High-solid-content water-based silicon nitride slurry for direct writing forming and preparation method of high-solid-content water-based silicon nitride slurry

Abstract

The invention relates to high-solid-content water-based silicon nitride slurry for direct writing forming and a preparation method of the high-solid-content water-based silicon nitride slurry. The high-solid-content water-based silicon nitride slurry for direct writing molding comprises 60-76 wt% of silicon nitride powder, 0.2-1 wt% of a dispersing agent, 0.1-3 wt% of a thickening agent, a sintering aid and water, the sintering aid powder accounts for 0-12wt% of the total mass of the silicon nitride powder and the sintering aid.

Description

Technical Field

[0001] The invention relates to a high-solid-content water-based silicon nitride slurry for direct writing and a preparation method thereof, belonging to the technical field of ceramic preparation. Background Art

[0002] Silicon nitride (Si3N4) is a structural and functional integrated ceramic material with excellent performance. It is widely used in machinery, metallurgy, chemistry, aviation, semiconductor and other fields due to its excellent properties such as high hardness, high toughness, high temperature resistance, corrosion resistance and good electrical properties. Traditional molding methods, such as injection molding and gel casting molding, can be used for the near-net shape manufacturing of Si3N4 ceramics with simple or complex shapes, but the ability to control the pores is limited. In contrast, additive manufacturing technology (3D printing technology) can more accurately control the shape and internal structure (or microstructure) of ceramic green parts, providing a solution to the molding and processing problems of special-shaped and personalized silicon nitride ceramic parts.

[0003] Common methods for 3D printing of ceramic materials include digital light processing (DLP), selective laser sintering (SLS), high-temperature fused deposition modeling (FDM), and direct ink writing (DIW). DIW is based on extruding a flowable ceramic paste or ink through a nozzle and building 3D parts by stacking filaments. This method can quickly manufacture complex structures of various ceramic materials at a relatively low cost and is one of the most commonly used additive manufacturing technologies in ceramic manufacturing. In the initial stage of development of this technology, it was believed that the printing raw materials could be ink-like systems with lower viscosity, that is, the printing raw materials were directly ejected from the extruder head. However, with the development and improvement of printing technology types, DIW printing raw materials only correspond to slurry systems with higher viscosity. High-viscosity printing slurry can make the printing raw materials present filamentous characteristics when extruded from the extruder head, and have better molding performance.

[0004] Current research on direct writing technology focuses on the design of oxide ceramic direct writing 3D printing slurry formulas, while research on non-oxide ceramic printing formulas is relatively rare, and there is very little systematic research on the direct writing 3D printing process and sintering manufacturing of Si3N4 ceramics. Summary of the invention

[0005] To this end, the present invention provides a high-solid content water-based silicon nitride slurry for direct writing and a preparation method thereof.

[0006] On the one hand, the present invention provides a high-solid content water-based silicon nitride slurry for direct writing molding, comprising: 60-76wt% of silicon nitride powder, 0.2-1wt% of dispersant, 0.1-3wt% of thickener, sintering aid and water; the sintering aid powder accounts for 0-12wt% of the total mass of the silicon nitride powder and the sintering aid.

[0007] The present invention directly affects the viscosity of the slurry by controlling the solid phase content, dispersant and thickener content of the silicon nitride powder, thereby affecting the extrudability and shape retention of the slurry. The slurry prepared by the present invention has appropriate viscosity, strong shape retention ability, and can achieve excellent printing effect.

[0008] Preferably, the D of the silicon nitride powder 50 The range is 0.5 to 1.2 μm; the specific surface area of ​​the silicon nitride powder is 8 to 12 m 2 / g, the α phase accounts for more than 95%.

[0009] Preferably, the sintering aid powder includes at least one of aluminum oxide powder, yttrium oxide powder, silicon oxide powder, magnesium oxide powder and strontium oxide powder.

[0010] Preferably, the sintering aid powder accounts for 0-12wt% of the total mass of the silicon nitride powder and the sintering aid.

[0011] Preferably, the dispersant comprises at least one of a copolymer of isobutylene and maleic anhydride (Iaobam104), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyethyleneimine (PEI), ammonium polyacrylate (PAA-NH4), polyacrylamide (PMA), and polyacrylic acid (PAA). Isobam104 is preferably used as a bonding-dispersant for direct writing slurry. Isobam104 is a nontoxic, water-soluble copolymer, which is copolymerized by isobutylene and maleic anhydride, and contains three functional groups of -COONH4, -CONH2 and anhydride, wherein the anhydride is hydrolyzed to obtain -COOH. By utilizing steric hindrance effect and electrostatic effect, this copolymer can be well used as a dispersant. In addition, because it contains a multifunctional structure, the functional groups can react at room temperature, and a three-dimensional gel system is obtained by crosslinking, and it is not a free radical reaction, so an initiator and a catalyst are not required, and it can be carried out under air conditions. The optimal content of the dispersant is adjusted according to the different contents of ceramic powders to achieve a good dispersion effect of the ceramic particles in the slurry, so as to obtain a water-based ceramic slurry with high solid content and low viscosity.

[0012] Preferably, the thickener includes at least one of hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and polyvinyl pyrrolidone (PVP). In the uniformly dispersed water-based ceramic slurry, cellulose with good water solubility and suitable viscosity is added. The cellulose can combine with water molecules to form hydrogen bonds, thereby effectively adjusting the free water content in the slurry and increasing the slurry viscosity to make the slurry have a paste-like property, so that the printed filament has excellent shape retention ability. Preferably, the viscosity of the high solid content water-based silicon nitride slurry is 30 to 120 Pa·s.

[0013] On the other hand, the present invention provides a method for preparing a high-solid content water-based silicon nitride slurry for direct writing molding, comprising: adding a dispersant to water for primary mixing, then adding ceramic powder for secondary mixing, and finally adding a thickener for vacuum degassing and mixing to obtain the high-solid content water-based silicon nitride slurry for direct writing molding.

[0014] Preferably, the primary mixing method is ultrasonic mixing, the power of the ultrasonic mixing is 100 to 500 W, and the ultrasonic mixing time is 5 to 10 minutes; The secondary mixing method is ball milling, and the parameters of the ball milling include: a rotation speed of 240 to 400 rpm and a time of 1 to 5 hours: The parameters of the vacuum degassing and mixing include: vacuum degree <5 kPa, rotation speed of 1500-2200 rpm, and vacuum degassing time of 1-3 min.

[0015] In another aspect, the present invention provides a method for preparing a silicon nitride ceramic, comprising: (1) using 3D printing direct writing technology to print a high solid content water-based silicon nitride slurry for direct writing to obtain a 3D printed silicon nitride wet blank; (2) Drying, degreasing and sintering the obtained silicon nitride wet blank to obtain silicon nitride ceramics.

[0016] Preferably, in step (1), the parameters of the 3D printing direct writing technology include: printing speed of 1 to 6 mm / s; needle tube inner diameter of 400 to 1000 μm; filling spacing of 0.4 to 1.6 mm; layer thickness of 0.2 to 0.8 mm.

[0017] Preferably, in step (2), the drying temperature is room temperature and the drying time is 6 to 24 hours; The degreasing temperature is 500-700°C and the time is 3-6 hours; The sintering temperature is 1500-1800° C., the sintering time is 2-5 hours, and the atmosphere is nitrogen.

[0018] Beneficial effects of the present invention: The invention provides a method for preparing a water-based silicon nitride slurry with a high solid content for direct writing technology. The slurry formula has a suitable viscosity to meet the extrudability requirements of direct writing technology, and the printing filament has excellent shape retention ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the preparation method of the water-based silicon nitride slurry of the present invention; Figure 2 To print the image of the wet blank; Figure 3The viscosity test results of Examples 1-4 are as follows; Figure 4 This is a cross-sectional SEM image of Example 1. DETAILED DESCRIPTION

[0020] The present invention is further described below by the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0021] In the present disclosure, the silicon nitride slurry includes ceramic powder, and the solid content of the silicon nitride powder is 60-76wt% (the solid content of the silicon nitride powder is 60-76wt%, and the solid content of the silicon nitride composite powder is 60-80wt%). It also includes a binder-dispersant with a content of 0.2-1wt% of the total mass of the slurry and a thickener with a content of 0.1-3wt%. The silicon nitride slurry prepared by the present invention meets the requirements of direct writing molding and has good extrudability. The printed silicon nitride ceramic product has excellent interlayer support and shape retention ability, and does not collapse and deform after drying, debonding, and sintering.

[0022] In an embodiment of the present invention, the dispersant includes: a copolymer of isobutylene and maleic anhydride (Iaobam104), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyethyleneimine (PEI), ammonium polyacrylate (PAA-NH4), polyacrylamide (PMA), polyacrylic acid (PAA), or a combination thereof.

[0023] In an embodiment of the present invention, the thickener includes: hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), polyvinyl pyrrolidone (PVP) or a combination thereof.

[0024] The following is an exemplary description of a method for preparing a high solid content water-based silicon nitride slurry suitable for direct writing.

[0025] A silicon nitride slurry with a solid phase content of 60-76 wt% of silicon nitride powder is prepared, wherein the silicon nitride slurry comprises a binder-dispersant with a content of 0.2-1 wt% of the total mass of the slurry and a thickener with a content of 0.1-3 wt%.

[0026] The prepared paste is filled into a tube and then degassed in a vacuum degassing machine.

[0027] In an optional embodiment, the silicon nitride ceramic slurry is prepared by the following steps: S1, weighing 60-80wt% of silicon nitride composite powder, 0.2-1wt% of dispersant and 0.1-3wt% of thickener by weight percentage; S2, adding a certain mass of dispersant weighed to deionized water, and ultrasonically mixing for 5-10 minutes; S3, adding a certain mass of silicon nitride composite powder weighed to an aqueous solution containing a binder-dispersant, and ball milling at 240-400rpm for 1-5h; S4, adding a certain mass of thickener weighed to the mixed slurry, and vacuum degassing at 1500-2200rpm for 1-3min to obtain silicon nitride slurry. Among them, 88-95wt% of silicon nitride powder and 5-12wt% of sintering aid are weighed and mixed by weight percentage; S2, the mixed powder is sieved through a 100-mesh sieve to obtain silicon nitride composite powder. The silicon nitride powder used in the present invention has a D 50 The range is 0.5~1.2μm, and the specific surface area is 8~12m 2 / g, the α phase accounts for more than 95%. The silicon nitride powder used in the present invention has a D 50 The range, specific surface area range, and α-phase content are not limited thereto, and those skilled in the art can make reasonable selections based on actual needs.

[0028] The structure is designed in the software, and the silicon nitride slurry is printed using 3D printing direct writing technology to obtain a 3D printed silicon nitride wet blank.

[0029] The silicon nitride wet blank obtained by direct writing is dried, degreased and sintered to obtain a silicon nitride ceramic finished product.

[0030] In an embodiment of the present invention, the dispersant, thickener and lubricant in the silicon nitride ceramic slurry include but are not limited to the above substances, and those skilled in the art can make reasonable selections according to needs.

[0031] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​​​exemplified below.

[0032] Examples 1-8 and Comparative Examples 1-5: The distribution ratio (mass ratio) of each component of the silicon nitride slurry prepared by the present invention is shown in Table 1:

[0033] The preparation methods of the above examples and comparative examples are the same, and the specific steps are as follows: Silicon nitride powder and a sintering aid are mixed, and the mixture is passed through a 100-mesh sieve to obtain a silicon nitride composite powder; a dispersant is added to deionized water, and ultrasonic mixing is performed for 5 minutes to obtain a premixed liquid; the silicon nitride composite powder is added to the premixed liquid, and the mixture is ball-milled in a planetary ball mill for 1 hour, the ball milling medium is silicon nitride balls, and the ball milling speed is 300 r / min; a thickener and a lubricant are added to the ball-milled slurry, and the silicon nitride ceramic paste is obtained after vacuum mixing at speeds of 1500 rpm and 2200 rpm for 1 minute respectively.

[0034] After the paste is loaded into the printing tube, the tube is placed in a vacuum degassing machine with the nozzle facing down and mixed for 1 min at 1000 rpm and 2000 rpm respectively to eliminate the bubbles generated during the tube loading process as much as possible. The DIW 3D printer consists of a three-axis gantry with a multi-axis motion controller. The linear positioning accuracy of the platform is ±5μm and the feedback resolution is 1μm. The printing speed is 3mm / s, the inner diameter of the needle tube is 600μm, the filling spacing is 1mm, and the layer thickness is 0.35mm.

[0035] The paste was deposited layer by layer on a glass slide coated with petroleum jelly. The petroleum jelly as a coating layer allows the blank to easily debond from the substrate and reduces cracking during drying. Various sample geometries were printed; bending bars for mechanical testing, honeycomb lattices with different macroporous structures to illustrate the paste's ability to print more complex geometries. In order to suppress the rapid drying and bending deformation of the wet blank that was extruded first at the bottom layer and facilitate the printing process of all samples, the drying rate of the wet blank during printing was controlled by adjusting the substrate temperature.

[0036] The samples were dried under ambient conditions for 24 hours and no visible cracks were observed. To remove the polymer, the dried green body was heated to 600 °C in air at a heating rate of 3 °C / min for 3 hours. Sintering was carried out in N2 atmosphere at 1700 °C for 2 hours.

[0037] The viscosity of the silicon nitride slurry prepared by the present invention was tested, and the results showed that the slurries of Examples 1-6 all had shear thinning behavior, which met the requirements of the rheological properties of the direct writing slurry. Comparative Examples 1-5 were compared with Example 5, where Comparative Examples 1-5 only changed the content of silicon nitride powder without adjusting the amount of thickener added, and the slurry viscosity was too low or too high, which did not meet the printing requirements (Comparative Examples 4-5 / the slurry viscosity was too high to be measured). Examples 7 and 8 respectively selected polyethylene glycol and ammonium polyacrylate as dispersants, and the slurry viscosity was higher than that of Example 5, proving that its dispersion effect was weaker than Isobam.

[0038] Table 2 shows the performance parameters of porous silicon nitride ceramics prepared by the present invention. <![CDATA[Density / (g·cm -3 )]]> Bending strength / MPa Compressive strength / Mpa Example 1 2.02 98.3 543.1 Example 2 2.03 96.4 498.7 Example 3 1.96 88.9 455.2 Example 4 1.88 76.4 389.9 Example 5 2.18 117.2 659.8 Example 6 2.35 124.0 735.6 Example 7 2.09 79.3 479.2 Example 8 2.15 84.9 523.8 .

[0039] From Table 2 and Figure 2 , 3 4 It can be seen that the porous silicon nitride ceramics obtained by the water-based silicon nitride slurry prepared by the method of the present invention can meet the actual use conditions. Adjusting the content of dispersant and thickener and the change of the solid content of the powder will affect the porosity of the porous ceramics and thus affect its mechanical properties.

[0040] The present invention has been described above in conjunction with specific embodiments. These specific embodiments are merely exemplary and cannot be used to limit the scope of protection of the present invention. Those skilled in the art may make various modifications, changes or substitutions without departing from the essence of the present invention. Therefore, various equivalent changes made according to the present invention still fall within the scope covered by the present invention.

Claims

1. A high solid content water-based silicon nitride slurry for direct writing, characterized in that: include: 60-76wt% of silicon nitride powder, 0.2-1wt% of dispersant, 0.1-3wt% of thickener, sintering aid and water; the sintering aid powder accounts for 0-12wt% of the total mass of silicon nitride powder and sintering aid.

2. The high solid content water-based silicon nitride slurry for direct writing according to claim 1, characterized in that: The D of the silicon nitride powder 50 The range is 0.5 to 1.2 μm; the specific surface area of ​​the silicon nitride powder is 8 to 12 m 2 / g, the α phase accounts for more than 95%.

3. The high solid content water-based silicon nitride slurry for direct writing according to claim 1 or 2, characterized in that: The sintering aid powder includes at least one of aluminum oxide powder, yttrium oxide powder, silicon oxide powder, magnesium oxide powder and strontium oxide powder.

4. The high solid content water-based silicon nitride slurry for direct writing according to any one of claims 1 to 3, characterized in that: The sintering aid powder accounts for 0 to 12 wt % of the total mass of the silicon nitride powder and the sintering aid.

5. The high solid content water-based silicon nitride slurry for direct writing according to any one of claims 1 to 4, characterized in that: The dispersant includes at least one of a copolymer of isobutylene and maleic anhydride (Iaobam104), polyvinyl alcohol (PVA), polyethyleneimine (PEI), ammonium polyacrylate (PAA-NH4), polyacrylamide (PMA), polyacrylic acid (PAA), and polyethylene glycol (PEG).

6. The high solid content water-based silicon nitride slurry for direct writing according to any one of claims 1 to 5, characterized in that: The thickener comprises at least one of hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and polyvinyl pyrrolidone (PVP); Preferably, the viscosity of the high solid content water-based silicon nitride slurry is 30 to 120 Pa·s.

7. A method for preparing a high solid content water-based silicon nitride slurry for direct writing molding according to any one of claims 1 to 6, characterized in that: include: After adding the dispersant into water for a primary mixing, the ceramic powder is added for a secondary mixing, and finally the thickener is added for vacuum degassing and mixing to obtain the high solid content water-based silicon nitride slurry for direct writing.

8. The preparation method according to claim 7, characterized in that: The primary mixing method is ultrasonic mixing, the power of the ultrasonic mixing is 100 to 500 W, and the ultrasonic mixing is 5 to 10 minutes; The secondary mixing method is ball milling, and the parameters of the ball milling include: a rotation speed of 240 to 400 rpm and a time of 1 to 5 hours: The parameters of the vacuum degassing and mixing include: vacuum degree <5 kPa, rotation speed of 1500-2200 rpm, and vacuum degassing time of 1-3 min.

9. A method for preparing silicon nitride ceramics, characterized in that: include: (1) using 3D printing direct writing technology to print the high solid content water-based silicon nitride slurry for direct writing according to any one of claims 1 to 6 to obtain a 3D printed silicon nitride wet blank; (2) Drying, degreasing and sintering the obtained silicon nitride wet blank to obtain silicon nitride ceramics.

10. The preparation method according to claim 9, characterized in that: In step (1), the parameters of the 3D printing direct writing technology include: a printing speed of 1 to 6 mm / s; a needle tube inner diameter of 400 to 1000 μm; a filling spacing of 0.4 to 1.6 mm; and a layer thickness of 0.2 to 0.8 mm.

11. The preparation method according to claim 9 or 10, characterized in that: In step (2), the drying temperature is room temperature and the drying time is 6 to 24 hours; The degreasing temperature is 500-700°C and the time is 3-6 hours; The sintering temperature is 1500-1800° C., the heat preservation time is 2-5 hours, and the atmosphere is nitrogen atmosphere.

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