STRUCTURE AND THE POINT OF ZERO CHARGE OF MAGNESIUM ALUMINUM HYDROXIDE

Positively charged magnesium aluminium hydroxide sol has been prepared by coprecipitation. The structure and properties were studied using X -ray diffraction (XRD), thermogravimetry (TG), differential thermal an alysis (DTA), transmission election microscopy (TEM), FTIR and potenti ometric titration (PT). The structure was shown to be hydrotalcite-lik e; the lattice constants a and c both increased with decreasing mole f raction of Al, x = [Al]/([Al] + [Mg]); the highest value of x was 0.33 2. Three weight loss peaks were detected by TG-DTA of the sol particle s. IR spectroscopy showed that the position of the OH-stretching vibra tion peak shifted to high frequency and the peaks broadened with decre asing x. PT showed that the sol particles bore positive charges; the p oint of zero charge (pzc) and the amount of permanent positive charge both increased with increasing x.