Ammonia Sensor Porous Layer for Co-firing Impedance
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Solution Overview
Problem
The impedance of ammonia sensors in urea SCR systems increases due to co-firing, leading to reduced detection accuracy caused by a decrease in the three-phase boundary area between the reference electrode and the solid electrolyte body.
Innovation Solution
Incorporating an insulating porous layer between the electrically insulating member and the reference electrode, or making part of the solid electrolyte body porous, to increase the inflow of the target gas and maintain or enhance the three-phase boundary area, thereby suppressing impedance rise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a stack of the reference electrode and the solid electrolyte body is formed on a green insulating layer and then they are co-fired, then the manufacturing process is simplified, but the insulating layer shrinks, the reference electrode becomes dense, and the area of the three-phase boundary is reduced, causing impedance to rise
Solution Approach 1:
The patent introduces a porous layer between the insulating layer and the reference electrode. This porous layer maintains gas permeability and prevents the reference electrode from becoming overly dense during co-firing, thereby preserving the three-phase boundary area and preventing impedance rise while still allowing the co-firing process to proceed.
Solution Approach 2:
The porous layer acts as an intermediary component between the insulating layer and the reference electrode. It mediates the interaction during co-firing by providing a buffer that prevents direct contact and excessive densification of the reference electrode, thus maintaining the three-phase boundary area while enabling the simplified co-firing manufacturing process.
2Strength
If the reference electrode becomes dense due to co-firing, then the structural integrity is improved, but the area of the three-phase boundary is reduced, causing impedance to rise
Solution Approach 1:
The porous layer provides a controlled porous structure that allows gas diffusion while preventing the reference electrode from becoming excessively dense. This maintains adequate three-phase boundary area for low impedance while still allowing the reference electrode to achieve sufficient structural integrity through controlled sintering.
Solution Approach 2:
The patent creates a composite structure consisting of the insulating layer, porous layer, reference electrode, and solid electrolyte body. This composite structure balances the competing requirements of structural integrity and gas permeability by distributing functions across different layers, allowing the reference electrode to be structurally sound without becoming overly dense.
3Device complexity
If the area of the three-phase boundary is reduced, then the device complexity is reduced, but the impedance rises, reducing detection accuracy
Solution Approach 1:
The porous layer increases the effective surface area available for gas diffusion and three-phase boundary formation without significantly increasing device complexity. The porous structure provides numerous pathways and surfaces for gas interaction, maintaining large effective boundary area while adding only a single layer component to the overall device structure.
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 maintains or improves the detection accuracy of ammonia sensors by preventing impedance increases during co-firing, ensuring reliable gas concentration measurements.
Implementation Method 1
an insulating porous layer made of an electrically insulating porous material and disposed between the electrically insulating member and the reference electrode. The insulating porous layer has many pores in its interior and on its surface.
Implementation Method 2
a solid electrolyte body, and a detection electrode that are stacked in this order on the electrically insulating member
Data Source
AI summary
An ammonia detection section is disposed on an electrically insulating layer and includes a reference electrode, a solid electrolyte body for ammonia, and a detection electrode that are stacked in this order on the electrically insulating layer. In the ammonia detection section, a three-phase boundary is formed at the interface between the reference electrode and the solid electrolyte body for ammonia, and another three-phase boundary is formed at the interface between the detection electrode and the solid electrolyte body for ammonia. The concentration of ammonia in exhaust gas is thereby detected. The ammonia detection section includes a porous layer formed of an electrically insulating porous material and disposed between the insulating layer and the reference electrode.