Gas Sensor Ceramic Layer Shrinkage Stress Mitigation
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Solution Overview
Problem
Conventional gas sensors experience cracking issues due to differential shrinkage between ceramic layers during the firing process, particularly at the atmosphere introduction hole, leading to functional failure under thermal stress.
Innovation Solution
Incorporating a ceramic layer with a lower shrinkage-starting temperature between the ceramic layers exposed to the internal space to mitigate stress and prevent cracking, while ensuring the new layer does not hinder air flow or expose itself to external damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a burning-off paste or sheet is used to form the atmosphere introduction hole, then the hole can be formed without deforming the ceramic layers, but differential shrinkage occurs between the paste and ceramic layers during firing, causing cracks to develop
Solution Approach 1:
A fourth ceramic layer is introduced as an intermediary between the first and third ceramic layers at the periphery of the internal space. This intermediate layer has different shrinkage characteristics than the adjacent layers, acting as a buffer to reduce differential shrinkage stress and prevent crack formation between the first and third ceramic layers during the firing process.
Solution Approach 2:
The sensor element employs a composite multi-layer ceramic structure where the fourth ceramic layer is composed of different materials than the first and third layers. This composite approach allows each layer to have optimized properties, with the fourth layer specifically selected to have intermediate shrinkage characteristics that bridge the gap between the other layers, preventing stress concentration and cracking.
2Strength
If the fourth ceramic layer is added to prevent cracking, then crack resistance improves, but the device structure becomes more complex
Solution Approach 1:
The fourth ceramic layer is not applied throughout the entire sensor element but is selectively positioned only at the periphery of the internal space where cracks are most likely to form. This localized application provides crack prevention exactly where needed while minimizing the addition of structural complexity to the overall device.
Solution Approach 2:
The ceramic structure is segmented into functionally distinct layers, with the fourth layer specifically dedicated to stress management at the critical interface between the first and third layers. This segmentation allows each layer to perform its specific function optimally without requiring the entire structure to be redesigned.
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 solution effectively prevents cracking between ceramic layers, ensuring the sensor's integrity and functionality, even under thermal and water exposure, by allowing controlled shrinkage and maintaining air flow pathways.
Implementation Method 1
the difference between shrinkages F1 and F2 causes stress between the layers, resulting in development of the above-mentioned crack K
Implementation Method 2
imparting thermal shock such as multiple heat cycles on the sensor element
Implementation Method 3
a paste 505 that contains burning-off carbon is charged into the hollow space of a third-layer green sheet 503G
Implementation Method 4
fired to burn off the paste 505, thereby forming the atmosphere introduction hole 510
Data Source
AI summary
A sensor element (10) having a laminate structure, and extending in an axial direction AX, the sensor element including a first and second ceramic layers (118B, 115) disposed apart from each other in a laminating direction; a third ceramic layer (118) intervening between the first and second ceramic layers in the laminating direction and having a hollow space (10G) formed therein; and an internal space which is the hollow space surrounded by the first ceramic layer, the second ceramic layer, and the third ceramic layer, wherein, at a periphery (10f) of the internal space, a fourth ceramic layer (181) containing as a main component a ceramic material different from that contained as a main component in the first and third ceramic layers intervenes between the first ceramic layer and the third ceramic layer which are exposed to the internal space. Also disclosed is a method for manufacturing the gas sensor element.