Process for the preparation of beta silicon carbide powder

Abstract

The application discloses a preparation method of beta-phase silicon carbide powder and relates to the technical field of silicon carbide preparation. The method comprises the following steps: heating a solid-phase reaction high-temperature furnace until the temperature in the solid-phase reaction high-temperature furnace is 900-1100 DEG C, the heat preservation time is 8-12 h, and inert gas which does not react with carbon-silicon mixed powder is introduced into the solid-phase reaction high-temperature furnace during the heating process so that the pressure in the solid-phase reaction high-temperature furnace is 80-120 mTorr; continuously heating the solid-phase reaction high-temperature furnace until the temperature in the solid-phase reaction high-temperature furnace is 1300-1500 DEG C, the heat preservation time is 10-20 h, and the inert gas is introduced into the solid-phase reaction high-temperature furnace during the heating process so that the pressure in the solid-phase reaction high-temperature furnace is 0-50 mTorr. The method improves the axial and radial uniformity of the crucible, makes the reaction efficiency of the silicon carbide powder higher, and basically has no residual free silicon and free carbon.

Description

Technical Field

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

[0002] High-purity β-phase silicon carbide (β-SiC) plays a crucial role in several high-end industrial fields due to its unique cubic crystal structure and excellent comprehensive properties. β-phase silicon carbide powder is mainly prepared using the following methods: 1) Chemical vapor deposition: Using gases such as silane as a source, SiC can be generated in the gas phase to obtain nanoscale powders with extremely high purity, but the equipment is expensive, the output is low and the cost is high. 2) Sol-gel method: A molecularly uniform precursor is formed through a solution chemical reaction, and then molecular-level mixing can be achieved through heat treatment. The powder quality is high, but the production cycle is long and the process control is complex. 3) Mechanical grinding and purification: Mechanical grinding and chemical purification of industrial silicon carbide are low-cost, but the purity is limited and it is difficult to meet the requirements of semiconductor grade. 4) Improved self-propagating high-temperature synthesis method: Silicon powder and carbon powder undergo a direct solid-state reaction: Si + C → SiC. This method has relatively low cost, high output per furnace, and mature technology.

[0003] Among them, the improved self-propagating high-temperature synthesis method is currently the mainstream method for the industrial preparation of high-purity β-phase silicon carbide, but it still has some technical problems that need to be solved: 1) Uneven mixing of raw materials and carbon encapsulation: Silicon powder and carbon powder differ in density and particle size, and are prone to stratification during mixing and reaction, resulting in local imbalance of silicon-carbon stoichiometry. 2) Silicon volatilization leads to pollution and imbalance: Silicon is easily volatilized at the reaction temperature to form silicon vapor, which disrupts the silicon-carbon ratio of the raw materials, resulting in residual free carbon in the synthesized powder and a decrease in purity; 3) Uneven thermal field: Traditional single-layer crucible designs are prone to temperature gradients in the radial and axial directions, resulting in inconsistent reaction degrees; 4) Free carbon / silicon residue and subsequent treatment: In addition to uneven mixing of raw materials, the solid-phase reaction itself has diffusion limitations, which may lead to incomplete reaction and residual free carbon. Additional decarbonization processes (such as high-temperature oxidation) are required to remove free carbon, which increases the number of processes and may introduce new pollution risks. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a method for preparing β-phase silicon carbide powder to solve the technical problems existing in the prior art.

[0005] To achieve the above objectives, an embodiment of the present invention provides a method for preparing β-phase silicon carbide powder, comprising the following steps: Step A: Mix silicon powder and carbon powder, and load the silicon-carbon mixture into a graphite crucible; Step B: Place the graphite crucible into the solid-state reaction high-temperature furnace and purge the air from the furnace. Step C: Heat the solid-state reaction high-temperature furnace until the temperature inside the furnace reaches 900-1100℃, and hold it for 8-12 hours. At the same time, during the heating process, an inert gas that does not react with the carbon-silicon mixed powder is introduced into the solid-state reaction high-temperature furnace so that the pressure inside the furnace is 80-120 mTorr. Step D: Continue to heat the solid-state reaction high-temperature furnace until the temperature inside the solid-state reaction high-temperature furnace is 1300-1500℃, and hold for 10-20 hours. At the same time, inert gas is introduced into the solid-state reaction high-temperature furnace during the heating process so that the pressure inside the solid-state reaction high-temperature furnace is 0-50mTorr. Step E: Continue to heat the solid-state reaction high-temperature furnace until the temperature inside the solid-state reaction high-temperature furnace is 1700-1900℃, and hold it for 15-40 hours. At the same time, inert gas is introduced into the solid-state reaction high-temperature furnace during the heating process so that the pressure inside the solid-state reaction high-temperature furnace is 10-30 Torr. Step F involves cooling the product in the graphite crucible in the furnace while continuously introducing inert gas into the high-temperature solid-phase reaction furnace during the cooling process, thereby obtaining β-phase silicon carbide powder.

[0006] Optionally, in step A, the mass percentage of silicon powder is 65-85 wt%, and the mass percentage of carbon powder is 15-35 wt%.

[0007] Optionally, in step A, the mass percentage of silicon powder is 74–82 wt%, and the mass percentage of carbon powder is 18–26 wt%.

[0008] Optionally, in step A, the particle size of the silicon powder is 10–100 μm, and the particle size of the carbon powder is 10–100 μm.

[0009] Optionally, in step A, the purity of the silicon powder is ≥99.9999%, and the purity of the carbon powder is ≥99.9999%.

[0010] Optionally, in step C, the rotation speed of the graphite crucible is 1 to 9 rad / min, and the rotation direction is changed every 0.8 to 1.2 h.

[0011] Optionally, in step D, the rotation speed of the graphite crucible is 1 to 9 rad / min, and the rotation direction is changed every 0.4 to 0.6 h.

[0012] Optionally, in step E, the rotation speed of the graphite crucible is 1 to 9 rad / min, and the rotation direction is changed every 0.4 to 0.6 h.

[0013] Optionally, the flow rate of the inert gas is 10–80 L / min.

[0014] Alternatively, the inert gas may be argon or helium.

[0015] One embodiment of the above invention has the following advantages or beneficial effects: the low-temperature activation stage, carried out below the ignition temperature, increases the radial and axial heat transfer time of the powder in the crucible, making the powder more uniformly heated; the medium-temperature reaction stage is at the critical point of the ignition temperature, avoiding excessively vigorous reactions that could lead to problems such as carbon coating, incomplete reaction, and abnormal grain growth; the high-temperature grain growth stage, carried out above the ignition temperature, further eliminates problems such as incomplete reaction and incomplete grain growth in the medium-temperature reaction stage through high-temperature diffusion, ensuring that the reaction is complete in all parts of the furnace. Therefore, this embodiment of the invention improves the axial and radial uniformity of the crucible through the coordinated operation of three stages of temperature-crucible rotation-pressure, resulting in higher reaction efficiency of silicon carbide powder and virtually no residual free silicon and free carbon.

[0016] The further effects of the aforementioned unconventional alternative methods will be explained below in conjunction with specific implementation methods. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a schematic diagram of the main process of the preparation method of β-phase silicon carbide powder according to an embodiment of the present invention; Figure 2 This is an XRD comparison diagram of the product obtained in the embodiments of the present invention and the product obtained in the prior art; Figure 3 This is a photographic comparison between the product obtained in the embodiments of the present invention and the product obtained in the prior art; Figure 4 This is a SEM comparison image of the product obtained in the embodiments of the present invention and the product obtained in the prior art. Detailed Implementation

[0018] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of the present invention, including various details to aid understanding. These details should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0019] Figure 1 This is a schematic diagram of the main process of a method for preparing β-phase silicon carbide powder according to an embodiment of the present invention. As one embodiment of the present invention, such as... Figure 1 As shown, the preparation method of β-phase silicon carbide powder may include the following steps: Step A: Mix silicon powder and carbon powder, and load the silicon-carbon mixture into a graphite crucible.

[0020] First, high-purity silicon powder (purity ≥ 99.9999%) and high-purity carbon powder (purity ≥ 99.9999%) are added to a mixer and mixed evenly to obtain a silicon-carbon mixed powder. After mixing, the silicon-carbon mixed powder is placed into a calcined high-purity graphite crucible. The silicon powder can be of any shape (e.g., near-spherical, semi-spherical, irregular angular, etc.), and the carbon powder can be of any shape (e.g., near-spherical, irregular angular, flake-like, fibrous, tubular carbon, etc.).

[0021] Considering that silicon easily volatilizes at the reaction temperature, forming silicon vapor and disrupting the silicon-to-carbon ratio of the raw materials, resulting in residual free carbon in the synthesized powder and a decrease in the purity of the β-phase silicon carbide powder, this invention proposes increasing the mass percentage of silicon powder. Even if silicon volatilizes during subsequent reactions, it will not cause an imbalance in the silicon-to-carbon ratio, thereby improving the purity of the β-phase silicon carbide powder. In some embodiments of this invention, the mass percentage of silicon powder is 65–85 wt%, and the mass percentage of carbon powder is 15–35 wt%, which can improve the purity of the β-phase silicon carbide powder. Optionally, the mass percentage of silicon powder is 74–82 wt%, and the mass percentage of carbon powder is 18–26 wt%. Optionally, the mass percentage of silicon powder is 76–80 wt%, and the mass percentage of carbon powder is 20–24 wt%. Preferably, the mass percentage of silicon powder is 67–73 wt%, and the mass percentage of carbon powder is 27–33 wt%, which can further improve the purity of the β-phase silicon carbide powder. For example, the mass percentage of silicon powder can be 78.11% and the mass percentage of carbon powder can be 21.89%; the mass percentage of silicon powder can be 80.2% and the mass percentage of carbon powder can be 19.8%; the mass percentage of silicon powder can be 69.25% and the mass percentage of carbon powder can be 30.75%; the mass percentage of silicon powder can be 71.38% and the mass percentage of carbon powder can be 18.62%; the mass percentage of silicon powder can be 70.19% and the mass percentage of carbon powder can be 29.81%. This embodiment of the invention does not limit these possibilities. Optionally, the particle size of the silicon powder is 10–100 μm, for example, the particle size of the silicon powder can be 20 μm, 28 μm, 35 μm, 50 μm, 75 μm, 88 μm, or 100 μm. Optionally, the particle size of the carbon powder is 10–100 μm, for example, the particle size of the carbon powder can be 22 μm, 28 μm, 31 μm, 45 μm, 70 μm, 92 μm, or 98 μm.

[0022] In some embodiments of the present invention, the frequency of the mixer can be set to 10–80 Hz, and the forward and reverse rotation times can be set to 0.5–3 hours to ensure uniform mixing of silicon powder and carbon powder. For example, the frequency of the mixer can be set to 15 Hz, 20 Hz, 30 Hz, 51 Hz, 66 Hz, or 75 Hz, and the forward and reverse rotation times can be set to 0.6 hours, 0.8 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 2.8 hours, respectively. The embodiments of the present invention do not impose any limitations on these settings.

[0023] Step B: Place the graphite crucible into the solid-state reaction high-temperature furnace and purge the air from the furnace.

[0024] The solid-state reaction high-temperature furnace can be a single crystal furnace, a graphite tube atmosphere furnace, a vacuum graphite box furnace, a vacuum graphite carbon tube resistance furnace, or an induction heating graphite high-temperature furnace, etc., and the embodiments of the present invention do not limit this.

[0025] After placing the graphite crucible into the solid-state reaction furnace, adjust the throttle valve opening and vacuum pump frequency to slowly evacuate the furnace. The evacuation rate can be ≤10 Torr / min, and the ultimate vacuum <20 mTorr. When the vacuum level is <20 mTorr, stop evacuating and introduce an inert gas (such as argon or helium) that does not react with the silicon carbide powder into the furnace until the pressure inside the furnace reaches atmospheric pressure. The inert gas flow rate can be 10–80 L / min. Then, slowly evacuate the furnace again. When the vacuum level is <20 mTorr, stop evacuating and introduce inert gas into the furnace until the pressure inside the furnace reaches atmospheric pressure. Repeat this evacuation-inert gas introduction operation 4–8 times until all air is expelled from the furnace, with a leakage rate ≤20 mTorr / h. Optionally, the flow rate of the inert gas can be 12 L / min, 20 L / min, 35 L / min, 42 L / min, 50 L / min, 68 L / min, or 72 L / min, and this embodiment of the invention does not impose any limitation on it. It should be noted that after the final vacuuming is completed, the solid-state reaction high-temperature furnace is close to a vacuum.

[0026] Step C: Heat the solid-state reaction high-temperature furnace until the temperature inside the furnace reaches 900-1100℃, and hold it for 8-12 hours. At the same time, during the heating process, an inert gas that does not react with the carbon-silicon mixed powder is introduced into the solid-state reaction high-temperature furnace so that the pressure inside the furnace is 80-120 mTorr.

[0027] After completely purging the air from the solid-state reaction high-temperature furnace, the furnace is heated until the temperature reaches 900–1100°C (below the system ignition temperature), and held at this temperature for 8–12 hours. Simultaneously, during the heating process, an inert gas (such as argon or helium) that does not react with the silicon-carbon mixture is introduced into the furnace, maintaining a pressure of 80–120 mTorr within the furnace. It is understood that, in the embodiments of this invention, the temperature within the solid-state reaction high-temperature furnace refers to the average temperature within the furnace. The flow rate of the inert gas can be 10–80 L / min, for example, 12 L / min, 20 L / min, 35 L / min, 42 L / min, 50 L / min, 68 L / min, or 72 L / min; this embodiment of the invention does not impose any limitations on this.

[0028] In step C, the low-vacuum environment effectively removes oxygen-containing functional groups from the carbon powder surface and the oxide film from the silicon powder surface. Simultaneously, prolonged temperature equalization ensures complete heat penetration of the entire batch of powder, eliminating localized carbon / silicon segregation caused by mixing. Furthermore, step C is the activation stage, which does not trigger a reaction, ensuring that the carbon-silicon ratio in all micro-regions of the entire system is close to the global stoichiometry, thus preventing subsequent localized component excesses from the outset.

[0029] In some embodiments of the present invention, after the air inside the solid-state reaction high-temperature furnace is completely purged, the furnace is heated until the temperature inside reaches 920°C, and the holding time is 11.2 hours. Simultaneously, argon gas is introduced into the furnace during the heating process to maintain a pressure of 95 mTorr inside the furnace. In other embodiments of the present invention, after the air inside the solid-state reaction high-temperature furnace is completely purged, the furnace is heated until the temperature inside reaches 950°C, and the holding time is 11 hours. Simultaneously, argon gas is introduced into the furnace during the heating process to maintain a pressure of 90 mTorr inside the furnace. In some embodiments of the present invention, after the air inside the solid-state reaction high-temperature furnace is completely purged, the furnace is heated until the temperature inside reaches 1000°C, and the holding time is 10 hours. Simultaneously, argon gas is introduced into the furnace during the heating process, resulting in a pressure of 100 mTorr inside the furnace. In still other embodiments of the present invention, after the air inside the solid-state reaction high-temperature furnace is completely purged, the furnace is heated until the temperature inside reaches 1080°C, and the holding time is 9.3 hours. Simultaneously, argon gas is introduced into the furnace during the heating process, resulting in a pressure of 88 mTorr inside the furnace. In some other embodiments of the present invention, after the air in the solid-state reaction high-temperature furnace is completely purged, the solid-state reaction high-temperature furnace is heated until the temperature inside the solid-state reaction high-temperature furnace reaches 1090°C and the holding time is 8.5h. At the same time, argon gas is introduced into the solid-state reaction high-temperature furnace during the heating process, so that the pressure inside the solid-state reaction high-temperature furnace is 105mTorr.

[0030] Optionally, in step C, the rotation speed of the graphite crucible is 1–9 rad / min, and the rotation direction is changed every 0.8–1.2 h. For example, the rotation speed of the graphite crucible can be 2 rad / min, 3.3 rad / min, 4 rad / min, 4.6 rad / min, 5 rad / min, 7 rad / min, or 8.2 rad / min, and the rotation direction is changed every 0.85 h, 0.92 h, 0.98 h, 1.11 h, 1.14 h, or 1.18 h.

[0031] Step D: Continue to heat the solid-state reaction high-temperature furnace until the temperature inside the furnace reaches 1300–1500℃, and hold for 10–20 hours. Simultaneously, during the heating process, inert gas is introduced into the solid-state reaction high-temperature furnace to maintain a pressure of 0–50 mTorr inside the furnace.

[0032] After the heat preservation process in step C is completed, the solid-state reaction high-temperature furnace is heated further until the temperature inside the furnace reaches 1300–1500°C (the melting point of silicon is 1410°C, reaching the critical point for reaction ignition). The heat preservation time is 10–20 hours. Simultaneously, an inert gas (such as argon or helium) is introduced into the solid-state reaction high-temperature furnace during the heating process to maintain a pressure of 0–50 mTorr (lower vacuum). The flow rate of the inert gas can be 10–80 L / min, for example, 12 L / min, 20 L / min, 35 L / min, 42 L / min, 50 L / min, 68 L / min, or 72 L / min. This embodiment of the invention does not impose any limitations on this.

[0033] Step D is the stable reaction stage. In step D, the extremely low vacuum can promptly remove trace amounts of gaseous byproducts generated during the reaction (such as residual oxygen and CO generated from the reaction of C), promoting the forward reaction. Moreover, the low pressure allows for faster diffusion of carbon and silicon atoms, ensuring sufficient contact and reaction between them. Simultaneously, the temperature is strictly controlled to not exceed 1500℃ to prevent violent silicon vaporization. The reaction propagates smoothly layer by layer, achieving a conversion rate of over 95%. It avoids the formation of a dense SiC shell encasing unreacted carbon and silicon powder due to excessively high temperatures causing deflagration.

[0034] In some embodiments of the present invention, after step C, the solid-state reaction furnace is further heated until the temperature inside the furnace reaches 1350°C, and the holding time is 18 hours. Simultaneously, an inert gas is introduced into the furnace during the heating process, resulting in a pressure of 10 mTorr inside the furnace. In other embodiments of the present invention, after step C, the solid-state reaction furnace is further heated until the temperature inside the furnace reaches 1388°C, and the holding time is 17.8 hours. Simultaneously, an inert gas is introduced into the furnace during the heating process, resulting in a pressure of 35 mTorr inside the furnace. In still other embodiments of the present invention, after step C, the solid-state reaction furnace is further heated until the temperature inside the furnace reaches 1410–1500°C, and the holding time is 15 hours. Simultaneously, an inert gas is introduced into the furnace during the heating process, resulting in a pressure of 2 mTorr inside the furnace. In some embodiments of the present invention, after step C, the solid-state reaction high-temperature furnace is further heated until the temperature inside the furnace reaches 1420°C, and the holding time is 13 hours. Simultaneously, inert gas is introduced into the furnace during the heating process, resulting in a pressure of 2 mTorr inside the furnace. In other embodiments of the present invention, after step C, the solid-state reaction high-temperature furnace is further heated until the temperature inside the furnace reaches 1480°C, and the holding time is 11.6 hours. Simultaneously, inert gas is introduced into the furnace during the heating process, resulting in a pressure of 45 mTorr inside the furnace.

[0035] Optionally, in step D, the rotation speed of the graphite crucible is 1–9 rad / min, and the rotation direction is changed every 0.4–0.6 h. For example, the rotation speed of the graphite crucible can be 2 rad / min, 3.3 rad / min, 4 rad / min, 4.6 rad / min, 5 rad / min, 7 rad / min, or 8.2 rad / min, and the rotation direction is changed every 0.42 h, 0.46 h, 0.48 h, 0.51 h, 0.55 h, or 0.58 h.

[0036] Step E: Continue heating the solid-state reaction high-temperature furnace until the temperature inside the furnace reaches 1700–1900℃, and hold for 15–40 hours. Simultaneously, during the heating process, inert gas is introduced into the solid-state reaction high-temperature furnace to maintain a pressure of 10–30 Torr inside the furnace.

[0037] After the heat preservation process in step D is completed, the solid-state reaction high-temperature furnace is heated further until the temperature inside the furnace reaches 1700–1900°C, and the heat preservation time is 15–40 hours. Simultaneously, an inert gas (such as argon or helium) is introduced into the furnace during the heating process, so that the pressure inside the furnace is 10–30 Torr (significantly higher than the previous two stages). The flow rate of the inert gas can be 10–80 L / min, for example, 12 L / min, 20 L / min, 35 L / min, 42 L / min, 50 L / min, 68 L / min, or 72 L / min. This embodiment of the invention does not impose any limitations on this.

[0038] Step E is the high-temperature completion stage, during which grain growth occurs. In step E, the saturated vapor pressure of silicon can reach several Torr at 1700–1900℃. This significant increase in pressure can suppress the high-temperature volatilization of silicon, preventing localized silicon deficiency and residual free carbon after silicon loss. At the same time, the diffusion capacity of carbon and silicon atoms is increased by more than 10 times at high temperatures, allowing the small amount of unreacted components and slight component deviations in micro-regions that were trapped in the previous stage to fully react through diffusion. Moreover, the long-term heat preservation ensures that the reaction is completed in all parts of the furnace, and the content of free silicon and free carbon can be reduced to <0.5%, essentially achieving zero residue.

[0039] In some embodiments of the present invention, after step D, the solid-state reaction furnace is further heated until the temperature inside the furnace reaches 1740°C, and the holding time is 38 hours. Simultaneously, an inert gas is introduced into the furnace during the heating process, resulting in a pressure of 13 Torr inside the furnace. In other embodiments of the present invention, after step D, the solid-state reaction furnace is further heated until the temperature inside the furnace reaches 1775°C, and the holding time is 35 hours. Simultaneously, an inert gas is introduced into the furnace during the heating process, resulting in a pressure of 17 Torr inside the furnace. In still other embodiments of the present invention, after step D, the solid-state reaction furnace is further heated until the temperature inside the furnace reaches 1800°C, and the holding time is 27 hours. Simultaneously, an inert gas is introduced into the furnace during the heating process, resulting in a pressure of 19 Torr inside the furnace. In some embodiments of the present invention, after step D, the solid-state reaction high-temperature furnace is further heated until the temperature inside the furnace reaches 1835°C, and the holding time is 22 hours. Simultaneously, inert gas is introduced into the furnace during the heating process, resulting in a pressure of 21 Torr inside the furnace. In other embodiments of the present invention, after step D, the solid-state reaction high-temperature furnace is further heated until the temperature inside the furnace reaches 1890°C, and the holding time is 16 hours. Simultaneously, inert gas is introduced into the furnace during the heating process, resulting in a pressure of 28 Torr inside the furnace.

[0040] Optionally, in step E, the rotation speed of the graphite crucible is 1–9 rad / min, and the rotation direction is changed every 0.4–0.6 h. For example, the rotation speed of the graphite crucible can be 2 rad / min, 3.3 rad / min, 4 rad / min, 4.6 rad / min, 5 rad / min, 7 rad / min, or 8.2 rad / min, and the rotation direction is changed every 0.42 h, 0.46 h, 0.48 h, 0.51 h, 0.55 h, or 0.58 h.

[0041] Step F involves cooling the product in the graphite crucible in the furnace while continuously introducing inert gas into the high-temperature solid-phase reaction furnace during the cooling process, thereby obtaining β-phase silicon carbide powder.

[0042] After the self-propagating reaction is completed, the product in the graphite crucible is cooled with the furnace, and an inert gas (such as argon or helium) is continuously introduced during the cooling process. After cooling is completed, the material is removed. The flow rate of the inert gas can be 10 to 80 L / min, for example, 12 L / min, 20 L / min, 35 L / min, 42 L / min, 50 L / min, 68 L / min or 72 L / min. This embodiment of the invention does not limit the flow rate.

[0043] The purpose of this invention is to solve the technical problem of low silicon carbide powder yield caused by uneven raw material mixing, silicon / carbon ratio imbalance, and uneven thermal field during the preparation of high-purity silicon carbide powder. This invention precisely controls the raw material ratio and optimizes the thermal field process, developing a high-purity β-phase silicon carbide powder with a yield exceeding 85%, thus solving the problems of incomplete self-propagating reaction and residual free silicon / carbon leading to low silicon carbide powder preparation yield.

[0044] The advantage of this invention is that it uses a gradient heating method for self-propagating reaction, which solves the problem of low powder yield caused by abnormal temperature measurement due to crucible rotation and volatile matter blocking in the furnace during high-temperature reaction.

[0045] The low-temperature activation stage, conducted below the ignition temperature, increases the radial and axial heat transfer time of the powder within the crucible, resulting in more uniform heating. The medium-temperature reaction stage occurs at the critical point of the ignition temperature, preventing excessively vigorous reactions that could lead to carbon coating, incomplete reaction, and abnormal grain growth. The high-temperature grain growth stage, conducted above the ignition temperature, further addresses the incomplete reaction and incomplete grain growth issues of the medium-temperature stage through high-temperature diffusion, ensuring complete reaction at all points in the furnace. Therefore, this embodiment of the invention, through the coordinated operation of three stages—temperature, crucible rotation, and pressure—improves the axial and radial uniformity of the crucible, resulting in higher reaction efficiency of silicon carbide powder and virtually no residual free silicon or free carbon.

[0046] To help understand the solution of the present invention, several specific embodiments are given below for detailed description.

[0047] Example 1

[0048] Step 1): Weigh out 69.08 wt% high-purity silicon powder (purity ≥ 99.9999%) and 30.92 wt% high-purity carbon powder (purity ≥ 99.9999%) by mass percentage, and add both silicon and carbon powders into a V-type mixer for mixing. The particle size of both silicon and carbon powders is 50 μm. The mixer frequency is set to 30 Hz, and the forward and reverse rotation times are set to 1 hour. After mixing, the carbon-silicon mixed powder is placed into a calcined high-purity graphite crucible.

[0049] Step 2): Place the graphite crucible into the solid-state reaction high-temperature furnace. Adjust the opening of the throttle valve and the frequency of the vacuum pump in the solid-state reaction high-temperature furnace to slowly evacuate the furnace. The evacuation rate can be ≤10 Torr / min, and the ultimate vacuum should be <20 mTorr. Stop evacuating when the vacuum level is <20 mTorr.

[0050] Step 3): After the vacuuming is completed, open the argon gas valve and introduce argon gas into the solid-state reaction high-temperature furnace until the pressure inside the furnace reaches atmospheric pressure. The argon gas flow rate is set to 10-80 L / min.

[0051] Step 4), repeat the above evacuation-argon flow operation 4 to 8 times until the air in the solid-phase reaction high-temperature furnace is completely discharged and the leakage rate is ≤20mTorr / h.

[0052] It should be noted that after the final vacuuming, the solid-phase reaction high-temperature furnace is close to a vacuum.

[0053] Step 5) Heat the solid-state reaction furnace until the temperature inside reaches 1000℃, and hold at that temperature for 9 hours. Simultaneously, argon gas (which does not react with the silicon-carbon mixture) is introduced into the furnace during the heating process, maintaining a pressure of 100 mTorr inside the furnace. During this process, the graphite crucible rotates at 6 rad / min, and the rotation direction is changed every hour.

[0054] Step 6) Continue heating the solid-state reaction furnace until the temperature inside the furnace reaches 1380℃, and hold at that temperature for 15 hours. Simultaneously, argon gas is introduced into the furnace during the heating process to maintain a pressure of 5 mTorr inside the furnace. During this process, the graphite crucible rotates at a rate of 5 rad / min, and the rotation direction is changed every 0.5 hours.

[0055] Step 7) Continue heating the solid-state reaction furnace until the temperature inside reaches 1800℃, and hold at that temperature for 36 hours. Simultaneously, argon gas is introduced into the furnace during the heating process to maintain a pressure of 25 Torr. During this process, the graphite crucible rotates at 7 rad / min, and the rotation direction is changed every 0.5 hours.

[0056] Step 8): After the self-propagating reaction is complete, the product in the graphite crucible is cooled with the furnace, and argon gas is continuously introduced during the cooling process. After cooling is complete, the product is removed. The flow rate of argon gas can be 10–80 L / min.

[0057] Example 2

[0058] The difference between this preparation method and that of Example 1 is that in step 1), 71.11 wt% of high-purity silicon powder (purity ≥ 99.9999%) and 28.89 wt% of high-purity carbon powder (purity ≥ 99.9999%) are weighed.

[0059] Example 3

[0060] The difference between this preparation method and that of Example 1 is that in step 1), 72.85 wt% of high-purity silicon powder (purity ≥ 99.9999%) and 27.15 wt% of high-purity carbon powder (purity ≥ 99.9999%) are weighed.

[0061] Example 4

[0062] The difference between this preparation method and that of Example 1 is that in step 1), 68.78 wt% of high-purity silicon powder (purity ≥ 99.9999%) and 31.22 wt% of high-purity carbon powder (purity ≥ 99.9999%) are weighed.

[0063] Example 5

[0064] The difference between this method and the preparation method in Example 1 is that in step 5), the solid-state reaction high-temperature furnace is heated until the temperature inside the furnace reaches 910°C, and the holding time is 9.2 hours. Simultaneously, argon gas that does not react with the silicon-carbon mixture is introduced into the furnace during the heating process, resulting in a pressure of 88 mTorr inside the furnace. During this process, the graphite crucible rotates at 8 rad / min, and the rotation direction is changed every 0.8 hours.

[0065] Example 6

[0066] The difference between this method and the preparation method in Example 1 is that in step 5), the solid-state reaction high-temperature furnace is heated until the temperature inside the furnace reaches 980°C, and the holding time is 8.4 h. Simultaneously, argon gas that does not react with the silicon-carbon mixture is introduced into the furnace during the heating process, resulting in a pressure of 83 mTorr inside the furnace. During this process, the graphite crucible rotates at 7 rad / min, and the rotation direction is changed every 1.1 h.

[0067] Example 7

[0068] The difference between this method and the preparation method in Example 1 is that in step 5), the solid-state reaction high-temperature furnace is heated until the temperature inside the furnace reaches 1095°C, and the holding time is 11.3 hours. Simultaneously, argon gas that does not react with the silicon-carbon mixture is introduced into the furnace during the heating process, resulting in a pressure of 93 mTorr inside the furnace. During this process, the graphite crucible rotates at 3 rad / min, and the rotation direction is changed every 1.2 hours.

[0069] Example 8

[0070] The difference between this method and the preparation method in Example 1 is that in step 6), the solid-state reaction high-temperature furnace is heated until the temperature inside the furnace reaches 1320°C, and the holding time is 11 hours. Simultaneously, argon gas is introduced into the furnace during the heating process to maintain a pressure of 2 mTorr. During this process, the graphite crucible rotates at 3 rad / min, and the rotation direction is changed every 0.45 hours.

[0071] Example 9

[0072] The difference between this method and the preparation method in Example 1 is that, in step 6), the solid-state reaction high-temperature furnace is heated until the temperature inside the furnace reaches 1440°C, and the holding time is 16 hours. Simultaneously, argon gas is introduced into the furnace during the heating process to maintain a pressure of 30 mTorr. During this process, the graphite crucible rotates at a rate of 6 rad / min, and the rotation direction is changed every 0.6 hours.

[0073] Example 10

[0074] The difference between this method and the preparation method in Example 1 is that in step 6), the solid-state reaction high-temperature furnace is heated until the temperature inside the furnace reaches 1480°C, and the holding time is 19.5 h. Simultaneously, argon gas is introduced into the furnace during the heating process to maintain a pressure of 45 mTorr inside the furnace. During this process, the graphite crucible rotates at a rate of 9 rad / min, and the rotation direction is changed every 0.52 h.

[0075] Example 11

[0076] The difference between this method and the preparation method in Example 1 is that in step 7), the solid-state reaction high-temperature furnace is heated until the temperature inside the furnace reaches 1810°C, and the holding time is 18 hours. Simultaneously, argon gas is introduced into the furnace during the heating process to maintain a pressure of 25 Torr. During this process, the graphite crucible rotates at 8 rad / min, and the rotation direction is changed every 0.4 hours.

[0077] Example 12

[0078] The difference between this method and the preparation method in Example 1 is that in step 7), the solid-state reaction high-temperature furnace is heated until the temperature inside the furnace reaches 1750°C, and the holding time is 30 hours. Simultaneously, argon gas is introduced into the furnace during the heating process to maintain a pressure of 25 Torr. During this process, the graphite crucible rotates at a rate of 2 rad / min, and the rotation direction is changed every 0.46 hours.

[0079] Example 13

[0080] The difference between this method and the preparation method in Example 1 is that, in step 7), the solid-state reaction high-temperature furnace is heated until the temperature inside the furnace reaches 1835°C, and the holding time is 22 hours. Simultaneously, argon gas is introduced into the furnace during the heating process to maintain a pressure of 25 Torr. During this process, the graphite crucible rotates at a rate of 4 rad / min, and the rotation direction is changed every 0.58 hours.

[0081] Original Technology 1: The difference between this preparation method and that of Example 1 is that in step 1), 70 wt% of high-purity silicon powder (purity ≥ 99.9999%) and 30 wt% of high-purity carbon powder (purity ≥ 99.9999%) are weighed, that is, the stoichiometric ratio of silicon powder to carbon powder is 1:1.

[0082] The following steps are used instead of steps 5), 6), and 7 of Example 1: The solid-state reaction high-temperature furnace was heated at a rate of 3℃ / min until the temperature inside the furnace reached 1800℃, and the holding time was 35 hours. Simultaneously, argon gas was introduced into the furnace during the heating process to maintain a pressure of 10 Torr inside the furnace.

[0083] Original technology 2; The difference between this preparation method and that of Example 1 is that in step 1), 71 wt% of high-purity silicon powder (purity ≥ 99.9999%) and 29 wt% of high-purity carbon powder (purity ≥ 99.9999%) are weighed, that is, the stoichiometric ratio of silicon powder to carbon powder is 1.05:1.

[0084] The following steps are used instead of steps 5), 6), and 7 of Example 1: The solid-state reaction high-temperature furnace was heated at a rate of 3℃ / min until the temperature inside the furnace reached 1800℃, and the holding time was 35 hours. Simultaneously, argon gas was introduced into the furnace during the heating process to maintain a pressure of 10 Torr inside the furnace.

[0085] The products prepared in the embodiments of the present invention are compared with the products prepared by the prior art (original technology 1, original technology 2), including particle size and purity testing, X-ray diffraction (XRD), and scanning electron microscopy (SEM).

[0086] The particle size and purity of the products obtained in the embodiments of the present invention are compared with those obtained by the prior art, as shown in Table 1.

[0087] Table 1 Particle size and purity data

[0088] As can be seen from Table 1, the silicon carbide powder in the product prepared by this invention has higher purity.

[0089] Figure 2 This is an XRD comparison diagram of the product obtained in the embodiments of the present invention and the product obtained by the prior art. For example... Figure 2 As shown, the product prepared by this invention contains no free silicon or free carbon, while the product prepared by the prior art contains free silicon and free carbon. Due to uneven and incomplete reactions, impurity elements in techniques 1 and 2 are trapped inside silicon carbide and are difficult to volatilize and remove at high temperatures.

[0090] Figure 3 This is a photographic comparison between the product obtained in the embodiments of the present invention and the product obtained in the prior art. Figure 4 These are SEM comparison images of the products prepared according to the embodiments of the present invention and the products prepared by prior art. For example... Figure 3 and Figure 4 As shown, the product of the original technology 1 contains free carbon, the powder is generally agglomerated, the microstructure is incomplete, the surface is rough, the reaction is incomplete, and the purity is only 5N5; the product of the original technology 2 still contains free silicon, the powder is locally uneven, the microstructure still has rough grain surface and incomplete reaction, and the purity is only 5N5; the product prepared by the present invention has no color difference, better uniformity, more complete grain surface and small particle size dispersion.

[0091] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing β-phase silicon carbide powder, characterized in that, Includes the following steps: Step A: Mix silicon powder and carbon powder, and load the silicon-carbon mixture into a graphite crucible; Step B: Place the graphite crucible into the solid-state reaction high-temperature furnace and purge the air from the solid-state reaction high-temperature furnace. Step C: The solid-state reaction high-temperature furnace is heated until the temperature inside the solid-state reaction high-temperature furnace reaches 900-1100℃, and the holding time is 8-12h. At the same time, during the heating process, an inert gas that does not react with the carbon-silicon mixed powder is introduced into the solid-state reaction high-temperature furnace, so that the pressure inside the solid-state reaction high-temperature furnace is 80-120mTorr. Step D: Continue to heat the solid-state reaction high-temperature furnace until the temperature inside the solid-state reaction high-temperature furnace is 1300-1500℃, and hold for 10-20 hours. At the same time, during the heating process, the inert gas is introduced into the solid-state reaction high-temperature furnace so that the pressure inside the solid-state reaction high-temperature furnace is 0-50mTorr. Step E: Continue to heat the solid-state reaction high-temperature furnace until the temperature inside the solid-state reaction high-temperature furnace is 1700-1900℃, and hold for 15-40 hours. At the same time, during the heating process, the inert gas is introduced into the solid-state reaction high-temperature furnace so that the pressure inside the solid-state reaction high-temperature furnace is 10-30 Torr. Step F involves cooling the product in the graphite crucible in the furnace, and continuously introducing the inert gas into the solid-state reaction high-temperature furnace during the cooling process to obtain β-phase silicon carbide powder.

2. The method according to claim 1, characterized in that, In step A, the mass percentage of the silicon powder is 65-85 wt%, and the mass percentage of the carbon powder is 15-35 wt%.

3. The method according to claim 2, characterized in that, In step A, the mass percentage of the silicon powder is 74-82 wt%, and the mass percentage of the carbon powder is 18-26 wt%.

4. The method according to any one of claims 1-3, characterized in that, In step A, the particle size of the silicon powder is 10-100 μm, and the particle size of the carbon powder is 10-100 μm.

5. The method according to any one of claims 1-3, characterized in that, In step A, the purity of the silicon powder is ≥99.9999%, and the purity of the carbon powder is ≥99.9999%.

6. The method according to claim 1, characterized in that, In step C, the rotation speed of the graphite crucible is 1 to 9 rad / min, and the rotation direction is changed every 0.8 to 1.2 h.

7. The method according to claim 1, characterized in that, In step D, the rotation speed of the graphite crucible is 1 to 9 rad / min, and the rotation direction is changed every 0.4 to 0.6 h.

8. The method according to claim 1, characterized in that, In step E, the rotation speed of the graphite crucible is 1 to 9 rad / min, and the rotation direction is changed every 0.4 to 0.6 h.

9. The method according to claim 1, characterized in that, The flow rate of the inert gas is 10–80 L / min.

10. The method according to claim 1 or 9, characterized in that, The inert gas is argon or helium.

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