A One-Step Ultrasonic Spray Pyrolysis Approach to Large-Scale Synthesis of Silica Microspheres

Abstract

This paper proposes a novel and simple one-step ultrasonic spray pyrolysis (USP) approach to prepare silica (SiO2) microspheres, in which only one chemical reagent—silica sol, is used as precursor. In this approach, aerosol droplets of silica sol generated by a ultrasonic nebulizer are transformed into its SiO2 microspheres through water evaporation, precipitation, drying, dehydration and densification in a tube furnance. The products were investigated by scanning electron microscopy, X-ray diffraction, energy dispersive spectrometer, Fourier transform infrared spectroscopy and thermogravimetry, respectively. Above characterizations showed that all the products were dry, unifrom, regular and smooth silica microspheres. The SiO2 concentrations of silica sols have a significant influence on the diameters and size distributions of the products. The microspheres prepared using silica sol with a low mass concentration (e.g. 10%) showed a narrow size distribution; most microspheres ranged from 1.0 to 1.4 μm in diameter. This approach shows great potential in large-scale synthesis of silica microspheres for two reasons: 1) USP is a continuous large-scale method; 2) silica sols are nontoxic and have been industrially produced.