Phase transition mechanisms involved in the formation of structurally stable β-Ca3(PO4)2-α-Al2O3 composites

Composite powders comprising various proportions of β-Tricalcium phosphate [β-Ca3(PO4)2] and α-Alumina (α-Al2O3) were synthesized by wet precipitation and then heat treated for drying and crystalline phase development. The phase formation mechanism was assessed through a set of characterization techniques including XRD, FT-IR and Raman spectra, and quantitative Rietveld refinement analysis. Al2O3 additions delayed the transformation kinetics from calcium deficient apatite to β-Ca3(PO4)2 and preserved the thermal stability of β-Ca3(PO4)2 − α-Al2O3 composites till 1400 °C. Such enhancement of thermal stability was due to the occupancy of Al3+ at both Ca2+(4) and Ca2+(5) lattice sites of β-Ca3(PO4)2. Beyond the occupancy saturation limit for Al3+, the excess of aluminium crystallized as α-Al2O3. Morphological analysis revealed the growth of rod-like α-Al2O3 platelets on the surface of micron sized β-Ca3(PO4)2 grains. The mechanical data obtained from indentation of bulk composites displayed enhanced hardness and Young's modulus with increasing α-Al2O3 content in the composites.