Preparation method of high-purity layered lining material for granular silicon fluidized bed reactor

Abstract

According to the method, a high-purity carbon raw material is used for isostatic pressing to form a carbon matrix, and construction of a matrix carbon structure is completed by controlling raw material composition and pressurization degree. The carbon structure on the service side is regulated and controlled by dipping in a resin solution, so that surface pores are filled with residual carbon with high reaction activity, the later silicon-carbon reaction can be quickly and sufficiently carried out on the surface, and the reaction is terminated after the pores are completely blocked by silicon carbide generated by the reaction. After purification, a SiC layer with the content of aluminum, iron and boron being smaller than 100 ppm, the total content of other microelements being smaller than 50 ppm and the thickness being larger than 30 micrometers is finally formed on the service side, and a C / Si / SiC layer with the thickness being larger than 400 micrometers is generated in the middle. According to the layered material prepared through the method, the carbon matrix and the silicon carbide are connected very tightly and are difficult to fall off during service, the external carbon material can be directly used as a heating element, and energy conservation and environmental protection are achieved. Integrated forming is adopted, later splicing is not needed, the preparation process is simple and efficient, cost is low, and the method is suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention belongs to the field of fluidized bed reactor linings, and in particular relates to a method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor. Background Art

[0002] Polysilicon is the most important and basic functional material for the semiconductor industry, electronic information industry, and solar photovoltaic cell industry. The existing processes for producing polysilicon mainly include the Siemens process and the fluidized bed process. The fluidized bed process is the future development direction of granular silicon materials for photovoltaic and semiconductor industries because of its advantages such as continuous production and low energy loss.

[0003] As the core component of the reactor, the fluidized bed lining needs to withstand the erosion of silane, hydrogen, and silicon particles under high temperature conditions, requiring the material to have high purity, wear resistance, and high strength. In addition, most fluidized bed reactors use external heating to provide heat, that is, heating through the lining and / or reactor isolation layer, which requires the material to have high thermal conductivity.

[0004] The main materials for fluidized bed linings are quartz, silicon, graphite, and silicon carbide ceramic materials. Quartz materials have low strength and poor wear resistance, and are prone to peeling and pollution during service, so they are not widely used. Silicon linings do not have pollution problems, but they are difficult to make and there are no reports of successful applications. Existing research mainly focuses on graphite and silicon carbide materials.

[0005] On the service side that is in direct contact with the material, silicon carbide materials with higher strength and better wear resistance have great advantages. For example, the high-purity silicon carbide linings prepared in patents CN 115532178 A, CN116440813A, CN 116440813 A, etc. all use silicon carbide as the main material, that is, silicon carbide is generated on the surface of the material by silicon infiltration and sintering. However, silicon carbide materials cannot be used as heating elements. Selecting this material as the lining means that a heating device must be set up externally to heat by thermal radiation or heat conduction. These two heating methods usually cause a large energy loss to the system and easily cause the temperature of the reactor to be greater than the temperature of the material inside the reactor, which in turn causes polysilicon to deposit on the inner wall of the reactor, hindering the transfer of heat to the inside of the fluidized bed. In severe cases, the furnace needs to be shut down for maintenance. Therefore, on the heating side of the lining, graphite materials with high electrical conductivity, high thermal conductivity, and uniform heat transfer are more advantageous. When it is selected as the material of the heating side of the lining, it can be directly used as a heating element.

[0006] The service environment of fluidized bed granular silicon is relatively harsh, requiring a strong connection between the service side and the heating side materials; Patent CN108138992A uses a method of depositing a high-purity silicon carbide coating on the surface of isostatically pressed graphite to prepare the reactor lining. The connection between the coating deposited on the surface and the graphite body is weak, and the coating is easy to fall off during service, which leads to the release of internal graphite and reduces the quality of granular silicon; Patent CN106458608A uses CVD to prepare silicon carbide coating. This method has the advantage of high purity, but the CVD process grows the coating slowly, the preparation cost is high, and there is also a risk of falling off during service.

[0007] In general, silicon carbide and graphite each have their own advantages in serving as the lining and heating side of the granular silicon fluidized bed, and the tightness of the connection between the two will directly affect the service life of the material. Summary of the invention

[0008] In order to solve the technical problems existing in the prior art, the purpose of the present invention is to provide a method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor.

[0009] The present invention adopts the following technical solutions to achieve the above-mentioned purpose: A method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor, the specific steps of the preparation method are as follows: S1, mixing the carbon raw materials and pre-pressing them into blocks in a mold, then crushing and sieving the blocks to prepare carbon material powder for use; S2, introducing the carbon material powder prepared in S1 into an isostatic pressing mold, and isostatic pressing to obtain a hollow cylindrical carbon matrix; S3, impregnating the carbon matrix prepared in S2 with an organic resin solution to regulate the carbon structure on the service side so that the surface pores are filled with residual carbon with high reactivity; then curing and debinding; the carbon matrix is ​​directly used as a heating element on the heating side; S4, placing the green body prepared in S3 in a graphite crucible, stacking high-purity silicon powder inside the green body, and performing silicon infiltration sintering under vacuum conditions, so that the silicon-carbon reaction occurs quickly and fully on the surface. When the silicon carbide generated by the reaction completely blocks the pores, the reaction is terminated; the content of aluminum, iron, and boron in the silicon carbide generated on the service side is less than 200ppm, and other trace elements are less than 100ppm; then cooling to obtain a sintered body; S5. Place the sintered body obtained in step S4 in a purification furnace for purification treatment; after purification, a SiC layer with aluminum, iron, and boron contents less than 100 ppm, the sum of other trace elements less than 50 ppm, and a normal temperature wear coefficient μ less than 0.4 is finally formed on the service side, and a C / Si / SiC layer with a thickness of more than 400 microns is generated in the middle.

[0010] The raw materials in S1 include 35-60wt% artificial graphite powder, 10-35wt% carbon black powder, 8-25wt% coke powder, and 2-10wt% asphalt. The total impurity content of each raw material is less than 2000ppm.

[0011] S2 is sealed, vacuumed, pressurized, pressure maintained, pressure released, and demoulding, wherein the pressure value during the pressurization process is 30-200MPa, and the pressure maintenance time is 5-150min.

[0012] In the S2 isostatic die, an insulating layer is attached to the outside of the inner steel core. The insulating material is one of plastic, paper, and wood to prevent the blank from directly contacting the steel core.

[0013] The organic resin solution in S3 refers to a solution obtained by dissolving one or more of phenolic resin, epoxy resin or furan resin in an organic solvent; later, the surface-improved green body is obtained by heat preservation at 780-900°C for 1-5h under nitrogen or carbon-buried atmosphere.

[0014] The total impurity content of silicon powder used in S4 is less than 200ppm, of which the Fe content is less than 50ppm and the Al content is less than 50ppm.

[0015] The silicon powder used in S4 is surface treated in the following manner: simple silicon particles, carbon black and Si3N4 powder are added and stirred evenly in a weight ratio of 94.5-98.5:1-5:0.1-0.5, and then an organic binder solution is added and stirred to make the carbon black and Si3N4 powder evenly adhere to the surface of the simple silicon particles, and then dried to obtain surface-treated simple silicon particles.

[0016] The organic binder solution may be selected from commonly used polyvinyl alcohol, polyvinyl butyral, hydroxymethyl cellulose, dextrin solution, etc., of appropriate concentration.

[0017] The amount of organic binder solution added is 0.5-1.5% of the total mass of elemental silicon particles, carbon black and Si3N4 powder.

[0018] In S4, silicon nitride combined with silicon carbide or recrystallized silicon carbide refractory products are used as auxiliary tooling during the sintering of the green body. They are placed at the upper and lower openings of the hollow cylindrical green body to form a closed space, and silicon particles with a coating layer on the surface are placed on the upper surface of the refractory product at the lower opening.

[0019] The vacuum siliconizing sintering process in S4 is: low temperature 0-1200°C, heating rate 4-12°C / min; high temperature 1200-1700°C, hold 0-1 hour, heating rate 5-10°C / min.

[0020] The purified atmosphere in S5 is at least one of chlorine, hydrogen chloride, fluorine, and difluorochloromethane.

[0021] The purification temperature in S5 is 700-1300 °C, and the temperature is kept for 1-5 h.

[0022] The present invention proposes a method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor, wherein high-purity carbon is selected as a matrix material, which reacts with silicon on a service side to generate silicon carbide. Since silicon carbide is generated in situ, the connection between the carbon matrix and silicon carbide is very tight and is difficult to fall off during service. On the heating side, the carbon material used in the present invention can be directly used as a heating element.

[0023] After purification, the content of aluminum, iron and boron is less than 100ppm, the sum of other trace elements is less than 50ppm, the wear coefficient at room temperature is μ<0.4, and the thickness is greater than 30 microns.

[0024] The invention adopts integrated molding, does not need later splicing, has a simple and efficient preparation process, is low in cost, and is suitable for large-scale industrial production.

[0025] Compared with the prior art, the present invention uses high-purity carbon raw materials to isostatically press the carbon matrix, and the construction of the matrix carbon structure can be completed by controlling the raw material composition and the degree of pressurization. By impregnating the resin solution, the carbon structure of the service side can be regulated so that the surface pores are filled with highly reactive residual carbon, so that the later silicon-carbon reaction can occur quickly and fully on the surface. When the silicon carbide generated by the reaction completely blocks the pores, the reaction terminates; after purification, a SiC layer with a content of aluminum, iron, and boron less than 100ppm, a total of other trace elements less than 50ppm, and a normal temperature wear coefficient μ less than 0.4 is finally formed on the service side, and a C / Si / SiC layer with a thickness of more than 400 microns is generated in the middle. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the SEM image of the service side; Figure 2 for Figure 1 SEM magnified image of area Ⅰ in the middle. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with the embodiments. It should be understood that the following embodiments are only used to illustrate the present invention rather than to limit the present invention.

[0028] Example 1: A method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor, the process comprising: S1, prepare 80wt% artificial graphite powder, 20wt% carbon black powder, 22wt% coke powder, and 8wt% asphalt, and the total impurity content of each raw material is less than 2000ppm; mix the carbon raw materials and pre-press them into blocks in a mold, then crush and sieve the blocks to prepare carbon material powder; S2, introducing the carbon material powder prepared in S1 into an isostatic pressing mold, and performing sealing, vacuuming, pressurizing, holding pressure, releasing pressure, and demolding, and isostatic pressing to obtain a hollow cylindrical carbon matrix; wherein the pressure value during the pressurizing process is 60 MPa, and the holding time is 30 min; a layer of paper is attached to the outside of the inner steel core as an isolation layer to prevent the blank from directly contacting the steel core; S3, using epoxy resin and furan resin in a mass ratio of 1:1 to dissolve in ethylene glycol to prepare an organic solution, impregnating the carbon matrix prepared in S2, and then heat-preserving at 850° C. for 3 h in a carbon-buried atmosphere to obtain a green body with improved surface; S4, placing the green body prepared in S3 in a graphite crucible, stacking high-purity silicon powder inside the green body, performing siliconization sintering under vacuum conditions, and cooling to obtain a sintered body; wherein the total impurity content of the silicon powder used is 42ppm, wherein the Fe content is 2ppm, and the Al content is 5ppm; adding single-substance silicon particles, carbon black and Si3N4 powder according to a weight ratio of 95:4.8:0.2, stirring evenly, and then adding organic binder solution polyvinyl alcohol (PVA), stirring so that the carbon black and Si3N4 powder are evenly attached to the surface of the single-substance silicon particles, and then drying, Obtaining the single-substance silicon particles after surface treatment; the mass of polyvinyl alcohol (PVA) is 1% of the total mass of the single-substance silicon particles, carbon black and Si3N4 powder; using silicon nitride combined with silicon carbide as auxiliary tooling during green body sintering, placing it at the upper and lower openings of the hollow cylindrical green body to form a closed space, and placing silicon particles with a coating layer on the surface on the upper surface of the refractory product at the lower opening; the vacuum siliconizing sintering process is: low temperature 0-1200℃, heating rate 8℃ / min; high temperature 1200-1700℃, maintained for 1 hour, heating rate 6℃ / min; S5, placing the sintered body obtained in step S4 in a purification furnace for purification treatment. The purification atmosphere is chlorine gas. The purification temperature is 1000° C. and the temperature is maintained for 3 hours.

[0029] The GDMS test data of silicon carbide on the service side of the purified product are as follows (unit: ppm): Normal temperature wear coefficient μ=0.335.

[0030] Example 2 A high-purity layered lining material for a granular silicon fluidized bed reactor and a preparation method thereof, the process is as follows: S1, prepare 40wt% artificial graphite powder, 30wt% carbon black powder, 25wt% coke powder, 5wt% asphalt, and the total impurity content of each raw material is less than 2000ppm; mix the carbon raw materials and pre-press them into blocks in a mold, then crush and sieve the blocks to prepare carbon material micro-particles; S2, introducing the carbon material powder prepared in S1 into an isostatic pressing mold, and performing sealing, vacuuming, pressurizing, holding pressure, releasing pressure, and demolding, and isostatic pressing to obtain a hollow cylindrical carbon matrix; wherein the pressure value during the pressurizing process is 85 MPa, and the holding time is 120 min; a layer of plastic is attached to the outside of the inner steel core as an isolation layer to prevent the blank from directly contacting the steel core; S3, using phenolic resin dissolved in ethylene glycol to prepare an organic solution, impregnating the carbon matrix prepared in S2, and then keeping it at 780° C. for 5 hours in a carbon-buried atmosphere to obtain a green body with improved surface; S4, placing the green body prepared in S3 in a graphite crucible, piling high-purity silicon powder inside the green body, performing silicon infiltration sintering under vacuum conditions, and cooling to obtain a sintered body; wherein the total impurity content of the silicon powder used is 143 ppm, of which the Fe content is 25 ppm and the Al content is 45 ppm. According to the weight ratio of 97:2.8:0.2, silicon particles, carbon black and Si3N4 powder are added and stirred evenly, and then hydroxymethyl cellulose (CMC) is added and stirred to make carbon black and Si3N4 powder evenly adhere to the surface of silicon particles, and then dried to obtain silicon particles after surface treatment; the mass of hydroxymethyl cellulose (CMC) is 0.8% of the total mass of silicon particles, carbon black and Si3N4 powder; recrystallized silicon carbide is used as an auxiliary tool for sintering the blank, and it is placed at the upper and lower openings of the hollow cylindrical blank to form a closed space, and silicon particles with a coating layer on the surface are placed on the upper surface of the refractory product at the lower opening; the vacuum silicon infiltration sintering process is: low temperature 0-1200℃, heating rate 12℃ / min; high temperature 1200-1700℃, maintained for 1 hour, heating rate 5℃ / min; S5, placing the sintered body obtained in step S4 in a purification furnace for purification treatment, the purification atmosphere is hydrogen chloride, the purification temperature is 700° C., and the temperature is kept for 5 hours.

[0031] The GDMS test data of silicon carbide on the service side of the purified product are as follows (unit: ppm): Normal temperature wear coefficient μ=0.347.

[0032] Example 3. A high-purity layered lining material for a granular silicon fluidized bed reactor and a preparation method thereof, the process being: S1, prepare 35wt% artificial graphite powder, 35wt% carbon black powder, 20wt% coke powder, and 10wt% asphalt, and the total impurity content of each raw material is less than 2000ppm; mix the carbon raw materials and pre-press them into blocks in a mold, then crush and sieve the blocks to prepare carbon material powder; S2, introducing the carbon material powder prepared in S1 into an isostatic pressing mold, and subjecting the mold to sealing, vacuuming, pressurizing, holding pressure, releasing pressure, and demolding, isostatic pressing is performed to obtain a hollow cylindrical carbon matrix; wherein the pressure value during the pressurizing process is 200 MPa, and the holding time is 5 min; a layer of paper is attached to the outside of the inner steel core as an isolation layer to prevent the blank from directly contacting the steel core; S3, using phenolic formaldehyde and furan resin in a mass ratio of 1:1 to dissolve in ethanol to prepare an organic solution, impregnating the carbon substrate prepared in S2, and then heating at 900° C. for 4 h in a nitrogen atmosphere to obtain a green body with improved surface; S4, placing the green body prepared in S3 in a graphite crucible, stacking high-purity silicon powder inside the green body, performing silicon infiltration sintering under vacuum conditions, and cooling to obtain a sintered body; wherein the total impurity content of the silicon powder used is 25ppm, wherein the Fe content is 17ppm, and the Al content is 2ppm; adding silicon particles, carbon black and Si3N4 powder in a weight ratio of 98.5:1:0.5, stirring evenly, and then adding an organic binder solution polyvinyl butyral (PVB), stirring to make the carbon black and Si3N4 powder evenly adhere to the surface of the silicon particles, and then drying to obtain surface-treated silicon particles. The mass of polyvinyl butyral (PVB) is 0.5% of the total mass of elemental silicon particles, carbon black and Si3N4 powder; silicon nitride combined with silicon carbide is used as auxiliary tooling during the sintering of the blank, which is placed at the upper and lower openings of the hollow cylindrical blank to form a closed space, and silicon particles with a coating layer on the surface are placed on the upper surface of the refractory product at the lower opening; the vacuum siliconization sintering process is: low temperature 0-1200℃, heating rate 4℃ / min; high temperature 1200-1700℃, maintained for 1 hour, heating rate 5℃ / min; S5, placing the sintered body obtained in step S4 in a purification furnace for purification treatment. The purification atmosphere is fluorine gas. The purification temperature is 1000° C. and the temperature is maintained for 3 hours.

[0033] The GDMS test data of silicon carbide on the service side of the purified product are as follows (unit: ppm): Normal temperature wear coefficient μ=0.305.

Claims

1. A method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor, the specific steps of the preparation method are as follows: S1, mixing the carbon raw materials and pre-pressing them into blocks in a mold, then crushing and sieving the blocks to prepare carbon material powder for use; S2, introducing the carbon material powder prepared in S1 into an isostatic pressing mold, and isostatic pressing to obtain a hollow cylindrical carbon matrix; S3, impregnating the carbon matrix prepared in S2 with an organic resin solution to regulate the carbon structure on the service side so that the surface pores are filled with residual carbon with high reactivity; then curing and debinding; the carbon matrix is ​​directly used as a heating element on the heating side; S4, placing the green body prepared in S3 in a graphite crucible, stacking high-purity silicon powder inside the green body, and performing silicon infiltration sintering under vacuum conditions, so that the silicon-carbon reaction occurs quickly and fully on the surface. When the silicon carbide generated by the reaction completely blocks the pores, the reaction is terminated; the content of aluminum, iron, and boron in the silicon carbide generated on the service side is less than 200ppm, and other trace elements are less than 100ppm; then cooling to obtain a sintered body; S5. Place the sintered body obtained in step S4 in a purification furnace for purification treatment; after purification, a SiC layer with aluminum, iron, and boron contents less than 100 ppm, the sum of other trace elements less than 50 ppm, and a normal temperature wear coefficient μ less than 0.4 is finally formed on the service side, and a C / Si / SiC layer with a thickness of more than 400 microns is generated in the middle.

2. The method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor according to claim 1, characterized in that: The raw materials in step S1 include 35-60wt% artificial graphite powder, 10-35wt% carbon black powder, 8-25wt% coke powder, and 2-10wt% asphalt, and the total impurity content of each raw material is less than 2000ppm.

3. The method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor according to claim 1, characterized in that: The isostatic pressing in step S2 includes sealing, vacuuming, pressurizing, holding pressure, releasing pressure, and demolding, wherein the pressure value in the pressurizing process is 30-200 MPa, and the holding pressure time is 5-150 min; an isolation layer is attached to the outside of the inner steel core, and the isolation material is one of plastic, paper, and wood to prevent the blank from direct contact with the steel core.

4. The method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor according to claim 1, characterized in that: The organic resin solution in step S3 refers to a solution obtained by dissolving one or more of phenolic resin, epoxy resin or furan resin in an organic solvent; and the surface-improved green body is obtained by heat preservation at 780-900° C. for 1-5 hours under nitrogen or carbon-buried atmosphere.

5. The method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor according to claim 1, characterized in that: The total impurity content of silicon powder used in step S4 is less than 200ppm, wherein the Fe content is less than 50ppm, and the Al content is less than 50ppm; according to the weight ratio of (94.5-98.5):(1-5):(0.1-0.5), simple silicon particles, carbon black and Si3N4 powder are added and stirred evenly, and then the organic binder solution is added and stirred to make the carbon black and Si3N4 powder evenly adhere to the simple silicon particles, and then dried to obtain the surface-treated simple silicon particles.

6. The method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor according to claim 5, characterized in that: The organic binder solution is a solution of polyvinyl alcohol, polyvinyl butyral, hydroxymethyl cellulose, or dextrin at an appropriate concentration; The mass of the organic binder solution is 0.5-1.5% of the total mass of the elemental silicon particles, carbon black and Si3N4 powder.

7. The method for preparing a high-purity layered lining material for a granular silicon fluidized bed reactor according to claim 1, characterized in that: In S4, silicon nitride combined with silicon carbide or recrystallized silicon carbide refractory products are used as auxiliary tooling during the sintering of the blank, which are placed at the upper and lower openings of the hollow cylindrical blank to form a closed space, and silicon particles with a coating layer on the surface are placed on the upper surface of the refractory product at the lower opening; the vacuum silicon infiltration sintering process is: low temperature 0-1200°C, heating rate 4-12°C / min; high temperature 1200-1700°C, maintained for 0-1 hour, heating rate 5-10°C / min.

8. The high-purity layered lining material for a granular silicon fluidized bed reactor and the preparation method thereof according to claim 1, characterized in that: The vacuum siliconizing sintering process in step S4 is: low temperature 0-1200° C., heating rate 4-12° C. / min; high temperature 1200-1700° C., hold for 0-1 hour, heating rate 5-10° C. / min.

9. The high-purity layered lining material for a granular silicon fluidized bed reactor and the preparation method thereof according to claim 1, characterized in that: In step S5, the purification atmosphere is at least one of chlorine, hydrogen chloride, fluorine, and difluorochloromethane; the purification temperature is 700-1300° C., and the temperature is kept for 1-5 hours.

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