Abstract: Using magnesium nitrate as reaction material , hexagonal flake magnesium hydroxide were synthesized with gaseous ammonia as precipitator in one-step hydrothermal method .The product was characterized with scanning electron microscope ( SEM) and X-ray powder diffraction ( XRD) .The results show that the optimum temperature was 120 ℃.Growth habit of magnesium hydroxide wais analyzed theoretically through Morphology program .Morphology program is used to calculate the surface energy , surface attachment energy and crystal area percentage of the main exposed surface .The results show that the main exposed surface of magnesium hydroxide will be (001) plane and the regularly exposed surface of magnesium hydroxide will be ( 101 ) plane, most of the morphology of magnesium hydroxide will display the shape of orthohexagonal flake , but will be mixed with irregular hexagonal flake structure .The calculated results are identical with the experimental results .Non-ideality of morphology is caused by exposure degree of ( 001 ) plane changing with temperature .The results lay a foundation for further research on nonideal morphology mechanism .

Key words: Using magnesium nitrate as reaction material , hexagonal flake magnesium hydroxide were synthesized with gaseous ammonia as precipitator in one-step hydrothermal method .The product was characterized with scanning electron microscope ( SEM) and X-ray powder diffraction ( XRD) .The results show that the optimum temperature was 120 ℃.Growth habit of magnesium hydroxide wais analyzed theoretically through Morphology program .Morphology program is used to calculate the surface energy , surface attachment energy and crystal area percentage of the main exposed surface .The results show that the main exposed surface of magnesium hydroxide will be (001) plane and the regularly exposed surface of magnesium hydroxide will be ( 101 ) plane, most of the morphology of magnesium hydroxide will display the shape of orthohexagonal flake , but will be mixed with irregular hexagonal flake structure .The calculated results are identical with the experimental results .Non-ideality of morphology is caused by exposure degree of ( 001 ) plane changing with temperature .The results lay a foundation for further research on nonideal morphology mechanism .