WC-C Peritectic Fixed-Point Cell for High-Temperature Calibration
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Solution Overview
Problem
Conventional temperature fixed-point cells are limited to below 1085°C due to graphite crucible dissolution, leading to inaccurate temperature calibration and reduced purity of metals, making it difficult to achieve precise temperature scales above the copper point, especially in high-temperature ranges where existing methods suffer from low accuracy and material limitations.
Innovation Solution
A temperature fixed-point cell using a graphite crucible with a metal carbon compound forming a peritectic structure, such as tungsten carbide-carbon (WC-C), allowing for accurate calibration by interpolating between fixed points up to 2500°C, eliminating the need for expensive noble metals and improving durability and emissivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a graphite crucible is used to contain pure metal for temperature calibration, then the calibration can be performed below 1085°C, but the graphite crucible dissolves at higher temperatures making it impossible to achieve fixed points above the copper point
Solution Approach 1:
The patent uses a composite material consisting of metal carbide particles dispersed in a metal matrix. This composite structure allows the fixed-point material to withstand temperatures above 1085°C without dissolving the graphite crucible, thereby extending the calibration range while maintaining crucible stability. The metal carbide component provides high-temperature resistance while the metal matrix ensures proper melting behavior for temperature calibration.
2Temperature
If pure metal with high melting point is used for fixed point above copper point, then temperature range is extended, but the metal dissolves graphite crucible reducing purity and lowering freezing point
Solution Approach 1:
The composite material of metal carbide in metal matrix prevents direct contact between pure metal and graphite crucible, eliminating graphite dissolution. This maintains the purity of the fixed-point material and ensures accurate freezing point measurement even at temperatures above the copper point. The metal carbide acts as a protective phase that does not react with graphite.
Solution Approach 2:
The invention creates a localized protective layer of metal carbide at the interface between the fixed-point material and the graphite crucible. This local modification prevents graphite dissolution only where it would occur (at the crucible wall interface), while maintaining the bulk properties of the pure metal for accurate temperature calibration.
3Measurement precision
If conventional fixed-point cell is used, then calibration below copper point is achieved, but temperature scale above copper point requires extrapolation reducing accuracy
Solution Approach 1:
The metal carbide-metal matrix composite enables direct measurement of fixed points in the high-temperature range above the copper point, eliminating the need for extrapolation. This provides accurate calibration data throughout an extended temperature range from below the copper point up to temperatures exceeding 1085°C, significantly improving both measurement precision and temperature range coverage.
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
This solution enhances the accuracy of temperature calibration in high-temperature ranges by using a stable and inexpensive WC-C peritectic point, reducing the number of required fixed points and simplifying the calibration process, while maintaining high reproducibility and stability, thus overcoming the limitations of existing methods.
Implementation Method 1
a metal carbon compound which forms a peritectic structure with carbon
Implementation Method 2
observing the melting and the freezing of alumina at 2050°C with a radiation thermometer, and adopting the melting point as the fixed point
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
A temperature fixed-point cell (4) is configured with a crucible (1) composed of carbon and a fixed-point material enclosed in the crucible. The fixed-point material has a peritectic structure of carbon and a carbon compound. A thermometer (9) is calibrated by installing the temperature fixed-point crucible in a furnace, increasing or decreasing the ambient temperature thereof, measuring the temperature of the temperature fixed-point cell with the thermometer, observing the state of temperature change, and using this state of temperature change as a basis for the calibration. This invention is aimed at realizing a fixed point in the temperature range exceeding the copper point and accomplishing great improvement in accuracy in the calibration of radiation thermometers, thermocouples and all thermometers used in high temperature ranges.