Thermal stability of nano structured fly ash synthesized by high energy ball milling

Abstract

In this paper, an attempt has been made to modify the micro sized fly ash into nano structured fly ash using High Energy Ball Mill. The smooth, glassy and an inert surface of the fly ash can be altered to a rough and more reactive state by this technique. Ball milling was carried out for the total duration of 30 hours. The sample was taken out after every 5 hours of milling for characterizing. The nano structured fly ash was characterized for its crystallite size, lattice strain and percentage of crystallinity by using X-Ray Diffractometer. It was found that for the 30 hrs milling, the crystallite size was reduced from 92 nm to 29 nm and the percentage of crystallinity got reduced from 63% to 38%. The size, shape and texture of the fresh as well as nano structured fly ash were studied using Scanning Electron Microscopy (SEM). The fresh fly ash particles are mostly spherical in shape. The shape of the 30h milled particles is irregular and the surface morphology is rough. Isothermal annealing was carried out on 30 h ball milled
fly ash from 100 to 800 0C for various times. The initial grain size of 29 nm for as-milled sample increased to 30.9 nm and 31.7
nm after annealing for 8 h at 100 and 200 0C respectively. Whereas this trend was slightly higher for higher temperatures, this increase was in the order of 29 nm to 33.43 nm, 35.35 nm, 36.53 nm, 37.78 nm, 40.42 nm, 41.93 nm after annealing for 4 h at 300, 400, 500, 600, 700 and 800 0C respectively. Hence, small crystallite size enhancement with good amount of residual strain recovery was observed during the isothermal annealing.

Keywords: Nano materials, Particulates and Powders, XRD- analysis; Fly ash.