کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1482959 991582 2011 6 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
NMR investigation of the crystallization mechanism of LaF3 and NaLaF4 phases in aluminosilicate glasses
موضوعات مرتبط
مهندسی و علوم پایه مهندسی مواد سرامیک و کامپوزیت
پیش نمایش صفحه اول مقاله
NMR investigation of the crystallization mechanism of LaF3 and NaLaF4 phases in aluminosilicate glasses
چکیده انگلیسی

The structure of transparent F-containing nano-crystalline glass-ceramics has been investigated by means of Nuclear Magnetic Resonance as well as X-ray Diffraction as a function of the processing conditions. LaF3 or NaLaF4 are crystallized depending on the glass composition: low silica content and low modifier to alumina ratios lead to crystallization of LaF3, while increasing SiO2 and decreasing Al2O3 results in NaLaF4 nano-crystals. NMR results show that fluorine in glasses is involved in Al–F–Na or La–F environments, the later constituting pre-nucleation sites. After annealing, crystallization of either LaF3 or NaLaF4 crystals takes place, which is correlated with an increase in the intensity of fluorine resonance of La–F environment and a decrease in the Al–F–Na one. The description of the local environment around F, Al and Na is in accordance with a crystallization model of these materials. In low silica containing glasses, it starts from La–F sites and progresses thanks to fluorine diffusion from Al–F–Na bonds until crystal growth is limited through the increase in the viscosity of the glass matrix around crystals. In high silica glasses, long annealing times give rise to crystallization of NaF after NaLaF4 crystals have formed and a silica-enriched region around them inhibits further crystal growth.

Research Highlights
► Nanocrystallization of LaF3 and NaLaF4 phases in aluminosilicate glasses by NMR.
► Fluorine diffuses from Al-F-Na in the glass matrix to form La-F bonds in crystals.
► Low silica-containing glasses produce LaF3 phase crystallization.
► High silica-containing glasses give rise to NaLaF4 phase precipitation.
► NaF phase is formed one fluorine is not allowed to further diffuse into crystals.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Non-Crystalline Solids - Volume 357, Issue 5, 1 March 2011, Pages 1463–1468
نویسندگان
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