Gas Sensor Element with Heat Insulating Space and Porous Layers
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Solution Overview
Problem
Existing gas sensors with porous protective layers face issues with water-induced cracking due to inadequate water resistance, particularly when exposed to large amounts of water, and may experience delamination or detachment of the protective layers, leading to impaired performance.
Innovation Solution
A gas sensor design featuring an elongated planar ceramic body with an internal chamber system, electrochemical pump cells, and a heater, where a porous first leading-end protective layer is surrounded by a heat insulating space and a second porous protective layer with higher porosity covers the side surfaces, ensuring strong adhesion and preventing delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous protective layer is provided directly on the element base to prevent water-induced cracking, then water resistance is improved, but delamination and detachment of the protective layer occur due to poor adhesion
Solution Approach 1:
A heat insulating space is introduced as an intermediary between the porous protective layer and the element base. This space acts as a mediator that prevents direct thermal contact while maintaining adhesion through controlled anchoring portions, thereby preventing delamination and detachment while preserving water resistance.
Solution Approach 2:
The protective layer is designed with spatially varying properties: it has anchoring portions that contact the element base for adhesion, and non-contact portions separated by heat insulating spaces to prevent thermal shock. This local differentiation of contact and insulation zones resolves the contradiction between adhesion strength and water resistance.
2Strength
If the porous protective layer is directly joined to the dense solid electrolyte layer to improve adhesion, then delamination is reduced, but water-induced cracking still occurs due to thermal shock conduction
Solution Approach 1:
The heat insulating space serves as a thermal intermediary that blocks direct heat conduction from the porous protective layer to the element base. This prevents thermal shock propagation while allowing mechanical adhesion through anchoring portions, thereby eliminating water-induced cracking without sacrificing adhesion.
Solution Approach 2:
The protective layer is segmented into multiple functional zones: anchoring portions for adhesion and non-contact portions separated by heat insulating spaces for thermal isolation. This segmentation allows simultaneous achievement of strong adhesion and thermal shock prevention.
3Object-affected harmful factors
If a space is provided between the porous protective layer and the element base to reduce thermal conduction, then water resistance is improved, but adhesion is insufficient leading to delamination
Solution Approach 1:
The protective layer exhibits local quality differentiation with anchoring portions that contact the element base for strong adhesion, and non-contact portions separated by heat insulating spaces for thermal isolation. This spatial variation in contact properties simultaneously achieves both adhesion and thermal shock resistance.
Solution Approach 2:
The protective layer is divided into functionally distinct segments: anchoring portions providing mechanical bonding and non-contact portions providing thermal insulation. This segmentation enables the structure to satisfy both adhesion requirements and thermal shock resistance without delamination.
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
This configuration significantly enhances water resistance and prevents water-induced cracking by interposing a heat insulating space between the protective layers and the element base, maintaining adhesion and improving the sensor's durability under high-temperature conditions.
Implementation Method 1
a single heat insulating space interposed between the first leading-end protective layer and the element base in the first range
Implementation Method 2
a sensor element including a porous protective layer adhering to one leading end surface of an element base while having a space between the layer and a side surface perpendicular to the leading end surface of the element base. This configuration is effective in terms of weakening thermal conduction from the porous protective layer to the element base
Implementation Method 3
at least one electrochemical pump cell including an outer pump electrode located on an outer surface of the ceramic body, an inner pump electrode located to face the at least one internal chamber, and a solid electrolyte located between the outer pump electrode and the inner pump electrode, the at least one electrochemical pump cell pumping in and out oxygen between the at least one internal chamber and an outside
Implementation Method 4
a heater buried in a predetermined range on a side of the one end portion of the ceramic body
Data Source
AI summary
A first leading-end protective layer surrounding a first range at least including a leading end surface of an element base is included on a side of one end portion. A single heat insulating space is interposed between the first layer and the element base in the first range. The element base further includes a second leading-end protective layer having a larger porosity than the first layer, and located on a whole side surface at least in the first range. An end portion of the first layer opposite the one end portion is a fixed portion to the second layer. A portion where the fixed portion is in contact with the second layer is 10% to 50%, in area, of the first range. The fixed portion and the second layer make an end portion angle of 5° to 15° in an end portion of the heat insulating space.