Hydroxyapatite-alumina platelet composites

摘要

Hydroxyapatite matrix composites containing alumina platelets were produced by slip casting and hot pressing with the aim of achieving a homogeneous and controlled microstructural design to improve the mechanical reliability. With the use of Al_2O_3 platelets of large size ( PHI approx approx 12 mu m), the behaviour of aqueous suspensions of composite mixtures remains quasi-Newtonian. From 30 volpercent of small platelets ( PHI approx approx 5 mu m) it becomes shear-thinning. Orientation phenomena of platelets are responsible for the modifications of the flow. Due to the disk-shaped morphology of alumina, a compromise must also be found to optimise particulate rearrangement during casting. After hot pressing, a preferred orientation of Al_2O_3 platelets is obtained. Fracture toughness of composites containing small platelets increases up to 200 percent that of the monolithic matrix in the direction parallel to platelet faces and reaches 400 percent in the perpendicular direction. Large platelets lead to an increase of residual thermoelastic stresses inducing a microcracking of the matrix. It is concluded that both the size and the aspect ratio of platelets are of prime importance for the toughening of HAP based bioceramics.