Preparation method of high-purity submicron 3C-SiC powder

Abstract

The invention belongs to the technical field of powder preparation, and relates to a preparation method of submicron 3C-SiC powder, which comprises the following steps: (1) mixing silicon powder, a carbon-containing raw material and a fluorine-containing raw material according to a certain proportion, fully ball-milling and uniformly mixing the powder and then drying, (2) putting the dried powder into an atmosphere furnace, introducing argon atmosphere, heating to 1400-1500 DEG C, preserving heat for 1-3 hours, and cooling to room temperature to obtain the submicron 3C-SiC powder. And (3) putting the reacted powder into a muffle furnace, and carrying out carbon removal treatment, so as to obtain the high-purity 3C-SiC powder. And the prepared powder is uniform in morphology and granularity and relatively high in purity. The method is simple, has low requirements on instruments and equipment, and is suitable for batch production. The 3C-SiC powder synthesized and prepared through the method is uniform in particle size (about 130 nm) and special in morphology, and a spherical structure is formed. The method is relatively simple in preparation process and convenient to operate, and lays a certain foundation for industrial production.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic non-metallic materials and relates to a method for preparing sub-micron high-purity 3C-SiC powder. Technical Background

[0002] Silicon carbide (SiC) is a very important engineering structural material. It has high mechanical strength, good chemical stability, high-temperature stability, excellent corrosion resistance, and a wide range of raw material sources. It has extensive applications in industries such as abrasive materials, engineering ceramics, and refractory materials. SiC has many crystal structures, such as 4H, 6H, 3C, 15R, etc. Among them, 4H, 6H and other crystal forms of SiC belong to the hexagonal crystal system, and their band gaps are about 3.2 - 3.6. The 3C crystal form of SiC belongs to the cubic crystal system, and its band gap is about 1.6 - 2.8. The 15R crystal form of SiC belongs to the orthorhombic crystal system, and its band gap is between cubic SiC and hexagonal SiC. Among them, in addition to the advantages of SiC as a structural material, 3C-SiC has a relatively narrow band gap. It is a typical representative of the third-generation semiconductors after the first-generation semiconductors such as Si and Ge and the second-generation semiconductors such as GaAs and InSb. It has characteristics such as high breakdown electric field, high saturated electron velocity, high thermal conductivity, high electron density, high mobility, and the ability to withstand high power. It has broad application prospects in fields such as semiconductor lighting, satellite navigation, power electronics, digital communication, aerospace, lasers, and detectors. It is an integrated material with both structural properties and functional applications.

[0003] 3C-SiC powder is the main raw material for preparing 3C-SiC ceramic products and is the basis and top priority in the preparation of 3C-SiC ceramics. The quality of 3C-SiC powder largely determines the performance of SiC ceramics. Especially in fields such as semiconductors, aerospace, digital communication, and thermoelectric materials, the main performance aspects they focus on, such as band gap, dielectric constant, breakdown field strength, electron drift saturation velocity, thermal conductivity, electron mobility, etc., are closely related to the micro-morphology, crystal structure, impurity content, defect density, grain size, etc. of 3C-SiC ceramics. Therefore, it is necessary to require that the 3C-SiC used as raw material has high purity, low impurity content, suitable particle size distribution, band gap, etc. This poses high requirements for the preparation of 3C-SiC.

[0004] At present, a variety of methods for preparing 3C-SiC powder have been developed. The main methods include mechanical alloying, sol-gel, self-propagating high-temperature synthesis, chemical vapor deposition, molten salt-assisted synthesis, and carbothermal reduction method, etc. The content of impurity phases in the 3C-SiC powder prepared by mechanical alloying will increase with the prolongation of the preparation time. Therefore, the reaction rate and purity are not easy to control. The preparation process of sol-gel is relatively complex and the cost is relatively high. At present, only a small amount can be prepared under laboratory conditions, and it is difficult to carry out industrial production. The self-propagating high-temperature synthesis process is difficult to precisely control in terms of temperature and reaction rate, lacks a controllable gas-phase transport process, the prepared powder has a large particle size, low purity, and uneven morphology, which limits its performance in practical applications. The chemical vapor deposition method is similar to the sol-gel method, with complex equipment, high cost, and low output, and it is not easy to achieve mass production. The 3C-SiC powder prepared by the molten salt method will have a small amount of salt or its ionic components remaining on the final product due to the internal interaction between the salt and the product. This will affect its physical and chemical properties, making it difficult to produce high-quality products. At present, the carbothermal reduction method is mainly used in industrial production of 3C-SiC powder. At present, 3C-SiC powder with larger particles can be prepared, and some manufacturers also have small-particle products, most of which are ground from large-particle products, and a part of impurities will be introduced, which are difficult to remove, bringing many adverse effects to the performance of 3C-SiC ceramic products. Summary of the Invention

[0005] The present invention realizes a new method for preparing submicron 3C-SiC powder. The prepared powder has uniform morphology and particle size and high purity. This method is simple and has low requirements for instrument equipment, and is suitable for batch production.

[0006] The reaction raw materials of the present invention are composed of a mixture of silicon powder, carbon-containing raw materials, and fluorine-containing raw materials, and include the following steps:

[0007] (1) Weigh 50-80 wt% of silicon powder with a purity of 99.99 wt% and a particle size of 40-200 mesh, 20-40 wt% of carbon-containing raw materials with a purity of 99.95 wt% and a particle size of about 40-5000 mesh, and 5-30 wt% of fluorine-containing raw materials with a particle size of about 40-1000 mesh as an additive;

[0008] (2) Put the above powders into a SiC ball mill tank, add alcohol as a dispersion liquid, and use SiC balls as the ball milling medium. After ensuring that all components are uniformly mixed by ball milling, dry them;

[0009] (3) Heat the powder to 1400-1600 °C in an atmosphere furnace under an argon atmosphere (purity 99.999 vol%) and hold for 1-5 hours;

[0010] (4) Sinter in a muffle furnace for 1 - 3 hours in an air atmosphere at 600 - 700 °C to remove excess carbon;

[0011] Further, the graphite in step (1) refers to a raw material mainly composed of carbon, which can be coke, graphite, carbon black, etc. The fluorine-containing raw material in step (1) refers to an organic compound containing fluorine, and may also contain elements such as silicon and carbon at the same time, such as fluororubbers or fluororesins like polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, etc.;

[0012] Further, the dispersion alcohol in step (2) can be one or more of acetone, gasoline, hexane, heptane, etc.;

[0013] Further, the ball milling time in step (2) is 1 - 8 hours;

[0014] Further, the ball-to-material ratio of ball milling in step (2) is 20 - 30∶1.

[0015] Further, the drying temperature in step (2) is 60 - 80 °C, and the drying time is 3 - 10 hours.

[0016] Further, the heating rate in step (3) is 2 - 5 °C / min.

[0017] The present invention proposes a preparation scheme for 3C-SiC powder. During the reaction of Si and C, a reduction system of Si-C-F is established, and the synthesis process is controlled by the generation of SiF4 or related gas phases, thereby preparing 3C-SiC powder with controllable particle size, high purity, uniform particle size distribution, small band gap, high carrier concentration, and good sintering performance.

[0018] The advantages and innovations of the present invention are as follows: An invention of a preparation method for submicron 3C-SiC powder realizes the control of the grain size and morphology of 3C-SiC by controlling process parameters such as the content of fluorine-containing additives, temperature, and time. The prepared 3C-SiC powder has uniform particle size, and the smallest median particle size reaches about 130 nm, and the morphology is spherical. The preparation process of this method is relatively simple, the size and shape of SiC particles are controllable, which lays a certain foundation for industrial production. Detailed Embodiments

[0019] The technical solution of the present invention will be further described below with specific embodiments. It should be noted that for ordinary technicians in the technical field, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

[0020] Example 1:

[0021] Weigh 7 g of silicon powder with a purity of 99.99% and a particle size of 40 - 200 mesh, 3 g of graphite with a purity of 99.95% and a particle size of 1000 mesh, and 1 g of polyvinylidene fluoride with a particle size of 1000 mesh. Put the above powders into a SiC ball mill jar, add alcohol as a dispersion liquid, use SiC balls as the ball milling medium, with a ball-to-material ratio of 25:1. After ball milling for 2 h, dry in a constant temperature blast drying oven at 60 °C for 6 h. Heat the powder to 1500 °C at a heating rate of 5 °C / min in an argon atmosphere, and keep it at this temperature for 1 h to obtain the product. Sinter the synthesized product in a muffle furnace at 700 °C in an air atmosphere for 1 h to remove the excess carbon.

[0022] Example 2:

[0023] Weigh 7 g of silicon powder with a purity of 99.99% and a particle size of 40 - 200 mesh, 3 g of graphite with a purity of 99.95% and a particle size of 1000 mesh, and 1 g of polytetrafluoroethylene with a particle size of 1000 mesh. Put the above powders into a SiC ball mill jar, add alcohol as a dispersion liquid, use SiC balls as the ball milling medium, with a ball-to-material ratio of 25:1. After ball milling for 2 h, dry in a constant temperature blast drying oven at 60 °C for 6 h. Heat the powder to 1500 °C at a heating rate of 5 °C / min in an argon atmosphere, and keep it at this temperature for 1 h to obtain the product. Sinter the synthesized product in a muffle furnace at 700 °C in an air atmosphere for 1 h to remove the excess carbon.

[0024] Example 3:

[0025] Weigh 7 g of silicon powder with a purity of 99.99% and a particle size of 40 - 200 mesh, 3 g of graphite with a purity of 99.95% and a particle size of 1000 mesh, and 2 g of polytetrafluoroethylene with a particle size of 1000 mesh. Put the above powders into a SiC ball mill jar, add alcohol as a dispersion liquid, use SiC balls as the ball milling medium, with a ball-to-material ratio of 25:1. After ball milling for 2 h, dry in a constant temperature blast drying oven at 60 °C for 6 h. Heat the powder to 1500 °C at a heating rate of 5 °C / min in an argon atmosphere, and keep it at this temperature for 1 h to obtain the product. Sinter the synthesized product in a muffle furnace at 700 °C in an air atmosphere for 1 h to remove the excess carbon.

[0026] Example 4:

[0027] Weigh 7 g of silicon powder with a purity of 99.99% and a particle size of 40 - 200 mesh, 3 g of carbon black with a purity of 99.95% and a particle size of 1000 mesh, and 3 g of polytetrafluoroethylene with a particle size of 1000 mesh. Put the above powders into a SiC ball mill jar, add alcohol as a dispersion liquid, use SiC balls as the ball milling medium, with a ball-to-material ratio of 25:1. After ball milling for 2 h, dry in a constant temperature blast drying oven at 60 °C for 6 h. Heat the powder to 1500 °C at a heating rate of 5 °C / min in an argon atmosphere, and keep it at this temperature for 1 h to obtain the product. Sinter the synthesized product in a muffle furnace at 700 °C in an air atmosphere for 1 h to remove the excess carbon.

[0028] In the present invention, since polytetrafluoroethylene provides a partial carbon source, a carbon-rich environment is provided for the formation of 3C-SiC. Under carbon-rich conditions, the formation of silicon carbide is mainly limited by the silicon content, which means that the yield of silicon carbide will depend to a large extent on the available amount of silicon.

[0029] When using polytetrafluoroethylene as the fluorine-containing raw material, the XRD detection results show 3C-SiC, and no other phases are detected. The median particle size of the powder with 0 wt% addition is 2 μm, the median particle size of the powder with 10 wt% addition is 500 nm, the median particle size of the powder with 20 wt% PTFE addition is about 100 nm, and the median particle size of the powder with 30 wt% addition is about 300 nm.

Claims

1. A method for preparing high-purity sub-micron 3C-SiC powder, characterized in that, The reaction raw materials are composed of silicon powder, carbon-containing raw materials and fluorine-containing raw materials. The preparation steps of 3C-SiC powder are as follows: (1) Weigh 50 - 80 wt% of silicon powder with a purity of 99.99 wt% and a particle size of 40 - 200 mesh, 20 - 40 wt% of carbon-containing raw materials with a purity of 99.95 wt% and a particle size of 40 - 5000 mesh, and 5 - 30 wt% of fluorine-containing raw materials with a particle size of 40 - 1000 mesh as additives; (2) Put the above powders into a SiC ball mill tank, add alcohol as a dispersion liquid, and use SiC balls as ball milling media. After ensuring that all components are evenly mixed by ball milling, dry them; (3) Heat the powder to 1400 - 1600 °C in an argon atmosphere with a purity of 99.999 vol% in an atmosphere furnace and keep it warm for 1 - 5 hours; (4) Sinter in a muffle furnace for 1 - 3 hours in an air atmosphere at 600 - 700 °C to remove excess carbon.

2. The method for preparing submicron 3C-SiC powder as claimed in claim 1, wherein The graphite in step (1) refers to raw materials with carbon as the main component, which can be coke, graphite, or carbon black. The fluorine-containing raw materials in step (1) refer to organic substances containing fluorine, and can also contain silicon and carbon elements at the same time, including polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride fluororubber, or fluororesin.

3. The method for preparing submicron 3C-SiC powder according to claim 1, characterized in that, The dispersion liquid alcohol in step (2) is one or several of acetone, gasoline, hexane, and heptane.

4. The method for preparing submicron 3C-SiC powder as claimed in claim 1, wherein, The ball milling time in step (2) is 1 - 8 hours.

5. The method for preparing submicron 3C-SiC powder according to claim 1, characterized in that, The ball-to-material ratio of ball milling in step (2) is 20 - 30∶1.

6. The method for preparing submicron 3C-SiC powder according to claim 1, wherein, The drying temperature in step (2) is 60 - 80 °C, and the drying time is 3 - 10 hours.

7. The method for preparing submicron 3C-SiC powder according to claim 1, characterized in that, The heating rate in step (3) is 2 - 5 °C / min.