Method for preparing silicon carbide ceramic from silicon waste and waste graphite

Abstract

The invention discloses a method for preparing silicon carbide ceramic by utilizing silicon waste and waste graphite. The method specifically comprises the following steps: (1) respectively crushing diamond wire cutting silicon waste and a waste crystal pulling graphite crucible; (2) mixing diamond wire cutting silicon waste powder, waste crystal pulling graphite crucible powder and silicon carbide powder to obtain a mixture; and (3) sequentially pressing, roasting, washing and drying the mixture to obtain the catalyst. Diamond wire cutting silicon waste and waste crystal pulling graphite crucibles in the monocrystalline silicon industry serve as raw materials, the silicon carbide ceramic material is prepared through the processes of crushing, mixing, pressing, roasting, washing, drying and the like, and finally the high-density silicon carbide ceramic material is obtained. Meanwhile, by recycling the diamond wire cutting silicon waste and the waste crystal pulling graphite crucible in the monocrystalline silicon industry, resource waste can be reduced, environmental pollution can be reduced, the utilization rate of the waste is increased, and a new thought is provided for recycling of the two kinds of waste.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon carbide ceramics, and more specifically, to a method for preparing silicon carbide ceramics by using silicon waste and waste graphite. Background Art

[0002] Silicon carbide (SiC) ceramics have excellent mechanical, thermal, chemical, and electrical properties, and have received increasing attention in the fields of aerospace and energy. Silicon carbide ceramics have the advantages of high temperature resistance, heat resistance, low bulk density, large specific surface area, high mechanical strength, etc., and have been applied in many engineering fields, such as high-temperature dust filtration, sensors, thermal barrier coatings, water separation and purification, and bioengineering.

[0003] Silicon rods are cut into silicon wafers. Currently, the main cutting process for silicon rods is the diamond wire sawing method. During the cutting process, about 35% of the high-purity silicon enters the waste (Diamond Wire Sawing Silicon Waste, DWSSW) in the form of waste. Currently, the research on DWSSW mainly focuses on separation and purification methods such as laser-assisted vacuum smelting, two-step sintering and acid leaching, and directional solidification to obtain high-purity silicon, and there is less research on other potential applications.

[0004] Graphite products play a key role in the development of photovoltaic technology, including the manufacture of polysilicon raw materials, the pulling of single-crystal silicon rods, and the casting of polysilicon ingots. Due to the excellent density, hardness, compressive strength, high temperature resistance, high pressure resistance, and stable performance of graphite materials, they can be made into silicon-graphite crucibles for polysilicon purification and single-crystal silicon pulling processes. Currently, the research on waste pulling graphite crucibles mainly focuses on processes such as foam flotation, electrostatic separation, microwave radiation, and electrochemistry for regeneration and purification.

[0005] Therefore, how to develop a method for synthesizing a highly dense silicon carbide crucible using diamond wire sawing silicon waste and waste pulling graphite crucibles as raw materials is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a method for preparing silicon carbide ceramics by using silicon waste and waste graphite to solve the deficiencies in the prior art.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A method for preparing silicon carbide ceramics by using silicon waste and waste graphite specifically includes the following steps:

[0009] (1) Crush the diamond wire sawing silicon waste and the waste pulling graphite crucible respectively to obtain diamond wire sawing silicon waste powder and waste pulling graphite crucible powder;

[0010] (2) Mix the waste silicon powder cut by diamond wire, the waste graphite crucible powder for crystal pulling, and the silicon carbide powder to obtain a mixed material;

[0011] (3) Press, roast, wash, and dry the mixed material in sequence to obtain silicon carbide ceramics.

[0012] Furthermore, in the above step (1), the equipment for crushing is an acoustic resonance instrument, the resonance frequency is 20 - 50 Hz, the resonance time is 5 - 30 min, and the acceleration is 50 - 100 g.

[0013] Furthermore, in the above step (2), the mass ratio of the waste silicon powder cut by diamond wire, the waste graphite crucible powder for crystal pulling, and the silicon carbide powder is 1:(1 - 2.5):(0.1 - 1).

[0014] The beneficial effects of the above further steps are as follows: In the present invention, the waste silicon cut by diamond wire and the waste graphite crucible after crystal pulling in the slicing process of the single-crystal silicon industry are used as the silicon source and carbon source. There is no need to treat the impurities in the raw materials, which simplifies the entire process flow and has a lower preparation cost compared with traditional industries. At the same time, it can effectively reduce environmental pollution and resource waste, realizing the high-value utilization of two types of waste materials, namely, the waste silicon cut by diamond wire and the waste graphite crucible in the single-crystal silicon industry, and providing a new idea for the recycling of the two types of waste materials. In addition, in the mixing process of the present invention, silicon carbide powder is added as the seed crystal during the roasting process. The crystal nuclei with an orderly arrangement of silicon carbide atoms are preferentially formed on the surface of the seed crystal, which is beneficial to the synthesis of silicon carbide and improves the conversion rate of the reactants. At the same time, it significantly inhibits the abnormal migration of grain boundaries during the sintering process, effectively closes the micro-pores and strengthens the grain boundary bonding strength, and effectively improves the density of the prepared silicon carbide ceramics.

[0015] Furthermore, in the above step (2), the equipment for mixing is an acoustic resonance instrument, the resonance frequency is 50 - 100 Hz, the resonance time is 10 - 80 min, and the acceleration is 50 - 100 g.

[0016] The beneficial effects of the above further steps are as follows: In the present invention, an acoustic resonance instrument is used for mixing, which destroys particle agglomeration, increases the specific surface area, improves the contact efficiency of reactants, and the mixing efficiency is several to dozens of times that of traditional mixing technologies, achieving uniform and dead-angle-free mixing. At the same time, dislocations, grain boundaries and other defects are introduced into the raw materials, reducing the reaction activation energy, promoting the reactant molecules to be in an excited state, effectively reducing the reaction temperature and energy consumption during the roasting process. Moreover, it can also effectively avoid problems such as impurity introduction and raw material oxidation in traditional mixing methods such as ball milling.

[0017] Further, in the above step (3), the pressing equipment is a high-pressure briquetting machine, the pressure is 5-40 MPa, and the pressure holding time is 30-180 s; the diameter of the pellet after pressing is 15-50 mm, and the thickness is 3-8 mm.

[0018] Further, in the above step (3), the roasting equipment is a crucible and a high-temperature reaction furnace; the material of the crucible is graphite, alumina, zirconia or silicon nitride; the high-temperature reaction furnace is a vacuum induction furnace, a box-type resistance furnace or a tube-type resistance furnace.

[0019] Further, in the above step (3), the roasting temperature is 1000-2500 °C, and the time is 0.5-4 h.

[0020] Further, in the above step (3), the washing reagent is deionized water, the ultrasonic frequency is 30-180 kHz, the ultrasonic power is 0-300 W, and the washing time is 5-120 min.

[0021] Further, in the above step (3), the drying equipment is a vacuum drying oven, the vacuum degree is 0.05-0.09 MPa, the temperature is 60-120 °C, and the drying time is 2-12 h.

[0022] Further, in the above step (3), the bulk density of the silicon carbide ceramic is 2.65-3.01 g·cm -3 , and the flexural strength is 200-450 Mpa.

[0023] As can be seen from the above technical solutions, compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] The present invention uses the waste silicon cut by diamond wire and the waste graphite crucible for crystal pulling in the single crystal silicon industry as raw materials, and prepares silicon carbide ceramic materials through processes such as crushing, mixing, pressing, roasting, washing and drying, and finally obtains high-density silicon carbide ceramic materials; at the same time, the recycling of the waste silicon cut by diamond wire and the waste graphite crucible for crystal pulling in the single crystal silicon industry by the present invention can reduce resource waste, reduce environmental pollution, improve the utilization rate of waste materials, and provide a new idea for the recycling of the two waste materials. Specific Embodiments

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] Example 1

[0027] Method for preparing silicon carbide ceramics by using silicon waste and waste graphite, specifically including the following steps:

[0028] (1) Raw material crushing

[0029] Place the diamond wire cut silicon waste and the used pulling graphite crucible in an acoustic resonance instrument for sufficient crushing. The resonance frequency is 20 Hz, the resonance time is 5 min, and the acceleration is 50 g to obtain diamond wire cut silicon waste powder and used pulling graphite crucible powder;

[0030] (2) Raw material mixing

[0031] Weigh the diamond wire cut silicon waste powder, the used pulling graphite crucible powder and the silicon carbide powder according to the mass ratio of 1:1.1:0.1, and perform sufficient mixing through an acoustic resonance instrument. The resonance frequency is 50 Hz, the resonance time is 10 min, and the acceleration is 50 g to obtain a mixture;

[0032] (3) Pellet pressing

[0033] Place the mixture in a high-pressure briquetting machine and keep the pressure at 5 MPa for 30 s for pellet pressing to obtain pellets with a diameter of 15 mm and a thickness of 3 mm;

[0034] (4) Roasting

[0035] Place the pellets in a graphite crucible and put them into a vacuum induction furnace, and roast at 1200 °C for 0.5 h to obtain silicon carbide crystal blocks;

[0036] (5) Washing

[0037] Place the silicon carbide crystal blocks in deionized water for ultrasonic washing. The ultrasonic frequency is 30 kHz, the ultrasonic power is 100 W, and the washing time is 10 min to remove the unreacted raw materials and obtain clean silicon carbide crystal blocks;

[0038] (6) Drying

[0039] Place the clean silicon carbide crystal blocks in a vacuum drying oven for drying. The vacuum degree is 0.05 MPa, the temperature is 60 °C, and the drying time is 4 h to obtain silicon carbide ceramics with a bulk density of 2.65 g·cm -3 and a flexural strength of 200 Mpa.

[0040] Example 2

[0041] Method for preparing silicon carbide ceramics by using silicon waste and waste graphite, specifically including the following steps:

[0042] (1) Raw material crushing

[0043] The silicon waste cut by diamond wire and the used graphite crucible for crystal pulling are respectively placed in an acoustic resonance instrument for sufficient crushing. The resonance frequency is 30 Hz, the resonance time is 10 min, and the acceleration is 60 g, obtaining silicon waste powder cut by diamond wire and used graphite crucible powder for crystal pulling;

[0044] (2) Raw material mixing

[0045] Weigh the silicon waste powder cut by diamond wire, the used graphite crucible powder for crystal pulling and silicon carbide powder according to the mass ratio of 1:1.2:0.15, and conduct sufficient mixing through an acoustic resonance instrument. The resonance frequency is 60 Hz, the resonance time is 20 min, and the acceleration is 60 g, obtaining a mixed material;

[0046] (3) Pellet pressing

[0047] Place the mixed material in a high-pressure pellet press, and keep the pressure at 10 MPa for 60 s for pellet pressing, obtaining pellets with a diameter of 15 mm and a thickness of 4 mm;

[0048] (4) Roasting

[0049] Place the pellets in an alumina crucible and put them into a box-type resistance furnace, roast at 1400 °C for 1 h, obtaining silicon carbide crystal blocks;

[0050] (5) Washing

[0051] Place the silicon carbide crystal blocks in deionized water for ultrasonic washing. The ultrasonic frequency is 40 kHz, the ultrasonic power is 200 W, and the washing time is 15 min to remove the unreacted raw materials, obtaining clean silicon carbide crystal blocks;

[0052] (6) Drying

[0053] Place the clean silicon carbide crystal blocks in a vacuum drying oven for drying. The vacuum degree is 0.06 MPa, the temperature is 70 °C, and the drying time is 6 h, obtaining silicon carbide ceramics with a bulk density of 2.71 g·cm -3 and a flexural strength of 240 Mpa.

[0054] Example 3

[0055] A method for preparing silicon carbide ceramics using silicon waste and waste graphite specifically includes the following steps:

[0056] (1) Raw material crushing

[0057] The silicon waste cut by diamond wire and the used graphite crucible for crystal pulling are respectively placed in an acoustic resonance instrument for sufficient crushing. The resonance frequency is 40 Hz, the resonance time is 15 min, and the acceleration is 70 g, obtaining silicon waste powder cut by diamond wire and used graphite crucible powder for crystal pulling;

[0058] (2) Raw material mixing

[0059] Weigh the diamond wire cut silicon waste powder, waste pulling graphite crucible powder and silicon carbide powder according to the mass ratio of 1:1.5:0.3, and mix them thoroughly through an acoustic resonance instrument. The resonance frequency is 70 Hz, the resonance time is 30 min, and the acceleration is 70 g to obtain a mixture.

[0060] (3) Pellet pressing

[0061] Place the mixture in a high-pressure pellet press and press it under a pressure of 15 MPa for 90 s to obtain pellets with a diameter of 20 mm and a thickness of 4 mm.

[0062] (4) Roasting

[0063] Place the pellets in an alumina crucible and put them into a tube resistance furnace, and roast them at 1500 °C for 2 h to obtain silicon carbide crystal blocks.

[0064] (5) Washing

[0065] Place the silicon carbide crystal blocks in deionized water and wash them ultrasonically. The ultrasonic frequency is 50 kHz, the ultrasonic power is 150 W, and the washing time is 20 min to remove the unreacted raw materials and obtain clean silicon carbide crystal blocks.

[0066] (6) Drying

[0067] Place the clean silicon carbide crystal blocks in a vacuum drying oven for drying. The vacuum degree is 0.07 MPa, the temperature is 80 °C, and the drying time is 8 h to obtain silicon carbide ceramics with a bulk density of 2.78 g·cm -3 and a flexural strength of 290 Mpa.

[0068] Example 4

[0069] A method for preparing silicon carbide ceramics using silicon waste and waste graphite specifically includes the following steps:

[0070] (1) Raw material crushing

[0071] Respectively place the diamond wire cut silicon waste and the waste pulling graphite crucible in an acoustic resonance instrument for sufficient crushing. The resonance frequency is 50 Hz, the resonance time is 20 min, and the acceleration is 70 g to obtain the diamond wire cut silicon waste powder and the waste pulling graphite crucible powder.

[0072] (2) Raw material mixing

[0073] Weigh the diamond wire cut silicon waste powder, waste pulling graphite crucible powder and silicon carbide powder according to the mass ratio of 1:1.5:0.4, and mix them thoroughly through an acoustic resonance instrument. The resonance frequency is 80 Hz, the resonance time is 40 min, and the acceleration is 80 g to obtain a mixture.

[0074] (3) Pellet pressing

[0075] Place the mixed material in a high-pressure pellet press, keep the pressure at 20 MPa for 120 s for pellet pressing, and obtain pellets with a diameter of 20 mm and a thickness of 5 mm;

[0076] (4) Roasting

[0077] Place the pellets in a zirconia crucible and put it into a vacuum induction furnace, roast at 1700 °C for 2 h to obtain silicon carbide crystal blocks;

[0078] (5) Washing

[0079] Place the silicon carbide crystal blocks in deionized water for ultrasonic washing, the ultrasonic frequency is 70 kHz, the ultrasonic power is 150 W, and the washing time is 30 min to remove the unreacted raw materials and obtain clean silicon carbide crystal blocks;

[0080] (6) Drying

[0081] Place the clean silicon carbide crystal blocks in a vacuum drying oven for drying, the vacuum degree is 0.07 MPa, the temperature is 80 °C, and the drying time is 10 h to obtain silicon carbide ceramics with a bulk density of 2.83 g·cm -3 and a flexural strength of 350 Mpa.

[0082] Example 5

[0083] A method for preparing silicon carbide ceramics using silicon waste and waste graphite, specifically including the following steps:

[0084] (1) Raw material crushing

[0085] Place the wire-cut silicon waste and the used pulling graphite crucible in an acoustic resonance instrument for sufficient crushing, the resonance frequency is 50 Hz, the resonance time is 30 min, and the acceleration is 80 g to obtain wire-cut silicon waste powder and used pulling graphite crucible powder;

[0086] (2) Raw material mixing

[0087] Weigh the wire-cut silicon waste powder, the used pulling graphite crucible powder and the silicon carbide powder according to the mass ratio of 1:2:0.5, and perform sufficient mixing through an acoustic resonance instrument, the resonance frequency is 80 Hz, the resonance time is 50 min, and the acceleration is 80 g to obtain a mixed material;

[0088] (3) Pellet pressing

[0089] Place the mixed material in a high-pressure pellet press, keep the pressure at 30 MPa for 180 s for pellet pressing, and obtain pellets with a diameter of 20 mm and a thickness of 5 mm;

[0090] (4) Calcination

[0091] The pellets were placed in a silicon nitride crucible and placed in a vacuum induction furnace, and calcined at 1800°C for 3 hours to obtain a silicon carbide crystal block;

[0092] (5) Washing

[0093] The silicon carbide crystal block is placed in deionized water for ultrasonic washing, the ultrasonic frequency is 100kHz, the ultrasonic power is 200W, and the washing time is 45min to remove unreacted raw materials and obtain a clean silicon carbide crystal block;

[0094] (6) Drying

[0095] The clean silicon carbide crystal block was placed in a vacuum drying oven for drying at a vacuum degree of 0.05 MPa, a temperature of 100 °C, and a drying time of 10 h to obtain a bulk density of 2.92 g cm -3 , silicon carbide ceramics with a flexural strength of 410Mpa.

[0096] Example 6

[0097] The method for preparing silicon carbide ceramics using silicon waste and waste graphite specifically comprises the following steps:

[0098] (1) Raw material crushing

[0099] The diamond wire cutting silicon waste and the waste crystal pulling graphite crucible are placed in an acoustic resonance instrument for full crushing, respectively, with a resonance frequency of 50 Hz, a resonance time of 30 min, and an acceleration of 80 g, to obtain diamond wire cutting silicon waste powder and waste crystal pulling graphite crucible powder;

[0100] (2) Raw material mixing

[0101] Diamond wire cutting silicon waste powder, waste crystal pulling graphite crucible powder and silicon carbide powder are weighed in a mass ratio of 1:2:0.3, and fully mixed by an acoustic resonance instrument with a resonance frequency of 80 Hz, a resonance time of 60 min, and an acceleration of 80 g to obtain a mixture;

[0102] (3) Pressing pellets

[0103] The mixture was placed in a high-pressure pelletizing machine and pelletized at a pressure of 20 MPa for 120 seconds to obtain pellets with a diameter of 20 mm and a thickness of 5 mm.

[0104] (4) Calcination

[0105] The pellets were placed in a graphite crucible and placed in a vacuum induction furnace, and calcined at 1800°C for 3 hours to obtain a silicon carbide crystal block;

[0106] (5) Washing

[0107] The silicon carbide crystal block is placed in deionized water and ultrasonically washed. The ultrasonic frequency is 120 kHz, the ultrasonic power is 220 W, and the washing time is 50 min to remove the unreacted raw materials, obtaining a clean silicon carbide crystal block;

[0108] (6) Drying

[0109] The clean silicon carbide crystal block is placed in a vacuum drying oven for drying. The vacuum degree is 0.06 MPa, the temperature is 120 °C, and the drying time is 10 h, obtaining silicon carbide ceramics with a bulk density of 3.01 g·cm -3 and a flexural strength of 450 Mpa.

[0110] Example 7

[0111] A method for preparing silicon carbide ceramics using silicon waste and waste graphite, specifically including the following steps:

[0112] (1) Raw material crushing

[0113] The wire saw cut silicon waste and the used single crystal pulling graphite crucible are respectively placed in an acoustic resonance instrument for sufficient crushing. The resonance frequency is 50 Hz, the resonance time is 30 min, and the acceleration is 80 g, obtaining wire saw cut silicon waste powder and used single crystal pulling graphite crucible powder;

[0114] (2) Raw material mixing

[0115] The wire saw cut silicon waste powder, the used single crystal pulling graphite crucible powder and silicon carbide powder are weighed according to a mass ratio of 1:2:0.8 and sufficiently mixed through an acoustic resonance instrument. The resonance frequency is 80 Hz, the resonance time is 60 min, and the acceleration is 80 g, obtaining a mixed material;

[0116] (3) Pellet pressing

[0117] The mixed material is placed in a high-pressure pellet press and pellet pressed under a pressure of 20 MPa for 120 s, obtaining pellets with a diameter of 20 mm and a thickness of 5 mm;

[0118] (4) Roasting

[0119] The pellets are placed in a graphite crucible and put into a vacuum induction furnace, roasted at 1800 °C for 3 h, obtaining silicon carbide crystal blocks;

[0120] (5) Washing

[0121] The silicon carbide crystal block is placed in deionized water and ultrasonically washed. The ultrasonic frequency is 120 kHz, the ultrasonic power is 220 W, and the washing time is 50 min to remove the unreacted raw materials, obtaining a clean silicon carbide crystal block;

[0122] (6) Drying

[0123] Place the clean silicon carbide crystal blocks in a vacuum drying oven for drying. The vacuum degree is 0.06 MPa, the temperature is 120 °C, and the drying time is 10 h to obtain silicon carbide ceramics with a bulk density of 2.81 g·cm -3 and a flexural strength of 350 Mpa.

[0124] Performance Test

[0125] Take the silicon carbide ceramic samples prepared in Examples 1-7 respectively, and test their bulk density and flexural strength.

[0126] The test results are shown in Table 1.

[0127] Table 1 Bulk density and flexural strength of silicon carbide ceramic samples in Examples 1-7

[0128] Silicon carbide ceramic sample <![CDATA[Bulk density / g·cm -3 > Flexural strength / Mpa Example 1 2.65 200 Example 2 2.71 240 Example 3 2.78 290 Example 4 2.83 350 Example 5 2.92 410 Example 6 3.01 450 Example 7 2.81 350

[0129] As can be seen from Table 1, the following conclusions can be drawn based on the experimental conditions and results of Examples 1-7:

[0130] 1. By prolonging the acoustic resonance time, increasing the frequency, increasing the acceleration and other mixing conditions, the purpose of destroying particle agglomeration, reducing the reaction activation energy and achieving uniform and dead-end-free mixing can be achieved.

[0131] 2. By increasing the smelting temperature, prolonging the holding time and other smelting conditions, the purpose of promoting the synthesis of silicon carbide and improving the density of silicon carbide ceramics can be achieved.

[0132] 3. It can be seen from the experimental results that adding silicon carbide powder during the mixing process can promote the synthesis of silicon carbide and improve the density of silicon carbide ceramic materials. However, adding excessive silicon carbide powder may lead to insufficient contact between the silicon source and the carbon source, hindering the synthesis of silicon carbide. The optimal addition amount of silicon carbide powder is about 10 wt%.

[0133] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing silicon carbide ceramics using silicon waste and waste graphite, characterized in that: The specific steps include: (1) respectively crushing the diamond wire cutting silicon waste and the waste crystal pulling graphite crucible to obtain diamond wire cutting silicon waste powder and the waste crystal pulling graphite crucible powder; (2) mixing diamond wire cutting silicon waste powder, waste crystal pulling graphite crucible powder and silicon carbide powder to obtain a mixture; (3) The mixed material is pressed, calcined, washed and dried in sequence to obtain the silicon carbide ceramic.

2. The method for preparing silicon carbide ceramics using silicon waste and waste graphite according to claim 1, characterized in that: In step (1), the crushing equipment is an acoustic resonator with a resonance frequency of 20 to 50 Hz, a resonance time of 5 to 30 min, and an acceleration of 50 to 100 g.

3. The method for preparing silicon carbide ceramics using silicon waste and waste graphite according to claim 1, characterized in that: In step (2), the mass ratio of the diamond wire cutting silicon waste powder, the waste crystal pulling graphite crucible powder and the silicon carbide powder is 1:(1-2.5):(0.1-1).

4. The method for preparing silicon carbide ceramics using silicon waste and waste graphite according to claim 1, characterized in that: In step (2), the mixing device is an acoustic resonator with a resonance frequency of 50 to 100 Hz, a resonance time of 10 to 80 min, and an acceleration of 50 to 100 g.

5. The method for preparing silicon carbide ceramics using silicon waste and waste graphite according to claim 1, characterized in that: In step (3), the pressing equipment is a high-pressure ball press, the pressure is 5-40 MPa, and the pressure holding time is 30-180 s; the diameter of the ball after pressing is 15-50 mm and the thickness is 3-8 mm.

6. The method for preparing silicon carbide ceramics using silicon waste and waste graphite according to claim 1, characterized in that: In step (3), the calcining equipment is a crucible and a high-temperature reaction furnace; the material of the crucible is graphite, alumina, zirconia or silicon nitride; the high-temperature reaction furnace is a vacuum induction furnace, a box-type resistance furnace or a tubular resistance furnace.

7. The method for preparing silicon carbide ceramics using silicon waste and waste graphite according to claim 1, characterized in that: In step (3), the calcination temperature is 1000-2500° C. and the calcination time is 0.5-4 h.

8. The method for preparing silicon carbide ceramics using silicon waste and waste graphite according to claim 1, characterized in that: In step (3), the washing reagent is deionized water, the ultrasonic frequency is 30 to 180 kHz, the ultrasonic power is 0 to 300 W, and the washing time is 5 to 120 min.

9. The method for preparing silicon carbide ceramics using silicon waste and waste graphite according to claim 1, characterized in that: In step (3), the drying equipment is a vacuum drying oven with a vacuum degree of 0.05 to 0.09 MPa, a temperature of 60 to 120° C., and a drying time of 2 to 12 hours.

10. The method for preparing silicon carbide ceramics using silicon waste and waste graphite according to claim 1, characterized in that: In step (3), the volume density of the silicon carbide ceramic is 2.65 to 3.01 g·cm -3 , the bending strength is 200~450Mpa.