Structure and Nanohardness of Compact Hydroxyapatite-Based Ceramics

—The substructure of hydroxyapatite ceramics produced by cold-pressing nanocrystalline hydroxyapatite powder, followed by annealing for 1–12 h at 1150°C, has been studied by transmission electron microscopy, and the hardness and modulus of elasticity of the ceramics have been determined using nanoindentation. The results demonstrate that the compaction process leads to coalescence of nanoparticles of the starting powder, which ensures a minimum hardness of the compact with a 50% relative density. The hardness and modulus of elasticity of HA ceramics increase with increasing firing time as a consequence of improvement of its substructure (an increase in grain size and a decrease in pore size and density).