Microstructure And Properties Of SiO₂/Mg Composite

Amorphous SiO2was made from Rice husks by means of citric acid leaching and calcinating, and annealed at1150℃to transform to crystalline structure.2wt%-SiO2/Mg composite was fabricated by means of Spark Plasma Sintering (SPS) technique, and hot extruded at400℃. The phase transformation during SPS at different temperature was analyzed by X-ray diffraction determination; The microstructure of SiO2/Mg composite and the elemental distribution were studied by means of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) respectively. The pole figure was evaluated to discuss the effects of annealing on the preferred orientation of SiO2/Mg composite. Compression behavior was tested to evaluate the mechanical properties of SiO2/Mg composite.The results show acid leaching and calcinating is an effective method to prepare high purity amorphous SiO2, which could be transformed to crystalline structure annealed at1150℃. The average diameter of SiO2decreased with the increasing milling time. The particle size reached about9.56μm with the milling time of80hours, and decreased slightly with increasing milling time.9.56μm. The reaction temperature between amorphous SiO2and mg powders is465℃. The reactivity of SiO2was reduced by annealing treatment leading to a increase of54℃to that between crystalline SiO2and mg powders. H2O and O2were apt to be adsorbed to the surface of both SiO2and Mg powers, leading to the producing of extraordinary fine MgO. Mg2Si and MgO were generated by the interface-reaction when the sintering temperature was over the reaction between SiO2and Mg.The fine SiO2powers distributed on the surface of Mg powers contributed to the formation of flow line after hot extrusion. The agglomerating SiO2powers were apt to crack during hot extrusion, resulting in the increase porosity. The matrix recrystallized during hot extrusion, and exhibited a strong<1010>//ED fiber texture. The texture style did not chang during the subsequent annealing treatment. An increased sintering temperature is helpful to raise the elastic ratio since the atom diffusion is more active at a higher temperature. Meanwhile, the value of the yield strength usually exhibits a reverse tendency.