Abstract: The nanopowders of magnesium aluminium layered double hydroxides (Mg-Al-CO_3 LDHs) were prepared from the reaction of the salt solution of MgCl_2·6H_2O, AlCl_3·6H_2O and precipitating agent of Na_2CO_3, NaOH in a two-stage reactor with up and down reaction chamber. The effects of reactant concentration, stirring speed, surfactant type on the crystal structure, particle size, and size distributionthe have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), laser particle size distribution analyzer. The results demonstrated that the product synthesized in the optimum conditions has excellent uniform and plate structure with a particle size of approximately 30-50 nm, and has higher degrees of crystallinity. As the reactant concentration increasing, particle size became smaller and more uniform; stirring speed increasing, particle size decreased and particle size distribution curve became narrower. The reasult also indicated that different types of surfactants have a significant influence on the crystal structure.

Key words: reactor;nanoparticle;LDHs;homogeneous nucleation