The principle and characteristics of molybdenum-rhenium alloy high-temperature thermocouples
The molybdenum-rhenium (Mo-Re) alloy thermocouple is a high-temperature temperature sensor that operates based on the Seebeck effect and can provide reliable temperature measurement in extremely high-temperature environments. Its working principle is to utilize two molybdenum-rhenium alloys with different rhenium contents (such as Mo-5Re as the positive electrode and Mo-20Re as the negative electrode) to generate thermoelectric potential under the temperature gradient. By measuring this voltage, the temperature can be calculated, and the output signal has a linear relationship with the temperature. The core materials of molybdenum-rhenium thermocouples are diverse in selection. The common Mo-5Re/Mo-20Re combination has a temperature measurement range of 0-2300°C and has good high-temperature stability. The Mo-41Re/Mo-50Re combination is suitable for the measurement of higher temperatures (>2500°C), but it has a higher cost. Due to the fact that molybdenum-rhenium alloys are prone to oxidation in oxidizing atmospheres, protective measures are usually required, such as using them in inert gas environments, or adopting ceramic sleeves (such as Al₂O₃, ZrO₂) or metal armor (such as Ta, W) for protection to extend their service life. In terms of lead connection, molybdenum-rhenium alloy wire is used at the high-temperature end, while nickel-based alloys (such as Inconel) are used for transition at the low-temperature end to avoid cold end errors.
The structure and material properties of molybdenum-rhenium thermocouples
The structural design of molybdenum-rhenium thermocouples fully takes into account their stability and reliability in high-temperature environments. The selection of its core materials directly determines the temperature measurement range and performance of the thermocouple. The Mo-5Re and Mo-20Re alloy combination has become the most commonly used choice due to its excellent high-temperature stability and moderate cost, and is suitable for the temperature measurement range of 0-2300°C. For applications with higher temperatures, such as extreme environments exceeding 2500°C, the combination of Mo-41Re and Mo-50Re alloys is more suitable, although its cost is higher. To protect molybdenum-rhenium alloys from oxidation, thermocouples are usually used in an inert gas environment (such as argon or hydrogen), or ceramic sleeves (such as alumina or zirconia) are adopted to isolate oxygen. In highly corrosive environments, such as when in contact with molten metals, metal armor (such as tantalum or tungsten) is also used to protect thermocouples. In addition, the design of the lead connection is also of vital importance. The high-temperature end uses molybdenum-rhenium alloy wire, while the low-temperature end uses nickel-based alloys (such as Inconel alloy) for transition to ensure the accuracy and reliability of the measurement.
Application fields of molybdenum-rhenium thermocouples
Molybdenum-rhenium alloy thermocouples play a significant role in multiple key fields due to their outstanding high-temperature performance and stability. In the aerospace field, it is widely used in rocket engine testing, for monitoring the high temperatures (2000~3000°C) of combustion chambers and nozzles, as well as for measuring the temperature distribution of aerodynamic heating in the thermal protection systems of supersonic aircraft. In the fields of metallurgy and materials science, molybdenum-rhenium thermocouples are used in high-temperature melting furnaces to monitor the melting process of refractory metals such as titanium, zirconium, and tungsten, as well as to precisely control the temperature gradient in single crystal growth furnaces (such as sapphire and silicon carbide). In the nuclear industry, it is used for temperature monitoring of nuclear reactor cores and for measuring the ultra-high-temperature areas around the plasma in fusion experimental devices (such as tokamaks). In addition, in scientific research experiments, molybdenum-rhenium thermocouples are also frequently used in the study of superconducting materials and high-pressure and high-temperature experiments (such as diamond anvil experiments) to measure the phase transition temperature of materials.
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