Preparation method of high-purity additive-free silicon carbide ceramic

Abstract

The invention discloses a preparation method of high-purity additive-free silicon carbide ceramic, and belongs to the field of silicon carbide ceramic preparation. The invention aims to solve the problem that high-strength silicon carbide ceramic cannot be manufactured under the condition that a sintering aid is not introduced in the prior art. The method comprises the following steps: 1, grading and preparing slurry; 2, preparing prefabricated raw ceramic powder; 3, pre-pressing and forming; and 4, hot pressed sintering. The method is used for preparing the high-purity additive-free silicon carbide ceramic.

Description

Technical Field

[0001] The invention belongs to the field of silicon carbide ceramic preparation. Background Art

[0002] Silicon carbide ceramics are an advanced ceramic material with low density, high hardness, high temperature resistance, oxidation resistance, strong chemical stability, relatively small thermal expansion, and excellent thermal conductivity. They are widely used in high-tech fields such as aerospace, semiconductors, and wear-resistant parts. However, the sintering temperature of silicon carbide is usually as high as 2000℃~2200℃, and the material is easy to decompose or gasify at high temperatures, which not only places high demands on sintering equipment, but also prolongs the reaction cycle and increases huge production costs. Therefore, in order to obtain dense silicon carbide ceramics, traditional processes usually require the addition of sintering aids (such as alumina and yttrium oxide) to reduce the sintering temperature, and at the same time, the mechanical strength of silicon carbide ceramics can also be enhanced. However, this addition method may introduce impurities, reduce the purity and performance of the material, especially in the semiconductor industry, which has extremely high purity requirements. These are all problems that need to be solved at this stage. Summary of the invention

[0003] The present invention aims to solve the problem in the prior art that high-strength silicon carbide ceramics cannot be manufactured without introducing a sintering aid, and further provide a method for preparing high-purity additive-free silicon carbide ceramics.

[0004] A method for preparing high-purity additive-free silicon carbide ceramics is carried out according to the following steps:

[0005] 1. Grading and slurry preparation:

[0006] The silicon carbide powder is mixed with water by sand grinding to obtain a mixed slurry;

[0007] The silicon carbide powder is a mixture of silicon carbide powder with an average particle size of 60 nm and silicon carbide powder with an average particle size of 3 μm;

[0008] 2. Preparation of prefabricated ceramic raw powder:

[0009] The mixed slurry is dried, crushed, ground and sieved to obtain prefabricated ceramic raw powder;

[0010] 3. Pre-pressing:

[0011] Pre-pressing the prefabricated ceramic raw powder into a shape to obtain a ceramic blank;

[0012] 4. Hot pressing sintering:

[0013] The ceramic blank is placed in a graphite mold for hot pressing and sintering, and finally cooled to room temperature to obtain high-purity additive-free silicon carbide ceramics.

[0014] The beneficial effects of the present invention are:

[0015] 1. The present invention uses high-purity silicon carbide powder with an average particle size of 60nm and an average particle size of 3μm as raw materials, disperses them evenly through high-energy sand milling, and prepares high-purity silicon carbide ceramics through particle grading without adding any other sintering aids. In a high-temperature vacuum environment, the silicon carbide ceramics are rapidly sintered through a hot pressing sintering process combined with external pressure.

[0016] 2. In the present invention, when the mass ratio of 60nm and 3μm silicon carbide is 9:1, the bulk density of silicon carbide ceramics can reach 3.06g / cm 3 , the density can reach 95%, the Vickers hardness is 21.6GPa, and the fracture toughness is 3.52MPa·m 1 / 2 , the compressive strength is 1563MPa; and the thermal conductivity of silicon carbide ceramics reaches 103.4W / (m·K).

[0017] 3. The present invention has the advantages of short reaction time and high product quality, which not only significantly reduces the production cost, but also realizes the preparation of high-purity additive-free silicon carbide ceramics with excellent room temperature thermal conductivity and can be used in the field of semiconductor silicon carbide ceramics. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The microscopic morphology and XRD spectrum of the silicon carbide powder described in step 1 of Example 1, (a) and (b) are microscopic morphology of silicon carbide powder with an average particle size of 60 nm, (c) is an XRD spectrum of silicon carbide powder with an average particle size of 60 nm, (d) and (e) are microscopic morphology of silicon carbide powder with an average particle size of 3 μm, and (f) is an XRD spectrum of silicon carbide powder with an average particle size of 3 μm;

[0019] Figure 2 XRD patterns of high-purity additive-free silicon carbide ceramics prepared in Examples 1 to 5 and comparative experiments;

[0020] Figure 3 SEM images of the surface of high-purity additive-free silicon carbide ceramics prepared in Examples 1 to 5 and comparative experiments, (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4, (e) Example 5, (f) comparative experiment;

[0021] Figure 4 The bulk density and mechanical properties of high-purity additive-free silicon carbide ceramics prepared in Examples 1 to 5 and comparative experiments;

[0022] Figure 5 The room temperature thermal conductivity of the high-purity additive-free silicon carbide ceramics prepared in Examples 1 to 5 and the comparative experiment. DETAILED DESCRIPTION

[0023] Specific implementation method 1: This implementation method is a method for preparing high-purity additive-free silicon carbide ceramics, which is carried out according to the following steps:

[0024] 1. Grading and slurry preparation:

[0025] The silicon carbide powder is mixed with water by sand grinding to obtain a mixed slurry;

[0026] The silicon carbide powder is a mixture of silicon carbide powder with an average particle size of 60 nm and silicon carbide powder with an average particle size of 3 μm;

[0027] 2. Preparation of prefabricated ceramic raw powder:

[0028] The mixed slurry is dried, crushed, ground and sieved to obtain prefabricated ceramic raw powder;

[0029] 3. Pre-pressing:

[0030] Pre-pressing the prefabricated ceramic raw powder into a shape to obtain a ceramic blank;

[0031] 4. Hot pressing sintering:

[0032] The ceramic blank is placed in a graphite mold for hot pressing and sintering, and finally cooled to room temperature to obtain high-purity additive-free silicon carbide ceramics.

[0033] The beneficial effects of this embodiment are:

[0034] 1. This embodiment uses high-purity silicon carbide powder with an average particle size of 60nm and an average particle size of 3μm as raw materials, disperses them evenly through high-energy sand milling, and prepares high-purity silicon carbide ceramics through particle grading without adding any other sintering aids. In a high-temperature vacuum environment, the silicon carbide ceramics are rapidly sintered through a hot pressing sintering process combined with external pressure.

[0035] 2. In this embodiment, when the mass ratio of 60nm and 3μm silicon carbide is 9:1, the bulk density of silicon carbide ceramics can reach 3.06g / cm 3 , the density can reach 95%, the Vickers hardness is 21.6GPa, and the fracture toughness is 3.52MPa·m 1 / 2 , the compressive strength is 1563MPa; and the thermal conductivity of silicon carbide ceramics reaches 103.4W / (m·K).

[0036] 3. This embodiment has the advantages of short reaction time and high product quality. It not only significantly reduces the production cost, but also realizes the preparation of high-purity additive-free silicon carbide ceramics with excellent room temperature thermal conductivity and can be used in the field of semiconductor silicon carbide ceramics.

[0037] Specific embodiment 2: This embodiment is different from specific embodiment 1 in that the purity of the silicon carbide powder in step 1 is above 99.9%. Other aspects are the same as those of specific embodiment 1.

[0038] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that the mass percentage of the silicon carbide powder with an average particle size of 60 nm in the silicon carbide powder described in step 1 is 10% to 90%. The rest is the same as specific implementation method 1 or 2.

[0039] Specific embodiment 4: This embodiment differs from one of specific embodiments 1 to 3 in that the mass ratio of silicon carbide powder to water in step 1 is 1:(2-7). Others are the same as specific embodiment 3.

[0040] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the sand milling and mixing described in step 1 is specifically performed for 6 hours to 20 hours at a rotation speed of 200 r / min to 600 r / min and a ball-to-material mass ratio of (2 to 6):1. The rest is the same as specific embodiments 1 to 4.

[0041] Specific implementation method 6: This implementation method is different from specific implementation methods 1 to 5 in that the sieving in step 2 is through a 20-80 mesh sieve. The rest is the same as specific implementation methods 1 to 5.

[0042] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the pre-pressing in step 3 is to pre-press the prefabricated ceramic raw powder for 10 to 50 minutes under a pressure of 20 MPa to 100 MPa to obtain a ceramic blank. The rest is the same as specific embodiments 1 to 6.

[0043] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the hot pressing sintering described in step 4 is carried out in a vacuum environment at a temperature of 1800°C to 1950°C and a pressure of 30MPa to 50MPa for 5min to 30min. The rest is the same as specific embodiments 1 to 7.

[0044] Specific embodiment 9: This embodiment is different from specific embodiments 1 to 8 in that: in step 4, under the conditions of vacuum degree of 0.1Pa to 1Pa and pressure of 30MPa to 50MPa, the temperature is first increased to 900℃ to 1050℃ at a heating rate of 50℃ / min to 100℃ / min, then increased to 1400℃ to 1650℃ at a heating rate of 20℃ / min to 50℃ / min, and finally increased to 1800℃ to 1950℃ at a heating rate of 10℃ / min to 20℃ / min. The rest is the same as specific embodiments 1 to 8.

[0045] Specific embodiment 10: This embodiment differs from Specific embodiments 1 to 9 in that in step 4, the temperature is lowered to room temperature at a rate of 10°C / min to 50°C / min under the conditions of a vacuum degree of 0.1Pa to 1Pa and a pressure of 30MPa to 50MPa. The rest is the same as Specific embodiments 1 to 9.

[0046] The following examples are used to verify the beneficial effects of the present invention:

[0047] Embodiment 1:

[0048] A method for preparing high-purity additive-free silicon carbide ceramics is carried out according to the following steps:

[0049] 1. Grading and slurry preparation:

[0050] At a rotation speed of 300 r / min and a ball-to-material mass ratio of 5:1, the silicon carbide powder and water were sand-milled and mixed for 10 hours to obtain a mixed slurry;

[0051] The silicon carbide powder is a mixture of silicon carbide powder with an average particle size of 60 nm and silicon carbide powder with an average particle size of 3 μm;

[0052] The mass ratio of the silicon carbide powder with an average particle size of 60 nm to the silicon carbide powder with an average particle size of 3 μm is 1:9, that is, the mass percentage of the silicon carbide powder with an average particle size of 60 nm in the silicon carbide powder is 10%;

[0053] The mass ratio of the silicon carbide powder to water is 1:4;

[0054] The silicon carbide powder is sourced from Inner Mongolia Haite Huacai Technology Co., Ltd., with a purity of more than 99.9%;

[0055] 2. Preparation of prefabricated ceramic raw powder:

[0056] The mixed slurry is dried, crushed, ground and passed through a 60-mesh sieve to obtain a prefabricated ceramic raw powder;

[0057] 3. Pre-pressing:

[0058] Under the condition of 70 MPa, the prefabricated ceramic raw powder was pre-pressed for 30 minutes to obtain a ceramic green body;

[0059] 4. Hot pressing sintering:

[0060] The ceramic blank is placed in a graphite mold, and under the conditions of a vacuum degree of 0.1Pa and a pressure of 50MPa, the temperature is first increased to 1000°C at a heating rate of 50°C / min, then increased to 1600°C at a heating rate of 20°C / min, and finally increased to 1900°C at a heating rate of 10°C / min. Under the conditions of a vacuum degree of 0.1Pa, a temperature of 1900°C and a pressure of 50MPa, hot pressing and sintering are carried out for 30 minutes. Finally, under the conditions of a vacuum degree of 0.1Pa and a pressure of 50MPa, the temperature is cooled to room temperature at a cooling rate of 20°C / min to obtain high-purity additive-free silicon carbide ceramics.

[0061] Embodiment 2: This embodiment is different from Embodiment 1 in that the mass ratio of the silicon carbide powder with an average particle size of 60 nm to the silicon carbide powder with an average particle size of 3 μm in step 1 is 3:7, that is, the mass percentage of the silicon carbide powder with an average particle size of 60 nm in the silicon carbide powder is 30%. Others are the same as Embodiment 1.

[0062] Embodiment 3: This embodiment is different from Embodiment 1 in that the mass ratio of the silicon carbide powder with an average particle size of 60 nm to the silicon carbide powder with an average particle size of 3 μm in step 1 is 1:1, that is, the mass percentage of the silicon carbide powder with an average particle size of 60 nm in the silicon carbide powder is 50%. Others are the same as Embodiment 1.

[0063] Embodiment 4: This embodiment is different from Embodiment 1 in that the mass ratio of the silicon carbide powder with an average particle size of 60 nm to the silicon carbide powder with an average particle size of 3 μm in step 1 is 7:3, that is, the mass percentage of the silicon carbide powder with an average particle size of 60 nm in the silicon carbide powder is 70%. Others are the same as Embodiment 1.

[0064] Embodiment 5: This embodiment is different from Embodiment 1 in that the mass ratio of the silicon carbide powder with an average particle size of 60 nm to the silicon carbide powder with an average particle size of 3 μm in step 1 is 9:1, that is, the mass percentage of the silicon carbide powder with an average particle size of 60 nm in the silicon carbide powder is 90%. Others are the same as Embodiment 1.

[0065] Comparative experiment: The difference between this embodiment and the first one of the embodiments 1 to 4 is that the mass percentage of the silicon carbide powder with an average particle size of 60 nm in the silicon carbide powder described in step 1 is 100%. The rest is the same as the embodiment 1.

[0066] Figure 1 These are the micromorphology images and XRD patterns of the silicon carbide powder described in step 1 of Example 1, (a) and (b) are micromorphology images of silicon carbide powder with an average particle size of 60 nm, (c) is the XRD pattern of silicon carbide powder with an average particle size of 60 nm, (d) and (e) are micromorphology images of silicon carbide powder with an average particle size of 3 μm, and (f) is the XRD pattern of silicon carbide powder with an average particle size of 3 μm; it can be seen from the figures that the particle sizes of the two silicon carbide powders are different, and the composition is pure β-SiC.

[0067] Figure 2 The XRD patterns of the high-purity additive-free silicon carbide ceramics prepared in Examples 1 to 5 and the comparative experiment; in the figure, 10% to 100% represents that the mass percentage of the silicon carbide powder with a particle size of 60 nm in the silicon carbide powder is 10% to 100%; as can be seen from the figure, the physical phases of the prepared silicon carbide ceramics are basically the same, all of which are β-SiC, and almost no α-SiC is found, indicating that the high-purity silicon carbide ceramics are successfully prepared by the method in the embodiment.

[0068] Figure 3 The SEM images of the surface of high-purity silicon carbide ceramics without additives prepared in Examples 1 to 5 and comparative experiments, (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4, (e) Example 5, (f) comparative experiment; As can be seen from the figure, there are more pores in the high-purity silicon carbide ceramics prepared in Example 1; the pores in the high-purity silicon carbide ceramics prepared in Examples 2 to 4 gradually decrease; and the high-purity silicon carbide ceramics prepared in Example 5 have the least pores on the polished surface; the high-purity silicon carbide ceramics prepared in the comparative experiment have more pores, and the silicon carbide ceramics are not dense, showing large pores. This shows that the high-purity silicon carbide ceramics prepared in Example 5 have the best performance.

[0069] Tested according to national standards GB / T 25995-2010, GB / T16534-2009, GB / T 23806-2009 and GB / T8489-2006; Figure 4 The bulk density and mechanical properties of high-purity additive-free silicon carbide ceramics prepared in Examples 1 to 5 and comparative experiments; as shown in the figure, when the mass ratio of 60nm and 3μm silicon carbide in Example 5 is 9:1, the bulk density of the silicon carbide ceramic can reach 3.06g / cm 3 , the density can reach 95%, the Vickers hardness is 21.6GPa, and the fracture toughness is 3.52MPa·m 1 / 2 , and the compressive strength is 1563 MPa. This shows that the high-purity additive-free silicon carbide ceramic prepared in Example 5 has the best mechanical properties.

[0070] Figure 5The room temperature thermal conductivity of the high-purity additive-free silicon carbide ceramics prepared in Examples 1 to 5 and the comparative experiment; as can be seen from the figure, the thermal conductivity of the high-purity additive-free silicon carbide ceramics prepared in Example 5 is as high as 103.4 W / (m·K), indicating that the high-purity silicon carbide ceramics prepared by the method in the example have excellent thermal response speed in actual semiconductor applications.

Claims

1. A method for preparing high-purity additive-free silicon carbide ceramics, characterized in that It is carried out in the following steps:

1. Grading and slurry preparation: The silicon carbide powder is mixed with water by sand grinding to obtain a mixed slurry; The silicon carbide powder is a mixture of silicon carbide powder with an average particle size of 60 nm and silicon carbide powder with an average particle size of 3 μm; 2. Preparation of prefabricated ceramic raw powder: The mixed slurry is dried, crushed, ground and sieved to obtain prefabricated ceramic raw powder; 3. Pre-pressing: Pre-pressing the prefabricated ceramic raw powder into a shape to obtain a ceramic blank; 4. Hot pressing sintering: The ceramic blank is placed in a graphite mold for hot pressing and sintering, and finally cooled to room temperature to obtain high-purity additive-free silicon carbide ceramics.

2. The method for preparing high-purity additive-free silicon carbide ceramics according to claim 1, characterized in that The purity of the silicon carbide powder described in step 1 is above 99.9%.

3. The method for preparing high-purity additive-free silicon carbide ceramics according to claim 1, characterized in that The mass percentage of the silicon carbide powder with an average particle size of 60 nm in the silicon carbide powder described in step 1 is 10% to 90%.

4. The method for preparing high-purity additive-free silicon carbide ceramics according to claim 1, characterized in that The mass ratio of the silicon carbide powder to water described in step 1 is 1:(2-7).

5. The method for preparing high-purity additive-free silicon carbide ceramics according to claim 1, characterized in that The sand milling mixing described in step 1 is specifically performed for 6h to 20h at a rotation speed of 200r / min to 600r / min and a ball-to-material mass ratio of (2 to 6):

1.

6. The method for preparing high-purity additive-free silicon carbide ceramics according to claim 1, characterized in that The sieving described in step 2 is through a 20-80 mesh sieve.

7. The method for preparing high-purity additive-free silicon carbide ceramics according to claim 1, characterized in that The pre-pressing in step 3 is to pre-press the prefabricated ceramic raw powder for 10 to 50 minutes under a pressure of 20 MPa to 100 MPa to obtain a ceramic green body.

8. The method for preparing high-purity additive-free silicon carbide ceramics according to claim 1, characterized in that The hot pressing sintering described in step 4 is specifically carried out in a vacuum environment at a temperature of 1800° C. to 1950° C. and a pressure of 30 MPa to 50 MPa for 5 min to 30 min.

9. The method for preparing high-purity additive-free silicon carbide ceramics according to claim 1, characterized in that In step 4, under the conditions of vacuum degree of 0.1Pa~1Pa and pressure of 30MPa~50MPa, the temperature is first increased to 900℃~1050℃ at a heating rate of 50℃ / min~100℃ / min, then increased to 1400℃~1650℃ at a heating rate of 20℃ / min~50℃ / min, and finally increased to 1800℃~1950℃ at a heating rate of 10℃ / min~20℃ / min.

10. The method for preparing high-purity additive-free silicon carbide ceramics according to claim 1, characterized in that In step 4, under the conditions of vacuum degree of 0.1Pa-1Pa and pressure of 30MPa-50MPa, the temperature is lowered to room temperature at a cooling rate of 10°C / min-50°C / min.

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