A kind of full hollow silicon carbide microbead and its preparation method

Abstract

The application discloses full-hollow silicon carbide microbeads and a preparation method thereof, and belongs to the field of inorganic filler preparation. The method comprises the following steps: mixing silicon powder and silica sol according to a mixing ratio, and spraying and drying the mixture into microbeads by a spray dryer; performing film coating treatment, drying treatment, solidification treatment and carbonization treatment on the microbeads to obtain carbonized microbeads; performing sintering treatment on the carbonized microbeads, infiltrating the outer film with liquid silicon, and generating a silicon carbide shell; the silicon dioxide in the core and the liquid silicon react to generate silicon monoxide gas which is discharged, and the discharged silicon monoxide gas reacts with carbon in the outer shell to generate full-hollow silicon carbide microbeads. The application not only solves the problem that the core of the hollow silicon carbide microbeads prepared by the prior art is in a honeycomb or layered form and is not completely hollow, greatly reduces the weight of the silicon carbide microbeads, but also effectively enhances the strength of the silicon carbide microbeads, and avoids the problem of breakage of the full-hollow silicon carbide microbeads.

Description

Technical Field

[0001] This invention belongs to the field of inorganic filler preparation, specifically the preparation of hollow microspheres, and more specifically relates to a fully hollow silicon carbide microsphere and its preparation method. Background Technology

[0002] Hollow microspheres, as a novel multifunctional material, possess excellent physical and chemical properties. As a filler, when incorporated into composite materials through specific processes, their overall performance can be several times or even tens of times better than that of the matrix material. Hollow silicon carbide microspheres, when used in metals, can replace lithium in reducing weight and strengthening the metal. Without altering the original metal's properties, they can transform it into a lighter and stronger material, such as magnesium alloys, aluminum alloys, titanium alloys, and stainless steel, thereby creating ultralight, high-strength, and low-expansion metal-based composite materials. Such materials possess processing properties such as weldability, extrusion molding, die casting, and casting, making them suitable for applications where weight reduction is paramount, i.e., where every gram counts. They are particularly useful in aerospace, rockets and satellites, loitering munitions, and bulletproof armor, and can also be used in civilian applications such as drones, electric vehicles, and maglev high-speed trains.

[0003] CN112047343A discloses a method for preparing hollow silicon carbide microspheres. The method uses graphene oxide and carbon nanotubes as raw materials to prepare porous graphite microspheres, then coats the porous graphite microspheres with silica sol modified with a silane coupling agent, and finally strengthens them with silicon nitride and silicon carbide micropowder to form dense hollow silicon carbide microspheres. This method yields surface-reinforced and dense hollow silicon carbide microspheres. However, it cannot solve the problem of sufficient contact between the silicon and carbon sources, resulting in a relatively high carbon content and low strength in the microspheres.

[0004] CN1l5521162A discloses a method for preparing hollow silicon carbide microspheres, which allows layered graphene to fully contact with silica sol, with the layered graphene uniformly distributed in silica gel, and the silicon source and carbon source able to fully react. However, the layered graphene is distributed in a layered or honeycomb pattern within the silica sol, and the prepared hollow silicon carbide microspheres have a honeycomb or layered core and are not completely hollow. Summary of the Invention

[0005] In view of the above-mentioned problems existing in the prior art, the first technical problem to be solved by the present invention is to provide a method for preparing fully hollow silicon carbide microspheres; the second technical problem to be solved by the present invention is to provide fully hollow silicon carbide microspheres prepared by the method.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for preparing fully hollow silicon carbide microspheres includes the following steps:

[0008] S1. Mix silicon powder and silica sol according to the dosage ratio, and then spray dry them into microbeads using a spray dryer;

[0009] S2. The microspheres are coated, dried, cured and carbonized to obtain carbonized microspheres.

[0010] S3. The carbonized microspheres are sintered, and the liquefied elemental silicon is impregnated into the outer film to form a silicon carbide shell; the silicon dioxide in the core and the liquid silicon react to generate silicon monoxide gas, which is then discharged to form a completely hollow silicon carbide microsphere.

[0011] A method for preparing fully hollow silicon carbide microspheres specifically includes the following steps:

[0012] (1) Mix elemental silicon powder and silica sol according to the dosage ratio, and then spray dry them into microbeads using a spray dryer;

[0013] (2) Coating the microbeads with a coating agent to obtain coated microbeads;

[0014] (3) The coated microbeads are placed in a reaction vessel and dried and cured by heating with vegetable oil as a medium to obtain cured microbeads.

[0015] (4) The solidified microspheres are carbonized in a carbonization furnace to obtain carbonized microspheres.

[0016] (5) The carbonized microspheres are placed in a silicon carbide sintering furnace for sintering treatment. The liquefied elemental silicon wets the outer coating to generate a silicon carbide shell. The silicon dioxide in the core and the liquid phase silicon react to generate silicon monoxide gas, which is discharged to form a hollow silicon carbide microsphere. The discharged silicon monoxide gas reacts with the carbon on the surface of the shell to further generate a dense silicon carbide shell.

[0017] In some embodiments of the present invention, in step (1), elemental silicon powder and silica sol are mixed in a ratio of 1 to 5: 5 to 10.

[0018] In some embodiments of the present invention, in step (1), elemental silicon powder and silica sol are mixed in a ratio of 1 to 3: 2 to 7.

[0019] Preferably, in some embodiments of the present invention, in step (1), elemental silicon powder and silica sol are mixed in a ratio of 3:7.

[0020] In some embodiments of the present invention, in step (1), the silicon powder is made of polycrystalline silicon, monocrystalline silicon, or metallic silicon, and is ground into ultrafine elemental silicon powder.

[0021] In some embodiments of the present invention, in step (1), the particle size of the elemental silicon powder is 0.1 μm to 5 μm.

[0022] In some embodiments of the present invention, in step (2), the coating agent is a water-soluble phenolic resin.

[0023] In some embodiments of the present invention, in step (2), the coating agent is a sucrose solution.

[0024] In some embodiments of the present invention, in step (3), when drying and curing the microspheres, peanut oil is used as a medium for heating to perform the drying and curing processes.

[0025] In some embodiments of the present invention, in step (3), the drying temperature is 80°C to 200°C and the drying time is 10 to 60 minutes.

[0026] In some embodiments of the present invention, in step (3), the curing temperature is 120-170°C and the curing time is 30-120 min.

[0027] Preferably, in some embodiments of the present invention, the curing temperature in step (3) is 150°C.

[0028] In some embodiments of the present invention, in step (4), the carbonization temperature is 800-1000°C and the carbonization time is 60-180 min.

[0029] Preferably, in some embodiments of the present invention, the carbonization time in step (4) is 70 min.

[0030] In some embodiments of the present invention, in step (5), the sintering temperature is 1400-2000°C and the sintering time is 2-6 hours.

[0031] Preferably, in some embodiments of the present invention, the sintering time in step (5) is 5 hours.

[0032] In some embodiments of the present invention, in step (5), the silicon dioxide and liquid silicon in the core react at 1800°C to 2000°C to generate silicon monoxide gas, which is then discharged to form hollow silicon carbide microspheres; the discharged silicon monoxide gas reacts with the carbon on the surface of the outer shell to generate a dense silicon carbide outer shell.

[0033] Hollow silicon carbide microspheres were prepared by the above method.

[0034] The beneficial effects of this invention are as follows:

[0035] This invention uses a mixture of silicon and silicon dioxide as the core. The silicon and silicon dioxide react in a reduction reaction to generate silicon monoxide gas, which is then released. This released silicon monoxide gas reacts with the carbon coating on the outer shell to form fully hollow silicon carbide microspheres. This invention not only solves the problem that the core of hollow silicon carbide microspheres prepared in the prior art is honeycomb or layered and not completely hollow, greatly reducing the weight of the silicon carbide microspheres, but also achieves a lower density for the same strength, effectively enhancing the strength of the silicon carbide microspheres and avoiding the breakage problem of fully hollow silicon carbide microspheres. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The technical solutions provided by each embodiment of this invention will be described in detail below with reference to the embodiments.

[0037] Example 1

[0038] Polycrystalline silicon (purchased from Dezhou Jinghuo Technology Glass Co., Ltd.) was ground into ultrafine elemental silicon powder. The elemental silicon powder was mixed with silica sol (silica content of 30%, purchased from Zhengzhou Yunchuang Chemical Products Co., Ltd.) at a ratio of 3g:7mL, and spray-dried into microbeads using a spray dryer. The spray inlet temperature was set to 180-200℃, the spray outlet temperature to 70-100℃, the spray interval to 3-5 seconds, the spray time to 1-2 seconds, and the spray pressure to 10-20MPa. The microspheres were then coated with a 20% sucrose solution at a 1:1 ratio. The coated microspheres were then placed in a reactor and dried and cured using peanut oil as a heating medium. The drying temperature was 100℃ for 30 minutes, and the curing temperature was 140℃ for 120 minutes. The cured microspheres were then carbonized in a carbonization furnace at 800℃ for 180 minutes. The carbonized microspheres were then sintered in a silicon carbide sintering furnace at 1800℃ for 5 hours. The liquefied elemental silicon impregnated the outer coating, forming a silicon carbide shell. The silicon dioxide and liquid silicon in the core reacted at 1800℃–2000℃ to generate silicon monoxide gas, which was then released, forming fully hollow silicon carbide microspheres. The released silicon monoxide gas reacted with the carbon on the shell surface to form a dense silicon carbide shell.

[0039] The particle size, isostatic compressive strength, and density of the fully hollow silicon carbide microspheres prepared according to the JC / T 2284-2014 standard are as follows:

[0040] The hollow silicon carbide microspheres have a particle size of 10–20 μm, an isostatic compressive strength (hydraulic pressure method) of 200 MPa, and a density of 0.9 g / cm³. 3 .

[0041] Example 2

[0042] Monocrystalline silicon (purchased from Dezhou Jinghuo Technology Glass Co., Ltd.) was ground into ultrafine elemental silicon powder. The elemental silicon powder was mixed with silica sol (silica content of 30%, purchased from Zhengzhou Yunchuang Chemical Products Co., Ltd.) at a ratio of 3g:7mL, and then spray-dried into microbeads using a spray dryer. The spray inlet temperature was set to 180-200℃, the spray outlet temperature to 70-100℃, the spray interval to 3-5 seconds, the spray time to 1-2 seconds, and the spray pressure to 10-20MPa. Then, 11% (by weight) of water-soluble phenolic resin (purchased from Shanghai Maclean Biochemical Technology Co., Ltd., purity: BR) was mixed with the microspheres at a 1:1 ratio to form coated microspheres. The coated microspheres were then placed in a reaction vessel and dried and cured using peanut oil as a heating medium to obtain cured microspheres. The drying temperature was 200℃ for 20 minutes, and the curing temperature was 170℃ for 30 minutes. After curing, the microspheres are carbonized in a carbonization furnace at 1000℃ for 60 minutes to obtain carbonized microspheres. The carbonized microspheres are then placed in a silicon carbide sintering furnace and sintered at 2000℃ for 2 hours. The liquefied elemental silicon impregnates the outer coating to form a silicon carbide shell. The silicon dioxide and liquid silicon in the core react at 1800℃~2000℃ to generate silicon monoxide gas, which is then released to form a completely hollow silicon carbide microsphere. The released silicon monoxide gas reacts with the carbon on the surface of the shell to form a dense silicon carbide shell.

[0043] The particle size, isostatic compressive strength, and density of the fully hollow silicon carbide microspheres prepared according to the JC / T 2284-2014 standard are as follows:

[0044] The hollow silicon carbide microspheres have a particle size of 10–20 μm, an isostatic compressive strength (hydraulic pressure method) of 200 MPa, and a density of 0.9 g / cm³. 3 .

[0045] Example 3

[0046] Metallic silicon (purchased from Dezhou Jinghuo Technology Glass Co., Ltd.) was ground into ultrafine elemental silicon powder. The elemental silicon powder was mixed with silica sol (silica content of 30%, purchased from Zhengzhou Yunchuang Chemical Products Co., Ltd.) at a ratio of 3g:7mL, and spray-dried into microbeads using a spray dryer. The spray inlet temperature was set to 180-200℃, the spray outlet temperature to 70-100℃, the spray interval to 3-5 seconds, the spray time to 1-2 seconds, and the spray pressure to 10-20MPa. The microspheres were then coated with a 22% sucrose solution at a 1:1 ratio. The coated microspheres were then placed in a reactor and dried and cured using peanut oil as a heating medium. The drying temperature was 80℃ for 60 minutes, and the curing temperature was 120℃ for 120 minutes. The cured microspheres were then carbonized in a carbonization furnace at 900℃ for 120 minutes. The carbonized microspheres were then sintered in a silicon carbide sintering furnace at 1800℃ for 4 hours. The liquefied elemental silicon impregnated the outer coating, forming a silicon carbide shell. The silicon dioxide and liquid silicon in the core reacted at 1800℃–2000℃ to generate silicon monoxide gas, which was then released, forming fully hollow silicon carbide microspheres. The released silicon monoxide gas reacted with the carbon on the shell surface to form a dense silicon carbide shell.

[0047] The particle size, isostatic compressive strength, and density of the fully hollow silicon carbide microspheres prepared according to the JC / T 2284-2014 standard are as follows:

[0048] The hollow silicon carbide microspheres have a particle size of 10–20 μm, an isostatic compressive strength (hydraulic pressure method) of 200 MPa, and a density of 0.9 g / cm³. 3 .

[0049] Comparative Example 1

[0050] 3% by mass of 3-10 layers of few-layer graphene (purchased from Anhui Mujia New Material Technology Co., Ltd.) and 15% by mass of silica sol (the silica sol contains 30% silica and was purchased from Zhengzhou Yunchuang Chemical Products Co., Ltd.) were mixed, and 7% by mass of 95% ethanol aqueous solution was added to obtain a mixed sol. Then, 0.09% by mass of ammonia water was added to form an alcohol gel.

[0051] An aging agent consisting of 3% silica sol and 10% 95% ethanol aqueous solution was added to age the alcohol gel at 50°C for 14 hours. Then, 14.91% trimethylchlorosilane was added for modification at 50°C for 120 minutes. Finally, 15% n-hexane was added for solvent replacement at 45°C for 4 hours.

[0052] Then, the solvent-displaced alcohol gel was placed in a dryer for graded drying. The first-stage drying temperature was 70℃ and the first-stage drying time was 2h. The second-stage drying temperature was 100℃ and the second-stage drying time was 2h. The third-stage drying temperature was 130℃ and the third-stage drying time was 2h, thus preparing the aerogel.

[0053] Aerogel was pulverized into fine aerogel particles with a particle size of 75µm-100µm using an air jet mill. The fine aerogel particles were then processed using a spherical shaping machine with a cylindrical grinding media rotation speed of 2500rpm and a processing time of 120min to prepare aerogel microspheres.

[0054] A 10% (w / w) solution of 22% sucrose (22g sucrose dissolved in distilled water, diluted to 100ml) was added to coat the aerogel microspheres. The microspheres were then dried using an airflow dryer with an inlet temperature of 250℃, an outlet temperature of 70℃, and a drying time of 30s. Following this, the microspheres underwent curing in a dryer for 3 hours at 140℃. Finally, they were carbonized in a muffle furnace for 3 hours at 500℃ to obtain porous graphite microspheres. Hollow silicon carbide microspheres were then prepared by mixing 22% (w / w) silicon powder (3000 mesh particle size, purchased from Shandong Dezhou Jinghuo Company) with the porous graphite microspheres and sintering them in a silicon carbide sintering furnace for 4 hours at 1800℃.

[0055] The particle size, isostatic compressive strength, and density of the hollow silicon carbide microspheres prepared according to the JC / T 2284-2014 standard are as follows:

[0056] The hollow silicon carbide microspheres have a particle size of 75-100 μm, an isostatic compressive strength (hydraulic pressure method) of 140 MPa, and a density of 0.5 g / cm³.

Claims

1. A method for preparing fully hollow silicon carbide microspheres, characterized in that, Includes the following steps: S1. Mix silicon powder and silica sol according to the dosage ratio, and then spray dry them into microbeads using a spray dryer; S2. The microspheres are coated, dried, cured and carbonized to obtain carbonized microspheres. S3. The carbonized microspheres are sintered, and the liquefied elemental silicon wets the outer film to form a silicon carbide shell; the silicon dioxide and liquid silicon in the core react to generate silicon monoxide gas, which is then discharged to form a completely hollow silicon carbide microsphere. In step S1, the silicon powder is elemental silicon powder; the average particle size of the elemental silicon powder is 0.1 μm to 5 μm.

2. The method for preparing fully hollow silicon carbide microspheres according to claim 1, characterized in that, In step S1, silicon powder and silica sol are mixed in a ratio of 1-5:2-10.

3. The method for preparing fully hollow silicon carbide microspheres according to claim 2, characterized in that, In step S1, silicon powder and silica sol are mixed in a ratio of 1-3:2-7.

4. The method for preparing fully hollow silicon carbide microspheres according to claim 1, characterized in that, In step S2, the microbeads are coated with a coating agent, which is one of water-soluble phenolic resin and sucrose solution.

5. The method for preparing fully hollow silicon carbide microspheres according to claim 1, characterized in that, In step S2, when drying and curing the microspheres, peanut oil is used as a medium for heating to carry out the drying and curing processes. The drying temperature is 80℃~200℃ and the drying time is 0~60min; the curing temperature is 120~170℃ and the curing time is 30~120min.

6. The method for preparing fully hollow silicon carbide microspheres according to claim 1, characterized in that, In step S2, the carbonization temperature is 800–1000℃ and the carbonization time is 60–180 min.

7. The method for preparing fully hollow silicon carbide microspheres according to claim 1, characterized in that, In step S3, the sintering temperature is 1400–2000℃ and the sintering time is 2–6 hours.

8. The method for preparing fully hollow silicon carbide microspheres according to claim 1, characterized in that, In step S3, the silicon dioxide and elemental silicon in the core react at 1800℃~2000℃ to generate silicon monoxide gas, which is then released to form hollow silicon carbide microspheres; the released silicon monoxide gas reacts with the carbon on the outer shell to generate a dense silicon carbide shell.

9. Hollow silicon carbide microspheres prepared by the method according to any one of claims 1 to 8.