Gas Sensor Element Buffer Layer to Prevent Firing Cracks
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Solution Overview
Problem
Cracks occur in the gas introduction portion of gas sensor elements during manufacturing due to the shrinkage of the carbon paste layer overlapping the opening, which is formed larger than necessary to account for printing misalignment, causing the unfired gas introduction portion to be pulled and torn by the peripheral edge of the shrinking paste layer.
Innovation Solution
A gas sensor element design that includes a buffer layer made of ceramic with a lower shrinkage start temperature than the gas introduction portion, positioned to overlap the boundary between the gas introduction portion and the second ceramic structure, and a reinforcing layer to support the structure, along with specific materials like zirconia and alumina for the buffer and gas introduction portions, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the carbon paste layer is formed with a large size to account for printing misalignment, then the printing alignment tolerance is improved, but the gas introduction portion is pulled and torn by the shrinking paste layer during firing
Solution Approach 1:
A buffer layer made of zirconia-containing ceramic is introduced between the carbon paste layer and the gas introduction portion. This intermediary layer absorbs the shrinkage stress during firing, preventing the carbon paste layer from directly pulling and tearing the gas introduction portion, thus resolving the contradiction between allowing printing misalignment and maintaining structural integrity
Solution Approach 2:
The shrinkage start temperature of the buffer layer is designed to be lower than that of the gas introduction portion. During firing, the buffer layer shrinks first at lower temperatures, accommodating the shrinkage of the carbon paste layer before the gas introduction portion shrinks, thereby preventing mechanical damage to the gas introduction portion
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 suppresses defects such as cracks in the gas introduction portion, ensuring the integrity and functionality of the gas sensor element.
Implementation Method 1
a buffer layer which is made of ceramic composed of a material having a lower shrinkage start temperature than a material forming the gas introduction portion
Data Source
AI summary
A gas sensor element includes: a first ceramic structure (100A) having a detection cell (120); a second ceramic structure (100B) having a pump cell (110) disposed apart from the first ceramic structure in a lamination direction; and a third ceramic structure (100C) having a frame-shaped body (200) surrounding a space (150a) formed between the first and second ceramic structures, the frame-shaped body including a gas introduction portion (151) and a peripheral wall portion (141). A gap (150b) connected to the space (150a) is formed between an opposed surface (151b1) and the second ceramic structure. A ceramic buffer layer (300) having a lower shrinkage start temperature than a material for forming the gas introduction portion is formed on the opposed surface so as to overlap a boundary portion X between an edge (150b1) on the external side of the gap and the second ceramic structure when viewed in the lamination direction.