Preparation and characterization of compositionally graded multilayered hydroxyapatite/zirconia ceramics

Preparation and characterization of multilayered ceramics with graded struc ture of hydroxyapatite (HAP)/partially stabilized zirconia (PSZ) was studie d, it was difficult to prepare two-layered bodies only consisting a layer o f HAP and a layer of PSZ, because these layers could not bond to each other by conventional sintering procedure. Due to peeling off, it was also diffi cult to prepare three-layered bodies consisting of a monolithic HAP layer, a layer of HAP and PSZ with weight ratio 1/1, and a PSZ layer, Then, five- and sevenlayered HAP/PSZ bodies with graded structure were prepared by atmo spheric heating (1450 degrees C, 2 h) in an electric furnace, In this case, HAP reacted with PSZ at high temperature, and the resulting product was ca lcium zirconium oxide (Ca0.15Zr0.85O1.85). Seven- and eight-layered HAP/PSZ bodies with graded structure were also prepared by hot-pressing (1150 degr ees C, 1350 degrees C), In this case, the layers bonded very firmly to each other and no peeling off was observed even upon cutting and grinding opera tions, When the sintering temperature was 1350 degrees C, small cracks para llel to the press direction were generated in the layer of monolithic HAP, The cracks were not detected in any of the remaining layers after sintering at 1150 degrees C, No chemical reaction between HAP and PSZ was found by o rdinary XRD analysis in the multilayered body prepared by hot-pressing, The graded structure was confimed by elemental analytical results of Ca and Zr , The bending strength of the seven-layered HAP/PSZ body was much higher th an that of monolithic HAP. The Vickers hardness value of the layer consisti ng of monolithic HAP was 4.3 GPa, increasing with increasing the fraction o f PSZ to reach 12.0 GPa in the layer of monolithic PSZ.