Solid State Synthesis of Mg2Si/MgO Composites from an Elemental Mixture Powder of Magnesium and Rice Husk Silica †

The utilization of silica particles originating in rice husks as reinforcements for magnesium is discussed. The reactivity of magnesium with silica particles in the solid state to synthesize magnesium silicide (Mg 2 Si) was investigated by DTA and XRD analysis. Finer silica particles were more effective for reacting with magnesium at low temperature due to the increase of their surface area in contact with magnesium. Amorphous silica was more useful for the reaction than the crystalline form. The reactivity of rice husk silica was superior to that of the conventional mineral silica particles because of not only its amorphous structure but the larger specific surface area caused by the pore structures. In the case of a green compact of the elemental mixture of silica particles and Mg powder, the silica particle size was not effective on the reactivity because the coarse particles are fractured into fine ones by cold compaction at the applied pressure of 600 MPa. The distribution of Mg 2 Si intermetallics in magnesium powder composites consolidated by the SPS process was investigated by XRD and SEM-EDS analysis. When the sintering temperature was over the exothermic temperature of the elemental mixtures of silica particles and Mg powder in the DTA profile, the synthesis of Mg 2 Si occurs completely occurs during sintering. The density and hardness of their composites sintered over the ignition temperature of the DTA profile were remarkably high because of the good densification by the high reactivity and the distribution of Mg 2 Si hard compounds.