冷冻干燥技术制备非晶态粉体的机理研究

利用XRD,SEM研究了冷冻干燥技术制备非晶态粉体的形貌及其形成过程,建立了快速冷冻条件下溶质粒子偏聚模型,结果表明:冷冻干燥技术制备的粉体为表面光滑的无定形态,形貌主要为片状和条柱状,有少量六边形态,低温冷冻时,水以冰的形式冻结,溶质以盐的形式析出,形成冰盐两相;空气回温时,非晶冰向晶态冰转化,微晶粒盐偏析到冰相界面,冰晶大小和形态不同导致非晶态粉体呈现不同形貌,溶液浓度较高时,主要是片状和条柱状非晶态粉体;溶液浓度较低时,盐的偏聚与溶液浓度本身无关,易出现六边形态的非晶态粉体。

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.