Method for preparing silicon carbide powder from silicon wafer cutting waste
High-purity silicon carbide powder was prepared by acid washing and oxidation treatment of silicon wafer cutting waste, which solved the problem of high-purity silicon source demand in existing technologies and achieved efficient resource utilization and cost reduction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GCL NEW (SHANGHAI) PHOTOVOLTAIC TECH CO LTD
- Filing Date
- 2024-10-11
- Publication Date
- 2026-04-14
AI Technical Summary
In existing technologies, the reuse of silicon wafer cutting waste and the preparation of silicon carbide powder require high-purity silicon sources, which leads to resource waste and increased costs.
Impurities in the silicon sludge are removed by acid washing. Silicon powder and carbon powder are mixed and heated in a vacuum or inert atmosphere to react. Then, excess carbon powder is removed by oxidation in an oxygen atmosphere to obtain high-purity silicon carbide powder.
The preparation of high-purity silicon carbide powder has been achieved, solving the problems of resource waste and high cost, and improving the utilization efficiency of silicon wafer cutting waste.
Abstract
Description
Technical Field
[0001] This application relates to the field of silicon carbide preparation technology, and in particular to a method for preparing silicon carbide from silicon wafer cutting waste. Background Technology
[0002] During the manufacturing process of photovoltaic silicon wafers, 20% to 30% of silicon material is lost. This material eventually exists as silicon sludge along with the cutting fluid after the pressure filtration process. Most of this silicon sludge is sold at low prices as low-quality cutting waste, resulting in a serious waste of resources.
[0003] Silicon carbide (SiC) powder is an important engineering ceramic material with excellent high-temperature mechanical properties, chemical stability, and wear resistance, thus finding wide applications in fields such as power electronics, automotive manufacturing, and aerospace. Its preparation techniques typically include the following methods: carbothermal reduction, chemical vapor deposition, solid-state reaction, silicon carbide precursor decomposition, and others. High-purity silicon carbide powder prepared using these methods all require high-purity silicon and carbon sources, significantly increasing costs. Summary of the Invention
[0004] The purpose of this application is to provide a method for preparing silicon carbide from silicon wafer cutting waste. The method involves acid washing to remove some impurities from the silicon sludge, followed by drying. The dried silicon powder raw material is then mixed with carbon powder and reacted. The resulting silicon carbide powder is oxidized in an O2 atmosphere to remove excess carbon powder, thereby obtaining high-purity silicon carbide powder. This method solves the problems of reusing silicon wafer cutting waste and requiring a high-purity silicon source for preparing silicon carbide powder in the prior art.
[0005] To achieve one of the above-mentioned objectives, one embodiment of this application provides a method for preparing silicon carbide from silicon wafer cutting waste, comprising the following steps:
[0006] Pickling: Add the waste silicon sludge generated from silicon wafer cutting to a mixed acid solution, stir, filter, and then wash with water until neutral;
[0007] Drying: The acid-washed silica mud is dried to constant weight to obtain silica powder raw material;
[0008] Solid-phase synthesis: Silicon powder raw material and carbon powder are stirred and mixed and then placed in a graphite crucible. The mixture is heated and reacted in a vacuum atmosphere or inert gas to obtain silicon carbide powder.
[0009] Purification: Silicon carbide powder is placed in an O2 atmosphere to oxidize and remove unreacted carbon powder.
[0010] As a further improvement of one embodiment of this application, it also includes a second acid washing, in which the purified silicon carbide powder is added to a hydrofluoric acid solution for a second acid washing, and then stirred, filtered, and washed with water until neutral.
[0011] As a further improvement of one embodiment of this application, it also includes re-drying, drying the silicon carbide powder after re-acid washing to constant weight to obtain silicon carbide powder with a particle size of 2 to 5 micrometers.
[0012] As a further improvement of one embodiment of this application, the mass ratio of silicon powder raw material to carbon powder is 2.45:1 to 2.57:1.
[0013] As a further improvement of one embodiment of this application, the mixed acid solution includes a hydrofluoric acid solution, the hydrofluoric acid solution accounting for 10-30% of the total volume of all substances in the mixed acid solution, and the mass percentage of hydrofluoric acid in the hydrofluoric acid solution is 40%.
[0014] As a further improvement of one embodiment of this application, the mixed acid solution also includes a nitric acid solution, which accounts for 5 to 20% of the total volume of all substances in the mixed acid solution, with the remainder being water; wherein, the mass percentage of nitric acid in the nitric acid solution is 68%.
[0015] As a further improvement of one embodiment of this application, the particle size of the silicon powder raw material obtained after acid washing and drying is 0.5 to 1.2 micrometers.
[0016] As a further improvement of one embodiment of this application, in the solid-phase synthesis process, silicon powder raw material and carbon powder placed in a graphite crucible are fed into a silicon carbide sintering furnace and heated to 1250-2100°C for a reaction time of 2-5 hours.
[0017] As a further improvement of one embodiment of this application, in the purification step, the silicon carbide powder is purified by reacting at 600-800°C for 2-8 hours.
[0018] As a further improvement of one embodiment of this application, in the drying step, the drying atmosphere is a vacuum or an inert atmosphere, the drying temperature is 60-80°C, and the drying time is 8-10 hours.
[0019] One or more technical solutions provided in this application have at least the following technical effects or advantages:
[0020] The method for preparing silicon carbide from silicon wafer cutting waste provided in this application involves acid washing of silicon sludge to remove some impurities, followed by drying. The dried silicon powder raw material is then mixed with carbon powder and reacted. The resulting silicon carbide powder is oxidized in an O2 atmosphere to remove excess carbon powder, thereby obtaining high-purity silicon carbide powder. Detailed Implementation
[0021] The present invention will be described in detail below with reference to specific embodiments, but these embodiments do not limit the present invention. Any changes in reaction conditions, reactants or raw material amounts made by those skilled in the art based on these embodiments are included within the protection scope of the present invention.
[0022] This application provides a method for preparing silicon carbide from silicon wafer cutting waste, including the following steps:
[0023] Pickling: Add the waste silicon sludge generated from silicon wafer cutting to a mixed acid solution, stir, filter, and then wash with water until neutral;
[0024] Drying: The acid-washed silica mud is dried to constant weight to obtain silica powder raw material;
[0025] Solid-phase synthesis: Silicon powder raw material and carbon powder are stirred and mixed and then placed in a graphite crucible. The mixture is heated and reacted in a vacuum atmosphere or inert gas to obtain silicon carbide powder.
[0026] Purification: Silicon carbide powder is placed in an O2 atmosphere to oxidize and remove unreacted carbon powder.
[0027] The moisture content of the silicon sludge produced by silicon wafer cutting is usually 40-45%. Before drying, the silicon sludge is first added to a mixed acid solution for acid washing. The mixed acid solution is used to wash away most of the impurities in the silicon sludge. Then, it is washed with water until neutral to avoid the acid in the mixed acid solution adhering to the silicon surface during the drying process and introducing new impurities.
[0028] Silicon powder, obtained by acid washing to remove most impurities and drying, is mixed with carbon powder and reacted under heat in a vacuum or inert gas atmosphere. This avoids oxidation of the silicon powder and carbon powder due to contact with oxygen, which would produce silicon dioxide impurities and waste carbon source. After the silicon powder and carbon powder react to obtain silicon carbide powder, the silicon carbide powder is placed in an O2 atmosphere. This prevents unreacted carbon powder from remaining in the silicon carbide powder and forming new impurities. The remaining carbon powder reacts with O2 to form CO2 gas, which separates from the silicon carbide powder, ensuring the purity of the silicon carbide powder.
[0029] In some embodiments, after the silicon carbide powder is purified, it is further acid-washed again. The purified silicon carbide powder is added to a hydrofluoric acid solution for acid washing again, and then stirred, filtered, and washed with water until neutral.
[0030] The purification step removes any residual carbon powder. However, if the reaction between silicon powder and carbon powder is incomplete, silicon powder may remain. When O2 is used to remove carbon powder in the purification step, the silicon powder will also be oxidized into silicon dioxide by O2. Silicon dioxide reacts with hydrofluoric acid in a hydrofluoric acid solution to form water-soluble silicon tetrafluoride. After filtration and washing, it can be ensured that there is no residual silicon powder in the silicon carbide powder, thus making the silicon carbide purer.
[0031] In some embodiments, the process further includes re-drying after acid washing, drying the acid-washed silicon carbide powder to constant weight to obtain silicon carbide powder with a particle size of 2-5 micrometers. The silicon carbide after re-acid washing has a high moisture content and needs to be dried again to finally obtain silicon carbide powder with a particle size of 2-5 micrometers.
[0032] In some embodiments, the mass ratio of silicon powder to carbon powder is 2.45:1 to 2.57:1. In silicon carbide, the molar ratio of carbon to silicon is 1:1. A larger proportion of silicon powder is used to ensure that the carbon powder fully participates in the reaction without residue. Furthermore, the graphite crucible can also serve as a carbon source to react with the silicon powder, thus ensuring that the silicon powder also fully participates in the reaction without residue.
[0033] In some embodiments, the mixed acid solution includes a hydrofluoric acid solution, which accounts for 10-30% of the total volume of all substances in the mixed acid solution, and the mass percentage of hydrofluoric acid in the hydrofluoric acid solution is 40%.
[0034] Hydrofluoric acid reacts with the silica in silica sludge to form water-soluble silicon tetrafluoride, which is carried away with the water during washing, thus removing the silica from the sludge. While silicon in the silica sludge can also react with hydrofluoric acid, the reaction is slower, resulting in less silicon consumption. Furthermore, some metallic impurities in the silica sludge can also be removed by reacting with hydrofluoric acid.
[0035] In some embodiments, the mixed acid solution further comprises a nitric acid solution, which accounts for 5-20% of the total volume of all substances in the mixed acid solution, with the remainder being water; wherein the mass percentage of nitric acid in the nitric acid solution is 68%.
[0036] That is, the mixed acid solution is a mixture of hydrofluoric acid and nitric acid, with nitric acid mainly used to remove metal elements from silica sludge. Of course, in addition to hydrofluoric acid, the acid in the mixed acid solution can also be one or more selected from nitric acid, hydrochloric acid, and sulfuric acid.
[0037] In some embodiments, the silicon powder raw material obtained after acid washing and drying has a particle size of 0.5 to 1.2 micrometers. The silicon sludge waste generated from silicon wafer cutting has a very small particle size and a large specific surface area, which is conducive to reacting with carbon powder to form silicon carbide.
[0038] In some embodiments, during the solid-phase synthesis process, silicon powder raw materials and carbon powder placed in a graphite crucible are fed into a silicon carbide sintering furnace and heated to 1250–2100°C for a reaction time of 2–5 hours.
[0039] In some embodiments, during the purification step, the silicon carbide powder is purified by reacting at 600–800°C for 2–8 hours. Raising the temperature to the level at which carbon and oxygen react can remove residual carbon powder from the silicon carbide powder without wasting energy.
[0040] In some embodiments, during the drying step, the drying atmosphere is a vacuum or an inert atmosphere, the drying temperature is 60–80°C, and the drying time is 8–10 hours. Drying in a vacuum or inert atmosphere can prevent silicon oxidation or other reactions that generate new impurities.
[0041] The technical solution of this application will be further described below with reference to some specific embodiments.
[0042] Example 1
[0043] Acid washing: Add 2.5 kg of silica mud to a mixed acid solution of 10 L of nitric acid and hydrofluoric acid, wherein the volume ratio of hydrofluoric acid solution, nitric acid solution and water is 4:1:15, the mass percentage of hydrofluoric acid in the hydrofluoric acid solution is 40%, and the mass percentage of nitric acid in the nitric acid solution is 68%. Stir for 2 hours, filter, and wash with water until neutral.
[0044] Drying: The acid-washed silica mud is placed in a vacuum drying oven and dried at 80°C for 8 hours to obtain silica powder raw material.
[0045] Solid-phase synthesis: 1.225 kg of silicon powder raw material and 0.5 kg of carbon powder were mixed and stirred evenly and then placed in a graphite crucible and placed in a silicon carbide sintering furnace. The furnace body was then evacuated and heated to 1800℃ for 4 hours. After that, it was cooled to room temperature to obtain silicon carbide powder.
[0046] Purification: Place silicon carbide powder in a muffle furnace, fill it with O2 and heat it to 800°C. React for 4 hours to remove unreacted carbon powder.
[0047] Second acid washing: Add the purified silicon carbide to hydrofluoric acid solution for a second acid washing, filter, and wash with water until neutral.
[0048] Second drying: The silicon carbide powder that has been acid-washed again is dried at 80°C under vacuum to constant weight to obtain silicon carbide powder with an average particle size of 4μm, a purity of 99.99%, and a silicon carbide crystal form of 3C.
[0049] Example 2
[0050] Acid washing: Add 2.5 kg of silica mud to a mixed acid solution of 10 L of nitric acid and hydrofluoric acid, wherein the volume ratio of hydrofluoric acid solution, nitric acid solution and water is 4:1:15, the mass percentage of hydrofluoric acid in the hydrofluoric acid solution is 40%, and the mass percentage of nitric acid in the nitric acid solution is 68%. Stir for 2 hours, filter, and wash with water until neutral.
[0051] Drying: The acid-washed silica mud is placed in a vacuum drying oven and dried at 80°C for 8 hours to obtain silica powder raw material.
[0052] Solid-phase synthesis: 1.225 kg of silicon powder raw material and 0.5 kg of carbon powder were mixed and stirred evenly and then placed in a graphite crucible and placed in a silicon carbide sintering furnace. The furnace body was then evacuated and heated to 1300℃ for 4 hours. The temperature was then raised to 2100℃ for 4 hours and then cooled to room temperature to obtain silicon carbide powder.
[0053] Purification: Place silicon carbide powder in a muffle furnace, fill it with O2 and heat it to 800°C. React for 4 hours to remove unreacted carbon powder.
[0054] Second acid washing: Add the purified silicon carbide to hydrofluoric acid solution for a second acid washing, filter, and wash with water until neutral.
[0055] Second drying: The silicon carbide powder that has been acid-washed again is dried at 80°C under vacuum to constant weight to obtain silicon carbide powder with an average particle size of 50μm, a purity of 99.99%, and a silicon carbide crystal form of 4H.
[0056] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
[0057] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this application.
Claims
1. A method for preparing silicon carbide from silicon wafer cutting waste, characterized in that, Includes the following steps: Pickling: Add the waste silicon sludge generated from silicon wafer cutting to a mixed acid solution, stir, filter, and then wash with water until neutral; Drying: The acid-washed silica mud is dried to constant weight to obtain silica powder raw material; Solid-phase synthesis: Silicon powder raw material and carbon powder are stirred and mixed and then placed in a graphite crucible. The mixture is heated and reacted in a vacuum atmosphere or inert gas to obtain silicon carbide powder. Purification: Silicon carbide powder is placed in an O2 atmosphere to oxidize and remove unreacted carbon powder.
2. The method for preparing silicon carbide from silicon wafer cutting waste according to claim 1, characterized in that, It also includes a second acid washing process, in which the purified silicon carbide powder is added to a hydrofluoric acid solution for a second acid washing, and then stirred, filtered, and washed with water until neutral.
3. The method for preparing silicon carbide from silicon wafer cutting waste according to claim 2, characterized in that, It also includes drying again, drying the silicon carbide powder after the second acid washing to a constant weight, to obtain silicon carbide powder with a particle size of 2 to 5 micrometers.
4. The method for preparing silicon carbide from silicon wafer cutting waste according to claim 1, characterized in that, The mass ratio of silicon powder raw material to carbon powder is 2.45:1 to 2.57:
1.
5. The method for preparing silicon carbide from silicon wafer cutting waste according to claim 1, characterized in that, The mixed acid solution contains a hydrofluoric acid solution, which accounts for 10-30% of the total volume of all substances in the mixed acid solution, and the mass percentage of hydrofluoric acid in the hydrofluoric acid solution is 40%.
6. The method for preparing silicon carbide from silicon wafer cutting waste according to claim 5, characterized in that, The mixed acid solution also contains a nitric acid solution, which accounts for 5-20% of the total volume of all substances in the mixed acid solution, with the remainder being water; among which, the mass percentage of nitric acid in the nitric acid solution is 68%.
7. The method for preparing silicon carbide from silicon wafer cutting waste according to claim 6, characterized in that, The particle size of the silicon powder raw material obtained after acid washing and drying is 0.5 to 1.2 micrometers.
8. The method for preparing silicon carbide from silicon wafer cutting waste according to claim 1, characterized in that, During solid-phase synthesis, silicon powder and carbon powder placed in a graphite crucible are fed into a silicon carbide sintering furnace and heated to 1250–2100°C for 2–5 hours.
9. The method for preparing silicon carbide from silicon wafer cutting waste according to claim 1, characterized in that, In the purification step, silicon carbide powder is purified by reacting at 600-800℃ for 2-8 hours.
10. The method for preparing silicon carbide from silicon wafer cutting waste according to claim 1, characterized in that, During the drying process, the drying atmosphere is a vacuum or inert atmosphere, the drying temperature is 60-80℃, and the drying time is 8-10 hours.