H. Robert et al., The influence of glass composition on nucleation crystallisation microstructure and properties of apatite-mullite glass-ceramics, GL SCI T-GL, 73, 2000, pp. 146-153
Citations number
16
Categorie Soggetti
Material Science & Engineering
Journal title
GLASS SCIENCE AND TECHNOLOGY-GLASTECHNISCHE BERICHTE
Glasses from the system SiO2-Al2O3-P2O5-CaO-CaF2 can crystallise to fluorap
atite(Ca-5(PO4)(3)F) and mullite (2SiO(2)3Al(2)O(3)). The present paper inv
estigates the influence of fluorine content and calcium to phosphate (Ca:P)
ratio on the nucleation and crystallisation behaviour, of apatite glass-ce
ramics. Fluorine is critical to apatite formation and in the absence of flu
orine P tricalcium phosphate is formed rather than fluorapatite, Increasing
fluorine content results in a decrease in glass transition temperature(Tg)
and peak crystallisation temperatures(Tc)s. Bulk nucleation of fluorapatit
e is favoured in glass compositions with a Ca:P ratio of 1.67 and by high f
luorine contents. Glasses with Ca:P ratios lower or higher than 1.67 tend t
o surface nucleate. However such glasses can be made to bulk nucleate by ho
lding for one hour above Tg. Bulk nucleation occurs via prior amorphous pha
se separation (APS).
Mullite forms following crystallisation of apatite, but anorthite and an al
uminium phosphate phase may also form depending on the glass composition.
Compositions either side of the apatite stoichiometry give rise to less cry
stal nucleation than compositions at the apatite stoichiometry and give ris
e to apatite crystals that coarsen more readily on heat treatment. Biaxial
flexural strength and fracture toughness depend on the apatite volume fract
ion and size.