热液环境下氢氧化镁结晶形态机理研究

Mechanism of Forming Mg(OH)_2 with Acicular or Fibrous Crystallizing Morphology under Hydrothermal Conditions

研究了热液环境下氢氧化镁结晶形态形成机理。根据负离子多面体配位生长理论,构造了氢氧化镁的生长基元,计算了相应于不同维数和多重数n的水镁石生长基元稳定能。根据不同生长基元稳定能的计算结果,发现氢氧化镁的生长基元稳定能在1维方向(n×1×1),随着n值的增大而较快地增大,而二维方向生长基元稳定能为负值,这说明:氢氧化镁晶体是在1维方向(此方向平行于氢氧化镁晶体结构的基本层)优先生长,形成氢氧化镁针状或纤维状结晶形态。并由此推断,陕南黑木林的天然纤维状水镁石矿最初应该是在地壳局部形成的1种热压的环境里,在1种热液状态下生成的。

Mg(OH)2 samples with acicular or fibrous crystallizing morphology were successfully prepared by one-step reaction method under hydrothermal conditions and indexed as a hexagonal crystal system based on the results of XRD and TEM. Moreover, based on the theoretical model of anionic coordination polyhedron growth units, the growth mechanism and growth habit of the Mg(OH)2 crystals under hydrothermal conditions were first investigated in depth. It was concluded, after calculating the stability energy of the growth unit of Mg(OH)2 crystalline, that the growth direction of the growth unit of the Mg(OH)2 crystal tends to favor a one-dimensional direction, parallel to the basic layer of the Mg(OH)2 crystal. Accordingly, we propose that natural brucite with fibred crystallizing morphology was formed under hydrothermal conditions in the earth thousands years ago.