微波对碱式碳酸镁结晶过程的影响

在微波外场作用下,利用氯化镁和碳酸钠溶液反应结晶法直接合成碱式碳酸镁晶体。通过对比微波、水浴两种加热方式下镁离子变化曲线和产物的差异,XRD、FTIR,SEM等对相转移过程的物相分析表征,探索微波对反应的强化影响。结果表明,反应结晶直接合成碱式碳酸镁过程分为絮状物→出现晶体→完全转变为球状碱式碳酸镁3个阶段。微波对反应3个阶段中都有强化作用,促进絮状物的形成,加快相转变,提高反应转化率,微波加热条件下在粒径分布与组装方式与水浴加热方式均有不同,微波作用下较小颗粒是由纳米片层平行组装而成,而较大颗粒可能是无定形物在球状小颗粒表面继续转变,形成交错的表层纹理的大颗粒碱式碳酸镁。

Effect of Microwave on the Crystallization Process of Hydromagnesite

In the strengthening of microwave, a novel homogeneous precipitation of hydromagnesite by the reaction of MgCl₂ and Na₂CO₃ solution was investigated. In the reaction process, samples with a certain time interval were taken by pipettes. The variation of magnesium ions concentration as time was studied by EDTA titration. Product obtained was washed by ethanol and dried at 333.2 K for 6 hours. The crystal phase and morphology of samples were characterized by XRD, SEM and FTIR. The reaction process could be divided into three stages: flocculus, crystal appearance, and sphere-like hydromagnesite. Compared with water-bath heating, this study was focus on the strengthening of microwave by both continuous stirring method and stirring-aging method. The results show that microwave has great strengthening effect on three stages, which could promote the formation of flocculus, accelerate the phase transition, and increase the conversion rate. The diameter and the assembly method of the product prepared by water-bath heating are different from that by microwave radiation. In the microwave field, the smaller particles were parallel assembled by nano-layers. The amorphous material is going transition upon the smaller product, so the bigger particles with crisscross surface are formed.