Structural insights of glass-reinforced hydroxyapatite composites by Rietveld refinement

Phase transformations and interstitial and/or substitution of trace element s during the liquid-phase sintering process of P2O5-CaO-MgO glass-reinforce d hydroxyapatite (GR-HA) composites were examined by X-ray diffraction and Rietveld analyses. Using the Rietveld method for structure refinement, chan ges in the lattice parameters of the two main phases of the composites, hyd roxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), as well as chang es in several bond lengths and in the occupancy of the hydroxyl oxygen site in the HA phase structure were assessed. The glasses gave rise to formatio n of between approximately 45 and 50% of beta-TCP, with evidence for the Mg 2+ enhancing the formation of beta-TCP. Between 1300 and 1350 degrees C, th e beta-TCP inverts to alpha-TCP, without further decomposition of the resid ual HA. The glasses showed evidence for stabilisation of the hydroxyl group located in the hydroxyl channels. This is supported by measurements of the hydroxyl channel radius (R-c), the Ca-2-OH bond length and the hydroxyl ox ygen occupancy (0(occ)). Results showed that the Mg2+ containing glasses in duced the beta-TCP phase formation in the structure of GR-HA composites and retarded the beta-TCP into alpha-TCP transformation at higher temperatures . The chemical composition of the P2O5 glasses also induces modifications i n the lattice parameters of the crystallographic phases present in the micr ostructure of the composites. This suggests some substitution of Mg2+-for-C a2+ in the beta-TCP structure during the liquid-phase sintering process. (C ) 2000 Elsevier Science Ltd. All rights reserved.