Preparation and properties of inhomogeneous hydroxyapatite ceramics

Inhomogeneous ceramics of hydroxyapatite (HA) were prepared by sintering briquettes in which an inhomogeneous distribution of density was made by pressing HA powder into a die with rough walls. The resulting sample of such a ceramic is a hard thin shell with a loose core, and it is characterized by an inhomogeneous macro- and microstructure. It is a sintered conglomerate from HA grains containing grain boundary macropores in contact with the surface and micropores located inside the grains, part of which are also associated with the free surface. The highest value of microhardness is fixed on the surface of the sample. The radial distribution of microhardness in the (cylindrical) sample has an axisymmetric, nonmonotonic character and, on the whole, shows the decrease of microhardness (the increase of porosity) from the surface to the center. The highest values of microhardness, crushing strength, and fracture strength are close to those known for ceramics of moderate strength.