CN116902986B - Method for purifying silicon material by utilizing dual actions of magnetic separation and spin-type directional solidification - Google Patents
Method for purifying silicon material by utilizing dual actions of magnetic separation and spin-type directional solidification Download PDFInfo
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- 239000002210 silicon-based material Substances 0.000 title claims abstract description 76
- 238000007711 solidification Methods 0.000 title claims abstract description 46
- 230000008023 solidification Effects 0.000 title claims abstract description 46
- 238000000034 method Methods 0.000 title claims abstract description 30
- 238000007885 magnetic separation Methods 0.000 title claims abstract description 20
- 230000009977 dual effect Effects 0.000 title claims abstract description 15
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 59
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 57
- 239000010703 silicon Substances 0.000 claims abstract description 57
- 239000012535 impurity Substances 0.000 claims abstract description 40
- 239000002184 metal Substances 0.000 claims abstract description 31
- 238000001816 cooling Methods 0.000 claims abstract description 13
- 239000012141 concentrate Substances 0.000 claims abstract description 6
- 229910021419 crystalline silicon Inorganic materials 0.000 claims abstract description 6
- 238000005266 casting Methods 0.000 claims description 47
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 26
- 239000000112 cooling gas Substances 0.000 claims description 14
- 229910052786 argon Inorganic materials 0.000 claims description 13
- 238000010438 heat treatment Methods 0.000 claims description 13
- 230000006698 induction Effects 0.000 claims description 8
- 238000004321 preservation Methods 0.000 claims description 3
- 238000012544 monitoring process Methods 0.000 claims description 2
- 238000000746 purification Methods 0.000 abstract description 26
- 239000007788 liquid Substances 0.000 abstract description 14
- 230000000694 effects Effects 0.000 abstract description 9
- 230000005684 electric field Effects 0.000 abstract description 7
- 238000005204 segregation Methods 0.000 abstract description 7
- 238000000926 separation method Methods 0.000 abstract description 7
- 239000013078 crystal Substances 0.000 abstract description 6
- 239000000463 material Substances 0.000 abstract description 4
- 238000002844 melting Methods 0.000 abstract description 3
- 230000008018 melting Effects 0.000 abstract description 3
- 230000000052 comparative effect Effects 0.000 description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 5
- 238000004140 cleaning Methods 0.000 description 5
- 229910002804 graphite Inorganic materials 0.000 description 5
- 239000010439 graphite Substances 0.000 description 5
- 239000000155 melt Substances 0.000 description 5
- 238000009413 insulation Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- 239000011863 silicon-based powder Substances 0.000 description 2
- 229910021422 solar-grade silicon Inorganic materials 0.000 description 2
- 238000013019 agitation Methods 0.000 description 1
- 239000013590 bulk material Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C1/00—Magnetic separation
- B03C1/02—Magnetic separation acting directly on the substance being separated
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/037—Purification
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B28/00—Production of homogeneous polycrystalline material with defined structure
- C30B28/04—Production of homogeneous polycrystalline material with defined structure from liquids
- C30B28/06—Production of homogeneous polycrystalline material with defined structure from liquids by normal freezing or freezing under temperature gradient
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/02—Elements
- C30B29/06—Silicon
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Crystallography & Structural Chemistry (AREA)
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Abstract
The invention provides a method for purifying a silicon material by utilizing the dual actions of magnetic separation and rotary directional solidification, which comprises the steps of melting the silicon material, effectively improving the fluidity of the melted material by utilizing a furnace body rotating motor, and then utilizing the magnetic directional separation action of charged metal impurities under a high-strength externally-applied longitudinal directional magnetic field and the directional solidification action of precise heat balance control to directionally migrate and concentrate the metal impurities on the upper surface and the lower surface in the rotary flowing liquid silicon material; and then the purification is completed by precisely cooling gradient control and directional solidification of a thermal balance management system and removing the head and the tail of the silicon ingot so as to obtain the solar-energy-level high-purity crystalline silicon. The invention can not only effectively separate the impurities with small segregation coefficient, but also separate the impurities with larger segregation coefficient; compared with the electric field, the magnetic field applied by the invention is not limited by the conductivity, and has good penetrability, better separation effect, higher efficiency and good safety. The purity of the crystal silicon obtained by purification can reach 6N level, and the crystal silicon is obviously superior to the traditional purification effect.
Description
Technical Field
The invention belongs to the technical field of chemical industry, and particularly relates to a method for purifying a silicon material by utilizing the dual actions of magnetic separation and spin-type directional solidification.
Background
With the rapid development of the photovoltaic industry, the demand of solar-grade silicon materials is rapidly increased, so that the price of the silicon materials is rapidly raised; on the other hand, the photoelectric conversion rate of the solar cell is higher and higher, and the downstream manufacturer also puts more severe demands on the purity of the silicon material. To address the above-described challenges, the industry has focused on waste materials generated during the manufacturing process. According to statistics, silicon powder generated in the silicon wafer production process accounts for about 30% of all silicon materials, if the silicon powder can be recovered and purified for production, the silicon resource can be saved definitely, and the environmental protection pressure can be reduced greatly.
In the prior art, various silicon material purification methods are developed successively, such as a directional solidification purification method, such as schemes described in patent applications CN2018107958005 and CN202210568885X, an electric field directional solidification purification method, such as schemes described in patent applications CN2009100519224 and CN2010101484259, and multi-stage wet purification and the like. However, the above method has some disadvantages:
1) The directional solidification purification method is limited by the difficulty in precisely controlling the temperature gradient in the solidification process of the silicon material, and the segregation coefficient of some metal impurities is smaller, so that the purification uniformity is greatly limited; 2) Though the impurities can be further removed by an external electric field and an electric field directional solidification purification method, the electric field driving separation is long under the condition of low metal impurity content due to a non-good conductor of the silicon material in the casting furnace, and a certain safety risk exists; 3) The purification effect of the multistage wet purification process is difficult to meet the requirements of solar-grade silicon materials.
Subsequent researchers have proposed patent applications such as CN2016110269121, CN2012105268012 that use an externally applied magnetic field to adjust the solid-liquid interface or that use magnetic field agitation to promote crystallization. However, in these schemes, since the silicon material is a non-ionized material, and the high viscosity characteristics of the molten silicon material and the medium-low strength magnetic field used, the bulk material lacks an effective response to the magnetic field, and the cooling crystallization process is not precisely controlled, so that it is difficult to obtain a remarkable effect.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a method for purifying a silicon material by utilizing the dual actions of magnetic separation and spin-on directional solidification. The technical problems to be solved by the invention are realized by the following technical scheme:
The invention provides a method for purifying a silicon material by utilizing the dual actions of magnetic separation and spin-type directional solidification, which comprises the following steps:
S100, selecting a silicon material to be purified, and adding the silicon material to be purified into a high-temperature vacuum casting furnace provided with a furnace body rotating motor, a cooling gas conduit and a thermal balance management system;
s200, purifying a high-temperature vacuum casting furnace, heating the high-temperature vacuum casting furnace until silicon materials to be purified are melted, and keeping the temperature in the high-temperature vacuum casting furnace constant through a thermal balance management system;
S300, starting a furnace body rotating motor to enable the melted silicon material to be purified to be kept in a flowing state, and applying a longitudinal directional magnetic field to a high-temperature vacuum casting furnace to enable metal impurities in the melted silicon material to be purified to directionally migrate and concentrate on the surface under the action of magnetic separation;
S400, opening a bottom heat-insulating layer of the high-temperature vacuum casting furnace, introducing cooling gas into the high-temperature vacuum casting furnace, and utilizing a thermal balance management system to monitor and control the temperature of the high-temperature vacuum casting furnace in real time, so that the furnace body is directionally solidified from the bottom to the whole to obtain a silicon ingot;
S500, rapidly cooling the silicon ingot, taking out the silicon ingot from the high-temperature vacuum casting furnace, and finishing the cooled silicon ingot to remove the head and the tail to obtain high-purity crystalline silicon.
The invention provides a method for purifying silicon material by utilizing the dual actions of magnetic separation and rotary directional solidification, which comprises the steps of melting the silicon material by adopting a casting process, effectively improving the fluidity of the melted material by utilizing a furnace body rotating motor, and then utilizing the magnetic directional separation action of charged metal impurities under a high-strength externally-applied longitudinal directional magnetic field and the directional solidification action of precise heat balance control to lead the metal impurities to directionally migrate in the rotationally-flowing liquid silicon material and concentrate on the upper surface and the lower surface; and then the purification is completed by precisely cooling gradient control and directional solidification of a thermal balance management system and removing the head and the tail of the silicon ingot so as to obtain the solar-energy-level high-purity crystalline silicon. The invention can not only effectively separate the impurities with small segregation coefficient, but also separate the impurities with larger segregation coefficient; the magnetic field applied in the process has better penetrability than the electric field, is not limited by the conductivity, and has better separation effect, higher efficiency and good safety. The purity of the crystal silicon obtained by purification can reach 6N level, and the crystal silicon is obviously superior to the traditional multi-level wet purification effect.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Drawings
FIG. 1 is a schematic flow chart of a method for purifying a silicon material by using dual actions of magnetic separation and spin-on directional solidification;
FIG. 2 is a schematic diagram of the dual effects of magnetic separation and spin-directional solidification provided by the invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but embodiments of the present invention are not limited thereto.
With reference to fig. 1 and 2, the present invention provides a method for purifying a silicon material by using dual actions of magnetic separation and spin-on directional solidification, comprising:
S100, selecting a silicon material to be purified, and adding the silicon material to be purified into a high-temperature vacuum casting furnace provided with a furnace body rotating motor, a cooling gas conduit and a thermal balance management system;
The heat balance management system is used for monitoring the temperatures of different parts of the furnace bottom, the furnace body and the furnace top in real time, and timely and automatically adjusting the heating power of the heater, the opening size of the heat preservation layer, the flow of cooling gas and the rotating speed of the rotating motor of the furnace body according to the temperature changes of the different parts in the furnace; and is also used for precisely controlling the cooling rate within the interval of 1.5-2.0 ℃/min.
S200, purifying a high-temperature vacuum casting furnace, heating the high-temperature vacuum casting furnace until silicon materials to be purified are melted, and keeping the temperature in the high-temperature vacuum casting furnace constant through a thermal balance management system;
the method comprises the following steps:
s210, vacuumizing a high-temperature vacuum casting furnace, and introducing argon;
s220, repeating the step S210 for a plurality of times until the high-temperature vacuum casting furnace is kept in a high-purity argon state, wherein the high-purity argon state is that the purity of the argon is more than 99.999%;
And S230, heating the high-temperature vacuum casting furnace by a heater until the silicon material to be purified is melted, and keeping the temperature in the high-temperature vacuum casting furnace constant by a thermal balance management system.
Wherein the heating range of the heater is 1550-1600 ℃.
S300, starting a furnace body rotating motor to enable the melted silicon material to be purified to be kept in a flowing state, and applying a longitudinal directional magnetic field to a high-temperature vacuum casting furnace to enable metal impurities in the melted silicon material to be purified to directionally migrate and concentrate on the surface under the action of magnetic separation;
wherein the applied longitudinally oriented magnetic field is a continuous magnetic field or a pulsed magnetic field.
The S300 of the present invention includes:
S310, starting a furnace body rotating motor, and enabling the rotating speed to be 30-50 revolutions per minute so as to enable the melted silicon material to be purified to keep a flowing state;
s320, controlling the high-temperature vacuum casting furnace to preserve heat through a heat balance management system, and applying a longitudinal directional magnetic field to the high-temperature vacuum casting furnace for 1-3 hours, wherein the magnetic induction intensity is 6000-10000 Gs, so that metal impurities in the melted silicon material to be purified directionally migrate and are enriched on the surface under the action of magnetic separation.
S400, opening a bottom heat-insulating layer of the high-temperature vacuum casting furnace, introducing cooling gas into the high-temperature vacuum casting furnace, and utilizing a thermal balance management system to monitor and control the temperature of the high-temperature vacuum casting furnace in real time, so that the furnace body is directionally solidified from the bottom to the whole to obtain a silicon ingot;
The S400 of the present invention includes:
s410, opening a bottom heat-insulating layer of the high-temperature vacuum casting furnace, and introducing cooling gas into the high-temperature vacuum casting furnace to directionally start solidification of silicon materials in the furnace body from the bottom to the top;
S420, controlling the temperature of the furnace body by using a thermal balance management system, so that the solidification speed is 2-5 mm/h until all the silicon materials in the furnace body are solidified to obtain silicon ingots.
S500, rapidly cooling the silicon ingot, taking out the silicon ingot from the high-temperature vacuum casting furnace, and finishing the cooled silicon ingot to remove the head and the tail to obtain high-purity crystalline silicon.
The purification process and purification accuracy of the present invention are described below by way of example.
Example 1:
260kg of 4N purity silicon material is added into a graphite crucible, and the furnace body is closed; and then vacuumizing the whole system, filling high-purity argon into the whole system, and cleaning for many times, wherein the vacuum degree is kept below 5 Pa. After the heater heats and melts the silicon material, a rotating motor is started, and the rotating speed is 40 revolutions per minute; applying a longitudinal directional magnetic field from top to bottom, wherein the magnetic induction intensity is 6000Gs; and the furnace lining heat insulation layer and the heater are used for preserving heat for 3 hours, the temperature of the heater is controlled at 1550 ℃, and the temperature of each part of the furnace body is monitored in real time by utilizing a heat balance management system, so that the silicon material is ensured to be in a molten state.
The heat-insulating layer at the bottom of the furnace body is opened, the temperature of the furnace bottom, the furnace body and the furnace top are monitored in real time by utilizing a heat balance management system, the heating power of a heater, the opening size of the heat-insulating layer, the flow rate of cooling gas and the rotating speed of a rotating motor are timely and automatically adjusted according to the temperature change of the different parts in the furnace, the cooling rate of a silicon material is controlled to be in the range of 1.5-2.0 ℃/min, so that the silicon liquid is directionally solidified from the bottom, gradually upwards until the silicon liquid is completely solidified, and the average solidification speed is controlled to be about 2mm/h. The external magnetic field is kept on in the directional solidification process, and the magnetic field is turned off after the whole solidification. And removing the head and the tail of the silicon ingot after the silicon ingot is discharged from the furnace, wherein the total content of metal impurities detected by the obtained silicon ingot is 0.048ppmWt. The total content of the metal impurities of the removed head and tail scraps is 12.438ppmWt and 11.230ppmWt respectively.
Example 2:
260kg of 4N purity silicon material is added into a graphite crucible, and the furnace body is closed; and then vacuumizing the whole system, filling high-purity argon into the whole system, and cleaning for many times, wherein the vacuum degree is kept below 5 Pa. After the heater heats and melts the silicon material, a rotating motor is started, and the rotating speed is 30 revolutions per minute; applying a longitudinal directional magnetic field from top to bottom, wherein the magnetic induction intensity is 10000Gs; and the furnace lining heat insulation layer and the heater are used for preserving heat for 1 hour, the temperature of the heater is controlled at 1550 ℃, and the temperature of each part of the furnace body is monitored in real time by utilizing a heat balance management system, so that the silicon material is ensured to be in a molten state.
The heat-insulating layer at the bottom of the furnace body is opened, the temperature of the furnace bottom, the furnace body and the furnace top are monitored in real time by utilizing a heat balance management system, the heating power of a heater, the opening size of the heat-insulating layer, the flow rate of cooling gas and the rotating speed of a rotating motor are timely and automatically adjusted according to the temperature change of the different parts in the furnace, the cooling rate of a silicon material is controlled to be in a range of 1.5-2.0 ℃/min, so that the silicon liquid is directionally solidified from the bottom, gradually upwards until the silicon liquid is completely solidified, and the average solidification speed is controlled to be about 4mm/h. The external magnetic field is kept on in the directional solidification process, and the magnetic field is turned off after the whole solidification. And removing the head and the tail of the silicon ingot after the silicon ingot is discharged from the furnace, wherein the total content of metal impurities of the obtained silicon ingot is 0.066ppmWt. The total content of the metal impurities of the removed head and tail scraps is 11.402ppmWt and 11.038ppmWt respectively.
Example 3:
Other conditions were the same as in example 1, the vacuum degree of the casting system was 3Pa or less, and the silicon material was heated and melted; the temperature of the heater is controlled at 1600 ℃, the motor rotation speed is 50 revolutions per minute, the heat preservation control time is 1 hour, the external magnetic field is a pulse magnetic field, the impact interval time is 30s, and the magnetic induction intensity is 10000Gs; the solidification speed was controlled during directional solidification to be about 5mm/h on average. And removing the head and the tail of the silicon ingot after discharging, wherein the total content of the detected metal impurities of the obtained silicon ingot is 0.042ppmWt. The total content of the metal impurities of the removed head and tail scraps is 10.565ppmWt and 10.358ppmWt respectively.
The purification effect of the present invention will be described below by comparing purification schemes in the prior art.
Comparative example 1: no directional external magnetic field is applied in the purification process
260Kg of 4N purity silicon material is added into a graphite crucible, and the furnace body is closed; and then vacuumizing the whole system, filling high-purity argon into the whole system, and cleaning for many times, wherein the vacuum degree is kept below 5 Pa. After the heater heats and melts the silicon material, the rotating motor is started, the rotating speed is 40 revolutions per minute, the temperature of the heater is controlled at 1550 through the furnace lining heat insulation layer and the heater for 3 hours, and the temperature of each part of the furnace body is monitored in real time by utilizing the heat balance management system, so that the silicon material is in a molten state.
The heat-insulating layer at the bottom of the furnace body is opened, the temperature of the furnace bottom, the furnace body and the furnace top are monitored in real time by utilizing a heat balance management system, the heating power of a heater, the opening size of the heat-insulating layer, the flow rate of cooling gas and the rotating speed of a rotating motor are timely and automatically adjusted according to the temperature change of the different parts in the furnace, the cooling rate of a silicon material is controlled to be in the range of 1.5-2.0 ℃/min, so that the silicon liquid is directionally solidified from the bottom, gradually upwards until the silicon liquid is completely solidified, and the average solidification speed is controlled to be about 2mm/h. The external magnetic field is kept on in the directional solidification process, and the magnetic field is turned off after the whole solidification. And removing the head and the tail of the silicon ingot after the silicon ingot is discharged from the furnace, wherein the total content of the detected metal impurities of the obtained silicon ingot is 1.921ppmWt. The total content of the metal impurities of the removed head and tail scraps is 10.008ppmWt and 10.211ppmWt respectively.
Comparative example 2: purification by a common ingot furnace without a rotating motor and a heat balance management system
260Kg of 4N purity silicon material is added into a graphite crucible, and the furnace body is closed; and then vacuumizing the whole system, filling high-purity argon into the whole system, and cleaning for many times, wherein the vacuum degree is kept below 5 Pa. After the heater heats and melts the silicon material, a longitudinal directional magnetic field from top to bottom is applied, and the magnetic induction intensity is 6000Gs; and the temperature of the heater is controlled at 1550 deg.C through the heat insulating layer of furnace lining and the heater for 3 hours.
And opening a heat-insulating layer at the bottom of the furnace body, and controlling the silicon material to be slowly cooled, so that the silicon liquid is directionally solidified from the bottom to gradually upwards until the silicon liquid is completely solidified. The external magnetic field is kept on in the directional solidification process, and the magnetic field is turned off after the whole solidification. And removing the head and the tail of the silicon ingot after the silicon ingot is discharged from the furnace, wherein the total content of the detected metal impurities of the obtained silicon ingot is 4.370ppmWt. The total content of the metal impurities of the removed head and tail scraps is 8.776ppmWt and 7.890ppmWt respectively.
The technical scheme of the invention is as follows: during the purification process, 5000Gs of directional external magnetic field is applied
260Kg of 4N purity silicon material is added into a graphite crucible, and the furnace body is closed; and then vacuumizing the whole system, filling high-purity argon into the whole system, and cleaning for many times, wherein the vacuum degree is kept below 5 Pa. After the heater heats and melts the silicon material, a rotating motor is started, and the rotating speed is 40 revolutions per minute; applying a longitudinal directional magnetic field from top to bottom, wherein the magnetic induction intensity is 5000Gs; and the furnace lining heat insulation layer and the heater are used for preserving heat for 3 hours, the temperature of the heater is controlled at 1550 ℃, and the temperature of each part of the furnace body is monitored in real time by utilizing a heat balance management system, so that the silicon material is ensured to be in a molten state.
The heat-insulating layer at the bottom of the furnace body is opened, the temperature of the furnace bottom, the furnace body and the furnace top are monitored in real time by utilizing a heat balance management system, the heating power of a heater, the opening size of the heat-insulating layer, the flow rate of cooling gas and the rotating speed of a rotating motor are timely and automatically adjusted according to the temperature change of the different parts in the furnace, the cooling rate of a silicon material is controlled to be in the range of 1.5-2.0 ℃/min, so that the silicon liquid is directionally solidified from the bottom, gradually upwards until the silicon liquid is completely solidified, and the average solidification speed is controlled to be about 2mm/h. The external magnetic field is kept on in the directional solidification process, and the magnetic field is turned off after the whole solidification. And removing the head and the tail of the silicon ingot after the silicon ingot is discharged from the furnace, wherein the total content of metal impurities detected by the obtained silicon ingot is 1.072ppmWt. The total content of the metal impurities of the removed head and tail scraps is 11.112ppmWt and 12.031ppmWt respectively.
As can be seen from comparative examples 1 and 2, the present invention adopts different technical schemes for the same silicon material to be purified as compared with comparative example, and the total content of detected metal impurities in the silicon ingot obtained in comparative example 1 is 1.921ppmWt. The total content of the metal impurities of the removed head and tail scraps is 10.008ppmWt and 10.211ppmWt respectively. The total content of the detected metal impurities in the silicon ingot obtained in comparative example 2 was 4.370ppmWt. The total content of the metal impurities of the removed head and tail scraps is 8.776ppmWt and 7.890ppmWt respectively. The total content of detected metal impurities in the silicon ingot obtained by the technical scheme of the invention is 1.072ppmWt. The total content of the metal impurities of the removed head and tail scraps is 11.112ppmWt and 12.031ppmWt respectively. The invention can purify silicon ingot to reduce impurity obviously and raise impurity obviously. Compared with the prior art, the invention has higher purification precision.
The invention provides a method for purifying silicon material by utilizing the dual actions of magnetic separation and rotary directional solidification, which comprises the steps of melting the silicon material by adopting a casting process, effectively improving the fluidity of the melted material by utilizing a furnace body rotating motor, and then utilizing the magnetic directional separation action of charged metal impurities under a high-strength externally-applied magnetic field and the directional solidification action of precise heat balance control to lead the metal impurities to directionally migrate in the rotationally-flowing liquid silicon material and concentrate on the upper surface and the lower surface; and then the purification is completed by precisely cooling gradient control and directional solidification of a thermal balance management system and removing the head and the tail of the silicon ingot so as to obtain the solar-energy-level high-purity crystalline silicon. The invention can not only effectively separate the impurities with small segregation coefficient, but also separate the impurities with larger segregation coefficient; the magnetic field applied in the process has better penetrability than the electric field, is not limited by the conductivity, and has better separation effect, higher efficiency and good safety. The purity of the crystal silicon obtained by purification can reach 6N level, and the crystal silicon is obviously superior to the traditional multi-level wet purification effect.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
Although the application is described herein in connection with various embodiments, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed application, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the "a" or "an" does not exclude a plurality.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (4)
1. The method for purifying the silicon material by utilizing the dual actions of magnetic separation and spin directional solidification is characterized by comprising the following steps:
S100, selecting a silicon material to be purified, and adding the silicon material to be purified into a high-temperature vacuum casting furnace provided with a furnace body rotating motor, a cooling gas conduit and a heat balance management system;
S200, purifying the high-temperature vacuum casting furnace, heating the high-temperature vacuum casting furnace until the silicon material to be purified is melted, and keeping the constant temperature in the high-temperature vacuum casting furnace through a thermal balance management system;
s300, starting the furnace body rotating motor to enable the melted silicon material to be purified to keep a flowing state, and applying a longitudinal directional magnetic field to the high-temperature vacuum casting furnace to enable metal impurities in the melted silicon material to be purified to directionally migrate and concentrate on the surface under the action of magnetic separation;
S400, opening a bottom heat-insulating layer of the high-temperature vacuum casting furnace, introducing cooling gas into the high-temperature vacuum casting furnace, and utilizing the thermal balance management system to monitor and control the temperature of the high-temperature vacuum casting furnace in real time, so that the furnace body is directionally solidified from the bottom to the whole to obtain a silicon ingot;
S500, rapidly cooling a silicon ingot, taking out the silicon ingot from the high-temperature vacuum casting furnace, finishing the cooled silicon ingot, and removing the head and the tail of the cooled silicon ingot to obtain high-purity crystalline silicon;
The heat balance management system is used for monitoring the temperatures of different parts of the furnace bottom, the furnace body and the furnace top in real time, and timely and automatically adjusting the heating power of the heater, the opening size of the heat preservation layer, the flow of cooling gas and the rotating speed of the rotating motor of the furnace body according to the temperature changes of the different parts in the furnace; the cooling rate is accurately controlled within a range of 1.5-2.0 ℃/min, the applied longitudinal directional magnetic field is a continuous magnetic field or a pulsed magnetic field, and the magnetic induction intensity is 6000-10000 Gs;
S400 includes:
S410, opening a bottom heat-insulating layer of the high-temperature vacuum casting furnace, and introducing cooling gas into the high-temperature vacuum casting furnace to directionally start solidification of silicon materials in the furnace body from the bottom to the top;
and S420, controlling the temperature of the furnace body by using the thermal balance management system so as to enable the solidification speed to be 2-5 mm/h until all the silicon materials in the furnace body are solidified to obtain silicon ingots.
2. The method for purifying a silicon material by using the dual actions of magnetic separation and spin-on directional solidification as claimed in claim 1, wherein S200 comprises:
s210, vacuumizing the high-temperature vacuum casting furnace, and introducing argon;
S220, repeating the step S210 for a plurality of times until the high-temperature vacuum casting furnace is kept in a high-purity argon state, wherein the high-purity argon state is that the purity of the argon is more than 99.999%;
and S230, heating the high-temperature vacuum casting furnace by a heater until the silicon material to be purified is melted, and keeping the temperature in the high-temperature vacuum casting furnace constant by a thermal balance management system.
3. The method for purifying a silicon material by using the dual actions of magnetic separation and spin-on directional solidification as claimed in claim 2, wherein the heating range of the heater is 1550-1600 ℃.
4. The method for purifying a silicon material by using the dual actions of magnetic separation and spin-on directional solidification as claimed in claim 1, wherein S300 comprises:
S310, starting the furnace body rotating motor, and enabling the rotating speed to be 30-50 revolutions per minute so as to enable the melted silicon material to be purified to keep a flowing state;
S320, controlling the high-temperature vacuum casting furnace to preserve heat through the thermal balance management system, and applying a longitudinal directional magnetic field to the high-temperature vacuum casting furnace for 1-3 hours, wherein the magnetic induction intensity is 6000-10000 Gs, so that metal impurities in the melted silicon material to be purified directionally migrate and are enriched on the surface under the action of magnetic separation.
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