MAS NMR study of the crystallisation process of apatite-mullite glass ceramics

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  • Imperial College London
  • Kyushu University


The crystallisation behaviour of 4.5SiO2.3Al2O 3. 1.5P2O5.(5-z)CaO.zCaf2 glasses with z between 0 and 3 were investigated using differential scanning calorimetry (DSC), x-ray diffraction analysis and 27Al, 29Si, 31P and 19F magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The glasses showed two exothermic peaks at Tp1 and Tp2 due to crystallisation, which decreased in temperature with fluorine content. In the nonfluorine containing glass (z=0), whitlockite (Ca 3(PO4)2 and anorthite (2SiO2.Al 2O3.CaO) were the final crystallisation products. In the fluorine containing glasses (z=2 and 3), fluorapatite (FAP) (Ca 5(PO4)3, crystallised at Tp1 and mullite (2SiO2.3Al2O3) at Tp2. MAS-NMR results showed that a glass phase remained after crystallisation. The coordination state of the phosphate species in the glass drastically changed during crystallisation. five coordinate Al, Al(V), in the glass containing fluoride disappeared after crystallisation of mullite. The 27Al and 29Si MAS-NMR spectra did not change significantly during fluorapatite crystallisation, but changed markedly on mullite formation. 19F MAS-NMR demonstrated the presence of FAP in the heat treated glasses. In the glasses with a higher fluorine content than that required to convert all the Ca and P to FAP a Al-F-Ca(n) type species remained in the residual glass phase.


Original languageEnglish
Pages (from-to)127-133
Number of pages7
JournalPhysics and Chemistry of Glasses
Issue number2
Publication statusPublished - Apr 2004