Gas Sensor Element Electrode Shrinkage and Blackening Prevention
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Solution Overview
Problem
Conventional gas sensor elements face issues with blackening and green breakage of the solid electrolyte member during manufacturing, leading to impaired function and cracking upon firing, due to insufficient oxygen supply and thermal shrinkage differences between ceramic and metal components.
Innovation Solution
Incorporating a ceramic porous member to sandwich and protect the end portions of the cavity side electrode, preventing shrinkage and ensuring adequate oxygen supply, thereby preventing blackening and green breakage of the solid electrolyte member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the end portion of the electrode is held and covered by a dense member to restrain shrinkage, then green breakage is restrained, but oxygen supply to the electrode portion becomes insufficient causing blackening
Solution Approach 1:
The patent applies different material properties to different regions: the dense member covers only the end portion of the electrode to prevent shrinkage, while the middle portion remains exposed to oxygen. This local differentiation allows simultaneous achievement of shrinkage restraint and adequate oxygen supply, preventing both green breakage and blackening.
Solution Approach 2:
The electrode coverage is segmented into two distinct zones: a covered end portion for shrinkage restraint and an uncovered middle portion for oxygen supply. This segmentation resolves the contradiction by allowing each zone to fulfill its specific function without interfering with the other.
2Ease of manufacture
If the green solid electrolyte sheet is heated in debindering step, then organic components are removed, but volume shrinkage occurs causing green breakage
Solution Approach 1:
The dense member is positioned to cover the electrode end portion before the debindering heating process begins. This preliminary protective action restrains the electrode during the subsequent volume shrinkage that occurs when organic components are removed, preventing green breakage while allowing the debindering process to complete successfully.
3Adaptability or versatility
If thermal shrinkage difference between ceramic and metal occurs during firing, then temperature change is accommodated, but cracking is produced in the solid electrolyte member
Solution Approach 1:
The dense member is strategically positioned at the end portion of the electrode where thermal shrinkage differences would concentrate stress. This localized coverage acts as a stress-distributing element that accommodates thermal expansion differences during firing while preventing crack initiation and propagation in the solid electrolyte member.
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 blackening and green breakage of the solid electrolyte member during manufacturing, ensuring the gas sensor element's integrity and accuracy in detecting gases post-firing.
Implementation Method 1
the porous member is provided in a hollow cavity so as to sandwich at least a part of an end portion of a cavity side electrode... ensuring adequate oxygen supply
Data Source
AI summary
A gas sensor element of an air/fuel ratio sensor has a structure in which at least a part of an end portion of a porous electrode is sandwiched between a porous member and a solid electrolyte member. Therefore, it is possible to restrain shrinkage of the porous electrode during manufacture of the gas sensor element, which shrinkage would otherwise occur at the time of heating in a debindering step or at the beginning of a firing step, whereby occurrence of green breakage in the solid electrolyte member is restrained. Thus, cracking due to green breakage is restrained from occurring in the solid electrolyte member produced through firing. Since the end portion of the porous electrode can receive oxygen through the porous member, blackening of the solid electrolyte member can be prevented.