Role of ion substitution and lattice water in the densification of cold-sintered hydroxyapatite

High-density hydroxyapatite (HA) compacts were achieved by cold sintering of co-precipitated powders at temperatures lower than 200 degrees C without addition of any solvent. Critical factors affecting the densification behavior including the source of powders, the type of solvent, applied pressure, sintering temperature and time were investigated. The presence of lattice water together with ion substitution in the co-precipitated HA powders has a significant effect on the densification. A novel viewpoint that is essentially different from classical dissolution precipitation mechanism in cold sintering was proposed; i.e., the formation of hydrogen bonds between the HA particles plays a critical role in the densification. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.