Graphite Crucible Slits for Induction Silicon Melting
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Solution Overview
Problem
Existing methods for melting silicon using electromagnetic induction face challenges such as contamination from graphite crucibles and significant heat loss in cold copper crucibles, with current solutions either causing carbon contamination or complicating the melting process with additional heat sources.
Innovation Solution
A graphite crucible with vertically formed first slits on its walls and second slits on the bottom to allow intense electromagnetic induction without shielding, preventing silicon melt contact with the crucible walls and reducing heat loss by using indirect melting combined with contact-free electromagnetic induction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If indirect melting with heat from graphite crucible is used, then silicon melting is achieved, but carbon contamination occurs and crucible cleavage happens
Solution Approach 1:
The crucible wall is segmented by forming radial slits that divide the continuous graphite structure into separated sections. This segmentation prevents direct contact between silicon melt and large areas of graphite surface, reducing carbon contamination while maintaining the crucible's heating function through indirect melting.
Solution Approach 2:
An oxide coating layer is applied to the inner surface of the graphite crucible as an intermediary barrier between the graphite and silicon melt. This coating prevents direct chemical reaction and carbon contamination while allowing heat transfer from the graphite crucible to melt the silicon through indirect heating.
2Object-affected harmful factors
If SiC coating is applied on inner surface of graphite crucible, then reaction between graphite and silicon melt is suppressed, but coating exfoliation occurs reducing crucible lifespan
Solution Approach 1:
The crucible wall is segmented by forming radial slits that reduce the stress concentration on the SiC coating. This segmentation prevents large-area coating exfoliation by distributing mechanical stresses from thermal expansion and silicon melt pressure across multiple smaller sections, thereby extending crucible lifespan while maintaining contamination protection.
3Object-affected harmful factors
If cold copper crucible is used, then contact between silicon melt and crucible is prevented, but severe heat loss occurs requiring assistant heat source
Solution Approach 1:
The graphite crucible serves as an intermediary heating element that is heated by electromagnetic induction and then transfers heat indirectly to the silicon melt through the oxide coating barrier. This intermediary approach prevents direct contact between silicon and graphite (avoiding contamination) while minimizing heat loss compared to water-cooled copper crucibles, as graphite has lower thermal conductivity to the environment.
4Loss of energy
If graphite crucible shields electromagnetic waves, then electromagnetic force cannot be delivered into crucible, but indirect melting with heat is achieved
Solution Approach 1:
The continuous graphite wall is segmented by forming radial slits that allow electromagnetic waves to penetrate through the crucible wall. This segmentation reduces the shielding effect of graphite, enabling electromagnetic energy to reach the silicon material directly while the oxide coating prevents contamination, thereby improving melting efficiency through combined direct and indirect heating.
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 approach enables efficient and contamination-free silicon melting with reduced heat loss, achieving high purity silicon through effective electromagnetic induction and agitation, while maintaining a low-cost fabrication process.
Implementation Method 1
When an alternating current is applied to an induction coil wound around a crucible to induce magnetic field variation, an induction current is created on the surface of metal to be melted and generates Joule s heat
Implementation Method 2
an induction current is created on the surface of metal to be melted and generates Joule s heat
Implementation Method 3
indirect melting with heat from a graphite crucible
Implementation Method 4
the induction current interacts with a magnetic field to generate the Lorentz force in molten metal. Since the Lorentz force is always directed toward an inner center of the crucible and provides a pinch effect or electromagnetic pressure effect
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
Disclosed herein are a graphite crucible for electromagnetic induction- based silicon melting and an apparatus for silicon melting/refining using the same, which performs a melting operation by a combination of indirect melting and direct melting. The crucible is formed of a graphite material and includes a cylindrical body having an open upper part through which a silicon raw material is charged into the crucible, and an outer wall surround by an induction coil, wherein a plurality of first slits are vertically formed through the outer wall and an inner wall of the crucible, and a plurality of second slits are vertically formed from an edge of a disc-shaped bottom of the crucible toward a center of the bottom.