Multilayer Insulation for Silicon Refining
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Solution Overview
Problem
Conventional silicon refining devices using vacuum melting have low P removal rates and high operational costs, with issues such as Si evaporation through insulation materials impairing heat insulation and leading to SiC deposition, which reduces P removal efficiency and increases facility costs.
Innovation Solution
A silicon refining device with a molten metal surface thermal insulation member featuring a multilayer structure of laminated insulation material, where three or more laminates are separated by specific intervals, providing radiant heat insulation and preventing Si penetration into the insulation material, thus maintaining high P removal rates and productivity while minimizing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer insulation material is used to cover the molten metal surface, then the device configuration is simple, but Si penetrates the insulation material causing loss of heat insulation function and SiC deposition
Solution Approach 1:
The single-layer insulation material is divided into multiple layers (first insulation layer, second insulation layer, and optionally third insulation layer) with different material compositions and functions. Each layer serves specific purposes: the first layer prevents Si penetration, the second layer provides heat insulation, and the third layer (if present) prevents oxidation. This segmentation resolves the contradiction by maintaining structural simplicity while improving reliability through functional differentiation.
Solution Approach 2:
The patent uses composite insulation structure combining different materials (e.g., alumina, silica, zirconia) in multiple layers. Each material is selected for its specific properties: alumina for chemical stability and Si penetration resistance, silica for heat insulation, zirconia for high-temperature stability. This composite approach maintains relatively simple device configuration while significantly improving the reliability of heat insulation function.
2Manufacturing precision
If vacuum melting is used for P removal, then high purity silicon can be produced, but the P removal rate is low resulting in low productivity
Solution Approach 1:
The patent optimizes vacuum melting parameters including temperature control (maintaining silicon molten state at 1414°C melting point), pressure control (vacuum degree), and insulation layer thickness parameters. By precisely controlling these parameters and using the multi-layer insulation structure to maintain stable thermal conditions, the P removal rate is enhanced while maintaining high silicon purity, thus resolving the contradiction between manufacturing precision and productivity.
3Manufacturing precision
If extended vacuum melting operations are performed, then high purity silicon is produced, but insulation efficiency deteriorates due to Si penetration and SiC deposition
Solution Approach 1:
The multi-layer insulation structure segments the insulation function across different layers with different material properties. The first layer (alumina) specifically prevents Si penetration, while subsequent layers maintain heat insulation. This segmentation allows extended operations without insulation efficiency deterioration, as each layer performs its specific function independently.
Solution Approach 2:
The patent designs the insulation layer structure where the first layer (exposed to molten silicon) can be replaced or regenerated while maintaining the overall insulation structure. This approach allows extended operations by periodically maintaining or replacing the consumption-prone first layer, thus maintaining insulation efficiency over extended periods while continuing high purity silicon production.
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
The device achieves high P removal rates and maintains insulation efficiency over extended operations, ensuring high purity silicon production with reduced SiC deposition and operational costs, making it suitable for industrial-scale solar cell production.
Implementation Method 1
a decompression vessel (5) provided with a vacuum pump (6)
Implementation Method 2
a heating device (8) that heats the crucible (7)
Implementation Method 3
heating and melted into an inactive gas under decompression, enabling P removal by maintaining the obtained silicon molten metal for a constant time under decompression and at a temperature no lower than the melting point
Implementation Method 4
P with a higher vapor pressure than Si is selectively vaporized by this P removal operation
Implementation Method 5
a molten metal surface thermal insulation member (1) arranged on an upper portion of the crucible (7) to cover an upper portion of the silicon molten metal (9) and having an exhaust opening (2) with an opening area smaller than the silicon molten metal surface area, wherein the molten metal surface thermal insulation member (1) comprises a laminated insulation material with a multilayer structure in which three or more laminates are laminated at predetermined intervals from each other, and which exhibits a radiant heat insulating function
Implementation Method 6
the laminated insulation material with a multilayer structure in which three or more laminates are laminated at predetermined intervals from each other... preventing Si penetration into the insulation material
Implementation Method 7
a decompression vessel (5) provided with a vacuum pump (6)... P removal by maintaining the obtained silicon molten metal for a constant time under decompression
Data Source
AI summary
Provided is a silicon refining device that is used when industrially producing silicon of high purity by vacuum melting, has a high P removal rate and thus high productivity, and is a practical device cost-wise with a simple and cheap device configuration. This silicon refining device comprises, in a decompression vessel provided with a vacuum pump, a crucible that contains a metal silicon material, a heating device that heats the crucible, and a molten metal surface thermal insulation member that covers the upper portion of silicon molten metal and has an exhaust opening with an opening area that is smaller than the silicon molten metal surface area. The molten metal surface thermal insulation member comprises a laminated insulation material with a multilayer structure in which three or more laminates are laminated at predetermined intervals from each other, and which exhibits a radiant heat insulating function based on the multilayer structure.