阴离子对Mg(OH)2晶体生长及形貌的影响机理

摘要

以轻烧粉、氯化铵、硝酸铵、乙酸铵、硫酸铵为原料,氨气为沉淀剂,采用氨循环法制备氢氧化镁晶体,并通过扫描电镜(SEM)、X射线衍射(XRD)对其进行表征分析.采用Materials Studio分子模拟软件中的CASTEP模块,计算了Cl?、NO?3、CH3COO?对氢氧化镁晶体(001)、(101)晶面生长的影响.结果表明,采用不同的镁盐得到不同形貌的氢氧化镁晶体阴离子电负性越大,对晶体形貌影响越小;Mg(OH)2晶体的(001)、(101)晶面能量与布居数分析表明,Cl?、NO?3、CH3COO?使晶体的(001)、(101)面的表面能增大、Fermi能级减小,阴离子与(001)、(101)晶面之间形成新的具有微弱共价性的离子键,影响晶体晶面的生长.理论计算较好地解释了不同形貌的氢氧化镁晶体的形成原因.%The magnesium hydroxide crystals were prepared by ammonia circulation method, using light burning powder, ammonium chloride, ammonium nitrate, ammonium acetate and ammonium sulfate as raw materials and ammonia gas as precipitant. X-ray diffraction(XRD) and scanning electron microscopy(SEM) have been employed to characterize these products. The effects of Cl?, NO?3 and CH3COO? on the growth of (001) and (101) crystal planes of magnesium hydroxide crystals were calculated by the CASTEP module in the Materials Studio molecular simulation software. The results showed that magnesium hydroxide crystals with different morphologies were obtained by different magnesium salts. The larger the anionic electronegativity was, the smaller the effect on the crystal morphology. The (001) and (101) crystal face energy and population analysis of Mg(OH)2 crystals showed that the surface energy increased and Fermi energy decreased of (001) and (101) planes of the crystals with Cl?, NO?3 and CH3COO?. New ionic bond with weak covalency was formed between anion and the (001) and (101) planes which affected the growth of the crystal plane. The theoretical calculations explained the formation of magnesium hydroxide crystals with different morphologies.