Synthesis of Si/MgO/Mg2SiO4 Composite from Rice Husk-Originated Nano-Silica

Abstract

Silica exists in Rice husk, an agriculture waste, as a naturally occurring phase. In first step, acidic pre-treatment and calcination of the rice husk were performed to obtain nano-silica, in which various sizes of the nano-silica, totally with sizes under 80 nm, were achieved. Second, to reduce nano-silica to elemental Si and subsequently formation of the composite, Mg used as the reducing agent. In this work, the as-obtained composite mainly is the product of magnesiothermic reduction reaction of the nano-silica, which finally resulted in formation of elemental Si (silicon), MgO (magnesia) and Mg₂SiO₄ (magnesium silicate). The as-synthesized composite can be used as anode in lithium ion batteries. The products in each step were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (FESEM and HRSEM) techniques. X-ray powder diffraction patterns confirmed the formation of almost amorphous silica while the FE-SEM images were representing the spherical silica particles at various calcination temperatures. After the magnesiothermic reduction process, HRSEM micrographs indicated the formation of Si-MgO-Mg₂SiO₄ composite with particle sizes of 180-300 nm. The phase composition analysis was calculated by Rietveld method The electrical response of the Si/MgO/Mg₂SiO₄ composite was measured to be of 6×108 Ω.m resulted from I-V measurement.