MAS-NMR investigations of the crystallization behaviour of lithium aluminum silicate (LAS) glasses containing P₂O₅ and TiO₂ nucleants

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• 作者：A. Ananthanarayanan ; G.P. Kothiyal ; L. Montagne ; B. Revel
• 关键词：Glass ; Glass ceramics ; Lithium alumino-silicate ; MAS-NMR ; P₂O₅ ; TiO₂
• 刊名：Journal of Solid State Chemistry
• 出版年：2010
• 出版时间：June 2010
• 年：2010
• 卷：183
• 期：6
• 页码：1416-1422
• 全文大小：665 K

文摘

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.