Low-temperature synthesis of ultra-high-temperature HfC and HfCN nanoparticles

Hafnium carbide (HfC) and carbonitride (HfCxNy) nanoparticles were synthesized via reduction of HfO2 oxide with calcium hydride in the presence of carbon or carbon/nitrogen, refractory phases were synthesized at 1473 K, respectively. The average particle size of the obtained materials was in the range of 50–90 nm, allowing them to be ranged in a class of nanodispersed powders. The synthesized HfC had a lattice parameter of 0.4640 nm, which corresponds to the HfC1.0 stoichiometry. The diffraction spectra of the HfCxNy can be described by two isomorphic phases of approximate stoichiometry HfC0.91N0.09 (0.4629 nm) and HfC0.58N0.42 (0.4591 nm). Both HfC and HfCxNy nanoparticles had a predominantly cubic morphology, TEM observations revealed the presence of the continuous amorphous film with a thickness of 4–5 nm on their surface. The excess of reducing agent and external atmospheric pressure (argon) above the reaction volume were identified as the technological parameters, which strongly affect the quality of the synthesized HfCN powder. Also, it was shown that the formation of refractory HfC and HfCN particles under the presented experimental conditions is controlled by the dissolution-precipitation mechanism.