Preparation method of high-strength and high-thermal-conductivity reaction-sintered silicon carbide ceramic based on direct-writing type 3D printing

Abstract

The invention relates to a preparation method of high-strength high-thermal-conductivity reaction-sintered silicon carbide ceramic based on direct-writing type 3D printing, polyvinylpyrrolidone (PVP) and sodium alginate are introduced into printing slurry, and the high surface energy of the PVP and the sodium alginate effectively prevents the printed slurry from being disintegrated and agglomerated, so that the high-strength high-thermal-conductivity reaction-sintered silicon carbide ceramic is obtained. The slurry with good rheological property can be smoothly extruded out like liquid during printing, and the shape of the slurry can be kept without collapse after the slurry is extruded out. The introduced polyvinylpyrrolidone (PVP) and sodium alginate react with liquid metal silicon during sintering, so that the content of free silicon is reduced, and the strength of a finished product is greatly improved.

Description

Technical Field

[0001] The invention relates to a preparation method of high-strength and high-thermal conductivity reaction-sintered silicon carbide ceramics based on direct-write 3D printing. Background Art

[0002] Silicon carbide ceramics are an advanced material widely used in various application fields such as electronic packaging, aerospace, and armor protection. Traditional ceramic molding technology cannot directly produce workpieces with complex shapes. The hardness of silicon carbide ceramics is second only to diamond. Due to high hardness, brittleness, adhesion, and fine dust and debris generated during processing, it is difficult to process. Therefore, 3D printing technology is needed to produce such workpieces. For 3D printing of ceramics, direct writing (DIW) and digital light processing curing (DLP) are mainly used. However, silicon carbide has a strong absorption of ultraviolet rays, which easily leads to low curing efficiency and is not easy to directly print silicon carbide green bodies with high solid content. DIW, also known as free extrusion molding, has the characteristics of low cost and no dependence on ultraviolet rays. The printing accuracy can be adjusted according to demand. For DIW, the rheological properties of the slurry can be adjusted by adding binders and dispersants to the solvent. In addition, in addition to adding α-SiC, a certain amount of carbon black can be added to the solid component to achieve liquid metal silicon at sintering temperature. Reaction with the carbon black therein generates β-SiC. However, due to the low strength of metallic silicon, the free silicon in the ceramic matrix will reduce the overall strength. Therefore, the mechanical properties of silicon carbide 3D printing have always been at a low level.

[0003] The sintering methods of silicon carbide can be divided into sintered silicon carbide ceramics (SSiC) and reaction sintered silicon carbide ceramics (RBSiC). For 3D printed workpieces, RBSiC has become the only choice due to its extremely low sintering shrinkage rate, low sintering temperature and close size. The free silicon in RBSiC ceramics can fill the pores of the ceramic body and avoid the adverse effects of the pores of the ceramic body on the material properties. In addition, the presence of free silicon helps to increase the bulk density of the product. However, the presence of free silicon and the complexity of the workpiece structure pose new challenges to reaction sintered silicon carbide.

[0004] In summary, the current DIW of silicon carbide materials still faces the following problems in practical applications: 1) There is free silicon, and the Si content in the ceramic is too high, resulting in poor overall mechanical properties. 2) The slurry rheological properties are poor, and the ratio of binder and dispersant is improper, resulting in easy collapse of the printed body or clogging of the nozzle. 3) The particle size needs to be adjusted. If the silicon carbide particle size is too large, there will be more gaps in the green body, and these gaps will eventually be filled by Si, and the mechanical properties and thermal conductivity of silicon are not as good as those of silicon carbide, thus affecting its performance. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method for preparing high-strength and high-thermal conductivity reaction-sintered silicon carbide ceramics based on direct-writing 3D printing.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing high-strength and high-thermal-conductivity reaction-sintered silicon carbide ceramics based on direct-write 3D printing comprises the following steps:

[0008] 1) preparing a slurry with a solid content of 60-70%, wherein the liquid component of the slurry is deionized water dissolved with polyvinyl pyrrolidone (PVP) and sodium alginate, and the solid components are carbon black and α-SiC;

[0009] 2) The slurry is subjected to vacuum degassing to obtain a degassed slurry;

[0010] 3) The degassed slurry is 3D printed to obtain a green embryo, which is then dried and reaction-sintered to obtain a high-strength and high-thermal-conductivity reaction-sintered silicon carbide ceramic.

[0011] Preferably according to the present invention, in step 1), the mass content of polyvinyl pyrrolidone in the liquid component of the slurry is 0.5-2%.

[0012] Further preferably, in step 1), the mass content of polyvinyl pyrrolidone in the slurry liquid component is 0.8-1.2%.

[0013] Most preferably, in step 1), the mass content of polyvinyl pyrrolidone in the slurry liquid component is 1%.

[0014] Preferably according to the present invention, in step 1), the mass content of sodium alginate in the slurry liquid component is 0.5-2%.

[0015] Further preferably, in step 1), the mass content of sodium alginate in the slurry liquid component is 0.8-1.2%.

[0016] Most preferably, in step 1), the mass content of sodium alginate in the slurry liquid component is 1%.

[0017] Preferably according to the present invention, in step 1), carbon black accounts for 30-40% and α-SiC accounts for 70-30% of the solid components.

[0018] Further preferably, in step 1), carbon black accounts for 35% and α-SiC accounts for 65% of the solid components.

[0019] Preferably according to the present invention, in step 1), the particle size of α-SiC is 0.1-0.8 micrometers.

[0020] Further preferably, in step 1), the particle size of α-SiC is 0.5 micrometer.

[0021] Preferably according to the present invention, in step 3), the drying time of the raw embryo is 40-50 hours.

[0022] The vacuum degassing and reaction sintering are carried out according to conventional techniques in the art.

[0023] The present invention introduces polyvinyl pyrrolidone (PVP) and sodium alginate into the printing slurry. The high surface energy of polyvinyl pyrrolidone (PVP) and sodium alginate effectively prevents the printed slurry from disintegrating and agglomerating, and obtains a slurry with good rheological properties. The introduced polyvinyl pyrrolidone (PVP) and sodium alginate react with liquid metal silicon during sintering, reduce the content of free silicon, and improve the mechanical properties of the sintered finished product. In summary, the key introduction of polyvinyl pyrrolidone (PVP) and sodium alginate slurry can be smoothly extruded like a liquid during printing, and can also maintain its shape without collapse after being extruded. In addition, the free silicon content is reduced, which greatly improves the strength of the finished product.

[0024] The technical features and advantages of the present invention are as follows:

[0025] 1. Good rheological properties: The present invention introduces polyvinyl pyrrolidone (PVP) and sodium alginate into the printing slurry. The high surface energy of polyvinyl pyrrolidone (PVP) and sodium alginate effectively prevents the printed slurry from disintegrating and agglomerating. The obtained slurry has good rheological properties, ensuring that it can be smoothly extruded like a liquid during printing, and can also maintain its shape without collapsing after being extruded.

[0026] 2. Lower free silicon content: The polyvinyl pyrrolidone (PVP) and sodium alginate introduced in the present invention react with liquid metal silicon during sintering, thereby reducing the free silicon content, greatly improving the strength of the finished product, and improving the mechanical properties of the sintered finished product.

[0027] 3. Excellent mechanical properties: Due to the low content of free silicon and the small particle size of silicon carbide, the strength of the finished product is greatly improved. The density of the obtained DIW compact workpiece is 3.06g / cm 3 The bending strength and hardness are 296.4Mpa and 19.5Gpa respectively, and the fracture toughness is 6.1MPa·m 1 / 2 , with high bending strength, high hardness and high fracture toughness.

[0028] 4. Excellent thermal conductivity: Due to the compactness of the workpiece, there is less phonon scattering during heat conduction. Its room temperature thermal conductivity is 148W / (m·K), which has high thermal conductivity. The high temperature thermal conductivity of 500℃ is 61.0W / (m·K).

[0029] 5. The present invention significantly improves the mechanical properties of the DIW workpiece by adjusting the particle size of the silicon carbide raw material and the content of carbon black. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a top view SEM image of the silicon carbide ceramic prepared in Example 1;

[0031] Figure 2 is a cross-sectional SEM image of the silicon carbide ceramic prepared in Example 1;

[0032] Figure 3 is a side view SEM image of the silicon carbide ceramic prepared in Example 1;

[0033] Figure 4 Graphs showing the viscosity of the DIW slurry of Example 1 (a) and the oscillation scan of the DIW slurry (b).

[0034] Figure 5 : is the polished metallographic image of the silicon carbide ceramic prepared in Example 1. DETAILED DESCRIPTION

[0035] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings, but is not limited thereto.

[0036] The raw materials used in the examples are all conventional raw materials, and the equipment used are all conventional equipment and commercially available products.

[0037] Example 1

[0038] The preparation method of high-strength and high-thermal-conductivity reaction-sintered silicon carbide ceramics based on direct writing 3D printing is as follows:

[0039] 1) The specific operation of preparing 30 g of slurry according to this ratio is to add 0.1 g of PVP, 0.1 g of sodium alginate, 19.5 g of α-SiC (particle size 0.5 μm) and 10.5 g of carbon black to 10 g of deionized water in sequence and mix them evenly using a homogenizer to obtain a slurry;

[0040] 2) The slurry is subjected to vacuum degassing to obtain a degassed slurry;

[0041] 3) The degassed slurry is 3D printed to obtain a green embryo, which is then dried and reaction-sintered to obtain a high-strength and high-thermal-conductivity reaction-sintered silicon carbide ceramic.

[0042] Experimental Example 1

[0043] SEM images of reaction sintered silicon carbide ceramics are shown in Figure 1-Figure 3 As shown in Figure 2, the microstructure of silicon carbide ceramics presents a continuous honeycomb structure.

[0044] Experimental Example 2

[0045] 1. Test the rheological properties of the slurry after degassing in step 2 of Example 1. The results are shown in Figure 4a, it can be seen that the viscosity of the slurry gradually decreases with the shear rate, indicating that the slurry is suitable for DIW or extrusion molding, which facilitates the smooth extrusion of the slurry. Figure 4 As shown in Figure b, it can be seen that with the increase of shear strain, the storage modulus and loss modulus of the slurry gradually decrease, and the two curves they represent intersect. The intersection can divide the graph into two parts. The storage modulus in the left half is greater than the loss modulus, that is, the slurry maintains the characteristics of a solid in this state; while the loss modulus in the right half begins to exceed the storage modulus, that is, the characteristics of the slurry in this state tend to be liquid characteristics. This shows that the slurry can be extruded smoothly like a liquid during printing, and can also maintain its shape without collapsing after being extruded.

[0046] 2. The polished metallographic image of the high-strength and high-thermal-conductivity reaction-sintered silicon carbide ceramic obtained in Example 1 is as follows: Figure 5 As shown, the dark gray area is silicon carbide, and the light gray area is free silicon. Using imageJ to calculate the area, it can be found that the free silicon accounts for about 9%. Due to the higher carbon content of the green body, the free silicon content of the reaction-sintered silicon carbide ceramic of the present invention is lower than that of most reaction-sintered silicon carbides. The moderate free silicon content greatly improves the strength of the reaction-sintered silicon carbide ceramic.

[0047] 3. Due to the low content of free silicon and the small particle size of silicon carbide, the strength of the finished product is greatly improved. The density of the obtained DIW compact workpiece is 3.06g / cm 3 The bending strength and hardness are 296.4Mpa and 19.5Gpa respectively, and the fracture toughness is 6.1MPa·m 1 / 2 , with high bending strength, high hardness and high fracture toughness.

[0048] 4. Due to the compactness of the workpiece, there is less phonon scattering during heat conduction. Its room temperature thermal conductivity is 148W / (m·K), which has high thermal conductivity. Its high temperature thermal conductivity of 500℃ is 61.0W / (m·K).

Claims

1. A method for preparing high-strength and high-thermal-conductivity reaction-sintered silicon carbide ceramics based on direct writing 3D printing, comprising the following steps: 1) preparing a slurry with a solid content of 60-70%, wherein the liquid component of the slurry is deionized water dissolved with polyvinyl pyrrolidone (PVP) and sodium alginate, and the solid components are carbon black and α-SiC; 2) The slurry is subjected to vacuum degassing to obtain a degassed slurry; 3) The degassed slurry is 3D printed to obtain a green embryo, which is then dried and reaction-sintered to obtain a high-strength and high-thermal-conductivity reaction-sintered silicon carbide ceramic.

2. The preparation method according to claim 1, characterized in that: In step 1), the mass content of polyvinyl pyrrolidone in the slurry liquid component is 0.5-2%.

3. The preparation method according to claim 1, characterized in that: In step 1), the mass content of polyvinyl pyrrolidone in the slurry liquid component is 0.8-1.2%.

4. The preparation method according to claim 1, characterized in that: In step 1), the mass content of sodium alginate in the slurry liquid component is 0.5-2%.

5. The preparation method according to claim 1, characterized in that: In step 1), the mass content of sodium alginate in the slurry liquid component is 0.8-1.2%.

6. The preparation method according to claim 1, characterized in that: In step 1), carbon black accounts for 30-40% and α-SiC accounts for 70-30% of the solid components.

7. The preparation method according to claim 1, characterized in that: In step 1), carbon black accounts for 35% and α-SiC accounts for 65% of the solid components.

8. The preparation method according to claim 1, characterized in that: In step 1), the particle size of α-SiC is 0.1-0.8 micrometers.

9. The preparation method according to claim 1, characterized in that: In step 1), the particle size of α-SiC is 0.5 micrometer.

10. The preparation method according to claim 1, characterized in that: In step 3), the drying time of the raw embryo is 40-50 hours.

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