Platinum Thermocouple Wire Nitrogen Doping Creep Strength
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Solution Overview
Problem
Platinum thermocouple wires with pure platinum as the negative electrode suffer from low creep strength and early rupture due to grain growth, and the addition of zirconium oxide to enhance strength can lead to breakage and electromotive force deviations, especially in thin wires under load and reducing atmospheres.
Innovation Solution
Incorporating a nitrogen mass concentration of 10 to 100 ppm into the platinum wire to slow crystal grain growth and prevent slip at grain boundaries without using metal oxides, maintaining a platinum purity of 4 N or more and controlling impurity concentrations to minimize electromotive force interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If zirconium oxide is dispersed in the platinum wire to increase strength, then creep strength is improved, but the wire is likely to break and electromotive force deviation occurs
Solution Approach 1:
The invention removes zirconium oxide and other metal oxides from the platinum wire composition entirely. By extracting the harmful oxide dispersoids and replacing them with a pure platinum structure containing controlled impurity elements (Cu, Ni, Rh, Ir, Pd, Au, Ag, Pt) within specific concentration ranges, the wire achieves both high creep strength and reliability without oxide-induced breakage or electromotive force deviation.
Solution Approach 2:
The invention changes the compositional parameters by precisely controlling the concentrations of multiple impurity elements within specific ranges (e.g., Cu: 0.001-0.1 wt%, Ni: 0.001-0.1 wt%, Rh: 0.001-0.05 wt%). This parameter optimization allows the platinum wire to achieve enhanced creep strength through controlled solid solution strengthening while maintaining electrical stability and avoiding the harmful effects of oxide dispersion.
2Adaptability or versatility
If the wire diameter is reduced to 700 μm or less for general thermocouple use, then the thermocouple becomes more versatile, but zirconium oxide becomes a starting point of breakage
Solution Approach 1:
The invention extracts zirconium oxide from the wire composition, eliminating the oxide-induced breakage initiation sites that plague thin-wired thermocouples. This removal allows the wire to be manufactured with diameters of 700 μm or less while maintaining high reliability and breakage resistance, thereby expanding the versatility of thermocouple applications.
Solution Approach 2:
The invention creates a composite-like structure within pure platinum by incorporating controlled amounts of multiple impurity elements (Cu, Ni, Rh, Ir, Pd, Au, Ag) that work synergistically to strengthen the matrix. This internal composite approach provides reinforcement without the harmful effects of discrete oxide particles, enabling thin wire diameters to achieve both versatility and breakage resistance.
3Strength
If zirconium oxide is added to increase strength, then creep resistance is improved, but electromotive force deviation occurs in reducing atmosphere
Solution Approach 1:
The invention removes zirconium oxide and other reducible metal oxides from the platinum wire composition. By eliminating these oxide phases that can decompose in reducing atmospheres and cause electromotive force deviation, the wire maintains both high creep resistance and stable electromotive force characteristics under reducing conditions through controlled impurity element addition.
Solution Approach 2:
The invention optimizes the compositional parameters by controlling the concentrations of stable impurity elements (Cu: 0.001-0.1 wt%, Ni: 0.001-0.1 wt%, Rh: 0.001-0.05 wt%, Ir: 0.001-0.05 wt%, Pd: 0.001-0.05 wt%, Au: 0.001-0.05 wt%, Ag: 0.001-0.05 wt%) within specific ranges. This parameter control achieves creep resistance through solid solution strengthening while ensuring electromotive force stability in reducing atmospheres by avoiding reducible oxide phases.
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 approach effectively increases the creep strength of platinum thermocouple wires by suppressing crystal grain growth and slip, preventing early rupture even at high temperatures and reducing the risk of electromotive force deviations, while avoiding the issues associated with metal oxide dispersion.
Implementation Method 1
containing a predetermined amount of a nitrogen element in a platinum wire... crystal growth is slowed in order to prevent damage caused by creep without dispersing a metal oxide, and occurrence of slip at crystal grain boundaries is slowed
Data Source
AI summary
A platinum wire in which crystal grain growth is slowed in order to prevent damage caused by creep without dispersing a metal oxide, and occurrence of slip at crystal grain boundaries is slowed. A platinum thermocouple wire that is used in a negative electrode of a platinum-based thermocouple and has a nitrogen mass concentration of 10 to 100 ppm, and when structure observation of the cross section of the wire in a longitudinal direction is performed, a structure is observed in which there is a plurality of crystal grains, which have an aspect ratio {(length of major axis)/(length of minor axis perpendicular to major axis)} of 5 or more and elongate in the longitudinal direction of the wire, in a wire thickness direction.