Low-Temperature Synthesis of Ultra-High-Temperature HfC and HfCN Nanoparticles

Hafnium carbide (HfC) and carbonitride (HfC x N y ) nanoparticles were synthesized via reduction of the HfO 2 oxide with calcium hydride in the presence of carbon or carbon/nitrogen, refractory phases were synthesized at 1473 K, respectively. An average particle size of the obtained materials laid 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 HfC 1.0 stoichiometry. The diffraction spectra of the HfC x N y can be described by two isomorphic phases of approximate stoichiometry HfC 0.91 N 0.09 (0.4629 nm) and HfC 0.58 N 0.42 (0.4591 nm). Both HfC and HfC x N y nanoparticles had a predominantly cubic morphology, TEM observations revealed presence of the continuous amorphous film with a thickness of 4 - 5 nm on their surface. 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-deposition mechanism.