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.