Gas Sensor Element Dual Porous Protection Layer
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Solution Overview
Problem
Conventional gas sensors face issues with cracking due to water adhesion and reduced strength when using high-porosity porous protection layers, which can lead to sudden cooling and damage, especially when exposed to exhaust gases containing poisoning substances.
Innovation Solution
A gas sensor element with a dual porous protection layer structure, where the inner layer has higher porosity and is composed of ceramic particles and fiber filaments with a specific length and volume percentage, while the outer layer has lower porosity to trap substances and prevent water adhesion, enhancing thermal insulation and strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the porosity of the porous protection layer is increased to improve thermal insulation, then thermal insulation performance is improved, but the strength of the layer is lowered
Solution Approach 1:
The invention uses a composite porous layer combining ceramic particles and ceramic fiber filaments. The ceramic particles provide structural framework and strength, while the ceramic fiber filaments create a three-dimensional network that enhances both mechanical strength and thermal insulation. This composite structure allows the layer to maintain high porosity (30-70%) for thermal insulation while achieving sufficient strength through the synergistic effect of particles and fibers.
Solution Approach 2:
The invention creates a layered structure with different porosity levels. The inner porous layer (直接接触检测元件) has higher porosity (50-70%) for superior thermal insulation, while the outer porous layer has lower porosity (30-50%) for better mechanical strength and trapping of harmful substances. This spatial variation in porosity allows each layer to optimize its function while contributing to overall system performance.
2Strength
If fine particles are used to form the porous layer to improve strength, then the strength of the layer is improved, but cracking is likely to occur during drying
Solution Approach 1:
The invention combines ceramic particles with ceramic fiber filaments in a composite porous layer. The fiber filaments act as a flexible three-dimensional network that can accommodate shrinkage stresses during drying without breaking, preventing cracking. The particles provide structural framework, while the fibers bridge gaps and distribute stresses, ensuring both strength and crack resistance.
Solution Approach 2:
The invention changes the physical parameters of the porous layer by incorporating fiber filaments with specific length (10-200 μm) and aspect ratio. The fibers provide flexibility and stress distribution capability that spherical particles alone cannot provide, allowing the layer to maintain integrity during the drying process while achieving the desired strength.
3Device complexity
If a single porous protection layer is used to simplify structure, then device complexity is reduced, but the ability to simultaneously provide thermal insulation and trap harmful substances is compromised
Solution Approach 1:
The invention divides the porous protection layer into two distinct layers: an inner porous layer and an outer porous layer. The inner layer with higher porosity (50-70%) is optimized for thermal insulation to protect the detection element from sudden cooling. The outer layer with lower porosity (30-50%) is optimized for trapping poisoning substances and water droplets. This segmentation allows each layer to perform its specific function effectively.
Solution Approach 2:
The invention applies different porosity characteristics to different spatial locations. The inner layer (closer to the detection element) has higher porosity for thermal insulation, while the outer layer (exposed to exhaust gas) has lower porosity for filtering harmful substances. This spatial differentiation of properties optimizes the overall protection performance.
Data Source
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AI summary
Provided are a gas sensor element whose cracking caused by adhesion of water is suppressed by covering the gas sensor element with two porous protection layers, and in which cracking is suppressed in an inner porous layer having higher porosity and the strength of the layer is improved; and a gas sensor incorporating the gas sensor element. The gas sensor element 100 includes a detection portion 150 including a solid electrolyte body 105 and a pair of electrodes 104 and 106 disposed on the solid electrolyte body; and a porous protection layer 20 covering the detection portion, wherein the porous protection layer includes an inner porous layer 21 and an outer porous layer 23; the inner porous layer is higher in porosity than the outer porous layer; the inner porous layer contains, as main components, ceramic particles 21a, and ceramic fiber filaments 21b which are mainly formed of a ceramic material and which have a mean fiber length of 70 to 200 µm; and the amount of the ceramic fiber filaments is 25 to 75 vol% on the basis of the total amount of the ceramic particles and the ceramic fiber filaments, the total amount being taken as 100 vol%.