Abstract： High purity and “card room” shape magnesium hydroxide powders were prepared by the method of direct precipitation with light calcined magnesium powders as raw materials and ammonia as precipitation agent. The effect of concentration of magnesium sulfate, reaction temperature, reaction time, ratio of ammonia to magnesium ion and whisking speed on synthesis of magnesium hydroxide was studied by the experiment of single factor, and the optimum experimental conditions were obtained. The prepared sample was modified respectively by the methods of adding different dispersants and hydrothermal. The sample was analyzed by SEM, XRD and XRF. The results show that multiple types of dispersants have little modification effect on magnesium hydroxide. The crystallinity and other properties of magnesium hydroxide after modification by hydrothermal are improved variously. Hydrothermal adding sodium hydroxide with concentration of 6 mol/L has the best effect, and the magnesium hydroxide powders with weak polarity, more regular morphology, good thermal stability and excellent crystallinity is obtained. The mass fraction of magnesium hydroxide is greater than 99.94% and the yield is 87.92%.

Keywords: magnesium hydroxide powders; dispersant; hydrothermal method; sodium hydroxide