Preparation of Super Soft Granules from Nanosized Ceramic Powders by Spray Freezing

Owing to their extremely high specific surfaces and their high surface-to-volume ratios nanosized ceramic powders show a strong tendency to agglomeration and poor flowability. For improved properties of these powders during storage, transport and shaping a granulation step is necessary. However, the granules must be completely destroyed during dry pressing or redispersion; otherwise, the advantages of nanoparticles in comparison to conventional powders will not be realized. Spray freezing is a new granulation technique which combines the advantages of a conventional granulation by spray drying and a sublimation drying process. Different suspensions of nanosized oxide powders were rapidly frozen by spray freezing and subsequently dried by freeze drying. Thus, capillary forces can be excluded by this process. The achieved granulates show spheric granules with very low strength, improved flowability and increased bulk density. They were redispersible and can be destroyed under very low pressures.