Pt-Rh-Sr Alloy Electrode Wire Grain Growth Resistance
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Solution Overview
Problem
Conventional platinum-rhodium alloy electrode wires in temperature sensors experience grain coarsening and reduced strength at high temperatures, leading to potential breakage and instability over long-term use.
Innovation Solution
A ternary platinum-rhodium alloy with 0.1 to 1.5 mol% Sr, 22 to 40 mol% Rh, and the remainder composed of Pt and unavoidable impurities is used, where second-phase precipitated grains composed of Sr and Pt are dispersed in a matrix phase, restricting grain boundary movement and enhancing strength through precipitation strengthening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional binary platinum-rhodium alloy is used as electrode wire material, then good processability and initial strength are achieved, but grain coarsening occurs at high temperatures leading to reduced strength and reliability
Solution Approach 1:
The patent applies composite material principle by creating a ternary platinum-rhodium-strontium alloy where Sr forms a second phase dispersed in the Pt-Rh matrix. This composite structure prevents grain boundary coarsening at high temperatures while maintaining strength and electrical conductivity, resolving the contradiction between initial strength and long-term reliability.
Solution Approach 2:
The patent changes the compositional parameters by adding Sr element (0.1-2.0 at%) to the Pt-Rh alloy system. This parameter change induces precipitation hardening and forms a stable second phase that pins grain boundaries, preventing the grain coarsening that occurs in conventional binary Pt-Rh alloys at high temperatures.
2Temperature
If platinum-rhodium alloy is used at high temperatures for long term, then heat resistance is maintained, but grain growth occurs causing crystal grains to coarsen and increase breakage probability
Solution Approach 1:
The patent applies preliminary action by pre-forming fine Sr-containing precipitates during alloy fabrication that will serve as grain boundary pinning sites during high-temperature service. This preliminary precipitation structure prevents subsequent grain growth, maintaining grain structure stability throughout the operational temperature range.
Solution Approach 2:
The patent extracts Sr element from the conventional binary Pt-Rh alloy system and introduces it as a third component. This extracted element forms a distinct second phase that can be controlled to precipitate in specific patterns, actively managing grain structure stability without interfering with the base alloy's heat resistance properties.
3Strength
If Sr is added to form second phase precipitates, then grain boundary movement is restricted and strength is enhanced, but excessive Sr may degrade electrical conductivity
Solution Approach 1:
The patent applies partial action by limiting Sr content to a specific range (0.1-2.0 at%, preferably 0.1-1.0 at%). This controlled partial addition is sufficient to form the necessary precipitates for grain boundary pinning and precipitation strengthening, while remaining below the threshold that would create excessive second phase and degrade electrical conductivity.
Solution Approach 2:
The patent optimizes the concentration parameter of Sr addition to achieve the desired balance. By controlling Sr content within specific ranges, the patent achieves optimal precipitate density that provides adequate grain boundary pinning for strength enhancement while maintaining sufficient electrical conductivity for sensor operation.
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 ternary platinum-rhodium alloy maintains high-temperature strength and durability, preventing electrode wire breakage and ensuring reliable operation at elevated temperatures without degrading electrical or thermal conductivity.
Implementation Method 1
second-phase composed essentially of Sr and Pt whose precipitated grains are dispersed in a matrix phase, and an area ratio of the second phase at a cross section is not greater than 25%
Implementation Method 2
second-phase composed essentially of Sr and Pt whose precipitated grains are dispersed in a matrix phase... restricting grain boundary movement
Data Source
AI summary
A temperature sensor includes: a temperature sensing element including a temperature sensing portion, electrical characteristics of which vary depending on temperature, and an electrode wire for outputting an electric signal from the temperature sensing portion to the outside; and a sheath core wire (signal wire) electrically connected to the electrode wire. The electrode wire is made of a platinum-rhodium alloy. The platinum-rhodium alloy is composed of 0.1 to 1.5 mol % of Sr, 22 to 40 mol % of Rh, and a remainder composed of Pt and unavoidable impurities. The platinum-rhodium alloy has a second-phase mainly composed of Sr and Pt whose precipitated grains are dispersed in a matrix phase. An area ratio of the second phase at a cross section is not greater than 25%.