Plasma-chemical synthesis of highly dispersed core–shell structures from a mechanical mixture of titanium carbide and titanium nickelide

Abstract

In this paper, we studied the formation of ultrafine and nanocrystalline core–shell structures based on refractory compounds of titanium with nickel during plasma-chemical synthesis of a mechanical mixture of TiC and TiNi in a low-temperature nitrogen plasma. Cooling took place in an intensely swirling nitrogen flow in a quenching chamber. The derived products were separated in a vortex-type cyclone and a bag-type fabric filter. After processing, the products were subjected to encapsulation aimed at reducing the pyrophoricity for long-term storage of the resulting finely dispersed powders under normal conditions. X-ray diffraction and high-resolution transmission electron microscopy were used to study the resulting powder products of plasma-chemical synthesis, and density measurements were conducted. Additionally, to define the average particle size more accurately, the specific surface was measured using the BET method. The instrumental research revealed the presence of ultra- and nanodispersed particles with a core–shell structure in the powder products. These particles included titanium carbide-nitride compounds as a refractory core and metallic nickel as a metallic shell. In addition, the presence of complex titanium-nickel nitride Ti0.7Ni0.3N was recorded. According to direct measurements, the average particle size of the nanocrystalline fraction is 18.9 ± 0.2 nm. The obtained research results enabled us to develop a chemical model of crystallization of TiCxNy–Ni core–shell structures, which is implemented in a hardening chamber at a crystallization rate of 105 °С/s. To fabricate the model, we used the reference data on the boiling and crystallization temperatures of the elements and compounds being a part of highly dispersed compositions and recorded by X-ray diffraction, as well as the ΔG(t) dependences for TiC and TiN.