Study on Mechanism of Precursor Powder Prepared by Freeze-drying

The precursor powder of freeze drying was investigated by means of X-ray diffraction and scanning electron microscopy.The“segregation of solute model”is established and discussed.The results show that the precursor powder is amorphous with a smooth surface.The morphology of powder is flaky,club-shaped and a little hexagonal.In the low-temperature-freezing stage,the water is frozen as ice phase,while the solute pre- cipitate as the salt phase.In the temperature-raising stage,the amorphous ice would crystallize.The micro- crystal would segregate at the process of ice crystallization.Because the morphology and the size of the ice crystal are different,the amorphous powder forms differently.When the concentration of the solution is high, the main amorphous powder is flaky and club-shaped,and it appears hexagonal pattern when the concentra- tion is low.