MAS-NMR investigations of the crystallization behaviour of lithium aluminum silicate (LAS) glasses containing P2O5 and TiO2 nucleants |
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Authors: | A. Ananthanarayanan G.P. Kothiyal B. Revel |
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Affiliation: | a Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Centre, Mumbai 400085, India b Université Lille Nord de France - UMR CNRS 8181, USTL, 59655 Villeneuve d’Ascq, France |
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Abstract: | Lithium aluminum silicate (LAS) glass of composition (mol%) 20.4Li2O-4.0Al2O3-68.6SiO2-3.0K2O-2.6B2O3-0.5P2O5-0.9TiO2 was prepared by melt quenching. The glass was then nucleated and crystallized based on differential thermal analysis (DTA) data and was characterized by 29Si, 31P, 11B and 27Al MAS-NMR. XRD and 29Si NMR showed that lithium metasilicate (Li2SiO3) is the first phase to c form followed by cristobalite (SiO2) and lithium disilicate (Li2Si2O5). 29Si MAS-NMR revealed a change in the network structure already for the glasses nucleated at 550 °C. Since crystalline Li3PO4, as observed by 31P MAS-NMR, forms concurrently with the silicate phases, we conclude that crystalline Li3PO4 does not act as a nucleating agent for lithium silicate phases. Moreover, 31P NMR indicates the formation of M-PO4 (M=B, Al or Ti) complexes. The presence of BO3 and BO4 structural units in all the glass/glass-ceramic samples is revealed through 11B MAS-NMR. B remains in the residual glass and the crystallization of silicate phases causes a reduction in the number of alkali ions available for charge compensation. As a result, the number of trigonally coordinated B (BO3) increases at the expense of tetrahedrally coordinated B (BO4). The 27Al MAS-NMR spectra indicate the presence of tetrahedrally coordinated Al species, which are only slightly perturbed by the crystallization. |
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Keywords: | Glass Glass ceramics Lithium alumino-silicate MAS-NMR P2O5 TiO2 |
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