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    Structural insights of glass-reinforced hydroxyapatite composites by Rietveld refinement

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    Phase transformations and interstitial and/or substitution of trace elements during the liquid-phase sintering process of P2O5-CaO-MgO glass-reinforced hydroxyapatite (GR-HA) composites were examined by X-ray diffraction and Rietveld analyses. Using the Rietveld method for structure refinement, changes in the lattice parameters of the two main phases of the composites, hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), as well as changes 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 formation of between approximately 45 and 50% of beta-TCP, with evidence for the Mg2+ enhancing the formation of beta-TCP. Between 1300 and 1350 degrees C, the beta-TCP inverts to alpha-TCP, without further decomposition of the residual 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 oxygen occupancy (0(occ)). Results showed that the Mg2+ containing glasses induced 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 in the lattice parameters of the crystallographic phases present in the microstructure of the composites. This suggests some substitution of Mg2+-for-Ca2+ in the beta-TCP structure during the liquid-phase sintering process. (C) 2000 Elsevier Science Ltd. All rights reserved.

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    Description

    Title : Structural insights of glass-reinforced hydroxyapatite composites by Rietveld refinement
    Author(s) : MA Lopes, JC Knowles, JD Santos
    Abstract : Phase transformations and interstitial and/or substitution of trace elements during the liquid-phase sintering process of P2O5-CaO-MgO glass-reinforced hydroxyapatite (GR-HA) composites were examined by X-ray diffraction and Rietveld analyses. Using the Rietveld method for structure refinement, changes in the lattice parameters of the two main phases of the composites, hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), as well as changes 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 formation of between approximately 45 and 50% of beta-TCP, with evidence for the Mg2+ enhancing the formation of beta-TCP. Between 1300 and 1350 degrees C, the beta-TCP inverts to alpha-TCP, without further decomposition of the residual 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 oxygen occupancy (0(occ)). Results showed that the Mg2+ containing glasses induced 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 in the lattice parameters of the crystallographic phases present in the microstructure of the composites. This suggests some substitution of Mg2+-for-Ca2+ in the beta-TCP structure during the liquid-phase sintering process. (C) 2000 Elsevier Science Ltd. All rights reserved.
    Keywords : glass reinforced hydroxyapatite composites, mg apatites, rietveld refinement, beta tcp, liquid phase sintering, beta tricalcium phosphate, hydroxylapatite, magnesium

    Subject : unspecified
    Area : Other
    Language : English
    Year : 2000

    Affiliations UCL
    Journal : Biomaterials
    Volume : 21
    Issue : 18
    Publisher : ELSEVIER SCI LTD
    Pages : 1905-10
    Url : http://discovery.ucl.ac.uk/110569/

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