High solid content silicon nitride ceramic slurry, silicon nitride ceramic and preparation method

Abstract

The application discloses a high-solid-content silicon nitride ceramic slurry, a silicon nitride ceramic and a preparation method, and relates to the technical field of silicon nitride ceramics. The preparation method of the high-solid-content silicon nitride ceramic slurry provided by the application comprises the following steps: S1, powder modification: 85-95 parts of silicon nitride powder, 5-10 parts of a sintering aid and 0.5-4 parts of a modifier are ball milled, and then the ball-milled product is taken out, dried and sieved to obtain modified powder; S2, preparation of the slurry: the modified powder is uniformly mixed with resin, a dispersing and leveling agent and an initiator to prepare a silicon nitride ceramic slurry with a solid content of 20-60 vol%; wherein, the dispersing and leveling agent accounts for 0.5-3 wt% of the mass of the modified powder; and the initiator accounts for 1-4 wt% of the mass of the resin. Under the synergistic action of the long-molecular-chain modifier and the matching small-molecular-chain dispersing and leveling agent, the slurry can be used to prepare a silicon nitride ceramic slurry with a solid content of more than 50 vol%, low viscosity and self-leveling.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon nitride ceramics, in particular to a high-solid-content silicon nitride ceramic slurry, a silicon nitride ceramic and a preparation method. BACKGROUND

[0002] Silicon nitride ceramics have been widely used in various industrial fields, including ceramic cutters, bearing balls and missile infrared radar covers, due to their superior bending strength, fracture toughness, hardness, wear resistance, oxidation stability, dielectricity and reliability. However, it is still challenging to prepare silicon nitride ceramics with complex shapes and fine features (such as microchannels and triple periodic minimal surfaces) using traditional methods, because they are highly dependent on molds. Therefore, additive manufacturing as a moldless, high-precision and robust forming process has attracted more and more attention. Among various additive manufacturing strategies, digital light processing (DLP) based photopolymerization is a representative method with high forming precision and surface quality, and has attracted considerable attention in the field of ceramic additive manufacturing.

[0003] In order to obtain low-defect, high-density and high-performance light-cured silicon nitride ceramics, especially for large-size samples, high solid content is a necessary prerequisite. Because it can reduce the risk of deformation or cracking due to higher shrinkage during debinding and sintering processes. In addition, high solid content helps to densify at lower sintering temperature, resulting in finer grain size and thus improving the strength and hardness of silicon nitride. Moreover, high solid content also means less amount of organic matter used, thereby reducing environmental pollution and lowering cost. In order to obtain high solid content silicon nitride slurry, current research mainly improves the rheological properties of the slurry through organic modification, dispersant optimization and particle grading. However, the solid content of most of the current research is still ≤50vol%, and all of them are focused on lower oxides.

[0004] On the one hand, it is difficult to ensure stable dispersion between particles at high solid content due to the low surface charge of silicon nitride powder itself. On the other hand, it is difficult to obtain high solidification depth and precision due to its high absorbance and refractive index. Furthermore, the modifiers and dispersing leveling agents in current research all play a separate role, and the performance of improving the rheological properties and solid content of the slurry is limited, so it is difficult to prepare silicon nitride ceramics with low shrinkage, high performance and large size. Therefore, there is a gap in theoretical basis and practical operation in further optimizing the modifier or dispersant, and there are still many challenges in preparing high solid content silicon nitride slurry and high performance DLP silicon nitride parts. SUMMARY

[0005] The technical problem solved by the present application is to provide a high-solid-content silicon nitride photocuring ceramic slurry and a preparation method thereof based on the deficiencies mentioned in the background art, and to prepare a silicon nitride sintered body with low shrinkage and high performance by using the slurry.

[0006] To solve the above problems, the present application proposes the following technical solutions:

[0007] In one aspect, the present application provides a preparation method of a high-solid-content silicon nitride ceramic slurry, comprising the following steps:

[0008] S1, powder modification: 85-95 parts by mass of silicon nitride powder, 5-10 parts by mass of sintering aid, and 0.5-4 parts by mass of modifier are ball milled, and then the ball-milled powder is taken out, dried, and sieved to obtain modified powder;

[0009] S2, preparation of slurry: the modified powder is uniformly mixed with resin, dispersing leveling agent, and initiator to prepare a silicon nitride ceramic slurry with a solid content of 20-60 vol%;

[0010] The amount of the dispersing leveling agent is 0.5-3 wt% of the mass of the modified powder;

[0011] The amount of the initiator is 1-4 wt% of the mass of the resin;

[0012] The modifier is a long-chain organic molecule with a molecular mass of 1500-4000;

[0013] The dispersing leveling agent is a small-molecule organic molecule with a molecular mass of less than 1500.

[0014] Specifically, in step S1, during ball milling, silicon nitride milling balls and anhydrous ethanol are added, and the amounts of the milling balls and the anhydrous ethanol are 1-3 times and 1-2 times the mass of the silicon nitride powder, respectively.

[0015] To better contact and mix the raw materials, the rotation speed of the ball mill is 250-400 r / min, and the ball milling time is 2-5 h. After ball milling, the powder is taken out, dried, and sieved, the drying temperature is 50-70℃, and the mesh size of the sieve is 100-300 mesh.

[0016] The purpose of the present application is to prepare a high-solid-content, low-viscosity silicon nitride ceramic slurry. The present application proves by experiments that a silicon nitride ceramic slurry with low viscosity and self-leveling can be obtained when the solid content is 20-60 vol%. To reduce the shrinkage rate of subsequent debinding and sintering and improve the bulk density of silicon nitride ceramic, the solid content of the silicon nitride ceramic slurry of the present application is preferably 40-60 vol%, and more preferably 50-60 vol%.

[0017] Further, the D50 particle size of the silicon nitride powder is 0.5-1.2 μm, and the specific surface area is 9-12 m 2 / g.

[0018] Further, the sintering aid is at least one of alumina, magnesium oxide, and yttrium oxide, and the particle size is 0.2-1.0 μm.

[0019] Further, the modifier used in the present application is a long-chain organic compound, and the molecular weight of the long-chain organic compound is between 1500 and 4000, and specifically, the modifier is at least one of Solspersen 80000, KMT 3004, KMT 3007, KTM 3020, and KMT 3331.

[0020] Further, the dispersing leveling agent used in the present application is a small-molecule organic compound, and the molecular weight of the small-molecule organic compound is less than 1500, and specifically, the dispersing leveling agent is at least one of KMT-5517, KMT-5519, BYK 110, and BYK 111.

[0021] It should be noted that after the powder modification in step S1, the long-chain hydrophobic groups on the outside of the modified powder play a role of steric hindrance to disperse the particles from each other, which can improve the rheological properties and solid content of the slurry to a certain extent. However, when the solid content of the slurry reaches 50 vol% or more, the steady-state packing density between the particles is high, and under the shear stress of the fixed-height doctor blade, the hydrophobic long-chain molecules on the surface of the powder are easily entangled with each other, causing shear thickening and accompanying viscosity increase. However, the present application uses a small-molecule organic compound as a dispersing leveling agent, which cooperates with the long-chain modifier to effectively reduce the slurry concentration under high solid content, and prepare a high-solid-content and low-viscosity silicon nitride ceramic slurry.

[0022] Further, the resin is at least one of PPTTA, HDDA, TMPTA, BPA1OEODMA, DOP, and n-octanol.

[0023] Further, the initiator is at least one of 819, TPO, and camphorquinone.

[0024] On the other hand, the present application provides a high-solid-content silicon nitride ceramic slurry prepared by the above preparation method.

[0025] In another aspect, the present application provides a preparation method of a silicon nitride ceramic, which uses the high-solid-content silicon nitride ceramic slurry or the high-solid-content silicon nitride ceramic slurry prepared by the above preparation method as a raw material, performs DLP molding, prints a green body, and then performs debinding and sintering on the green body to obtain a silicon nitride ceramic.

[0026] Further, the sintering temperature is 1800-1850 DEG C, the air pressure is 0.1-2 MPa, and the holding time is 1-4 h.

[0027] In another aspect, the application provides a silicon nitride ceramic prepared by the method.

[0028] Compared with the prior art, the application has the following technical effects:

[0029] The method for preparing the high-solid-content silicon nitride ceramic slurry can prepare a silicon nitride ceramic slurry with a solid content of more than 50 vol%, low viscosity and self-leveling property.

[0030] The high-solid-content silicon nitride ceramic slurry is modified by using a long-chain organic modifier on the surface of the silicon nitride powder, realizes the hydrogen bond physical adsorption on the surface of the powder, enhances the steric hindrance dispersion between the high-specific-surface-area powder particles, and helps to improve the high-solid-content and low-viscosity properties of the slurry. Meanwhile, the small-molecule-chain dispersing leveling agent matched with the long-chain modifier is introduced into the slurry, which can prevent the direct contact of the long-chain modifier due to the high solid content, and the small-molecule-chain dispersing leveling agent can also act as a lubricant between the long chains. The slurry provided by the application further improves the rheological properties of the slurry under the synergistic action of the long-chain modifier and the matched small-molecule-chain dispersing leveling agent, and realizes the preparation of a high-solid-content (more than 50 vol%) silicon nitride ceramic slurry.

[0031] The silicon nitride ceramic slurry provided by the application has the characteristics of strong photocuring ability, high solid content, low viscosity and reliable stability, and is suitable for preparing dense silicon nitride ceramic parts by DLP printing. Experimental results show that the bending strength, hardness and fracture toughness of the DLP silicon nitride ceramic part prepared from the slurry provided by the application are up to 880.34±33.25 MPa, 16.52±0.43 GPa and 6.12±0.37 MPa·m 1 / 2 , respectively. That is, the DLP silicon nitride ceramic part prepared from the slurry of the application has excellent mechanical properties, even exceeding the samples prepared by traditional dry pressing + cold isostatic pressing.

[0032] The significant differences between the DLP silicon nitride ceramic components prepared by the slurry provided by this invention and existing silicon nitride DLP technologies are as follows: Firstly, the high solids content silicon nitride slurry (>50 vol%) can significantly reduce the amount of organic additives used (total organic additive content <20 wt%), reducing the shrinkage of the silicon nitride green body during debinding and sintering (linear shrinkage rate in the maximum shrinkage direction <19.5%), thereby reducing the risk of defects such as cracking and interlayer debonding. Secondly, the higher solids content DLP silicon nitride slurry (60 vol%) can increase the packing density between particles in the green body sample, thereby preparing silicon nitride ceramics with high green body density, high sintering density (>97.5%), and high structural complexity, which helps to achieve densification at lower sintering temperatures. Compared with samples formed by low solids content slurry and dry pressing, the samples have finer and more uniform grain sizes (e.g., Figure 2 (As shown), this method enables the fabrication of DLP silicon nitride ceramics that balance high shape complexity with high strength and high hardness. Ultimately, a complex DLP silicon nitride ceramic construct with superior mechanical properties was fabricated (strength > 850 MPa, hardness > 16 GPa, toughness > 5 MPa·m). 1 / 2 ). Attached Figure Description

[0033] Figure 1 The silicon nitride ceramic samples with various complex shapes were obtained by DLP printing, debinding and sintering of the 55 vol% high solid content slurry prepared in Example 3.

[0034] Figure 2 SEM microstructure images of silicon nitride sintered samples prepared for Comparative Example 8 (45 vol%), Comparative Example 9 (dry pressing), and Example 4 (60 vol%) are shown. In the figure, a is the sample of Comparative Example 8; b is the sample of Comparative Example 9; and c is the sample of Example 4. Detailed Implementation

[0035] The technical solutions in the embodiments will now be clearly and completely described with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] It should be understood that the terminology used in this specification of embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of the invention. As used in this specification of embodiments of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0037] Example 1

[0038] The embodiment of the present application provides a high solid content silicon nitride ceramic slurry and a preparation method thereof, meanwhile, the embodiment also provides that the high solid content silicon nitride ceramic slurry is used as a raw material of DLP, and a dense silicon nitride ceramic is prepared through DLP printing. The specific preparation process is as follows:

[0039] Step S1 powder modification: 0.7 mu m D50 particle size silicon nitride (specific surface area is 11 m 2 / g), 0.2 mu m aluminum oxide and 1 mu m aluminum oxide additives are added into a ball mill tank, 2wt% powder quality KMT 3020 long molecular chain organic matter is added, 1.5 times of silicon nitride grinding balls and alcohol are added, and a planetary ball mill is used to mill at 350r / min for 4h. After ball milling, it is placed in a 60 DEG C oven for drying, and then sieved with a 300 mesh screen to obtain modified powder.

[0040] Step S2 slurry preparation: the modified powder is mixed with PPTTA, HDDA, n-octanol resin, 0.5wt% BYK110 small molecular chain organic matter and 2wt% 819 initiator, and a planetary ball mill is used to mill at 350r / min for 4h to obtain 50vol% silicon nitride DLP slurry, and the viscosity thereof is 2.54Pa·s at a shear rate of 30s -1 .

[0041] Step S3 ceramic preparation: the above-mentioned silicon nitride DLP slurry is subjected to DLP printing to prepare a green body, and then is subjected to degreasing and sintering, the sintering temperature is 1800 DEG C, the sintering pressure is 0.1 MPa, and the sintering time is 2h, so that the silicon nitride ceramic is obtained.

[0042] Embodiment 2

[0043] The embodiment of the present application provides a high solid content silicon nitride ceramic slurry and a preparation method thereof, meanwhile, the embodiment also provides that the high solid content silicon nitride ceramic slurry is used as a raw material of DLP, and a dense silicon nitride ceramic is prepared through DLP printing. The specific preparation process is as follows:

[0044] Step S1 powder modification: 0.7 mu m D50 particle size silicon nitride (specific surface area is 11 m 2 / g), 0.2 mu m aluminum oxide and 1 mu m aluminum oxide additives are added into a ball mill tank, 2wt% powder quality KMT 3020 long molecular chain organic matter is added, 1.5 times of silicon nitride grinding balls and alcohol are added, and a planetary ball mill is used to mill at 350r / min for 4h. After ball milling, it is placed in a 60 DEG C oven for drying, and then sieved with a 300 mesh screen to obtain modified powder.

[0045] Step S2: preparing slurry: mixing the modified powder with PPTTA, HDDA, DOP resin, 2wt% KMT-5519 small molecular chain organic matter, and 2wt% 819 initiator, using a planetary ball mill at 350r / min for 4h to obtain 55vol% silicon nitride DLP slurry, which has a viscosity of 8.76Pa·s at a shear rate of 30s -1 .

[0046] Step S3: preparing ceramic: DLP printing the above-mentioned silicon nitride DLP slurry to obtain a green body, then performing debinding and sintering, the sintering temperature is 1800℃, the sintering pressure is 0.1MPa, and the sintering time is 2h, to obtain a silicon nitride ceramic.

[0047] Example 3

[0048] The embodiment of the present application provides a high solid content silicon nitride ceramic slurry and a preparation method thereof, meanwhile, the embodiment also provides a dense silicon nitride ceramic prepared by using the high solid content silicon nitride ceramic slurry as a raw material of DLP and through DLP printing. The specific preparation process is as follows:

[0049] Step S1: powder modification: adding 0.7μm D50 particle size silicon nitride (specific surface area is 11m 2 / g), 0.2μm aluminum oxide and 1μm yttrium oxide additives into a ball mill tank, adding 2wt% KMT 3331 long molecular chain organic matter of powder mass, adding 1.5 times of silicon nitride grinding balls and alcohol, and using a planetary ball mill at 350r / min for 4h. After ball milling, drying in a 60℃ oven, and then sieving through a 100 mesh sieve to obtain the modified powder.

[0050] Step S2: preparing slurry: mixing the modified powder with PPTTA, BPA1OEODMA, DOP resin, 1wt% BYK111 small molecular chain organic matter, and 2wt% TPO initiator, using a planetary ball mill at 350r / min for 4h to obtain 55vol% silicon nitride DLP slurry, which has a viscosity of 5.36Pa·s at a shear rate of 30s -1 .

[0051] Step S3: preparing ceramic: DLP printing the above-mentioned silicon nitride DLP slurry to obtain a green body, then performing debinding and sintering, the sintering temperature is 1800℃, the sintering pressure is 0.1MPa, and the sintering time is 2h, to obtain a silicon nitride ceramic.

[0052] Referring to Figure 1 , the embodiment provides a ceramic sample with a micro-channel and a three-period minimum surface structure prepared by debinding and sintering after printing the 55vol% silicon nitride DLP slurry prepared in Example 3, which can realize the preparation of a high-complexity silicon nitride ceramic.

[0053] Embodiment 4

[0054] The embodiment of the present application provides a high solid content silicon nitride ceramic slurry and a preparation method thereof, meanwhile, the embodiment also provides that the high solid content silicon nitride ceramic slurry is used as a raw material of DLP, and a dense silicon nitride ceramic is prepared through DLP printing. The specific preparation process is as follows:

[0055] Step S1 powder modification: 0.7 μm D50 particle size silicon nitride (specific surface area is 11 m 2 / g), 0.2 μm aluminum oxide and 1 μm yttrium oxide additives are added into a ball mill tank, 2wt% powder quality KMT 3020 long molecular chain organic matter is added, 1.5 times of silicon nitride grinding balls and alcohol are added, and a planetary ball mill is used for ball milling at 350r / min for 4h. After ball milling is completed, drying is carried out in an oven at 60 DEG C, and then sieving is carried out through a 100 mesh screen to obtain modified powder.

[0056] Step S2 slurry preparation: the modified powder is mixed with PPTTA, BPA1OEODMA, DOP resin, 2wt% BYK110 small molecular chain organic matter and 2wt% TPO initiator, and then a planetary ball mill is used for ball milling at 350r / min for 4h to obtain 60vol% silicon nitride DLP slurry, and the viscosity of the slurry is 18.76Pa·s at a shear rate of 30s -1 .

[0057] Step S3 ceramic preparation: the above-mentioned silicon nitride DLP slurry is subjected to DLP printing to prepare a green body, and then the green body is subjected to degreasing and sintering, the sintering temperature is 1800 DEG C, the sintering pressure is 0.1MPa, and the sintering time is 2h, so that the silicon nitride ceramic is obtained.

[0058] Embodiment 5

[0059] The embodiment of the present application provides a high solid content silicon nitride ceramic slurry and a preparation method thereof, meanwhile, the embodiment also provides that the high solid content silicon nitride ceramic slurry is used as a raw material of DLP, and a dense silicon nitride ceramic is prepared through DLP printing. The specific preparation process is as follows:

[0060] Step S1 powder modification: 0.7 μm D50 particle size silicon nitride (specific surface area is 11 m 2 / g), 0.2 μm aluminum oxide and 1 μm yttrium oxide additives are added into a ball mill tank, 2wt% powder quality KMT 3020 long molecular chain organic matter is added, 1.5 times of silicon nitride grinding balls and alcohol are added, and a planetary ball mill is used for ball milling at 350r / min for 4h. After ball milling is completed, drying is carried out in an oven at 60 DEG C, and then sieving is carried out through a 100 mesh screen to obtain modified powder.

[0061] Step S2: preparing slurry: mixing the modified powder with PPTTA, HDDA, DOP resin, 2wt% of BYK110 small molecule chain organic matter, and 2wt% of 819 initiator, using a planetary ball mill at 350r / min for 4h to obtain 60vol% of silicon nitride DLP slurry, which has a viscosity of 20.40Pa·s at a shear rate of 30s -1 .

[0062] Step S3: preparing ceramic: printing the above-mentioned silicon nitride DLP slurry by DLP to obtain a green body, and then performing debinding and sintering, wherein the sintering temperature is 1800℃, the sintering pressure is 0.1MPa, and the sintering time is 2h, to obtain a silicon nitride ceramic.

[0063] Comparative Example 1

[0064] The present application provides a silicon nitride ceramic slurry and a preparation method thereof, and also provides a silicon nitride ceramic prepared by using the silicon nitride ceramic slurry as a raw material of DLP and printing by DLP. The specific preparation process is as follows:

[0065] Step S1: powder modification: adding 0.7μm D50 particle size silicon nitride (specific surface area is 11m 2 / g), 0.2μm aluminum oxide and 1μm yttrium oxide additives into a ball mill tank, adding 2wt% of KMT 3020 long molecule chain organic matter based on the mass of the powder, adding 1.5 times of silicon nitride grinding balls and alcohol, and using a planetary ball mill at 350r / min for 4h. After ball milling, dry in a 60℃ oven, and then sieve with a 100 mesh sieve to obtain the modified powder.

[0066] Step S2: preparing slurry: mixing the modified powder with PPTTA, BPA1OEODMA, DOP resin, 2wt% of TPO initiator, and using a planetary ball mill at 350r / min for 4h to obtain 55vol% of silicon nitride DLP slurry, which has a viscosity of 30.74Pa·s at a shear rate of 30s -1 .

[0067] Step S3: preparing ceramic: the above-mentioned slurry has too high viscosity, and cannot be uniformly and completely coated in the exposure area during printing, so DLP printing cannot be performed.

[0068] Comparative Example 2

[0069] The present application provides a silicon nitride ceramic slurry and a preparation method thereof, and also provides a silicon nitride ceramic prepared by using the silicon nitride ceramic slurry as a raw material of DLP and printing by DLP. The specific preparation process is as follows:

[0070] Step S1 powder preparation: silicon nitride with a D50 particle size of 0.7 μm (specific surface area of 11 m 2 / g), 0.2 μm of alumina and 1 μm of yttrium oxide additive were added to the ball mill tank, 1.5 times of silicon nitride grinding balls and alcohol were added, and a planetary ball mill was used at 350 r / min for 4 h. After ball milling, it was placed in an oven at 60°C for drying, and then sieved with a 100 mesh screen to obtain the powder.

[0071] Step S2 slurry preparation: the above powder was mixed with PPTTA, BPA1OEODMA, DOP resin, 3wt% of BYK110 small molecule chain organic matter, and 2wt% of TPO initiator, and a planetary ball mill was used at 350 r / min for 4 h to obtain a 55vol% silicon nitride DLP slurry, which had a viscosity of 26.68 Pa·s at a shear rate of 30 s -1 .

[0072] Step S3 ceramic preparation: the above slurry has too high viscosity and cannot be uniformly and completely coated in the exposed area during printing, so DLP printing cannot be performed.

[0073] Comparative Example 3

[0074] The present application provides a silicon nitride ceramic slurry and a preparation method thereof, and also provides a silicon nitride ceramic prepared by using the silicon nitride ceramic slurry as a raw material for DLP printing. The specific preparation process is as follows:

[0075] Step S1 powder modification: silicon nitride with a D50 particle size of 0.7 μm (specific surface area of 11 m 2 / g), 0.2 μm of alumina and 1 μm of yttrium oxide additive were added to the ball mill tank, 1.5 times of silicon nitride grinding balls and alcohol were added, and a planetary ball mill was used at 350 r / min for 4 h. After ball milling, it was placed in an oven at 60°C for drying, and then sieved with a 100 mesh screen to obtain the powder.

[0076] Step S2 slurry preparation: the above modified powder was mixed with PPTTA, BPA1OEODMA, DOP resin, 3wt% of BYK110 small molecule chain organic matter, and 2wt% of TPO initiator, and a planetary ball mill was used at 350 r / min for 4 h to obtain a 55vol% silicon nitride DLP slurry, which had a viscosity of 26.68 Pa·s at a shear rate of 30 s -1 .

[0077] Step S3 ceramic preparation: the above slurry has too high viscosity and cannot be uniformly and completely coated in the exposed area during printing, so DLP printing cannot be performed.

[0078] Comparative Example 4

[0079] The present application provides a silicon nitride ceramic slurry and a preparation method thereof, and also provides a silicon nitride ceramic prepared by using the silicon nitride ceramic slurry as a raw material of DLP and printing by DLP. The specific preparation process is as follows:

[0080] Step S1 powder modification: silicon nitride with a D50 particle size of 0.7 μm (specific surface area of 11 m 2 / g), 0.2 μm of alumina and 1 μm of yttrium oxide additives are added to a ball mill tank, 2wt% of KTM 3007 long molecular chain organic matter of powder mass is added, 1.5 times of silicon nitride grinding balls and alcohol are added, and a planetary ball mill is used at 350 r / min for 4h. After ball milling, it is placed in an oven at 60°C for drying, and then sieved with a 100 mesh screen to obtain modified powder.

[0081] Step S2 slurry preparation: the above modified powder is mixed with PPTTA, BPA1OEODMA, DOP resin, 2wt% of KMT3020 long molecular chain organic matter, and 2wt% of TPO initiator, and a planetary ball mill is used at 350 r / min for 4h to obtain a 55vol% silicon nitride DLP slurry, which has a viscosity of 45.30 Pa·s at a shear rate of 30 s -1 .

[0082] Step S3 ceramic preparation: the above slurry has too high viscosity and cannot be uniformly and completely coated in the exposed area during printing, so DLP printing cannot be performed.

[0083] Comparative Example 5

[0084] The present application provides a silicon nitride ceramic slurry and a preparation method thereof, and also provides a silicon nitride ceramic prepared by using the silicon nitride ceramic slurry as a raw material of DLP and printing by DLP. The specific preparation process is as follows:

[0085] Step S1 powder modification: silicon nitride with a D50 particle size of 0.7 μm (specific surface area of 11 m 2 / g), 0.2 μm of alumina and 1 μm of yttrium oxide additives are added to a ball mill tank, 2wt% of KTM 3007 long molecular chain organic matter of powder mass is added, 1.5 times of silicon nitride grinding balls and alcohol are added, and a planetary ball mill is used at 350 r / min for 4h. After ball milling, it is placed in an oven at 60°C for drying, and then sieved with a 100 mesh screen to obtain modified powder.

[0086] Step S2: preparing slurry: the modified powder is mixed with PPTTA, BPA1OEODMA, DOP resin, 2wt% KMT3331 long molecular chain organic matter, and 2wt% TPO initiator, and a planetary ball mill is used to mill at 350r / min for 4h to obtain a 55vol% silicon nitride DLP slurry, which has a viscosity of 29.77Pa·s at a shear rate of 30s -1 .

[0087] Step S3: preparing ceramic: the above slurry has too high viscosity, and cannot be uniformly and completely coated on the exposed area during printing, so DLP printing cannot be performed.

[0088] Comparative Example 6

[0089] The present application provides a silicon nitride ceramic slurry and a preparation method thereof, and also provides a silicon nitride ceramic prepared by using the silicon nitride ceramic slurry as a raw material of DLP and through DLP printing. The specific preparation process is as follows:

[0090] Step S1: powder modification: 0.3μm silicon nitride (specific surface area 16m 2 / g), 0.2μm aluminum oxide, and 1μm yttrium oxide additives are added to a ball mill tank, 3wt% of the powder mass of BYK110 small molecular chain organic matter is added, 1.5 times of the silicon nitride grinding ball and alcohol are added, and a planetary ball mill is used to mill at 350r / min for 4h. After the ball milling is completed, the modified powder is dried in an oven at 60℃, and then sieved with a 100 mesh sieve to obtain the modified powder.

[0091] Step S2: preparing slurry: the modified powder is mixed with PPTTA, BPA1OEODMA, DOP resin, 2wt% KMT3331 long molecular chain organic matter, and 2wt% TPO initiator, and a planetary ball mill is used to mill at 350r / min for 4h to obtain a 55vol% silicon nitride DLP slurry, which has a viscosity of 29.77Pa·s at a shear rate of 30s -1 .

[0092] Step S3: preparing ceramic: the above slurry has too high viscosity, and cannot be uniformly and completely coated on the exposed area during printing, so DLP printing cannot be performed.

[0093] Comparative Example 7

[0094] The present application provides a silicon nitride ceramic slurry and a preparation method thereof, and also provides a silicon nitride ceramic prepared by using the silicon nitride ceramic slurry as a raw material of DLP and through DLP printing. The specific preparation process is as follows:

[0095] Step S1: powder preparation: 0.7μm silicon nitride (specific surface area 11m2 / g), 0.2 μm of alumina and 1 μm of yttrium oxide additives into a ball mill tank, 1.5 times of silicon nitride grinding balls and alcohol are added, a planetary ball mill is used for ball milling at 350 r / min for 4 h. After ball milling, drying is carried out in an oven at 60 DEG C, and then sieving is carried out with a 100 mesh screen to obtain a powder.

[0096] Step S2: preparation of slurry: the above powder is mixed with PPTTA, BPA1OEODMA, DOP resin, 3wt% of BYK110 small molecule chain organic matter and 2wt% of TPO initiator, a planetary ball mill is used for ball milling at 350 r / min for 4 h to obtain 50vol% of silicon nitride DLP slurry, and the viscosity thereof is 14.75 Pa s at a shear rate of 30 s -1 .

[0097] Step S3: preparation of ceramic: the above silicon nitride DLP slurry is subjected to DLP printing to obtain a green body, and then the green body is subjected to debinding and sintering, the sintering temperature is 1800 DEG C, the sintering pressure is 0.1 MPa, and the sintering time is 2 h, so as to obtain a silicon nitride ceramic.

[0098] Comparative Example 8

[0099] The present application provides a silicon nitride ceramic slurry and a preparation method thereof, and the present application also provides a dense silicon nitride ceramic prepared by using the high solid content silicon nitride ceramic slurry as a raw material of DLP and through DLP printing. The specific preparation process is as follows:

[0100] Step S1: powder modification: 0.7 μm of silicon nitride (specific surface area is 11 m 2 / g), 0.2 μm of alumina and 1 μm of alumina additives into a ball mill tank, 2wt% of KMT 3020 long molecule chain organic matter based on the mass of the powder is added, 1.5 times of silicon nitride grinding balls and alcohol are added, a planetary ball mill is used for ball milling at 350 r / min for 4 h. After ball milling, drying is carried out in an oven at 60 DEG C, and then sieving is carried out with a 300 mesh screen to obtain a modified powder.

[0101] Step S2: preparation of slurry: the modified powder is mixed with PPTTA, HDDA, n-octanol resin, 0.5wt% of BYK110 small molecule chain organic matter and 2wt% of 819 initiator, a planetary ball mill is used for ball milling at 350 r / min for 4 h to obtain 45vol% of silicon nitride DLP slurry, and the viscosity thereof is 1.64 Pa s at a shear rate of 30 s -1 .

[0102] Step S3: Preparation of ceramic: the above-mentioned silicon nitride DLP slurry was subjected to DLP printing to obtain a green body, and then the green body was subjected to debinding and sintering to obtain silicon nitride ceramic, wherein the sintering temperature was 1800 DEG C, the sintering pressure was 0.1 MPa, and the sintering time was 2 h.

[0103] Comparative Example 9

[0104] The present application provides a silicon nitride ceramic and a preparation method thereof, and specifically provides a silicon nitride ceramic prepared by using a conventional dry pressing forming method. The specific preparation process is as follows:

[0105] Step S1: Preparation of powder: 15 g of silicon nitride (specific surface area: 11 m 2 / g) with a D50 particle size of 0.7 μm, 0.2 μm of alumina, and 1 μm of yttrium oxide additives were added to a ball mill tank, 1.5 times of silicon nitride grinding balls and alcohol were added, and a planetary ball mill was used for ball milling at 350 r / min for 4 h. After ball milling, the mixture was dried in an oven at 60 DEG C, and then sieved through a 100-mesh sieve to obtain a mixed powder.

[0106] Step S2: Preparation of compact: 15 g of the above-mentioned mixed powder was poured into a circular mold with a diameter of 50 mm, a unidirectional pressure of 10 MPa was applied and the pressure was maintained for 1 min, and then the pressure was released and the compact was demolded to obtain a preliminarily formed compact. The preliminarily formed compact was then placed into a cold isostatic pressing machine and subjected to pressure maintaining at 200 MPa for 300 s, and then the pressure was released to obtain a compacted compact.

[0107] Step S3: Preparation of ceramic: the above-mentioned silicon nitride compact was placed into a sintering furnace for sintering, wherein the sintering temperature was 1800 DEG C, the sintering pressure was 0.1 MPa, and the sintering time was 2 h, and then silicon nitride ceramic was obtained.

[0108] As can be seen from Examples 1-5 and Comparative Examples 1-7, the high solid content silicon nitride ceramic slurry provided by the present application uses a long molecular chain organic modifier to modify the surface of the silicon nitride powder, and at the same time, a small molecular chain dispersing leveling agent matching the long molecular chain modifier is introduced into the slurry, which can significantly increase the solid content and reduce the viscosity of the slurry. The viscosity of the prepared slurry is 20.40 Pa·s at a conventional doctor blade shear rate when the solid content is 60 vol%, and the slurry can still be subjected to DLP printing. The shrinkage and performance parameters of the ceramic obtained in different directions (XYZ axis) are shown in Table 1. The viscosity of the slurry prepared in Comparative Example 1-6 is >25 Pa·s at a conventional doctor blade shear rate when the solid content is 55 vol%, and even reaches 60.31 Pa·s, which cannot be uniformly and completely coated in the exposure area during printing, and cannot be subjected to DLP printing. It can be seen that the slurry provided by the present application has better rheological property and higher solid content, and further obtains light-cured silicon nitride ceramic with low shrinkage, high density and high mechanical property.

[0109] Table 1: Performance of ceramic prepared in different examples

[0110]

[0111] Regarding the line shrinkage range in Table 1: This is because the shrinkage of a slurry in different directions (XYZ) after printing is not exactly the same, generally speaking, the shrinkage of XY is close and small, and the shrinkage of the Z axis is large because it is the stacking direction, and the present application selects the minimum and maximum values of the line shrinkage in different directions as the shrinkage range.

[0112] As can be seen from the results in Table 1, at the same solid content, the ceramic slurry prepared by the synergistic strategy of long molecular chain powder modification and short molecular chain dispersion modification in Example 1 has lower viscosity than that of Comparative Example 7, which is beneficial to the slurry to be coated and discharged more easily during printing, improves the uniformity of the slurry coating, and further reduces the defects in the green body, and the ceramic part obtained finally has higher mechanical properties than that of Comparative Example 7. As can be seen from the results of Examples 1-5, the higher the solid content of the slurry, the higher the green density and the lower the sintering shrinkage, which reduces the possibility of warping and cracking of the green body during sintering and improves the mechanical properties of the final sintered body. Further see Figure 2 The method of the present application can prepare a silicon nitride ceramic slurry with a solid content of 60vol% and low viscosity suitable for DLP printing, and the ceramic part prepared from the high solid content slurry has finer and more uniform grain size, and the performance even exceeds that of the ceramic prepared by traditional dry pressing + cold isostatic pressing method, which expands the application of DLP silicon nitride ceramic.

[0113] In summary, by synergistic dispersion control of long molecular chain modifier and small molecule dispersant, the present application realizes the preparation of high solid content, low viscosity DLP silicon nitride slurry of high specific surface area powder raw material, also realizes the low shrinkage and densification sintering of DLP silicon nitride printing parts, and further obtains high-performance DLP silicon nitride ceramic with strength > 850MPa, hardness > 16GPa, toughness > 5MPa·m 1 / 2 .

[0114] In the above examples, the description of each example has its own emphasis, and the parts not described in detail in a certain example can be referred to the related description of other examples.

[0115] The above is a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present application, and these modifications or replacements should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a high solids content silicon nitride ceramic slurry, characterized by, The method comprises the following steps: S1, powder modification: 85-95 parts by mass of silicon nitride powder, 5-10 parts by mass of sintering aid, and 0.5-4 parts by mass of modifier are ball milled, and then the mixture is dried and sieved to obtain modified powder; S2, preparation of slurry: the modified powder is uniformly mixed with resin, dispersing leveling agent, and initiator to prepare silicon nitride ceramic slurry with a solid content of 50-60 vol%; The dispersing leveling agent is used in an amount of 0.5-3 wt% of the mass of the modified powder; The initiator is used in an amount of 1-4 wt% of the mass of the resin; The modifier is a long-chain organic molecule with a molecular mass of 1500-4000; The dispersing leveling agent is a small-molecule organic molecule with a molecular mass of less than 1500; The modifier is at least one of Solspersen 80000, KMT 3004, KMT 3007, KTM 3020, and KMT 3331; and the dispersing leveling agent is at least one of KMT-5517, KMT-5519, BYK 110, and BYK 111.

2. The method for preparing high solid content silicon nitride ceramic slurry as described in claim 1, characterized in that, The D50 particle size of the silicon nitride powder is 0.5-1.2 μm, the specific surface area is 9-12 m 2 / g.

3. The method for preparing high solid content silicon nitride ceramic slurry as described in claim 1, characterized in that, The sintering aid is at least one of aluminum oxide, magnesium oxide, and yttrium oxide, and has a particle size of 0.2-1.0 μm.

4. The method for preparing high solid content silicon nitride ceramic slurry as described in claim 1, characterized in that, The resin is at least one of PPTTA, HDDA, TMPTA, BPA1OEODMA, DOP, and n-octanol.

5. The method for preparing high solid content silicon nitride ceramic slurry as described in claim 1, characterized in that, The initiator is at least one of 819, TPO, and camphorquinone.

6. A high solids silicon nitride ceramic slurry, characterized by, The method is prepared by any one of claims 1-5.

7. A method for producing a silicon nitride ceramic, characterized by, The high-solid-content silicon nitride ceramic slurry of claim 6 or the high-solid-content silicon nitride ceramic slurry prepared by any one of the preparation methods of claims 1-5 is used as raw material to perform DLP molding, print a green body, and then perform debinding and sintering on the green body to obtain silicon nitride ceramic.

8. A silicon nitride ceramic, characterized by, The method is prepared by claim 7.

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