Hydrothermal Synthesis and Characterization of One-dimensional Magnesium Hydroxide Chloride Hydrate in CaO-MgCl2-H2O System

One-dimensional magnesium hydroxide chloride hydrate (MHCH) with different structures and morphologies was prepared in CaO-MgCl2-H2O system via a hydrothermal method. The effects of MgCl2 concentration, molar ratio of CaO to MgCl2 (R), and hydrothermal conditions on the structure and morphology of MHCH were investigated. It was found that MHCH could be prepared when the concentration of MgCl2 was greater than 3mol/L and R was less than 0.5. Both the diameter and radius length ratio of MHCH increased with the MgCl2 concentration and R, and the optimum conditions of preparing MHCH were ［MgCl2］=4mol/L and R=0.05. The phases of MHCH was strongly depended on the reaction temperature, where phase 3 (Mg2(OH)3Cl·4H2O) was stable below 150℃ and phase 9 (Mg10(OH)18Cl2·5H2O) was formed above 150℃. In this reaction system at room temperature,Mg3(OH)5Cl·3H2O and phase 5 (Mg3(OH)5Cl·4H2O) appeared firstly, they were both transformed to phase 3 after aged for 1 d. Phase 3 could be converted to phase 9 during hydrothermal treatment at 160℃.