WO2020244484A1

WO2020244484A1 - High-purity sic ceramic prepared by normal-pressure solid phase sintering and preparation method therefor

Info

Publication number: WO2020244484A1
Application number: PCT/CN2020/093788
Authority: WO
Inventors: 杨勇; 刘盟; 黄政仁; 姚秀敏; 刘学建
Original assignee: 中国科学院上海硅酸盐研究所
Priority date: 2019-06-03
Filing date: 2020-06-01
Publication date: 2020-12-10
Also published as: CN110204338A

Abstract

Provided are a high-purity SiC ceramic prepared by normal-pressure solid-phase sintering and a preparation method therefor. The preparation method for the high-purity SiC ceramic comprises: (1) adding α-SiC powder and an aqueous solution containing a sintering aid into a solvent and mixing to obtain SiC slurry, wherein the sintering aid comprises a B source and a C source, the B source is boric acid, and the C source is selected from at least one of D-fructose and glucose; (2) drying and forming the SiC slurry to obtain an SiC blank; (3) conducting vacuum debonding to the SiC blank, placing the debonded SiC blank in an inert atmosphere, and sintering for 30-120 minutes at 2,050°C-2,250°C to obtain the high-purity SiC ceramic. The addition amount of the element B in the B source accounts for 0.1-1wt% of the mass of the α-SiC powder, and the addition amount of the element C in the C source does not exceed 5 wt% of the mass of the α-SiC powder.

Description

Atmospheric solid-phase sintered high-purity SiC ceramic and preparation method thereof

Technical field

The invention relates to a high-purity SiC ceramic sintered at normal pressure and solid phase and a preparation method thereof, belonging to the field of materials.

Background technique

In China's semiconductor industry, chip manufacturing occupies a core position. As the country pays more attention to the semiconductor industry, a large number of fabs have established production lines in my country in recent years. According to statistics, there are currently more than 60 foundries established in China. Closely related to it are the various devices needed in semiconductor processing. Among them, high-purity silicon carbide (SiC) materials have many excellent properties, such as high strength, hardness, rigidity, chemical stability, excellent oxidation resistance and wear resistance, etc., occupying a relatively high proportion of the prepared devices. A large proportion.

At present, SiC ceramic devices widely used in semiconductor processing are mainly prepared by recrystallization and sintering. Although recrystallized SiC has extremely high purity and does not contain any metal phase and glass phase, it has low density and low strength. With the further development of the semiconductor industry, the performance of recrystallized SiC ceramic devices has been unable to meet the requirements for processing devices of larger wafer processing.

Through hot press sintering or spark plasma sintering, although high-density SiC ceramics can be prepared without adding sintering aids, the sintering conditions are relatively harsh, and neither of these two methods are suitable for the preparation of large sizes. , Ceramic parts with complex shapes.

Using the normal pressure solid phase sintering method, although dense SiC ceramics can be prepared, the residual B element in the resulting ceramic is more than 0.3%, and the residual free carbon is more than 2%. If the amount of sintering aid added is directly reduced, although the residual amount of residual aid can be reduced, it will also reduce the driving force for sintering, and the density of the sample may be greatly reduced.

Summary of the invention

Based on the difficulty of densifying SiC ceramics without adding sintering aids, the present invention provides a method for preparing high-purity SiC ceramics applied to semiconductor manufacturing. The method adopts normal pressure solid phase sintering, and meets the requirements of semiconductor processing applications by adding a very low content of specific sintering aids.

In one aspect, the present invention provides a method for preparing high-purity SiC ceramics, including:

(1) Add ɑ-SiC powder and an aqueous solution containing a sintering aid to a solvent and mix to obtain a SiC slurry. The sintering aid is a source of B and a source of C, the source of B is boric acid, and the source of C At least one selected from D-fructose and glucose;

(2) Drying and molding the obtained SiC slurry to obtain a SiC body;

(3) After vacuum debonding, the obtained SiC body is placed in an inert atmosphere, and sintered at 2050-2250°C for 30-120 minutes to obtain the high-purity SiC ceramic;

The addition amount of the B element in the B source is 0.1 to 1 wt% of the mass of the ɑ-SiC powder, and the addition amount of the C element in the C source does not exceed 5 wt% of the mass of the ɑ-SiC powder.

In this disclosure, ɑ-SiC powder is selected as the raw material, and B source (boric acid), which is easily soluble in solvents such as water and ethanol, is selected. It has high solubility in water and is composed of H, B, and O elements. The smallest soluble molecule) and C source (at least one of D-fructose and glucose), the two are more uniformly dispersed. At the same time, the addition amount of B element in the B source is controlled to be 0.1 to 1 wt% of the mass of the ɑ-SiC powder, and the addition amount of the C element in the C source does not exceed 5 wt% of the mass of the ɑ-SiC powder. After vacuum debonding, in the sintering process at 2050-2250°C, source B and source C can achieve the effect of increasing the driving force of sintering with a smaller amount of sintering aid. Finally, the excellent performance of high purity and high density of SiC ceramics is realized. Specifically, because silicon carbide is a covalent compound, the ratio of its grain boundary energy to surface energy is large, so it is difficult to sinter and compact. Atmospheric solid-phase sintered silicon carbide ceramics usually choose B and C as sintering aids. Among them, the main role of B element is solid-dissolved into the silicon carbide lattice to reduce its grain boundary energy, and the main role of C element is to reduce silicon carbide particles. The silica on the surface increases its surface energy. Through the combined action of the above two mechanisms, the driving force for sintering is improved and the silicon carbide ceramic is densified. Generally, boron carbide and carbon powder are used as sintering aids. Because the sintering aids are in solid phase and are hardly soluble in solvents such as absolute ethanol, it is difficult to disperse uniformly. As shown in Figure 1, in the present invention, boric acid, _D -fructose, glucose system, etc. are used as sintering aids, which can be dissolved in water and absolute ethanol, and can be more uniformly dispersed in the slurry in the form of a liquid phase. When mixing, the sintering aid is heated and dissolved in deionized water because boric acid and _D -fructose have higher solubility in water, and the solubility increases with the increase of temperature (the above process can be realized by ball milling). During the debonding process, boric acid and _D -fructose are decomposed to generate boron oxide and carbon, which are present on the surface of silicon carbide particles. Due to the volatility of boron oxide, a large amount of boron oxide volatilizes during the debonding process, and the remaining boron oxide will form a eutectic together with silicon dioxide (the ball milling process generally oxidizes the SiC surface to form a SiO ₂ layer). Mixture: 2H ₃ BO ₃ → B ₂ O ₃ + 3H ₂ O (g) (1); C ₆ H ₁₂ O ₆ → 6C+6H ₂ O (g) (2). During the sintering process, when the temperature rises to about 1550°C, the carbothermal reaction begins to occur until the sintering temperature (for example, 2050-2250°C) and holding for a certain time (for example, 30 to 120 minutes), the carbothermal reaction continues to occur: 2B ₂ O ₃ +7C→B ₄ C+6CO(g) (3); SiO ₂ +3C→SiC+2CO(g) (4); 2SiO ₂ +SiC→3SiO(g)+CO(g) (5) . The boron carbide produced by the in-situ reaction is smaller than the boron carbide particles directly added, and is easier to solid-dissolve into the silicon carbide crystal lattice, so the grain boundary energy can be sufficiently low with a very small amount of B element. Moreover, the solid solubility of element B in the silicon carbide lattice is about 0.2 wt% at 2100°C and less than 0.4 wt% at 2200°C. Therefore, the 0.11 to 0.14 wt% residual B content of this patent is sufficient to make the silicon carbide grain boundary low enough, and the residual B elements can be solid-dissolved into the silicon carbide crystal lattice and will not remain at the grain boundary.

Preferably, the average particle size of the ɑ-SiC powder is 0.1 to 1 μm; the purity of the ɑ-SiC powder is ≥ 99.86%.

Preferably, the source B and the source C are added to water, and heated to dissolve at 60-90° C. to obtain the aqueous solution containing the sintering aid. The beneficial effect of this step is that the boric acid and fructose can be fully dissolved in the slurry and the uniformity of the dispersion of the sintering aid can be improved.

Preferably, the solvent is absolute ethanol or water.

Preferably, the solid content of the SiC slurry is 20-60 wt%. Although the dissolution of the sintering aid can be promoted by increasing the amount of solvent, too much sintering aid will reduce the solid content of the slurry, which may cause the slurry to stratify during the drying process and reduce the uniformity of the sintering aid dispersion.

Preferably, the drying temperature is 60-100°C, and the time is 3-8 hours.

Preferably, the forming method is dry pressing and/or cold isostatic pressing, the pressure of the dry pressing is 5-100 MPa, and the pressure of the cold isostatic pressing is 150-200 MPa, and the pressure is maintained. The time is 1 to 3 minutes.

Preferably, the vacuum debonding temperature is 600-1200°C, the time is 30-120 minutes, and the vacuum degree is less than 100Pa. Different debonding systems (changes in heating rate and holding time) will change the B content of the sample after debonding.

On the other hand, the present invention provides a high-purity SiC ceramic prepared according to the above-mentioned preparation method, characterized in that the purity of the high-purity SiC ceramic is more than 99.5% by weight, and the density is more than 98%.

Preferably, the free carbon content in the high-purity SiC ceramic is less than 0.15wt%; the O element content is less than 0.15wt%; the B element content is less than 0.15wt%; in the high-purity SiC ceramic, B, C, O and Si are removed Except for the elements, the total amount of other elements is less than 0.015wt%.

Benefits:

The invention can easily prepare large-sized and complex-shaped ceramic parts through the normal pressure solid phase sintering method, and is suitable for industrial production. On the premise of ensuring high density, reduce the content of sintering aids as much as possible, reduce the amount of residual B and C, and obtain high-purity and dense silicon carbide ceramics. And this method can reduce the manufacturing cost to a great extent, and provide strong technical support for the "curve overtaking" of my country's semiconductor industry.

Description of the drawings

Figure 1 is a schematic diagram of preparing high-purity silicon carbide according to the present invention;

Figure 2 shows the relationship between the Gibbs free energy of the carbothermal reduction reaction and the temperature during the sintering process. It can be seen from the figure that B ₂ O ₃ and SiO ₂ undergo the carbothermal reduction reaction to generate B ₄ C and SiC. The temperature is 1567℃ and 1521℃ respectively; when the temperature is higher than 1877℃, the self-deoxygenation reaction of SiC can occur;

Fig. 3 is a BSD (Backscattered Electron Image) test result of the high-purity SiC ceramic prepared by the present invention after plasma etching;

Figure 4 is the XRD (X-ray diffraction) test result of the high-purity SiC ceramic prepared by the present invention;

5 is the SEM (secondary electron image) test result of the high-purity SiC ceramic prepared by the present invention after being corroded by NaOH at 500°C;

6 is the SEM (secondary electron image) test result of the high-purity SiC ceramic prepared by the present invention after being corroded by NaOH at 500°C;

Figure 7 is a SEM (secondary electron image) image of the silicon carbide ceramic prepared in Comparative Example 1;

Figure 8 is a BSD (backscattered electron image) image of the silicon carbide ceramic prepared in Comparative Example 2;

Table 1 in FIG. 9 shows the GDMS (glow discharge mass spectrometry) test results of the high-purity SiC ceramic prepared in Example 1.

Detailed ways

The present invention will be further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, not to limit the present invention.

In the present disclosure, a conventional solid-phase sintering method is used to prepare high-purity SiC ceramics with a purity higher than 99.5% by weight and a density higher than 98%. In an alternative embodiment, the free carbon content in the high-purity SiC ceramic is less than 0.15 wt%. The content of B and O elements in the high-purity SiC ceramics are both less than 0.15wt%. In addition, in high-purity SiC ceramics, in addition to B, C, O and Si elements, the total amount of other elements is less than 0.015wt%. The following exemplarily illustrates the preparation method of the high-purity SiC ceramic provided by the present invention.

Ɑ-SiC powder is used as raw material, B source and C source are used as sintering aids, water or/and ethanol are added as solvent, and SiC slurry is obtained after mixing. The average particle size of ɑ-SiC powder can be 0.1 to 1 μm, and the purity is ≥99.86%. Preferably, the average particle size of ɑ-SiC powder is 0.6 μm and the purity is 99.86%. The B source can be boric acid. The addition amount of B element in the B source in the sintering aid is controlled to be 0.1-1wt% of the mass of the ɑ-SiC powder. The C source may be at least one of _D -fructose and glucose, preferably D-fructose. Control the addition of C source in the sintering aid to not exceed 5wt% of the mass of ɑ-SiC powder. The solid content of the obtained SiC slurry may be 20-60 wt%, preferably 30-50 wt%. If calculated by mass, preferably, the mass ratio of the ɑ-SiC powder, B source (for example, boric acid, etc.) and C source (for example, D-fructose, etc.) may be 50:1:5. Among them, the mixing method can be ball mill mixing. The ball milling process uses a planetary ball mill and SiC grinding balls. The rotating speed of the ball milling process can be 200-400r/min, and the time can be 4 to 48 hours. In the above ball milling process, the surface of the silicon carbide particles will be oxidized, forming a very thin silicon dioxide oxide layer, and boric acid and fructose are wrapped on the surface (see Figure 1). Preferably, the time of the ball milling process is 24 hours, and the rotation speed is 300 r/min.

In an alternative embodiment, the sintering aid is placed in deionized water and heated to dissolve to obtain an aqueous solution containing the sintering aid. Then, the ɑ-SiC powder, the aqueous solution containing the sintering aid, and the solvent (for example, absolute ethanol, etc.) are mixed through ball milling to obtain a SiC slurry. The heating and dissolution temperature may be 60 to 90°C, preferably 80°C.

After drying and forming the SiC slurry, a SiC body is made. The drying temperature can be 60-100°C, and the drying time is 3-8 hours. Preferably, the drying temperature is 60°C, and the drying time is 6 hours. Wherein, the molding method is dry pressing and/or cold isostatic pressing and the dry pressing pressure is 5-100 MPa (for example, 20 MPa). The cold isostatic pressing molding pressure can be 150～200MPa, and the pressure holding time can be 1～3 minutes. Preferably, the pressure of cold isostatic pressing is 200 MPa, and the pressure holding time is 2 minutes.

The SiC green body is vacuum debonded and sintered in a normal pressure inert atmosphere to obtain high-purity SiC ceramics. The process of vacuum debonding can be carried out in a debonding furnace. The vacuum debonding temperature is 600-1200°C, the holding time is 30-120 minutes, and the vacuum degree is less than 100 Pa. Among them, boric acid forms boron oxide in the debonding process, and the amount of boron oxide volatilization is related to the debonding system. The higher the debonding temperature and the longer the holding time, the more boron oxide will volatilize. The B element content in the SiC body after vacuum debonding is not less than 0.1wt%. The atmospheric inert atmosphere can be carried out in an atmospheric sintering furnace. The sintering temperature may be 2050-2250°C (for example, 2100°C), the holding time may be 30-120 minutes, and the sintering atmosphere may be an inert atmosphere. For example, the inert atmosphere may be argon, helium, neon, or the like.

In the present invention, the obtained high-purity SiC ceramics can be used in the field of semiconductor manufacturing.

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 construed 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 present invention. The scope of protection. The specific process parameters in the following examples are only an example in the appropriate range, that is, those skilled in the art can make selections within the appropriate range through the description herein, and are not limited to the specific values illustrated below.

Example 1

Preparation of SiC slurry: Weigh 2g boric acid (addition of element B is 0.35wt% of ɑ-SiC powder mass) and 10g D-fructose (addition of C element is 1.8wt% of ɑ-SiC powder mass) , Placed in a glass beaker containing 30ml of deionized water, heated to 80 ℃ to prepare a mixed solution. Weigh 100g of ɑ-SiC powder, 150g of absolute ethanol, 150g of SiC grinding balls and the prepared mixed solution and place them in a nylon ball milling tank. Place the ball mill in a planetary ball mill for ball milling. The average particle size of ɑ-SiC powder is 0.6μm, the purity is 99.86%, the diameter of the SiC grinding ball is 5mm, the speed of the ball mill is 300r/min, and the milling time is 24 hours;

Preparation of raw material powder: the ceramic slurry after ball milling is placed in an electric blast drying box for drying, and then ground and sieved to obtain raw material powder. The temperature of the drying oven is set to 60°C, the drying time is 6 hours, and the sieve used for sieving is a 100 mesh sieve;

Preparation of SiC body: the raw material powder is prepared into a body after dry pressing and cold isostatic pressing. The dry pressing molding pressure is 20MPa, the cold isostatic pressing molding pressure is 200MPa, and the pressure holding time is 2 minutes;

Preparation of high-purity SiC ceramics: After the green body is placed in a debonding furnace for vacuum debonding, it is then placed in an atmospheric sintering furnace for sintering to obtain high-purity and high-density SiC ceramics. The vacuum debonding temperature is 900°C, the holding time is 30 minutes, and the vacuum degree is less than 20Pa. The sintering temperature is 2100°C, the holding time is 60 minutes, and the sintering atmosphere is atmospheric pressure argon atmosphere.

The density of the SiC ceramic prepared in Example 1 is 98.42%, the purity is about 99.6%, and the free carbon content is 0.12 wt%.

Fig. 3 is a BSD image of the high-purity SiC ceramic prepared in Example 1 after plasma etching. The result shows that the prepared SiC ceramic has clean grain boundaries and no obvious second phase. The SiC crystal grains are mainly columnar crystals, and some of the columnar crystals are longer than 450μm and have a high aspect ratio. Figure 4 is the XRD pattern of the high-purity SiC ceramic prepared in Example 1. The results show that the main crystal phases of the prepared SiC ceramic are 4H-SiC and 6H-SiC.

Table 1 in FIG. 9 shows the GDMS (glow discharge mass spectrometry) test results of the high-purity SiC ceramic prepared in Example 1 (only elements with a content greater than 0.1 ppm are shown in the table). It can be seen from Table 1 that the content of B and O elements in the SiC ceramic prepared in Example 1 is less than 0.15 wt%, and the total content of other impurity elements is less than 0.015 wt%. Glow Discharge Mass Spectrometry (GDMS) is a powerful method for detecting the impurity composition of high-purity materials. Because this material is silicon carbide, C and Si are elements of the substrate, which cannot be detected by GDMS. Therefore, free carbon is measured by a carbon-sulfur analyzer.

Example 2

Preparation of SiC slurry: Weigh 2.5g boric acid (addition of B element is 4.5wt% of ɑ-SiC powder mass) and 15g D-fructose (addition of C element is 0.26wt% of ɑ-SiC powder mass ), placed in a glass beaker containing 40ml of deionized water, heated to 60°C to prepare a mixed solution. Weigh 100g of ɑ-SiC powder, 150g of absolute ethanol, 150g of SiC grinding balls and the prepared mixed solution and place them in a nylon ball milling tank. Place the ball mill in a planetary ball mill for ball milling. The average particle size of ɑ-SiC powder is 0.2μm, the purity is 99.86%, the diameter of the SiC grinding ball is 5mm, the speed of the ball mill is 200r/min, and the milling time is 48 hours;

Preparation of SiC body: the raw material powder is prepared into a body after dry pressing and cold isostatic pressing. The dry pressing molding pressure is 80MPa, the cold isostatic pressing molding pressure is 200MPa, and the pressure holding time is 3 minutes.

Preparation of high-purity SiC ceramics: After the green body is placed in a debonding furnace for vacuum debonding, it is then placed in an atmospheric sintering furnace for sintering to obtain high-purity and high-density SiC ceramics. The vacuum debonding temperature is 800°C, the holding time is 90 minutes, and the vacuum degree is less than 20Pa. The sintering temperature is 2050°C, the holding time is 120 minutes, and the sintering atmosphere is atmospheric pressure argon atmosphere.

The purity of the high-purity SiC ceramic prepared in Example 2 is about 99.5%, the density is 98.36%, the amount of free carbon is 0.14% by weight, and the content of element B is 0.14% by weight. So it is mainly free carbon and residual B that affect the purity of the sample. Figure 5 is an SEM image of the high-purity SiC ceramic prepared in Example 2 after corrosion. The result shows that the prepared SiC ceramic has clean grain boundaries and no obvious second phase.

Example 3

Preparation of SiC slurry: Weigh 3.5g boric acid (addition of B element is 0.6wt% of ɑ-SiC powder mass) and 15g D-fructose (addition of C element is 2.5wt% of ɑ-SiC powder mass ), placed in a glass beaker containing 40ml of deionized water, and heated to 80°C to prepare a mixed solution. Weigh 150g of ɑ-SiC powder, 200g of absolute ethanol, 200g of SiC grinding balls and the prepared mixed solution and place them in a nylon ball milling tank. Place the ball mill in a planetary ball mill for ball milling. The average particle size of ɑ-SiC powder is 0.8μm, the purity is 99.5%, the diameter of the SiC grinding ball is 5mm, the speed of the ball mill is 400r/min, and the milling time is 24 hours;

Preparation of raw material powder: the ceramic slurry after ball milling is placed in an electric blast drying box for drying, and then ground and sieved to obtain raw material powder. The temperature of the drying oven is set to 80℃, the drying time is 4 hours, and the sieve used for sieving is 80 mesh sieve;

Preparation of SiC body: the raw material powder is prepared into a body after dry pressing and cold isostatic pressing. The dry pressing molding pressure can be 60MPa, the cold isostatic pressing molding pressure is 150MPa, and the pressure holding time is 3 minutes;

Preparation of high-purity SiC ceramics: After the green body is placed in a debonding furnace for vacuum debonding, it is then placed in an atmospheric sintering furnace for sintering to obtain high-purity and high-density SiC ceramics. The vacuum debonding temperature is 1100°C, the holding time is 30 minutes, and the vacuum degree is less than 50Pa. The sintering temperature is 2200°C, the holding time is 30 minutes, and the sintering atmosphere is atmospheric pressure argon atmosphere. The prepared high-purity SiC ceramic has a purity of about 99.5%, a density of 98.13%, a free carbon content of 0.14 wt%, and a B element content of 0.14 wt%.

Example 4

Preparation of SiC slurry: Weigh 2g of boric acid (addition of element B is 0.35wt% of ɑ-SiC powder mass) and 10g of glucose (addition of C element is 1.8wt% of ɑ-SiC powder mass), set In a glass beaker containing 30ml of deionized water, heat to 80°C to prepare a mixed solution. Weigh 100g of ɑ-SiC powder, 150g of absolute ethanol, 150g of SiC grinding balls and the prepared mixed solution and place them in a nylon ball milling tank. Place the ball mill in a planetary ball mill for ball milling. The average particle size of ɑ-SiC powder is 0.6μm, the purity is 99.86%, the diameter of the SiC grinding ball is 5mm, the speed of the ball mill is 300r/min, and the milling time is 24 hours;

The purity of the SiC ceramic prepared in Example 4 is about 99.5%, the density is 98.22%, the free carbon content is 0.14 wt%, and the B element content is 0.13 wt%. Figure 6 is an SEM image of the high-purity SiC ceramic prepared in Example 2 after corrosion. The result shows that the prepared SiC ceramic has clean grain boundaries and no obvious second phase.

Comparative example 1

Preparation of SiC slurry: Weigh 2g of boric acid (addition of element B is 0.35wt% of the mass of ɑ-SiC powder), place it in a glass beaker containing 30ml of deionized water, and heat to 80°C to prepare a mixed solution. Weigh 100g of ɑ-SiC powder, 150g of absolute ethanol, 150g of SiC grinding balls and the prepared mixed solution and place them in a nylon ball milling tank. Place the ball mill in a planetary ball mill for ball milling. The average particle size of ɑ-SiC powder is 0.6μm, the purity is 99.86%, the diameter of the SiC grinding ball is 5mm, the speed of the ball mill is 300r/min, and the milling time is 24 hours;

The density of the SiC ceramic prepared in this comparative example 1 is 52.94%. Figure 7 is an SEM image of the silicon carbide ceramic prepared in Comparative Example 1. The result shows that the sample is extremely non-compact and has a lot of pores.

Comparative example 2

Preparation of SiC slurry: Weigh 10g D-fructose (the amount of C element added is 1.8wt% of the mass of ɑ-SiC powder), place it in a glass beaker filled with 30ml deionized water, and heat it to 80°C to prepare a mixed solution . Weigh 100g of ɑ-SiC powder, 150g of absolute ethanol, 150g of SiC grinding balls and the prepared mixed solution and place them in a nylon ball milling tank. Place the ball mill in a planetary ball mill for ball milling. The average particle size of ɑ-SiC powder is 0.6μm, the purity is 99.86%, the diameter of the SiC grinding ball is 5mm, the speed of the ball mill is 300r/min, and the milling time is 24 hours;

The density of the SiC ceramic prepared in this comparative example 2 is 59.57%. Figure 8 is a BSD diagram of the silicon carbide ceramic prepared in Comparative Example 2. The results show that the sample is extremely non-compact, with a large number of pores, the sample is extremely non-compact, with a large number of pores, and there is more free carbon.

Claims

A method for preparing high-purity SiC ceramics is characterized in that it comprises:

(1) Add ɑ-SiC powder and an aqueous solution containing a sintering aid to a solvent and mix to obtain a SiC slurry. The sintering aid is a source of B and a source of C, the source of B is boric acid, and the source of C At least one selected from D-fructose and glucose;

(2) Drying and molding the obtained SiC slurry to obtain a SiC body;

(3) After vacuum debonding, the resulting SiC body is placed in an inert atmosphere and sintered at 2050-2250°C for 30-120 minutes to obtain the high-purity SiC ceramic;

The addition amount of the B element in the B source is 0.1 to 1 wt% of the mass of the ɑ-SiC powder, and the addition amount of the C element in the C source does not exceed 5 wt% of the mass of the ɑ-SiC powder.
The preparation method according to claim 1, wherein the average particle size of the ɑ-SiC powder is 0.1 to 1 μm; and the purity of the ɑ-SiC powder is ≥99.86%.
The preparation method according to claim 1 or 2, characterized in that the source B and the source C are added to water and heated to dissolve at 60-90° C. to obtain the aqueous solution containing the sintering aid.
The preparation method according to any one of claims 1 to 3, wherein the solvent is absolute ethanol or water.
The preparation method according to any one of claims 1 to 4, wherein the solid content of the SiC slurry is 20-60 wt%.
The preparation method according to any one of claims 1 to 5, wherein the drying temperature is 60-100°C, and the time is 3-8 hours.
The preparation method according to any one of claims 1 to 6, wherein the forming method is dry pressing or/and cold isostatic pressing; the pressure of the dry pressing is 5-100 MPa, The pressure of the cold isostatic pressing is 150 to 200 MPa, and the pressure holding time is 1 to 3 minutes.
The preparation method according to any one of claims 1-7, wherein the vacuum debonding temperature is 600-1200°C, the time is 30-120 minutes, and the vacuum degree is less than 100Pa.
A high-purity SiC ceramic prepared according to the preparation method of any one of claims 1-8, wherein the purity of the high-purity SiC ceramic is more than 99.5 wt%, and the density is more than 98%.
The high-purity SiC ceramic according to claim 9, wherein the free carbon content in the high-purity SiC ceramic is <0.15wt%; the O element content is <0.15wt%; the B element content is <0.15wt%; Except B, C, O and Si elements in pure SiC ceramics, the total amount of other elements is less than 0.015wt%.