Efficacy of ultrasonic treatment for dispersing nanoparticles: A correlation with microstructure

Abstract

In this study, an attempt was made to disperse 1 wt% of alumina nanoparticles (20–30 nm) in AZ91D matrix through two different methods (i) Mechanical Stirring (MS) and (ii) Mechanical stirring followed by Ultrasonic Treatment (MUST) at 1.75 kW/20 kHz. The density and porosity of both squeeze casted nanocomposites were determined. Further, the efficacy of UST for dispersing alumina nanoparticles was evaluated by examining the microstructure of nanocomposites through High Resolution Scanning Electron Microscopy (HR-SEM) and Optical Microscopy (OM). The HR-SEM images of MS revealed the formation of clusters of nanoparticles due to mechanical stirring. In the case of MUST, a prodigious improvement in the dispersion of nano particulates due to the application of UST was evident. This was confirmed by the instantaneous measurement of sizes of spots displayed in the HR-SEM images during the microstructure analysis. OM image showed significance in grain refinement for MUST composite as compared to MS. The average grain size was 310 µm and 175 µm for MS and MUST nanocomposites respectively.