Molten Silicon Purification by Oxygen Slagging of Boron and Titanium
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Solution Overview
Problem
Existing silicon materials, particularly those derived from lunar regolith, contain impurities such as boron and titanium that negatively affect their electrical properties and performance in semiconductor and solar cell applications.
Innovation Solution
A method and system for removing boron and titanium impurities from molten silicon by introducing oxygen to form oxides, which are then separated as a slag layer using buoyancy and oxidation, followed by mechanical removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon is produced from lunar regolith using molten oxide electrolysis, then silicon can be obtained in liquid state from oxide feedstock, but the resulting silicon contains impurities such as boron and titanium that significantly impact its properties and performance
Solution Approach 1:
The patent changes the physical state parameter of silicon from solid to liquid by heating to molten state, enabling impurity removal through phase-dependent separation processes. The molten state allows boron and titanium to be selectively oxidized and removed via slag formation, resolving the contradiction between ease of manufacture from regolith and achieving high purity silicon.
Solution Approach 2:
The patent introduces strong oxidizing conditions to the molten silicon to accelerate the oxidation of boron and titanium impurities. By controlling oxidation reactions in the molten state, boron and titanium are converted to oxides that form a separable slag layer, enabling effective impurity removal while maintaining production efficiency from lunar regolith.
2Ease of manufacture
If boron is present in silicon, then silicon can be produced from common raw materials, but boron negatively affects electrical properties and reduces conductivity
Solution Approach 1:
The patent converts the harmful effect of boron impurity into a beneficial separation process. By introducing controlled oxidation conditions to molten silicon, boron is transformed from a harmful conductive impurity into boron oxide that forms a separable slag phase. This converts the harmful presence of boron into a useful separation mechanism that removes boron while preserving silicon's electrical properties.
3Ease of manufacture
If titanium is present in silicon, then silicon can be produced from lunar regolith minerals, but titanium introduces traps in silicon lattice and affects charge carrier mobility
Solution Approach 1:
The patent utilizes the parameter change of silicon to molten state to enable selective oxidation of titanium. In the molten phase, titanium can be oxidized and separated via slag formation, removing the harmful titanium impurity that would otherwise introduce lattice traps and reduce charge carrier mobility in the final solid silicon product.
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
High-purity silicon is achieved, suitable for semiconductor and solar cell fabrication, by effectively reducing the concentration of boron and titanium impurities through controlled oxidation and slag formation.
Implementation Method 1
allowing the oxygen to bubble through the molten silicon so as to oxidize at least some of the boron and titanium impurities in the molten silicon
Implementation Method 2
a slag of boron oxide and titanium oxide may form on the top surface of the molten silicon as a result of respective buoyancies of the oxidized boron and titanium
Data Source
AI summary
A method and system for removing boron and titanium impurities from silicon is presented. An example of the method includes holding molten silicon in a container, introducing oxygen into the molten silicon from a bottom region of the container, allowing the oxygen to bubble through the molten silicon so as to oxidize at least some of the boron and titanium impurities in the molten silicon, forming a slag of boron oxide and titanium oxide on the top surface of the molten silicon, and removing the slag from the surface of the molten silicon.