A High Temperature Instrument for Consecutive Measurements of Thermal Conductivity, Electrical Conductivity, and Seebeck Coefficient

Abstract

A device for measuring a plurality of material properties is designed to include accurate sensors configured to consecutively obtain thermal conductivity, electrical conductivity, and Seebeck coefficient of a single sample while maintaining a vacuum or inert gas environment. Four major design factors are identified as sample-heat spreader mismatch, radiation losses, parasitic losses, and sample surface temperature variance. The design is analyzed using finite element methods for high temperature ranges up to 1000 °C as well as ultra-high temperatures up to 2500 °C. A temperature uncertainty of 0.46% was estimated for a sample with cold and hot sides at 905.1 and 908.5 °C, respectively. The uncertainty at 1000 °C was calculated to be 0.7% for a ΔT of 5 °C between the hot and cold sides. The thermal conductivity uncertainty was calculated to be −8.6% at ∼900 °C for a case with radiative gains, and +8.2% at ∼1000 °C for a case with radiative losses, indicating the sensitivity of the measurement to the temperature of the thermal guard in relation to the heat spreader and sample temperature. Lower limits of −17 and −13% error in thermal conductivity measurements were estimated at the ultra-high temperature of ∼2500 °C for a single-stage and double-stage radiation shield, respectively. It is noted that this design is not limited to electro-thermal characterization and will enable measurement of ionic conductivity and surface temperatures of energy materials under realistic operating conditions in extreme temperature environments.