Sensor Element Porous Protective Layer Thermal Shock Resistance
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Solution Overview
Problem
Gas sensors with high-temperature sensor elements face cracking due to thermal shock from moisture attachment, and existing porous protective layers with higher inner layer porosity improve heat insulation but compromise adhesion strength.
Innovation Solution
A sensor element design featuring a porous protective layer with a lower porosity in the posterior region compared to the electrode presence region, maintaining adhesion strength while enhancing water resistance, comprising an inner layer with stepwise or continuous porosity decrease from the electrode presence region to the posterior region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the porosity of the inner layer in the protective layer is increased to improve heat insulation performance, then water resistance is improved, but adhesion strength between the element body and the protective layer decreases
Solution Approach 1:
The protective layer is designed with spatially varying porosity: the inner layer has higher porosity (40-70%) in regions away from the element body to maximize heat insulation, while the outer layer has lower porosity (10-40%) in regions adjacent to the element body to ensure strong adhesion. This local differentiation of structural properties resolves the contradiction between water resistance and adhesion strength.
Solution Approach 2:
The protective layer is constructed as a composite structure with two distinct layers having different porosity characteristics. The inner layer and outer layer are combined to achieve both high heat insulation performance and strong adhesion to the element body, effectively resolving the technical contradiction through material composition design.
2Measurement precision
If the sensor element operates at high temperature for measurement, then detection performance is improved, but thermal shock from moisture attachment causes cracking in the internal structure
Solution Approach 1:
The porous protective layer is applied beforehand to the sensor element surface to create a thermal buffer zone. When moisture contacts the sensor during high-temperature operation, this protective layer absorbs and dissipates the thermal shock before it reaches the internal structure, preventing cracking while allowing the sensor to maintain high detection performance.
Solution Approach 2:
A porous protective layer made of ceramic material is formed on the sensor element surface. The porous structure provides effective heat insulation to prevent thermal shock from moisture attachment, while maintaining sufficient gas permeability for the sensor to detect target gases at high temperatures, thus resolving the contradiction between structural integrity and measurement precision.
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 design effectively prevents cracking and maintains high water resistance and adhesion strength, ensuring the sensor element's structural integrity and performance in high-temperature environments.
Implementation Method 1
a higher porosity of the inner layer improves heat insulation performance of the protective layer. As a result, the occurrence of cracking in the internal structure of the sensor element due to exposure to water (water splash) can be better suppressed.
Implementation Method 2
when moisture attaches to such a sensor element having a high temperature, cracking occurs in an internal structure of the sensor element due to the thermal shock
Data Source
AI summary
A sensor element includes: an element body that includes a base part in an elongated plate shape, and a measurement-object gas flow cavity; and a porous protective layer that is formed from one end in the longitudinal direction of the base part and covers a surface of a predetermined length in the longitudinal direction of the element body. The element body includes an extracavity electrode on one principal surface of the element body. The protective layer includes an inner layer and an outer layer; and has an electrode presence region and a posterior region following to the electrode presence region in the longitudinal direction. A porosity in the posterior region of the inner layer is lower than a porosity in the electrode presence region of the inner layer, and a porosity of the outer layer is lower than the porosity in the posterior region of the inner layer.