Mechanochemical synthesis and characterisation of niobium silicide nanoparticles

Mechanochemical synthesis (MCS) investigations of niobium silicide powders in Nb ₂ O ₅ –]SiO ₂ –]Mg powder mixtures were conducted via high-energy ball milling and leaching by means of process parameters such as the milling duration, initial Nb ₂ O ₅ crystal structure, and excess Mg amount. The compositional, thermal, and microstructural properties of the products were characterised using X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), particle size analysis (PSA), stereomicroscopy (SM), scanning electron microscopy (SEM), and transmission electron microscopy/energy-dispersive spectrometry (TEM/EDS). After the 5 h milling of the stoichiometric mixtures, an instantaneous ignition occurred and NbSi ₂ , Nb ₅ Si ₃ , Nb, and MgO phases formed with some residual Mg. In addition, the use of excess Mg inhibited the formation of Nb ₅ Si ₃ . Afterwards, leaching treatments (in a 4 M HCl solution) completely removed the Mg-based phases from the synthesised products. The XRD calculations revealed that the resultant product consisted of 97 wt% NbSi ₂ and 3 wt% Nb ₅ Si ₃ phases. The TEM analyses indicated that each Nb silicide nanoparticle was coated with a SiO ₂ layer. According to random measurements, the average particle size of the Nb silicide cores and average thickness of the SiO ₂ layer were approximately 61 and 7.5 nm, respectively.