A method for preparing nano-silicon carbide

Abstract

This invention belongs to the field of silicon carbide preparation technology and provides a method for preparing nano-sized silicon carbide. The silicon-carbon precursor decamethylcyclopentasiloxane of this invention undergoes pyrolysis in a hydrogen plasma and argon plasma environment to produce silicon carbide gas. Rapid cooling of the silicon carbide gas ensures the production of small-sized nano-sized silicon carbide. Simultaneously, the molar ratio of carbon, silicon, and oxygen in decamethylcyclopentasiloxane is 2:1:1, where the oxygen converts half of the carbon into carbon monoxide, leaving a 1:1 molar ratio of carbon to silicon, resulting only in silicon carbide. Furthermore, the byproduct carbon monoxide is gaseous and will not contaminate the final silicon carbide product. Even if elemental carbon and silicon are generated, their content is extremely low, thus ensuring the purity of the final silicon carbide. Data from the examples show that the obtained nano-sized silicon carbide has a purity ≥95% and a size of 20–500 nm.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide preparation technology, and more particularly to a method for preparing nano-silicon carbide. Background Technology

[0002] Silicon carbide (SiC) possesses many excellent properties, such as high temperature resistance, high hardness, high mechanical strength, low coefficient of thermal expansion, unique optical properties, and high-temperature semiconductor characteristics. These properties make it widely used in functional or structural components, such as electronic devices, solar cells, and solar water splitters. Over the past few decades, scientists have proposed various methods for synthesizing SiC, including carbothermal reduction, chemical vapor deposition (CVD), electrochemical etching, and chemical etching. Among these, carbothermal reduction requires high temperatures and long reaction times, resulting in the sintering of silicon carbide into large particles. CVD processes also typically produce silicon carbide nanoparticles with relatively large particle sizes. Electrochemical / chemical etching methods can prepare small-sized silicon carbide nanoparticles, but their relatively high cost limits their further applications. Summary of the Invention

[0003] In view of this, the object of the present invention is to provide a method for preparing nano-silicon carbide. The preparation method provided by the present invention can obtain nano-silicon carbide at a low cost.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing nano-silicon carbide, comprising the following steps:

[0006] Using decamethylcyclopentasiloxane as a silicon-containing carbon precursor and argon as the arc-initiating atmosphere gas, the silicon-containing carbon precursor was pyrolyzed by magnetic rotating arc plasma method in the environment of hydrogen plasma and argon plasma, and then rapidly cooled to obtain the nano-silicon carbide.

[0007] The cooling rate of the rapid cooling is ≥2000K / s.

[0008] Preferably, the parameters of the magnetic rotating arc plasma method include: the arc current is 100-3000A and the excitation current is 100-1000A.

[0009] Preferably, the feed rate of the decamethylcyclopentasiloxane is 0.9 to 900 kg / h.

[0010] Preferably, the atmosphere for generating the hydrogen plasma environment includes hydrogen gas, and the volume ratio of hydrogen gas to argon gas is (0-100):1, wherein the hydrogen gas content is not 0.

[0011] Preferably, the total flow rate of the hydrogen and argon is 1–4000 Nm³. 3 / h.

[0012] Preferably, the rapid cooling includes indirect water cooling or contact air cooling.

[0013] Preferably, the quenching gas used in the contact gas cooling includes argon; the flow rate of the quenching gas is 0–6000 Nm³. 3 / h, and the flow rate of the quenching gas is not 0.

[0014] Preferably, the size of the nano-silicon carbide is 20–500 nm.

[0015] This invention provides a method for preparing nano-sized silicon carbide, comprising the following steps: using decamethylcyclopentasiloxane as a silicon-carbon precursor and argon as the arc-initiating atmosphere gas, the silicon-carbon precursor is pyrolyzed using a magnetic rotating arc plasma method in a hydrogen plasma and argon plasma environment, followed by rapid cooling to obtain the nano-sized silicon carbide; the rapid cooling rate is ≥2000 K / s. The silicon-carbon precursor decamethylcyclopentasiloxane of this invention undergoes pyrolysis in a hydrogen plasma and argon plasma environment to produce silicon carbide gas; the rapid cooling of the silicon carbide gas ensures the yield of small-sized nano-sized silicon carbide. Meanwhile, in decamethylcyclopentasiloxane, the molar ratio of carbon, silicon, and oxygen is 2:1:1. Under hydrogen plasma conditions, the oxygen converts half of the carbon into carbon monoxide, leaving a 1:1 molar ratio of carbon to silicon, which can only produce silicon carbide. Furthermore, the byproduct carbon monoxide is gaseous and will not contaminate the final silicon carbide product; the carbon monoxide can be collected and reused. Even if elemental carbon and silicon are produced, their amounts are extremely small, thus ensuring the purity of the final silicon carbide. Data from the examples show that the purity of the obtained nano-silicon carbide is ≥95%, and the size is 20–500 nm. The preparation method provided by this invention yields nano-silicon carbide with small size. Attached Figure Description

[0016] Figure 1 XRD patterns of nano-silicon carbide prepared under different quenching gas flow rates;

[0017] Figure 2 TEM images of silicon carbide nanoparticles prepared under different quenching gas flow rates;

[0018] Figure 3 XRD patterns of silicon carbide nanoparticles prepared under different average arc powers;

[0019] Figure 4 TEM images of silicon carbide nanoparticles prepared under different average arc powers. Detailed Implementation

[0020] This invention provides a method for preparing nano-silicon carbide, comprising the following steps:

[0021] Using decamethylcyclopentasiloxane as a silicon-containing carbon precursor and argon as the arc-initiating atmosphere gas, the silicon-containing carbon precursor was pyrolyzed by magnetic rotating arc plasma method in the environment of hydrogen plasma and argon plasma, and then rapidly cooled to obtain the nano-silicon carbide.

[0022] The cooling rate of the rapid cooling is ≥2000K / s.

[0023] Unless otherwise specified, all raw materials used in this invention are preferably commercially available products.

[0024] In this invention, the feed rate of the decamethylcyclopentasiloxane is preferably 0.9 to 900 kg / h, more preferably 0.9 to 300 kg / h, and even more preferably 10 to 200 kg / h.

[0025] In this invention, the atmosphere for generating the hydrogen plasma environment includes hydrogen gas. In this invention, the argon gas serves both as the arc-starting atmosphere gas and as the environment for generating argon plasma. In this invention, the volume ratio of hydrogen to argon is preferably (0–100):1, wherein the hydrogen content is not zero. In this invention, the volume ratio of hydrogen to argon is more preferably 1–50:1, and even more preferably 1:1. In this invention, the total flow rate of hydrogen and argon is preferably 1–4000 Nm³. 3 / h, more preferably 3.6~2000Nm 3 / h, more preferably 100~1000Nm 3 / h.

[0026] In this invention, the parameters of the magnetic rotating arc plasma method include: the arc current is preferably 100–3000 A, more preferably 120–1000 A, and even more preferably 150–300 A; the excitation current is preferably 100–1000 A, more preferably 400–800 A. In this invention, the arc current of 100–3000 A corresponds to an arc operating power of 10–10000 kW. In this invention, the arc's energy output is preferably 5–5000 g / min.

[0027] In this invention, the rapid cooling preferably includes indirect water cooling or contact gas cooling. In this invention, the quenching gas used in the contact gas cooling preferably includes argon; the flow rate of the quenching gas is preferably 0–6000 Nm³. 3 / h, and the flow rate of the quenching gas is not 0, more preferably 2-6 Nm³. 3 / h, further preferably 4Nm 3 / h.

[0028] In this invention, the method for preparing the nano-silicon carbide is preferably carried out in a coal-to-acetylene plasma reactor with coking suppression and online coking removal functions as disclosed in Chinese Patent Publication No. CN110918026A.

[0029] In this invention, decamethylcyclopentasiloxane is used as a silicon-containing carbon precursor, argon is used as the arc-initiating atmosphere gas, and the silicon-containing carbon precursor is pyrolyzed using a magnetic rotating arc plasma method in a hydrogen plasma and argon plasma environment. After rapid cooling, the preferred specific process for obtaining the nano-silicon carbide is as follows:

[0030] Argon gas is used to replace the air in the plasma reactor. The power supply is started to generate plasma under an argon atmosphere. Hydrogen gas is then introduced to convert the atmosphere into a mixture of argon plasma and hydrogen plasma. After stable operation, a hydraulic pump is started, and a silicon-carbon precursor is fed into the plasma reactor under the drive of a carrier gas. The silicon-carbon precursor decomposes to form silicon carbide gas. The silicon carbide gas is then rapidly cooled to form nano-silicon carbide, which is collected. In this invention, the rapid cooling device preferably includes a device for loading quenching gas or a water-cooling device installed on the outer wall of the plasma reactor. In this invention, when the rapid cooling is a contact-type gas cooling, the quenching gas preferably enters the plasma reactor through a quenching nozzle. In this invention, the quenching gas preferably comes into countercurrent contact with the silicon carbide gas, which is more conducive to improving the rapid cooling efficiency.

[0031] In this invention, the size of the nano-silicon carbide is preferably 20-500 nm, more preferably 100-300 nm.

[0032] The nano-silicon carbide provided by this invention has a small size.

[0033] The following detailed description of the preparation method of nano-silicon carbide provided by the present invention is based on the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0034] Example 1

[0035] The preparation of nano-silicon carbide is disclosed in Chinese Patent No. CN110918026A, which has the functions of inhibiting coking and online coking removal.

[0036] This embodiment illustrates that different quenching temperature gradients caused by different quenching gas flow rates have a significant control effect on the particle size of silicon carbide.

[0037] The specific steps are as follows:

[0038] Argon gas is introduced to displace the air in the plasma reactor. After the air is completely displaced, the electric arc is started in an argon atmosphere. The arc current is set to 150A (corresponding to an arc operating power of 20-25kW), and the excitation current is set to 400A. Then, hydrogen gas is introduced into the plasma reactor. Once the arc operates stably in the hydrogen and argon atmosphere, a mixed atmosphere of hydrogen and argon plasma is formed (the volume ratio of H2 to Ar in generating the mixed atmosphere is 1:1, and the total flow rate is 3.6 Nm³). 3 / h); then, decamethylcyclopentasiloxane, a silicon-carbon precursor, is introduced via a hydraulic pump (feed rate of 0.9 kg / h). The decamethylcyclopentasiloxane is cracked at the electric arc to form silicon carbide gas. The steel cylinder containing quenching argon is then opened, allowing the quenching gas (flow rates of quenching argon and 0 Nm³) to be released. 3 / h、2Nm 3 / h、4Nm 3 / h、6Nm 3 The silicon carbide gas is introduced into the plasma reactor through a quenching nozzle at / h, and the generated silicon carbide gas is cooled and collected.

[0039] Figure 1 XRD patterns of nano-silicon carbide prepared under different quenching gas flow rates, from... Figure 1 It can be seen that there are multiple diffraction peaks at 2θ≈35.6°, 41.4°, 60.0°, 71.4° and 75.1°, which correspond to the diffraction crystal planes of 3C-SiC at (111), (200), (220), (311) and (222), respectively, indicating that 3C-SiC is the main crystalline phase in the product. The sample has obvious amorphous SiO2 diffraction peaks at 2θ≈23°, proving that part of the product is oxidized to SiO2; the purity of the nano-silicon carbide is about 95%.

[0040] Figure 2 TEM images of silicon carbide nanoparticles prepared under different quenching gas flow rates, from... Figure 2 It can be seen that: similar hexagonal and spherical SiC particles are produced. With the increase of quenching gas flow, the number of large particles above 300nm is reduced. Overall, the particle size of the prepared products is mostly 100-300nm, and the smallest particle size is 30nm.

[0041] Example 2

[0042] The preparation of nano-silicon carbide is disclosed in Chinese Patent No. CN110918026A, which has the functions of inhibiting coking and online coking removal.

[0043] This embodiment investigates the effect of arc operating power on the temperature inside the plasma torch on silicon carbide products.

[0044] The specific steps are as follows:

[0045] Argon gas is introduced to replace the air in the plasma reactor. After the air is completely replaced, the electric arc is started in an argon atmosphere, with the excitation current set to 400A. The operating power of the arc is controlled by adjusting the arc's operating current to 13–16 kW, 18–24 kW, 21–29 kW, and 25–28 kW. Hydrogen gas is then introduced into the plasma reactor. Once the arc operates stably in the hydrogen and argon atmosphere, a mixed atmosphere of hydrogen and argon plasma is formed (the volume ratio of H2 to Ar in generating the mixed atmosphere is 1:1, and the total flow rate is 3.6 Nm³). 3 The silicon-carbon precursor, decamethylcyclopentasiloxane, is fed via a hydraulic pump at a rate of 0.9 kg / h. The decamethylcyclopentasiloxane is decomposed at an electric arc to form silicon carbide gas. The cylinder containing argon quenching gas is then opened, allowing the quenching gas (flow rate of argon quenching gas to be 4 Nm³ / h) to be released. 3 The silicon carbide gas is introduced into the plasma reactor through a quenching nozzle at / h, and the generated silicon carbide gas is cooled and collected.

[0046] Figure 3 XRD patterns of nano-silicon carbide prepared under different arc operating powers are shown. Figure 3 It can be seen that five characteristic peaks of 3C-SiC were obtained under different arc operating powers, confirming that 3C-SiC is the main crystalline phase in the product, but still contains a small amount of impurity SiO2 (22°); the purity of nano silicon carbide is 95%.

[0047] Figure 4 TEM images of silicon carbide nanoparticles prepared under different arc operating powers, from... Figure 4 It can be seen that: both produce SiC particles with similar three-dimensional hexagonal and spherical shapes, and the particle size increases with the increase of the arc power. The intensity of the diffraction peak of the (111) crystal plane also increases with the increase of the arc power. The smallest particle size is 20 nm at low power, and the particle size of the prepared nano-silicon carbide is mostly 100-200 nm.

[0048] Example 3

[0049] The preparation of nano-silicon carbide is disclosed in Chinese Patent No. CN110918026A, which has the functions of inhibiting coking and online coking removal.

[0050] This embodiment demonstrates the application of a large-scale plasma reactor in the preparation of silicon carbide nanoparticles.

[0051] The specific steps are as follows:

[0052] Argon gas is introduced to replace the air in the plasma reactor. After the air is completely replaced, the plasma arc is started in an argon atmosphere. The arc current is set to 3000A (corresponding to an arc operating power of 6MW), and the excitation current is set to 1000A. Then, hydrogen gas is introduced into the plasma reactor. After the arc operates stably in the hydrogen and argon atmosphere, a mixed atmosphere of hydrogen and argon plasma is formed (the volume ratio of H2 to Ar in generating the mixed atmosphere is 1:1, and the total flow rate is 4000 Nm³). 3 / h); The silicon-carbon precursor decamethylcyclopentasiloxane is fed into the plasma reactor via a hydraulic pump at a feed rate of 300 kg / h. The decamethylcyclopentasiloxane is cracked at the electric arc to form silicon carbide gas, and a large flow rate of quenching gas (argon quenching gas flow rate of 6000 Nm³) is added. 3 The silicon carbide gas is introduced into the plasma reactor through a quenching nozzle at / h, and the generated silicon carbide gas is cooled and collected.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing nano-silicon carbide, characterized in that, The steps are as follows: Using decamethylcyclopentasiloxane as a silicon-containing carbon precursor and argon as the arc-initiating atmosphere gas, the silicon-containing carbon precursor was pyrolyzed by magnetic rotating arc plasma method in the environment of hydrogen plasma and argon plasma, and then rapidly cooled to obtain the nano-silicon carbide. The rapid cooling rate is ≥2000K / s; The parameters of the magnetic rotating arc plasma method include: the arc current is 100-3000A; The rapid cooling is a contact gas cooling method, and the quenching gas used in the contact gas cooling includes argon; the flow rate of the quenching gas is 0–6000 Nm³. 3 / h, and the flow rate of the quenching gas is not 0; the quenching gas is in countercurrent contact with the silicon carbide gas; The method for preparing nano-silicon carbide is carried out in a coal-to-acetylene plasma reactor with functions of inhibiting coking and online coking removal.

2. The preparation method according to claim 1, characterized in that, The parameters of the magnetic rotating arc plasma method include: excitation current of 100-1000A.

3. The preparation method according to claim 1, characterized in that, The feed rate of the decamethylcyclopentasiloxane is 0.9–900 kg / h.

4. The preparation method according to claim 1, characterized in that, The atmosphere that generates the hydrogen plasma environment includes hydrogen gas, and the volume ratio of hydrogen gas to argon gas is (0-100):1, wherein the hydrogen gas content is not 0.

5. The preparation method according to claim 4, characterized in that, The total flow rate of hydrogen and argon is 1–4000 Nm³. 3 / h.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The size of the nano-silicon carbide is 20–500 nm.

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