Abstract: The acicular nanocrystalline Mg, Al-hydrotalcite flame-retardant agent, its length being about 100nm and its
diameter being about 10nm, was prepared by the liquid method at normal atmosphere. The effect of preparation technology, which includes the raw
material choice, adding raw material sequence, NaOH concentration, and nucleation temperature, on its phase composition was discussed. And it is
found that the sufficient condition of obtaining nanocrystalline Mg, Al-hydrotalcite is as follows: (1) raw materials must be solubility; (2)
pH value of the reaction solution must be greater than 12; (3) the nucleation temperature must be higher than 45℃; and (4) the adding raw
material sequence must be that adding raw material MgCl₂ follows the other three raw materials. Moreover, it is put forward that the nucleation
process of nanocrystalline Mg,Al-hydrotalcite is as follows: firstly, Al₁₃(OH)₃₂⁷⁺ ions are attracted on the surface of amorphous
Mg(OH)₂ and Al³⁺ ions diffuse in the Mg(OH)₂; secondly, CO₃^2- is inserted in the framework for the balance of the electron valence;
finally, the nucleation of nanocrystalline Mg,Al-hydrotalcite is quickly finished.

Key words: Mg, Al-hydrotalcite, preparation technology, reaction mechanism, nanocrystalline