Comparative study on the characteristics of ball-milled coal fly ash

Abstract

High-energy mill (HEM) has a wide application in material preparation, activation and synthesis. In the present study, fly ash was selected to be milled by HEM under the speed of 700 rpm and the ball-to-powder ratio of 10:1 by weight, but varied periods of milling time. The changes in physical and morphology properties of the milled fly ash were determined using BET analysis and scanning electron microscope, those of chemical properties were determined using X-ray diffraction, mercury intrusion porosimetry and Fourier transform infrared, and their thermal properties were determined using thermogravimetric analysis (TG). The obtained data implied that the ball-milling treatment leads to reductions in both particle size and crystallite size of the milled fly ash, and also changes of their microstructural and functional groups, and loss of crystallinity. The milling time was found an important factor to impact extent of those changes. The large particles of the original fly ash regularly in an average of 5 μm were significantly broken down to much smaller particles (average diameter 300 nm), and the pore size distribution was also greatly changed by the ball-milling treatment and shown a close relevant to the milling time. Both patterns from FTIR and TG indicated the decrease in intensity of –OH stretching vibration peak and increase in peak widths of the ball-milled fly ash with the increase in the ball-milling time, implying along ball-milling time leading the ball-milled fly ash toward more amorphousness and likely the higher reactivity.