4H-SiC and its ultrafast preparation method and application

Abstract

The application relates to the technical field of high-temperature preparation of SiC materials, and particularly discloses a 4H-SiC, a superfast preparation method and application thereof, the preparation method comprising the following steps: uniformly mixing SiC raw materials, an organic additive and a sintering additive in water to form a slurry mixture, obtaining a SiC sample through a material forming process, and high-temperature sintering the SiC sample in a carbon-based powder medium, and cooling to obtain the 4H-SiC; the high-temperature sintering method is as follows: through control of a pulse current, superfast heating and holding are realized; the superfast heating rate is 200-10000 DEG C / min; the superfast heating time is 15s-150s; and the holding time is 20s-600s. The preparation process time is greatly shortened, the energy utilization rate is greatly improved, the production efficiency of the polycrystalline 4H-SiC is improved, the 4H phase content is high, the conductivity is high, and the low-cost industrialized production is facilitated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature preparation of SiC materials, and particularly relates to 4H-SiC and an ultrafast preparation method and application thereof. BACKGROUND

[0002] SiC materials have many excellent properties such as low density, high hardness, high thermal conductivity, wide band gap, high saturated carrier migration speed and high critical breakdown field strength, and have been applied to many fields such as aerospace, thermal nuclear energy, photoelectric transmission and high-power semiconductor as structural ceramic materials and semiconductor materials. Among the main classifications of SiC, 3C-SiC, 4H-SiC and 6H-SiC, 4H-SiC has the characteristics of wider band gap and higher electron mobility. However, the existing method system for manufacturing 4H-SiC is relatively single, the material manufacturing process is complex, the production capacity is low, and the time and economic cost of the production process are greatly increased, which seriously restricts the industrialized mass production and application of 4H-SiC.

[0003] For example, Chinese patent application CN104562206A discloses a method for improving the crystal form stability of 4H-SiC crystals grown by physical vapor transport method. The method puts SiC raw materials in a graphite crucible placed in a single crystal growth furnace, uses a magnetic polarity surface as a seed crystal growth surface, fixes the seed crystal directly above the SiC raw materials, and places graphite materials on the path of the sublimated components of the SiC raw materials transported to the seed crystal. The crystal growth is carried out by introducing an atmosphere into the growth furnace, maintaining the pressure in the single crystal growth furnace at 5-40 mbar and the temperature at 2100-2240℃, so as to improve the crystal form stability of 4H-SiC single crystals. However, the process of this method is complex, the 4H-SiC crystals can only be longitudinally long and thick, it is difficult to realize lateral expansion, and the material component ratio of C / Si needs to be strictly controlled during the growth process. A high material component C / Si ratio is beneficial to inhibit the growth interface step coalescence and improve the growth stability of 4H-SiC, but according to the sublimation characteristics of SiC, a high C / Si ratio generally requires a high growth temperature, and a high growth temperature will promote the formation of 6H-SiC and 15R-SiC crystal forms, which is not conducive to the stable growth of 4H-SiC crystal form. Moreover, in the process of producing 4H-SiC by this method, the gaseous substances produced by the sublimation and decomposition of the growth source under low pressure and high temperature are transported upward to the seed crystal at low temperature under the driving of the pressure gradient formed by the temperature gradient between the raw materials and the seed crystal, and are crystallized and grown in the supersaturated atmosphere. The crystallization and growth process is slow, and the growth period is long.

[0004] For another example, Chinese patent application CN102268735A discloses a method for improving the stability of 4H-SiC single crystal crystal form. The method uses sublimation to heat SiC raw material powder to sublimation, establishes an optimal temperature and pressure range, establishes a specific axial temperature gradient in the growth chamber to promote the sublimation of SiC raw material to the seed crystal, and increases the axial temperature gradient by moving the crucible, changing the heat preservation state, etc. to increase the probability of 4H-SiC growth, and stabilize the crystal form throughout the process. However, this method is complex, has high requirements for the process of single crystal growth furnace, and needs to meet the setting requirements of heating system, water cooling device, heat preservation device, etc., has high production cost, and does not improve the slow growth rate of 4H-SiC.

[0005] For another example, Hao Bin. Research on preparation of silicon carbide powder by microwave sintering [J]. Current Technology of Silicate Bulletin, March 2015, Vol. 34, No. 3, pp. 864-867. discloses a method for preparing silicon carbide powder. Silicon dioxide and carbon black are mixed uniformly according to a certain silicon-carbon atomic ratio, zinc powder is added as a catalyst, and the mixture is loaded into a quartz crucible. The quartz crucible is placed in a microwave oven, the microwave power and time are adjusted, and the mixture is subjected to carbothermic reduction reaction by pneumatic microwave heating to generate silicon carbide powder. After cooling and crushing the reaction product, it is washed with hydrochloric acid and water to remove impurities, dried with ethanol, and a pure single-phase 3C-SiC powder is obtained. This method uses microwave sintering, which can achieve fast and overall heating, high heating rate, short heating time, energy saving and time saving. However, microwave sintering requires a special microwave oven and insulation material, which has high equipment cost, and requires high uniformity and stability of the microwave field, otherwise it will affect the uniformity and efficiency of the reaction. The yield of silicon carbide prepared by this method can exceed 60%, but the crystal type produced is single crystal 3C-SiC, and 4H-SiC cannot be obtained.

[0006] Andrew G, Yinsheng L, Sebastian R B, et al. Pressureless flash sintering of a-SiC: Electrical characteristics and densification [J]. Acta Materialia, 2022, 241. A pressureless flash sintering method of SiC is disclosed, using B and C sintering aids mixed with SiC powder in a certain stoichiometric ratio and adding a binder, and by 200Mpa cold isostatic pressing into a rod-shaped block, the block-shaped sample is placed in an alumina tube furnace, holes are drilled at both ends of the sample, and then it is threaded to the tungsten wire installed on the movable flash sintering device, the entire connecting device is sealed in the tube furnace, the current-carrying lead wire is drawn out from the furnace end sealing strip and connected to the direct current power source for pressureless flash sintering, the heating rate is fast, the rapid heating is carried out in a short time, and the reaction product obtained at the end is a-SiC, 4H-SiC cannot be obtained, and the pressureless sintering has high requirements for sintering conditions and high cost.

[0007] Zhang Yong, He Xinbo, Qu Xuanhui, et al. Preparation of dense silicon carbide ceramics by spark plasma sintering process [J]. Mechanical engineering materials, 2008, (03): 45-47+51. A method for preparing silicon carbide ceramics by spark plasma sintering process is disclosed. High-purity SiC powder is mixed with 10% sintering aid by ball milling, drying and sieving to 240 mesh to obtain fine powder, which is placed in a graphite mold and sintered in a SPS sintering furnace. Spark plasma sintering (SPS) is a new powder metallurgy technology for preparing bulk materials, which is characterized by instantaneous discharge and high temperature plasma between particles during sintering, which can break or remove impurities (such as oxide film) and adsorbed gas on the surface of powder particles, activate the surface of powder particles and improve the sintering quality and efficiency. The heating rate is 373℃ / min, the sintering temperature is 1600℃, the holding time is 5min, the pressure is 5Mpa, and finally high-purity high-density SiC is obtained, 4H-SiC cannot be obtained, and the cost of SPS sintering is high.

[0008] Chinese patent application CN115196967A discloses a method for preparing silicon carbide composite ceramic by spark plasma sintering. The method mixes high-purity SiC powder, nano-boron carbide powder, and carbon powder or graphene with deionized water, performs magnetic stirring and ultrasonic stirring to obtain a uniform mixed slurry, adds an organic binder and a dispersant to the mixed slurry, then performs ball milling to obtain a wet mixed slurry, controls the spray pressure and inlet temperature to spray the wet mixed slurry to obtain a powder with a particle size of 90-240 μm, and uses a tablet press to pre-press the granulated powder to obtain a ceramic blank. The ceramic blank is loaded into a graphite mold and placed in a spark plasma sintering furnace, a pressure is applied, and sintering is performed by heating and holding, and then the furnace is cooled to obtain a nano-powder modified SiC composite ceramic. This method can produce high-performance composite ceramics at a relatively low temperature, overcoming the difficulties of high temperature and high pressure in the process, and the product is high-toughness SiC ceramic. However, the SPS sintering equipment is expensive, the sintering conditions are strict, the sintering process involves multiple influencing factors, which is difficult to control and prone to errors, and a certain atmospheric pressure condition needs to be created during the sintering process. The sintering time is long and the efficiency is low, and the final product is a composite SiC without 4H-SiC.

[0009] Chinese patent application CN109336609A discloses a method for preparing SiC by spark plasma liquid phase sintering. The method mixes high-purity SiC powder, rare earth oxides, and a solvent to prepare a slurry, the rare earth oxides are at least two of CeO2, Y2O3, and Er2O3; the obtained slurry is dried, sieved, and formed to obtain a body; the body is subjected to glow discharge plasma sintering under pressure and inert atmosphere to obtain the glow discharge plasma liquid phase sintered SiC ceramic. The SiC ceramic prepared by this method has high thermal conductivity and electrical insulation performance, and the preparation process has fewer steps. However, the heating rate is slow, the heating and holding time is long, the production efficiency is low, the SPS sintering process requires an inert atmosphere for pressure and a certain atmospheric pressure condition, the sintering process is complex and prone to errors, and the product is high-purity high-density SiC without 4H-SiC.

[0010] Zhang Hao, Wang Yingmin, Chen Jianli, et al. Synthesis of high purity alpha-SiC powder [J]. Semiconductor technology, 2021, 46(10): 779-782+807. A method for synthesizing high purity 4H-SiC is disclosed, which mixes high purity C powder and Si powder according to a certain stoichiometric ratio, then loads it into a graphite crucible, and then puts it into a medium frequency induction furnace, vacuums and heats to 1800℃, maintains for a period of time, so that 3C-SiC powder is generated. The synthesized 3C-SiC powder is taken out and crushed with SiC ceramic rod and mortar, so that the particle size is less than 500μm. The crushed 3C-SiC powder is loaded into the graphite crucible again, put into the medium frequency induction furnace, vacuumize and heat to 2100℃, and pass in high purity argon and hydrogen mixed gas, maintain for a period of time, so that 3C-SiC is converted into 4H-SiC powder. However, in addition to containing 4H-SiC, the product also contains a small amount of other phases, such as 3C, 6H, 15R, and if high purity 4H-SiC is required, a purification process operation is also required; and the process of this method is complex, which needs to be synthesized twice, crushed once, phase transition and recrystallization once, the process is relatively complex, the time is relatively long, and the cost is relatively high.

[0011] Therefore, there is an urgent need for a 4H-SiC preparation method with simple process, low cost, short time consumption, high production rate and high purity. SUMMARY

[0012] The present application provides a 4H-SiC and its ultra-fast preparation method and application, which realizes ultra-fast heating by controlling the raw material formula and the efficiency of carbon-based conductive powder generating Joule heat, shortens the preparation time of 4H-SiC, and improves the production efficiency.

[0013] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0014] The present application provides a 4H-SiC ultra-fast preparation method, comprising the following steps:

[0015] S1, uniformly mixing SiC raw material powder, organic additives and sintering additives in water to form a slurry mixture;

[0016] S2, obtaining a SiC sample by a material forming process;

[0017] S3, under the protection of inert gas, high temperature sintering of the SiC sample in carbon-based powder medium, and then cooling to obtain the 4H-SiC;

[0018] The method for high-temperature sintering of the carbon-based powder medium in step S3 is as follows: in the insulating material filled with the carbon-based conductive powder, a super-fast temperature rise is realized by controlling a pulse current, and then the temperature is kept constant; the rate of the super-fast temperature rise is 200-10000 ℃ / min; the time of the super-fast temperature rise is 15s-150s; and the time of the temperature keeping is 20s-600s.

[0019] Preferably, the rate of the super-fast temperature rise is 1000-10000 ℃ / min; the time of the super-fast temperature rise is 15s-150s; and the time of the temperature keeping is 200s-300s.

[0020] Preferably, the SiC raw material in step S1 is α-SiC and / or β-SiC; the organic auxiliary agent in step S1 comprises at least one of D-fructose, polyethylene glycol, polyacrylic acid and hydroxymethyl cellulose; and the sintering auxiliary agent in step S1 comprises B2O3 and / or B(OH)3.

[0021] Preferably, the organic auxiliary agent in step S1 comprises D-fructose, polyethylene glycol, polyacrylic acid and hydroxymethyl cellulose. The D-fructose and the hydroxymethyl cellulose serve as a carbon source, and the polyethylene glycol and the polyacrylic acid serve as a binder.

[0022] Further preferably, the organic auxiliary agent in step S1 is composed of D-fructose, polyethylene glycol, polyacrylic acid and hydroxymethyl cellulose in a mass ratio of 1-3:3-5:0.5-3:0.1-1.

[0023] Preferably, the mass ratio of the SiC raw material, the organic auxiliary agent and the sintering auxiliary agent in step S1 is 100:1-5:0.1-3; and the material forming process in step S2 comprises a dry pressing forming method and / or a 3D printing forming method.

[0024] Further preferably, the mass ratio of the SiC raw material, the organic auxiliary agent and the sintering auxiliary agent in step S1 is 100:2-5:0.1-3.

[0025] Most preferably, the mass ratio of the SiC raw material, the organic auxiliary agent and the sintering auxiliary agent in step S1 is 100:5:3.

[0026] Preferably, the inert gas in step S3 comprises at least one of helium, neon and argon; and the content of the 4H-SiC in step S3 is greater than 50%.

[0027] Further preferably, the inert gas in step S3 is argon.

[0028] Preferably, the control pulse current comprises a waveform of the control pulse current, a size of the pulse current and a frequency of the pulse current; the waveform of the pulse current comprises a square wave, a trapezoidal wave, a triangular wave, a sawtooth wave or a sine wave; the size of the pulse current is 1mA-500A, and the frequency of the pulse current is 0-300Hz.

[0029] Preferably, the method for controlling the pulse current comprises inserting two electrodes into the carbon-based conductive powder, embedding the SiC sample in the powder between the two electrodes, and controlling the pulse current.

[0030] Preferably, the insulating material comprises an alumina crucible, a boron nitride crucible, a quartz crucible or a mullite crucible; and the carbon-based conductive powder is at least one of carbon black powder, graphite powder, graphene powder, carbon fiber powder and carbon nanomaterial powder.

[0031] Specifically, SiC raw material powder, organic additives and sintering additives are mixed in deionized water in a certain proportion to form a slurry mixture, the slurry mixture is dried to obtain a powder, and the powder is formed to obtain a SiC sample. A carbon-based powder medium ultrafast high-temperature sintering furnace is set up, the furnace body structure comprises an outer layer of insulating high-temperature resistant crucible, an inner wall paved with heat insulating refractory material, graphite electrodes placed in the holes on both sides of the furnace body to act as positive and negative electrode materials for high-temperature sintering, and carbon-based conductive powder filled as conductive heating and heat preservation material; the SiC sample is covered in the carbon-based conductive powder and located between the two electrodes; a high-temperature resistant thin-walled sleeve is installed on one of the electrodes through a hole. One end of the sleeve extends to a distance of 2mm from the electrode, and the other end extends to the outside of the furnace body and an infrared temperature measuring instrument is built outside to measure the real-time temperature of the sample during the ultrafast high-temperature sintering process through the sleeve. The electrodes at both ends of the furnace body are connected to the output current of the control pulse power supply, and the current generates Joule heat. By controlling the waveform, size and frequency of the output current of the control pulse power supply, the heating rate and holding time of the sample are controlled, and finally the 4H-SiC is obtained.

[0032] The application also provides a 4H-SiC prepared by the above preparation method.

[0033] The application also provides an application of the above 4H-SiC or the 4H-SiC prepared by the above preparation method in structural devices, optical devices, power devices, radio frequency devices, optoelectronic devices and sensors.

[0034] Compared with the prior art, the application has the following beneficial effects:

[0035] (1) The present application uses carbon-based conductive powder as a heating medium and a heat preservation medium, generates high-efficiency Joule heat through a load current, realizes ultrafast heating of a sample, and the heating rate can reach 10000 ℃ / min. The high-temperature preparation of a difficult-to-sinter material SiC can be completed within a few minutes. Compared with the existing physical vapor transport method, the chemical vapor deposition method, the microwave sintering method, the spark plasma sintering method, and the self-propagating high-temperature synthesis method, the preparation process time of the present application is greatly shortened, and the energy utilization rate is greatly improved.

[0036] (2) The carbon-based conductive powder of the present application acts as a heating medium and a heat preservation medium, and also provides a rich carbon source for the sintering process of SiC raw materials. Ultrafast heating in a carbon-rich environment can induce the formation of lattice defects during the development of SiC grains, and a large amount of 4H-SiC can be formed in the sintered product. The SiC composite ceramic prepared by the present application has high 4H phase content and high conductivity, and improves the production efficiency of polycrystalline 4H-SiC, which is beneficial to the low-cost industrial production of polycrystalline 4H-SiC.

[0037] (3) The method of the present application is a pressureless ultrafast sintering method, which does not use external pressure in the preparation process of the 4H phase-rich SiC composite material, and the entire sintering process can be completed at standard atmospheric pressure. Therefore, the method has no limitation on the molding method, shape and size of the sample. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The schematic diagram of the ultrafast high-temperature sintering structure (sample, electrode, carbon-based powder medium, and insulating material) in Example 1 of the present application is shown in the figure.

[0039] Figure 2 The sintering temperature rise rate curve in Example 1 of the present application is shown in the figure.

[0040] Figure 3 The XRD pattern of the sintered product in Example 1 of the present application is shown in the figure.

[0041] Figure 4 The SEM image of the sintered product in Example 1 of the present application is shown in the figure.

[0042] Figure 5 The sintering temperature rise rate curve in Example 2 of the present application is shown in the figure.

[0043] Figure 6 The XRD pattern of the sintered product in Example 2 of the present application is shown in the figure.

[0044] Figure 7 The sintering temperature rise rate curve in Example 3 of the present application is shown in the figure.

[0045] Figure 8 The XRD pattern of the sintered product in Example 3 of the present application is shown in the figure.

[0046] Figure 9 Sintering temperature ramp profile for Inventive Example 1;

[0047] Figure 10 Sintered product XRD pattern for Inventive Example 1;

[0048] Figure 11 Sintering temperature ramp profile for Inventive Example 2;

[0049] Figure 12 Sintered product XRD pattern for Inventive Example 2;

[0050] Figure 13 Sintering temperature ramp profile for Inventive Example 3;

[0051] Figure 14 Sintered product XRD pattern for Inventive Example 3. DETAILED DESCRIPTION

[0052] The present application will now be described in greater detail hereinafter by way of specific examples which should not be construed as in limiting the scope of the application, but merely as being illustrative and representative thereof.

[0053] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges are included in the range unless it states otherwise. The range format is used as shorthand for describing endpoints contained therein; both of which are understood as being open-ended ranges. Any value or range of values described herein can be extended to include other similar values or ranges thereof. Whenever a numerical range is given, it should be understood that any other desired characteristics not explicitly defined are incorporated by reference. Other than in the examples, or where otherwise indicated, all numbers expressing quantities of materials, reaction conditions, and so forth used in the specification and associated claims are to be understood as being modified in all instances by the term "about." Unless otherwise indicated, the use of relational terms, if any, such as "about," "approximately," "essentially," "substantially," and "typically," among others, are intended to convey that a given numerical property limit is approximated and / or "plus or minus" a terminal precision range or tolerance limit. Unless otherwise indicated, the use of relational terms, if any, such as "about," "approximately," "essentially," "substantially," and "typically," among others, are intended to convey that a given numerical property limit is approximated and / or "plus or minus" a terminal precision range or tolerance limit. Unless otherwise indicated, the use of relational terms, if any, such as "about," "approximately," "essentially," "substantially," and "typically," among others, are intended to convey that a given numerical property limit is approximated and / or "plus or minus" a terminal precision range or tolerance limit.

[0054] All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present application without creative effort shall fall within the scope of the present application. The experimental methods described in the following examples are all routine methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0055] Example 1

[0056] A method for preparing 4H-SiC:

[0057] S1, uniformly mix the α-SiC raw material powder, an organic aid (consisting of D-fructose, polyethylene glycol, polyacrylic acid, and hydroxymethyl cellulose in a mass ratio of 1:5:0.5:0.1), and B2O3 in deionized water to form a slurry mixture, wherein the mass ratio of α-SiC, the organic aid, and B2O3 is 100:5:3;

[0058] S2, spray granulation and drying of the slurry mixture and cold isostatic pressing at 200Mpa to form a block to obtain a SiC sample;

[0059] S3, set the sintering furnace, fill the graphite powder in the alumina crucible as a heater, insert two electrodes into the graphite powder, and fill the SiC sample in the powder between the two electrodes;

[0060] S4, set the output waveform of the pulse current to be a square wave, the pulse frequency is 50Hz, under the protection of inert gas argon, the current increases at a rate of 5A / s, the corresponding heating rate is 1000℃ / min, the target temperature 2100℃ is reached in less than 150s, and the current size is adjusted for 300s, the total processing time of the whole process is not more than 10min;

[0061] S5, after cooling, the 4H-SiC is obtained, and the relative content of 4H-SiC is (61±3)% through XRD pattern phase analysis and semi-quantitative calculation.

[0062] Example 2

[0063] A method for preparing 4H-SiC:

[0064] S1, uniformly mix the β-SiC raw material powder, an organic aid (consisting of D-fructose, polyethylene glycol, polyacrylic acid, and hydroxymethyl cellulose in a mass ratio of 2:5:2:1), and B2O3 in deionized water to form a slurry mixture, wherein the mass ratio of β-SiC, the organic aid, and B2O3 is 100:1:2; add photosensitive resin in the slurry mixture for 3D printing;

[0065] S2, 3D printing of the slurry mixture to obtain a SiC sample;

[0066] S3, set the sintering furnace, fill the carbon nanomaterial powder in the quartz crucible as a heater, insert two electrodes into the graphite powder, and fill the SiC sample in the powder between the two electrodes;

[0067] S4, the output waveform of the pulse current is set to be a sine wave, the pulse frequency is 300 Hz, under the protection of inert gas argon, the current is increased at a rate of 1 A / s, the corresponding temperature rising rate is 200℃ / min, the target temperature 2100℃ is reached in less than 12 min, and the current size is adjusted for 200 s of heat preservation, and the total processing time of the whole process is not more than 20 min;

[0068] S5, after cooling, the 4H-SiC is obtained, and through XRD spectrum phase analysis and semi-quantitative calculation, the relative content of 4H-SiC reaches (53±4) %.

[0069] Example 3

[0070] A 4H-SiC preparation method:

[0071] S1, uniformly mix α-SiC raw material powder, organic additives (consisting of D-fructose, polyethylene glycol, polyacrylic acid, and hydroxymethyl cellulose in a mass ratio of 3:3:3:0.5) and B2O3 in deionized water to form a slurry mixture, wherein the mass ratio of α-SiC, organic additives and B2O3 is 100:2:0.1;

[0072] S2, spray granulation and drying of the slurry mixture and 200Mpa cold isostatic pressing to form a block to obtain a SiC sample;

[0073] S3, set the sintering furnace, fill the carbon black powder in the mullite crucible as a heater, insert two electrodes into the carbon black powder, and fill the SiC sample in the powder between the two electrodes;

[0074] S4, set the output waveform of the pulse current to be a sine wave, the pulse frequency is 100 Hz, under the protection of inert gas argon, the current is increased at a rate of 500 A / s, the corresponding temperature rising rate is 10000℃ / min, the target temperature 2100℃ is reached in less than 15 s, and the current size is adjusted for 200 s of heat preservation, and the total processing time of the whole process is not more than 5 min;

[0075] S5, after cooling, the 4H-SiC is obtained, and through XRD spectrum phase analysis and semi-quantitative calculation, the relative content of 4H-SiC reaches (70±3) %.

[0076] Comparative Example 1

[0077] Compared with Example 1, the only difference is that the temperature rising rate in step S4 is 50℃ / min, the target temperature 2100℃ is reached, and the heat preservation time is 800 s. Other methods are the same as Example 1.

[0078] Comparative Example 2

[0079] Compared with Example 1, the only difference is that the organic auxiliary agent in step S1 is composed of D-fructose, polyethylene glycol, polyacrylic acid and hydroxymethyl cellulose with a mass ratio of 0.01:0.5:5:0.01. Other methods are the same as those in Example 1.

[0080] Comparative Example 3

[0081] Compared with Example 1, the only difference is that the mass ratio of the α-SiC, the organic auxiliary agent and B2O3 in step S1 is 100:8:0.02. Other methods are the same as those in Example 1.

[0082] Effect Example

[0083] The 4H-SiC samples of Examples 1-3 and Comparative Examples 1-3 are respectively taken, and XRD patterns are obtained by X-ray diffraction. The phase composition of the samples is obtained by qualitative analysis of the XRD patterns, and the content of 4H-SiC is obtained by quantitative analysis of the XRD patterns and XRD semi-quantitative calculation. The conductivity of 4H-SiC of Examples 1-3 and Comparative Examples 1-3 is measured by direct current conductivity measurement method. In the direct current conductivity measurement method, the test equipment is usually a standard resistor and a direct current power supply, and the conductivity of the sample is calculated by measuring the direct current conductivity value of the sample. The specific results are shown in Table 1.

[0084] Table 1: Content of 4H-SiC in each group

[0085] Group Content / wt% Conductivity (Siemens / m (S / m)) Example 1 61±3 3.3e+05 Example 2 53±4 2.5e+05 Example 3 70±3 5.3e+05 Comparative Example 1 6±2 1.2e+03 Comparative Example 2 15±3 5.8e+03 Comparative Example 3 21±4 1.3e+04

[0086] According to the results, the 4H-SiC prepared by the preparation method of the examples has a higher relative content and higher conductivity compared with the 4H-SiC of the comparative examples.

[0087] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the present application, and is not a limitation on the protection scope of the present application. Simple modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A method for ultra-rapid production of 4H-SiC, characterized by: The method comprises the following steps: S1, uniformly mixing SiC raw material powder, organic additives and sintering additives in water to form a slurry mixture; S2, obtaining a SiC sample by a material forming process; S3, under the protection of inert gas, performing high-temperature sintering of the SiC sample in a carbon-based powder medium, and then cooling to obtain the 4H-SiC; The method of high-temperature sintering of the carbon-based powder medium in step S3 is as follows: in an insulating material filled with carbon-based conductive powder, an ultrafast heating is realized by controlling pulse current, and then holding; the rate of the ultrafast heating is 1000-10000 ℃ / min; the time of the ultrafast heating is 15s-150s; the time of the holding is 200s-300s; The mass ratio of the SiC raw material, the organic additives and the sintering additives in step S1 is 100:1-5:0.1-3; The organic additives in step S1 are composed of D-fructose, polyethylene glycol, polyacrylic acid and hydroxymethyl cellulose with a mass ratio of 1-3:3-5:0.5-3:0.1-1; The sintering additives in step S1 are B2O3 and / or B(OH)3; The mass content of the 4H-SiC in step S3 is greater than 50%; The method of controlling pulse current in step S3 comprises inserting two electrodes into the carbon-based conductive powder, and filling the SiC sample in the powder between the two electrodes to control pulse current.

2. The method of claim 1, wherein: The SiC raw material in step S1 is α-SiC and / or β-SiC.

3. The method of claim 1, wherein: The material forming process in step S2 comprises dry pressing forming method and / or 3D printing forming method.

4. The method of claim 1, wherein: The inert gas in step S3 comprises at least one of helium, neon and argon.

5. The method of claim 1, wherein: The controlling pulse current comprises controlling the waveform, the size and the frequency of the pulse current; the waveform of the pulse current comprises square wave, trapezoidal wave, triangular wave, sawtooth wave or sine wave; the size of the pulse current is 1mA-500A, and the frequency of the pulse current is 0-300Hz.

6. The method of claim 1, wherein: The insulating material comprises alumina crucible, boron nitride crucible, quartz crucible or mullite crucible; the carbon-based conductive powder comprises at least one of carbon black powder, graphite powder, graphene powder, carbon fiber powder and carbon nanomaterial powder.

7. A 4H-SiC characterized by: Prepared by the method of any one of claims 1-6.

8. The 4H-SiC of claim 7 or the 4H-SiC prepared by the method of any one of claims 1-6 is applied in structural devices, optical devices, power devices, radio frequency devices, optoelectronic devices and sensors.

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