Vol 28, No 3 (2019)

–The gas-sensing properties of nickel ferrite (NiFe₂O₄) and nickel oxide (NiO) nanoparticles prepared by a self-sustaining levitation-jet synthesis (LJS) method are reported. These have been compared to the gas-sensing properties of a NiO sensor prepared using a commercially sourced powder. The microstructure, surface area, particle size, and morphology varied widely across the sensors fabricated. It was anticipated that these contrasting properties would play a key role in either enhancing or worsening the sensing capabilities of the materials. Gases of interest included ethanol, toluene, and carbon monoxide as well as the gas response of the sensors was investigated at different operating temperatures. In general, the sensors responded to gases with different degrees of sensitivity. Among the sensors with higher surface areas, one provided noticeable enhancements in sensitivity towards gases when compared, for instance, to the sensitivity of the commercially based NiO sensor. The NiFe₂O₄ sensor presented most promise as a gas sensor to ethanol and, to a greater or lesser degree, towards toluene gas. In general, sensors were poorly responsive to the carbon monoxide concentrations tested. This study is one of the first reports of using LJS-based powders for gas sensing applications and it highlights the suitability of the method to fabricate size- and shape-controlled nanomaterials for the detection of environmentally relevant gases.

Fine powders of pure Si₂N₂O were SHS-produced under pressure of nitrogen gas from mixtures doped with FeCl₃ · 6H₂O, and the influence of process conditions was explored by XRD and SEM/EDS. Pure 2D-nanopowders of Si₂N₂O were obtained in the presence of 15 × 10^–3 M FeCl₃ · 6H₂O in green 3Si + SiO₂ mixture at P(N₂) = 5 MPa.

A Ti–Zr alloy was prepared by magnesiothermic reduction from TiO₂–ZrO₂–Mg mixtures followed by acid leaching and the influence of leaching conditions on the quality of final product was explored. For nitric and hydrochloric acids as leaching agents, conditions for complete removal of MgO from crude TiZr–MgO combustion product had been optimized. The resistance of combustion-synthesized Ti–Zr alloy to elution with nitric acid was higher than that with hydrochloric acid.