The Research On Magnesium Oxide Powders Preparation By Magnesium Chloride And Different Source Of Calcium

This paper is about the new technics to prepare the MgO powders using the materials of magnesium chloride and calcium carbonate(calcium oxide,dolomite). This research has laid a solid foundation for using our abundant brine resources to prepare high purity MgO powders. MgO was synthesized via solid state reaction and molten salt methods by using MgCl2,MgCl2·6H2O and CaCO3, CaO, CaMg(CO3)2 as starting materials, and LiCl as flux. Thermo-decomposing process of starting materials, synthetic reaction of MgO was studied by using TG/DSC and high temperature XRD analysis. The product powders were characterized with XRD and SEM. The influenc of different raw materials, synthesis temperature, holding time and the relative content of molten salt on the performances of the products have been studied.The results show that using MgCl2 and CaCO3, MgCl2 and CaMg(CO3)2 as raw materials respectively, the prepared magnesium oxides had the mixed morphologies and uneven size distributions. Using MgCl2 and CaO as raw materials, the prepared magnesium oxides were characterized with a uniform size distribution and a near sphere-like and octahedron morphology. Whereas using MgCl2·6H2O and CaCO3, MgCl2·6H2O and CaO, MgCl2·6H2O and MgCa(CO3)2 as raw materials, all of products had the mixed morphologies and uneven size distributions, in which the product has a relatively better reactive activity when MgCl2·6H2O and CaCO3 has been used as raw materials. Using PEG, SDBS and CTAB as surfactant in experiment, the prepared Mg(OH)2 precursor have different morphologies. The prepared Mg(OH)2 precursor have flake morphologies when PEG has been used as surfactant. Whereas using SDBS and CTAB as surfactant respectively, the prepared Mg(OH)2 precursor have globular aggregates morphologies and triangle aggregates morphologies. Lower synthesis temperature of MgO powders not only has better sintering activity, but also could improve the sintering densification of MgO powders. A higher heat treatment temperature, longer holding time and the increase of LiCl addition content were favorable for the growth of magnesium oxide crystals, resulting in the decrease of crystal cell volume and reactive activity.The B2O3 impurities and a small amount of SiO2, Al2O3 impurities could be removed by molten salt method to purify MgO powders.