Preparation method of high-strength silicon carbide hollow spheres

Abstract

The invention belongs to the field of preparation of inorganic non-metallic materials, and particularly relates to a preparation method of high-strength silicon carbide hollow spheres. The preparation method comprises the following steps: mixing silicon carbide powder, a binder, a curing agent and other raw materials to form precursor slurry, coating the surface of a polymer sphere by adopting a coating spraying method, and carrying out drying curing, degreasing treatment and high-temperature sintering to prepare the SiC ceramic hollow sphere. Key processes such as raw material component proportioning and sphere dispersity optimization are broken through, and the SiC ceramic hollow sphere with good sphericity and controllable particle size is successfully prepared. The SiC hollow spheres prepared by a'spray coating method 'not only have lower envelope density, but also have the maximum analogy strength up to 13.61 MPa.cm < 3 > / g which is obviously superior to that of commercially available Al2O3 hollow spheres, and the SiC hollow spheres prepared by the method are used as filler particles to hopefully prepare light and high-strength aluminum-based composite foam.

Description

Technical Field

[0001] The invention belongs to the field of inorganic non-metallic material preparation, and in particular relates to a method for preparing high-strength hollow silicon carbide spheres. Background Art

[0002] Ceramic hollow spheres, with their light weight, high specific surface area, excellent fluid dynamics, excellent corrosion resistance and high temperature resistance, are widely used in many key fields such as aerospace, chemical engineering, marine engineering, machinery manufacturing, military protection, etc., and have become an important cornerstone and core element for promoting technological innovation in various industries of the national economy. It is particularly worth mentioning that SiC ceramic hollow spheres, as an idealized high-performance material, combine high hardness, high strength, high stability, low thermal expansion coefficient, anti-radioactivity, radiation resistance and excellent wave absorption performance, showing extraordinary comprehensive performance. When these high-strength SiC ceramic hollow spheres are evenly integrated into the metal matrix (such as aluminum alloy, magnesium alloy), the metal-based composite foam material born not only inherits the advantages of the raw materials, but also gives the material excellent impact resistance, wave absorption and stealth capabilities, and high-temperature heat insulation and fireproof properties. These unique properties make this type of material show great application potential and value in the explosion protection of armored vehicles, anti-collision energy absorption design in the transportation field, and heat insulation and fireproof needs of the aerospace industry, and have become a hot focus of in-depth exploration and industrial application practice in the academic community in recent years.

[0003] In view of the technical challenges faced by SiC materials in the densification sintering process, and the particularity of the hollow ball structure increases its molding difficulty, the relevant reports on the preparation technology of SiC hollow balls are particularly scarce. U.S. Patent US4671909 proposes a method, that is, melting ceramic raw materials in a high-temperature furnace and using air blowing technology to obtain hollow balls of corresponding materials. However, the hollow balls prepared by this process have a high breakage rate, and the breakage rate of products sold on the market exceeds 30%, and the strength stability is poor. In addition, the application scope of this process is limited, and only a few types of ceramic hollow balls such as alumina and zirconia can be successfully prepared. There is no report on the successful preparation of SiC hollow balls. In patent CN102557594B, carbon black, flour and water are used as raw materials, and after mixing and molding, they are extruded into template balls, and then the ceramic hollow ball blank is prepared by a one-time injection of ceramic powder for rolling ball coating. Subsequently, after a series of steps such as natural drying, low-temperature calcination, medium-temperature calcination and high-temperature calcination, a ceramic hollow ball is finally obtained. However, the sintering of SiC materials is extremely difficult. Even under normal pressure conditions, the addition of sintering aids requires a high temperature of 2100°C to 2200°C to achieve densification sintering, which undoubtedly leads to huge energy consumption and high costs. What is even more difficult is that this method is difficult to ensure the uniformity of the hollow sphere shell, and adhesion is prone to occur, resulting in unstable product performance and low production efficiency. Therefore, it is difficult to prepare high-performance and high-strength SiC hollow spheres in large quantities at low cost using this method. Therefore, it is difficult for existing technologies to prepare SiC hollow spheres with good sphericity, uniform sphere wall thickness, complete and dense, high strength and low cost. Summary of the invention

[0004] In order to solve the problem that the existing technology methods are difficult to prepare silicon carbide hollow balls with good sphericity, uniform wall thickness, integrity and density, high strength and low cost, the present invention proposes a new preparation method, the specific steps are as follows:

[0005] A method for preparing high-strength silicon carbide hollow spheres comprises the following steps:

[0006] (1) Silicon carbide powder, aluminum oxide powder, yttrium oxide, a binder, a dispersant, a curing agent and anhydrous ethanol are ball-milled and stirred to obtain a precursor slurry with a certain viscosity, a polymer ball is used as a template, and the polymer ball is continuously rotated and tumbled in a coating machine under the action of directional continuous air supply, and the precursor slurry is coated on the surface of the polymer ball in a high-speed spraying manner, so that it adheres layer by layer and accumulates to form a shell of a certain thickness, and finally, after curing and molding treatment, a polymer ball / SiC / binder precursor element ball with a core-shell structure can be prepared;

[0007] (2) The polymer sphere / SiC / binder precursor sphere is dried and degreased by a heating process to obtain a hollow SiC / C sphere. The SiC / C hollow sphere is mixed with silicon powder in a vacuum environment and sintered at a high temperature to obtain a high-strength silicon carbide hollow sphere.

[0008] The method for preparing the high-strength hollow silicon carbide spheres is characterized in that in the step (1), the silicon carbide powder is α-SiC with a particle size of 10 μm to 20 μm.

[0009] In the above-mentioned method for preparing high-strength silicon carbide hollow spheres, in the step (1), the polymer sphere material is EPS polystyrene or STMMA copolymer, the polymer sphere diameter is 1mm to 30mm, the dispersant is polyvinyl butyral, ammonium polyacrylate or tetramethylammonium hydroxide, and the curing agent is p-toluenesulfonic acid monohydrate.

[0010] In the above-mentioned method for preparing high-strength hollow silicon carbide balls, in step (1), the binder is phenolic resin, ethyl silicate or polyvinyl alcohol, and 20g to 50g of the binder is added per cubic decimeter of polymer balls.

[0011] In the above-mentioned method for preparing high-strength silicon carbide hollow spheres, in the step (1), the precursor slurry is prepared by mixing anhydrous ethanol, silicon carbide powder, aluminum oxide powder, binder, yttrium oxide, dispersant, and curing agent in a ratio of 80:35:8:6:1:1:1, and the precursor slurry can be obtained after ball milling and stirring.

[0012] In the above-mentioned method for preparing high-strength silicon carbide hollow spheres, in the step (1), the precursor slurry is introduced into the spray port of the coating machine through a delivery pump at a speed of 8 rpm, and is rapidly atomized under the drive of high-speed compressed air, and is directionally coated on the surface of the polymer spheres in a boiling state to form a core-shell structure, and the coating is continued until the shell reaches the expected thickness, thereby obtaining a polymer sphere / SiC / binder sphere with a thickness of 150 μm to 300 μm.

[0013] In the above-mentioned method for preparing high-strength silicon carbide hollow spheres, in the step (2), the drying is to heat the coated spheres at 80°C to 160°C to complete the solidification of the shell layer and the shrinkage of the core polymer spheres, thereby obtaining SiC / binder hollow spheres.

[0014] The preparation method of the above-mentioned high-strength silicon carbide hollow spheres, in the step (2), the dried SiC / binder hollow spheres are transferred to a sintering furnace for degreasing treatment, heated to 600°C at a heating rate of 5°C / min to completely burn the EPS polystyrene spheres, and then heated to 900°C at 10°C / min and kept warm for 2h to remove excess organic matter in the shell layer, so that only silicon carbide and residual carbon are left in the shell material, i.e., SiC / C hollow spheres.

[0015] The method for preparing the above-mentioned high-strength silicon carbide hollow spheres, in the step (2), SiC / C hollow spheres are mixed with silicon powder, and subjected to high-temperature sintering treatment in a silicon carbide sintering furnace, the outer layer of silicon carbide ceramic powder is sintered into silicon carbide hollow spheres, and the hollow spheres are connected to each other and sintered into one, so as to obtain high-strength SiC hollow spheres.

[0016] In the above-mentioned method for preparing high-strength silicon carbide hollow spheres, the high-temperature sintering is to raise the temperature to 850°C to 1550°C at a heating rate of 50°C / min and keep the temperature for 3 hours.

[0017] The significant advantages and beneficial effects of the present invention are:

[0018] 1. The present invention innovatively proposes a technical method for preparing ceramic hollow sphere particles by "spray coating", breaks through key processes such as the ratio of raw material components and optimization of sphere dispersion, and successfully prepares SiC ceramic hollow spheres with good sphericity and controllable particle size.

[0019] 2. The SiC hollow spheres prepared by the "spray coating method" of the present invention not only have a lower envelope density, but also have a maximum analog strength of up to 13.61 MPa·cm 3 / g, significantly better than the commercially available Al2O3 hollow spheres (whose analog strength is only 3.56MPa·cm 3 / g), and it is expected that a lightweight and high-strength aluminum-based composite foam can be prepared by using the SiC hollow spheres prepared in this experiment as filler particles.

[0020] 3. The process has low preparation cost, simple preparation process, and is easy to mass produce. In addition, the prepared SiC / SiC hollow spheres have high relative density, uniform and dense microstructure, and the strength is greatly improved after the sphere wall is densified. The high-strength SiC hollow spheres synthesized by the present invention have important research significance and practical value, and are easy to realize industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a process flow chart of the preparation of high-strength SiC hollow spheres of the present invention.

[0022] Figure 2 The XRD diagrams of the high-strength SiC hollow spheres of the present invention after being treated at different temperatures.

[0023] Figure 3 These are SEM images (cross-sectional morphologies) of the high-strength SiC hollow spheres of the present invention after treatment at different temperatures, (a) at 1450°C, (b) at 1750°C, (c) at 1500°C, and (d) at 1550°C.

[0024] Figure 4This is a SEM image of the high-strength SiC hollow sphere of the present invention.

[0025] Figure 5 This is a real picture of the high-strength SiC hollow sphere of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0027] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0028] Example 1

[0029] Preparation method of high strength silicon carbide hollow spheres Figure 1 As shown,

[0030] 1) The precursor slurry is prepared by ball milling. The precursor slurry comprises anhydrous ethanol, silicon carbide powder, aluminum oxide powder, phenolic resin, yttrium oxide, polyvinyl butyral, and p-toluenesulfonic acid monohydrate in a mass ratio of 80:35:8:

[0031] 6:1:1:1, and after ball milling, stirring and mixing, a precursor slurry can be obtained, wherein the silicon carbide powder is α-SiC with a particle size of about 20 μm, and the aluminum oxide powder has a particle size of about 0.45 μm.

[0032] 2) Using EPS polystyrene polymer balls as templates, the polymer balls are continuously rotated and tumbled in the coating machine under the action of directional continuous air supply. The slurry prepared above is coated on the surface of the polymer balls by high-speed spraying, so that it adheres layer by layer and accumulates to form a shell of a certain thickness.

[0033] 3) The EPS polystyrene balls coated with the precursor slurry are placed in a drying oven at 100° C. for 3 hours to complete the curing of the EPS shell layer and the shrinkage of the core polymer ball, thereby obtaining a dry EPS polystyrene ball coated with a powder outer layer.

[0034] 4) Repeat 2) and 3) until the thickness of the ceramic powder layer on the polymer ball reaches about 230 μm.

[0035] 5) After drying, the product is transferred to a sintering furnace for degreasing treatment and heated to 600°C at a heating rate of 5°C / min to completely burn out the EPS polystyrene balls. Then, the product is heated to 900°C at a rate of 10°C / min and kept warm for 2 hours to remove excess organic matter in the shell layer, leaving only silicon carbide and residual carbon in the shell material, i.e., SiC / C hollow balls.

[0036] 6) The SiC / C hollow spheres are mixed with an appropriate amount of silicon powder, and sintered in a silicon carbide sintering furnace. The temperature is raised to 1450°C at a heating rate of 50°C / min. After being kept warm for 3 hours, the outer layer of silicon carbide ceramic powder is sintered into silicon carbide hollow spheres, and the hollow spheres are connected to each other and sintered into one, thereby obtaining high-strength SiC hollow spheres.

[0037] Example 2

[0038] Except that the high temperature sintering temperature selected in step 6) is 1475°C, all other steps and process parameters are the same as those in Example 1.

[0039] Example 3

[0040] Except that the high temperature sintering temperature selected in step 6) is 1500°C, all other steps and process parameters are the same as those in Example 1.

[0041] Example 4

[0042] Except that the high temperature sintering temperature selected in step 6) is 1550°C, all other steps and process parameters are the same as those in Example 1.

[0043] Example 5

[0044] Except that the high temperature sintering temperature selected in step 6) is 850°C, all other steps and process parameters are the same as those in Example 1.

[0045] Figure 2 The XRD diagrams of high-strength SiC hollow spheres prepared in Examples 1 to 5 are shown in the results in the figure. After degreasing at 850°C, the hollow sphere embryos are mainly SiC phase and C phase, and no other impurity peaks are detected. After reacting at a high temperature of 1450°C for 3h, silicon vapor reacts with residual carbon in the sphere wall to generate silicon carbide, the main carbon peak at 2θ=30° disappears, and the two carbon peaks between 25°~26° and 43°~44° are significantly weakened; when the temperature reaches 1475°C, the C peak is already very weak, and an obvious Si phase (2θ=47.5° or so) appears; and when the temperature reaches 1500°C, the C peak in the sphere wall completely disappears. At this time, in addition to the SiC phase, there is also a very strong Si diffraction peak. The above results show that with the increase of temperature, a large amount of silicon elemental infiltration enters the pores of the sphere wall and reacts with residual carbon to generate SiC, and some excess silicon fills the micropores of the sphere wall to densify it.

[0046] Figure 3The SEM images (cross-sectional morphology) of the high-strength SiC hollow spheres prepared in Examples 1 to 4 after being treated at different temperatures. The high-strength SiC hollow spheres prepared by the present invention have a main component (SiC) of the sphere wall derived from two parts, one of which is the SiC particles in the precursor slurry, and the other is the SiC generated by high-temperature reaction. Data show that the melting point of silicon particles is 1410°C. When the furnace temperature reaches the melting point of silicon element, as the silicon particles melt, silicon liquid and silicon vapor enter the hollow sphere wall and react with residual carbon to generate silicon carbide, and connect the SiC particles introduced in the precursor slurry to form a continuous SiC sphere wall. As can be seen from the figure, under the condition of sufficient silicon source, the sphere wall is still in a loose structure after sintering at 1450°C for 3h. When the sintering temperature is increased to 1475°C, the sphere wall tends to be densified. Further increasing the sintering temperature to 1500°C, the sphere wall is already very dense, and continuing to increase the sintering temperature (1550°C) has little effect on the density of the sphere wall.

[0047] Figure 4 This is a SEM image of the high-strength SiC hollow sphere prepared in Example 1. Through observation, it can be clearly seen that the SiC hollow sphere has a smooth surface, a dense sphere wall structure and a uniform wall thickness distribution. The high-strength SiC hollow sphere not only has an excellent microscopic morphology at the microscopic level. In addition, the hollow sphere presents a distinct hollow structural feature, and its diameter is about 3 mm.

[0048] Figure 5 This is a real picture of the high-strength SiC hollow sphere prepared in Example 4. The diameter size corresponds to the SEM image, and the hollow sphere in the real picture shows a good overall morphology, which fully demonstrates the superb and precise preparation process.

[0049] Table 1 Physical characteristic parameters of SiC hollow spheres prepared at different temperatures

[0050]

[0051] Table 1 shows the physical characteristic parameters of the high-strength SiC hollow spheres of the present invention after being treated at different temperatures. It can be seen from the table that for spheres with similar particle sizes, after the temperature rises from 1475°C to 1500°C, the envelope density of the spheres is greatly improved, and the analog strength of the corresponding spheres is also 4 to 5 times. Combining the XRD and SEM characterization results, it can be seen that when the reaction temperature is low (below 1475°C), due to the slow melting of silicon, less silicon element permeates into the pores of the hollow sphere embryo containing residual carbon through capillary action, and the generated SiC grains are smaller. The prepared SiC hollow sphere wall contains more micropores and is not a densified shell. Therefore, the analog strength of the sphere is low (2MPa·cm 3 / g or less). When the temperature exceeds 1500℃, a large amount of silicon enters the interior of the sphere wall, the SiC grains grow further, and the pores between the grains are filled with silicon, forming a densified sphere wall, and the analog strength of the sphere is greatly improved.

[0052] Table 2 Physical characteristic parameters of commercially available Al2O3 hollow spheres with different particle sizes

[0053]

[0054] Table 2 shows the physical characteristic parameters of commercially available Al2O3 hollow spheres with different particle sizes. The highest analog strength of Al2O3 hollow spheres is only 3.56 MPa·cm 3 / g, and the overall envelope density of the sphere is relatively large (the lowest is 0.77g / cm 3 ). The SiC hollow spheres prepared in this study have higher analog strength at similar envelope density, and have the significant advantages of light weight and high strength, providing an excellent filler particle for the preparation of lightweight and high-strength metal-based composite foams.

[0055] The present invention is not limited to the aforementioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process disclosed or any new combination.

[0056] Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing high-strength silicon carbide hollow spheres, characterized in that: The following steps are involved: (1) Silicon carbide powder, aluminum oxide powder, yttrium oxide, a binder, a dispersant, a curing agent and anhydrous ethanol are ball-milled and stirred to obtain a precursor slurry with a certain viscosity, a polymer ball is used as a template, and the polymer ball is continuously rotated and tumbled in a coating machine under the action of directional continuous air supply, and the precursor slurry is coated on the surface of the polymer ball in a high-speed spraying manner, so that it adheres layer by layer and accumulates to form a shell of a certain thickness, and finally, after curing and molding treatment, a polymer ball / SiC / binder precursor element ball with a core-shell structure can be prepared; (2) The polymer sphere / SiC / binder precursor sphere is dried and degreased by a heating process to obtain a hollow SiC / C sphere. The SiC / C hollow sphere is mixed with silicon powder in a vacuum environment and sintered at a high temperature to obtain a high-strength silicon carbide hollow sphere.

2. The method for preparing high-strength hollow silicon carbide spheres according to claim 1, characterized in that: In the step (1), the silicon carbide powder is α-SiC and has a particle size of 10 μm to 20 μm.

3. The method for preparing high-strength silicon carbide hollow spheres according to claim 1, characterized in that: In the step (1), the polymer ball material is EPS polystyrene or STMMA copolymer, the polymer ball diameter is 1 mm to 30 mm, the dispersant is polyvinyl butyral, ammonium polyacrylate or tetramethylammonium hydroxide, and the curing agent is p-toluenesulfonic acid monohydrate.

4. The method for preparing high-strength silicon carbide hollow spheres according to claim 1, characterized in that: In the step (1), the binder is phenolic resin, ethyl silicate or polyvinyl alcohol, and 20 g to 50 g of the binder is added per cubic decimeter of polymer balls.

5. The method for preparing high-strength hollow silicon carbide spheres according to claim 1, characterized in that: In the step (1), the precursor slurry is prepared by mixing anhydrous ethanol, silicon carbide powder, aluminum oxide powder, a binder, yttrium oxide, a dispersant, and a curing agent in a ratio of 80:35:8:6:1:1:1, and the precursor slurry is obtained by mixing by ball milling.

6. The method for preparing high-strength hollow silicon carbide spheres according to claim 1, characterized in that: In the step (1), the precursor slurry is introduced into the spray port of the coating machine through a delivery pump at a speed of 8 rpm, and is quickly atomized under the drive of high-speed compressed air, and is directionally coated on the surface of the polymer ball in a boiling state to form a core-shell structure. The coating is continued until the shell reaches the expected thickness, thereby obtaining a polymer ball / SiC / binder ball with a thickness of 150 μm to 300 μm.

7. The method for preparing high-strength hollow silicon carbide spheres according to claim 1, characterized in that: In the step (2), the drying is to heat the coated spheres at 80°C to 160°C to complete the solidification of the shell layer and the shrinkage of the core polymer spheres, thereby obtaining SiC / binder hollow spheres.

8. The method for preparing high-strength hollow silicon carbide spheres according to claim 1, characterized in that: In the step (2), the dried SiC / binder hollow balls are transferred to a sintering furnace for degreasing treatment, heated to 600°C at a heating rate of 5°C / min to completely burn out the EPS polystyrene balls, and then heated to 900°C at a rate of 10°C / min and kept warm for 2 hours to remove excess organic matter in the shell layer, leaving only silicon carbide and residual carbon in the shell material, i.e., SiC / C hollow balls.

9. The method for preparing high-strength hollow silicon carbide spheres according to claim 1, characterized in that: In the step (2), the SiC / C hollow spheres are mixed with an appropriate amount of silicon powder and subjected to high-temperature sintering in a silicon carbide sintering furnace. The outer layer of silicon carbide ceramic powder is sintered into silicon carbide hollow spheres, and the hollow spheres are connected to each other and sintered into one, thereby obtaining high-strength SiC hollow spheres.

10. The method for preparing high-strength hollow silicon carbide spheres according to claim 1, characterized in that: The high temperature sintering is to raise the temperature to 850°C-1550°C at a heating rate of 50°C / min and keep the temperature for 3 hours.

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