Thermophysical properties of Rh ₃X for ultra-high temperature applications

Thermal conductivity and thermal expansion were measured for the L1 ₂ intermetallic compounds Rh ₃X (X = Ti, Zr, Hf, V, Nb, Ta) in the temperature range 300-1100 K to evaluate the feasibility of applying the compounds as ultra-high temperature structural materials. The thermal conductivities of Rh ₃X are widely distributed over the range 32-103 W m ^-1 K ^-1 at 300 K, but the differences between the thermal conductivities diminish at higher temperatures. A trend is observed in that the thermal conductivity of Rh ₃X is greater if the constituent X belongs to Group 5 rather than to Group 4 in the Periodic Table. The coefficient of thermal expansion (CTE) values of Rh ₃X increase slightly with increasing temperature; values are concentrated around 10 × 10 ^-6 K ^-1 at 800 K. CTE values of Rh ₃X decrease as X appears lower in the Periodic Table. It is demonstrated that Rh ₃Nb and Rh ₃Ta are suitable for ultra-high temperature structural applications due to their higher thermal conductivities and smaller CTE values.