Purified Silicon via Electromagnetic Stirring and Decanting
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Solution Overview
Problem
Current methods for purifying solid silicon metal are inefficient, often using contaminant carbon tools, are complex, costly, or difficult to implement industrially, and fail to achieve high purity grades required for new applications.
Innovation Solution
A method involving electromagnetic stirring (EMS) of liquid silicon in a crucible-lined mould for unidirectional solidification, followed by tilting and decanting to separate excess liquid enriched in impurities, resulting in a higher purity solid silicon ingot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mechanical stirring (carbon rod) and gas injection are used to purify liquid silicon, then iron content is reduced, but the process becomes complex and expensive due to consumable graphite rods and potential oxidation
Solution Approach 1:
The patent replaces mechanical stirring with electromagnetic stirring. An electromagnetic stirrer generates a magnetic field that induces circulation currents in the liquid silicon, achieving stirring without mechanical contact. This eliminates the need for consumable graphite rods and reduces process complexity while maintaining purification effectiveness.
Solution Approach 2:
The patent introduces an electromagnetic field as an intermediary to transfer momentum to the liquid silicon. The electromagnetic stirrer acts as a mediator that couples electrical energy to mechanical motion of the liquid silicon through induced eddy currents, avoiding direct mechanical contact and its associated complexities.
2Manufacturing precision
If graphite electrodes are used to keep the top surface liquid during centrifugation, then dendritic solidification is prevented, but expensive consumables are used and contamination risk increases
Solution Approach 1:
The patent replaces graphite electrodes with an electromagnetic stirrer that can selectively agitate only the liquid portion of the silicon. By controlling the electromagnetic field parameters, the stirrer maintains the top surface liquid without requiring consumable electrodes, thereby eliminating contamination risks and associated costs.
Solution Approach 2:
The patent changes the physical parameters of the electromagnetic field (frequency, intensity, distribution) to achieve differential effects on liquid versus solid silicon. The electromagnetic stirrer parameters are optimized to agitate liquid silicon while leaving solidified portions undisturbed, preventing dendritic solidification without mechanical contact.
3Manufacturing precision
If high-speed rotation of heavy industrial moulds is used to prevent dendritic solidification, then purification is improved, but the process becomes difficult to implement industrially
Solution Approach 1:
The patent replaces high-speed mechanical rotation of heavy moulds with electromagnetic stirring. The electromagnetic stirrer generates controlled circulation patterns in the liquid silicon without requiring the entire mould to rotate at high speeds. This dramatically reduces mechanical stress and makes the process industrially implementable while maintaining purification quality.
Solution Approach 2:
The patent segments the silicon into liquid and solid phases and applies different treatments to each. The electromagnetic stirrer selectively agitates only the liquid portion, preventing dendritic solidification locally where it occurs, without requiring global rotation of the entire heavy industrial mould.
4Manufacturing precision
If electromagnetic stirring is used for unidirectional solidification, then silicon purity is increased and process is simplified, but energy consumption increases
Solution Approach 1:
The patent optimizes electromagnetic field parameters (frequency, amplitude, distribution) to achieve efficient stirring with minimal energy input. By tuning the electromagnetic stirrer parameters to match the characteristics of liquid silicon, the system achieves effective purification while minimizing energy consumption compared to conventional methods.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively increases silicon purity, avoids contaminant carbon tools, simplifies the process, and reduces costs, making it suitable for industrial implementation and recycling of low-grade silicon materials.
Implementation Method 1
stirring the liquid silicon by means of electromagnetic stirring (EMS)
Implementation Method 2
solidifying the liquid silicon by unidirectional solidification from the crucible-lined walls
Data Source
AI summary
The present invention refers to a method for obtaining purified silicon metal, the method comprising the steps of providing liquid silicon in a crystallisation mould wherein the crystallisation mould comprises crucible-lined walls; solidifying the liquid silicon by unidirectional solidification from the crucible-lined walls of the mould while stirring the liquid silicon by means of electromagnetic stirring (EMS); stopping the unidirectional solidification when a percentage of the liquid silicon has solidified; decanting the excess liquid silicon; wherein the step of decanting the excess non-solidified liquid silicon comprises the steps of tilting the crystallisation mould upside down, under electromagnetic stirring (EMS) and emptying the excess non-solidified liquid silicon from the crystallisation mould by turning off electromagnetic stirring (EMS). The invention further refers to a device comprising aa crystallisation mould; an electromagnetic stirrer; and a decanting mechanism. Finally, the invention recites the use of the device in a method for obtaining purified silicon metal.