Structure Development of Hectorite in Hydrothermal Crystallization Synthesis Process

Hectorite was synthesized in hydrothermal system by using lithium fluoride, magnesium chloride, water glass, and ammonium hydroxide as starting materials. The structure development in synthesis processes was in- vestigated by chemical composition analysis, powder X-ray diffraction(XRD), field emission scanning electron microscopy(SEM), Fourier transform infrared spectroscopy(FTIR), thermogravimetry and differential scanning calorimetry(TG-DSC)and laser nano particle size analyzer. The influences of synthesis parameters such as crystal- lization time, hydrothermal temperature and reactant ratio on the structure development of hectorite were explored and discussed. Some hectorite could be formed in 6 h, and the crystallization was completed in 72 h. Between 6 and 49 h the hydrothermal systems comprised hectorite, lithium silicate, lithium fluoride, and magnesium hydrox- ide. The crystallinity of hectorite could be enhanced with more Li substitution for octahedral Mg when the amount of lithium fluoride increased, leading to somewhat higher layer charge, thus more exchangeable cations in the interlayers. With the increasing of the temperature of hydrothermal crystallization the crystallinity of hectorite in- creased accordingly. Under less crystallization time, the obtained hectorite had smaller particle sizes and narrow size distribution with poor crystallinity, on the contrary, the products was in better crystallinity with larger grain sizes and higher thermal stability when the crystallization time was long enough.