SiC Ignitor Coating for Oxidation Resistance
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Solution Overview
Problem
Silicon carbide (SiC) ignitors fail due to oxidation when exposed to oxidizing atmospheres at elevated temperatures, leading to increased resistance and eventual failure in gas oven environments, as existing protective coatings do not provide adequate longevity or maintain electrical properties.
Innovation Solution
A thin layer of silicon dioxide (SiO2) with a thickness between 0.1 μm and 5 μm is applied to the SiC ignitor to impede oxygen diffusion, slowing oxidation and maintaining electrical properties without altering the underlying SiC material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon dioxide layer is formed by oxidizing SiC particles in the pores of SiC body, then a protective coating is created, but the silicon dioxide layer devitrifies and undergoes phase change leading to flaking
Solution Approach 1:
The patent applies a silicon dioxide coating to the SiC ignitor before it is exposed to oxidizing conditions during normal operation. This preliminary coating prevents the SiC particles in the pores from oxidizing during manufacturing, and the coating remains stable during subsequent use because the SiC particles are already protected from oxidation that would cause devitrification
Solution Approach 2:
The patent removes the problematic step of oxidizing SiC particles to form the silicon dioxide layer. Instead of forming the coating through oxidation (which causes devitrification), the coating is applied directly in a stable form that does not undergo phase changes during service
2Reliability
If SiC ignitor is exposed to oxidizing atmosphere at elevated temperatures, then oxidation occurs forming silica layer, but the resistance increases causing current drop below minimum requirement
Solution Approach 1:
The patent uses a thin, sacrificial silicon dioxide coating that provides temporary protection during the critical period of operation. The coating slows oxidation sufficiently to maintain electrical resistance within acceptable limits for the required service life of the ignitor
Solution Approach 2:
The patent changes the oxidation rate parameter by introducing a silicon dioxide coating that acts as a diffusion barrier. This reduces the rate at which oxygen reaches the SiC particles, thereby controlling the formation of silica and maintaining electrical resistance within operational specifications
3Object-affected harmful factors
If existing protective coatings are applied to SiC ignitor, then some protection against oxidation is provided, but acceptable life in gas oven environments is not achieved
Solution Approach 1:
The patent uses a composite structure consisting of SiC particles embedded in a silicon dioxide matrix. The SiC provides structural integrity and electrical conductivity, while the silicon dioxide provides oxidation protection. This composite approach achieves both durability and oxidation resistance required for long service life in gas oven environments
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 SiO2 coating significantly extends the operational life of SiC ignitors by slowing oxidation and maintaining electrical properties, with coated ignitors lasting 2% to 100% longer than uncoated ones, while ensuring a continuous and uniform protection against oxidation.
Implementation Method 1
The SiO2 layer(s) impedes the diffusion of oxygen to the underlying SiC, thus slowing the oxidation rate of the SiC
Implementation Method 2
The oxidizing atmosphere penetrates the pores of the SiC material and reacts at the surface of the pores to form a silica (i.e., silicon dioxide or SiO2) layer
Data Source
AI summary
An ignitor that includes at least one layer of silicon dioxide coating a silicon carbide material, methods of making and using the ignitor, and a kit that includes the ignitor are provided. The silicon dioxide coating is not intended to be removed prior to use. Rather, it is intended to remain on the ignitor during use.