Sintering behavior of ZrC, NbC, TaC, and (Zr_0.33, Nb_0.33, Ta_0.33)C and the effects of powder impurities

When mixed with uranium carbide, solid solutions of niobium carbide (NbC), tantalum carbide (TaC), and zirconium carbide (ZrC) are potential fuel candidates for nuclear thermal propulsion applications due to their high melting temperatures, stability in hot hydrogen, and low cross section of absorption for thermal neutrons. In this study, the spark plasma sintering (SPS) conditions to reach >95% relative density were determined for NbC, TaC, and ZrC mono-carbides and (Zr_0.33, Nb_0.33, Ta_0.33)C. Oxide impurities found in one feedstock of ZrC were determined to significantly impact the SPS sintering conditions of the mono-carbide and tri-carbide samples containing the impure ZrC powder. The sintering temperature required to reach >95% relative density for the tri-carbide mixtures was found to be influenced most by the constituent with the lowest melting temperature, ZrC. The calculated densification activation energies for (Zr_0.33, Nb_0.33, Ta_0.33)C were comparable to those of the ZrC powders, with impurity content varying based on the material supplier.