Through the analysis of thermodynamics,relationship between equilibrium phase of thihydrate and boehmite with temperature
and caustic mole ratio in the system of
sodium aluminate solution was determined.The perfect crystal and pure boehmite was synthesized by hydrothermal process using thihydrate as precursor and it was propitious to conversing from thihydrate to boehmite when the temperature increased,the reaction time prolonged and the granularity of precursor decreased.Using boehmite as a seed to precipitate sodium aluminate solution,the results of seeded precipitation show that
the ratio of seeded decomposition reduces when the concentration of decomposition solution increases;the ratio of seeded decomposition increases when the granularity of seed decreases and the time of seeded decomposition is prolonged.Sodium aluminate solution only precipitates boehmite and the largest ratio of seeded decomposition reaches(43.19%) when the temperature is above 95 ℃;whereas the product of precipitation is thihydrate when the temperature is below 85 ℃.The experiment results are in good accordance with theoretical analysis.