Abstract: Using the coprecipitation method,magnesium aluminium hydroxide sol charged positive was prepared.The structure and composition were studied with powder XRD,TEM,TGA-DTA, FT-IRand chemical analysis.Results showed that the structure of magnesium aluminium hydroxide was hydrotalcite-like,and belonged to hexagonal system;lattice constants a and c both increased with the increase of the molar ratio of Mg/Al.The shape of magnesium aluminium hydroxide particles is hexagonal plate and the mean particle size is 11.7nm.Three peaks of obtained magnesium aluminium hydroxide caused by weight losses were detected:the first peak(around 160 ℃)might be attributed to physical adsorption water and interlayer water;the second one(around 258℃)was due to elimination of crystalline water and the third one(around 400℃)was due to the dehydroxylation of the mixed metal hydroxide layers.The first and the second weight loss peaks were superimposed and widen when the molar ratio of Mg/AI was above 2.84.

Key words: Magnesium aluminium hydroxide, Positive sol, Coprecipitation