Innovative Reuse of Agricultural Wastes as Industrial Raw Materials to Form Magnesium Composites

Abstract

Innovative reuse process of rice husks (RH), being one of the representative agricultural wastes, has been developed to fabricate magnesium composites by solid-state reaction to form magnesium silicide (Mg₂Si) reinforcements, having high hardness and Young’s modulus. From a view point of the biomass energy, rice husks, including about 70 mass% organics, could be effectively used as environmentally benign fuels to supply electric power or biomass ethanol. Considering that the most of the rice husk wastes after absorbing organics is SiO₂, the solid-state synthesis of Mg₂Si compounds by reaction of SiO₂ with magnesium was suggested in this study. First of all, the effect of the acid washing treatment to remove organics of rice husks on the crystallization of amorphous SiO₂ was evaluated by TG-DTA and XRD analysis. The carbon content of 0.05% in the wastes was drastically reduced by using acid-washed rice husks, compared to that of non acid-washed ones (0.19%). When employing the wastes with and without the acid washing treatment, the crystallization temperature is about 1273 and 1073 K, respectively. The latter showed the lower crystallization temperature because the reaction of the alkaline contents, such as K, P, and Ca, with SiO₂ during heating caused to decrease the SiO₂ melting point. Rice husk wastes burned at 1273 K after the acid treatment was mixed with AZ31 magnesium alloy powder to fabricate the magnesium composites including Mg₂Si dispersoids. Microscope observation and XRD analysis indicated that the amorphous SiO₂ included the wastes was more effective to promote Mg₂Si formation.