Coated silicon nitride whiskers, light-cured silicon nitride compositions reinforced with coated silicon nitride whiskers, and methods of making and using the same

Abstract

This invention belongs to the field of silicon nitride ceramic technology, specifically relating to a silicon nitride-coated whisker, a photocurable silicon nitride composition reinforced with silicon nitride-coated whiskers, its preparation method, and its application. A silicon nitride-coated whisker comprises a core layer and a coating layer; the core layer is a silicon nitride whisker; the coating layer comprises magnetic materials and / or other field-responsive materials; the other field-responsive materials include inorganic nanoparticles or composite oxides capable of inducing the orientation of silicon nitride whiskers under the coupling of electric fields, composite fields, or shear fields; the mass of the coating layer is 0.1–20 wt% of the mass of the core layer. This invention endows silicon nitride whiskers with external field responsiveness by coating them with magnetic materials and / or other field-responsive materials, thereby enabling the whiskers to achieve directional alignment during photocuring and improving the utilization efficiency of the reinforcing phase.

Description

Technical Field

[0001] This invention belongs to the field of silicon nitride ceramic technology, specifically relating to a silicon nitride-coated whisker, a photocurable silicon nitride composition reinforced by silicon nitride-coated whiskers, its preparation method and application. Background Technology

[0002] Silicon nitride ceramics possess high strength, high toughness, wear resistance, thermal shock resistance, and good high-temperature stability, making them promising for applications in wear-resistant components, bearings, cutting tools, hot-end structural components, and electronic packaging. However, near-net-shape forming of silicon nitride ceramics, especially photopolymerization near-net-shape forming, still presents significant challenges. On the one hand, the high refractive index and strong light scattering of silicon nitride powder limit the curing depth of the slurry; on the other hand, traditional silicon nitride sintered bodies still suffer from high brittleness and rapid crack propagation, making it difficult to simultaneously achieve complex structural forming and high mechanical properties.

[0003] To improve the toughness and strength of silicon nitride ceramics, existing technologies often employ the introduction of fibers, whiskers, or long rod-shaped grains as reinforcing phases, achieving toughening through mechanisms such as crack deflection, crack bridging, and whisker pull-out. However, commonly added silicon nitride whiskers are often randomly distributed in the slurry and green body, resulting in limited reinforcement efficiency and a tendency to agglomerate and exhibit localized orientation disorder, leading to insufficient improvement in the mechanical properties of photocurable silicon nitride ceramics. Furthermore, existing external field-assisted orientation methods primarily focus on plate-like particles, magnetic particles, or metal fibers, which are difficult to achieve stable, efficient, and controllable directional alignment under low external field strengths for silicon nitride whiskers with weak intrinsic magnetic response. Directly adding free magnetic particles to the system can easily cause problems such as increased slurry viscosity, intensified agglomeration, enhanced light absorption, and increased sintering defects. Simultaneously, since the magnetic particles are not effectively combined with the silicon nitride whiskers, it is difficult to effectively drive and orient the whiskers, thus hindering photocuring and final performance improvement.

[0004] Therefore, there is an urgent need for a new technical solution that can endow silicon nitride whiskers with external field response capability, improve their orientation alignment capability during photopolymerization forming process, and further improve the mechanical properties of silicon nitride ceramics after sintering. Summary of the Invention

[0005] To address at least one deficiency in existing technologies, this invention aims to provide a silicon nitride-coated whisker, a photocurable silicon nitride composition reinforced with silicon nitride whiskers, its preparation method, and its applications. This invention imparts external field responsiveness to silicon nitride whiskers by coating the surface with magnetic and / or other field-responsive materials, thereby enabling the whiskers to achieve directional alignment during photocuring and improving the utilization efficiency of the reinforcing phase. When silicon nitride whiskers are added as a reinforcing phase to a silicon nitride powder system, an oriented distribution structure is formed in the sintered body, which is beneficial for crack deflection, bridging, and pull-out toughening, thus significantly improving the flexural strength and fracture toughness of silicon nitride ceramics.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a silicon nitride coated whisker, comprising a core layer and a coating layer; The core layer is a silicon nitride whisker; The coating layer includes magnetic materials and / or other field-responsive materials; The other field-responsive materials include inorganic nanoparticles or composite oxides that can induce the orientation of silicon nitride whiskers under the coupling of electric field, composite field or shear field. The mass of the coating layer is 0.1 to 20 wt% of the mass of the core layer.

[0007] The magnetic material and / or other field-responsive material in the coating layer described in this invention are prepared by magnetic precursors or other field-responsive precursors. Using precursors can better coat the surface of silicon nitride whiskers.

[0008] Preferably, the mass of the coating layer is 0.5 to 10 wt% of the mass of the core layer.

[0009] Preferably, the silicon nitride whiskers have a length of 1–50 μm, a diameter of 0.1–2 μm, and an aspect ratio of 5–100.

[0010] The silicon nitride whiskers coated in this invention are selected with specific lengths, diameters, and aspect ratios, which facilitates their uniform dispersion and directional arrangement in the slurry, and enables them to exert crack deflection, bridging, and pull-out toughening effects. If the size is too small, the toughening effect is limited; if the size or aspect ratio is too large, entanglement and agglomeration are likely to occur.

[0011] More preferably, the silicon nitride whiskers have a length of 3 to 20 μm and a diameter of 0.2 to 1 μm.

[0012] Preferably, the coating layer has a thickness of 5–500 nm.

[0013] In the coated silicon nitride whiskers of the present invention, when the coating layer thickness is 5–500 nm, the high aspect ratio of the whiskers can be maintained while ensuring coating continuity and field response capability. If the coating layer is too thin, incomplete coating is likely to occur; if it is too thick, the effective aspect ratio of the whiskers is likely to be reduced, thereby affecting sintering densification and interfacial bonding performance.

[0014] More preferably, the coating layer has a thickness of 10–200 nm.

[0015] Preferably, the magnetic material includes at least one of Fe, Co, Ni, Fe3O4, γ-Fe2O3, CoFe2O4, and NiFe2O4.

[0016] Preferably, the magnetic material includes at least one of Fe3O4, γ-Fe2O3, and CoFe2O4.

[0017] Preferably, the inorganic nanoparticles include at least one of BaTiO3, ZnO, and TiO2.

[0018] Preferably, the composite oxide includes at least one of BiFeO3, BaTiO3-CoF2O4 composite oxide, and BaTiO3-NiFe2O4 composite oxide.

[0019] This invention also claims protection for a method for preparing the aforementioned coated silicon nitride whiskers, comprising the following steps: A magnetic precursor and / or other field-responsive precursor are dispersed in a solvent to form a coating solution. Silicon nitride whiskers are added to the coating solution and dispersed, adsorbed and deposited to obtain coated silicon nitride whiskers. Solid-liquid separation, drying and heat treatment are then performed to obtain coated silicon nitride whiskers.

[0020] Preferably, the solvent includes at least one of water, ethanol, and isopropanol.

[0021] Preferably, the magnetic precursor includes at least one of iron salt, cobalt salt, and nickel salt.

[0022] More preferably, the magnetic precursor includes at least one of FeCl3, FeCl2, CoCl2, NiCl2, ferric nitrate, cobalt nitrate, and nickel nitrate.

[0023] Preferably, the other field-responsive precursors include at least one of the following: a combination of barium acetate and tetraisopropyl titanate, a combination of strontium acetate and tetraisopropyl titanate, and zinc acetate.

[0024] Preferably, the deposition reaction includes at least one of precipitation, sol-gel, chemical deposition, and in-situ growth methods.

[0025] The precipitation method, sol-gel method, chemical deposition method, and in-situ growth method described in this invention are all methods known to those skilled in the art.

[0026] Preferably, the drying temperature is 60~80℃ and the drying time is 10~24h.

[0027] Preferably, the heat treatment is performed by holding the temperature at 200–900°C in an inert atmosphere for 0.5–4 hours.

[0028] In the preparation process of silicon nitride coated whiskers of the present invention, the whisker dispersion state, precursor concentration, reaction temperature, pH value, reaction time, and heat treatment conditions all affect the uniformity and field response performance of the coating layer. Insufficient dispersion or excessively rapid reaction can easily cause particle agglomeration, insufficient heat treatment can lead to incomplete decomposition of the precursor, while excessive heat treatment may cause coarsening of the coated particles.

[0029] This invention also claims protection for a photocurable silicon nitride composition reinforced with coated silicon nitride whiskers, comprising the following components: Ceramic solid phase, photosensitive resin, reactive diluent, photoinitiator and dispersant; The ceramic solid phase includes: coated silicon nitride whiskers, silicon nitride powder, and sintering aids.

[0030] Preferably, based on 100 parts by weight of the total ceramic solid phase, the coated silicon nitride whiskers are 1-20 parts, the silicon nitride powder is 82-93 parts, and the sintering aid is 5-10 parts; relative to 100 parts by weight of the ceramic solid phase, the photosensitive resin is 15-25 parts, the reactive diluent is 5-15 parts, the photoinitiator is 0.5-2 parts, and the dispersant is 0.5-3 parts.

[0031] Preferably, the amount of silicon nitride whiskers added is 1 to 20 wt% based on the total mass of the ceramic solid phase.

[0032] More preferably, the amount of the coated silicon nitride whiskers added is 3 to 12 wt% based on the total mass of the ceramic solid phase.

[0033] Preferably, the median particle size D50 of the silicon nitride powder is 0.1–5 μm.

[0034] In the photocurable silicon nitride composition of the present invention, silicon nitride powder with a median particle size D50 of 0.1 to 5 μm is selected. The sintered ceramic product can achieve high density. When the particle size of the selected silicon nitride powder is not suitable, the density of the final sintered ceramic product is low.

[0035] More preferably, the median particle size D50 of the silicon nitride powder is 0.3 to 1.5 μm.

[0036] Preferably, the sintering aid includes at least one of Y2O3, Al2O3, MgO, and AlN.

[0037] Preferably, the reactive diluent includes at least one of 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, and trimethylolpropane triacrylate.

[0038] Preferably, the photoinitiator includes at least one of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0039] Preferably, the dispersant includes at least one of DISPERBYK-111, Solsperse 17000, and Hypermer KD-1.

[0040] This invention also claims a method for preparing the aforementioned photocurable silicon nitride composition reinforced with silicon nitride whiskers, comprising the following steps: Silicon nitride powder, coated silicon nitride whiskers, sintering aid, photosensitive resin, reactive diluent, photoinitiator and dispersant are mixed to prepare photocurable silicon nitride slurry; The prepared slurry is oriented under the action of an external magnetic field and / or other external fields, and is simultaneously or subsequently exposed to solidify and form a green body. The obtained preform is degreased and sintered to obtain the photocurable silicon nitride composition reinforced with silicon nitride whiskers.

[0041] Preferably, the strength of the external magnetic field is 0.01 to 5 T.

[0042] In the preparation method of the photocurable silicon nitride composition of this invention, an external magnetic field strength of 0.01–5 T is applied, which can provide sufficient orientation torque for the coated silicon nitride whiskers, achieving their directional alignment. When the magnetic field strength is too low, the orientation driving force is insufficient, and the whisker alignment is not obvious; when the magnetic field strength is too high, it is easy to cause the agglomeration of whiskers or magnetic particles, resulting in uneven slurry distribution and local defects. Preferably, the magnetic field strength is 0.05–1 T to balance orientation efficiency and dispersion stability.

[0043] More preferably, the strength of the applied magnetic field is 0.05 to 1 T.

[0044] Preferably, the other external fields include electric fields, composite fields, or shear fields.

[0045] Preferably, the applied voltage of the electric field is 10~30V.

[0046] Preferably, the directional arrangement time is 5 s to 30 min.

[0047] Preferably, the conditions for exposure curing are: irradiation with ultraviolet or near-ultraviolet light with a wavelength of 365–405 nm, and an exposure light intensity of 5–50 mW / cm². 2 The single-layer exposure time is 1–60 s.

[0048] The present invention also claims the use of the aforementioned coated silicon nitride whiskers, or the photocurable silicon nitride composition reinforced by the aforementioned coated silicon nitride whiskers, in stereolithography or digital light processing.

[0049] Preferably, the photocurable silicon nitride composition reinforced with silicon nitride whiskers has a flexural strength ≥742 MPa and a fracture toughness ≥7.6 MPa·m. 1 / 2 .

[0050] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides silicon nitride whiskers with external field response capability by coating the surface of the whiskers with magnetic materials and / or other field-responsive materials, thereby enabling the whiskers to achieve directional alignment during photocuring and improving the utilization efficiency of the reinforcing phase.

[0051] (2) In this invention, silicon nitride whiskers are added to the silicon nitride powder system as a reinforcing phase, forming an oriented distribution structure in the sintered body, which is beneficial for crack deflection, bridging and pull-out toughening, thereby significantly improving the bending strength and fracture toughness of silicon nitride ceramics.

[0052] (3) The present invention adopts a technical route that combines “whisker surface coating - external field induced orientation - photocuring”, which avoids the problems of agglomeration, increased viscosity and increased defects caused by directly adding free magnetic particles to the system.

[0053] (4) The process route of the present invention is clear and applicable to the preparation of complex structural parts of photocurable silicon nitride ceramics, and has good application prospects. Detailed Implementation

[0054] 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.

[0055] 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.

[0056] Example 1: A silicon nitride coated whisker Components: Includes a core layer and a cladding layer; The core layer is a silicon nitride whisker; The coating layer is a magnetic material; the magnetic material is Fe3O4.

[0057] The mass of the coating layer is 5 wt% of the mass of the core layer, based on the mass of the coating layer.

[0058] The silicon nitride whiskers have a length of 5–15 μm and a diameter of 0.3–0.8 μm.

[0059] The coating layer has a thickness of 200 nm.

[0060] Preparation method: FeCl3·6H2O and FeCl2·4H2O were dissolved in deionized water at a molar ratio of 2:1, and an appropriate amount of ethanol was added (the volume ratio of deionized water to ethanol was 4:1) to prepare a mixed iron salt solution, forming a coating solution. Silicon nitride whiskers were added to the coating solution, mechanically stirred for 30 min and ultrasonically dispersed for 20 min to ensure uniform dispersion of the whiskers. Under nitrogen protection, ammonia water was slowly added dropwise to the resulting system, controlling the pH to 9-10, and reacted at 60℃ for 1 h to allow Fe3O4 to be deposited in situ on the surface of the silicon nitride whiskers, resulting in coated silicon nitride whiskers. These whiskers were centrifuged, washed sequentially with deionized water and ethanol, dried at 80℃ for 12 h, and then heat-treated at 400℃ under an inert atmosphere for 1 h to obtain coated silicon nitride whiskers.

[0061] Example 2: A silicon nitride coated whisker Includes a core layer and a wrapper layer; The core layer is a silicon nitride whisker; The coating layer is a magnetic material; the magnetic material is γ-Fe2O3. The mass of the coating layer is 1 wt% of the mass of the core layer, based on the mass of the coating layer.

[0062] The silicon nitride whiskers are 30–50 μm long and 1–2 μm in diameter.

[0063] The coating layer has a thickness of 5 nm.

[0064] Preparation method: Fe(NO3)3 and Fe2(SO4)3 were dissolved in deionized water at a molar ratio of 2:1, and an appropriate amount of ethanol was added (the volume ratio of deionized water to ethanol was 4:1) to prepare a mixed iron salt solution, forming a coating solution. Silicon nitride whiskers were added to the coating solution, mechanically stirred for 30 min and ultrasonically dispersed for 20 min to ensure uniform dispersion of the whiskers. Under nitrogen protection, ammonia water was slowly added dropwise to the resulting system, controlling the pH to 9-10, and reacted at 60℃ for 1 h to allow γ-Fe2O3 to be deposited in situ on the surface of the silicon nitride whiskers, resulting in coated silicon nitride whiskers. These whiskers were centrifuged, washed sequentially with deionized water and ethanol, dried at 60℃ for 24 h, and then heat-treated at 200℃ under an inert atmosphere for 4 h to obtain coated silicon nitride whiskers.

[0065] Example 3: A silicon nitride coated whisker Includes a core layer and a wrapper layer; The core layer is a silicon nitride whisker; The coating layer is made of other field-responsive materials; The other field-responsive material is a BaTiO3-CoFe2O4 composite oxide; The mass of the coating layer is 20 wt% of the mass of the core layer, based on the mass of the coating layer.

[0066] Preferably, the silicon nitride whiskers have a length of 1 to 3 μm and a diameter of 0.1 to 0.2 μm.

[0067] The coating layer has a thickness of 500 nm.

[0068] Preparation method: BaTiO3 and CoFe2O4 were dissolved in deionized water at a molar ratio of 2:1, and an appropriate amount of ethanol was added (the volume ratio of deionized water to ethanol was 4:1) to prepare a mixed solution, forming a coating solution. Silicon nitride whiskers were added to the coating solution, mechanically stirred for 30 min and ultrasonically dispersed for 20 min to ensure uniform dispersion of the whiskers. Under nitrogen protection, ammonia was slowly added dropwise to the resulting system, controlling the pH to 9-10, and reacted at 60℃ for 1 h to allow the BaTiO3-CoFe2O4 composite oxide to be deposited in situ on the surface of the silicon nitride whiskers, resulting in coated silicon nitride whiskers. These whiskers were centrifuged, washed sequentially with deionized water and ethanol, dried at 80℃ for 10 h, and then heat-treated at 900℃ under an inert atmosphere for 1 h to obtain coated silicon nitride whiskers.

[0069] Example 4: A silicon nitride coated whisker Compared with Example 1, the only difference in this example is that the length of the silicon nitride whiskers is 0.5 μm and the diameter is 3 μm.

[0070] The preparation method is the same as in Example 1.

[0071] Example 5: A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers Components: (parts by weight) 100 parts ceramic solid phase, 20 parts photosensitive resin, 10 parts reactive diluent, 1 part photoinitiator and 1 part dispersant; The ceramic solid phase comprises: 8 parts of coated silicon nitride whiskers prepared in Example 1, 82 parts of silicon nitride powder, and 10 parts of sintering aid.

[0072] The amount of silicon nitride whiskers added is 8 wt% based on the total mass of the ceramic solid phase.

[0073] The median particle size D50 of the silicon nitride powder is 0.8 μm.

[0074] The sintering aid is Y2O3; The reactive diluent is 1,6-hexanediol diacrylate; The photoinitiator is diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; The dispersant is DISPERBYK-111.

[0075] Preparation method: Silicon nitride powder, coated silicon nitride whiskers, sintering aid, photosensitive resin, reactive diluent, photoinitiator and dispersant are mixed to prepare photocurable silicon nitride slurry; The prepared slurry was oriented and aligned for 30 seconds under an external magnetic field with a strength of 0.2 T, and then cured by exposure to 405 nm light with an exposure intensity of 30 mW / cm². 2 The single-layer exposure time is 30 s to obtain the preform; The obtained preform was degreased (800°C) and sintered (1800°C) to obtain the photocurable silicon nitride composition reinforced with silicon nitride whiskers.

[0076] Example 6: A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers Components: (parts by weight) The composition includes 100 parts ceramic solid phase, 15 parts photosensitive resin, 5 parts reactive diluent, 0.5 parts photoinitiator, and 0.5 parts dispersant. The ceramic solid phase comprises: 3 parts of coated silicon nitride whiskers prepared in Example 2, 92 parts of silicon nitride powder, and 5 parts of sintering aid.

[0077] The amount of silicon nitride whiskers added is 3 wt% based on the total mass of the ceramic solid phase.

[0078] The median particle size D50 of the silicon nitride powder is 0.3 μm.

[0079] The sintering aid is Al2O3; The reactive diluent is tripropylene glycol diacrylate; The photoinitiator is ethyl 2,4,6-trimethylbenzoylphenylphosphonate; The dispersant is Solsperse 17000.

[0080] Preparation method: Silicon nitride powder, coated silicon nitride whiskers, sintering aid, photosensitive resin, reactive diluent, photoinitiator and dispersant are mixed to prepare photocurable silicon nitride slurry; The prepared slurry was oriented and aligned for 30 minutes under an external magnetic field with a strength of 0.05T, and then simultaneously or subsequently subjected to 405 nm light exposure for curing and shaping, with an exposure intensity of 5 mW / cm². 2 The single-layer exposure time is 60 s to obtain the preform; The obtained preform was degreased (800°C) and sintered (1800°C) to obtain the photocurable silicon nitride composition reinforced with silicon nitride whiskers.

[0081] Example 7: A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers Components: (parts by weight) 100 parts ceramic solid phase, 25 parts photosensitive resin, 15 parts reactive diluent, 2 parts photoinitiator and 3 parts dispersant; The ceramic solid phase comprises: 10 parts of coated silicon nitride whiskers prepared in Example 3, 82 parts of silicon nitride powder, and 8 parts of sintering aid.

[0082] The amount of silicon nitride whiskers added is 10 wt% based on the total mass of the ceramic solid phase.

[0083] The median particle size D50 of the silicon nitride powder is 5 μm.

[0084] The sintering aid is MgO; The reactive diluent is trimethylolpropane triacrylate; The photoinitiator is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; The dispersant is Hypermer KD-1.

[0085] Preparation method: Silicon nitride powder, coated silicon nitride whiskers, sintering aid, photosensitive resin, reactive diluent, photoinitiator and dispersant are mixed to prepare photocurable silicon nitride slurry; The prepared slurry was subjected to a voltage of 24 V for 5 s to achieve directional alignment, and then simultaneously or subsequently subjected to 405 nm light exposure for curing and shaping, with an exposure intensity of 50 mW / cm². 2 The single-layer exposure time is 3 s to obtain the preform; The obtained preform was degreased (800°C) and sintered (1800°C) to obtain the photocurable silicon nitride composition reinforced with silicon nitride whiskers.

[0086] Example 8: A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers Compared with Example 5, the only difference in this example is that the silicon nitride coated whiskers prepared in Example 4 are used.

[0087] The preparation method is described in Example 5.

[0088] Example 9: A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers Compared with Example 5, the only difference in this example is that, based on the mass of the coating layer, the mass of the coating layer is 1 wt% of the mass of the core layer.

[0089] The preparation method is described in Example 5.

[0090] Example 10: A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers Compared with Example 5, the only difference in this example is that, based on the mass of the coating layer, the mass of the coating layer is 10 wt% of the mass of the core layer.

[0091] The preparation method is described in Example 5.

[0092] Example 11: A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers Compared with Example 5, the only difference in this example is that the amount of silicon nitride whiskers added is 5 wt% based on the total mass of the solid phase.

[0093] The preparation method is described in Example 5.

[0094] Example 12: A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers Compared with Example 5, the only difference in this example is that the amount of silicon nitride whiskers added is 12 wt% based on the total mass of the solid phase.

[0095] The preparation method is described in Example 5.

[0096] Example 13: A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers Compared with Example 5, the only difference in this example is that the amount of silicon nitride whiskers added is 30 wt% based on the total mass of the solid phase.

[0097] The preparation method is described in Example 5.

[0098] Example 14: A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers Compared with Example 5, the only difference in this example is that the median particle size D50 of the silicon nitride powder is 10 μm.

[0099] The preparation method is described in Example 5.

[0100] Comparative Example 1 Compared with Example 5, the only difference in this comparative example is that, in the coated silicon nitride whiskers, the mass of the coating layer is 25 wt% of the mass of the core layer.

[0101] The preparation method is described in Example 5.

[0102] Comparative Example 2 Compared with Example 5, the only difference in this comparative example is that no coated silicon nitride whiskers are added.

[0103] The preparation method is described in Example 5.

[0104] Comparative Example 3 Compared with Example 5, the only difference in this comparative example is that an equal amount of uncoated silicon nitride whiskers is used instead of coated silicon nitride whiskers.

[0105] The preparation method is described in Example 5.

[0106] Comparative Example 4 The components are the same as in Example 5.

[0107] Preparation method: Silicon nitride powder, coated silicon nitride whiskers, sintering aid, photosensitive resin, reactive diluent, photoinitiator and dispersant are mixed to prepare photocurable silicon nitride slurry; The prepared slurry was cured by exposure to 405 nm light with an intensity of 30 mW / cm². 2 The single-layer exposure time is 30 s to obtain the preform; The obtained preform was degreased (800°C) and sintered (1800°C) to obtain the photocurable silicon nitride composition reinforced with silicon nitride whiskers.

[0108] Compared with Example 5, the only difference in this comparative example is that the photocurable silicon nitride slurry prepared is not subjected to an external magnetic field treatment.

[0109] Experimental Example 1: Slurry Performance and Whisker Orientation Effect Test I. Experimental Samples The photocurable silicon nitride slurry and photocurable silicon nitride composition prepared in Examples 5-14 and Comparative Examples 1-4.

[0110] II. Experimental Methods (1) Test of apparent viscosity of slurry The apparent viscosity of each slurry group at 25℃ was tested using a rotational rheometer at a shear rate of 100 s⁻¹. -1 .

[0111] (2) Curing depth test Using a 405 nm light source, each group of photocurable silicon nitride slurries was exposed under the same exposure energy conditions, and their curing depth was measured.

[0112] (3) Test of whisker orientation The cross-section of the exposed and cured sample was observed by scanning electron microscopy, and the angle distribution between the long axis of silicon nitride whiskers and the direction of the set magnetic field was statistically analyzed to characterize the degree of whisker orientation. At the same time, an orientation factor can be introduced for quantitative evaluation, where the larger the orientation factor, the higher the degree of whisker orientation.

[0113] III. Experimental Results The test results are shown in Table 1.

[0114] Table 1. Properties and whisker orientation effects of each group of slurries

[0115] As shown in Table 1, the silicon nitride whisker system described in this embodiment of the invention can significantly improve the orientation of silicon nitride whiskers under an applied magnetic field while maintaining the photocurability of the slurry.

[0116] The experimental results of Examples 5 and 8 show that when the length and diameter of the silicon nitride whiskers in the coated silicon nitride whiskers are not suitable, the viscosity, curing depth and orientation of the prepared slurry all deteriorate.

[0117] The experimental results of Examples 5 and 9-10 show that the coating content has a significant impact on the slurry properties and whisker orientation behavior. Increasing the coating content is beneficial to improving the magnetic response and orientation degree of the whiskers, but it also leads to increased slurry viscosity and reduced curing depth. In contrast, Example 5 shows a better balance between orientation effect, slurry flowability and curing performance.

[0118] The experimental results of Examples 5 and 11-13 show that the amount of silicon nitride whiskers added also affects the slurry properties and orientation effect. When the amount added is low, the reinforcing phase content is limited, and the orientation effect is not obvious; when the amount added is high, the slurry viscosity increases and the curing depth decreases, which is not conducive to photocuring. When the amount of silicon nitride whiskers added is inappropriate, the viscosity, curing depth, and orientation degree of the resulting slurry deteriorate. The whisker addition amount shown in Example 5 is more conducive to balancing formability and orientation effect.

[0119] In Example 14, the median particle size D50 of the silicon nitride powder was unsuitable, resulting in a deterioration in the viscosity, curing depth, and orientation properties of the prepared slurry.

[0120] The experimental results of Comparative Examples 1 to 4 show that it is difficult to obtain the ideal whisker orientation effect when the coating layer is excessive, no whiskers are added, uncoated whiskers are added, or coated whiskers are added but no external magnetic field is applied. Furthermore, the slurry properties and curing properties of some systems are significantly reduced.

[0121] In summary, by constructing an appropriate amount of magnetic response coating layer on the surface of silicon nitride whiskers and combining it with orientation induced by an external magnetic field, the degree of orientation of silicon nitride whiskers can be significantly improved while ensuring that the slurry has a certain curing ability.

[0122] Experimental Example 2: Mechanical Property Testing of Sintered Body I. Sample Preparation Silicon nitride ceramic samples were prepared using the slurries obtained in Examples 5-14 and Comparative Examples 1-4, respectively, through the same photocuring, debinding, and sintering process.

[0123] Each group of samples was processed into standard mechanical property test strips for testing relative density, flexural strength, and fracture toughness.

[0124] II. Testing Methods (1) Relative density test The bulk density of the sample was determined using the Archimedes method, and the relative density was calculated in combination with the theoretical density.

[0125] (2) Bending strength test The sintered specimens were tested using the three-point bending method, and the bending strength of each group of specimens was recorded.

[0126] (3) Fracture toughness test The fracture toughness of the samples was tested using the single-sided pre-cracked beam method or the indentation method.

[0127] III. Experimental Results The test results are shown in Table 2.

[0128] Table 2 Mechanical properties of sintered bodies in each group

[0129] As shown in Table 2, the silicon nitride ceramic sintered body obtained in the embodiments of the present invention is superior to the comparative example in terms of relative density, flexural strength and fracture toughness. This indicates that the method of coating silicon nitride whiskers and combining them with the external magnetic field to induce orientation can effectively improve the comprehensive mechanical properties of photocured silicon nitride ceramics.

[0130] The experimental results of Examples 5 and 8 show that when the length and diameter of the silicon nitride whiskers in the coated silicon nitride whiskers are not suitable, the bending strength and fracture toughness of the obtained ceramic sintered products deteriorate.

[0131] Examples 5 and 9-10 show that the coating content affects the whisker's responsiveness, orientation degree, and final reinforcement effect. When the coating content is low, the whisker's orientation ability is limited, and the performance improvement is not significant; when the coating content is high, it adversely affects slurry forming and sintering densification. In comparison, Example 5 exhibits superior overall performance.

[0132] Examples 5 and 11-13 show that the amount of silicon nitride whiskers added also has a significant impact on mechanical properties. A low addition amount results in insufficient reinforcement and toughening; a high addition amount increases dispersion difficulty and introduces local defects, hindering further performance improvement. When the amount of silicon nitride whiskers added is inappropriate, the flexural strength and fracture toughness of the resulting sintered ceramic product deteriorate. The whisker addition amount shown in Example 5 is more conducive to obtaining better overall performance.

[0133] In Example 14, the median particle size D50 of the silicon nitride powder was unsuitable, resulting in a deterioration in the overall performance of the sintered ceramic product.

[0134] Comparative Examples 1 to 4 show that when the coating layer is excessive, only silicon nitride powder is added, uncoated whiskers are added, or coated whiskers are added but no external magnetic field is applied, it is difficult to simultaneously achieve densification behavior and directional reinforcement effect. Therefore, their strength and toughness are lower than those of Example 5 of the present invention.

[0135] In summary, this invention incorporates silicon nitride whiskers coated with a magnetic response layer or other field response layer as a reinforcing phase into a silicon nitride powder system, and applies an external magnetic field during photopolymerization to achieve oriented whisker alignment. This significantly improves the bending strength and fracture toughness of the sintered body while maintaining high density.

[0136] 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 silicon nitride-coated whisker, characterized in that, Includes a core layer and a wrapper layer; The core layer is a silicon nitride whisker; The coating layer includes magnetic materials and / or other field-responsive materials; The other field-responsive materials include inorganic nanoparticles or composite oxides that can induce the orientation of silicon nitride whiskers under the coupling of electric field, composite field or shear field. The mass of the coating layer is 0.1 to 20 wt% of the mass of the core layer.

2. The silicon nitride-coated whiskers as described in claim 1, characterized in that, The mass of the cladding layer is 0.5 to 10 wt% of the mass of the core layer, based on the cladding layer mass. The silicon nitride whiskers have a length of 1–50 μm, a diameter of 0.1–2 μm, and an aspect ratio of 5–100. The thickness of the coating layer is 5–500 nm; The magnetic material includes at least one of Fe, Co, Ni, Fe3O4, γ-Fe2O3, CoFe2O4, and NiFe2O4; The inorganic nanoparticles include at least one of BaTiO3, ZnO, and TiO2; The composite oxide includes at least one of BiFeO3, BaTiO3-CoF2O4 composite oxide, and BaTiO3-NiFe2O4 composite oxide.

3. A method for preparing silicon nitride coated whiskers as described in any one of claims 1 to 2, characterized in that, Includes the following steps: A magnetic precursor and / or other field-responsive precursor are dispersed in a solvent to form a coating solution. Silicon nitride whiskers are added to the coating solution and dispersed, adsorbed and deposited to obtain coated silicon nitride whiskers. Solid-liquid separation, drying and heat treatment are then performed to obtain coated silicon nitride whiskers.

4. The method for preparing coated silicon nitride whiskers as described in claim 3, characterized in that, The solvent includes at least one of water, ethanol, and isopropanol; The magnetic precursor includes at least one of iron salt, cobalt salt, and nickel salt; The other field-responsive precursors include at least one of the following: a combination of barium acetate and tetraisopropyl titanate, a combination of strontium acetate and tetraisopropyl titanate, and zinc acetate. The deposition reaction includes at least one of precipitation, sol-gel, chemical deposition, and in-situ growth methods; The drying temperature is 60~80℃, and the drying time is 10~24h; The heat treatment is performed by holding the temperature at 200–900°C in an inert atmosphere for 0.5–4 hours.

5. A photocurable silicon nitride composition reinforced with coated silicon nitride whiskers, characterized in that, Includes the following components: Ceramic solid phase, photosensitive resin, reactive diluent, photoinitiator and dispersant; The ceramic solid phase comprises: silicon nitride whiskers, silicon nitride powder, and sintering aids as described in any one of claims 1 to 2.

6. The photocurable silicon nitride composition with silicon nitride whisker reinforcement as described in claim 5, characterized in that, Based on 100 parts by weight of the total ceramic solid phase, the coated silicon nitride whiskers comprise 1-20 parts, the silicon nitride powder comprises 82-93 parts, and the sintering aid comprises 5-10 parts; relative to 100 parts by weight of the ceramic solid phase, the photosensitive resin comprises 15-25 parts, the reactive diluent comprises 5-15 parts, the photoinitiator comprises 0.5-2 parts, and the dispersant comprises 0.5-3 parts. The amount of the coated silicon nitride whiskers added, based on the total mass of the ceramic solid phase, is 1–20 wt%. The median particle size D50 of the silicon nitride powder is 0.1–5 μm; The sintering aid includes at least one of Y2O3, Al2O3, MgO, and AlN; The reactive diluent includes at least one of 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, and trimethylolpropane triacrylate. The photoinitiator includes at least one of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; The dispersant includes at least one of DISPERBYK-111, Solsperse 17000, and Hypermer KD-1.

7. A method for preparing a photocurable silicon nitride composition reinforced with coated silicon nitride whiskers as described in any one of claims 5-6, characterized in that, Includes the following steps: Silicon nitride powder, coated silicon nitride whiskers, sintering aid, photosensitive resin, reactive diluent, photoinitiator and dispersant are mixed to prepare photocurable silicon nitride slurry; The prepared slurry is oriented under the action of an external magnetic field and / or other external fields, and is simultaneously or subsequently exposed to solidify and form a green body. The obtained preform is degreased and sintered to obtain the photocurable silicon nitride composition reinforced with silicon nitride whiskers.

8. The preparation method according to claim 7, characterized in that, The strength of the applied magnetic field is 0.01–5 T; The time for the directional arrangement is 5 s to 30 min; The conditions for exposure curing are as follows: irradiation with ultraviolet or near-ultraviolet light with a wavelength of 365–405 nm, and an exposure intensity of 5–50 mW / cm². 2 The single-layer exposure time is 1–60 s.

9. The application of a photocurable silicon nitride composition reinforced with silicon nitride as described in any one of claims 1 to 2, or as described in any one of claims 5 to 6, in stereolithography or digital light processing.

10. The application as described in claim 9, characterized in that, The photocurable silicon nitride composition reinforced with silicon nitride whiskers has a flexural strength ≥742 MPa and a fracture toughness ≥7.6 MPa·m. 1 / 2 .

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