In-flight Synthesis of Nanosized ZrC Particles from Various Precursors in RF Thermal Plasma
Synthesis of zirconium carbide (ZrC) powder was investigated applying a non-conventional atmospheric radiofrequency (RF) thermal plasma process. In one case, zirconium dioxide (ZrO2) was reacted with solid carbon or with methane with varying molar ratio. In the other, zirconium-propoxide (NZP), containing both constituents, was thermally decomposed in the Ar plasma.
Temperature-dependent thermodynamic analysis was performed in the 500-5500 K temperature range to estimate the formation of possible equilibrium products for each reaction stoichiometry. Broad temperature range exists for the stability of solid ZrC for each explored reaction system. In accordance with this prediction, X-ray diffraction studies detected the ZrC as the major phase in all the prepared powders. The yield of particular runs ranged from 39 % to 98 %. Practically, full conversion was typical for the case of NZP precursor, however only partial conversion could be detected in ZrO2 reactions.
The average particle size of the powders falls between 10 nm and 100 nm depending on the type of the reaction systems (either calculated from the specific surface area or derived from broadening the XRD reflections). The transmission electron micrographs indicated mostly globular shape of the nanosize particles. Quantitative analysis of the surface of the powders by X-ray photoelectron spectroscopy revealed the presence of oxygen and carbon. Evaluating the spectra of the powders prepared from NZP, and taking in the account its spherical shape, a ZrC core covered by a very thin (≈1.0 nm) ZrO2 layer may be accounted for the measured oxygen and a thicker carbonaceous layer.