flexural strength of this example after sintering for 4 hours was 143 MPa. This is mainly due to the higher sintering temperature. The presence of aluminum dihydrogen phosphate causes the silicon nitride powder to decompose at a lower temperature, resulting in a decrease in overall strength.

[0106] Comparative Example 10

[0107] The difference between this comparative example and Example 1 is that the sintering temperature was changed to 1800℃, while the remaining process steps and parameters were the same as in Example 1, resulting in a different silicon nitride ceramic slurry. Compared with Example 1, the flexural strength of this example after sintering for 4 hours was 105 MPa. This is mainly due to the excessively high sintering temperature, which intensifies the decomposition of silicon nitride powder, leading to a sharp decrease in overall strength.

[0108] Table 5 Effect of different sintering temperatures on mechanical properties

[0109] Sintering temperature (°C) 1600 1650 1700 1750 1800 Flexural strength (MPa) 170 253 232 143 96 Porosity (%) 13.25 9.31 11.32 18.13 37.53

[0110] Figure 5 XRD characterization of silicon nitride ceramics at different temperatures. Figure 5It can be seen that an aluminate phase appears after degreasing and decarburization. This phase combines with the surface of silicon nitride powder to reduce the distance between the powder particles. As the temperature increases, this aluminate phase gradually disappears, and the sintered phase Y₂SiAlO₅N begins to form. This indicates that as the sintering temperature further increases, aluminum dihydrogen phosphate decomposes to form alumina, which acts as a sintering aid to further improve the density of the sintered ceramic. Simultaneously, we can observe that when the temperature rises above 1800℃, a significant high-temperature decomposition phase of silicon nitride appears.

[0111] As shown in Table 5, under the same aluminum dihydrogen phosphate addition, the mechanical properties of silicon nitride ceramics decrease with increasing temperature. This is mainly because silicon nitride ceramics decompose and fail with increasing temperature, leading to a decline in overall mechanical properties. Excessive aluminum dihydrogen phosphate can cause silicon nitride to decompose at lower temperatures, resulting in the overall failure of the silicon nitride ceramic material.

[0112] In summary, this invention utilizes high-refractive-index OPPEOA resin, low-viscosity HDDA resin, and photoinitiators and oxygen inhibitors to formulate a silicon nitride ceramic slurry with high solid content, low viscosity, and excellent curing performance. By leveraging the effect of the oxygen inhibitor KI on the curing performance of the silicon nitride slurry, the curing properties are improved, achieving a curing depth exceeding 100 μm. This enables high-precision, defect-free sample printing with a single-layer thickness of 50 μm, effectively reducing printing time and improving printing efficiency, and is more conducive to the molding process of large-size silicon nitride ceramic samples.

[0113] Meanwhile, high-temperature binders were introduced to investigate the effects of several different high-temperature binders on the silicon nitride sintering process. It was found that aluminum dihydrogen phosphate had a greater effect on the performance improvement of silicon nitride ceramics after sintering. At the same time, we optimized the sintering temperature and the amount of high-temperature binder added, determined the optimal amount of aluminum dihydrogen phosphate added, and achieved dense sintering of silicon nitride ceramics at a lower temperature, resulting in strong mechanical properties.

[0114] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A high-efficiency silicon nitride slurry based on photocuring, characterized in that: The high-efficiency silicon nitride slurry based on photocuring is composed of ceramic powder and photosensitive resin. The ceramic powder includes β-phase silicon nitride powder, sintering aid and high-temperature binder. The photosensitive resin includes photosensitive resin monomer, photoinitiator, oxygen barrier, dispersant and thixotropic agent. The ceramic powder contains 86-90% β-phase silicon nitride powder, 4-8% sintering aid, and 5-8% high-temperature binder by mass fraction. The photosensitive resin contains 90% photosensitive resin monomer by mass, 1-3% photoinitiator by mass, 1-4% dispersant by mass, 1-5% thixotropic agent by mass, and an oxygen barrier by mass of 1.5 or 2% of the photosensitive resin monomer by mass. The mass ratio of the ceramic powder to the photosensitive resin is 1:1; The β-phase silicon nitride powder has a particle size of 500 nm to 5 μm; the sintering aid is yttrium oxide powder with a particle size of 0.1 to 2 μm; the high-temperature binder is aluminum dihydrogen phosphate with a particle size of 0.1 to 2 μm. The photosensitive resin monomer comprises a mixture of o-phenylphenoxyethyl acrylate and 1,6-hexanediol diacrylate, wherein the content of o-phenylphenoxyethyl acrylate is 60-80 wt% and the content of 1,6-hexanediol diacrylate is 20-40 wt%. The photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and the oxygen inhibitor is potassium iodide; The dispersant is wetting and dispersing agent SP710, and the thixotropic agent is octamethylcyclotetrasiloxane.

2. The method for low-temperature sintering and molding of high-efficiency silicon nitride slurry as described in claim 1, characterized in that: The mixture of β-phase silicon nitride powder, sintering aid, and aluminum dihydrogen phosphate is ball-milled to obtain a ceramic mixed powder. A premix of photosensitive resin monomer, photoinitiator, and oxygen barrier is formed; A silicon nitride ceramic slurry is obtained by mixing ceramic powder, premixed liquid, dispersant and thixotropic agent; Silicon nitride ceramic slurry is printed using a photopolymer printer to form a silicon nitride printed blank. The printed blank is then cleaned, degreased and decarburized, and sintered. The sintering process is pressureless sintering under a nitrogen atmosphere, with a sintering temperature of 1650–1700℃ and a holding time of 2–5 hours.

3. The method as described in claim 2, characterized in that: The solid content of the silicon nitride ceramic slurry is 40-60 vol%.

4. The method as described in claim 2, characterized in that: The light source wavelength for the photocuring process is 405 nm, and the light intensity during curing is controlled between 6.56 and 25.36 mw / cm². 2 The curing time is controlled between 4 and 15 seconds; the degreasing-decarburizing process involves heating to 950–1150°C under a nitrogen atmosphere to remove organic matter and water molecules from aluminum dihydrogen phosphate, and then removing carbon elements under an air atmosphere at 500–700°C.

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