Sintering effects on chemical and physical properties of bioactive ceramics

The objective of this study was to characterize the chemical and physical properties of bioactive ceramics prepared from an aqueous paste containing hydroxyapatite (HA) and beta tri-calcium phosphate (beta-TCP). Prior to formulating the paste, HA and beta-TCP were calcined at 800 degrees C and 975 degrees C (11 h), milled, and blended into 15%/85% HA/beta-TCP volume-mixed paste. Fabricated cylindrical rods were subsequently sintered to 900 degrees C, 1100 degrees C or 1250 degrees C. The sintered specimens were characterized by helium pycnometry, X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), and inductively coupled plasma (ICP) spectroscopy for evaluation of porosity, crystalline phase, functional-groups, and Ca:P ratio, respectively. Mechanical properties were assessed via 3-point bending and diametral compression. Qualitative microstructural evaluation using scanning electron microscopy (SEM) showed larger pores and a broader pore size distribution (PSD) for materials sintered at 900 degrees C and 1100 degrees C,whereas the 1250 degrees C samples showed more uniform PSD. Porosity quantification showed significantly higher porosity for materials sintered to 900 degrees C and 1250 degrees C (p < 0.05). XRD indicated substantial deviations from the 15%/85% HA/beta-TCP formulation following sintering where lower amounts of HA were observed when sintering temperature was increased. Mechanical testing demonstrated significant differences between calcination temperatures and different sintering regimes (p < 0.05). Variation in chemical composition and mechanical properties of bioactive ceramics were direct consequences of calcination and sintering.