用 MgSO4制备不同水合碳酸镁晶体及晶体转变过程

Preparation and Crystal Transformation Process of Magnesium Carbonate Hydrate Using MgSO_4 as Raw Material

以MgSO4为原料,通过向MgSO4溶液中滴加(NH4)2CO3得到碳酸镁水合物。借助X射线衍射、扫描电子显微镜、差热分析及Raman光谱分析了转变过程中晶体组成和形态变化。研究发现,在25～45℃制备的产物均为单斜晶系、空间群为P21/n(14)的MgCO3 3H2O晶体;在50～60℃结晶产物存在由针状的MgCO3 3H2O晶体向单斜晶系、空间群为P21/c(14)的片状4MgCO3 Mg(OH)2 4H2O晶体的转变。从pH值变化和生长基元的形成对碳酸镁水合物晶体转变过程进行了分析。

Magnesium carbonate hydrates were prepared via dropping （NH4）2CO3 solution using MgSO4 as a raw material. The sam- ples prepared were characterized by scanning electron microscopy, X-ray diffraction, differential thermal analysis and Raman spec- troscopy, respectively. The results show that the product prepared at 25-45 ℃ is MgCO3·3H2O crystal, belonging to monoclinic sys- tem and space group P21/n（14）. The crystal transformation occurs in the temperature range of 50 ℃ and 60 ℃. During the process, the crystal composition changes from MgCO3·3H2O to 4MgCO3·Mg（OH）2·4H2O （space group P21/c（14））. The morphology of the crystals varies from needle-like to sheet-like. The transformation process of crystal is correlated to the solution pH value and the growth units.