Multi-stepwise pulse calorimetry for enthalpy and emissivity measurements on tantalum, considering gas-metal reactions at elevated temperatures

Refractory metals such as tantalum are widely used for high-temperature applications; however, the thermophysical properties of tantalum are not accurately determined at temperatures approaching the melting point. Combining dynamic and static calorimetric methods, the enthalpy and total hemispherical emissivity of tantalum were determined within the 1000-3230 K temperature range. The combined approach considers the influence of reactions between the metal, minor impurities, and residual gas within a high-vacuum environment. The tantalum sample consistently absorbs residual water vapor within the vacuum chamber. At temperatures near the tantalum melting point, the absorbed hydrogen and oxygen atoms are desorbed. The kinetic nature of the gas-metal reactions determines the appropriate conditions for enthalpy and emissivity measurements via dynamic and static calorimetry, respectively. The enthalpy measured under dynamic conditions favorably agrees with the literature data derived from levitation drop calorimetry, rather than those from classical pulse calorimetry, especially near the melting point.

Automated summary

The thermophysical properties of tantalum at high temperatures were investigated, and a combined approach of dynamic and static calorimetry was used to determine the enthalpy and emissivity of tantalum. The study considered the influence of reactions between the metal, minor impurities, and residual gas, as well as the absorption and desorption processes of hydrogen and oxygen atoms by the tantalum sample.