Phase transition mechanisms involved in the formation of structurally stable beta-Ca-3(PO4)(2)-alpha-Al2O3 composites

摘要

Composite powders comprising various proportions of beta-Tricalcium phosphate [beta-Ca-3(PO4)(2)] and a Alumina (alpha-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 beta-Ca-3(PO4)(2) and preserved the thermal stability of beta-Ca-3(PO4)(2) alpha-Al2O3 composites till 1400 C-omicron. Such enhancement of thermal stability was due to the occupancy of Al3+ at both Ca2+(4) and Ca2+(5) lattice sites of beta-Ca-3(PO4)(2). Beyond the occupancy saturation limit for Al3+, the excess of aluminium crystallized as alpha-Al2O3. Morphological analysis revealed the growth of rod-like alpha-Al2O3 platelets on the surface of micron sized beta-Ca-3(PO4)(2) grains. The mechanical data obtained from indentation of bulk composites displayed enhanced hardness and Young's modulus with increasing alpha-Al2O3 content in the composites. (C) 2017 Elsevier Ltd. All rights reserved.