Perovskite Thermistor with Complex Oxide Coating for High-Temperature Stability
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Solution Overview
Problem
Thermistor elements used in temperature sensors for internal combustion engines face challenges in maintaining stable resistance characteristics over a wide temperature range due to thermal oxidation and metal migration between the perovskite phase and reduction-resistant coatings in reducing atmospheres, leading to changes in resistance values.
Innovation Solution
A thermistor element with a perovskite phase and a reduction-resistant coating formed from a complex oxide containing A-site and B-site elements, where the coating is sintered simultaneously with the thermistor body to prevent metal migration and maintain stable resistance characteristics, using a composition like (Y, Sr)(Mn, Cr, Al)O3 with a complex oxide such as SrAl2O4 for the coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a metal tube is used to protect the thermistor element from condensation and soot, then the thermistor element can operate in harsh exhaust gas environments, but the metal tube oxidizes at high temperatures creating a reducing atmosphere that changes the thermistor resistance
Solution Approach 1:
The patent applies a composite coating structure consisting of an inner oxide layer (e.g., Al2O3, Cr2O3) and an outer reduction-resistant layer (e.g., Y2O3, SiO2, or complex oxides like Y3Al5O12). This multi-layer composite structure provides both protection from condensation/soot and resistance to thermal reduction, resolving the contradiction between environmental protection and resistance stability.
2Reliability
If a reduction-resistant coating is applied to the thermistor body, then the thermistor is protected from thermal reduction, but metal elements migrate between the perovskite phase and the coating causing composition changes and resistance drift
Solution Approach 1:
The patent carefully selects coating materials with specific chemical composition parameters that match or are compatible with the perovskite phase. By controlling the chemical composition parameters (selecting oxides with appropriate stability and compatibility), the patent prevents metal migration while maintaining reduction resistance, thus resolving the contradiction between protection and compositional stability.
Solution Approach 2:
The use of composite oxide coatings (e.g., Y-Al-O system, Sr-Al-O system) creates a chemically stable interface between the perovskite phase and the coating. The composite structure with specific stoichiometry prevents excessive metal migration by creating a diffusion barrier while maintaining the reduction-resistant properties, thereby resolving the contradiction.
3Temperature
If the thermistor element is designed for high temperature operation up to 900°C, then it can protect DPF and NOx catalyst, but the perovskite phase and coating compositions vary due to metal migration at high temperatures
Solution Approach 1:
The patent employs composite oxide coatings such as Y3Al5O12, SrAl2O4, or other complex oxides that remain chemically stable at high temperatures up to 900°C. These composite materials form a stable interface with the perovskite phase, preventing metal migration even under prolonged high-temperature exposure, thus enabling high-temperature operation while maintaining compositional stability.
Solution Approach 2:
The patent optimizes the chemical composition parameters of both the perovskite phase and the coating material to ensure compatibility at high temperatures. By selecting specific oxide compositions with matched thermal and chemical properties, the patent prevents composition drift during high-temperature operation, resolving the contradiction between temperature capability and stability.
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 enables stable resistance characteristics over a wide temperature range from -40°C to 900°C, minimizing resistance changes and ensuring accurate temperature measurements even under high-temperature, reducing conditions.
Implementation Method 1
A thermistor element is generally produced from a sintered conductive oxide that shows a change in resistance (specific resistance) with a change of temperature
Implementation Method 2
a reduction-resistant coating covering the thermistor body and formed of a complex oxide containing one or more of the at least one A-site element and one or more of the at least one B-site element
Implementation Method 3
Japanese Laid-Open Patent Publication No. 11-251109 discloses one type of thermistor element having a thermistor body formed of a sintered conductive oxide
Data Source
AI summary
A thermistor element includes a thermistor body and a reduction-resistant coating covering the thermistor body. The thermistor body contains a perovskite phase of perovskite-type crystal structure represented by the composition formula: ABO3 where A is at least one A-site element and B is at least one B-site element. The reduction-resistant coating is formed of a complex oxide containing one or more of the at least one A-site element and one or more of the at least one B-site element.