Gas Sensor Gettering Layer for Oxidation Suppression
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Solution Overview
Problem
Gas sensors used for NOx detection face degradation due to oxidation of electrodes and heater elements, leading to reduced sensitivity and increased heater resistance, caused by impurities such as Fe, Ti, Na, Ca, Mg, K, Ni, and Cu, which vaporize at high temperatures, affecting the accuracy and longevity of the sensor.
Innovation Solution
Incorporating a gettering layer made of zirconia with added SiO2 and Al2O3 between the solid electrolyte layers and electrodes to capture impurities, preventing their vaporization and maintaining the purity of Pt and Rh, thus suppressing oxidation and maintaining sensor sensitivity and heater integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sensor element is heated to high temperature (600-900°C) to enable electrochemical detection, then the electrochemical properties are exhibited, but the electrodes and heater are oxidized and impurities vaporize causing degradation
Solution Approach 1:
A protective layer is introduced as an intermediary between the electrodes/heater and the oxygen-containing atmosphere. This layer contains gettering materials (such as rare earth metals like Ce, La, Nd, or their oxides) that preferentially react with oxygen and impurities, preventing them from reaching and oxidizing the electrodes and heater elements. The protective layer acts as a barrier that mediates the interaction between the heated components and the harsh atmospheric environment.
Solution Approach 2:
The protective layer creates a locally inert environment around the electrodes and heater by consuming oxygen through gettering reactions. The gettering materials within the protective layer bind with oxygen to form stable oxides, effectively removing oxygen from the immediate vicinity of the electrodes and heater, thus creating an oxygen-depleted (inert) atmosphere that prevents oxidation of the sensitive components.
2Reliability
If impurities are present in the electrodes, then the vaporization of Pt and Rh is promoted, but the sensor sensitivity is degraded
Solution Approach 1:
The protective layer serves as an intermediary that captures impurities before they can catalyze the vaporization of electrode materials. The gettering materials in the protective layer bind with impurity elements (such as Fe, Ti, Na, Ca, Mg, K, Ni, Cu), preventing these impurities from interacting with the electrode surfaces and promoting vaporization of Pt and Rh.
Solution Approach 2:
The protective layer performs self-service by automatically gettering impurities and oxygen through chemical reactions. The gettering materials within the protective layer continuously react with incoming oxygen and impurity species, self-regulating the chemical environment around the electrodes without requiring external intervention, thus preventing vaporization and sensitivity degradation.
3Reliability
If the heater element is oxidized, then the heater resistance increases, but the heater element may break
Solution Approach 1:
The protective layer acts as a mediator between the oxygen-containing atmosphere and the heater element. The gettering materials in the protective layer consume oxygen through chemical reactions, preventing oxygen from reaching and oxidizing the heater element. This intermediary layer thus protects the heater from oxidation-induced resistance increase and potential breakage.
Solution Approach 2:
The protective layer creates an oxygen-depleted inert environment around the heater element by continuously binding with oxygen through gettering reactions. This locally inert atmosphere prevents oxidation of the heater element, maintaining its electrical resistance and structural integrity over time.
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 gettering layers effectively reduce the vaporization of Pt and Rh oxides, enhancing the long-term stability and accuracy of NOx detection by maintaining the catalytic activity and reducing the increase in heater resistance, leading to improved durability and performance of the gas sensor.
Implementation Method 1
a gettering layer located between the plurality of solid electrolyte layers and between the plurality of solid electrolyte layers and each of the pair of electrodes, and gettering impurities in a metal component of the electrodes and the heater part during driving of the gas sensor element
Implementation Method 2
it is necessary to heat the sensor element to a sensor element driving temperature that is a relatively high temperature of approximately 600° C. to 900° C., for example, using a heater provided inside the sensor element
Implementation Method 3
A limiting current gas sensor (NOx sensor) including a sensor element mainly formed of an oxygen-ion conductive solid electrolyte
Data Source
AI summary
A gas sensor element in which oxidation of electrodes and a heater occurring with continued use is suppressed is provided. The gas sensor element includes a plurality of solid electrolyte layers stacked one over another, and includes an electrochemical cell including a pair of electrodes and a portion of the plurality of solid electrolyte layers existing between the pair of electrodes; a heater part capable of heating the gas sensor element; and a gettering layer located between the plurality of solid electrolyte layers and between the plurality of solid electrolyte layers and each of the pair of electrodes, and gettering impurities in a metal component of the electrodes and the heater part during driving of the gas sensor element.