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Production and properties of glass bonded apatite-wollastonite bioceramics

Vakıfahmetoğlu, Çekdar
Apatite containing bioceramic materials are considered to be potentially useful for replacement or repair of natural bone. In the present study, the aim was to produce a new composite bioceramic containing crystalline apatite and wollastonite phases with a bimodal grain size distribution. The manufacturing scheme was based on the liquid phase sintering process in which the compacts pressed from powders of apatite (HAP or Si-HAP) and pseudowollastonite was sintered in the presence of a liquid phase. Three distinct fluxing agents, magnesium flux (MCAS), sodium feldspar and sodium frit (NCAS), were prepared to act as additives for generating the liquid phase during sintering. Among those, the use of sodium frit resulted in the expected bimodal microstructural assembly. During the sintering studies, it was discovered that the apatite component of the ceramic was prone to compositional modifications by reaction with the liquid phase. This interaction resulted in a formation of siliconized HAP which crystallized in the form of rod-like grains. Meanwhile wollastonite grains tended to exhibit faceted equiaxed morphology and bonded to rod-like apatite grains with the help of a glassy phase. The results showed significant enhancement in the mechanical properties of apatite-wollastonite composites compared to phase pure hydroxyapatite. For example, the sample with 47.5 wt% Si-HAP2 + 47.5 wt% W + 5 wt% NCASfrit had the highest value of flexural strength, 83.6 MPa, which was almost twice that of hydroxyapatite, 46.3 MPa. The results for other properties such as compressive strength, hardness and fracture toughness also demonstrated the benefit of apatite-wollastonite composite approach.