Effects of excess reactant amounts on the mechanochemically synthesized molybdenum silicides from MoO₃, SiO₂ and Mg blends

This study reports on the preparation of molybdenum silicide powders from MoO₃-SiO₂-Mg powder blends with a two-step process of mechanochemical synthesis and selective acid leaching. Mechanochemical synthesis was carried out at a short duration of 1 h using a high-energy ball mill. Subsequently, mechanochemically synthesized powders were eliminated from the unwanted Mg-based by-products by HCl leaching. Excess amounts of reactants were utilized with the intention of eliminating Mo phase and their effects were investigated on the yielded products. Phase and microstructural characterizations of the powder products were performed using X-ray diffractometer (XRD), particle size analyzer (PSA) and scanning electron microscope/enery dispersive X-ray spectrometer (SEM/EDX). Quantitative phase analysis (QPA) and crystallite size calculations were also conducted on the mechanochemically synthesized and leached powders using the Bruker AXS TOPAS software. All the leached powders consisted of α-MoSi₂, β-MoSi_2, Mo₅Si₃ and Mo phases. However, in case of using 80 wt.% excess amount of Mg, the occurrence of Mo phase was inhibited and powders containing dominant α-MoSi₂ (~ 73 wt.%), β-MoSi₂ (~ 11 wt.%) and Mo₅Si₃ (~ 16 wt.%) phases were obtained with an average crystallite size of about 70 nm.