Silicon Carbide Hot Surface Igniter Nitrogen Sintering
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Solution Overview
Problem
Existing methods for manufacturing hot surface igniters, particularly those using silicon carbide, fail to coordinate the addition of nitrogen with sintering temperature effectively, leading to insufficient nitrogen incorporation and suboptimal electrical properties, which affects the igniter's performance in achieving desired temperature levels and longevity.
Innovation Solution
A method involving sintering silicon carbide hot surface igniters in a partially-nitrogenated reducing atmosphere, with coordinated temperature profiles and nitrogen introduction during multiple sintering phases to achieve precise nitrogen incorporation and enhanced electrical properties, including a negative temperature coefficient and improved oxidation resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon carbide is sintered in a reducing atmosphere with nitrogen to adjust resistivity and provide oxidation resistance, then electrical properties and oxidation resistance are improved, but the coordination between nitrogen addition and sintering temperature is insufficient leading to suboptimal nitrogen incorporation
Solution Approach 1:
The patent applies preliminary action by introducing nitrogen into the sintering atmosphere before reaching the maximum sintering temperature, and maintaining nitrogen presence during the temperature ramp-up phase. This ensures that nitrogen is available for incorporation into the silicon carbide lattice at the optimal temperature range, achieving precise control over nitrogen content and resulting electrical properties without requiring post-processing adjustments
Solution Approach 2:
The patent implements dynamics by using a dynamic sintering process where the atmosphere composition changes continuously during the sintering cycle. The reducing atmosphere with nitrogen is maintained throughout the temperature ramp and hold phases, allowing the nitrogen partial pressure to be optimized at each temperature stage. This dynamic control enables precise coordination between temperature and nitrogen availability, achieving the desired resistivity and oxidation resistance
2Temperature
If room temperature resistivity is adjusted to achieve desired high temperature performance, then temperature performance can be optimized, but room temperature resistance does not correlate well with high temperature resistance leading to incorrect slotting
Solution Approach 1:
The patent applies parameter changes by controlling the sintering process parameters (temperature, atmosphere composition, and time) to achieve a specific nitrogen content in the silicon carbide lattice. This results in a material with a optimized negative temperature coefficient, where the resistivity at room temperature and high temperature are both optimized independently. The consistent resistivity behavior across temperatures enables accurate slotting based on room temperature measurements, as the correlated performance is achieved through controlled nitrogen incorporation during sintering
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 method results in igniters with optimized resistivity ratios, improved temperature performance, and extended lifespan by ensuring accurate nitrogen incorporation and oxidation resistance, addressing the limitations of previous processes.
Implementation Method 1
the silicon carbide vaporizes and recrystallizes with nitrogen incorporated as an n-type dopant into the silicon carbide lattice
Implementation Method 2
the silicon carbide vaporizes and recrystallizes with nitrogen incorporated as an n-type dopant into the silicon carbide lattice
Implementation Method 3
nitrogen incorporated as an n-type dopant into the silicon carbide lattice
Implementation Method 4
Current flowing through the ceramic body causes the body to heat up and increase in temperature
Implementation Method 5
the silicon carbide vaporizes and recrystallizes with nitrogen incorporated as an n-type dopant into the silicon carbide lattice
Data Source
AI summary
A method of making a hot surface igniter is described. A silicon carbide composition that includes both fines fraction and a coarse fraction is sintered in a nitrogen and argon reducing atmosphere in a manner that controls the incorporation of nitrogen with in the lattice of recrystallized silicon carbide. The controlled incorporation of nitrogen in the lattice provides enhanced control over heating and electrical properties, while simultaneously achieving a lower surface area fully recrystallized structure for oxidation resistance and long service life.