Silicon carbide powder and its preparation method and application

Abstract

The present invention discloses a silicon carbide powder, a preparation method, and an application thereof. The preparation method comprises the following steps: soaking hollow nano-silica in an aqueous solution of an organic nickel salt for 10-60 minutes, then evaporating the water to obtain a dry powder, calcining the dry powder and carbon powder under an inert atmosphere, and then expelling carbon at 600-800°C for 4-8 hours to obtain the silicon carbide powder; the silicon carbide powder has a β-SiC crystal form. The present invention uses hollow nano-silica as a silicon source for preparing the silicon carbide powder, which can improve the reactivity of the silicon source and the carbon source. Furthermore, an organic nickel salt is added, and the nickel element in the organic nickel salt can catalyze the reaction between carbon and silicon dioxide, thereby comprehensively improving the purity and performance of the silicon carbide powder.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic materials, and in particular relates to silicon carbide powder and a preparation method and application thereof. Background Art

[0002] Silicon carbide (SiC) is a strong covalently bonded compound material with excellent properties, including high-temperature resistance, wear resistance, corrosion resistance, radiation resistance, high hardness, high elastic modulus, high thermal conductivity, good high-temperature strength, low thermal expansion coefficient, good thermal shock resistance, high critical breakdown electric field, high saturated electron drift velocity, low dielectric constant, and good wave absorption. It has been widely used in many fields, particularly in high-tech fields such as aerospace, machinery, metallurgy, energy, environmental protection, chemical engineering, medicine, electronics, and military applications. The two most common crystalline forms of silicon carbide are α-SiC and β-SiC. β-SiC has a cubic crystal structure similar to diamond. Compared to the hexagonal α-SiC, β-SiC has higher hardness (Mohs hardness exceeding 9.5), better toughness, superior grindability, and reinforcement and toughening properties. β-SiC also exhibits superior sintering properties compared to α-SiC, and the finer the powder, the higher the sintering activity.

[0003] The preparation methods of silicon carbide powder in the prior art have the following problems: (1) Most of the silicon sources used are silicon dioxide or elemental silicon, which exists in two forms: crystalline and amorphous. The crystalline form has high purity but insufficient reactivity, while the amorphous form has high reactivity but insufficient purity. Therefore, it is necessary to provide silicon dioxide or elemental silicon with high purity and high reactivity. (2) When the prior art uses the carbon reduction method to prepare silicon carbide powder, the appropriate amount of metal salt (such as nickel salt, iron salt, etc.) can play a catalytic role in the reaction. However, the prior art does not consider the compatibility of metal salts in carbon sources and silicon sources, which affects the catalytic effect.

[0004] The existing technology uses the sol-gel method to prepare hollow nano-silica, which can produce silica with a high specific surface area. However, the template molecules (such as calcium carbonate, polystyrene, etc.) are not completely removed, resulting in insufficient purity of the hollow nano-silica. This is because most of the existing technologies only consider its adsorption properties, but do not consider the reactivity and purity required as a reaction material.

[0005] In summary, how to provide a silicon carbide powder and its preparation method and application, improve the reaction activity in the preparation process of silicon carbide powder while also improving the purity and performance of silicon carbide powder, is an urgent problem to be solved. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a silicon carbide powder and its preparation method and application. The present invention uses hollow nano-silica as a silicon source, which can improve the reaction activity of the silicon source and the carbon source. The hollow nano-silica forms liquid silicon faster during the high-temperature reaction process, which accelerates the precipitation of silicon carbide. In addition, an organic nickel salt is added. The organic part of the substance can serve as a partial carbon source, and the nickel element can catalyze the reaction between carbon and silicon dioxide, thereby comprehensively improving the purity and performance of the silicon carbide powder.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for preparing hollow nano-silica comprises the following steps:

[0009] A cationic compound is added to a suspension of nano-calcium carbonate (50-100 nm), the solution pH is adjusted to 9-10, and then heated to 40-80°C and stirred for 10-60 minutes. A sodium silicate solution is then slowly added while stirring. The mixture is aged for 2-5 hours, filtered, washed, dried at 100-120°C, and calcined at 300-600°C for 3-5 hours. Finally, impurities are dissolved with hydrochloric acid, filtered, washed, and dried to obtain hollow nano-silica. The cationic compound is aluminum acetylglutamide.

[0010] Preferably, the added amount of the cationic compound is 0.5-1.5% of the mass of the nano-calcium carbonate.

[0011] Preferably, the mass concentration of the nano-calcium carbonate suspension is 60-100 g / L, the mass concentration of silicon dioxide in the sodium silicate solution is 3-10%, and the mass ratio of sodium silicate solution to nano-calcium carbonate is 12-30% in terms of silicon dioxide / calcium carbonate.

[0012] The present invention also provides a method for preparing silicon carbide powder, which adopts the reaction of a carbon source and a silicon source, wherein the silicon source is the hollow nano-silicon dioxide prepared by the above method. The method for preparing silicon carbide powder comprises the following steps:

[0013] The hollow nano-silica is dried to obtain a dry powder, and the dry powder and carbon powder (50-500nm) are placed in an inert atmosphere (helium or argon) and calcined. After the calcination is completed, carbon is removed at 600-800°C for 40-80 minutes, and finally the temperature is cooled to room temperature at a rate of 8-20°C / min to obtain silicon carbide powder; the crystal form of the silicon carbide powder is β-SiC.

[0014] Preferably, an organic nickel salt is further added to the preparation method of the silicon carbide powder. In this case, the preparation method of the silicon carbide powder specifically comprises the following steps:

[0015] The hollow nano-silica is immersed in an organic nickel salt aqueous solution for 10-60 minutes, and then the water is evaporated to obtain a dry powder. The dry powder and carbon powder (50-500nm) are placed in an inert atmosphere (helium or argon) and calcined. After the calcination is completed, carbon is discharged at 600-800°C for 40-80 minutes, and finally the temperature is cooled to room temperature at a rate of 8-20°C / min to obtain silicon carbide powder; the crystal form of the silicon carbide powder is β-SiC.

[0016] The organic nickel salt is specifically nickel disodium ethylenediaminetetraacetate, nickel oxalate or nickel acetate, preferably nickel disodium ethylenediaminetetraacetate.

[0017] Preferably, the molar ratio of the hollow nano-silica to the carbon powder is 1:(1-1.2) in terms of silicon / carbon, and the molar ratio of the hollow nano-silica to the organic nickel salt is 1:(0.02-0.1) in terms of silicon / nickel.

[0018] Preferably, the calcination temperature is 1300-1600° C., the heating rate is 5-10° C. / min, and the calcination time is 1-3 h.

[0019] Preferably, after carbon removal, the powder is further subjected to impurity removal, and any one or both of acid washing and alkaline washing are used for impurity removal, the acid is one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid, and the alkali is one or more of sodium hydroxide, potassium hydroxide, and ammonia water, and the mass concentration of the acid and the alkali is 10-30%.

[0020] Preferably, the method for preparing silicon carbide powder further comprises exhausting the dry powder before calcination, wherein the exhausting treatment is as follows: heating the dry powder to 200-400°C at a rate of 6-15°C / min in a flowing inert atmosphere (helium or argon) and keeping the temperature for 5-30 minutes.

[0021] The present invention also provides an application of silicon carbide powder as a ceramic material.

[0022] Technical effects of the present invention:

[0023] 1. The present invention adopts a carbon reduction method to prepare silicon carbide powder, and uses hollow nano-silica as a silicon source, which can improve the reaction activity of the silicon source and the carbon source. The hollow nano-silica forms liquid silicon faster during the high-temperature reaction process, thereby accelerating the precipitation of silicon carbide.

[0024] 2. When the present invention uses nano-calcium carbonate as a template to prepare hollow nano-silica, a cationic compound is also added. The cationic compound can not only adhere to the surface of calcium carbonate (negatively charged under alkaline conditions) to form a positively charged structural layer, but also can react with sodium silicate to form a negatively charged silica gel adsorbed to promote the formation of silica on the surface of calcium carbonate.

[0025] The cationic compound of the present invention is preferably acetylglutamide aluminum, which contains polynuclear hydroxy bridge aluminum ions. When added to the nano calcium carbonate suspension, it can also condense on the calcium carbonate surface to improve the rheological properties of the nano calcium carbonate suspension, thereby promoting the coating of calcium carbonate by silicon dioxide and improving the coating rate.

[0026] 3. During the high-temperature calcination process of the hollow nano-silica prepared by the present invention, acetylglutamide aluminum can produce porous activated alumina, which can be used as a template to promote the formation of a porous structure in the inner pore wall of the hollow nano-silica. Acetylglutamide aluminum can also reinforce the strength of the inner layer of the hollow structure and improve the structural stability.

[0027] Compared with other cationic compounds (such as cationic surfactants), which are easily removed by high-temperature roasting and form carbon residues, reducing the purity of hollow nano-silica, the acetylglutamide aluminum of the present invention can be dissolved together with calcium carbonate by hydrochloric acid without leaving any carbon residue. In addition, the presence of acetylglutamide aluminum can make the removal of calcium carbonate more complete, reducing the amount of calcium carbonate remaining in the pores of the hollow particles.

[0028] 4. When preparing silicon carbide powder in the present invention, an organic nickel salt is also added. The organic part of the substance can serve as a partial carbon source, and the nickel element can catalyze the reaction between carbon and silicon dioxide, and a full reaction can be achieved in only 1-3 hours.

[0029] The organic nickel salt of the present invention is preferably nickel disodium ethylenediaminetetraacetate, which has the following functions: 1. It contains a large number of active groups and can adhere to the surface of hollow nano-silica to improve the dispersibility of silica powder and nickel salt in carbon powder, thereby preventing powder agglomeration or adhesion; 2. When the hollow nano-silica is immersed in a nickel salt aqueous solution, it can adsorb a large amount of nickel disodium ethylenediaminetetraacetate, so that the hollow nano-silica acts as a catalyst carrier, further improving the catalytic activity of nickel; 3. The nickel disodium ethylenediaminetetraacetate carbonizes and releases small molecules at high temperature, which plays a role in supporting the hollow structure of the hollow nano-silica, preventing the hollow structure from being destroyed before the temperature is raised to the calcining temperature, thereby maintaining the reaction activity of the hollow nano-silica; and 4. The nickel disodium ethylenediaminetetraacetate is adsorbed in the hollow nano-silica, and the amorphous carbon formed after the high-temperature carbonization can quickly and fully react with the silica, thereby promoting the formation of silicon carbide.

[0030] 5. When preparing silicon carbide powder in the present invention, there is a lot of air in the hollow structure of the hollow nano-silica used. Although the calcination reaction under an inert atmosphere is not easy to affect the purity of the silicon carbide product, the organic nickel salt adsorbed in the hollow structure is easily oxidized by this part of the air during the early heating process, affecting the catalytic activity of the organic nickel salt. Therefore, the hollow nano-silica needs to be exhausted before the calcination reaction.

[0031] Compared with conventional vacuum exhaust, which easily causes pressure on the hollow structure of hollow nano-silica and causes damage, the present invention performs a mild exhaust treatment on the hollow nano-silica in a flowing inert atmosphere before calcination. Through the heating treatment, part of the nickel disodium ethylenediaminetetraacetic acid is decomposed into small molecular gases by heat. These small molecular gases form a rapid outward airflow when heated, which promotes the replacement of the air in the hollow structure of the silica by the external inert atmosphere and improves the exhaust effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is an electron microscope scanning image of the silicon carbide powder prepared in the present invention;

[0033] Figure 2 The figure shows the XRD pattern of silicon carbide powder prepared in the present invention. DETAILED DESCRIPTION

[0034] The above scheme is further described below in conjunction with specific examples; it should be understood that these examples are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following examples; the implementation conditions adopted in the examples can be further adjusted according to specific requirements, and the implementation conditions not specified are generally the conditions in routine experiments.

[0035] Unless otherwise specified in the following examples, all raw materials were purchased from commercial sources or prepared by conventional methods in the art. Example 1

[0036] This embodiment provides a method for preparing silicon carbide (β-SiC) powder, which uses a reaction between a carbon source and a silicon source, wherein the silicon source is hollow nano-silica. The preparation method of the hollow nano-silica includes the following steps:

[0037] To a suspension of 50nm nano-calcium carbonate (80g / L) was added a cationic compound (aluminum acetylglutamide, 1% of the mass of the nano-calcium carbonate). The solution was adjusted to a pH of 9.5, then heated to 60°C and stirred for 30 minutes. A sodium silicate solution (6% silica) was then slowly added under stirring. The suspension was aged for 3 hours, filtered, washed, dried at 110°C, and calcined at 450°C for 4 hours. Finally, impurities were dissolved with hydrochloric acid, filtered, washed, and dried to obtain hollow nano-silica. The mass ratio of sodium silicate solution to nano-calcium carbonate was 20% silica / calcium carbonate.

[0038] The preparation method of β-SiC powder comprises the following steps:

[0039] Hollow nano-silica was immersed in an aqueous solution of an organic nickel salt (nickel disodium ethylenediaminetetraacetic acid) for 30 minutes. The water was then evaporated to obtain a dry powder. The dry powder and carbon powder (50 nm) were then calcined under an inert atmosphere (argon) at 1400°C, a heating rate of 7.5°C / min, and a calcination time of 2 hours. After calcination, carbon was removed at 700°C for 40 minutes, and then cooled to room temperature at a rate of 14°C / min. After carbon removal, the powder was cleaned of impurities and sequentially washed with acid (10% hydrochloric acid) and alkaline (15% sodium hydroxide) before drying to obtain β-SiC powder.

[0040] The molar ratio of the hollow nano-silica to the carbon powder is 1:1 in terms of silicon / carbon, and the molar ratio of the hollow nano-silica to the organic nickel salt is 1:0.06 in terms of silicon / nickel. Example 2

[0041] The difference between this embodiment and embodiment 1 is that the organic nickel salt in the preparation method of the β-SiC powder is nickel oxalate. Example 3

[0042] The difference between this embodiment and embodiment 1 is that the organic nickel salt in the preparation method of the β-SiC powder is nickel acetate. Example 4

[0043] The difference between this embodiment and embodiment 1 is that no organic nickel salt is added in the preparation method of β-SiC powder. In this case, the preparation method includes the following steps:

[0044] The hollow nano-silica was dried to obtain a dry powder. This powder was then calcined with carbon powder (50 nm) under an inert atmosphere (argon) at 1400°C, a heating rate of 7.5°C / min, and a calcination time of 2 hours. After calcination, carbon was removed at 700°C for 40 minutes, and then cooled to room temperature at a rate of 14°C / min. After carbon removal, the powder was acid-washed (with hydrochloric acid) to remove impurities and dried to obtain β-SiC powder.

[0045] The molar ratio of the hollow nano-silica to the carbon powder is 1:1.2 based on silicon / carbon. Example 5

[0046] Based on Example 1, this example provides a method for preparing silicon carbide (β-SiC) powder. The method for preparing silicon carbide powder also includes exhausting the dry powder before calcination. The exhaust treatment is as follows: heating the dry powder to 300°C in a flowing inert atmosphere (argon) at a rate of 10°C / min and keeping it warm for 15 minutes. Example 6

[0047] This embodiment provides a method for preparing silicon carbide (β-SiC) powder, which uses a reaction between a carbon source and a silicon source, wherein the silicon source is hollow nano-silica. The preparation method of the hollow nano-silica includes the following steps:

[0048] To a 60g / L suspension of nano-calcium carbonate (50nm), a cationic compound (aluminum acetylglutamide, 0.5% of the mass of the nano-calcium carbonate) was added. The solution was adjusted to a pH of 9, then heated to 40°C and stirred for 60 minutes. A sodium silicate solution (3% silica) was then slowly added under stirring. The solution was aged for 2 hours, filtered, washed, dried at 100°C, and calcined at 300°C for 5 hours. Finally, impurities were dissolved with hydrochloric acid, filtered, washed, and dried to obtain hollow nano-silica. The mass ratio of sodium silicate solution to nano-calcium carbonate was 12% (silicon dioxide / calcium carbonate).

[0049] The preparation method of β-SiC powder comprises the following steps:

[0050] Hollow nano-silica was immersed in an aqueous solution of an organic nickel salt (nickel disodium ethylenediaminetetraacetic acid) for 10 minutes, then the water was evaporated to obtain a dry powder. After degassing, the dry powder was calcined with carbon powder (50 nm) under an inert atmosphere (argon) at a temperature of 1300°C, a heating rate of 5°C / min, and a calcination time of 3 hours. After calcination, carbon was removed at 600°C for 80 minutes, and then cooled to room temperature at a rate of 8°C / min. After decarbonization, the powder was decontaminated and sequentially acid-washed (10% by mass hydrochloric acid) and alkaline-washed (15% by mass sodium hydroxide), and dried to obtain β-SiC powder.

[0051] The molar ratio of the hollow nano-silica to the carbon powder is 1:1.1 in terms of silicon / carbon, and the molar ratio of the hollow nano-silica to the organic nickel salt is 1:0.02 in terms of silicon / nickel.

[0052] The exhaust treatment of the dry powder is as follows: the dry powder is heated to 200°C at a rate of 6°C / min in a flowing inert atmosphere (argon) and kept at this temperature for 30 minutes. Example 7

[0053] This embodiment provides a method for preparing silicon carbide (β-SiC) powder, which uses a reaction between a carbon source and a silicon source, wherein the silicon source is hollow nano-silica. The preparation method of the hollow nano-silica includes the following steps:

[0054] To a 100g / L suspension of nano-calcium carbonate (50nm), a cationic compound (aluminum acetylglutamide, 1.5% of the mass of the nano-calcium carbonate) was added. The solution was adjusted to a pH of 10, then heated to 80°C and stirred for 10 minutes. A sodium silicate solution (10% silica) was then slowly added under stirring. The solution was aged for 5 hours, filtered, washed, dried at 120°C, and calcined at 600°C for 3 hours. Finally, impurities were dissolved with hydrochloric acid, filtered, washed, and dried to obtain hollow nano-silica. The mass ratio of sodium silicate solution to nano-calcium carbonate was 30% silica / calcium carbonate.

[0055] The preparation method of β-SiC powder comprises the following steps:

[0056] Hollow nano-silica was immersed in an aqueous solution of an organic nickel salt (nickel disodium ethylenediaminetetraacetic acid) for 60 minutes, then the water was evaporated to obtain a dry powder. After degassing, the dry powder was calcined with carbon powder (50 nm) under an inert atmosphere (argon) at 1600°C, a heating rate of 10°C / min, and a calcination time of 1 hour. After calcination, carbon was removed at 800°C for 60 minutes, and then cooled to room temperature at a rate of 20°C / min. After decarbonization, the powder was decontaminated and sequentially acid-washed (10% hydrochloric acid) and alkaline-washed (15% sodium hydroxide), and dried to obtain β-SiC powder.

[0057] The molar ratio of the hollow nano-silica to the carbon powder is 1:1.2 in terms of silicon / carbon, and the molar ratio of the hollow nano-silica to the organic nickel salt is 1:0.1 in terms of silicon / nickel.

[0058] The exhaust treatment of the dry powder is as follows: the dry powder is heated to 400°C at a rate of 15°C / min in a flowing inert atmosphere (argon) and kept at this temperature for 5 minutes.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that the silicon source for preparing the silicon carbide powder is ordinary silicon dioxide without a hollow structure.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 1 is that, in the preparation process of the hollow nano-silica, the cationic compound used is hexadecyltrimethylammonium bromide.

[0063] Comparative Example 3

[0064] The difference between this comparative example and Example 1 is that the cationic compound used in the preparation of the hollow nano-silica is dodecyltrimethylammonium chloride.

[0065] Comparative Example 4

[0066] The difference between this comparative example and Example 1 is that, during the preparation of the hollow nano-silica, the amount of the cationic compound added is 0.2% of the mass of the nano-calcium carbonate.

[0067] Comparative Example 5

[0068] The difference between this comparative example and Example 1 is that, during the preparation of the hollow nano-silica, the amount of the cationic compound added is 2.0% of the mass of the nano-calcium carbonate.

[0069] Comparative Example 6

[0070] This comparative example differs from Example 1 in that the organic nickel salt is directly added to the silicon carbide powder preparation method. The silicon carbide powder preparation method comprises the following steps: calcining hollow nano-silica, the organic nickel salt, and carbon powder under an inert atmosphere (argon) at a temperature of 1400°C, a heating rate of 7.5°C / min, and a calcination time of 2 hours. After calcination, carbon is removed at 700°C for 40 minutes, and then the temperature is cooled to room temperature at a rate of 14°C / min. After carbon removal, the powder is decontaminated, acid-washed (10% by mass hydrochloric acid), alkaline-washed (15% by mass sodium hydroxide), and dried to obtain β-SiC powder.

[0071] Comparative Example 7

[0072] The difference between this comparative example and Example 1 is that in the method for preparing silicon carbide powder, the molar ratio of hollow nano-silica to disodium nickel ethylenediaminetetraacetic acid is 1:0.01 in terms of silicon / nickel.

[0073] Comparative Example 8

[0074] The difference between this comparative example and Example 1 is that in the method for preparing silicon carbide powder, the molar ratio of hollow nano-silica to disodium nickel ethylenediaminetetraacetic acid is 1:0.12 in terms of silicon / nickel.

[0075] Comparative Example 9

[0076] The difference between this comparative example and Example 5 is that, in the method for preparing silicon carbide powder, the temperature for exhaust treatment of the dry powder before calcination is 150°C.

[0077] Comparative Example 10

[0078] The difference between this comparative example and Example 5 is that, in the method for preparing silicon carbide powder, the temperature for exhaust treatment of the dry powder before calcination is 450°C.

[0079] Comparative Example 11

[0080] The difference between this comparative example and Example 5 is that, in the method for preparing silicon carbide powder, the heating rate for exhaust treatment of the dry powder before calcination is 3° C. / min.

[0081] Comparative Example 12

[0082] The difference between this comparative example and Example 5 is that, in the method for preparing silicon carbide powder, the heating rate for exhaust treatment of the dry powder before calcination is 18° C. / min.

[0083] 1. Microstructure of silicon carbide powder prepared by the present invention

[0084] The silicon carbide powder product obtained in Example 5 of the present invention was scanned by electron microscope, and the results showed that Figure 1 It can be seen that the particle size is about 50nm, the particle size distribution is uniform, and the appearance is good. The XRD pattern of the product powder is shown in Figure 2 , it can be seen that the product is β-SiC powder.

[0085] 2. Effect of preparing hollow nano-silica by the present invention

[0086] 1. Basic properties of hollow nano-silica

[0087] The particle size, specific surface area and purity of the hollow nano-silica prepared in Example 1 and Comparative Examples 2-5 were measured respectively. The results are shown in Table 1.

[0088] Table 1

[0089]

[0090] It can be seen from Table 1 that, compared with Comparative Examples 2-5, the hollow nano-silica prepared in Example 1 of the present invention has a smaller particle size, a larger specific surface area and a higher purity.

[0091] 2. Strength of hollow nano-silica

[0092] The strength of the hollow nano-silica prepared in Example 1 and Comparative Examples 2-5 was measured respectively. The results are shown in Table 2.

[0093] The strength test method is:

[0094] A certain amount of carbon hollow nano-silica powder to be tested was weighed and stirred in a stirrer at a stirring speed of 1000 rpm for 30 minutes. The powder breakage was observed under an optical microscope to test the strength of the carbon hollow nano-silica.

[0095] Table 2

[0096]

[0097] As can be seen from Table 2, compared with Comparative Examples 2-5, the hollow nano-silica prepared in Example 1 of the present invention did not break after high-speed stirring, indicating that the hollow nano-silica has good strength and a relatively stable hollow structure, and can effectively maintain the catalytic support effect of the hollow nano-silica on the organic nickel salt.

[0098] 3. Viscosity of nano calcium carbonate suspension

[0099] The viscosity of the nano-calcium carbonate suspensions in the process of preparing hollow nano-silica in Example 1 and Comparative Examples 2-5 was measured respectively. The results are shown in Table 3.

[0100] Table 3

[0101]

[0102] As shown in Table 3, compared with Comparative Examples 2-5, the viscosity of the nano calcium carbonate suspension in the process of preparing hollow nano silica in Example 1 of the present invention is lower, and the easier it is for calcium carbonate to disperse in the system, the better the coating effect of sodium silicate on calcium carbonate.

[0103] 3. Basic properties of silicon carbide powder produced by the present invention

[0104] 1. Yield and purity of silicon carbide powder

[0105] The yield and purity of the silicon carbide powders obtained in Examples 1-7 of the present invention and Comparative Examples 1, 6-12 were measured. The results are shown in Table 4.

[0106] Table 4

[0107]

[0108] As can be seen from Table 4, the yield of silicon carbide powder prepared in Examples 1-7 of the present invention is in the range of 81.9%-97.7%, and the purity is in the range of 96.2-99.8%. Among them, the yield and purity of Examples 5-7 are higher, with a yield of up to 97.7% and a purity of up to 99.8.

[0109] Comparison of Examples 1-3 shows that when the organic nickel salt in Example 1 is disodium ethylenediaminetetraacetic acid nickel salt, the yield and purity of silicon carbide powder are higher. Comparison of Examples 1 and 4 shows that the addition of organic nickel salt can significantly improve the yield and purity of silicon carbide powder.

[0110] On the basis of Example 1, Example 5 performs exhaust treatment on the dry powder before calcination, as a result, the reaction yield and purity of silicon carbide are further improved.

[0111] Compared with Example 1, Comparative Example 1 uses ordinary silicon dioxide. Compared with Example 5, Comparative Examples 6-12 change the preparation steps of silicon carbide powder. As a result, the yield and purity of the silicon carbide powder prepared in Comparative Examples 1 and 6-12 decreased to varying degrees.

[0112] 2. Dispersion of all powders during the preparation of silicon carbide powder

[0113] The dispersion of all powders during the preparation of silicon carbide powder in Examples 1-4 was observed. The results are shown in Table 5.

[0114] Table 5

[0115]

[0116] The hollow nano-silica and carbon powder used in the preparation of the silicon carbide powder of the present invention are both nanometer-sized. Excessively small particle sizes can easily lead to agglomeration, resulting in uneven dispersion and impacting the overall reaction. As shown in Table 5, compared with Examples 2-4, Example 1 of the present invention significantly improves dispersion after impregnation of the hollow nano-silica with disodium nickel ethylenediaminetetraacetic acid, thereby enhancing the preparation of silicon carbide powder.

[0117] 3. Free carbon content of the powder obtained before carbon removal during the preparation of silicon carbide powder

[0118] During the preparation of the silicon carbide powders of Examples 1-7 and Comparative Examples 1, 6-12 of the present invention, the reaction effect during the preparation of the silicon carbide powders of the present invention was characterized by measuring the mass change of the powders before and after carbon removal and calculating the free carbon content of the silicon carbide powders obtained before carbon removal. The results are shown in Table 6.

[0119] Table 6

[0120]

[0121] As shown in Table 6, the free carbon content in the silicon carbide powders of Examples 1-5 before carbon removal ranged from 0.67% to 4.73%. The free carbon content in Example 5 was the lowest, at 0.67%, paving the way for smooth and rapid subsequent carbon removal and improving the purity of the silicon carbide powder. Furthermore, the free carbon content in the silicon carbide powder before carbon removal also indirectly reflects the activity and effectiveness of the carbon-silicon reaction of the present invention.

[0122] Comparison of Examples 1-3 shows that when the organic nickel salt in Example 1 is disodium nickel ethylenediaminetetraacetate, the free carbon content in the silicon carbide powder before carbon removal is low, indicating that the catalytic activity of disodium nickel ethylenediaminetetraacetate is higher. Based on Example 1, Example 5 further reduced the free carbon content by subjecting the dried powder to exhaust treatment before calcination, indicating that the catalytic activity of the organic nickel salt is further improved after exhaust treatment.

[0123] Compared with Example 1, Comparative Example 1 uses ordinary silicon dioxide. Compared with Example 5, Comparative Examples 6-12 change the preparation steps of silicon carbide powder. As a result, the free carbon content in the silicon carbide powder of Comparative Examples 1 and 6-12 before carbon removal increases to varying degrees, indicating that the reaction effect is deteriorated.

[0124] 4. Application of Silicon Carbide Powder Prepared by the Present Invention as Ceramic Material

[0125] The silicon carbide powders prepared in Examples 1, 5-7 of the present invention and Comparative Examples 1, 6-12 were hot pressed and sintered, and their sintering properties were measured. The results are shown in Table 7. The hot pressing and sintering conditions were: temperature of 1900°C, pressure of 30 MPa, and holding time of 40 min.

[0126] Table 7

[0127]

[0128] As shown in Table 7, the silicon carbide powders prepared in Examples 1, 5-7 of the present invention have good sintering properties, with relative densities ranging from 99.4% to 99.8% and bending strengths ranging from 664 to 735 MN / m. 2 In particular, the sintering performance of the silicon carbide powders obtained in Examples 5-7 is better.

[0129] Compared with Example 1, Comparative Example 1 uses ordinary silicon dioxide. Compared with Example 5, Comparative Examples 6-12 change the preparation steps of silicon carbide powder. As a result, the sintering properties of the silicon carbide powder are all deteriorated.

Claims

1. A method for preparing hollow nano-silica, characterized in that: The following steps are involved: A cationic compound is added to a nano-calcium carbonate suspension, the solution pH is adjusted to 9-10, and then heated to 40-80°C and stirred for 10-60 minutes. Then, a sodium silicate solution is slowly added under stirring, aged for 2-5 hours, filtered, washed, dried at 100-120°C, and calcined at 300-600°C for 3-5 hours. Finally, impurities are dissolved with hydrochloric acid, filtered, washed, and dried to obtain hollow nano-silica. The cationic compound is acetylglutamide aluminum.

2. The preparation method according to claim 1, wherein: The amount of the cationic compound added is 0.5-1.5% of the mass of the nano-calcium carbonate, the mass concentration of the nano-calcium carbonate suspension is 60-100 g / L, the mass concentration of silicon dioxide in the sodium silicate solution is 3-10%, and the mass ratio of sodium silicate solution to nano-calcium carbonate is 12-30% in terms of silicon dioxide / calcium carbonate.

3. A method for preparing silicon carbide powder, which is prepared by reacting a carbon source and a silicon source, characterized in that: The silicon source is hollow nano-silicon dioxide obtained by the method according to claim 1, and the preparation method of the silicon carbide powder comprises the following steps: The hollow nano-silica is dried to obtain dry powder, and the dry powder and carbon powder are placed in an inert atmosphere for calcination. After the calcination is completed, carbon is discharged at 600-800°C for 40-80 minutes, and finally the temperature is lowered to room temperature at a rate of 8-20°C / min to obtain silicon carbide powder; the crystal form of the silicon carbide powder is β-SiC.

4. The preparation method according to claim 3, wherein: The method for preparing the silicon carbide powder further includes adding an organic nickel salt, and the method for preparing the silicon carbide powder includes the following steps: The hollow nano-silica is immersed in an organic nickel salt aqueous solution for 10-60 minutes, and then the water is evaporated to obtain a dry powder, and the dry powder and carbon powder are calcined under an inert atmosphere. After the calcination is completed, silicon carbide powder is obtained; the crystal form of the silicon carbide powder is β-SiC; The organic nickel salt is specifically nickel disodium ethylenediaminetetraacetate, nickel oxalate or nickel acetate.

5. The preparation method according to claim 3 or 4, characterized in that: The molar ratio of the hollow nano-silica to the carbon powder is 1:(1-1.2) in terms of silicon / carbon; the calcination temperature is 1300-1600°C, the heating rate is 5-10°C / min, and the calcination time is 1-3h.

6. The preparation method according to claim 3 or 4, characterized in that: After carbon removal, the powder is also subjected to impurity removal, which is carried out by using either or both of acid washing and alkaline washing. The acid is one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid, and the alkali is one or more of sodium hydroxide, potassium hydroxide, and ammonia water.

7. The preparation method according to claim 4, characterized in that: The organic nickel salt is disodium ethylenediaminetetraacetic acid nickel salt.

8. The preparation method according to claim 4, characterized in that: The molar ratio of the hollow nano-silica to the organic nickel salt is 1:(0.02-0.1) in terms of silicon / nickel.

9. The preparation method according to claim 4, characterized in that: The preparation method further comprises performing exhaust treatment on the dry powder before calcination. The exhaust treatment comprises heating the dry powder to 200-400° C. at a rate of 6-15° C. / min in a flowing inert atmosphere and keeping the temperature for 5-30 minutes.

10. Use of silicon carbide powder prepared according to the method of claim 3 or 4 as a ceramic material.

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