Preparation method of boron-doped silicon carbide nanofiber powder

Abstract

The invention belongs to the technical field of inorganic non-metallic materials, and discloses a preparation method of boron-doped silicon carbide nanofiber powder. The preparation method comprises the following steps: mixing a silicon source, a boron source and a carbon source by adopting a sol-gel method to obtain mixed powder; and under a closed condition, carrying out vacuum microwave sintering on the mixed powder to obtain the boron-doped silicon carbide nanofiber powder. The mixed powder is subjected to vacuum tube sealing treatment to isolate air, so that the synthesized silicon carbide fiber powder is protected from being oxidized at high temperature, and boron oxide is prevented from being volatilized; the high-purity boron-doped silicon carbide nanofiber powder is prepared in a vacuum microwave sintering mode, and the purposes that the doping effect is good, the preparation time is shortened, and the prepared particle size is small and uniform in particle size distribution are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic non-metallic materials, and in particular to a method for preparing boron-doped silicon carbide nanofiber powder. Background Art

[0002] Silicon carbide (SiC) is a semiconductor material with excellent performance, which has the advantages of light weight, high hardness, wide bandgap, good semiconductor performance, good optical performance, good high temperature stability, good corrosion resistance, etc. SiC is a national strategic material. High-quality SiC is widely used in military, aviation, communication and other fields, and is considered to be one of the heat-resistant microwave absorbers. However, the electrical conductivity of SiC is low, so it must be doped and modified and adjusted within a certain range to achieve higher microwave absorption characteristics.

[0003] Typical methods for improving the dielectric properties of SiC include N-type doping (such as N, P doping) or P-type doping (such as Al, B doping). Common doping modification methods include combustion synthesis to prepare N-type doped silicon carbide powder, chemical deposition and oxidation surface modification to improve dielectric properties, etc. However, the above preparation methods will lead to uneven powder distribution, long preparation cycle and complex operation. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing boron-doped silicon carbide nanofiber powder, so as to solve the problems of uneven powder distribution, long preparation cycle and complicated operation in the existing silicon carbide doping and modification methods.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing boron-doped silicon carbide nanofiber powder, comprising the following steps:

[0007] A sol-gel method is used to mix a silicon source, a boron source and a carbon source to obtain a mixed powder;

[0008] Under closed conditions, the mixed powder is subjected to vacuum microwave sintering to obtain boron-doped silicon carbide nanofiber powder.

[0009] Preferably, in the preparation method, the silicon source includes one or more of tetraethyl orthosilicate, silicon powder, and silica sol;

[0010] The boron source includes boron oxide and / or boron powder;

[0011] The carbon source includes amorphous carbon powder and / or graphite powder.

[0012] Preferably, in the preparation method, the particle size of the carbon source is 400-500 nm.

[0013] Preferably, in the preparation method, the carbon source includes one or more of activated carbon, coal powder, and biochar powder.

[0014] Preferably, in the preparation method, the molar ratio of the silicon source to the carbon source is 1:3-4;

[0015] The mass of the boron source is 1-5% of the sum of the mass of the silicon source and the carbon source.

[0016] Preferably, in the preparation method, the sol-gel method specifically comprises the following steps:

[0017] Mixing a boron source, a carbon source and a water-ethanol mixed solvent, adding a silicon source thereto and dispersing the mixture until the mixture is in a colloidal state;

[0018] The molar ratio of the silicon source, the ethanol and the water is 1:5-6:5-6.

[0019] Preferably, in the preparation method, the conditions of the vacuum microwave sintering include: microwave input power of 2 to 2.4 kW, temperature of 1000 to 1200° C., and insulation time of 5 to 15 min.

[0020] Preferably, in the preparation method, the microwave heating frequency of the vacuum microwave sintering is 915 MHz or 2450 MHz.

[0021] Preferably, in the preparation method, vacuum microwave sintering the mixed powder specifically comprises the following steps:

[0022] The mixed powder is placed in a quartz tube for vacuum treatment; microwaves are used to penetrate the heat-insulating material to completely cover the quartz tube containing the mixed powder; the quartz tube is placed in a microwave oven for vacuum extraction and pressure drawing, and after the extraction and pressure drawing is completed, the quartz tube is sealed for vacuum microwave sintering.

[0023] Preferably, in the preparation method, the microwave-transmitting thermal insulation material comprises mullite thermal insulation wool;

[0024] The melting point of the microwave-transmitting heat-insulating material is 1400-1800°C.

[0025] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention uses tetraethyl orthosilicate as a silicon source and boron oxide as a boron source, and uniformly wraps the silicon source and the boron source on the surface of the carbon source through a sol-gel method, which helps to promote the full progress of the reaction; at the same time, the carbon source absorbs microwaves to form a local hot spot, and a high-temperature area is formed on the surface of the carbon source, which promotes the rapid progress of the reaction and allows the boron element to be smoothly doped into the silicon carbide fiber.

[0027] (2) The present invention adopts a vacuum treatment method to load the mixed powder into a quartz tube in a vacuum environment to isolate the air, prevent the volatilization of boron oxide, and promote the occurrence of discharge plasma effect, thereby preparing boron-doped silicon carbide nanofiber powder with uniform particle size.

[0028] (3) Microwave sintering, as a new type of energy, can significantly reduce the sintering temperature and greatly shorten the preparation time. In the scheme of the present application, under the condition of adjusting the microwave input power of 2 to 2.4 kW, the temperature is kept at 1000 to 1200°C for 5 to 15 minutes to obtain boron-doped silicon carbide nanofiber powder. The temperature and time are significantly lower than those of the traditional preparation method (for example, the carbon thermal reduction method mixes silicon powder and carbon powder in a certain proportion, usually using quartz sand and carbon black as raw materials. The mixture is placed in an electric furnace and heated to about 2000°C and then kept warm for 1 to 2 hours to react with the silicon powder and carbon powder to generate silicon carbide), thereby achieving the purpose of energy conservation and green environmental protection. Therefore, the present application adopts vacuum microwave sintering to prepare high-purity boron-doped silicon carbide nanofiber powder with a particle size of 50 to 100 nm, achieving the purpose of good doping effect, shortening preparation time, preparing small particle size and uniform particle size distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the description of the embodiments or the prior art are briefly introduced below.

[0030] Figure 1 This is the microwave sintering heating curve of Example 1 during preparation;

[0031] Figure 2 This is the XRD pattern of the boron-doped silicon carbide nanofiber powder obtained in Example 1;

[0032] Figure 3 This is a SEM image of the boron-doped silicon carbide nanofiber powder obtained in Example 1;

[0033] Figure 4 This is a physical picture of the boron-doped silicon carbide nanofiber powder obtained in Example 1;

[0034] Figure 5 This is a SEM image of the boron-doped silicon carbide nanofiber powder obtained in Example 2;

[0035] Figure 6 This is a SEM image of the boron-doped silicon carbide nanofiber powder obtained in Example 3;

[0036] Figure 7 This is a SEM image of the boron-doped silicon carbide nanofiber powder obtained in Example 4;

[0037] Figure 8 This is a SEM image of the boron-doped silicon carbide nanofiber powder obtained in Example 5;

[0038] Fig. 9 This is a SEM image of the boron-doped silicon carbide nanofiber powder obtained in Example 6;

[0039] Fig.10 This is the SEM image of the boron-doped silicon carbide nanofiber powder obtained in Example 7. DETAILED DESCRIPTION

[0040] The present invention provides a method for preparing boron-doped silicon carbide nanofiber powder, comprising the following steps:

[0041] A sol-gel method is used to mix a silicon source, a boron source and a carbon source to obtain a mixed powder;

[0042] Under closed conditions, the mixed powder is subjected to vacuum microwave sintering to obtain boron-doped silicon carbide nanofiber powder.

[0043] In the present invention, the silicon source preferably includes one or more of tetraethyl orthosilicate, silicon powder, and silica sol, and further preferably includes tetraethyl orthosilicate, silicon powder, or silica sol, and more preferably is tetraethyl orthosilicate.

[0044] In the present invention, the boron source preferably includes boron oxide and / or boron powder, and more preferably boron oxide.

[0045] In the present invention, the carbon source preferably includes amorphous carbon powder and / or graphite powder, and more preferably amorphous carbon powder.

[0046] In the present invention, the particle size of the carbon source is preferably 400 to 500 nm, more preferably 450 to 500 nm, and even more preferably 500 nm.

[0047] In the present invention, the carbon source preferably includes one or more of activated carbon, coal powder, and biochar powder, and further preferably includes activated carbon, coal powder, or biochar powder, and more preferably is activated carbon.

[0048] In the present invention, the molar ratio of the silicon source to the carbon source is preferably 1:3 to 4, more preferably 1:3 to 3.5, and more preferably 1:3.

[0049] In the present invention, the mass of the boron source is preferably 1 to 5% of the sum of the masses of the silicon source and the carbon source, more preferably 2 to 4%, and even more preferably 3%.

[0050] In the present invention, the sol-gel method preferably comprises the following steps:

[0051] The boron source, the carbon source and the water-ethanol mixed solvent are mixed, and the silicon source is added thereto for dispersion until the mixture is in a colloidal state.

[0052] In the present invention, the mixing conditions include: the rotation speed is preferably 200-300 r / min, more preferably 250-300 r / min, more preferably 300 r / min; the mixing time is preferably 20-30 min, more preferably 25-30 min, more preferably 30 min.

[0053] In the present invention, the dispersion rotation speed is preferably 200 to 300 r / min, more preferably 250 to 300 r / min, and even more preferably 300 r / min.

[0054] In the present invention, the molar ratio of the silicon source, the ethanol and the water is preferably 1:5-6:5-6, more preferably 1:5-5.5:5-5.5, and more preferably 1:5:5.

[0055] In the present invention, the mixing of the silicon source, the boron source and the carbon source preferably further comprises: drying.

[0056] In the present invention, the drying conditions include: the temperature is preferably 80-100°C, more preferably 90-100°C, and more preferably 100°C; the time is preferably 5-10h, more preferably 8-10h, and more preferably 10h.

[0057] In the present invention, the vacuum microwave sintering of the mixed powder preferably comprises the following steps:

[0058] The mixed powder is placed in a quartz tube for vacuum treatment; microwaves are used to penetrate the heat-insulating material to completely cover the quartz tube containing the mixed powder; the quartz tube is placed in a microwave oven for vacuum extraction and pressure drawing, and after the extraction and pressure drawing is completed, the quartz tube is sealed for vacuum microwave sintering.

[0059] In the present invention, the vacuum treatment preferably comprises the following steps:

[0060] The mixed powder is placed in a quartz tube for vacuuming and then sealed.

[0061] In the present invention, the vacuum degree of the vacuum extraction is preferably -0.01 to -0.1 MPa, more preferably -0.05 to -0.1 MPa, and more preferably -0.1 MPa.

[0062] In the present invention, the microwave-transmitting heat-insulating material preferably includes mullite heat-insulating wool.

[0063] In the present invention, the melting point of the microwave-transmitting heat-insulating material is preferably 1400-1800°C, more preferably 1500-1700°C, and even more preferably 1500°C.

[0064] In the present invention, the vacuum degree of the vacuum extraction is preferably -0.01 to -0.1 MPa, more preferably -0.05 to -0.1 MPa, and even more preferably -0.1 MPa.

[0065] In the present invention, the conditions for vacuum microwave sintering include: the microwave input power is preferably 2-2.4 kW, more preferably 2-2.2 kW, and more preferably 2 kW; the temperature is preferably 1000-1200°C, more preferably 1100-1200°C, and more preferably 1200°C; the insulation time is preferably 5-15 min, more preferably 8-12 min, and more preferably 10 min.

[0066] In the present invention, the microwave heating frequency of the vacuum microwave sintering is preferably 915 MHz or 2450 MHz, and more preferably 2450 MHz.

[0067] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] Example 1

[0069] This embodiment provides a method for preparing boron-doped silicon carbide nanofiber powder, comprising the following steps:

[0070] (1) Using the sol-gel method, 500 nm activated carbon (Shanghai McLean Company, C829813) was selected as the carbon source, deionized water, anhydrous ethanol, boric oxide and activated carbon were mixed, and stirred at 300 r / min for 30 min. Then, ethyl orthosilicate was gradually added according to the molar ratio of ethyl orthosilicate, anhydrous ethanol and water being 1:5:5, wherein the molar ratio of ethyl orthosilicate to activated carbon was 1:3, and boric oxide was 1wt% of the sum of the mass of ethyl orthosilicate and activated carbon. The mixture was stirred at 300 r / min until a colloidal state was obtained; and then dried at 100°C for 10 h to obtain a mixed powder;

[0071] (2) The mixed powder is placed in a quartz tube and vacuumed to -0.1 MPa and then sealed; the quartz tube containing the mixed powder is embedded in mullite insulation wool (melting point is 1500°C), and then covered with three layers of mullite insulation wool sheets, so that the mullite insulation wool completely covers the quartz tube; the quartz tube is placed in a microwave oven and the furnace cavity is vacuumed and pressurized to -0.1 MPa and then sealed, and vacuum microwave sintering is performed. The microwave sintering frequency is 2450 MHz, the input power is 2 kW, the temperature is raised to 1000°C, and the temperature is maintained for 10 minutes to obtain boron-doped silicon carbide nanofiber powder.

[0072] Example 2

[0073] The difference between this embodiment and embodiment 1 is that the heating temperature in step (2) is changed to 1100° C., and other parameter conditions are the same as those in embodiment 1.

[0074] Example 3

[0075] The difference between this embodiment and embodiment 1 is that the heating temperature in step (2) is changed to 1200° C., and other parameter conditions are the same as those in embodiment 1.

[0076] Example 4

[0077] This embodiment provides a method for preparing boron-doped silicon carbide nanofiber powder, comprising the following steps:

[0078] (1) Using the sol-gel method, 500 nm activated carbon (Shanghai McLean Company, C829813) was selected as the carbon source, deionized water, anhydrous ethanol, boric oxide and activated carbon were mixed, and stirred at 300 r / min for 30 min. Then, ethyl orthosilicate was gradually added according to the molar ratio of ethyl orthosilicate, anhydrous ethanol and water being 1:5:5, wherein the molar ratio of ethyl orthosilicate to activated carbon was 1:3, and boric oxide was 3 wt% of the sum of the mass of ethyl orthosilicate and activated carbon. The mixture was stirred at 300 r / min until a colloidal state was obtained; and then dried at 100°C for 10 h to obtain a mixed powder;

[0079] (2) The mixed powder is placed in a quartz tube and vacuumed to -0.1 MPa and then sealed; the quartz tube containing the mixed powder is embedded in mullite insulation wool (melting point is 1500°C), and then covered with three layers of mullite insulation wool sheets, so that the mullite insulation wool completely covers the quartz tube; the quartz tube is placed in a microwave oven and the furnace cavity is vacuumed and pressurized to -0.1 MPa and then sealed, and vacuum microwave sintering is performed. The microwave sintering frequency is 2450 MHz, the input power is 2 kW, the temperature is raised to 1000°C, and the temperature is maintained for 10 minutes to obtain boron-doped silicon carbide nanofiber powder.

[0080] Example 5

[0081] The difference between this embodiment and embodiment 4 is that the heating temperature in step (2) is modified to 1100° C., and other parameter conditions are the same as those in embodiment 4.

[0082] Example 6

[0083] The difference between this embodiment and embodiment 4 is that the heating temperature in step (2) is modified to 1200° C., and other parameter conditions are the same as those in embodiment 4.

[0084] Example 7

[0085] This embodiment provides a method for preparing boron-doped silicon carbide nanofiber powder, comprising the following steps:

[0086] (1) Using the sol-gel method, 500 nm activated carbon (Shanghai McLean Company, C829813) was selected as the carbon source, deionized water, anhydrous ethanol, boric oxide and activated carbon were mixed, and stirred at 300 r / min for 30 min. Then, ethyl orthosilicate was gradually added according to the molar ratio of ethyl orthosilicate, anhydrous ethanol and water being 1:5:5, wherein the molar ratio of ethyl orthosilicate to activated carbon was 1:3, and the boric oxide was 5 wt% of the sum of the mass of ethyl orthosilicate and activated carbon. The mixture was stirred at 300 r / min until a colloidal state was obtained; and then dried at 100°C for 10 h to obtain a mixed powder;

[0087] (2) The mixed powder is placed in a quartz tube and vacuumed to -0.1 MPa and then sealed; the quartz tube containing the mixed powder is embedded in mullite insulation wool (melting point is 1500°C), and then covered with three layers of mullite insulation wool sheets, so that the mullite insulation wool completely covers the quartz tube; the quartz tube is placed in a microwave oven and the furnace cavity is vacuumed and pressurized to -0.1 MPa and then sealed, and vacuum microwave sintering is performed. The microwave sintering frequency is 2450 MHz, the input power is 2 kW, the temperature is raised to 1000°C, and the temperature is maintained for 10 minutes to obtain boron-doped silicon carbide nanofiber powder.

[0088] Figure 1 This is the microwave sintering heating curve of boron-doped silicon carbide nanofiber powder prepared in Example 1. The results show that through microwave heating, the sample is heated to 1000°C at the 32nd minute, and the sintering temperature is controlled at 1000±10°C by adjusting the input power, and the insulation time is 10 minutes.

[0089] In order to characterize the phase composition and morphology of the obtained product, the boron-doped silicon carbide nanofiber powder prepared in Example 1 was subjected to phase analysis using a German Bruker D8 Focus X-ray diffraction analyzer (XRD). The results are as follows: Figure 2The boron-doped silicon carbide nanofiber powders prepared in Examples 1 to 7 were analyzed using a JEOL JSM-7200F scanning electron microscope (SEM) from Rigaku Corporation. The results are shown in FIG. Figure 3 , Figures 5 to 10 The actual image of the boron-doped silicon carbide nanofiber powder obtained in Example 1 is shown in FIG. Figure 4 shown.

[0090] Figure 2 The results show that the boron-doped silicon carbide nanofiber powder prepared by microwave sintering at 1000°C for 10 min has a high purity. Therefore, using tetraethyl orthosilicate, activated carbon and boron oxide as raw materials, using the sol-gel method and microwave sintering, the (111) and (200) diffraction peaks appear to be shifted, indicating that boron-doped silicon carbide nanofiber powder can be quickly prepared at low temperature.

[0091] Figure 3 The results show that the boron-doped silicon carbide nanofiber powder prepared by microwave sintering at 1000°C for 10 min has a small and uniform particle size of about 50 to 100 nm.

[0092] Figure 4 The results show that at high temperature, the mixed powder will form a core-shell structure in the quartz tube, and under the action of the gas generated inside, it will form a bubble shape, which together with the vacuum environment in the quartz tube can prevent the volatilization of boron oxide and prevent the synthesized SiC powder from being oxidized; after cooling to room temperature, a core-shell structure as shown in the figure is formed.

[0093] Figure 3 , Figures 5 to 10 The results show that with the increase of sintering temperature, the fiber length gradually increases, and the directional growth trend towards the airflow direction becomes increasingly obvious; Figure 3 , Figure 7 , Fig.10 The results show that with the increase of boron oxide doping amount, the fiber size is significantly reduced and becomes finer and denser; therefore, boron doping will reduce the particle size of boron-doped silicon carbide nanofiber powder.

[0094] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing boron-doped silicon carbide nanofiber powder, characterized in that: The following steps are involved: A silicon source, a boron source and a carbon source are mixed by a sol-gel method to obtain a mixed powder; Under closed conditions, the mixed powder is subjected to vacuum microwave sintering to obtain boron-doped silicon carbide nanofiber powder.

2. The preparation method according to claim 1, characterized in that: The silicon source includes one or more of tetraethyl orthosilicate, silicon powder, and silica sol; The boron source includes boron oxide and / or boron powder; The carbon source includes amorphous carbon powder and / or graphite powder.

3. The preparation method according to claim 1 or 2, characterized in that: The particle size of the carbon source is 400-500 nm.

4. The preparation method according to claim 3, characterized in that: The carbon source includes one or more of activated carbon, coal powder, and biochar powder.

5. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of the silicon source to the carbon source is 1:3-4; The mass of the boron source is 1-5% of the sum of the mass of the silicon source and the carbon source.

6. The preparation method according to claim 1, characterized in that: The sol-gel method specifically comprises the following steps: Mixing a boron source, a carbon source and a water-ethanol mixed solvent, adding a silicon source thereto and dispersing the mixture until the mixture is in a colloidal state; The molar ratio of the silicon source, the ethanol and the water is 1:5-6:5-6.

7. The preparation method according to claim 1, characterized in that: The vacuum microwave sintering conditions include: microwave input power of 2-2.4 kW, temperature of 1000-1200° C., and heat preservation time of 5-15 minutes.

8. The preparation method according to claim 1 or 7, characterized in that: The microwave heating frequency of the vacuum microwave sintering is 915 MHz or 2450 MHz.

9. The preparation method according to claim 8, characterized in that: The vacuum microwave sintering of the mixed powder specifically comprises the following steps: The mixed powder is placed in a quartz tube for vacuum treatment; microwaves are used to penetrate the heat-insulating material to completely cover the quartz tube containing the mixed powder; the quartz tube is placed in a microwave oven for vacuum extraction and pressure drawing, and after the extraction and pressure drawing is completed, the quartz tube is sealed for vacuum microwave sintering.

10. The preparation method according to claim 9, characterized in that: The microwave-transmitting heat-insulating material comprises mullite heat-insulating wool; The melting point of the microwave-transmitting heat-insulating material is 1400-1800°C.

Images