Multilayer SiC-Graphite Crucible Lining for Liquid Silicon
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Solution Overview
Problem
Graphite crucibles used for melting silicon in photovoltaic applications have a limited lifespan due to the formation of a non-durable silicon carbide barrier layer, which is consumed by carbon dissolution and oxidation, leading to adhesion issues and reduced resistance to liquid silicon and oxidation.
Innovation Solution
A multilayer silicon carbide/graphite composite structure is developed, featuring a carbon-based support layer, a surface layer of silicon carbide, and an intermediate layer with a high volume fraction of carbon nodules, enhancing durability and resistance to high temperatures and oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon carbide barrier layer is formed on graphite crucible surface, then protection against liquid silicon is improved, but the layer is consumed by carbon dissolution and oxidation reducing its durability
Solution Approach 1:
The barrier layer is segmented into multiple functional layers: a dense SiC surface layer for protection, an intermediate layer with SiC and unreacted carbon for transition, and a porous graphite support layer for structural integrity. This segmentation allows each layer to perform its specific function optimally while working together to extend overall durability.
Solution Approach 2:
The invention uses a composite structure combining silicon carbide and graphite materials with different properties. The SiC provides chemical resistance and protection, while the graphite provides structural support and controlled porosity. This composite approach creates a barrier layer that is more durable than pure SiC while maintaining protective properties.
2Duration of action of stationary object
If graphite crucible is used for melting silicon, then reusability is improved compared to silica crucibles, but adhesion issues occur due to limited lifetime of SiC barrier layer
Solution Approach 1:
Different regions of the crucible lining have different compositions and properties tailored to their specific functions. The surface layer has high SiC content for non-adhesion and chemical resistance, the intermediate layer has mixed composition for stress relief and transition, and the support layer has graphite structure for mechanical strength. This local quality variation prevents adhesion while maintaining overall crucible performance.
Solution Approach 2:
The intermediate layer acts as a mediator between the dense SiC surface layer and the porous graphite support. It contains both SiC and unreacted carbon, providing a gradual transition zone that prevents direct contact between molten silicon and the graphite support, thereby preventing adhesion while allowing stress relief and thermal gradient management.
3Reliability
If SiC barrier layer thickness is increased to improve protection, then resistance to liquid silicon is improved, but the layer becomes more susceptible to oxidation and carbon dissolution
Solution Approach 1:
The barrier system is segmented into layers with different SiC concentrations and functions. The surface layer provides the primary protective function with high SiC content, while the intermediate layer with lower SiC content and unreacted carbon provides transition and stress relief. This segmentation allows adequate protection without requiring excessive total thickness that would increase oxidation susceptibility.
Solution Approach 2:
The invention changes the compositional parameters across the barrier layer thickness. The surface layer has high SiC content (80-95%) for protection, while the intermediate layer has lower SiC content (30-70%) with unreacted carbon. This parameter variation optimizes the balance between protection and resistance to oxidation and carbon dissolution.
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 composite structure significantly extends the lifespan of crucibles by improving resistance to liquid silicon and oxidation, reducing adhesion, and providing better chemical protection against impurities, allowing for reuse at high temperatures up to 1600°C.
Implementation Method 1
the silicon infiltrates the carbon matrix, to a depth that mainly depends on the porosity of this matrix
Implementation Method 2
a layer of silicon carbide is formed by reaction at the interface
Implementation Method 3
For the parts in contact with an oxidizing atmosphere, the oxidation of the SiC will also have the effect of reducing the thickness of the layer
Data Source
Figure 1a~2
Figure 3~4
AI summary
The present invention relates to novel materials intended for being contacted with liquid silicon and having a multilayer architecture, the intermediate layer of which is formed by a silicon carbide matrix containing at least one carbon nodule. The invention also relates to the method for preparing said materials.