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CN-121974708-A - Silicon nitride ceramic microsphere based on sol-gel forming and reaction sintering and preparation method thereof

CN121974708ACN 121974708 ACN121974708 ACN 121974708ACN-121974708-A

Abstract

The invention discloses a silicon nitride ceramic microsphere based on sol-gel forming and reaction sintering and a preparation method thereof. The method adopts nano silicon powder as a silicon source to replace silicon nitride powder with higher price, and utilizes the high reactivity of the silicon nitride powder to generate silicon nitride through in-situ nitridation reaction. Zirconium oxychloride (ZrOCl 2 ) is selected as a zirconium source with the dual functions of gelation and sintering auxiliary agents, concentrated hydrochloric acid is matched for stabilizing glue solution, a catalyst is introduced, and microsphere molding is realized through a sol-gel process. The obtained liquid drops are molded in hot silicone oil, washed, dried and subjected to reaction sintering to convert a zirconium source into zirconium oxide so as to promote densification of silicon nitride. The finally prepared silicon nitride ceramic microsphere has good sphericity, high density, high nitriding rate and low impurity content, and the inside of the microsphere takes beta-silicon nitride as a main phase. The invention effectively solves the problems of easy cracking, high carbon impurity content and unstable nitriding rate of the microspheres in the traditional process, and provides a new way for preparing the high-performance silicon nitride ceramic microspheres at low cost.

Inventors

  • XU RUI
  • MA JINGTAO
  • DENG CHANGSHENG
  • LI ZIQIANG
  • ZHAO XINGYU
  • HAO SHAOCHANG
  • LI JIANJUN
  • LIU BING
  • TANG YAPING

Assignees

  • 清华大学

Dates

Publication Date
20260505
Application Date
20260202

Claims (10)

  1. 1. The preparation method of the silicon nitride ceramic microsphere based on sol-gel molding and reaction sintering is characterized by comprising the following steps of: (1) Mixing nano silicon powder, zrOCl 2 , concentrated hydrochloric acid, HMTA and urea, adding deionized water to fix the volume, and performing ultrasonic dispersion to obtain uniform glue solution; (2) Dripping the glue solution into hot dimethyl silicone oil through a liquid drop dispersing device, forming the liquid drops into spheres by utilizing surface tension, and completing gelation in the hot dimethyl silicone oil to obtain wet gel microspheres; (3) Ageing the wet gel microspheres in hot dimethyl silicone oil, and then sequentially adopting trichloroethylene, ammonia water and propylene glycol methyl ether to carry out combined washing; (4) Drying the washed gel microspheres to obtain dry gel microspheres; (5) And degreasing the dry gel microspheres in an air atmosphere, and then sintering in a protective atmosphere to obtain the silicon nitride ceramic microspheres.
  2. 2. The method of claim 1, wherein in step (1), the molar ratio of HMTA to zirconium ion is 1.1 to 1.5 and the molar ratio of urea to zirconium ion is 1.0 to 1.3, calculated as ZrO2 + .
  3. 3. The method according to claim 1, wherein the concentration of ZrOCl 2 in the dope is 0.1-0.5 mol/L; and/or the concentration of the nano silicon powder in the glue solution is 0.8-1.2 mol/L; and/or the particle size of the nano silicon powder is 1-500 nm; And/or the adding amount of the concentrated hydrochloric acid in the step (1) is satisfied that for zirconium ions with initial concentration of 0.1mol/L, 0.3-0.7 mL of the concentrated hydrochloric acid is added to each 50mL of the glue solution, and then each 0.1mol/L of the zirconium ion concentration is increased, and 0.5-1.5 mL of the concentrated hydrochloric acid is correspondingly increased.
  4. 4. The method of claim 1, wherein the glue solution further comprises a catalyst, the catalyst is nickel salt or iron salt, and the concentration of the catalyst in the glue solution is 0.05-0.15 mol/L.
  5. 5. The method of claim 1, wherein the temperature of the hot simethicone in step (2) is 75-95 ℃; And/or, the liquid drop dispersing device in the step (2) is provided with a circulating cooling system, so that the glue solution is not gelled in advance in the dropping process.
  6. 6. The method of claim 1, wherein the aging time in step (3) is 12 to 24 hours; And/or, in the step (3), the trichloroethylene, the ammonia water and the propylene glycol methyl ether are sequentially adopted to carry out combined washing for 2-3 times, 10-20 minutes each time, 1-2 times, 2-5 minutes each time, and 1-2 times, 2-5 minutes each time, by adopting the trichloroethylene and the ammonia water.
  7. 7. The method of claim 1, wherein the drying in step (4) is performed at 60 to 80 ℃ for 12 to 24 hours.
  8. 8. The method of claim 1, wherein the degreasing and sintering processes in the step (5) are controlled by temperature programming, and are sequentially carried out at 140-180 ℃, 230-270 ℃, 280-300 ℃, 420-480 ℃ and 1000-1200 ℃ for 1-2 hours, and sintered at 1400-1600 ℃ for 2-8 hours, wherein the temperature is raised to 420-480 ℃ and the previous stage is carried out in an air atmosphere to finish degreasing, and then the temperature is switched to a nitrogen or ammonia atmosphere and is continuously raised to the reaction sintering temperature.
  9. 9. Silicon nitride ceramic microspheres based on sol-gel forming and reaction sintering, which are prepared by the method of any one of claims 1-8, and are characterized in that the particle size of the microspheres is 500-700 μm, and the sphericity is 1.02-1.05.
  10. 10. The silicon nitride ceramic microspheres according to claim 9, wherein the density of the silicon nitride ceramic microspheres is 2.0-2.5 g/cm 3 , the nitriding rate is not lower than 90%, the silicon nitride mass fraction is not lower than 50%, and the carbon content is not higher than 10%.

Description

Silicon nitride ceramic microsphere based on sol-gel forming and reaction sintering and preparation method thereof Technical Field The invention relates to the technical field of advanced ceramic material preparation, in particular to a silicon nitride ceramic microsphere based on sol-gel forming and reaction sintering and a preparation method thereof. Background Silicon nitride (Si 3N4) ceramic microspheres have irreplaceable importance in the fields of high-speed precise bearings, grinding media, high-end functional fillers and the like due to excellent high hardness, low density, wear resistance and chemical stability. Currently, the main technical route for preparing silicon nitride ceramic microspheres in the industry and academia generally uses commercial Si 3N4 powder as a starting material. The specific process comprises adding sintering aid (such as Y 2O3、Al2O3) into Si 3N4 powder, preparing microsphere green compact by physical methods such as dry pressing/cold isostatic pressing, hot isostatic pressing, ball forming or spray granulation, and sintering and densification at high temperature to obtain the final product. However, this conventional process, starting with Si 3N4 powder, presents a series of technical bottlenecks that are difficult to break through. Firstly, the high-quality Si 3N4 powder has high cost, the morphology of the Si 3N4 powder particles is unfavorable for realizing uniform and compact particle accumulation in the subsequent forming process, and defects (such as layering, core inclusion and cracks) are extremely easy to introduce into the green compact. The problem is particularly remarkable when preparing micron-sized fine microspheres. Secondly, both pressing and spray granulation are physical agglomeration processes. The spray granulation method is characterized in that the solvent is volatilized violently in the rapid drying process of liquid drops, hollow structures are formed inside microspheres or pits are formed on the surfaces of the microspheres easily, and the strength and consistency of the final product are seriously affected. In addition, the physical method is extremely sensitive to the characteristics of fluidity, particle size distribution and the like of raw material powder, has a narrow process window and is poor in stability in large-scale production. More importantly, the existing method can not fundamentally solve the essential problem of insufficient sintering driving force of the Si 3N4 ceramic. Si 3N4 as a strongly covalent compound has a very low atomic self-diffusion coefficient and it is difficult to achieve complete densification by conventional solid phase sintering. Therefore, it is necessary to rely on a large amount of sintering aid and keep the temperature at an extremely high temperature for a long time, which not only significantly increases the energy consumption and cost, but also may deteriorate the high temperature performance and dielectric properties of the material due to the residue of the sintering aid. Disclosure of Invention The present invention aims to solve at least one of the technical problems in the related art to some extent. Therefore, the embodiment of the invention provides a silicon nitride ceramic microsphere based on sol-gel molding and reaction sintering and a preparation method thereof. Different from the traditional path of starting from Si 3N4 powder and ending from Si 3N4 products in the prior art, the invention provides a brand-new in-situ forming-reaction synthesis strategy, expensive commercial Si 3N4 powder is abandoned, and nano silicon powder with lower cost and higher reactivity is selected as a silicon source. The nanometer silicon powder is uniformly dispersed in a controllable gel system to form silicon-based gel microspheres which are uniform in components and complete and have no cracks, and then silicon in situ reacts in nitrogen or ammonia atmosphere by utilizing a reaction sintering mechanism to generate Si 3N4. The method can avoid structural defects caused by physical molding from the source, and can compensate sintering shrinkage by utilizing the volume expansion effect in the reaction process, so that the Si 3N4 ceramic microsphere with more complete structure and better performance is hopefully obtained. In a first aspect, the invention provides a method for preparing silicon nitride ceramic microspheres based on sol-gel molding and reaction sintering, which comprises the following steps: (1) Mixing nano silicon powder, zrOCl 2, concentrated hydrochloric acid, HMTA and urea, adding deionized water to fix the volume, and performing ultrasonic dispersion to obtain uniform glue solution; (2) Dripping the glue solution into hot dimethyl silicone oil through a liquid drop dispersing device, forming the liquid drops into spheres by utilizing surface tension, and completing gelation in the hot dimethyl silicone oil to obtain wet gel microspheres; (3) Ageing the wet gel microspheres in hot dimethyl s