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Master's Dissertation
DOI
https://doi.org/10.11606/D.76.2023.tde-05062023-141552
Document
Author
Full name
Hugo Rodrigues Damasceno
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2023
Supervisor
Committee
Eckert, Hellmut (President)
Rodrigues, Ana Candida Martins
Santagneli, Silvia Helena
Title in English
Solid-state NMR on the quadrupolar low-γ nucleus 25Mg: Application to glasses
Keywords in English
Aluminosilicate
Glass
Magnesium
NMR
Silicate
Abstract in English
In the present work, the structure of magnesium alumino and aluminosilicate glasses were studied using several techniques of Solid State NMR. The study employed high magnetic field strengths and fast magic angle spinning to address the structural organization of the glasses. The utility of dipolar spin echo decay and static ultrawide line NMR (WURST) was tested on isotopically enriched 25Mg samples to extract information about the relevant interactions concerning the 25Mg nuclei. The results of the study were complemented by additional static and high-resolution 27Al and 29Si NMR techniques, which addressed the structural organization of the silicate and alumosilicate networks surrounding the magnesium ions. The 29Si MAS NMR spectroscopy was employed for the study, but due to limitations in the amount of material available and long spin-lattice relaxation times, reliable signal deconvolution was not obtained. The spectra were found to be consistent with previously published data, but the study found that the average isotropic chemical shifts and full widths at half maximum were found to be identical for the samples with and without 25Mg isotopic enrichment for MAS 226 glass, with stronger deviations for the other compositions. The 27Al MAS-NMR results suggest the presence of two distinct aluminum coordination environments in the samples and a small fraction of six-coordinated aluminum in the sample iso MAS 25. The findings were further validated by complementary techniques such as 27Al MQMAS NMR spectra and SATRAS-NMR. All these results form the basis of a comprehensive description of the local structure of magnesium silicate and alumosilicate glasses.
Title in Portuguese
RMN do estado sólido no núcleo quadrupolar de baixo-γ 25Mg: aplicação em vidros
Keywords in Portuguese
Aluminosilicato
Magnésio
RMN
Silicato
Vidros
Abstract in Portuguese
No presente trabalho, a estrutura amostras de vidros de alumínio e aluminossilicato de magnésio foram estudadas usando várias técnicas de RNM de Estado Sólido. O estudo empregou altos campos magnéticos e MAS-NMR para estudar a organização estrutural dos vidros. Medida de spin echo decay e WURST foi testada em amostras enriquecidas com o isótopo 25Mg para obter informações sobre as interações relevantes a cerca do núcleo 25Mg. Os resultados obtidos foram complementados por métodos adicionais de RMN estático e de alta resolução para os núcleos 27Al e 29Si, onde a estrutura das redes silicatadas e aluminossilicatadas em torno dos íons de magnésio foram estudadas. O MAS-RMN sobre 29Si foi realizada no estudo, mas devido às limitações devido pouca quantidade de material disponível e aos longos tempos de relaxamento spin-rede, não foi obtido uma desconvolução de sinal confiável. Os espectros se mostraram consistentes com dados previamente publicados, mas o presente estudo descobriu que os desvios químicos isotrópicos médios e as larguras a meia altura foram idênticos para as amostras com e sem enriquecimento de 25Mg para o vidro MAS 226 e com desvios mais fortes para outras composições. Os resultados RMN sobre núcleo 27Al com técnica MAS sugerem a presença de dois ambientes de coordenação de alumínio distintos nas amostras e uma pequena fração de alumínio 6 coordenado na amostra iso MAS 25. Esses resultados foram ainda validados por técnicas complementares, como os espectros de NMR sobre o núcleo 27Al com as técnicas MQMAS e SATRAS-NMR. Esses resultados formam uma base descritiva abrangente da estrutura local de vidros de silicato e aluminossilicato de magnésio.
 
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Publishing Date
2023-06-13
 
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