The formation mechanism and morphology of the nickel particles by the ultrasound-aided spark discharge in different liquid media

•The higher purity of particles were generated in pure water than kerosene.•The narrower size distribution were generated in pure water than kerosene.•The narrowing distribution was improved by the ultrasound-aided.•Based on the attaching and entrapping cases, the forming mechanism was interpreted.•The ratio of closed hollow particles increases when ultrasound was added.

Spark discharge is widely applied in the fabrication process of the particles with very small sizes. The ultrasound-aided spark discharge process is based on the electrical discharge in the liquid media of the electrical discharge machining (EDM). In this paper, the morphology, element composition, and crystal structure of the Nickle particles produced by the ultrasound-aided spark discharge were observed and analyzed by SEM, EDS and XRD respectively. The EDS and XRD indicated that the purity of the nickel particles generated in pure water is higher than that in kerosene. Meanwhile the effects of dielectric media on the size distribution were also investigated. It was found that the size distribution of the particles in pure water is narrower than that in kerosene, but when the ultrasound was introduced into the generating process, the size distributions of the particles in both media have remarkable improvements (both became narrower). Based on the attaching and entrapping processes, the formation mechanism of different structural particles was also presented. Following the study on the changes of the effective densities and the ratios of the closed hollow particles in different experiments (with and without ultrasound), we found that, with the aid of ultrasound, the ratio of the closed hollow particles increased about 10-15%. In overall, the results in this paper provide a foundation for the some future research, such as the study on the control of the particle properties (in size and morphology) by improving the experimental conditions.

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