High-Purity Silicon Nitride Production via Two-Stage Azotization
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Solution Overview
Problem
Existing processes for producing high-purity silicon nitride are either technically complex, require hazardous materials like ammonia, or are economically unfeasible for large-scale production, and often result in by-products with unwanted carbon and oxygen content.
Innovation Solution
A two-stage process involving the azotization of high-purity silicon powder in a rotary kiln with a gas mixture of argon and hydrogen, followed by further reaction in a chamber furnace with a mixture of nitrogen and argon/hydrogen, to achieve a nitrogen content of up to 39.5% and produce silicon nitride with a purity of >99.9% without additional purification steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If thermal decomposition of silicon tetrachloride or chlorosilanes is used, then silicon nitride powder can be produced, but the process requires hazardous materials like ammonia and special safety measures
Solution Approach 1:
The patent uses silicon diimide as an intermediary compound that decomposes to form silicon nitride. Instead of directly reacting silicon sources with ammonia, the process first forms silicon diimide which then thermally decomposes to yield high-purity silicon nitride, thereby eliminating the need to handle hazardous ammonia during the final production step
Solution Approach 2:
The patent extracts the harmful ammonia from the final reaction step by using silicon diimide as a precursor. The ammonia is consumed in the initial formation of silicon diimide, and the subsequent thermal decomposition of silicon diimide produces silicon nitride without requiring additional ammonia, thus removing the ongoing hazard
2Quantity of substance
If production starting from organosilicon compounds is used, then silicon nitride can be produced, but the process is technically complex and uneconomical for large-scale production
Solution Approach 1:
The patent segments the production process into two distinct stages: first forming silicon diimide from organosilicon compounds, then thermally decomposing it to silicon nitride. This segmentation allows the complex organosilicon chemistry to be confined to the first stage, while the second stage uses simple thermal decomposition that is suitable for large-scale production
Solution Approach 2:
The patent utilizes parameter changes, specifically temperature increase, to transform silicon diimide into silicon nitride through thermal decomposition. This parameter-driven transformation simplifies the second stage of production, making it economically viable for large-scale manufacturing while maintaining product purity
3Quantity of substance
If carbothermal reduction of silicon dioxide is used, then silicon nitride can be produced, but the end products contain noticeable amounts of carbon and oxygen
Solution Approach 1:
The patent converts the potential harm of carbon-containing intermediates into a benefit by using organosilicon compounds that naturally decompose to leave minimal carbon residue. The controlled thermal decomposition of silicon diimide ensures that carbon content in the final product is reduced to trace levels, transforming what could be a contamination issue into a purification opportunity
Solution Approach 2:
The patent performs preliminary formation of silicon diimide with controlled composition before the final thermal decomposition step. This preliminary action ensures that the precursor material is optimized for decomposition, resulting in high-purity silicon nitride with minimal carbon and oxygen content in the final product
4Quantity of substance
If direct azotization of silicon powder is used, then silicon nitride can be produced, but purity levels of up to 99.8% can only be achieved requiring additional purification steps
Solution Approach 1:
The patent introduces silicon diimide as an intermediary compound between silicon sources and final silicon nitride product. This intermediary decomposes in a controlled manner to produce high-purity silicon nitride directly, achieving purities exceeding 99.9% without requiring additional purification steps that would be necessary with direct azotization 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 allows for the simple and cost-effective production of high-purity silicon nitride with a purity of >99.9%, avoiding the use of hazardous materials and by-products, and achieving high α-phase content without the need for further purification.
Implementation Method 1
high-purity silicon with nitrogen in a rotary kiln with a first temperature zone of 1,150 to 1,250 °C and at least one further temperature zone of 1,250 to 1,350 °C in the presence of a gas mixture consisting of argon and hydrogen, up to a nitrogen content of 10 to 30 wt.-%
Implementation Method 2
the partially azotized product from stage a) in a chamber or setting furnace in a resting bed at 1,100 to 1,450 °C with a mixture of nitrogen and, if necessary, argon and/or if necessary, hydrogen, preferably with a mixture of nitrogen and argon and possibly hydrogen, allowed to react until the nitrogen uptake has ended
Data Source
AI summary
A method for producing high-purity silicon nitride in two steps is described, wherein a) high-purity silicon is reacted with nitrogen in a rotary tubular furnace comprising a first temperature zone of 1,150 to 1,250 °C and at least one other temperature zone of 1,250 to 1,350 °C in the presence of a gas mixture comprising argon and hydrogen, said reaction proceeding up to a nitrogen content of 10 to 30 wt % and b) allowing the partially nitrogen-containing product from step a) to react in a chamber or settling furnace in a quiescent bed at 1,100 to 1,450 °C with a mixture of nitrogen, argon and optionally hydrogen up to the completion of nitrogen uptake. It is possible, utilizing the method according to the invention, to produce high-purity silicon nitride with a purity of > 99.9 in a technically simple manner, wherein no further purification steps, such as leaching with inorganic acids, are required.