Electromagnetically stirred material high-purity purification system and process

Abstract

This invention discloses a high-purity material purification system and process based on electromagnetic stirring, belonging to the field of material purification technology. The system employs a synergistic architecture of electromagnetic stirring and directional solidification, including a furnace body with a water-cooled shell structure, an electromagnetic stirring device that generates a rotating magnetic field to drive forced convection of the melt, a directional solidification component with closed-loop temperature gradient control, a vacuum refining component with a multi-stage series structure, and a control system for coordinated control of all components. The purification process includes steps such as raw material pretreatment, vacuum environment construction, melt heating and electromagnetic stirring, directional solidification purification, and product removal. This invention promotes uniform dispersion of impurities and disrupts the impurity enrichment layer at the solidification interface through electromagnetic stirring; achieves effective separation of impurities through solute redistribution effect via directional solidification; eliminates gaseous contamination through the vacuum environment; and achieves coordinated adjustment of each process step through the control system, significantly improving product purity and effective purification rate.

Description

Technical Field

[0001] This invention relates to the field of material purification technology, and provides a high-purity material purification system and process based on electromagnetic stirring drive. Background Technology

[0002] In high-tech fields such as new energy, semiconductors, and aerospace, the requirements for the purity of metallic materials are becoming increasingly stringent. Material purification is a process that separates and removes impurity elements from materials through physical or chemical methods, thereby improving the purity of the target element. Obtaining high-purity metallic materials requires comprehensive control of multiple contamination pathways, including eliminating solid-phase contamination introduced by the melting of crucible materials into the melt, suppressing gas-phase contamination caused by the reaction of oxygen and nitrogen in the air with the melt, and promoting the effective separation and removal of existing impurities in the melt.

[0003] In traditional purification equipment, the stirring, solidification, and vacuum maintenance processes are typically controlled by independent systems, lacking real-time linkage and adjustment capabilities between these processes, making it difficult to achieve coordinated optimization of process parameters. During directional solidification, failure to simultaneously maintain a vacuum environment and appropriate stirring intensity can lead to melt surface oxidation and impurity enrichment at the interface front, affecting the impurity removal effect.

[0004] Existing metal purification technologies are ineffective in melt mixing and impurity dispersion. Traditional purification equipment relies heavily on natural convection caused by temperature gradients for melt mixing, but natural convection is slow and has dead zones, making it difficult to achieve sufficient and uniform dispersion of impurities in the melt. During directional solidification, an impurity enrichment layer forms at the solidification interface front. If the stirring intensity is insufficient, this layer is difficult to break down, leading to some impurities being captured by the solidification front and unable to be effectively removed.

[0005] Existing metal material purification technologies lack precision in temperature gradient control. Traditional equipment lacks the ability to monitor and regulate the actual temperature distribution of the melt in real time. Fluctuations in the temperature gradient can cause changes in the solidification interface morphology, transforming it from a flat interface to a cellular or dendritic interface, increasing the probability of impurities being captured by the solid phase and reducing purification efficiency.

[0006] The aforementioned problems restrict the production efficiency and product quality of high-purity metal materials, making it difficult to meet the stringent purity requirements of high-end application fields. Summary of the Invention

[0007] To address the problems existing in the background technology, the present invention provides a high-purity material purification process based on electromagnetic stirring, comprising the following steps:

[0008] S1: Raw material pretreatment and addition: The metal raw material to be purified is crushed to the specified particle size, and surface contaminants are removed by ultrasonic cleaning or chemical cleaning. After drying, it is weighed and added to the furnace.

[0009] S2: Vacuum environment construction: Start the mechanical pump, Roots pump and diffusion pump in sequence to evacuate the furnace to a high vacuum state, turn off the vacuum pump and let it stand to detect the change in vacuum degree. After determining that the sealing is qualified, restart the vacuum pump to maintain the vacuum.

[0010] S3: Melt heating and electromagnetic stirring. The heating element is activated to heat the raw material. The temperature is monitored by an infrared thermometer. Once the melting temperature is reached, the electromagnetic stirring device is activated. The current is adjusted to make the electromagnetic coil generate a rotating magnetic field. Stirring continues until the impurities in the melt are evenly distributed.

[0011] S4: Directional solidification and purification. Start the heating element to heat the upper region of the melt, and start the cooling element to cool the lower region of the melt. Measure the upper and lower temperatures separately using an infrared thermometer. Adjust the power of the heating element and the water flow rate of the cooling element to make the temperature difference between the upper and lower parts reach the set value. Observe and control the speed at which the solidification interface moves from bottom to top. Maintain vacuum and stirring until solidification is complete.

[0012] S5: Remove the product. After solidification, turn off the electromagnetic stirring device. Inert gas is introduced into the furnace through the inert gas interface to atmospheric pressure. After cooling, open the outlet to remove the purified product.

[0013] Furthermore, the pretreatment and addition of raw material S1 includes the following specific steps:

[0014] S11: The metal raw material is fed into the crusher and crushed to a particle size of 5 mm to 10 mm; after crushing, it is screened and classified to achieve uniform particle size of the raw material.

[0015] S12: Place the crushed raw material into an ultrasonic cleaning tank, add cleaning solution, and ultrasonic cleaning for 10 to 30 minutes to remove surface oil and oxide scale and achieve surface cleaning.

[0016] S13: After the raw materials are washed and drained, place them in a drying oven, set the drying temperature to 100 degrees Celsius to 150 degrees Celsius, and the drying time to 1 hour to 3 hours to remove the moisture from the raw materials and achieve the drying of the raw materials;

[0017] S14: Take out the dried raw materials and weigh them. Calculate the feeding amount based on the effective volume of the furnace body. The feeding amount is 10% to 30% of the effective volume of the furnace body. Add the raw materials into the furnace body according to the calculated amount to achieve quantitative feeding.

[0018] S15: Close the top cover of the furnace body, check that the discharge port isolation door is closed, complete the raw material loading, and prepare for subsequent vacuum extraction.

[0019] Furthermore, the construction of the S2 vacuum environment includes the following specific steps:

[0020] S21: Open the solenoid valve on the vacuum pipeline, start the mechanical pump to begin vacuuming, observe the value displayed by the vacuum monitoring device, and stop the mechanical pump when the vacuum level reaches less than or equal to 800 Pa to achieve initial decompression in the furnace.

[0021] S22: Start the Roots pump to continue evacuating the vacuum. When the vacuum level reaches less than or equal to 5 Pa, stop the Roots pump to achieve a medium vacuum inside the furnace.

[0022] S23: Start the diffusion pump to continue evacuating the vacuum until the vacuum level reaches less than or equal to 1×10⁻⁶. -3 The diffusion pump is stopped at a certain time to achieve a high vacuum environment inside the furnace.

[0023] S24: Close the solenoid valve, record the vacuum level at this time, let it stand for 20 to 40 minutes, read the vacuum level again, calculate the change in vacuum level, and determine that the sealing performance is qualified when the change in vacuum level is less than or equal to 10 Pa, thus realizing the sealing test;

[0024] S25: Reopen the solenoid valve, start the diffusion pump to maintain the vacuum level, complete the establishment of the vacuum environment, and provide a low-oxygen environment for smelting.

[0025] Furthermore, the S3 melt heating and electromagnetic stirring includes the following specific steps:

[0026] S31: Start the heating element, set the heating rate from 5 degrees Celsius / minute to 15 degrees Celsius / minute, and gradually increase the power of the heating element;

[0027] S32: Continuously monitor the temperature inside the furnace using an infrared thermometer, record the temperature value every 5 to 10 minutes, and plot the heating curve;

[0028] S33: Stabilize the heating power when the temperature reaches the melting temperature. The melting temperature for silicon melt is 1420°C to 1480°C, and for aluminum melt is 650°C to 670°C. Maintain the temperature for 10 to 20 minutes to ensure that the raw materials are completely melted and realize the transformation of solid raw materials into liquid melt.

[0029] S34: After the melt is completely melted, start the current regulating device of the electromagnetic stirring device and set the stirring current. The stirring current is 380 amperes to 460 amperes for silicon melt and 240 amperes to 320 amperes for aluminum melt. The current generates a rotating magnetic field through the electromagnetic coil to start the stirring of the melt.

[0030] S35: Keep stirring running for 0.5 to 2 hours and observe the melt flow through the observation window. When the melt shows uniform rotating flow and no local static areas, it is determined that the stirring is sufficient and the impurities in the melt are uniformly dispersed.

[0031] Furthermore, the S4 directional solidification purification includes the following specific steps:

[0032] S41: Activate the heating element of the directional solidification component and set the heating element power to 20 kW to 100 kW; the heating element continuously heats the upper region of the melt to maintain a high temperature in the upper part;

[0033] S42: Simultaneously activate the cooling elements, open the cooling water valve, and adjust the water flow rate to 0.5 m / s to 2 m / s; the cooling water cools the lower part of the melt through the water cooling pipe, thereby reducing the temperature of the lower part.

[0034] S43: The temperature gradient is calculated by measuring the upper part of the furnace body with an infrared thermometer installed on the upper part of the furnace body and measuring the lower part of the furnace body with an infrared thermometer installed on the lower part of the furnace body, thus realizing the real-time calculation of the temperature gradient.

[0035] S44: Set the target temperature gradient according to the type of material to be purified; compare the measured temperature gradient with the target temperature gradient; when the measured temperature gradient is less than the target temperature gradient, increase the heating power or decrease the cooling water flow rate; when the measured temperature gradient is greater than the target temperature gradient, decrease the heating power or increase the cooling water flow rate, so as to achieve precise control of the temperature gradient.

[0036] S45: Observe the solidification interface of the melt, determine the position of the solid-liquid interface through the observation window or ultrasonic detection, and record the distance the solid-liquid interface moves over time.

[0037] S46: Keep the vacuum pump and electromagnetic stirrer running throughout the solidification process. The solidification time is 3 to 8 hours until the melt is completely solidified, thus completing the directional solidification and purification.

[0038] Furthermore, the removal of the S5 product includes the following specific steps:

[0039] S51: After the melt has completely solidified, turn off the current regulating device of the electromagnetic stirring device, cut off the current of the electromagnetic coil, and stop the generation of the magnetic field;

[0040] S52: Close the vacuum pipeline solenoid valve, stop the vacuum pump, and open the gas valve of the inert gas interface;

[0041] S53: Introduce argon or nitrogen gas with a purity of not less than 99.999% into the furnace. Control the gas filling rate to 10 liters / minute to 30 liters / minute using a flow meter. Observe the pressure gauge. When the pressure inside the furnace reaches 0.08 MPa to 0.12 MPa, close the gas valve to achieve inert gas protection.

[0042] S54: Maintain an inert gas atmosphere, stop the heating element and the cooling element, and naturally cool to 100 °C to 300 °C to achieve product cooling;

[0043] S55: Open the isolation door of the discharge port, use a high-temperature resistant tool to take out the purified product, and transfer it to the cooling area to continue cooling to room temperature;

[0044] S56: Cut a sample from the product, use an inductively coupled plasma mass spectrometer to detect the impurity content, confirm that the product purity meets the design requirements, complete the quality inspection, and achieve the acquisition and quality confirmation of the purified product.

[0045] The present invention also provides a high-purity purification system for materials based on electromagnetic stirring drive, including:

[0046] It includes a furnace body, an electromagnetic stirring device, a directional solidification component, a vacuum refining component and a control system; the furnace body adopts a water-cooled shell structure and is provided with an anti-adhesion coating to accommodate the melt and isolate the melt from the shell material; the electromagnetic stirring device is arranged on the outer periphery of the furnace body to generate a rotating magnetic field to drive the melt to generate forced convection, promote the uniform dispersion of impurities in the melt and destroy the impurity enrichment layer at the front of the solidification interface; the directional solidification component includes a heating element and a cooling element respectively arranged at the upper and lower parts of the axial direction of the furnace body, and a temperature gradient control unit for real-time temperature monitoring and closed-loop adjustment, making the solidification interface advance unidirectionally by establishing an axial temperature gradient, and using the solute redistribution effect to repel impurities to the liquid phase region; the vacuum refining component is connected to the furnace body by a multi-stage series vacuum pump system to establish a high-vacuum environment to eliminate gas-phase pollution sources and inhibit the oxidation reaction of the melt, and at the same time is provided with an inert gas interface for atmosphere protection when the product is taken out; the control system is signal-connected to the electromagnetic stirring device, the directional solidification component and the vacuum refining component to coordinately control the working states and process parameters of each component, and realize the linkage adjustment of the three process links of electromagnetic stirring, directional solidification and vacuum refining.

[0047] The beneficial effects achieved by the present invention are:

[0048] This invention designs electromagnetic stirring technology, directional solidification technology, and vacuum refining technology, constructing a purification system and method that integrates multiple technologies to achieve comprehensive control over different impurity sources and contamination pathways. The electromagnetic stirring device and the directional solidification component work collaboratively through a control system. During the melting stage, electromagnetic stirring ensures uniform dispersion of impurities in the melt. During the solidification stage, electromagnetic stirring continuously disrupts the impurity-rich layer at the solidification interface front, promoting the rapid migration of repelled impurities to the liquid phase region and preventing impurities from being captured by the solidification front, thereby significantly improving the impurity removal efficiency of the directional solidification process. The vacuum refining component maintains a low-oxygen environment throughout the melting and solidification processes, forming a three-stage linkage process architecture with electromagnetic stirring and directional solidification. This eliminates the problem of insufficient synergy between process stages and improves the overall purification efficiency.

[0049] The directional solidification assembly of this invention employs a design where heating and cooling elements are respectively arranged at the upper and lower axial sections of the furnace body. Combined with the closed-loop regulation function of the temperature gradient control unit, it achieves real-time monitoring and precise control of the axial temperature gradient, ensuring a flat and stable solidification interface that advances unidirectionally along the axial direction. Utilizing the solute redistribution effect at the solid-liquid interface, impurities are effectively repelled into the liquid phase region, and as the solidification process progresses, impurities accumulate in the final solidification region. The closed-loop control architecture automatically adjusts the heating power and cooling intensity based on the deviation between the measured temperature gradient and the target value, avoiding interface morphology instability caused by temperature gradient fluctuations, preventing dendrite growth and impurity trapping, and ensuring a stable and controllable solidification rate.

[0050] This invention employs a multi-stage series vacuum pump system in the vacuum refining component, achieving stepped extraction from atmospheric pressure to high vacuum. This provides a stable low-oxygen environment for the smelting process, effectively suppressing oxidation reactions in the molten metal and the dissolution of gaseous impurities, thus eliminating the impact of gaseous contaminants on product purity. The combination of the water-cooled shell structure and the vacuum environment eliminates both solid and gaseous contaminants, laying a clean process environment foundation for high-purity purification.

[0051] The control system of this invention adopts a unified scheduling system architecture, integrating the electromagnetic stirring device, directional solidification component, and vacuum refining component onto the same control platform. This achieves coordinated control and real-time linkage adjustment of parameters in each stage of the purification process, overcoming the shortcomings of traditional equipment where each process stage is controlled independently and difficult to link in real time. Key process parameters such as electromagnetic stirring intensity, temperature gradient, and vacuum degree are synchronously adjusted and optimized according to the purification progress, improving process stability and repeatability, and meeting the requirements for large-scale production of high-purity metallic materials. Through innovative design of the process method and system architecture, this invention achieves a significant improvement in product purity and effective purification rate, while reducing the need for mining primary mineral resources, resulting in good economic and social benefits. Attached Figure Description

[0052] Figure 1 This is a flow chart of the high-purity material purification process based on electromagnetic stirring drive according to the present invention.

[0053] Figure 2 This is a schematic diagram of the material high-purity purification system based on electromagnetic stirring drive according to the present invention. Detailed Implementation

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] Reference Figure 1 and Figure 2 The present invention provides a high-purity material purification process based on electromagnetic stirring, which combines electromagnetic stirring technology with directional solidification technology and purifies materials in a vacuum environment. The process of the present invention includes the following steps.

[0056] Step S1 involves raw material pretreatment and addition. In this step, the metal raw material to be purified is crushed to a specified particle size, and surface contaminants are removed using ultrasonic cleaning or chemical cleaning. After drying, it is weighed and added to the furnace. The purpose of raw material pretreatment is to remove oil, scale, and other impurities adhering to the surface of the raw material, preventing these surface impurities from entering the melt and causing contamination during the melting process. Crushing involves breaking large pieces of raw material into particles of appropriate size to facilitate subsequent cleaning and feeding operations. Smaller particle sizes also help to accelerate the melting rate and reduce melting time. Ultrasonic cleaning utilizes the cavitation effect generated by ultrasound in a liquid; ultrasound produces a large number of tiny bubbles in the liquid, and when these bubbles burst, they generate strong shock waves and micro-jet streams, effectively cleaning the surface of the raw material. Chemical cleaning uses chemical reagents to react with surface contaminants, dissolving or removing them. Drying removes moisture from the cleaned raw material by evaporation, preventing moisture from vaporizing and generating bubbles or reacting with the melt during high-temperature melting.

[0057] Step S1, raw material pretreatment and addition, specifically includes the following sub-steps. Step S11: The metal raw material is fed into a crusher and crushed to a particle size d, where d is the maximum cross-sectional diameter of the particle. The preferred particle size range can be determined based on the type of raw material and equipment conditions. After crushing, the material is sieved and graded to achieve uniform particle size. Sieving and grading refers to using a standard sieve to sort the crushed particles according to their particle size range, removing excessively large or small particles to ensure a uniform particle size distribution of the raw material added to the furnace, which is beneficial for achieving uniform heating and synchronous melting during subsequent melting. Step S12: The crushed raw material is placed in an ultrasonic cleaning tank, and cleaning fluid is added for ultrasonic cleaning to remove surface oil and oxide scale, achieving surface cleanliness. The cleaning fluid can be anhydrous ethanol, acetone, or a special cleaning agent; the appropriate cleaning fluid should be selected based on the material of the raw material and the type of contaminants. The frequency of ultrasonic cleaning is usually in the range of 20kHz to 50kHz. Higher frequencies result in finer cleaning but weaker penetration; the appropriate frequency must be selected based on the particle size and degree of contamination of the raw material. Step S13: After draining the cleaned raw materials, place them in a drying oven, set a suitable drying temperature and time, and remove the moisture from the raw materials to achieve drying. The drying temperature should be lower than the oxidation initiation temperature of the raw materials to prevent oxidation on the surface of the raw materials during the drying process. At the same time, the temperature should not be too low to ensure drying efficiency. Step S14: Take out the dried raw materials and weigh them. Calculate the feeding amount m based on the effective volume V of the furnace body. The calculation formula is m=ρV; where m is the actual feeding mass; ρ is the bulk density of the raw materials; and V is a certain proportion of the effective volume of the furnace body. Bulk density refers to the mass per unit volume of bulk materials in a natural stacked state, which is related to particle density and interparticle porosity. The calculation of the feeding amount needs to consider the volume change of the raw materials after melting and the space that needs to be reserved in the furnace body to prevent melt overflow or affect the electromagnetic stirring effect. Add the raw materials to the furnace body according to the calculated amount to achieve quantitative feeding. Step S15: Close the top cover of the furnace body, check that the discharge port isolation door is closed, complete the raw material loading, and prepare for subsequent vacuum extraction. The airtightness of the furnace body is a prerequisite for ensuring a vacuum environment. The sealing surfaces of the cover plate and isolation door should be clean and flat, and the sealing rings should be intact.

[0058] Step S2 involves establishing the vacuum environment. This step sequentially starts the mechanical pump, Roots pump, and diffusion pump to evacuate the furnace to a high vacuum. The vacuum pumps are then turned off, and the vacuum level is monitored. Once the seal is deemed satisfactory, the vacuum pumps are restarted to maintain the vacuum. Establishing a vacuum environment is crucial for high-purity purification. A vacuum removes air from the furnace, eliminating the possibility of oxygen, nitrogen, and other gases reacting with the high-temperature melt, preventing oxidation of the melt surface and the dissolution of gaseous impurities. A three-stage vacuum pump system is used because a single type of vacuum pump is insufficient to achieve the required high vacuum; multiple stages are connected in series to gradually reduce the pressure. The mechanical pump is a positive displacement pump that uses the rotation of its rotor to transport gas from the inlet to the outlet, suitable for evacuating from atmospheric pressure to low vacuum. The Roots pump is a dual-rotor positive displacement pump with a high pumping speed but a low compression ratio, requiring a backing pump. It is suitable for evacuating from low to medium vacuum. The diffusion pump uses the diffusion effect of a high-speed oil vapor stream to capture gas molecules, achieving high or even ultra-high vacuum, but it cannot directly evacuate at atmospheric pressure; the pressure must be reduced by a backing pump before it can operate.

[0059] The construction of the vacuum environment in step S2 specifically includes the following sub-steps. In step S21, open the solenoid valve on the vacuum pipeline, start the mechanical pump to evacuate the air, and observe the display value of the vacuum degree monitoring device. Stop the mechanical pump when the vacuum degree reaches the primary vacuum degree target value P1. The setting of the primary vacuum degree target value P1 should be within the effective working range of the mechanical pump. Usually, P1 can be set to not be greater than a certain preset value to ensure the normal startup and operation of the subsequent roots pump. After the initial decompression in the furnace body, most of the air in the furnace body has been discharged. In step S22, start the roots pump to continue evacuating the air. Stop the roots pump when the vacuum degree reaches the intermediate vacuum degree target value P2. The setting of the intermediate vacuum degree target value P2 should consider the ultimate vacuum degree of the roots pump and the startup pressure condition of the diffusion pump. P2 is usually set to not be greater than a certain lower preset value. At this time, the furnace body has reached a medium vacuum state. In step S23, start the diffusion pump to continue evacuating the air. Stop the diffusion pump when the vacuum degree reaches the high vacuum degree target value P3, where P3 is the high vacuum degree target value and is usually set at a lower level. The pumping principle of the diffusion pump is to use the heated diffusion pump oil to generate a high-speed vapor flow. After the gas molecules collide with the vapor flow, they are carried to the pump wall condensation area and thus are pumped out of the system. The ultimate vacuum degree that the diffusion pump can reach is very low, meeting the requirements for the vacuum degree in high-purity purification. In step S24, close the solenoid valve, record the vacuum degree at this time as P3, read the vacuum degree again as P4 after standing for a certain period of time, and calculate the vacuum degree change amount ΔP. The calculation formula is ΔP = P4 - P3; where ΔP is the vacuum degree change amount; P4 is the vacuum degree after standing; P3 is the vacuum degree before standing. When the vacuum degree change amount ΔP does not exceed the preset threshold, it is determined that the sealing performance is qualified, and the sealing performance detection is realized. The purpose of the sealing performance detection is to confirm that the furnace body system maintains a vacuum state after the vacuum pump is closed. If the vacuum degree rises too fast, it means that there is a leakage point that needs to be checked and processed. In step S25, reopen the solenoid valve, start the diffusion pump to maintain the vacuum degree at the P3 level, complete the establishment of the vacuum environment, and provide a low-oxygen environment for melting. During the subsequent melting and purification processes, continuously keep the vacuum pump running to maintain a stable vacuum state.

[0060] Step S3 involves melt heating and electromagnetic stirring. In this step, the heating element is activated to heat the raw material. The temperature is monitored using an infrared thermometer. Once the melting temperature is reached, the electromagnetic stirring device is activated. The current is adjusted to generate a rotating magnetic field in the electromagnetic coil, and stirring continues until impurities are evenly distributed in the melt. The heating process transforms the solid raw material into a liquid melt, creating conditions for subsequent electromagnetic stirring and directional solidification. The infrared thermometer is a non-contact temperature measuring instrument that calculates the temperature of an object by detecting the infrared radiation energy emitted by the object. It is particularly suitable when contact thermocouples cannot be used in a vacuum environment. Electromagnetic stirring utilizes the principle of electromagnetic induction to generate a Lorentz force in the conductive melt. This force is a volume force generated by the interaction between the magnetic field and the induced current in the melt, which can drive the melt to perform forced convection motion. The rotating magnetic field is a time-rotating magnetic field generated by a multiphase alternating current passing through a specifically arranged electromagnetic coil, causing the melt to rotate and flow, achieving thorough mixing of the melt.

[0061] Step S3, melt heating and electromagnetic stirring, specifically includes the following sub-steps: Step S31: Start the heating element, set the heating rate, and gradually increase the heating element power. The heating rate setting should consider the thermal expansion characteristics and thermal stress of the raw material. Excessive heating may cause raw material particles to crack or generate excessive thermal stress in the furnace structure. The heating element power is adjusted according to the heating rate requirements and heat loss; a gradual increase in power ensures stable heating. Step S32: Continuously monitor the furnace temperature using an infrared thermometer, recording the temperature value at regular intervals and plotting a heating curve. Recording the heating curve helps monitor whether the heating process is normal; any abnormal temperature changes can be promptly adjusted to adjust the heating power. The infrared thermometer should be aimed at a specific location on the melt surface or the inner wall of the furnace to ensure consistent and accurate measurements. Step S33: Stabilize the heating power when the temperature reaches the melting temperature Tm, where Tm is the melting temperature. Different materials have different melting points; the appropriate melting temperature should be set according to the type of material to be purified. Maintain the temperature for a certain period to ensure complete melting of the raw material, achieving the transformation from solid to liquid melt. Complete melting refers to the transformation of all solid raw material particles into a liquid state. This can be determined by observing the surface state of the melt through an observation window. Step S34: After the melt is completely melted, the current regulating device of the electromagnetic stirring device is activated, and the stirring current I is set. I is the stirring current; different materials have different melt conductivity and density, requiring different stirring currents. The current generates a rotating magnetic field through the electromagnetic coil, initiating the stirring of the melt. The strength of the rotating magnetic field is proportional to the number of coil turns and the current magnitude. The magnetic field frequency is the same as the current frequency, and a mains frequency or variable frequency power supply is typically used. Step S35: The stirring is maintained for a certain period. The melt flow state is observed through the observation window. When the melt exhibits uniform rotating flow without localized static areas, the stirring is considered sufficient, achieving uniform dispersion of impurities in the melt. The duration of electromagnetic stirring should be sufficient to ensure uniform distribution of impurities in the melt, eliminating the initial impurity concentration gradient and creating uniform initial conditions for effective impurity removal during subsequent directional solidification.

[0062] Step S4 is directional solidification purification. In this step, the heating element is activated to heat the upper region of the melt, while the cooling element is activated to cool the lower region. The upper and lower temperatures are measured separately using an infrared thermometer. The power of the heating element and the water flow rate of the cooling element are adjusted to achieve the set temperature difference. The upward movement speed of the solidification interface is observed and controlled, and vacuum and stirring are maintained until solidification is complete. The principle of directional solidification utilizes the solute redistribution effect. At the solid-liquid interface, due to the difference in equilibrium concentration of solutes in the solid and liquid phases, the solubility of most impurity elements in the solid phase is lower than that in the liquid phase, with an equilibrium distribution coefficient less than 1. Therefore, impurities are preferentially repelled into the liquid phase during solidification. By controlling the unidirectional advancement of the solidification interface, the repelled impurities continuously accumulate in the liquid phase, and the finally solidified area becomes an impurity-rich area. Removing this area yields a high-purity product. Maintaining electromagnetic stirring during directional solidification accelerates the dissipation of the impurity-rich layer at the interface front, improves the impurity mass transfer rate, and prevents excessively high local impurity concentrations from causing supercooling and interface instability.

[0063] Step S4, directional solidification purification, specifically includes the following sub-steps: Step S41: Activate the heating element of the directional solidification assembly and set the heating element power P1, where P1 is the heating power. The heating element continuously heats the upper region of the melt, maintaining a high temperature in the upper part. The heating power setting should ensure that the temperature of the upper region is maintained above the melting point, guaranteeing that the upper melt remains in a liquid state. Step S42: Simultaneously activate the cooling element, open the cooling water valve, and adjust the water flow rate v to the set value, where v is the cooling water flow rate. The cooling water cools the lower region of the melt through the water-cooling pipe, lowering the temperature of the lower part. The cooling rate is controlled by adjusting the water flow rate; the higher the water flow rate, the more heat the cooling water carries away, resulting in a greater cooling intensity. Step S43: Measure the upper temperature T1 using an infrared thermometer installed on the upper part of the furnace body, and the lower temperature T2 using an infrared thermometer installed on the lower part of the furnace body. Calculate the temperature gradient G using the formula G=(T1-T2) / L; where G is the axial temperature gradient; T1 is the upper measured temperature; T2 is the lower measured temperature; and L is the axial distance between the upper and lower measuring points. The temperature gradient is the temperature change per unit length and is a key control parameter in the directional solidification process, determining the morphological stability of the solidification interface and the solidification rate. Step S44: Set the target temperature gradient G0 according to the type of material to be purified, where G0 is the target temperature gradient. Different materials have different optimal temperature gradient ranges. Compare the measured temperature gradient G with the target temperature gradient G0. When G is less than G0, increase the heating power or decrease the cooling water flow rate; when G is greater than G0, decrease the heating power or increase the cooling water flow rate, achieving precise control of the temperature gradient. This method of adjustment based on the deviation between the measured value and the target value is a closed-loop control, stabilizing the temperature gradient near the set value and ensuring the stable progress of the solidification process. Step S45: Observe the solidification interface of the melt. Determine the position of the solid-liquid interface through an observation window or ultrasonic detection, and record the distance the solid-liquid interface moves over time. The solid-liquid interface is the boundary between the solid and liquid phases. During directional solidification, this interface moves from bottom to top. Ultrasonic detection utilizes the different propagation speeds of ultrasound waves in the solid and liquid phases to determine the interface position by detecting reflected waves. The speed at which the solidification interface moves, i.e., the solidification rate, is an important parameter affecting the purification effect. If the solidification rate is too fast, impurities will not have enough time to diffuse and will be captured by the solid phase; if it is too slow, production efficiency will be reduced. Step S46: Maintain the vacuum pump and electromagnetic stirring throughout the solidification process. The solidification process continues until the melt is completely solidified, completing the directional solidification purification. The solidification time depends on the melt volume, temperature gradient, and cooling intensity, and should be determined according to the actual situation. Maintaining a vacuum environment during solidification prevents air from entering and reacting with the melt, while maintaining electromagnetic stirring promotes mass transfer and removal of impurities.

[0064] Step S5 is product removal. After solidification in this step, the electromagnetic stirring device is turned off, and inert gas is introduced into the furnace through the inert gas interface to atmospheric pressure. After cooling, the discharge port is opened to remove the purified product. During the product removal stage, the furnace pressure needs to be restored to atmospheric pressure, and the product must be cooled to a safe temperature before removal. Inert gas is introduced instead of air to prevent oxidation of the high-temperature product surface during cooling. Inert gases such as argon or nitrogen do not react with metals and provide a protective atmosphere.

[0065] Step S5, product removal, specifically includes the following sub-steps: Step S51: After the melt has completely solidified, turn off the current regulating device of the electromagnetic stirring device, cut off the current to the electromagnetic coil, and stop the generation of the magnetic field. Continuing to stir after solidification is pointless; turning off the electromagnetic stirring saves energy. Step S52: Close the solenoid valve of the vacuum pipeline, stop the vacuum pump, and open the gas valve of the inert gas interface. Closing the solenoid valve isolates the vacuum pump from the furnace body, preventing the gas from being drawn away by the vacuum pump during inert gas filling. Step S53: Fill the furnace with high-purity inert gas, controlling the filling rate with a flow meter and observing the pressure gauge. After filling until the furnace pressure reaches the set value, close the gas valve to achieve inert gas protection. The purity of the inert gas should be high enough to avoid residual oxygen or other reactive gases contaminating the product. The filling rate should not be too fast to prevent airflow from impacting the product surface or stirring up residual dust inside the furnace. Step S54: Maintain the inert gas atmosphere, stop the heating and cooling elements, and allow the product to cool naturally to an appropriate temperature. Natural cooling refers to allowing the product to cool down naturally in an inert gas atmosphere without forced cooling. The final cooling temperature should be set considering the oxidation initiation temperature of the product material in air and the safety of the operators; typically, it must be cooled below this temperature for safe removal. Step S55: Open the outlet isolation door, use a high-temperature resistant tool to remove the purified product, and transfer it to the cooling area to continue cooling to room temperature. High-temperature resistant tools are those that can withstand the residual temperature of the product without deformation or damage, such as graphite pliers or ceramic clamps. Step S56: Cut a sample from the product and use an inductively coupled plasma mass spectrometer (ICP-MS) to detect impurity content, confirming that the product purity meets design requirements, completing quality inspection, and achieving the acquisition and quality confirmation of the purified product. Inductively coupled plasma mass spectrometry (ICP-MS) is a highly sensitive elemental analysis instrument that can simultaneously detect the content of multiple elements, with detection limits reaching ppb or even ppt levels, suitable for impurity analysis of high-purity materials.

[0066] This invention also provides an electromagnetic stirring-driven high-purity material purification system for implementing the above-mentioned process. The system includes a furnace body, an electromagnetic stirring device, a directional solidification assembly, a vacuum refining assembly, and a control system. The furnace body adopts a double-shell structure: an inner water-cooled shell with an anti-stick coating on its inner surface, and an outer protective shell. A water-cooling channel is formed between the inner and outer shells. The furnace body has a cover plate at the top and a discharge port and isolation door at the bottom, with the isolation door connected to the driving device. The furnace body is the core container of the entire system, used to contain the material to be purified and provide a place for melting and solidification. The double-shell structure design allows the inner water-cooled shell to remove heat through the cooling water flowing in the water-cooling channel, controlling the shell temperature and preventing overheating. The anti-stick coating on the inner surface prevents direct contact and adhesion between the melt and the shell material, while also preventing the shell material from dissolving into the melt and causing secondary contamination. This design achieves zero contact between the melt and the crucible material, fundamentally eliminating the crucible contamination problem commonly found in traditional crucible purification. The cover plate is used to seal the top opening of the furnace body, and a sealing structure is used between it and the furnace body to ensure a vacuum seal. The discharge port is located at the bottom of the furnace body for easy removal of the solidified product. The isolation door remains closed during the purification process and opens when the product is removed. A drive unit is used to control the opening and closing of the isolation door.

[0067] The inner water-cooled shell of the furnace body can be made of stainless steel or copper, with a silicon nitride coating applied to the inner surface as an anti-stick coating. The outer protective shell can be made of cold-rolled steel plate. Stainless steel offers good corrosion resistance and mechanical strength, while copper provides excellent thermal conductivity; the choice depends on specific requirements. The silicon nitride coating features high hardness, high temperature resistance, good chemical inertness, and non-wetting properties with molten metal, effectively preventing the molten metal from adhering to the shell. A spiral water-cooling pipe is installed within the water-cooling channel, connecting to an external water circulation system. The spiral water-cooling pipe design increases the contact area and flow path between the cooling water and the shell, improving cooling efficiency and uniformity. The isolation door at the bottom of the furnace body is connected to the discharge port via hinges. The drive unit can be hydraulic or electric, connected to the controller. Hydraulic drives offer high power and smooth operation, while electric drives offer fast response and high control precision; the choice depends on the discharge port size and operational requirements.

[0068] The electromagnetic stirring device is located around the periphery of the furnace body and includes an electromagnetic coil, a current regulating device, and a water-cooled jacket. The electromagnetic coil is arranged in a ring around the furnace body, and its two ends are electrically connected to the current regulating device. The water-cooled jacket surrounds the outside of the electromagnetic coil and is connected to the circulating water pump and cooling water tank via pipes. The electromagnetic stirring device is a key component for generating a rotating magnetic field to drive the convection of the melt. The ring arrangement of the electromagnetic coil around the furnace body ensures that the generated magnetic field acts on the entire melt area within the furnace body. The current regulating device is used to adjust the magnitude and frequency of the current flowing through the electromagnetic coil, thereby controlling the magnetic field strength and rotation speed. When the electromagnetic coil is energized, its temperature rises due to resistance heating. The water-cooled jacket is designed to cool the electromagnetic coil and prevent overheating, which could damage the insulation layer or degrade its performance. The circulating water pump and cooling water tank form a cooling water circulation system, providing a continuous flow of cooling water to the water-cooled jacket.

[0069] The electromagnetic coil of the electromagnetic stirring device is wound with high-temperature resistant copper wire, and the surface of the copper wire is coated with a ceramic insulation layer. The high-temperature resistant copper wire maintains good conductivity at high ambient temperatures, and the ceramic insulation layer withstands high temperatures and provides reliable electrical insulation. The electromagnetic coil can be connected to the current regulating device in either a star or delta connection. Star and delta connections are two basic connection methods for three-phase circuits. The line voltage of a star connection is √3 times the phase voltage, and the line current of a delta connection is √3 times the phase current. The choice can be made according to power supply conditions and power requirements. The current regulating device can use a low-voltage frequency converter. The frequency converter adjusts the frequency and amplitude of the output current, thereby adjusting the speed and intensity of the rotating magnetic field. The current regulating device is connected to the controller and receives commands from the controller to regulate the current. The circulating water pump and the cooling water tank are connected through inlet and return pipes to form a circulation loop. The circulating water pump is connected to the controller, and the controller can automatically adjust the pump speed according to the coil temperature.

[0070] The directional solidification assembly includes heating elements, cooling elements, a temperature gradient control unit, and infrared thermometers. The heating elements are arranged axially upwards along the furnace body, and the cooling elements are arranged axially downwards. Both heating and cooling elements are electrically connected to the temperature gradient control unit. Infrared thermometers are located on the upper and lower side walls of the furnace body and are signal-connected to the temperature gradient control unit. The directional solidification assembly establishes and maintains an axial temperature gradient in the melt, enabling directional advancement of the solidification interface. The heating elements, located in the upper part of the furnace body, maintain the high temperature of the upper melt, while the cooling elements, located in the lower part of the furnace body, cool the lower melt to promote preferential solidification. The temperature gradient control unit is the core control unit of the directional solidification assembly. It receives temperature signals from the infrared thermometers, compares them with the set target temperature gradient, and outputs control signals to adjust the power of the heating elements and the cooling intensity of the cooling elements. The infrared thermometers, located in the upper and lower parts, measure the temperature of the upper and lower regions of the melt in real time, providing data support for temperature gradient calculation and closed-loop control.

[0071] The heating elements of the directional solidification assembly can be either silicon molybdenum rods or induction coils, uniformly distributed along the furnace axis. Silicon molybdenum rods are resistance heating elements with advantages such as high temperature resistance, oxidation resistance, and long service life, making them suitable for heating high-temperature furnaces. Induction coils utilize the principle of electromagnetic induction to generate eddy currents within conductive materials, thus providing heating efficiency and precise temperature control. The uniform axial distribution facilitates a uniform radial temperature distribution. The cooling elements can be spiral water-cooled tubes, connected to a cooling water supply system including a water pump and a regulating valve to control the water flow rate. The spiral water-cooled tube design increases the cooling area and cooling water flow path, improving the cooling effect. The opening of the regulating valve controls the water flow rate, thereby controlling the cooling intensity. The electromagnetic stirring device works collaboratively with the directional solidification assembly through a control system, simultaneously performing electromagnetic stirring during the directional solidification process to promote mass transfer and removal of impurities.

[0072] The vacuum refining assembly includes a three-stage vacuum pump system, vacuum piping, a vacuum monitoring device, solenoid valves, and an inert gas interface. The three-stage vacuum pump system comprises a mechanical pump, a Roots pump, and a diffusion pump connected in series. One end of the vacuum piping connects to the top of the furnace body, and the other end connects to the three-stage vacuum pump system. The vacuum monitoring device and solenoid valve are both located on the vacuum piping. The inert gas interface is located on the vacuum piping, between the solenoid valve and the furnace body, and is connected to the gas supply system. The vacuum refining assembly is used to create and maintain a high vacuum environment within the furnace. The three-stage vacuum pump system uses a configuration of a mechanical pump, a Roots pump, and a diffusion pump connected in series to pump gas from atmospheric pressure to a high vacuum in stages. The vacuum piping serves as the gas flow channel, connecting the furnace body and the vacuum pump system. The vacuum monitoring device monitors the vacuum level within the furnace body in real time, providing feedback signals to the control system. The solenoid valve opens or closes the vacuum piping, isolating the furnace body from the vacuum pump when necessary. The inert gas interface is located between the solenoid valve and the furnace body, facilitating the introduction of inert gas into the furnace body after the solenoid valve is closed.

[0073] The mechanical pump, Roots pump, and diffusion pump of the vacuum refining assembly are connected in series via vacuum piping. The inlet of the mechanical pump is connected to the outlet of the Roots pump, and the inlet of the Roots pump is connected to the outlet of the diffusion pump. The inlet of the diffusion pump is connected to the furnace body via a vacuum pipe. This series configuration ensures that gas is discharged sequentially through the diffusion pump, Roots pump, and mechanical pump. Each pump operates within its effective working pressure range, collectively achieving a high vacuum. The mechanical pump, Roots pump, and diffusion pump are each connected to a controller, which controls the start and stop sequence of each pump. The start sequence should follow the principle of starting from the high-pressure stage to the low-pressure stage, i.e., start the mechanical pump first, start the Roots pump after the pressure decreases, and finally start the diffusion pump; the stop sequence is the reverse. A vacuum monitoring device is installed on the vacuum piping near the furnace body, and its signal output is connected to the controller. Proximity to the furnace body provides a more accurate reflection of the actual vacuum level inside the furnace. A solenoid valve is installed on the vacuum piping between the vacuum monitoring device and the diffusion pump, and its control terminal is connected to the controller. The solenoid valve is electrically controlled, providing a rapid response to the controller's opening and closing commands. The inert gas interface is located on the vacuum pipeline between the solenoid valve and the furnace body. This interface connects to the gas supply system via a pipeline. The gas supply system includes a gas cylinder, a pressure reducing valve, and a flow meter. The flow meter is connected to the controller via a signal connection. The pressure reducing valve reduces the high-pressure gas in the cylinder to a suitable working pressure, and the flow meter measures and controls the gas flow rate entering the furnace body. The vacuum refining assembly, through a three-stage series vacuum structure and an inert gas protection system, achieves low-oxygen environment control during the smelting process.

[0074] The control system includes a controller and a human-machine interface (HMI). The controller is connected to the current regulating device, temperature gradient control unit, three-stage vacuum pump system, vacuum monitoring device, and solenoid valves via signal connections. The HMI is connected to the controller. The control system is the command center of the entire purification system, responsible for the coordinated control of all components and the monitoring and adjustment of process parameters. The controller can be a programmable logic controller (PLC) or an industrial computer, with functions such as data acquisition, logical judgment, and command output. The controller is connected to each actuator and sensor via signal lines, receiving status information from the sensors and issuing control commands according to the preset control program and process parameters. The HMI is used by operators to input process parameters, start and stop each process, and monitor the system's operating status. It can be a touchscreen or industrial display combined with buttons. The HMI is connected to the controller to realize information interaction between humans and the system. Through the integrated control of the control system, functional components such as electromagnetic stirring, directional solidification, and vacuum refining work in coordination to achieve automated and precise control of the process.

[0075] Example 1: High-purity purification of silicon materials; in this example, the high-purity purification system and process of materials driven by electromagnetic stirring provided by the present invention are used to purify silicon materials to obtain solar-grade high-purity silicon products. The specific implementation process is as follows:

[0076] S1 Raw material pretreatment and addition. In step S11, the metallurgical-grade silicon raw material is put into a jaw crusher and crushed to a particle size d = 8 mm. After crushing, it is screened and classified using 8 mm and 6 mm standard sieves to obtain silicon particles with uniform particle sizes. In step S12, the crushed silicon particles are put into an ultrasonic cleaning tank, and a sodium hydroxide solution with a mass fraction of 3% is added as the cleaning solution. The ultrasonic cleaning time is 20 min, the ultrasonic frequency is 30 kHz, and the ultrasonic power density is 0.4 W / cm². After cleaning, it is rinsed 3 times with deionized water. In step S13, the cleaned silicon particles are drained and placed in an electrothermal blast drying oven. The drying temperature is set at 130 °C, and the drying time is 2 h. It is turned over every 30 min to ensure uniform heating. In step S14, the dried silicon raw material is weighed as 45 kg, the effective volume V of the furnace body = 0.5 m 3 , the bulk density ρ of the silicon raw material = 1350 kg / m 3 , and the feeding amount m = ρV × 25% = 168.75 kg is calculated according to the filling ratio of 25%. Actually adding 45 kg meets the requirements. In step S15, the top cover plate of the furnace body is closed, and it is checked that the isolation door of the discharge port is in the closed state to complete the raw material filling. S2 Vacuum environment construction; in step S21, the solenoid valve of the vacuum pipeline is opened, and a rotary vane mechanical pump with a pumping speed of 200 m 3 / h is started to pump vacuum. Observe the display value of the resistance vacuum gauge. When the vacuum degree reaches P1 = 8 × 10² Pa, the mechanical pump is stopped. This process takes about 15 min. In step S22, a roots pump with a pumping speed of 1200 m 3 / h is started to continue pumping vacuum. When the vacuum degree reaches P2 = 5 × 10 -2 Pa, the roots pump is stopped. This process takes about 12 min. In step S23, a silicone oil diffusion pump with a pumping speed of 3000 L / s is started to continue pumping vacuum. When the vacuum degree reaches P3 = 3 × 10 -4 Pa, the diffusion pump is stopped. This process takes about 18 min. In step S24, the solenoid valve is closed, and the initial vacuum degree P3 = 3 × 10 -4 Pa is recorded. After standing for 30 min, the vacuum degree P4 = 3.5 × 10 -4 Pa is read again. The change amount of the vacuum degree ΔP = P4 - P3 = 5 × 10 -5 Pa is calculated. Meeting the requirement of ΔP ≤ 10 Pa, it is determined that the sealing performance is qualified. In step S25, the solenoid valve is reopened, and the diffusion pump is started to maintain the vacuum degree at 3 × 10 -4Pa level. S3 Melt heating and electromagnetic stirring; In step S31, start the silicon molybdenum rod heating element, set the heating rate to 8 °C / min, and gradually increase the heating power from 0 to 80 kW. In step S32, record the temperature value every 8 minutes through an infrared thermometer and draw a heating curve. In step S33, when the temperature reaches the melting temperature Tm = 1450 °C, stabilize the heating power and keep the temperature stable for 15 minutes to ensure that the silicon raw material is completely melted. In step S34, start the electromagnetic stirring device, set the stirring current I = 420 A, the electromagnetic coil is connected in a star connection mode, generate a rotating magnetic field intensity of 0.05 T, and a frequency of 100 Hz. In step S35, keep the stirring running for 1 h. Through the observation window, it is observed that the melt shows uniform rotational flow, the flow velocity is about 0.2 m / s, and there is no local static area, and it is determined that the stirring is sufficient. S4 Directional solidification purification; In step S41, start the silicon molybdenum rod heating element of the directional solidification component, set the heating power P1 = 75 kW, and continuously heat the upper region of the melt. In step S42, start the spiral water-cooled pipe cooling element, adjust the cooling water flow velocity v = 1.2 m / s, and the cooling water temperature is 20 °C. In step S43, the upper infrared thermometer measures the temperature T1 = 1460 °C, the lower infrared thermometer measures the temperature T2 = 1310 °C, the axial distance between the upper and lower temperature measurement points L = 20 cm, and calculate the temperature gradient G = (1460 - 1310) / 20 = 7.5 °C / cm. In step S44, set the target temperature gradient G0 = 12 °C / cm, the measured G < G0, and increase the heating power to 85 kW and reduce the cooling water flow velocity to 1.0 m / s through the temperature gradient control unit. After adjustment, the temperature gradient reaches 12 °C / cm. In step S45, use ultrasonic detection to determine the position of the solid-liquid interface and record the interface movement speed as 1.5 mm / min. In step S46, keep the vacuum pump running and the electromagnetic stirring running, and the solidification time is 5 h until the silicon melt is completely solidified. S5 Product removal; In step S51, turn off the current adjustment device of the electromagnetic stirring device and cut off the 420 A current. In step S52, close the solenoid valve of the vacuum pipeline and stop the diffusion pump. In step S53, fill the furnace with argon with a purity of 99.999%, control the filling rate to 20 L / min, and fill until the furnace pressure reaches 0.10 MPa. In step S54, stop the heating and cooling elements and naturally cool to 200 °C. In step S55, open the isolation door of the discharge port, use a graphite fixture to take out the purified silicon ingot, and transfer it to the cooling area to continue cooling to room temperature. In step S56, cut a sample from the lower part of the silicon ingot, and use an inductively coupled plasma mass spectrometer (ICP-MS) to detect the impurity content. The detection result shows that the silicon purity reaches 99.9999%, meeting the requirements of solar-grade silicon.

[0077] Comparative Example 1: Directional solidification purification without electromagnetic stirring; Comparative Example 1 uses the same raw materials and equipment, but the electromagnetic stirring device is not activated during the purification process, and purification is carried out solely by directional solidification. In specific operation, steps S1 and S2 are exactly the same as in Example 1. In the melt heating stage (S3), only the heating element is activated to heat the silicon raw material to 1450℃ to completely melt it; the electromagnetic stirring device is not activated, and the melt is in a static or natural convection state. The temperature gradient control in the directional solidification purification stage (S4) is the same as in Example 1, with a target temperature gradient G0 = 12℃ / cm and a solidification time of 5 hours. The product removal step (S5) is the same as in Example 1.

[0078] Comparative Example 2: Electromagnetic stirring purification by atmospheric pressure melting; Comparative Example 2 uses the same raw materials and equipment, but the purification process is carried out under atmospheric pressure air atmosphere, without constructing a vacuum environment. S1 Raw material pretreatment and addition steps are the same as in Example 1. S2 Vacuum environment construction step is skipped, and subsequent operations are carried out directly under atmospheric pressure. S3 Melt heating and electromagnetic stirring stage: The heating element is activated to heat the silicon raw material to 1450°C, and the electromagnetic stirring device is activated with a stirring current of I=420A, maintaining stirring for 1 hour. S4 Directional solidification purification stage: The target temperature gradient G0=12°C / cm is set, and the solidification time is 5 hours. S5 When removing the product, no inert gas is introduced; the product is directly cooled in air and then removed.

[0079] Comparative Example 3: Purification using the traditional crucible method; Comparative Example 3 employed the traditional graphite crucible directional solidification method for purification. The crushed and cleaned silicon raw material was loaded into a graphite crucible, which was then placed inside a vacuum induction furnace. A vacuum was evacuated to a pressure of 3 × 10⁻⁶. -4 After Pa, induction heating is initiated to melt the silicon raw material at 1450℃, and the temperature is held for 30 minutes to ensure uniform melt distribution. Subsequently, a temperature gradient is established by controlling the power of the induction coil, with the upper temperature at 1460℃ and the lower temperature at 1310℃, a temperature gradient of approximately 12℃ / cm, and a solidification time of 5 hours. After solidification, argon gas is introduced to atmospheric pressure, and the silicon ingot is removed after cooling. In this method, the melt is in direct contact with the graphite crucible, and electromagnetic stirring and a water-cooled shell structure are not used.

[0080] Comparative Experiments: The following comparative experiments were conducted to primarily examine key indicators such as product purity, impurity distribution uniformity, oxygen content, and production efficiency. The experimental methods are as follows:

[0081] Product purity determination: The content of major metallic impurity elements (Fe, Al, Cu, Ca, Mg, Cr, Ni, Zn) in silicon ingots was determined using inductively coupled plasma mass spectrometry (ICP-MS) according to GB / T30067-2013 "Solar Grade Polycrystalline Silicon". Approximately 5g of sample was cut from the high-purity region at the bottom of the silicon ingot (10-20cm from the bottom), dissolved in acid, and diluted to an appropriate concentration for measurement. Each sample was measured three times, and the average value was used to calculate the silicon purity.

[0082] Evaluation of impurity distribution uniformity: Eight samples were taken from the bottom to the top of the silicon ingot along its axial direction, with one sample taken every 5 cm. The iron content in each sample was then determined. The uniformity of impurity distribution was evaluated using standard deviation and coefficient of variation; a smaller standard deviation indicates a more uniform distribution.

[0083] Oxygen content determination: The oxygen content in silicon ingots was determined by infrared absorption spectroscopy according to ASTM F121-2015 standard. The sample was prepared into a polished sheet with a thickness of approximately 2 mm, and the absorption peak intensity at 1107 cm⁻¹ was measured using a Fourier transform infrared spectrometer. The oxygen concentration was calculated based on the calibration curve, with the unit being ppm.

[0084] Effective purification rate calculation: The effective purification rate is defined as the percentage of the mass of the high-purity region (impurity content below a set threshold) in the silicon ingot relative to the total mass. For solar-grade silicon, the set threshold is a total impurity content ≤ 10 ppmw (parts per million by mass). The impurity content at each location along the silicon ingot's axial direction is measured, the length of the region meeting the requirements is calculated, and the effective purification rate is calculated based on the mass ratio.

[0085] Production efficiency assessment: Energy consumption per unit time and per unit mass is used as the production efficiency index. The total energy consumption of the entire purification process (including all electrical equipment such as heating, stirring, and vacuum pumps) is recorded, divided by the product mass and purification time to obtain the unit energy consumption index, expressed in kWh / (kg·h). The experimental results are shown in the table below:

[0086] Table 1 Comparison of silicon purity obtained by different methods

[0087]

[0088] Table 1 shows that Example 1 yielded the highest silicon purity, reaching 99.99996%, with a total impurity content of only 0.40 ppmw. In Comparative Example 1, due to the lack of electromagnetic stirring, the impurities in the melt were unevenly distributed, and some impurities failed to be effectively removed during solidification, resulting in a total impurity content of 1.60 ppmw and a purity reduction to 99.99984%. Comparative Example 2, smelted under atmospheric pressure, experienced severe oxidation of the silicon melt, with oxide inclusions becoming the main source of impurities. Simultaneously, nitrogen from the air dissolved into the melt, resulting in a total impurity content as high as 8.00 ppmw and a purity of only 99.9992%. Comparative Example 3 used a graphite crucible, where the graphite material dissolved into the melt, introducing carbon impurities. Additionally, ash impurities from the crucible material also contaminated the melt, resulting in a total impurity content of 6.00 ppmw and a purity of 99.9994%.

[0089] As shown in Table 1, electromagnetic stirring drives forced convection of the melt by generating a rotating magnetic field, which uniformly disperses impurities in the melt. During directional solidification, the impurity-rich layer at the solidification interface front is destroyed by convection, allowing impurities to migrate to the liquid phase region in a timely manner without being captured by the solid phase, thereby improving impurity removal efficiency. The vacuum environment eliminates oxygen and nitrogen contamination of the melt and prevents the formation of oxide and nitride inclusions. The water-cooled shell structure avoids direct contact between the melt and the crucible material, completely eliminating secondary contamination introduced by crucible dissolution.

[0090] Table 2 Comparison of impurity distribution uniformity

[0091]

[0092] Table 2 shows that the standard deviation of iron content distribution along the silicon ingot axis in Example 1 is 0.36 ppmw, while the standard deviation of Comparative Example 1 reaches 2.08 ppmw, which is 5.8 times that of Example 1. Although the coefficients of variation of the two are similar, the absolute impurity concentration of Example 1 is much lower than that of Comparative Example 1. Along the axial direction, the impurity content shows a trend of gradually increasing from the bottom to the top, which is consistent with the impurity distribution law of directional solidification, that is, impurities are repelled into the liquid phase during solidification and eventually accumulate at the top. The impurity concentration gradient of Example 1 is relatively gentle, with the iron content in the lower region (0-25 cm) maintained at a low level of 0.14-0.22 ppmw, accounting for 62.5% of the total length of the silicon ingot. The impurity concentration gradient of Comparative Example 1 is steep, with the iron content in the lower region being 0.35-1.15 ppmw, which is significantly higher than that of Example 1. As can be seen from Table 2, in Comparative Example 1 without electromagnetic stirring, the melt mainly relies on natural convection caused by the temperature gradient for mass transfer. The natural convection speed is slow and there are dead zones in the flow, resulting in large differences in impurity concentration in different regions. As the solidification interface advances, high-concentration impurities in localized areas are captured by the solid phase before they can diffuse, resulting in uneven impurity distribution. The forced convection velocity generated by electromagnetic stirring reaches 0.2 m / s, far exceeding the natural convection velocity. This forced convection rapidly mixes the various parts of the melt, eliminating concentration gradients and ensuring a uniform impurity distribution in the melt before solidification. Continuous electromagnetic stirring during solidification continuously removes impurities enriched at the interface front, maintaining a flat concentration distribution at the interface and preventing interface instability and impurity capture caused by supercooling. Therefore, Example 1 achieved a more uniform impurity distribution and a larger proportion of high-purity zones.

[0093] Table 3 Comparison of Oxygen Content

[0094]

[0095] Table 3 shows that Example 1 had the lowest oxygen content, at only 8.5 ppma. Comparative Example 1 had an oxygen content of 12.3 ppma, 44.7% higher than Example 1. Comparative Example 2, smelted in atmospheric air, had an oxygen content as high as 156.0 ppma, 18.4 times that of Example 1. Comparative Example 3 had an oxygen content of 15.8 ppma, slightly higher than Comparative Example 1. Oxygen content is a key indicator affecting the performance of silicon materials. Excessive oxygen content can lead to oxygen precipitation in the silicon lattice, reducing minority carrier lifetime and affecting the photoelectric conversion efficiency of solar cells. A vacuum environment is the core technology for controlling oxygen content. In Example 1, the vacuum level reached 3 × 10⁻⁶. -4 Pa corresponds to an oxygen partial pressure below 1 × 10⁻⁶. -6 At such a low oxygen partial pressure, the oxidation reaction of the silicon melt is suppressed to an extremely low level, and the dissolved oxygen content in the melt is very small. Comparative Example 2 was smelted in atmospheric air, where the oxygen partial pressure is approximately 2 × 10⁻⁶. 4 Pa is 10 Pa in a vacuum environment. 10 In Example 1, the surface of the silicon melt underwent severe oxidation to form silicon dioxide, and some of the oxides dissolved into the melt, leading to a sharp increase in oxygen content. Although Comparative Examples 1 and 3 also employed a vacuum environment, their oxygen content was still slightly higher than in Example 1. This is because electromagnetic stirring promoted the migration of dissolved oxygen from the melt interior to the surface and its removal through the vacuum system, accelerating the deoxidation process. In a static melt, dissolved oxygen migration mainly relies on diffusion, which is slow, while forced convection significantly accelerates the mass transfer rate. Furthermore, electromagnetic stirring also promoted the floating and separation of oxide inclusions in the melt, further reducing the oxygen content.

[0096] Table 4 Comparison of Effective Purification Rate and Energy Consumption

[0097]

[0098] Table 4 shows that the effective purification rate of Example 1 reached 70.0%, meaning that 70% of the mass area in the silicon ingot met the solar-grade purity requirement (total impurities ≤10ppmw). The effective purification rate of Comparative Example 1 was only 45.0%, and the effective purification rates of Comparative Examples 2 and 3 were even lower, at 12.5% ​​and 37.5%, respectively. From an energy consumption perspective, the unit energy consumption of Example 1 was 1.52 kWh / (kg·h), slightly higher than Comparative Examples 1 and 2. However, considering the effective purification rate, Example 1 has the best overall economic efficiency. The effective purification rate directly relates to the economic value of the product and the material utilization rate. During the directional solidification purification process, impurities gradually accumulate from the bottom to the top. Only areas with impurity content below the threshold can be used as qualified products; impurity-rich areas need to be removed or remelted. In Example 1, electromagnetic stirring resulted in a uniform distribution of impurities in the melt, leading to extremely low impurity content in the solid phase during the initial solidification stage. As solidification progressed, the repelled impurities gradually accumulated in the liquid phase. However, due to the initially uniform distribution, a long solidification distance was required for impurities to accumulate to excessive concentrations, resulting in a longer high-purity zone. In Comparative Example 1, the uneven distribution of impurities in the melt caused localized high-concentration areas to exceed the impurity limit in the solid phase early in solidification, shortening the length of the high-purity zone. In Comparative Example 2, severe oxidation contamination resulted in almost the entire silicon ingot exceeding the impurity limit, leading to an extremely low effective purification rate. In Comparative Example 3, crucible contamination caused the impurity content in the upper and middle regions to gradually exceed the limit.

[0099] Regarding energy consumption, Example 1 increased the power consumption of the electromagnetic stirring device by approximately 60kW × 1h = 60kWh, resulting in a total energy consumption increase of approximately 14% compared to Comparative Example 1. However, Example 1 achieved a 55.6% higher effective purification rate than Comparative Example 1, and the energy consumption per unit of qualified product was actually reduced by 26.3%. Although Comparative Example 2 omitted the energy consumption of the vacuum system, the product was almost unqualified and had no practical value. This invention, by appropriately increasing the energy consumption of electromagnetic stirring, achieves a significant improvement in purification effect and material utilization.

[0100] Table 5. Purification effect under different stirring currents (based on parameters varying in Example 1)

[0101]

[0102] Table 5 shows the effect of electromagnetic stirring current on the purification effect. When the stirring current increases from 0 to 420 A, the magnetic field strength increases from 0 to 0.05 T, and the melt flow rate increases from 0.02 m / s (natural convection) to 0.20 m / s, resulting in a continuous improvement in silicon purity and effective purification rate. When the current continues to increase to 520 A, although the flow rate further increases to 0.25 m / s, the purity and effective purification rate decrease slightly. At lower currents (240-340 A), the magnetic field strength and flow rate are low, convection is insufficient, melt mixing is limited, impurity homogenization is inadequate, and the improvement in purification effect is limited. When the current increases to 420 A, the flow rate reaches 0.20 m / s, at which point the convection intensity is sufficient to achieve thorough mixing of the melt and uniform dispersion of impurities within the stirring time, achieving the best purification effect. When the current is too high (520A), excessive convection may intensify surface disturbance of the melt, increasing the risk of gas entrainment and surface oxidation. Simultaneously, strong turbulence may disrupt the stability of the solidification interface, leading to a complex interface morphology, localized supercooling, and impurity trapping, thus reducing the purification effect. Furthermore, excessive current increases the heating of the electromagnetic coil, requiring stronger cooling and increasing energy consumption. Therefore, in Example 1, this invention selected 420A as the optimal stirring current for silicon purification, demonstrating the scientific nature of process parameter optimization.

[0103] Example 1 utilizes the synergistic combination of three core technologies: electromagnetic stirring, vacuum environment, and water-cooled shell, to obtain solar-grade high-purity silicon with a purity of 99.99996%, a total impurity content of only 0.40 ppmw, an oxygen content of 8.5 ppma, and an effective purification rate of 70.0%. All indicators are significantly superior to the comparative example using traditional methods. Electromagnetic stirring drives the melt to undergo forced convection through a rotating magnetic field, achieving uniform dispersion of impurities and breaking down the impurity enrichment layer at the interface, thus improving the impurity removal efficiency during the directional solidification process. The vacuum environment eliminates the contamination of the melt by oxygen and nitrogen in the air, inhibits oxidation and nitriding reactions, and reduces oxygen and nitrogen content. The water-cooled shell structure achieves zero contact between the melt and the crucible material, completely eliminating secondary pollution sources introduced by crucible dissolution.

[0104] Example 2: Recycling and purification of aluminum materials; This example uses the electromagnetic stirring-driven high-purity material purification system and process provided by this invention to recycle and purify waste aluminum alloys to obtain high-purity recycled aluminum products; The implementation process is as follows:

[0105] S1 Raw Material Pretreatment and Feeding: In step S11, the scrap aluminum alloy is fed into a hammer crusher and crushed to a particle size d=6mm. In step S12, the crushed aluminum particles are placed in an ultrasonic cleaning tank, with ethanol solution added as the cleaning fluid. The ultrasonic cleaning time is 15 minutes, and the ultrasonic frequency is 25kHz. In step S13, the cleaned aluminum particles are placed in a drying oven, with the drying temperature set at 110℃ and the drying time at 1.5 hours. In step S14, the dried aluminum raw material weighs 38kg, and the effective furnace volume V=0.5m³. 3 The bulk density of aluminum raw material is ρ = 900 kg / m³. 3 The material addition was calculated based on a 20% filling ratio, and 38 kg was actually added, meeting the requirements. In step S15, the top cover of the furnace was closed, completing the raw material loading. Step S2 establishes the vacuum environment; steps S21 to S25 are the same as in Example 1, with the final vacuum degree reaching P3 = 2.8 × 10⁻⁶. -4 Pa, the change in vacuum degree after standing for 30 minutes is ΔP = 4 × 10 -5 Pa, sealing is qualified. S3 Melt heating and electromagnetic stirring; In step S31, the induction coil heating element is started, the heating rate is set to 12℃ / min, and the heating power is gradually increased from 0 to 50kW. In step S32, the temperature value is recorded every 6 minutes using an infrared thermometer. In step S33, when the temperature reaches the melting temperature Tm=660℃, the heating power is stabilized, and the temperature is kept stable for 12 minutes to ensure that the aluminum raw material is completely melted. In step S34, the electromagnetic stirring device is started, the stirring current is set to I=280A, the electromagnetic coil adopts a delta connection, and a rotating magnetic field strength of 0.04T and a frequency of 80Hz is generated. In step S35, the stirring is maintained for 0.8h, and the melt is observed to exhibit uniform rotating flow through the observation window. S4 Directional solidification and purification; In step S41, the heating element is started, and the heating power is set to P1=45kW. In step S42, the cooling water flow rate is adjusted to v=1.5m / s. In step S43, the upper temperature T1 = 670℃, the lower temperature T2 = 540℃, and the axial distance L = 18cm. The calculated temperature gradient G = (670-540) / 18 = 7.2℃ / cm. In step S44, the target temperature gradient G0 = 6.5℃ / cm was set. The measured G > G0, so the heating power was reduced to 40kW and the cooling water flow rate was increased to 1.7m / s. After adjustment, the temperature gradient reached 6.5℃ / cm. In step S45, the solid-liquid interface movement speed was recorded as 2.0mm / min. In step S46, the solidification time was 4h. The product was removed after step S5. Steps S51 to S56 were similar to Example 1, involving the introduction of 99.999% pure argon gas and cooling to 150℃ before removing the aluminum ingot. ICP-MS testing showed that the aluminum purity reached 99.85%, with the main impurities being Fe content of 0.08%, Si content of 0.05%, and Cu content of 0.02%, meeting the A00 grade standard requirements for recycled aluminum.

[0106] Comparative Example 4: Aluminum recovery and purification without a vacuum environment; Comparative Example 4 used the same aluminum raw materials and equipment, but purification was carried out under a normal pressure nitrogen protective atmosphere without constructing a vacuum environment. Step S1 was the same. Step S2, the construction of the vacuum environment, was skipped, and nitrogen gas with a purity of 99.9% was introduced into the furnace to a pressure of 0.05 MPa before subsequent operations. The temperature and current parameters for steps S3, S4, and S5 were the same as in Example 2, but the entire process was carried out under a nitrogen atmosphere.

[0107] Comparative Example 5: Rapidly Cooled Aluminum Recovery; Comparative Example 5 used the same raw materials and vacuum electromagnetic stirring conditions, but employed rapid cooling instead of directional solidification. Steps S1 to S3 were the same as in Example 2. In stage S4, no temperature gradient was established; instead, heating was stopped after the melt was stirred evenly, and a full-power water cooling system was activated to rapidly cool the entire furnace body. The cooling water flow rate was v = 3.0 m / s, and the solidification time was approximately 1.5 h.

[0108] Comparative experiments were conducted between Example 2 and Comparative Examples 4 and 5, and the experimental results are as follows:

[0109] Table 6 Comparison of Aluminum Purity from Different Methods

[0110]

[0111] As shown in Table 6, Example 2 yielded the highest aluminum purity, reaching 99.85%, which meets the A00 grade standard for recycled aluminum (≥99.70%). Comparative Example 4, purified under a normal pressure nitrogen atmosphere, although nitrogen provides some protection, only achieved a nitrogen purity of 99.9%, with a residual oxygen content of approximately 0.1%. This still resulted in oxidation at the aluminum melt temperature of 660°C, forming alumina inclusions. The density of alumina is 3.95 g / cm³. 3 It is greater than the density of molten aluminum (approximately 2.38 g / cm³). 3 Oxide inclusions settle in the melt and are difficult to remove, becoming a source of impurity contamination. Furthermore, nitrogen gas dissolves into the molten aluminum in small amounts at high temperatures, increasing the nitrogen content. Therefore, the total impurity content of Comparative Example 4 reached 0.50%, and the purity dropped to 99.50%, only meeting the ADC12 grade cast aluminum alloy standard.

[0112] Although Comparative Example 5 employed vacuum and electromagnetic stirring, the rapid cooling method resulted in an excessively fast solidification rate of approximately 10 mm / min, five times that of Example 2. During rapid solidification, the solid-liquid interface advanced rapidly, and impurities repelled at the interface front did not have time to migrate to the liquid phase region far from the interface via diffusion and convection. A large number of impurities were captured by the solidification front and entered the solid phase, leading to a significant increase in the impurity content of the product. While rapid cooling shortened the solidification time, it sacrificed purification efficiency, resulting in a total impurity content of 0.75% and a purity of only 99.25%, meeting the ADC10 standard. A vacuum environment, by eliminating oxygen contamination and preventing oxidation reactions, is a necessary condition for obtaining high-purity aluminum. Directional solidification, by controlling a slower solidification rate, allows sufficient time for impurities to undergo mass transfer and separation, effectively removing impurities by utilizing the solute redistribution effect at the solid-liquid interface. Electromagnetic stirring accelerated the mass transfer rate of impurities during this process, further improving the impurity removal efficiency.

[0113] Table 7 Axial distribution of impurities in aluminum ingots (Example 2 and Comparative Example 5)

[0114]

[0115] Table 7 shows that the iron content in Example 2 exhibits a clear gradient distribution along the axial direction, gradually increasing from 0.06% at the bottom to 0.65% at the top, with a standard deviation of 0.19%. This indicates that impurities effectively migrate and accumulate from the bottom to the top during directional solidification. In Comparative Example 5, the iron content is more uniformly distributed along the axial direction, ranging from 0.18% to 0.38%, with a standard deviation of only 0.06%. This suggests that impurities do not have time to migrate axially during rapid cooling and are fixed in their respective positions. Directional solidification establishes an axial temperature gradient, causing the solidification interface to advance unidirectionally. Solute redistribution occurs at the interface, with the impurity element distribution coefficient k < 1 (the distribution coefficient of iron in aluminum is approximately 0.03). This means that the impurity concentration in the solid phase is only 3% of that in the liquid phase, with 97% of the impurities being repelled into the liquid phase. As solidification progresses, the liquid phase volume gradually decreases, and the impurity concentration gradually increases, with the final solidified top region becoming an impurity-rich area. In Example 2, the iron content in the lower 75% (0-24cm) region is ≤0.22%. This region, accounting for approximately 75% of the total mass, can be used as a high-purity product, demonstrating a high effective purification rate. In Comparative Example 5, due to rapid cooling, the entire aluminum ingot solidifies simultaneously, lacking a clear solidification interface and solute redistribution process. Impurities essentially maintain their original distribution, making purification and separation impossible. The impurity content of the entire aluminum ingot is high and uniform.

[0116] Table 8. Comparison of Efficiency and Economy of Aluminum Material Recycling and Refining

[0117]

[0118] Table 8 compares the three methods from the perspectives of production efficiency and economic benefits. Comparative Example 5, while having the shortest solidification time and lowest energy consumption, seemingly the most efficient, resulted in poor product quality, an effective purification rate of only 30%, and the lowest product value. Comparative Example 4 had 10.5% lower energy consumption than Example 2, but its product grade and effective purification rate were significantly lower, with a product value only 57% of Example 2. Example 2, despite having the highest energy consumption, obtained the highest grade A00 recycled aluminum, achieving an effective purification rate of 75% and high product added value. This invention, by appropriately extending the purification time and increasing necessary energy input, achieves a significant improvement in product purity and a leap in product grade, realizing the transformation of waste aluminum alloys from low-value recycling to high-value resource regeneration. A00-grade recycled aluminum can replace virgin aluminum in high-end fields such as aerospace and electronics, while ADC-grade aluminum alloys can only be used for general castings; their market value and application prospects differ significantly. Therefore, the economic and social benefits of this invention are both substantial.

[0119] Table 9. Effects of different temperature gradients on aluminum purification efficiency.

[0120]

[0121] Table 9 shows the data investigating the effect of temperature gradient on the purification effect of aluminum materials. When the temperature gradient increased from 3.5℃ / cm to 6.5℃ / cm, the solidification rate increased from 0.8 mm / min to 2.0 mm / min, and the aluminum purity and effective purification rate continued to improve, reaching the optimal values ​​of 99.85% and 75.0% at 6.5℃ / cm. When the temperature gradient continued to increase to 8.5℃ / cm and 10.5℃ / cm, although the solidification rate further increased to 3.2 mm / min and 4.5 mm / min, the purity and effective purification rate decreased. The temperature gradient determines the steepness of the temperature distribution at the solid-liquid interface. A larger temperature gradient is conducive to the formation of a flat and stable solidification interface, preventing cellular growth and dendrite growth caused by unstable interface morphology. A flat interface uniformly repels impurities, preventing impurities from being trapped in the dendrite interstices. However, the temperature gradient also affects the solidification rate; under the same heat extraction conditions, the larger the temperature gradient, the faster the interface propagation speed.

[0122] At lower temperature gradients (3.5-5.0℃ / cm), the solidification rate is slow. Although this provides sufficient diffusion time for impurities, the interface morphology is prone to instability, the temperature distribution in the liquid phase is gradual, and the supercooled region expands, easily forming cellular or dendritic morphologies. Impurities are captured between the dendrites, reducing the purification effect. At a moderate temperature gradient (6.5℃ / cm), the solidification rate is moderate, maintaining a flat interface while providing sufficient diffusion time for impurities. The forced convection from electromagnetic stirring further accelerates the migration of impurities from the interface front to the bulk liquid phase, achieving the best impurity removal effect. At excessively high temperature gradients (8.5-10.5℃ / cm), the solidification rate is too fast, exceeding the rate of impurity diffusion and convection mass transfer. The impurity-rich layer at the interface front is captured by the solidification front before it can dissipate, reducing the purification effect. This invention sets a target temperature gradient G0 = 5-8℃ / cm for aluminum material purification. In Example 2, 6.5℃ / cm was selected as the preferred value, achieving fine control of process parameters.

[0123] Example 3: Continuous Purification in Multiple Batches This example verifies the stability and reliability of the system of the present invention under continuous production conditions. Using the same process conditions as in Example 1, five batches of silicon material were continuously purified, with 45 kg of raw material per batch. Key process parameters and product quality indicators for each batch were recorded.

[0124] Table 10 shows the stability data from multiple batches of continuous purification.

[0125]

[0126] Table 10 shows that during the five batches of continuous purification, the coefficients of variation of the main process parameters were all less than 3%, the coefficient of variation of product silicon purity was only 0.001%, and the coefficient of variation of effective purification rate was 0.51%, indicating that the system of this invention has excellent process stability and repeatability. Key parameters such as vacuum degree, temperature, and current remained highly stable under the adjustment of the automatic control system, and the quality consistency of each batch of products was good. The control system of this invention integrates a PLC controller, a temperature gradient control unit, and a current regulation device to precisely control each process step, realizing the automation and standardization of the purification process. The long-term stable operation capability of the system provides a reliable guarantee for industrial applications and meets the requirements of large-scale continuous production. Multiple batch experiments also verified the durability of key components of the equipment. Electromagnetic coils, heating elements, vacuum systems, etc., maintained good performance after 25 hours of continuous operation, without failure or performance degradation, proving the reliability of the system design.

[0127] Supplementary experiments in Examples 2 and 3 and Comparative Examples 4 and 5 show that the present invention is applicable to the high-purity purification of silicon materials and the recycling and purification of other materials such as aluminum materials. By adjusting process parameters such as temperature gradient and stirring current, it can adapt to the physical properties and purification requirements of different materials.

[0128] This invention organically integrates three technologies: electromagnetic stirring, vacuum refining, and directional solidification. Electromagnetic stirring solves the problem of uneven distribution of impurities in the melt, creating ideal initial conditions for directional solidification. The vacuum environment eliminates gaseous contamination sources and reduces the content of gaseous impurities such as oxygen and nitrogen. Directional solidification utilizes the solute redistribution effect to achieve effective separation of impurities. The water-cooled shell structure eliminates crucible contamination sources. These four technologies address different impurity sources and contamination pathways, forming a comprehensive purification technology system. Although this invention increases the equipment investment and operating costs of the electromagnetic stirring device and vacuum system, it significantly improves product purity and effective purification rate, greatly enhancing product added value and material utilization. Through the vacuum environment and inert gas protection, this invention avoids harmful gas emissions, making the production process clean and environmentally friendly. In the field of resource recycling, this technology can purify waste metal materials to near-virgin material purity levels, achieving high-quality resource recycling, reducing the need for primary mineral resource extraction, and aligning with sustainable development strategies.

[0129] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-purity material purification process based on electromagnetic stirring, characterized in that, A high-purity purification system for materials based on electromagnetic stirring drive, comprising a furnace body, an electromagnetic stirring device, a directional solidification component, a vacuum refining component and a control system; the furnace body adopts a water-cooled shell structure and is provided with an anti-sticking coating, accommodating the melt and realizing the isolation between the melt and the shell material; the electromagnetic stirring device is arranged on the periphery of the furnace body, generating a rotating magnetic field to drive the melt to generate forced convection, promoting the uniform dispersion of impurities in the melt and destroying the impurity enrichment layer at the front of the solidification interface; the directional solidification component includes heating elements and cooling elements respectively arranged at the upper and lower parts of the axial direction of the furnace body, and a temperature gradient control unit for real-time monitoring of temperature and closed-loop regulation, making the solidification interface advance unidirectionally by establishing an axial temperature gradient, and using the solute redistribution effect to exclude impurities to the liquid phase region; the vacuum refining component adopts a multi-stage series vacuum pump system connected to the furnace body, establishing a high-vacuum environment to eliminate gas-phase pollution sources and inhibit the oxidation reaction of the melt, and at the same time is provided with an inert gas interface for atmosphere protection when the product is taken out; the control system is signal-connected to the electromagnetic stirring device, the directional solidification component and the vacuum refining component, coordinating and controlling the working states and process parameters of each component, and realizing the linkage regulation of the three process links of electromagnetic stirring, directional solidification and vacuum refining; Including the following steps: S1: Pretreatment and addition of raw materials. The metal raw materials to be purified are crushed to a specified particle size, and the surface contaminants are removed by ultrasonic cleaning or chemical cleaning. After drying, they are weighed and added to the furnace body; S2: Construction of vacuum environment. The mechanical pump, roots pump and diffusion pump are started in sequence to pump the inside of the furnace body to a high-vacuum state. The vacuum pump is closed and the vacuum degree change is detected by statically standing. After determining that the sealing performance is qualified, the vacuum pump is restarted to maintain the vacuum; The construction of the S2 vacuum environment includes the following specific steps: S21: Open the solenoid valve on the vacuum pipeline, start the mechanical pump to pump vacuum, observe the display value of the vacuum degree monitoring device, and stop the mechanical pump when the vacuum degree reaches less than or equal to 800 Pa, realizing the preliminary decompression inside the furnace body; S22: Start the roots pump to continue pumping vacuum, and stop the roots pump when the vacuum degree reaches less than or equal to 5 Pa, realizing medium vacuum inside the furnace body; S23: Start the diffusion pump to continue evacuating the vacuum until the vacuum level reaches less than or equal to 1×10⁻⁶. -3 The diffusion pump is stopped at a certain time to achieve a high vacuum environment inside the furnace. S24: Close the solenoid valve, record the vacuum degree at this time, read the vacuum degree again after standing for 20 to 40 minutes, calculate the change amount of the vacuum degree, and determine that the sealing performance is qualified when the change amount of the vacuum degree is less than or equal to 10 Pa, realizing the sealing performance detection; S25: Reopen the solenoid valve, start the diffusion pump to maintain the vacuum degree, complete the establishment of the vacuum environment, and provide a low-oxygen environment for melting; S3: Melting heating and electromagnetic stirring. Start the heating element to heat the raw materials, monitor the temperature through an infrared thermometer, start the electromagnetic stirring device after reaching the melting temperature, adjust the current to make the electromagnetic coil generate a rotating magnetic field, and continuously stir until the impurities in the melt are evenly distributed; S4: Directional solidification purification. The heating element is activated to heat the upper region of the melt, while the cooling element is activated to cool the lower region. The upper and lower temperatures are measured separately using an infrared thermometer. The power of the heating element and the water flow rate of the cooling element are adjusted to achieve the set temperature difference. The upward movement speed of the solidification interface is observed and controlled, maintaining vacuum and stirring until solidification is complete. S4 directional solidification purification includes the following specific steps: S41: Activate the heating element of the directional solidification component and set the heating element power to 20 kW to 100 kW; the heating element continuously heats the upper region of the melt to maintain a high temperature in the upper part; S42: Simultaneously activate the cooling elements, open the cooling water valve, and adjust the water flow rate to 0.5 m / s to 2 m / s; the cooling water cools the lower part of the melt through the water cooling pipe, thereby reducing the temperature of the lower part. S43: The temperature gradient is calculated by measuring the upper part of the furnace body with an infrared thermometer installed on the upper part of the furnace body and measuring the lower part of the furnace body with an infrared thermometer installed on the lower part of the furnace body, thus realizing the real-time calculation of the temperature gradient. S44: Set the target temperature gradient according to the type of material to be purified; compare the measured temperature gradient with the target temperature gradient; when the measured temperature gradient is less than the target temperature gradient, increase the heating power or decrease the cooling water flow rate; when the measured temperature gradient is greater than the target temperature gradient, decrease the heating power or increase the cooling water flow rate, so as to achieve precise control of the temperature gradient. S45: Observe the solidification interface of the melt, determine the position of the solid-liquid interface through the observation window or ultrasonic detection, and record the distance the solid-liquid interface moves over time. S46: Keep the vacuum pump and electromagnetic stirrer running throughout the solidification process. The solidification time is 3 to 8 hours until the melt is completely solidified, thus completing the directional solidification and purification. S5: Remove the product. After solidification, turn off the electromagnetic stirring device. Inert gas is introduced into the furnace through the inert gas interface to atmospheric pressure. After cooling, open the discharge port to remove the purified product.

2. The process according to claim 1, characterized in that, The pretreatment and addition of raw material S1 includes the following specific steps: S11: The metal raw material is fed into the crusher and crushed to a particle size of 5 mm to 10 mm; after crushing, it is screened and classified to achieve uniform particle size of the raw material. S12: Place the crushed raw material into an ultrasonic cleaning tank, add cleaning solution, and ultrasonic cleaning for 10 to 30 minutes to remove surface oil and oxide scale and achieve surface cleaning. S13: After the raw materials are washed and drained, place them in a drying oven, set the drying temperature to 100 degrees Celsius to 150 degrees Celsius, and the drying time to 1 hour to 3 hours to remove the moisture from the raw materials and achieve the drying of the raw materials; S14: Take out the dried raw materials and weigh them. Calculate the feeding amount based on the effective volume of the furnace body. The feeding amount is 10% to 30% of the effective volume of the furnace body. Add the raw materials into the furnace body according to the calculated amount to achieve quantitative feeding. S15: Close the top cover of the furnace body, check that the discharge port isolation door is closed, complete the raw material loading, and prepare for subsequent vacuum extraction.

3. The process according to claim 1, characterized in that, The S3 melt heating and electromagnetic stirring includes the following specific steps: S31: Start the heating element, set the heating rate from 5 degrees Celsius / minute to 15 degrees Celsius / minute, and gradually increase the power of the heating element; S32: Continuously monitor the temperature inside the furnace using an infrared thermometer, record the temperature value every 5 to 10 minutes, and plot the heating curve; S33: Stabilize the heating power when the temperature reaches the melting temperature. The melting temperature for silicon melt is 1420°C to 1480°C, and for aluminum melt is 650°C to 670°C. Maintain the temperature for 10 to 20 minutes to ensure that the raw materials are completely melted and realize the transformation of solid raw materials into liquid melt. S34: After the melt is completely melted, start the current regulating device of the electromagnetic stirring device and set the stirring current. The stirring current is 380 amperes to 460 amperes for silicon melt and 240 amperes to 320 amperes for aluminum melt. The current generates a rotating magnetic field through the electromagnetic coil to start the stirring of the melt. S35: Keep stirring running for 0.5 to 2 hours and observe the melt flow through the observation window. When the melt shows uniform rotating flow and no local static areas, it is determined that the stirring is sufficient and the impurities in the melt are uniformly dispersed.

4. The process according to claim 1, characterized in that, The removal of the S5 product includes the following specific steps: S51: After the melt has completely solidified, turn off the current regulating device of the electromagnetic stirring device, cut off the current of the electromagnetic coil, and stop the generation of the magnetic field; S52: Close the vacuum pipeline solenoid valve, stop the vacuum pump, and open the gas valve of the inert gas interface; S53: Introduce argon or nitrogen gas with a purity of not less than 99.999% into the furnace. Control the gas filling rate to 10 liters / minute to 30 liters / minute using a flow meter. Observe the pressure gauge. When the pressure inside the furnace reaches 0.08 MPa to 0.12 MPa, close the gas valve to achieve inert gas protection. S54: Maintain an inert gas atmosphere, stop the heating and cooling elements, and allow the product to cool naturally to 100 to 300 degrees Celsius to achieve product cooling; S55: Open the discharge port isolation door, use a high-temperature resistant tool to remove the purified product, and transfer it to the cooling area to continue cooling to room temperature; S56: Take a sample from the product, use an inductively coupled plasma mass spectrometer to detect the impurity content, confirm that the product purity meets the design requirements, complete the quality inspection, and achieve the acquisition and quality confirmation of the purified product.

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