Silicon carbide powder and its preparation process

Abstract

The present invention discloses a silicon carbide powder and its preparation process. The preparation process includes the following steps: Polymerization reaction: Take a carbon precursor and uniformly dissolve it in a solvent, add a silicon source, and stir to make the silicon source uniformly dispersed in the solution to obtain a mixed solution. Then, add a catalyst to the mixed solution, and under the action of the catalyst, the carbon precursor undergoes a polymerization reaction to obtain an organic polymer, and the silicon source is uniformly wrapped inside the organic polymer; Aging and drying: The organic polymer is aged under a constant temperature condition of 40-80°C to make the unreacted carbon precursor fully react, and the aged organic polymer is dried to obtain a dried organic polymer; High-temperature synthesis: Place the dried organic polymer in a graphite thermal field and transfer it to the furnace cavity. Under high-temperature conditions, the organic polymer is carbonized to form a carbon source, and the carbon source reacts with the silicon source to obtain high-purity silicon carbide powder. At the same time, a silicon carbide powder prepared by the above process is disclosed, and the silicon carbide powder has a microscopic structure of carbon-wrapped silicon.

Description

Technical Field

[0001] The present invention relates to the field of silicon carbide powder preparation, and in particular to a silicon carbide powder and a preparation process thereof. Background Art

[0002] Physical vapor transport is the most commonly used method for silicon carbide crystal growth. During the crystal growth process, when the temperature is higher than 1400 °C, the silicon component in the silicon carbide powder begins to melt and vaporize into silicon vapor, resulting in a much higher content of gaseous silicon in the growth chamber in the early stage of crystal growth than other components; the mixed vapor is transported towards the seed crystal under the drive of the axial temperature gradient and finally deposited on the surface of the seed crystal. In the early stage, the mixed vapor contains a large amount of gaseous silicon, and the gaseous silicon cools to form liquid silicon droplets and deposits on the crystal surface, making the silicon carbide crystal contain a large number of defects. Due to the excessive volatilization of silicon vapor in the early stage, the growth chamber in the later stage of crystal growth is a carbon-rich atmosphere, which also causes some carbon particles to enter the silicon carbide crystal, resulting in defects. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. For this reason, the present invention provides a preparation process of silicon carbide powder.

[0004] The present invention also provides a silicon carbide powder with a microstructure of carbon-coated silicon.

[0005] According to a preparation process of silicon carbide powder in the first aspect of the present invention, the following steps are included:

[0006] S1. Polymerization reaction: Take a carbon precursor and uniformly dissolve it in a solvent. The carbon precursor can obtain a porous organic polymer with a carbon skeleton structure through a polymerization reaction. Add a silicon source and stir to evenly disperse the silicon source in the solution to obtain a mixed solution. Then add a catalyst to the mixed solution. Under the action of the catalyst, the carbon precursor undergoes a polymerization reaction to obtain an organic polymer, and the silicon source is uniformly wrapped inside the organic polymer;

[0007] S2. Aging and drying: The organic polymer is aged under a constant temperature condition of 40 - 80 °C to allow the carbon precursor to fully react, and the aged organic polymer is dried to obtain a dried organic polymer;

[0008] S3. High-temperature synthesis: Place the dried organic polymer in a graphite thermal field and transfer it to a furnace chamber. Under high-temperature conditions, the carbon source reacts with the silicon source to obtain high-purity silicon carbide powder.

[0009] In addition, according to the preparation process of silicon carbide powder in the above embodiments of the present invention, the following additional technical features may also be included:

[0010] In some embodiments of the present invention, in the step S1,

[0011] the carbon precursor is resorcinol and formaldehyde, and the catalyst is sodium carbonate; or,

[0012] the carbon precursor is phloroglucinol and formaldehyde, and the catalyst is sodium carbonate; or,

[0013] the carbon precursor is chitosan, and the catalyst is acetic acid.

[0014] In some embodiments of the present invention, in the step S1, the silicon source is silicon particles, the particle size of the silicon particles is 3 μm - 30 μm, and the purity is 99.99%.

[0015] In some embodiments of the present invention, in the step S1, the solvent is one of deionized water, ethanol, and isopropanol.

[0016] In some embodiments of the present invention, in the step S1, the carbon-silicon molar ratio of the carbon precursor to the silicon source is (1 - 1.5):1, and the catalyst is added to the mixed solution in a volume ratio of 2% - 20%.

[0017] In some embodiments of the present invention, in the step S2, the aging time is 2 - 8 h, the drying method is normal temperature drying, and the normal temperature drying time is 5 - 20 h; or,

[0018] the drying method is freeze drying, and the freeze drying time is 10 - 100 h; or,

[0019] the drying method is supercritical drying, and the supercritical drying time is 5 - 15 h.

[0020] In some embodiments of the present invention, in the step S3, before the high-temperature synthesis step, a pulverization treatment and a screening separation are first performed, and the organic polymer is pulverized to 1.5 mm - 5 mm.

[0021] In some embodiments of the present invention, in the step S3, the pulverization treatment is performed using a grinding device, the grinding medium is silicon carbide grinding beads, the diameter of the silicon carbide grinding beads is 0.5 mm - 1 mm, and during grinding, the mass ratio of the silicon carbide grinding beads to the organic polymer is (0.5 - 2):1;

[0022] During the screening separation, a screening machine is used to separate the silicon carbide grinding beads from the ground organic polymer, and the screen aperture of the screening machine is 1 - 1.2 mm.

[0023] In some embodiments of the present invention, in the step S3, the specific steps of the high-temperature synthesis:

[0024] Load the sieved and separated organic polymer into a graphite crucible, transfer the assembled graphite crucible to a synthesis furnace. First, purge the furnace chamber of the synthesis furnace with an inert gas, and the purity of the inert gas is 99.99999%; the purging time is 0.5 - 1 h; then evacuate to make the vacuum degree of the furnace chamber at least 1×10 -5 mbar; after passing the leak rate detection, start to boost the pressure to 60 - 150 mbar; keep the pressure constant at 60 - 150 mbar, start heating, and the temperature of the furnace chamber of the synthesis furnace rises to 1000 - 1200 °C in 2 - 4 h, then keep the temperature constant for 5 - 10 h to make the organic polymer undergo anaerobic carbonization at this temperature to form a carbon source; then raise the temperature to 2100 - 2400 °C in 4 - 8 h, control the temperature to be constant at 2100 - 2400 °C, and the constant temperature time is 20 - 50 h to make the carbon source and silicon source fully participate in the reaction;

[0025] Then cool down to make the furnace chamber temperature cool to room temperature, and take out the graphite crucible to obtain block-shaped silicon carbide;

[0026] Crush the block-shaped silicon carbide and obtain silicon carbide powder of different sizes through classification and screening.

[0027] The silicon carbide powder according to the second aspect of the present invention is prepared by the above preparation process, and the silicon carbide powder has a microscopic structure with carbon coating silicon.

[0028] The additional aspects and advantages of the present invention will be partly given in the following description, partly become obvious from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0029] Figure 1 is a schematic flow chart of the preparation process of silicon carbide powder according to an embodiment of the present invention;

[0030] Figure 2 is a scanning electron microscope image of the silicon carbide powder obtained in Example 1;

[0031] Figure 3 is an energy spectrum diagram of the silicon carbide powder obtained in Example 1;

[0032] Figure 4 is a scanning electron microscope image of the aerogel block obtained in Example 2;

[0033] Figure 5 is a picture of silicon carbide ingots formed by growing crystals with the silicon carbide powder obtained in Example 1 and ordinary silicon carbide powder. Among them, a is the ingot grown from the silicon carbide powder obtained in Example 1, and b is the ingot grown from ordinary silicon carbide powder. Detailed Embodiments

[0034] Hereinafter, the content of the present invention will be described in detail. The description of the technical features recorded below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0035] In this specification, the numerical range expressed by "numerical value A to numerical value B" means a range including the end point numerical values A and B.

[0036] In this specification, unless otherwise specified, the "many", "multiple kinds", "multiple" in "many", "multiple kinds", "multiple" mean a numerical value of 2 or more.

[0037] In this specification, unless otherwise specified, "%" all represents mass percentage content.

[0038] In this specification, the meaning expressed by "can" includes both the meaning of performing a certain process and not performing a certain process.

[0039] In this specification, "optional" or "optionally" means that the events or circumstances described next may or may not occur, and this description includes the circumstances where the event occurs and the circumstances where the event does not occur.

[0040] In this specification, the "some specific / preferred embodiments", "some other specific / preferred embodiments", "embodiments", etc. mentioned refer to the specific elements (for example, features, structures, properties, and / or characteristics) related to the embodiment are included in at least one of the embodiments described here, and may or may not exist in other embodiments. In addition, it should be understood that the elements can be combined in various embodiments in any suitable manner.

[0041] In the first aspect of the present invention, the present invention provides a preparation process of silicon carbide powder. The process flow is referred to Figure 1 as shown, and includes the following steps:

[0042] S1. Polymerization reaction: Take a carbon precursor and dissolve it uniformly in a solvent. The carbon precursor can obtain a porous polymer with a carbon skeleton structure through a polymerization reaction. Add a silicon source and stir to make the silicon source uniformly dispersed in the solution to obtain a mixed solution. Then add a catalyst to the mixed solution. Under the action of the catalyst, the carbon precursor undergoes a polymerization reaction to obtain an organic polymer, and the silicon source is uniformly wrapped in the organic polymer;

[0043] S2. Aging and drying: The organic polymer is aged under a constant temperature condition of 40 - 80 °C to make the carbon precursor that has not fully reacted in step S1 react further sufficiently. Then dry the aged organic polymer to obtain the dried organic polymer;

[0044] S3. High-temperature synthesis: Place the dried organic polymer in a graphite heating field and transfer it to the furnace chamber. Under high-temperature conditions, the organic polymer is carbonized to form a carbon source, and the carbon source reacts with the silicon source to obtain high-purity silicon carbide powder.

[0045] It can be understood that in step S1, under the action of a catalyst, the carbon precursor undergoes a polymerization reaction to form a porous high-molecular organic polymer with a carbon skeleton structure. Since the silicon source has been uniformly dispersed in the solution of the carbon precursor before the polymerization reaction, it is uniformly distributed within the carbon skeleton during the polymerization reaction; in step S1, most of the carbon precursors participate in the reaction to form an organic polymer with a carbon skeleton structure, and a small amount of carbon precursors remain within the carbon skeleton. Then, through step S2, aging is carried out under constant temperature conditions to enable the unreacted carbon precursors in step S1 to fully react, thereby enhancing the strength of the carbon skeleton. Next, the aged organic polymer is subjected to a drying treatment; in step S3, under high-temperature conditions, the organic polymer is first carbonized to form a carbon source, and then the carbon source reacts with the silicon source to form silicon carbide.

[0046] In the above preparation method, in step S1, the carbon precursor is resorcinol and formaldehyde, and the catalyst is sodium carbonate.

[0047] In the above preparation method, in step S1, the carbon precursor is phloroglucinol and formaldehyde, and the catalyst is sodium carbonate.

[0048] In the above preparation method, in step S1, the carbon precursor is chitosan, and the catalyst is acetic acid.

[0049] In the above preparation method, in step S1, the silicon source is silicon particles, the particle size of the silicon particles is 3 μm - 30 μm, and the purity is 99.99%.

[0050] In the above preparation method, in step S1, the solvent is one of deionized water, ethanol, and isopropanol.

[0051] In the above preparation method, in step S1, the molar ratio of carbon to silicon in the carbon precursor and the silicon source is (1 - 1.5):1, and the catalyst is added to the mixed solution in a volume ratio of 2% - 20%. In other words, the volume of the catalyst accounts for 2% - 20% of the volume of the mixed solution.

[0052] In the above preparation method, in step S2, the aging temperature is 45 - 65 °C, the aging time is 2 - 8 h, the drying method is normal-temperature drying, and the normal-temperature drying time is 5 - 20 h; or,

[0053] The drying method is freeze-drying, and the freeze-drying time is 10 - 100 h; or,

[0054] The drying method is supercritical drying, and the supercritical drying time is 5 - 15 h.

[0055] In the above preparation method, in step S3, before the high-temperature synthesis step, comminution treatment and screening separation are first carried out, and the organic polymer is comminuted to 1.5 mm - 5 mm. The organic polymer is pre-comminuted and screened. The comminuted organic polymer is more likely to react to form silicon carbide at high temperature. The size of the polymer is mainly controlled to prevent damage to the physical structure of the carbon-coated silicon of the polymer. When the organic polymer is comminuted to less than 1.5 mm, the silicon particles may break away from the carbon skeleton; if the size of the comminuted organic polymer is greater than 5 mm, due to the large particle size, it is not conducive to the full reaction of silicon and carbon in the later stage;

[0056] In the above preparation method, in step S3, a grinding device is used for comminution treatment. The grinding medium is silicon carbide grinding beads, and the diameter of the silicon carbide grinding beads is 0.5 mm - 1 mm. During grinding, the mass ratio of the silicon carbide grinding beads to the organic polymer is (0.5 - 2):1; during screening separation, a screening machine is used to separate the silicon carbide grinding beads from the ground organic polymer, and the screen aperture of the screening machine is 1 - 1.2 mm.

[0057] In the above preparation method, in step S3, the specific steps of high-temperature synthesis are as follows:

[0058] The screened and separated organic polymer is loaded into a graphite crucible, and the assembled graphite crucible is transferred to a synthesis furnace. First, an inert gas is used to purge the furnace chamber of the synthesis furnace. The purity of the inert gas is 99.99999%; the purging time is 0.5 - 1 h; then, vacuum is pumped to make the vacuum degree of the furnace chamber at least 1×10 -5 mbar; after passing the leak rate detection, start to boost the pressure to 60 - 150 mbar; keep the pressure constant at 60 - 150 mbar, start heating, and the temperature of the furnace chamber of the synthesis furnace rises to 1000 - 1200 °C in 2 - 4 h, and then keep the temperature constant for 5 - 10 h to make the organic polymer undergo anaerobic carbonization to form a carbon source at this temperature; then, in 4 - 8 h, the temperature is raised to 2100 - 2400 °C, control the temperature to be constant at 2100 - 2400 °C, and the constant temperature time is 20 - 50 h to make the carbon source and the silicon source fully participate in the reaction;

[0059] Then, cool down to make the furnace chamber temperature cool to room temperature, and take out the graphite crucible to obtain block-shaped silicon carbide;

[0060] The block-shaped silicon carbide is comminuted, and silicon carbide powder of different sizes is obtained through classification screening.

[0061] In the second aspect of the present invention, the present invention provides a silicon carbide powder prepared by the above-mentioned preparation process, and the silicon carbide powder has a microstructure of carbon-encapsulated silicon. The silicon carbide powder of the prior art has a carbon-rich atmosphere in the crystal growth chamber in the later stage of crystal growth due to excessive volatilization of silicon vapor in the early stage of the preparation process, which also causes some carbon particles to enter the silicon carbide crystal to produce defects. The structure of carbon-encapsulated silicon in the present invention can effectively inhibit excessive sublimation of silicon in the early stage of crystal growth, and effectively improve the situation of silicon-rich in the early stage and carbon-rich in the later stage of the traditional crystal growth process, so that the silicon carbide vapor can be volatilized evenly at a ratio of 1:1 between silicon and carbon, which can effectively improve the quality of silicon carbide crystals.

[0062] Example

[0063] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0064] Example 1

[0065] Polymerization reaction: First, take 1000g of resorcinol and 1000g of formaldehyde and disperse them in 4L of ethanol solution. After stirring until the resorcinol is completely dissolved, add 2120g of silicon powder to the solution. The size of the silicon powder is 10-20μm and the purity is 99.99%; stir to disperse the silicon powder evenly in the solution, then add 200mL of 5% Na2CO3 solution to the solution, and heat the solution in a water bath to maintain the solution temperature at 50℃. After 5-10min, the mixed solution reacts to obtain a hydrogel, and the hydrogel is transferred to an aging box for water bath aging for 360min at 60℃; after aging, the hydrogel is transferred to a supercritical reactor and dried for 10h. After drying, the organic polymer is taken out. The dried organic polymer is weighed, and the total weight of the organic polymer is 4050g. The reason for the reduction in total weight is that part of the carbon precursor and silicon particles involved in the reaction are lost.

[0066] The carbon source precursor combination used in this embodiment is resorcinol and formaldehyde, and the catalyst is sodium carbonate. Under the action of the catalyst, resorcinol and formaldehyde undergo a polymerization reaction to obtain a high molecular polymer. The reaction equation is as follows:

[0067]

[0068] Reaction mechanism: Resorcinol has two hydroxyl functional groups. The p orbital where the lone pair electrons of the oxygen atom on the hydroxyl group and the π electron orbitals of the conjugated large π bond of the benzene ring of phenol overlap with each other to form a conjugated system. This causes the nuclear outer electrons of the oxygen atom to be biased towards the benzene ring, activating the benzene ring of resorcinol and making the hydrogen atoms on the hydroxyl group more active. Formaldehyde has an aldehyde group with relatively strong reactivity, which undergoes a condensation reaction with the hydroxyl group of resorcinol, ultimately generating a high molecular polymer and water.

[0069] The p orbital where the lone pair electrons of the oxygen atom in the phenolic hydroxyl group and the π electron orbitals of the conjugated large π bond of the benzene ring overlap with each other to form a conjugated system, causing the p electron cloud on the oxygen atom to transfer towards the benzene ring, increasing the electron cloud density on the benzene ring, activating the benzene ring, increasing the electron cloud density at the ortho and para positions of the hydroxyl group, enhancing the reactivity of the hydrogen atoms. In the formaldehyde molecule, due to the attraction of the oxygen atom, the electron cloud density on the carbon atom decreases. Under the action of an acid or a base, the hydrogen atoms at the ortho or para positions of phenol undergo an addition reaction with the carbonyl group of formaldehyde to form hydroxymethylphenol.

[0070] Crushing treatment: The organic polymer and silicon carbide grinding beads are added to a grinding tank. 5 kg of grinding beads are added, and the particle size of the grinding beads is 0.6 mm. The grinding tank uses a silicon carbide ceramic inner liner and is loaded on a sand mill for grinding. During the grinding process, samples are taken every 30 min to measure the particle size. When the grinding time is 5 h, the particle size of the organic polymer is 2 - 4 mm. At this time, the grinding is stopped and the grinding tank is taken out.

[0071] Screening separation: The mixture in the grinding tank is poured onto the screen of a screening machine. The screen is made of polytetrafluoroethylene material to prevent the introduction of impurities. The aperture of the screen is 1 mm. After screening for about 10 min, the organic polymer and the grinding medium are completely separated, and the material on the upper layer of the screen is collected, which is the ground organic polymer abrasive.

[0072] High-temperature synthesis: The ground organic polymer abrasive is loaded into a graphite crucible to ensure that the organic polymer is laid flat in the crucible. The assembled crucible is transferred to a synthesis furnace and purged with argon. The purity of argon is 99.99999%, and the purging time is 30 min. Then, the furnace cavity of the synthesis furnace is evacuated to make the vacuum degree of the furnace cavity reach 6×10 -6 mbar. After the vacuum degree reaches the requirement, a leak rate detection is carried out on the furnace platform. The leak rate detection time is 2 h. After the leak rate detection is qualified, the pressure is increased to make the furnace cavity pressure rise to 120 mbar.

[0073] Maintain the pressure at 120 mbar. After the constant pressure time is 5 min and it is confirmed that there is no obvious pressure fluctuation, start the heating device. In the first heating stage, the temperature is raised to 1200 °C in 3 h; keep the temperature constant for 8 h to decompose and carbonize the organic groups in the organic polymer.

[0074] After the constant temperature ends, it enters the second heating stage, heating up to 2300 °C in 6 hours, keeping the temperature constant for 40 hours. Silicon and carbon react at this temperature to obtain high-purity silicon carbide. Then, it is cooled down to cool the furnace cavity to room temperature, and the graphite crucible is taken out to obtain massive silicon carbide;

[0075] The massive silicon carbide is crushed and different-sized silicon carbide powders are obtained through classification screening.

[0076] Figure 2 It is the scanning electron microscope image of the silicon carbide particles prepared in Example 1. From Figure 2 it can be seen that the silicon carbide powder is composed of relatively regular small particles, which is the typical morphology of crystal grains; and the surface of the particles is relatively smooth and bright, indicating that the reaction between silicon and carbon is very sufficient and the growth of silicon carbide crystal grains is good.

[0077] Figure 3 And Table 1 is the energy spectrum diagram and data of the silicon carbide powder prepared in Example 1. From the data in Table 1, it can be known that the proportion of silicon atoms in the silicon carbide powder is 48.32%, and the proportion of carbon atoms is 49.86%. After calculation, the number ratio of silicon and carbon atoms is close to 1:1.

[0078] Spectrum processing: Peaks that may be ignored: 0.268, 2.039 keV

[0079] Processing options: All analyzed elements (normalized)

[0080] Number of repetitions = 2

[0081] Standard sample:

[0082] Energy spectrum data of the silicon carbide powder prepared in Example 1

[0083]

[0084] The purity of the silicon carbide powder prepared in Example 1 was detected by glow discharge mass spectrometry. The results are shown in Table 2. The detection results show that the purity of the silicon carbide powder is as high as 99.99992%.

[0085] Table 2 Detection results of the purity of the silicon carbide powder prepared in Example 1

[0086]

[0087]

[0088] Example 2

[0089] Polymerization reaction: The carbon source used in this example is chitosan, and the catalyst is acetic acid. Take 400 g of chitosan particles and disperse them in 2500 mL of deionized water, and stir well to make the chitosan evenly dispersed; then add 400 mL of glacial acetic acid to the solution and stir well to mix the glacial acetic acid evenly. Finally, add 300 g of granular silicon (calculated according to the carbon-silicon molar ratio of 1.4:1) to the solution while stirring, and the size of the granular silicon is 15 - 30 μm; then pour the mixed solution into a nylon container and let it stand for 5 h to obtain a bulk gel encapsulating the granular silicon.

[0090] After freezing the gel at -30 °C, transfer it to a freeze dryer and dry it for 48 h to obtain an aerogel block encapsulating silicon particles. The finally obtained aerogel block is about 650 g.

[0091] Reaction mechanism: The chemical name of chitosan is polyglucosamine (1-4)-2-amino-B-D-glucose, which has various functional groups such as amino, hydroxyl, and ether bonds. When it is dissolved in glacial acetic acid, the molecular spatial distance of chitosan molecules increases after dilution, and the functional groups have a larger activity space, thus enhancing their reactivity. Under the catalytic action of acetic acid, a condensation reaction occurs to obtain a high molecular polymer mainly composed of a carbon skeleton.

[0092] Figure 4 It is the scanning electron microscope image of the aerogel block prepared in Example 2. From Figure 4 it can be seen that silicon particles are loaded or encapsulated on the surface and inside of the aerogel, and the silicon particles are relatively evenly distributed.

[0093] Crushing treatment: Transfer the aerogel block to a planetary ball mill for crushing, add 0.6 kg of grinding beads, and the particle size of the grinding beads is selected as 0.8 mm; the grinding tank uses a silicon carbide ceramic inner liner, and load the grinding tank on the planetary ball mill for grinding; during the grinding process, take samples every 10 min to measure the particle size. When the grinding time is 30 min, the particle size of the organic polymer is 3 - 5 mm; stop grinding and take out the grinding tank.

[0094] Screening separation: Pour the mixture in the grinding tank onto the screen of a screening machine. The screen is made of polytetrafluoroethylene material to prevent the introduction of impurities. The aperture of the screen is 1.2 mm. After screening for 5 min, the powder and the grinding medium are completely separated, and collect the aerogel material on the upper layer of the screen.

[0095] High-temperature reaction: Load the screened aerogel material into a graphite crucible and make the abrasive spread evenly in the crucible; transfer the assembled crucible to a synthesis furnace, purge it with argon, the purity of argon is 99.99999%, and the purging time is 30 min; then evacuate the furnace chamber of the synthesis furnace to make the vacuum degree of the furnace chamber reach 6×10 -6mbar; After the vacuum degree reaches the requirement, the leak rate of the furnace platform is detected. The leak rate detection time is 2 h. After the leak rate detection is qualified, the pressure is increased to make the pressure in the furnace cavity rise to 100 mbar.

[0096] Keep the pressure at 100 mbar. After the constant pressure time is 5 min and it is confirmed that there is no obvious pressure fluctuation, start the heating device. In the first preheating stage, the temperature is raised to 400 °C within 1 h; keep the temperature constant for 1 h to remove the air and other impurities inside the aerogel; in the second temperature rising stage, the temperature is raised to 1000 °C within 2 h and kept at a constant temperature for 10 h to fully carbonize the aerogel into a carbon source.

[0097] After the constant temperature ends, enter the second heating stage. The temperature is raised to 2200 °C within 5 h and kept at a constant temperature for 30 h. The carbon source and the silicon source react at this temperature to obtain high-purity silicon carbide.

[0098] The purity of the silicon carbide powder prepared in Example 2 is detected by glow discharge mass spectrometry. As shown in Table 3, the detection results show that the purity of the silicon carbide powder is as high as 99.99996%.

[0099] Table 3 Detection results of the purity of the silicon carbide powder prepared in Example 2

[0100]

[0101]

[0102]

[0103] Example 3

[0104] The difference between Example 3 and Example 1 is only that

[0105] the carbon precursor is phloroglucinol and formaldehyde, the solvent is isopropanol, the drying method in step S2 is room temperature drying, the drying time is 12 h, and the other parts are exactly the same as those in Example 1.

[0106] Experimental Example

[0107] The silicon carbide powder in Example 1 and ordinary silicon carbide powder are used as raw materials for silicon carbide crystal growth. Among them, the ordinary silicon carbide powder is prepared by a conventional process. The preparation process is as follows:

[0108] Weigh a certain mass of carbon powder and silicon powder according to the molar ratio of silicon to carbon of 1:1. The purities of both the carbon powder and the silicon powder are greater than 99.99%; fully mix the carbon powder and the silicon powder and transfer them to a graphite crucible, and heat in a synthesis furnace; control the reaction temperature at 2200 °C, keep the temperature constant for 40 h, and the pressure in the furnace cavity is 120 mbar; make the silicon and carbon fully react to generate silicon carbide. It should be noted that the silicon carbide prepared by the conventional process does not have a microstructure with carbon coating silicon.

[0109] Two kinds of silicon carbide powders are crystallized through a conventional silicon carbide crystal growth process, ensuring that the crystal growth process parameters are the same. The silicon carbide crystal growth process is as follows:

[0110] The crucible includes a crucible lid and a crucible body. The seed crystal is loaded on the crucible lid, the silicon carbide powder is loaded into the crucible body, and the crucible lid and the crucible are assembled. The assembled crucible is placed in the reaction chamber, and argon gas is introduced into the reaction chamber. The purity of the argon gas is 99.99999%; the purging time is 0.5 - 1 h; then it is evacuated to make the vacuum degree of the reaction chamber reach 6×10 - 6 mbar; after passing the leak rate detection, the pressure is increased to 30 mbar.

[0111] At a constant pressure of 30 mbar, heating is started, and the temperature is raised to 2100 - 2400 °C in 10 h; the temperature is heated at a constant temperature for 100 h, then the pressure is increased to 120 mbar, and the temperature is decreased to room temperature in 24 h by programmed cooling.

[0112] After cooling to room temperature, the crucible is taken out to obtain silicon carbide crystals;

[0113] The ingot grown from the silicon carbide powder in Example 1 is named Crystal One, and the ingot grown from the ordinary silicon carbide powder is named Crystal Two.

[0114] Figure 5 In which, a and b are the pictures of Crystal One and Crystal Two respectively. From Figure 5 it can be clearly seen that the surface of Crystal One is smooth and has no macroscopic defects; there are some pits on the surface of Crystal Two.

[0115] At the same time, internal defect detection is carried out on Crystal One and Crystal Two. The results are shown in Table 4. It can be seen from Table 4 that the microtube density of Crystal One ≤ 0.05 cm -2 , the screw dislocation density is 57.24, the edge dislocation density is 173.46, the basal plane dislocation density is 106.86, and the total dislocation density is 337.56; the microtube density of Crystal Two ≤ 6 cm -2 , the screw dislocation density is 466.58, the edge dislocation density is 2147.79, the basal plane dislocation density is 329.43, and the total dislocation density is 34443.8.

[0116] Table 4 Crystal Defect Data

[0117]

[0118] As shown in Table 4, the density of overall defects and single defects in Crystal 1 is lower than that in Crystal 2. The screw dislocation density of Crystal 2 is 8 times that of Crystal 1; the edge dislocation density of Crystal 2 is 12 times that of Crystal 1; and the basal plane dislocation density of Crystal 2 is 3 times that of Crystal 1. This is mainly because in the early stage of crystal growth, due to the low sublimation temperature of silicon (~1400℃), silicon vapor sublimates first, resulting in a high silicon content in the atmosphere, mainly composed of Si, Si2C, and SiC; the elemental silicon in the gas phase is deposited on the interface of the silicon carbide crystal in the form of silicon droplets, changing the internal structure of the silicon carbide crystal and generating penetrating defects; due to the premature loss of silicon in the early stage of crystal growth, the carbon content in the gas phase is high in the later stage of crystal growth, mainly composed of C, SiC2, and SiC; a large number of carbon particles are mixed in the silicon carbide vapor and deposited on the interface of the silicon carbide crystal, forming carbon inclusions, which are also easy to form penetrating defects, namely screw dislocations and edge dislocations.

[0119] However, the silicon carbide powder in Example 1 has a microstructure of carbon-encapsulated silicon. When silicon reaches the sublimation point, it is restricted by the external carbon shell, which inhibits its sublimation. When carbon reaches the sublimation temperature, silicon is transferred to the crystal surface in the form of gas phase SiC, and the ratio of carbon to silicon in the gas phase component remains basically balanced, which also makes the overall quality of Crystal 1 higher.

[0120] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A preparation process of silicon carbide powder, characterized in that, It includes the following steps: S1. Polymerization reaction: Take a carbon precursor and dissolve it uniformly in a solvent, add a silicon source, stir to make the silicon source uniformly dispersed in the solution to obtain a mixed solution, then add a catalyst to the mixed solution, and under the action of the catalyst, the carbon precursor undergoes a polymerization reaction to obtain an organic polymer, and the silicon source is uniformly wrapped inside the organic polymer; S2. Aging and drying: The organic polymer is aged under a constant temperature condition of 40 - 80 °C to make the carbon precursor that has not fully reacted in step S1 react fully, and the aged organic polymer is dried to obtain a dried organic polymer; S3. High-temperature synthesis: Place the dried organic polymer in a graphite heat field and transfer it to the furnace cavity. Under high-temperature conditions, the organic polymer is carbonized to form a carbon source, and the carbon source reacts with the silicon source to obtain high-purity silicon carbide powder; The carbon precursor is resorcinol and formaldehyde, and the catalyst is sodium carbonate; or, The carbon precursor is phloroglucinol and formaldehyde, and the catalyst is sodium carbonate; or, The carbon precursor is chitosan, and the catalyst is acetic acid.

2. The preparation process of silicon carbide powder according to claim 1, characterized in that, In step S1, the silicon source is silicon particles, the particle size of the silicon particles is 3 μm - 30 μm, and the purity is 99.99%.

3. The preparation process of silicon carbide powder according to claim 1, characterized in that, In step S1, the solvent is one of deionized water, ethanol, and isopropanol.

4. The preparation process of silicon carbide powder according to claim 1, characterized in that, In step S1, the molar ratio of carbon to silicon in the carbon precursor and the silicon source is (1 - 1.5):1, and the catalyst is added to the mixed solution according to a volume ratio of 2% - 20%.

5. The preparation process of silicon carbide powder according to claim 1, characterized in that, In step S2, the aging time is 2 - 8 h, the drying method is normal-temperature drying, and the normal-temperature drying time is 5 - 20 h; or, The drying method is freeze-drying, and the freeze-drying time is 10 - 100 h; or, The drying method is supercritical drying, and the supercritical drying time is 5 - 15 h.

6. The preparation process of silicon carbide powder according to claim 1, characterized in that, In step S3, before the high-temperature synthesis step, a pulverization treatment and a screening separation are first performed, and the organic polymer is pulverized to 1.5 mm - 5 mm.

7. The preparation process of silicon carbide powder according to claim 6, characterized in that, In step S3, a grinding device is used for the pulverization treatment, the grinding medium is silicon carbide grinding beads, the diameter of the silicon carbide grinding beads is 0.5 mm - 1 mm, and during grinding, the mass ratio of the silicon carbide grinding beads to the organic polymer is (0.5 - 2):1; During the screening separation, a screening machine is used to separate the silicon carbide grinding beads from the ground organic polymer, and the screen aperture of the screening machine is 1 - 1.2 mm.

8. The preparation process of silicon carbide powder according to claim 7, characterized in that, In step S3, the specific steps of high-temperature synthesis: Load the sieved and separated organic polymer into a graphite crucible, transfer the assembled graphite crucible to a synthesis furnace. First, purge the furnace cavity of the synthesis furnace with an inert gas, the purity of the inert gas is 99.99999%; the purging time is 0.5 - 1 h; then evacuate to make the vacuum degree of the furnace cavity at least 1×10 -5 mbar; after passing the leak rate detection, start to boost the pressure to 60 - 150 mbar; keep the pressure constant at 60 - 150 mbar, start heating, the temperature of the furnace cavity of the synthesis furnace rises to 1000 - 1200 °C in 2 - 4 h, then keep the temperature constant for 5 - 10 h to make the organic polymer undergo anaerobic carbonization at this temperature to form a carbon source; then rise the temperature to 2100 - 2400 °C in 4 - 8 h, control the temperature to be constant at 2100 - 2400 °C, and the constant temperature time is 20 - 50 h to make the carbon source and silicon source fully participate in the reaction; After that, the temperature is lowered to cool the furnace cavity temperature to room temperature, and the graphite crucible is taken out to obtain block-shaped silicon carbide; The block-shaped silicon carbide is subjected to a pulverization treatment, and silicon carbide powders of different sizes are obtained through classification screening.

9. A silicon carbide powder, characterized in that, Prepared by using the preparation process according to any one of claims 1 - 8, the silicon carbide powder has a microstructure with carbon wrapping silicon.

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