花状五水合碳酸镁的制备及形成机理研究

以菱镁矿为原料，磷酸二氢钾为添加剂，通过水溶液法合成了花状五水合碳酸镁，利用扫描电子显微镜、X射线衍射和FT-IR对晶体的微观形貌、晶相组成进行了分析，探讨了热解时间对晶体形貌的影响，分析了其形成机理，研究了五水合碳酸镁的晶体结构.结果表明，热解时间为30min时，可获得长15~30μm，宽100~500nm的花状五水合碳酸镁.五水合碳酸镁晶体中Mg2+呈两种不同的八面体配位，分别构成水合络阳离子Mg(H2O)2+6和络阴离子〔Mg(H2O)4(CO2-3)2〕2-，其化学式为Mg(H2O)6·Mg(H2O)4(CO2-3)2.磷酸二氢钾在五水合碳酸镁表面的吸附作用，改变了各晶面的表面能和生长速度，促使其异质成核并逐渐叠合形成花状体.

Preparation and Formation Mechanism of Flower like Magnesium Carbonate Pentahydrated〓

Flower like magnesium carbonate pentahydrated was prepared by aqua solution method using magnesite as raw materials and potassium dihydrogen phosphate as additives. Microtopography and phase composition of the crystal were analyzed by scanning electron microscope(SEM)， X ray diffraction(XRD) and FT IR. The influence of thermal decomposition time on the crystal morphology was explored. The formation mechanism of products was studied， as well as crystal structure of magnesium carbonate pentahydrated. The results showed that flower like magnesium carbonate pentahydrated with 15~30 micrometers long and 100~500 nanometers wide， can be successfully synthesized under 30min of thermal decomposition time. For the magnesium carbonate pentahydrated crystal， Mg2+ presents two different octahedral coordination， which constitutes Mg(H2O)2+6 and［Mg(H2O)4(CO2-3)2］2-， and its chemical formula is Mg(H2O)6·Mg(H2O)4(CO2-3)2. The adsorption of potassium dihydrogen phosphate on the surface of magnesium carbonate pentahydrated changes the surface energy and growth rate of individual crystal faces， promotes it to nucleate and gradually superimpose flower like bodies.