Method for preparing dense ceramic from silica microspheres and long nanofibers

Abstract

The application discloses a method for preparing dense ceramics by using silica microspheres and long nanofibers, and belongs to the technical field of high-performance ceramic preparation. nw The carbon content is low, and the mechanical property is insufficient. Through the diffusion of the gas generated by the carbothermic reduction reaction, SiC is grown in the microspheres, and then the microspheres are mechanically mixed with a bonding agent. The ceramic green body is printed by SLS, and the polymer impregnation and pyrolysis process is optimized to obtain optical ceramics. The ceramic prepared by using the silica microspheres and the long nanofibers has a lower apparent porosity and a higher bulk density than a traditional 40 mu m commercial silica reference sample, and is more dense. The method simplifies the traditional composite process, and provides an efficient and low-cost preparation scheme for high-precision optical mirrors in the field of aviation and aerospace.

Description

Technical Field

[0001] This invention relates to the field of high-performance ceramic preparation technology, and particularly to a method for preparing dense ceramics by extending nanofibers within silica microspheres. Background Technology

[0002] Ceramics, with their superior high-temperature strength and mechanical stability, have become core materials in aerospace, energy, and other fields. However, traditional powder processing has significant limitations in shaping complex components and dispersing nanoparticles. While 3D printing technology offers possibilities for structural innovation, the uneven flow of traditional powders leads to defects in binder distribution. SiC nw Belonging to the category of one-dimensional linear nanomaterials, SiC exhibits few crystal defects, uniform composition, and high specific strength and specific elastic modulus. It is typically incorporated into ceramic matrix composites. nw This technology can improve the phase structure of composite materials and significantly enhance their mechanical properties. By using nanofiber technology within microspheres, it achieves a synergistic improvement in powder flowability and packing density, effectively promoting the uniform penetration of binders into the microsphere pores, significantly reducing the porosity of the preform, and enhancing structural compactness. Compared to traditional microparticle SLS printing technology, it is more effective in reducing interlayer voids and the residual Si and C content in silicon carbide ceramics. This technology enables the integrated additive manufacturing of complex silicon carbide ceramic components, simplifying the process while improving the material's mechanical properties, providing a key breakthrough for the industrial manufacturing of high-performance ceramics.

[0003] Chinese invention patent CN104785123A discloses a method for preparing hollow fiber ceramic membranes. First, a polymer solution is prepared and stirred thoroughly to obtain a spinning solution. The obtained spinning solution is poured into a stainless steel container and vacuum degassing is performed at room temperature for 2 hours to remove the air bubbles dissolved during stirring. The hollow fiber ceramic membrane precursor is obtained by air gap spinning.

[0004] Chinese invention patent CN104725031A discloses a method for in-situ growth of carbon nanofibers on the surface of hollow ceramic microspheres. It utilizes a non-solvent-induced phase separation principle to obtain a precursor for in-situ synthesis of carbon nanofibers / ceramic hollow microspheres. The precursor is then subjected to room temperature drying and carbonization sintering to finally obtain hollow microspheres of the carbon nanofiber / ceramic composite material.

[0005] In summary, most current hollow fiber processes are complex, costly, and involve interdependent and difficult-to-precise control of process parameters. Furthermore, the SLS printing process for ceramic powders requires precise control over powder shape and flowability. Therefore, developing a method for preparing micron-sized dense ceramic microspheres that is less dependent on raw materials, requires simpler equipment, and allows for easier control of process parameters is of great significance for the preparation of high-performance silicon carbide ceramics. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art by proposing a method for preparing nanofibers grown in situ within silica microspheres. The nanofibers have few crystal defects, uniform composition, and high specific strength and specific elastic modulus. By using a carbothermal reduction thermal evaporation method, silicon carbide nanofibers are grown in situ within silica microspheres, providing a method for preparing dense silica microspheres with low raw material dependence, simple process, and controllable process parameters.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] The method for in-situ growth of nanofibers within silica microspheres comprises the following steps:

[0009] Preparation of silica ceramic slurry: Silica powder is mixed with polymer and solvent in a certain proportion and added to a ball mill jar and mixed evenly to obtain a slurry. The polymer is polyethersulfone, chitosan or cellulose acetate, and the solvent is N-methylpyrrolidone, acetylacetone, acetone or dimethylacetamide. The mass fraction of silica powder is 20-50%, the mass fraction of polymer is 40-65%, and the mass fraction of solvent is 5-15%.

[0010] Preparation of silica microsphere precursor: Ceramic slurry is added to a syringe and electro-sprayed granulation is performed. The ionized micro-droplets are sprayed into a curing tank to undergo a cross-linking and curing reaction to form silica microspheres. The solution in the curing tank is one or a mixture of water, glycerol, and alcohol.

[0011] In-situ growth of nanowires: The prepared silica microspheres were cleaned with an alcohol solution and dried in an oven at a temperature of 35-55℃. Then, inert gas was introduced into a tube furnace to sinter and degrease the silica microspheres at a temperature of 1300-1600℃, a heating rate of 5-10℃, and a holding time of 3-6h. The resulting silica microspheres had a particle size distribution of 40-60μm.

[0012] SLS powder preparation: Silica microspheres with long internal nanowires are mixed with a binder using a mechanical mixing method to obtain a composite powder for SLS printing, wherein the mass fraction of the binder is controlled at 15-30%;

[0013] SLS printing: Set up the computer program for the SLS printing system and import the model slice data, then use SLS technology to print to obtain a ceramic blank;

[0014] Vacuum high-temperature pre-sintering: The printed optical ceramic preform is subjected to vacuum high-temperature pre-sintering in a tube furnace, allowing the binder to carbonize at high temperatures, with a vacuum degree of less than 10. -2Pa, temperature controlled at 800-1200℃;

[0015] Liquid silicon infiltration process: The obtained preform is subjected to liquid silicon infiltration treatment to remove residual Si and C from the sample, with a vacuum degree of less than 10. -3 Pa, with a silicon infiltration temperature of 1400-1750℃, ultimately yields a dense ceramic material.

[0016] The average particle size of the silica powder used in step (1) is 40 μm.

[0017] The adhesive used in further step (4) is phenolic resin or epoxy resin.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses the carbothermic reduction thermal evaporation method to grow silicon carbide nanowires on silicon dioxide microspheres, which makes the microspheres more fluid, reduces the porosity of the SLS printed blank, and reduces the residual Si and C in silicon carbide ceramics; (2) The SLS powder is prepared by mechanical mixing, which solves the problems of complex powder preparation process and serious environmental pollution, and ensures that the differences in physicochemical properties between powders are within a reasonable range, making it more suitable for SLS printing;

[0019] The resulting ceramic exhibits excellent mechanical properties; the nanowires enhance the bonding between the microspheres, improving the ceramic's strength and toughness. It also possesses good thermal properties, exhibiting high thermal conductivity and a low coefficient of expansion, enabling it to withstand high-temperature environments. Furthermore, this ceramic demonstrates excellent wear resistance and corrosion resistance, maintaining stable performance under harsh conditions, making it suitable for high-performance, complex structural components used in the aerospace field. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the preparation of dense ceramics by extending nanofibers inside silica microspheres, provided by the present invention.

[0021] Implementation Examples

[0022] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0023] Example 1

[0024] (1) Add silica powder with an average particle size of 40 μm and a mass fraction of 30%, N-methylpyrrolidone with a mass fraction of 10%, and polyethersulfone with a mass fraction of 60% to a ball mill jar and mix evenly to obtain a slurry.

[0025] (2) The slurry prepared in step (1) is electro-sprayed into granules. The tiny droplets sprayed out enter the curing tank and undergo cross-linking and curing reaction to form silica microspheres. The solution in the curing tank is a mixture of water, glycerol and alcohol.

[0026] (3) The silica microspheres prepared in step (2) were cleaned with alcohol solution and dried in an oven at 45°C. Then, inert gas was introduced into a tube furnace to sinter and degrease the silica microspheres at 1400°C, with a heating rate of 6°C / min and a holding time of 5h. The resulting silica microspheres had a particle size distribution of 40-60μm.

[0027] (4) In this example, silica ceramic microspheres with a particle size distribution of 40-60μm and long nanowires were screened out. The binder was phenolic resin. The mass ratio of silica ceramic microspheres to phenolic resin in the composite powder was 4:1.

[0028] (5) Set up the computer program for the SLS printing system and import the model slice data. Use SLS technology to print to obtain a ceramic blank.

[0029] (6) The silica ceramic blank printed in step (5) is subjected to vacuum high-temperature pre-sintering in a tube furnace to carbonize the binder at high temperature, while maintaining a vacuum level of 10. -3 Pa, temperature controlled at 1000℃.

[0030] (7) The blank obtained in step (6) is subjected to liquid silicon infiltration with a vacuum degree of less than 10. -3 Pa, with a silicon infiltration temperature of 1400℃, ultimately yields a dense ceramic material.

[0031] Example 2

[0032] (1) Add silica powder with an average particle size of 40 μm and a mass fraction of 40%, N-methylpyrrolidone with a mass fraction of 10%, and polyethersulfone with a mass fraction of 50% to a ball mill jar and mix evenly to obtain a slurry.

[0033] (2) The slurry prepared in step (1) is electro-sprayed into granules. The tiny droplets sprayed out enter the curing tank and undergo cross-linking and curing reaction to form silica microspheres. The solution in the curing tank is a mixture of water, glycerol and alcohol.

[0034] (3) The silica microspheres prepared in step (2) were cleaned with alcohol solution and dried in an oven at 55°C. Then, inert gas was introduced into a tube furnace to sinter and degrease the silica microspheres at 1500°C, with a heating rate of 6°C / min and a holding time of 5h. The resulting silica microspheres had a particle size distribution of 40-60μm.

[0035] (4) In this example, silica ceramic microspheres with a particle size distribution of 40-60μm and long nanowires were screened out. The binder was epoxy resin. The mass ratio of silica ceramic microspheres to epoxy resin in the composite powder was 7:3.

[0036] (5) Set up the computer program for the SLS printing system and import the model slice data. Use SLS technology to print to obtain a ceramic blank.

[0037] (6) The silica ceramic blank printed in step (5) is subjected to vacuum high-temperature pre-sintering in a tube furnace to carbonize the binder at high temperature, while maintaining a vacuum level of 10. -3 Pa, temperature controlled at 1200℃.

[0038] (7) The blank obtained in step (6) is subjected to liquid silicon infiltration with a vacuum degree of less than 10. -3 Pa, with a silicon infiltration temperature of 1600℃, ultimately yields a dense ceramic material.

Claims

1. A method for preparing dense ceramics using long nanofibers within silica microspheres, characterized in that, The method includes the following steps: (1) A slurry is prepared by mixing silica powder with a polymer and a solvent in a certain proportion and mixing them evenly in a ball mill jar. The polymer is polyethersulfone, chitosan or cellulose acetate, and the solvent is N-methylpyrrolidone, acetylacetone, acetone or dimethylacetamide. The mass fraction of silica powder is 20-50%, the mass fraction of polymer is 40-65%, and the mass fraction of solvent is 5-15%. (2) The slurry prepared in step (1) is electro-sprayed into granulation. The tiny droplets ionized by spraying are injected into the curing tank to undergo cross-linking and curing reaction to form silica microspheres. The solution in the curing tank is one or a mixture of water, glycerol, and alcohol. (3) The silica microspheres prepared in step (2) are cleaned with alcohol solution and dried in an oven at a temperature of 35-55℃. Then, inert gas is introduced into a tube furnace to sinter and degrease the silica microspheres at a temperature of 1300-1600℃, a heating rate of 5-10℃, and a holding time of 3-6h. The resulting silica microspheres have a particle size distribution of 40-60μm. (4) The silica microspheres with internal long nanowires prepared in step (3) are mixed with a binder by mechanical mixing to obtain a composite powder for SLS printing, wherein the mass fraction of the binder is controlled at 15-30%. (5) Set up the computer program for the SLS printing system and import the model slice data. Use SLS technology to print to obtain the ceramic blank. (6) The ceramic blank printed in step (5) is subjected to vacuum high-temperature pre-sintering in a tube furnace to carbonize the binder at high temperature, with a vacuum degree of less than 10. -2 Pa, temperature controlled at 800-1200℃. (7) The blank obtained in step (6) is subjected to liquid silicon infiltration with a vacuum degree of less than 10. -3 Pa, with a silicon infiltration temperature of 1400-1750℃, ultimately yields a dense ceramic material.

2. The method for preparing dense ceramics using long nanofibers within silica microspheres according to claim 1, characterized in that: The average particle size of the silica powder used in step (1) is 40 μm.

3. The method for preparing dense ceramics using long nanofibers within silica microspheres according to claim 1, characterized in that: The adhesive used in step (4) is phenolic resin or epoxy resin.

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