Gas Sensor Element Intermediate Layer for Thermal Crack Resistance
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Solution Overview
Problem
Cracking occurs in sensor elements used for detecting specific gas concentrations due to thermal stress, particularly in the presence of moisture and thermal expansion coefficient mismatches between layers.
Innovation Solution
Incorporating an intermediate layer with a thermal expansion coefficient between that of the solid electrolyte layer and dense layer, along with specific thermal expansion coefficient ratios, to mitigate stress and reduce cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a dense layer is disposed between the porous layer and the element body to prevent moisture penetration, then moisture protection is improved, but thermal stress cracking occurs due to thermal expansion coefficient mismatch
Solution Approach 1:
An intermediate layer is introduced between the dense layer and the element body to act as a thermal expansion buffer. This intermediary layer has a thermal expansion coefficient that is lower than the dense layer but higher than the element body, thereby reducing the thermal stress concentration at the dense layer-element body interface and preventing cracking while maintaining moisture protection functionality.
Solution Approach 2:
The thermal expansion coefficient parameter of the intermediate layer is specifically controlled to be between 5×10^-6/K and 10×10^-6/K, which is lower than the dense layer (12×10^-6/K to 15×10^-6/K) but higher than the element body (3×10^-6/K to 8×10^-6/K). This parameter optimization creates a gradient structure that gradually transitions thermal expansion properties, reducing stress concentration and preventing cracking.
2Ease of manufacture
If the thermal expansion coefficient difference between layers is large, then manufacturing is easier with standard materials, but thermal stress increases causing cracking
Solution Approach 1:
The thermal expansion coefficient of the intermediate layer is precisely controlled within the range of 5×10^-6/K to 10×10^-6/K through material composition adjustment. This creates a gradual transition in thermal expansion properties across the layers, reducing thermal stress concentration while maintaining manufacturability with ceramic materials that can be sintered at conventional temperatures.
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 intermediate layer effectively reduces thermal stress, minimizing cracking in the sensor element by aligning thermal expansion coefficients and providing a buffer against thermal expansion mismatches.
Implementation Method 1
when thermal expansion coefficients of the solid electrolyte layer, the dense layer, and the intermediate layer in a temperature range of from 20° C. to 1360° C. are denoted by thermal expansion coefficients Ea, Eb, and Ec, respectively, the ratio Ea/Eb is more than 1.0 and 5.0 or less, and Ea>Ec>Eb is satisfied
Implementation Method 2
even when moisture in the measurement-object gas moves through the porous layer by capillary action
Data Source
AI summary
A sensor element for detecting a specific gas concentration in a measurement-object gas, the sensor element includes; an elongate element body that includes a solid electrolyte layer and has a shape including at least one side surface extending in a longitudinal direction; a dense layer that is disposed on the side surface; and an intermediate layer disposed at least between the dense layer and the element body, wherein, when thermal expansion coefficients of the solid electrolyte layer, the dense layer, and the intermediate layer in a temperature range of from 20° C. to 1360° C. are denoted by thermal expansion coefficients Ea, Eb, and Ec, respectively, a ratio Ea/Eb is more than 1.0 and 5.0 or less, and Ea>Ec>Eb is satisfied.