Abstract: Ammonia method is one of the main methods to prepare magnesium hydroxide,and according to the different states of ammonia into the reaction system,ammonia method includes aqua ammonia precipitation method and gaseous ammonia precipitation method.In order to study the influence of ammonia in different states on particle characterization of magnesium hydroxide,magnesium chloride was used as reaction material,magnesium hydroxide were prepared respectively with aqua ammonia and gaseous ammonia as precipitant.Scanning electron microscope(SEM),X-ray powder diffraction(XRD) and laser particle size analyzer were used to characterize the products.The results showed that crystal forms of the magnesium hydroxide products obtained by these two methods both tended to be perfect with increasing reaction temperature,and the dispersion property was also improved.Magnesium hydroxide prepared by gaseous ammonia precipitation method presented inerratic cubic pieces(hexahedron structure) when reaction temperature was higher than 75℃,the dispersion property of the particles were better than those prepared by aqua ammonia precipitation method.Aqua ammonia concentration was also a significant factor affecting the morphology of magnesium hydroxide,and the particle size and dispersion property would gradually become close to the products of gaseous ammonia precipitation method with increasing aqua ammonia concentration.This work provided valuable reference for selection and application of ammonia precipitation method to prepare magnesium hydroxide.

Key words: magnesium hydroxide, particle characterization, aqua ammonia, gaseous ammonia

摘要： 氨法是制备氢氧化镁的主要方法之一，根据氨进入反应体系状态不同分为氨水法和氨气法两种工艺。为了确定氨水与氨气对氢氧化镁颗粒性质的影响，以氯化镁为原料,分别以氨水和氨气为沉淀剂制备氢氧化镁，并利用扫描电镜(SEM)、X射线衍射(XRD)、激光粒度分布仪对产品进行了表征。结果表明：两种沉淀剂制备的氢氧化镁颗粒晶型均随沉淀反应温度的升高趋向完整，颗粒的分散性也随温度的升高得到改善；当反应温度达到75℃以上时，氨气法制备的氢氧化镁呈四方块状(六面体结构)，颗粒的规则程度和分散性优于氨水法产品；氨水浓度对氨水法制备的氢氧化镁颗粒粒度及形貌也有较大影响，随氨水浓度的升高，产品粒度及分散性趋向于氨气法产品。本文研究可为氢氧化镁制备中氨法的选择及应用提供参考。

关键词: 氢氧化镁, 颗粒性质, 氨水, 氨气