Synthesis of nano-crystalline forsterite based on amorphous silica powder from natural sand by mechanical activation method

Abstract

The synthesis of nano-forsterite powders has been succeeded using an amorphous SiO2 powder base material from the purification of natural silica sands from Tanah Laut and MgO Merck with a combination of duration of mechanical activation and calcination temperature. The silica and magnesia powders are mixed and mechanically activated using ball mill for 1, 2, 3 hours. The mixture was then calcined at a temperature of 950, 1050, and 1150°C for 4 hours to form a forsterite powder. Phase characterization was performed using XRay Diffraction (XRD), while the crystalline size using Transmission Electron Microscopy (TEM). The analysis of diffraction data was done using the Rietica software method. Overall the phases formed after calcination are forsterite, periclase, cristobalite, and protoenstatite. The highest percentage of forsterite weight was obtained in the sample with a 3-hour mechanical activation treatment with a calcination temperature of 950 °C, i.e. 87.9 wt. At all temperatures, the forsterite content increases with increasing time of mechanical activation. An important invention in this study, when compared with earlier literature, is that high concentrations of forsterite can be formed at lower calcination temperatures. Observations with TEM show that the size of forsterite crystals is reduced along with the increase in the time of mechanical activation. The size of the forsterite crystals in the calcined samples of 950° C after mechanical activation for 3 hours was about 81 nm, whereas in the calcined samples 1050 °C without mechanical activation about 94 nm.