Crystallization of a high-strength lithium disilicate glass-ceramic: An XRD and solid-state NMR investigation

The phase evolution of a high flexural strength lithium disilicate (Li2S12O5: LS2) glass-ceramic in a complex SiO2-Li2O-Al2O3-MgO-P2O5-ZrO2 glass system has been investigated as a function of temperature using in situ and ex situ X-ray diffraction (XRD) and P-31 and Si-29 solid-state nuclear magnetic resonance (SSNMR) spectroscopy. In the base glass, lithium metasilicate (Li2SiO3: LS) crystallizes (at 525 degrees C) before LS2 (at 675 degrees C). Si-29 NMR shows that LS is not only formed from the Q(glass)((2)) species, but also by disproportionation of the Q(glass)((3)) units. The XRD data demonstrate the formation of a minor phase of MgAl2Si4O12 from the reaction of SiO2 with minor components of Al2O3 and MgO. Diffraction peaks of Li3PO4 are firstly detected at 675 degrees C, and they become evident at 750 degrees C and above. The evolution of phosphorus species in the glass as a function of temperature has been revealed by 31P NMR spectroscopy. Two Si-29 T-1 relaxation components were observed in samples across all temperatures, suggesting the presence of glass-in-glass phase separation in the base glass. A plot of Si-29 T-1 relaxation measurements shows discontinuity at 750 degrees C, indicating microstructural changes. A detailed crystallization mechanism of high-strength LS2 glass-ceramics is proposed. (C) 2016 Elsevier B.V. All rights reserved.