氯化钠对氧化镁水化产品形貌的影响

Effects of NaCl on Morphology of Products Prepared from Hydration of MgO

为考察以NaCl为晶型诱导剂,常压下水化反应制备一维状氢氧化镁的可行性,以六水氯化镁低温煅烧生成的活性氧化镁为原料,常压下水化合成氢氧化镁。结果表明:NaCl浓度为0.034 mol/L时,水化反应产品主要呈片状;NaCl浓度为0.171 mol/L时,水化产品呈槽沿的凹槽状;NaCl浓度为0.342 mol/L时,形成半管状产品,且分散性较好。即随着NaCl浓度的提高,水化产品逐渐向一维状趋势发展。当NaCl浓度较低时,新生成的氢氧化镁只能任意吸附在已生成的氢氧化镁晶体上,生成分散性较好的规则片状氢氧化镁;当NaCl浓度较高时,NaCl能够选择性地吸附在氢氧化镁的特定晶面上,使片状颗粒沿着垂直的晶面优先生长,最终发生定向排列形成槽状;随着NaCl浓度的进一步提高,Na^+易于扩散到[Mg(OH)_6]^(4-)八面体中,取代部分Mg^(2+)的位置,降低氢氧化镁生长的梯度能量,进而改变氢氧化镁晶体在不同方向的生长速率,有利于诱导晶体沿一维方向生长,可快速诱导生成一维管状产品。

To investigate the feasibility of preparing one-dimension magnesium hydroxide by hydration of magnesium oxide with NaCl as crystal inductive agent at atmospheric pressure,active magnesium oxide,which was prepared from low-temperature calcination of magnesium chloride hexahydrate,was employed as raw material and reacted with water under atmospheric pressure to produce magnesium hydroxide. Results indicate that when concentration of NaCl was 0. 034 mol/L,hydration products were mainly magnesium hydroxide nano-flakes; when concentration of NaCl was 0. 171 mol/L,the hydration products were in shape of groove with edges in several hundred nanometer; when concentration of NaCl was 0. 342 mol/L,semicanal products with good dispersity were obtained. In a word,as concentration of NaCl increased,hydration products gradually tended to be one-dimension morphology. When NaCl has a relatively low concentration,newly generated magnesium hydroxide particles can only adsorb to those already formed particles randomly,resulting in dispersive and regular flake-like magnesium hydroxide.When NaCl has a relatively high concentration,NaCl can selectively adsorb on specific crystal plane,leading to preferential growth of flake-like particles along the vertical crystal plane,and eventually orientational alignment occurs which forms groovelike products. When NaCl concentration further increases,these Na＋are apt to diffuse into[Mg（ OH）_6]^（4-） octahedron and replace part of Mg^（2＋）,so the gradient energy needed in the growth of magnesium hydroxide is reduced and growth rates of crystal planes that evolve towards different directions are altered,which are in favor of directing the growth of one-dimension nanostructure,so that semicanal products are rapidly generated.