热分解法制备三水碳酸镁晶须及其结晶动力学研究

Preparation and Crystallization Kinetics of Nesquehonite Whiskers with Thermal Decomposition Method

利用菱镁矿制备重镁水溶液,以此为前驱溶液,采用热分解法制备三水碳酸镁晶须。借助X射线衍射分析(XRD)和扫描电镜(SEM)探究热解时间、重镁水溶液浓度和搅拌速率对产物组成和形貌的影响,并研究结晶动力学。结果表明,在温度50℃、热解时间120 min、重镁水质量浓度为2. 75～3. 39 g/L时,热分解法制备得到平均直径为6. 0μm、平均长度为100μm的棒状MgCO_3·3H_2O晶须。随着时间和浓度增加,MgCO_3·3H_2O晶体表面或整个棒状结构会发生溶解重新形成无定形颗粒,并逐渐形成多孔棒状4MgCO_3·Mg(OH)_2·3H_2O。搅拌速率影响MgCO_3·3H_2O晶须的产率。MgCO_3·3H_2O晶体中,[MgO_6]正八面体通过Mg-O键以共顶点的方式紧密相连,沿化学键作用力较强的[010]方向无限连接形成长链。结晶动力学线性拟合结果表明重镁水溶液浓度增大,诱导期时间缩短。

Nesquehonite(MgCO3·3H2O)whiskers were prepared by thermal decomposition method using magnesium solution as precursor.The influence of pyrolytic time,concentration of magnesium solution and stirring rate on the decomposition process is analyzed.The phase composition and micro morphology of the products was characterized by X-ray diffraction(XRD)and scanning electron microscope(SEM).The results show that smooth rod-like MgCO3·3H2O whiskers with an average diameter of 6.0μm and an average length of 100μm was obtained at 50℃when the pyrolytic time was 120min and the concentration of magnesium solution was 2.75-3.39g/L.With the increase of time and concentration,the surface or the whole rod-like structure of MgCO3·3H2O crystal will dissolve to form amorphous particles,and gradually to form porous rod-like 4MgCO3·Mg(OH)2·4H2O.The stirring rate plays a great effect on the yield of MgCO3·3H2O whiskers.In MgCO3·3H2O crystal,[MgO6]octahedron is tightly connected by Mg-O bond in the form of a common vertex.The long chain is formed by infinite connection along the direction of[010]where the chemical bonding force is strong.The linear fitting results of crystallization kinetics showed that the concentration of magnesium solution increased,the induction time shortened.