DC Arc discharge synthesized zirconia nanoparticles: shed light on arc current effects on size, crystal structure, optical properties and formation mechanism

Abstract

In this study zirconia nanoparticles (NPs) were successfully synthesized via the direct current (DC) arc discharge method in water. Formation mechanism of NPs and the effect of arc current on morphological, structural and optical properties of NPs have been studied. The NPs were synthesized at four different currents in the 40–160 A range. SEM observations showed NPs are spherical in shape and their average size decrease from 40 to 22 nm by increasing the current from 40 to 160 A. XRD analysis revealed phase composition of NPs is a mixture of tetragonal and monoclinic for all the samples, and the phase fraction of NPs are arc current dependent in such a way that an increase in the current leads to an increase in the weight percent of the tetragonal phase. UV–vis spectroscopy indicated that the NPs exhibit optical characteristics of the wide energy band gap semiconductors with a significant amount of oxygen deficiency. Also the effect of the arc current on the energy band gap of NPs were investigated. An increase in the arc current decreases energy band gap of the NPs from 3.8 to 3.0 eV. Optical emission spectroscopy (OES) studies demonstrate formation of zirconia NPs at temperatures as high as 4953 K, thereby zirconium exited species react with some of oxygen containing species. Finally, Thermal radiation measurement is proposed as a nondestructive method to evaluate the active mechanisms in an arc discharge zone beside other methods such as OES.