Conductive Sintered Oxide Thermistor for Wide Temperature Range Stability
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Solution Overview
Problem
Thermistor elements used in temperature measurements, particularly in exhaust gas applications, face challenges in measuring a wide temperature range and maintaining stability at high temperatures, with existing conductive sintered oxides having temperature gradient constants above 2,000K and experiencing resistance changes over time.
Innovation Solution
A conductive sintered oxide with a perovskite structure, composed of specific elements like Yb, Lu, Sr, Al, Mn, and Cr, is developed, with carefully controlled coefficients c and d to achieve a temperature gradient constant of 2,000K or less and minimize resistance changes over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the temperature gradient constant is reduced to extend the measurable temperature range, then the temperature measurement range is improved, but the resistance stability at high temperatures deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the compositional parameters c and d in the perovskite structure formula (RE 1-c Sr c )M d O 3. By setting c between 0.18 and 0.40 and d between 0.67 and 0.93, the patent achieves a temperature gradient constant of 2000K or less while maintaining resistance stability. This involves changing the chemical composition parameters to simultaneously optimize both the temperature measurement range and high-temperature stability.
Solution Approach 2:
The patent uses composite materials by creating a perovskite structure containing multiple elements: RE (Yb and/or Lu and at least one Group IIIA element), M (Al and at least one element from Groups IVA, VA, VIA, VIIA, or VIII). This multi-element composite structure within the perovskite framework enables both the reduced temperature gradient constant and improved resistance stability that single-element materials cannot achieve.
2Reliability
If the coefficient d is increased to reduce resistance change over time, then the resistance stability is improved, but the constant B increases reducing temperature measurement capability
Solution Approach 1:
The patent resolves this contradiction through parameter changes by defining a specific range for coefficient d (0.67 ≤ d ≤ 0.93) in the perovskite structure. This parameter optimization ensures that the resistance stability is improved while the constant B remains at 2000K or less, maintaining temperature measurement capability. The precise control of this compositional parameter balances both requirements.
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 measurements over a wide temperature range from -40°C to +600°C, with minimal resistance change even after prolonged exposure to high temperatures, enhancing the precision and reliability of temperature sensors.
Implementation Method 1
a conductive sintered oxide which has electrically conductive properties and which changes in resistivity with a change in temperature
Data Source
Figure 1
Figure 2~3B
Figure 4
AI summary
A conductive sintered oxide which includes: a conductive crystal phase having a perovskite structure represented by (RE1-cSrc)MdO3, in which RE is a group of elements consisting of Yb and/or Lu and at least one element selected from Group IIIA elements excluding Yb, Lu and La, and M is a group of elements consisting of Al and at least one element selected from Groups IVA, VA, VIA, VIIA and VIII, a first insulating crystal phase represented by RE2O3, and a second insulating crystal phase represented by SrAl2O4. The conductive crystal phase has a coefficient c satisfying 0.18<c<0.50 and has a coefficient d satisfying 0.67≤d≤0.93. A content of a third insulating crystal phase represented by RE4Al2O9, the content of which may be zero, is smaller than the content of each of the first and second insulating crystal phases.