Methods: A series of multi-component alumino-silicate glasses were melted in an electric furnace, quenched, ball milled and re-homogenised to produce glasses. Glasses were heat treated via two step heat treatment cycles (nucleation and crystal growth). Glasses and glass-ceramics were characterised using X-ray Diffraction (XRD), Magic Angle Spinning- Nuclear Magnetic Resonance (MAS-NMR) and Scanning Electron Microscopy (SEM) to identify the phases, atomic structures and crystal morphology.
Results: XRD revealed glasses were amorphous and a Tetragonal leucite phase was identified for all glass-ceramics. Heat treated glasses showed denser and uniformly grown leucite crystals with spherical and fibre-like morphology. The 27Al MAS-NMR spectra of the glasses revealed the presence of aluminium in four-fold coordination, while the glass-ceramics showed sharp overlapped peaks in addition to Al(IV) species in the residual glass. The two-dimensional 27Al 3Q-MAS NMR spectrum of glass-ceramics clarified that the overlapping signals correspond to Al(IV) sites in the leucite phase. The ratio of aluminium distributed between the crystalline and residual glass phase may be related to the properties of the glass-ceramics.
Conclusions: Understanding the atomic structural changes of alumino-silicate glasses and glass-ceramics using solid state NMR provides independent evidence for interpreting the physical, chemical and mechanical properties of materials. Solid-state NMR can distinguish and quantify the amount of species in the crystalline and glass phases of glass-ceramics. This information is important in the characterisation of Dental glass–ceramics and can be used for formulation optimisation.