Effect of cooling rate and polyvinyl alcohol on the morphology of porous hydroxyapatite ceramics

Hydroxyapatite (HAP) ceramics with unidirectional lamellar pores and ceramic walls were fabricated by the unidirectional freezing process and freeze drying method. The composition of HAP aqueous slurry and the cooling rate both affected the shape and size of pores. The size of lamellar pores in HAP ceramic was longer than that in HAP ceramic with polyvinyl alcohol (PVA) additive. When the PVA additive was added into the slurries, there were smaller dendrite structures on the ceramic walls frozen with higher cooling rate, while the lower cooling rate resulted in the smooth surfaces. However, there was no obvious distinction between the ceramics without additive fabricated with different cooling rates.