US EPA

4836496 

Journal Article 

Characterization of SiO2-encapsulated WSi2/W5Si3 nanoparticles synthesized by a mechanochemical route 

Ovali, D; Agaogullari, D; Ovecoglu, ML 

2018 

1 

Ceramics International
ISSN: 0272-8842
EISSN: 1873-3956 

44 

8 

9442-9453 

10.1016/j.ceramint.2018.02.161 

WOS:000430522200089 

This study reports on the mechanochemical synthesis (MCS) of SiO2-encapsulated WSi2/W5Si3 nanoparticles starting from tungsten oxide (WO3), silicon dioxide (SiO2) and magnesium (Mg) powder blends. MCS process, carried out in a high-energy ball mill, was evaluated in terms of various milling time and initial composition of WO3-SiO2-Mg powders. A subsequent purification step using aqueous HCl solution was conducted on the as synthesized powders. Compositional, microstructural and thermal properties of the powders were characterized by using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and differential scanning calorimeter (DSC). Based on the adiabatic temperature values, SiO2-encapsulated WSi2/W5Si3 nanoparticles exhibit a high potential as a result of a mechanically induced self-sustaining reaction. The exothermic reaction took place after 20 min of milling, and WSi2, W5Si3, W, MgO, Mg2SiO4 and residual Mg phases were detected. The utilization of an optimized amount of excess Mg (3.5 mol) resulted in the elimination of unwanted Mg2SiO4 and W phases, leaving behind WSi2, W5Si3, Mg2Si, MgO and Mg. After removal of Mg-based by-products by leaching process, WSi2, W5Si3 and a very small amount of SiO2 phases were obtained. TEM analysis revealed that W silicide nanoparticles with an average size of 97 nm were encapsulated by SiO2 layers with an average thickness of 15 nm. 

Powders: solid state reaction A; Electron microscopy; Silicides D; Transition metal oxides D