This PhD thesis presents structural investigations of amorphous inorganic materials: oxide and oxynitride glasses and mesoporous bioactive glasses (MBGs), by solid-state Nuclear Magnetic Resonance (NMR). Lanthanum oxide and oxynitride [La-Si-(Al)-O-(N)] glasses have a large number of potential applications due to their physical properties. In our work we have studied, compared to previous investigations, significantly expanded ranges of glass compositions (for oxynitride glasses, including samples of very high nitrogen content, up to 53 % out of the anions). We have estimated local environments of 29Si and 27Al structural units (their coordination, polymerization degree and number of N incorporated into tetrahedral units) in the materials. We have suggested a random Al/Si distribution along with almost uniform non-bridging oxygen atoms distribution in aluminosilicate glasses. Silicon nitride was used as precursor in the oxynitride glass synthesis. We studied both α- and β-modifications of silicon nitride, 15N-enriched, as well as fully (29Si, 15N)-enriched samples. We have shown that the linewidths of 15N NMR spectra are dominated by J(29Si-15N) coupling in 29Si315N4 sample. Mesoporous bioactive glasses in the CaO-SiO2-P2O5 system show superior bioactivity (the ability to form a hydroxycarbonate apatite layer on the glass surface when exposed to body fluids) compared to conventional bioactive glasses due to their large surface area and uniform pore-size distribution. Previous studies suggested a homogeneous cation distribution over the MBG samples on a 10−20 nm length-scale. From our results, on the other hand, we may conclude that Si and P is not intimately mixed. We propose a structural model, in which the pore walls of MBGs are composed of a silica network, and a phosphate phase is present as nanometer-sized clusters that are dispersed on the pore wall.

Submitted by Maria Aparecida (cidazen@gmail.com) on 2017-05-16T15:07:08Z No. of bitstreams: 1 Edson Carvalho Paz.pdf: 1589088 bytes, checksum: 37f9b2d6613e1ce560c6a50e8dbf458f (MD5) / Made available in DSpace on 2017-05-16T15:07:08Z (GMT). No. of bitstreams: 1 Edson Carvalho Paz.pdf: 1589088 bytes, checksum: 37f9b2d6613e1ce560c6a50e8dbf458f (MD5) Previous issue date: 2015-06-30 / CAPES, CNPQ / In this work glass formation of CaF2-CaO-B2O3-TeO2 system (CBTx), with tellurium oxide concentrations varing from 20 to 50 wt%, was studied. In order to evaluate the glass forming ability of that system, six glass matrix were prepared and characterized to understand the behavior of their physical, thermal, structural, optical and spectroscopic properties. As far we know, this is the first report in the literature about this glass system. The preparation of glasses CBTx system was carried out keeping the Ca/B2O3. The prepared glass samples were characterized by X-ray diffraction (XRD), volumetric density (ρ), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), differential thermal analysis (DTA), specific heat (cp), refractive index (n), electronic polarizability (α), theoretical optical basicity (Λth), optical absorption coefficient (Ae) and band gap optical (Eopt). The results are discussed in terms of tellurium oxide content and structural properties of the glass samples. Density, thermal stability, refractive index, electronic polarizability and theoretical optical basicity values increase with TeO2 content, while transition temperature (Tg), specific heat, optical window and the band gap optical decrease; Raman and FTIR spectroscopy indicated that the network structure of studied glass is formed by BO3, BO4, TeO3, TeO3+1 and TeO4 units. The CBTx system showed a good ability to glass formation, especially the glass matrix of most TeO2 content (CBT50), which proved to be the most suitable for future work doping with rare earth ions and tests as optical amplifier in communication fibers or other photonic devices. / Neste trabalho apresentamos o estudo da formação de vidros no sistema [10CaF2-(30-0,4x)CaO-(60-0,6x)B2O3-xTeO2], em que 20 ≤ x ≥ 50 % em massa, denominado CBTx, com o objetivo de avaliar a habilidade de formação vítrea do referido sistema visando obter matrizes vítreas estáveis. Até onde sabemos, este é o primeiro relato na literatura de pesquisas sobre esse sistema. O preparo dos vidros no sistema CBTx foi realizado mantendo constante a razão Ca/B2O3. Neste trabalho sintetizamos seis amostras vítreas, as quais foram submetidas ao processo de caracterização por meio das seguintes análises: difração de raios-X (DRX), densidade de massa volumétrica (ρ), espectroscopia Raman, espectroscopia no infravermelho com transformada de Fourier (FTIR), análise térmica diferencial (DTA), calor específico (cp), índice de refração (n), polarizabilidade eletrônica (α), basicidade óptica teórica (Λth), coeficiente de absorção óptica (Ae) e band gap óptico (Eopt). Os resultados foram discutidos em função do conteúdo de óxido de telúrio e de suas alterações nas propriedades estruturais, térmicas, ópticas e espectroscópicas das amostras vítreas. Com o aumento da concentração de TeO2 nas amostras, houve aumento dos valores da densidade, da estabilidade térmica, do índice de refração, da polarizabilidade eletrônica e da basicidade óptica teórica; redução da temperatura de transição vítrea (Tg), do calor específico e da janela óptica e deslocamento do band gap óptico para menor energia; as espectroscopias Raman e FTIR indicaram que a estrutura da rede dos vidros sob investigação é formada por unidades BO3, BO4, TeO3, TeO3+1 e TeO4. O sistema CBTx apresentou uma boa habilidade de formação vítrea, com destaque para a matriz vítrea de maior teor estudado de TeO2 (CBT50), que se mostrou a mais indicada para trabalhos futuros de dopagem com íons terras raras e testes como amplificador óptico em fibras de comunicação ou outros dispositivos fotônicos.