Efficient production of Mg2Si in a fluidized-bed reactor

Abstract

High purity Mg2Si crystallines are a promising candidate for lightweight and structural materials due to their unique thermo-physical properties, and can also be used to produce polycrystalline silicon materials via non-chlorine route. A novel fluidized-bed route for production of high purity Mg2Si was proposed to realize such a high exothermic reaction. The fluidization quality of Mg and Si mixtures and Mg2Si formed were studied in cold or thermal conditions and the effects of processing conditions on purity and microstructures of Mg2Si were investigated. The results indicated that both the materials and its products have a good fluidization quality either in cold equipment or under a thermal reaction process over a wide range of gas velocity. The fluidized-bed method showed excellent efficiency for synthesizing high purity Mg2Si. A temperature range of 600–650 °C and a duration time of 2.0-h in Ar or H2 is suitable for synthesizing high purity Mg2Si (above 97 wt. %). It has greatly improved the reaction rate and shortened the duration time in comparison with a fixed bed. The equilibrium content of Mg2Si is independent of the carrier gases, but determined on the reaction temperature. The size and shape of Mg2Si crystallites can be adjusted by controlling the reaction temperature. The Mg2Si synthesis mechanism is according to the shrinking core model. The parabolic law model gives a good agreement to the kinetics data and the activation energy of Mg2Si formation is 58.4 ± 5 kJ/mol.