Hollow spherical nano silicon carbide powder as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ceramic materials, and particularly relates to hollow spherical nano silicon carbide powder as well as a preparation method and application thereof. The preparation method of the silicon carbide powder comprises the following steps: resorcinol and a formaldehyde solution are placed in an alkaline alcohol-water mixed solution for a condensation polymerization reaction, then tetraalkoxy silane is added for a hydrolysis condensation polymerization reaction, and phenolic resin coated silicon dioxide microspheres are obtained through a cocondensation polymerization reaction; and carrying out carbonization treatment to obtain carbon-coated silicon dioxide microspheres, and carrying out magnesiothermic reduction reaction to obtain the hollow spherical nano silicon carbide powder. The prepared hollow spherical nano silicon carbide powder is uniform in structure and high in sintering activity, in the process of preparing silicon carbide ceramic through sintering, the hollow structure is broken to generate a large number of new surfaces, the sintering driving force is enhanced, a sintering aid does not need to be introduced, and the silicon carbide ceramic can be obtained through rapid densification at low temperature; the microstructure and the mechanical property of the ceramic material can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic materials, and specifically relates to a hollow spherical nano-silicon carbide powder and its preparation method and application, and is particularly suitable for the preparation process of silicon carbide ceramic materials to increase ceramic density, reduce sintering temperature and improve performance. Background Art

[0002] Silicon carbide ceramics are widely used in aerospace, armor protection, nuclear energy engineering, chemical equipment and semiconductor fields due to their low density, high melting point, excellent mechanical properties, thermal properties, oxidation resistance and chemical stability. They are a structural ceramic material with important strategic value.

[0003] The excellent properties of silicon carbide are primarily due to its strongly covalently bonded crystal structure. However, the extremely high covalent bond content and extremely low surface self-diffusion coefficient of silicon carbide make it difficult to achieve dense sintering under conventional conditions. The production of fully densified silicon carbide ceramics using traditional sintering methods typically requires high temperatures exceeding 2000°C, which not only results in huge energy consumption but can also cause abnormal grain growth, thereby reducing the material's overall mechanical properties.

[0004] To address these issues, various technical solutions have been proposed to improve the sintering activity of silicon carbide, such as increasing the sintering pressure, extending the sintering time, or adding sintering aids to promote densification. However, these methods generally have certain limitations, such as the need for expensive high-temperature and high-pressure equipment, complex process conditions, and the potential for impurities introduced by the added sintering aids, which can affect the purity and high-temperature performance of silicon carbide ceramics.

[0005] During the ceramic sintering process, the sintering activity of the powder is a key factor in determining the densification efficiency. It is generally believed that the use of ultrafine nanopowders with smaller particle size and larger specific surface area can significantly improve sintering activity, thereby reducing sintering temperature, shortening holding time, increasing density, and optimizing microstructure. However, in practical applications, nanopowders are prone to agglomeration, resulting in an uneven ceramic microstructure and potentially inducing abnormal grain growth, which seriously affects the density and mechanical properties of the ceramic material. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of the prior art by providing a hollow spherical nano-silicon carbide powder, a preparation method, and applications thereof. By controlling the pH value of the system, the present invention precisely regulates the hydrolysis rate of tetraalkoxysilane, achieving precise control of the size of the silicon dioxide core layer, and thereby effectively regulating the particle size of the final silicon carbide powder. The resulting hollow spherical nanostructured silicon carbide powder has the characteristics of large specific surface area and high surface energy, significantly enhanced sintering activity, and can rapidly prepare dense, microstructurally uniform, and high-performance silicon carbide ceramics at low temperatures without introducing impurities.

[0007] To achieve the above technical objectives, the technical solution adopted in the embodiment of the present invention is: In a first aspect, an embodiment of the present invention provides a method for preparing hollow spherical nano-silicon carbide powder, comprising the following steps: (1) placing resorcinol and formaldehyde solution in an alkaline alcohol-water mixed solution for polycondensation reaction for 40-60 minutes, then adding tetraalkoxysilane for hydrolysis polycondensation reaction, and separating, washing and drying the co-polycondensation reaction product to obtain phenolic resin-coated silica microspheres; (2) carbonizing the phenolic resin-coated silica microspheres obtained in step (1) in an inert atmosphere to obtain carbon-coated silica microspheres; (3) mixing the carbon-coated silica microspheres obtained in step (2) with magnesium powder, performing a magnesium thermal reduction reaction in a protective atmosphere, and obtaining hollow spherical nano-silicon carbide powder after post-treatment; In step (1), the pH value of the alkaline alcohol-water mixed solution is 8-12.

[0008] Furthermore, in step (1), the volume ratio of anhydrous ethanol to deionized water in the alcohol-water mixed solution is 1:0.1-0.3.

[0009] Furthermore, in step (1), the tetraalkoxysilane includes one or more of tetramethoxysilane, tetraethoxysilane and tetrapropoxysilane.

[0010] Furthermore, in step (1), the mass ratio of the resorcinol to the formaldehyde solution is 1:1.2-1.5, the mass fraction of the formaldehyde solution is 30%-40%, and the mass ratio of the tetraalkoxysilane to the resorcinol is 6-9:1.

[0011] Furthermore, in step (2), the carbonization treatment is carried out in a nitrogen atmosphere at 700-800°C for 3-6 hours.

[0012] Furthermore, in step (3), the magnesium thermal reduction reaction is carried out by mixing carbon-coated silica microspheres and magnesium powder in a mass ratio of 1:0.6-0.8 and then loading the mixture into a sealed stainless steel reactor, and carrying out the reaction at 650-850°C under an argon atmosphere for 4-8 hours.

[0013] Furthermore, in step (3), the post-treatment includes the following steps: pickling with a hydrochloric acid solution having a concentration of 0.5-2 M to remove unreacted magnesium and generated magnesium oxide; drying the pickled product and calcining it at 600-800° C. in an air atmosphere to remove residual carbon; then etching with a hydrofluoric acid solution having a concentration of 0.5-2 M to remove residual silicon dioxide, and washing and drying to obtain hollow spherical nano-silicon carbide powder.

[0014] In the second aspect, the embodiment of the present invention provides a hollow spherical nano-silicon carbide powder, which is prepared by the preparation method described in the first aspect, wherein the particle size of the hollow spherical nano-silicon carbide powder is 280-720nm and the specific surface area is 110-150m 2 / g.

[0015] In a third aspect, an embodiment of the present invention provides an application of the hollow spherical nano-silicon carbide powder described in the second aspect, wherein the hollow spherical nano-silicon carbide powder is applied to prepare silicon carbide ceramics by low-temperature sintering, comprising the following steps: The hollow spherical nano-silicon carbide powder is loaded into a graphite mold, and the graphite mold is placed in a spark plasma sintering furnace and sintered under vacuum conditions. The sintering pressure is 40-70 MPa, the sintering temperature is controlled between 1700-1800°C, the heating rate is 50-200°C / min, and the holding time is 1-10 minutes. After the sintering is completed, the silicon carbide ceramic material is obtained by grinding.

[0016] Furthermore, the density of the silicon carbide ceramic material is 3.0-3.2 g / cm 3 , the relative density reaches 95%-99.9%, and the Vickers hardness is 25-33GPa.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adjusts the amount of ammonia added during the reaction to control the pH value of the system, thereby accurately adjusting the hydrolysis rate of tetraalkoxysilane, achieving precise control of the size of the silicon dioxide core layer, and further effectively regulating the particle size of the final silicon carbide powder. The obtained hollow spherical nanostructured silicon carbide powder has the characteristics of large specific surface area and high surface energy, and its sintering activity is significantly improved. It can quickly prepare dense, microstructured and high-performance silicon carbide ceramics at low temperature without introducing impurities.

[0018] (2) During the spark plasma sintering process for preparing silicon carbide ceramics, the hollow spherical shell structure collapses and breaks under the action of temperature and pressure, forming more small fragments. The presence of these fragments increases the surface energy of the system, thereby improving the sintering activity of the silicon carbide ceramics. High-density silicon carbide ceramics can be sintered at relatively low temperatures, effectively inhibiting abnormal grain growth and improving the structural uniformity and mechanical properties of the ceramic material. No sintering aids or impurities are required during the entire process, and the ceramic material has high purity and strong structural controllability. This preparation process is highly controllable and reduces energy consumption, is suitable for large-scale preparation, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 1 is the XRD spectrum of the hollow spherical nano-silicon carbide powder obtained in Example 1.

[0020] Figure 2 This is the SEM image of the hollow spherical nano-silicon carbide powder obtained in Example 1.

[0021] Figure 3 TEM image of the hollow spherical nano-silicon carbide powder obtained in Example 1.

[0022] Figure 4 This is the indentation image of the silicon carbide ceramic obtained in Example 1.

[0023] Figure 5 This is an SEM image of the fracture surface of the silicon carbide ceramic obtained in Example 1.

[0024] Figure 6 This is the SEM image of the hollow spherical nano-silicon carbide powder obtained in Example 2.

[0025] Figure 7 This is a TEM image of the hollow spherical nano-silicon carbide powder obtained in Example 2.

[0026] Figure 8 This is the indentation image of the silicon carbide ceramic obtained in Example 2.

[0027] Figure 9 This is the SEM image of the silicon carbide ceramic fracture obtained in Example 2.

[0028] Figure 10 This is the SEM image of the hollow spherical nano-silicon carbide powder obtained in Example 3.

[0029] Figure 11 This is a TEM image of the hollow spherical nano-silicon carbide powder obtained in Example 3.

[0030] Figure 12 This is the indentation image of the silicon carbide ceramic obtained in Example 3.

[0031] Figure 13 This is the SEM image of the silicon carbide ceramic fracture obtained in Example 3.

[0032] Figure 14 This is the indentation image of the silicon carbide ceramic obtained in Example 4.

[0033] Figure 15 This is an SEM image of the fracture surface of the silicon carbide ceramic obtained in Example 4.

[0034] Figure 16 This is the indentation image of the silicon carbide ceramic obtained in Example 5.

[0035] Figure 17 This is an SEM image of the fracture surface of the silicon carbide ceramic obtained in Example 5. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] Example 1 A method for preparing hollow spherical nano-silicon carbide powder comprises the following steps: (1) At room temperature, 6.5 mL of 28% ammonia water was added to a mixed solution consisting of 70 mL of anhydrous ethanol and 12 mL of deionized water. Subsequently, 0.4 g of resorcinol and 0.5 mL of 37% formaldehyde solution were added to the system and stirred for 40 min. Then, 3 mL of tetrapropoxysilane was added and the mixture was stirred at room temperature for 24 h. After the reaction was completed, the product was centrifuged, washed with water and ethanol in sequence, and then dried to obtain phenolic resin-coated silica microspheres. (2) carbonizing the phenolic resin-coated silica microspheres obtained in step (1) at 800° C. in a nitrogen atmosphere for 3 hours to obtain carbon-coated silica microspheres; (3) The carbon-coated silica microspheres were then mixed with magnesium powder in a mass ratio of 1:0.654, placed in a sealed stainless steel reactor, and heated to 660°C at a rate of 5°C / min under an argon atmosphere and kept at this temperature for 360 min to complete the magnesium thermal reduction reaction; The reaction product was washed with 2 M hydrochloric acid solution to remove unreacted magnesium and generated magnesium oxide, then calcined at 750°C in air atmosphere for 3 h to remove residual carbon, and finally etched with 2 M hydrofluoric acid solution to remove residual silicon dioxide. The product was washed with deionized water and dried to obtain hollow spherical nano-silicon carbide powder.

[0038] The specific surface area of ​​the powder was 133.746 m 2 / g. X-ray diffraction analysis showed that the powder is mainly 2H and 3C phase silicon carbide with high purity. Figure 1 As shown. SEM observation revealed that the obtained silicon carbide powder has a spherical structure with a spherical diameter of 492nm. Figure 2 As shown. TEM observation of a single hollow silicon carbide sphere revealed that it has a significant hollow structure, as shown Figure 3 As shown, it can be seen that the silicon carbide powder obtained above is a hollow spherical nanoporous structure.

[0039] The hollow spherical nano-silicon carbide powder is used for low-temperature sintering to prepare silicon carbide ceramics, comprising the following steps: The obtained hollow spherical nano-silicon carbide powder was loaded into a graphite mold coated with graphite paper, initially compacted at 40 MPa, and then placed in a spark plasma sintering furnace. The temperature was raised to 1750°C at a heating rate of 100°C / min, and the uniaxial pressure was gradually increased to 60 MPa. After keeping warm for 5 minutes, it was naturally cooled to room temperature. After cooling, the ceramic block was taken out, the surface carbon paper was removed, and it was ground and polished to finally obtain a dense, smooth-surfaced silicon carbide ceramic.

[0040] The density of silicon carbide ceramics was measured by Archimedes drainage method and was 3.1908 g / cm 3 , the relative density reaches 99.4%. Figure 4 As shown, its Vickers hardness is measured to be 31.13GPa. Figure 5 The figure shows the cross-sectional SEM image of silicon carbide ceramics. It can be seen that the cross-sectional structure of the ceramics is dense, the grains are evenly distributed, the particle size is at the nanometer level, and no obvious pores are observed.

[0041] Example 2 This example is basically the same as Example 1, except that the amount of ammonia water added in step (1) is adjusted to 1.85 mL. The final specific surface area is 148.887 m 2 / g of silicon carbide powder, SEM observation found that the obtained silicon carbide powder has a spherical structure with a spherical diameter of 294nm. Figure 6 As shown. TEM observation of a single hollow silicon carbide sphere revealed that it has a hollow structure, as shown Figure 7 As shown, it can be seen that the silicon carbide powder obtained above is a hollow spherical nanoporous structure.

[0042] The steps and process conditions for preparing silicon carbide ceramics by low-temperature sintering the hollow spherical nano-silicon carbide powder are the same as those in Example 1. After sintering the obtained hollow spherical porous silicon carbide powder, the density of the obtained silicon carbide ceramics was measured by the Archimedes drainage method to be 3.1549 g / cm³, and the relative density was 98.59%; the Vickers indentation diagram of the silicon carbide ceramic is as follows: Figure 8As shown in the figure, its Vickers hardness is measured to be 28.85 GPa. Figure 9 The figure shows a cross-sectional SEM image of silicon carbide ceramics. It can also be seen from the figure that the cross-section of the ceramic is dense, the grains are uniform and at the nanometer level.

[0043] Example 3 This example is basically the same as Example 1, except that the amount of ammonia water added in step (1) is adjusted to 7.4 mL. The final specific surface area is 114.443 m 2 / g of silicon carbide powder, SEM observation found that the obtained silicon carbide powder has a spherical structure with a spherical diameter of 686nm. Figure 10 As shown. TEM observation of a single hollow silicon carbide sphere revealed that it has a significant hollow structure, as shown Figure 11 As shown, it can be seen that the silicon carbide powder obtained above is a hollow spherical porous structure.

[0044] The steps and process conditions for low-temperature sintering the hollow spherical nano-silicon carbide powder to prepare silicon carbide ceramics are the same as those in Example 1. After sintering the obtained hollow spherical porous silicon carbide powder, the density of the obtained silicon carbide ceramics was 3.1921 g / cm³ and the relative density was 99.70% as measured by the Archimedes drainage method; the Vickers indentation of the silicon carbide ceramics was as follows: Figure 12 As shown in the figure, its Vickers hardness is measured to be 32.04 GPa. Figure 13 The figure shows a cross-sectional SEM image of silicon carbide ceramics. It can be observed that the ceramics also exhibit a dense structure with fine and uniform grains at the nanometer level.

[0045] Example 4 The preparation method of hollow spherical nano-silicon carbide powder in this embodiment is the same as that in Example 1, except that the sintering conditions are set differently when preparing silicon carbide ceramics by low-temperature sintering: The hollow spherical nano-silicon carbide powder obtained in Example 1 was loaded into a graphite mold coated with graphite paper and initially compacted at 40 MPa. The powder was then placed in a spark plasma sintering furnace and heated to 1700°C at a heating rate of 100°C / min. The uniaxial pressure was maintained at 40 MPa. After holding the temperature for 1 minute, the powder was naturally cooled to room temperature. After cooling, the ceramic block was taken out, the carbon paper on the surface was removed, and the powder was ground and polished to obtain a silicon carbide ceramic with a smooth surface.

[0046] The density of silicon carbide ceramics was measured by Archimedes drainage method and was 3.0486 g / cm 3 , the relative density reaches 95.26%. Figure 14 As shown in the figure, its Vickers hardness is measured to be 25.01 GPa. Figure 15The figure shows the cross-sectional SEM image of silicon carbide ceramics. It can be seen that the grains are small and evenly distributed, but there are a small amount of pores.

[0047] Example 5 The preparation method of hollow spherical nano-silicon carbide powder in this embodiment is the same as that in Example 1, except that the sintering conditions are set differently when preparing silicon carbide ceramics by low-temperature sintering: The hollow spherical nano-silicon carbide powder obtained in Example 1 was loaded into a graphite mold coated with graphite paper and initially compacted at 40 MPa. The powder was then placed in a spark plasma sintering furnace and heated to 1800°C at a heating rate of 100°C / min. The uniaxial pressure was gradually increased to 70 MPa. The powder was kept warm for 10 minutes and then naturally cooled to room temperature. After cooling, the ceramic block was taken out, the carbon paper on the surface was removed, and the powder was ground and polished to obtain a dense silicon carbide ceramic with a smooth surface.

[0048] The density of silicon carbide ceramics was measured by Archimedes drainage method and was 3.1943 g / cm 3 , the relative density reaches 99.82%. Figure 16 As shown, its Vickers hardness is measured to be 30.59GPa. Figure 17 The figure shows the cross-sectional SEM image of silicon carbide ceramics. It can be seen that the cross-sectional structure of the ceramics is dense and the grains are evenly distributed. As the sintering temperature increases and the holding time increases, the grain size increases.

[0049] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing hollow spherical nano-silicon carbide powder, characterized in that: The following steps are involved: (1) placing resorcinol and formaldehyde solution in an alkaline alcohol-water mixed solution for polycondensation reaction for 40-60 minutes, then adding tetraalkoxysilane for hydrolysis polycondensation reaction, and separating, washing and drying the co-polycondensation reaction product to obtain phenolic resin-coated silica microspheres; (2) carbonizing the phenolic resin-coated silica microspheres obtained in step (1) in an inert atmosphere to obtain carbon-coated silica microspheres; (3) mixing the carbon-coated silica microspheres obtained in step (2) with magnesium powder, performing a magnesium thermal reduction reaction in a protective atmosphere, and obtaining hollow spherical nano-silicon carbide powder after post-treatment; In step (1), the pH value of the alkaline alcohol-water mixed solution is 8-12.

2. The method for preparing hollow spherical nano-silicon carbide powder according to claim 1, characterized in that: In step (1), the volume ratio of anhydrous ethanol to deionized water in the alcohol-water mixed solution is 1:0.1-0.

3.

3. The method for preparing hollow spherical nano-silicon carbide powder according to claim 1, characterized in that: In step (1), the tetraalkoxysilane includes one or more of tetramethoxysilane, tetraethoxysilane and tetrapropoxysilane.

4. The method for preparing hollow spherical nano-silicon carbide powder according to claim 1, characterized in that: In step (1), the mass ratio of the resorcinol to the formaldehyde solution is 1:1.2-1.5, the mass fraction of the formaldehyde solution is 30%-40%, and the mass ratio of the tetraalkoxysilane to the resorcinol is 6-9:

1.

5. The method for preparing hollow spherical nano-silicon carbide powder according to claim 1, characterized in that: In step (2), the carbonization treatment is carried out in a nitrogen atmosphere at 700-800°C for 3-6 hours.

6. The method for preparing hollow spherical nano-silicon carbide powder according to claim 1, characterized in that: In step (3), the magnesium thermal reduction reaction is to mix carbon-coated silica microspheres and magnesium powder in a mass ratio of 1:0.6-0.8 and then put them into a sealed stainless steel reactor, and carry out the reaction at 650-850°C under an argon atmosphere for 4-8 hours.

7. The method for preparing hollow spherical nano-silicon carbide powder according to claim 1, characterized in that: In step (3), the post-treatment includes the following steps: pickling with a hydrochloric acid solution having a concentration of 0.5-2 M, drying the pickled product and calcining it at 600-800° C. in an air atmosphere, then etching with a hydrofluoric acid solution having a concentration of 0.5-2 M, and washing and drying to obtain hollow spherical nano-silicon carbide powder.

8. A hollow spherical nano-silicon carbide powder, characterized in that: The hollow spherical nano-silicon carbide powder is prepared by the preparation method according to any one of claims 1 to 7, wherein the particle size of the hollow spherical nano-silicon carbide powder is 280-720 nm and the specific surface area is 110-150 m 2 / g.

9. The use of the hollow spherical nano-silicon carbide powder according to claim 8, characterized in that: The hollow spherical nano-silicon carbide powder is used in the preparation of silicon carbide ceramics by low-temperature sintering, which includes the following steps: The hollow spherical nano-silicon carbide powder is loaded into a graphite mold, and the graphite mold is placed in a spark plasma sintering furnace and sintered under vacuum conditions. The sintering pressure is 40-70 MPa, the sintering temperature is controlled between 1700-1800°C, the heating rate is 50-200°C / min, and the holding time is 1-10 minutes. After the sintering is completed, the silicon carbide ceramic material is obtained by grinding.

10. The use of the hollow spherical nano-silicon carbide powder according to claim 9, characterized in that: The density of the silicon carbide ceramic material is 3.0-3.2 g / cm 3 , the relative density reaches 95%-99.9%, and the Vickers hardness is 25-33GPa.

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