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(Referência obtida automaticamente do Web of Science, por meio da informação sobre o financiamento pela FAPESP e o número do processo correspondente, incluída na publicação pelos autores.)

Medium-Range Order in Sol-Gel Prepared Al2O3-SiO2 Glasses: New Results from Solid-State NMR

Texto completo
Ren, Jinjun [1] ; Zhang, Long [2] ; Eckert, Hellmut [1, 3]
Número total de Autores: 3
Afiliação do(s) autor(es):
[1] Univ Munster, Inst Phys Chem, D-48149 Munster - Germany
[2] Chinese Acad Sci, Shanghai Inst Opt & Fine Mech, Shanghai 201800 - Peoples R China
[3] Univ Sao Paulo, Inst Fis Sao Carlos, BR-13590 Sao Carlos, SP - Brazil
Número total de Afiliações: 3
Tipo de documento: Artigo Científico
Fonte: Journal of Physical Chemistry C; v. 118, n. 9, p. 4906-4917, MAR 6 2014.
Citações Web of Science: 22

The medium-range order of 0.5Al(2)O(3)-xSiO(2) glasses (1 <= x <= 6) prepared via a new sol-gel route from the Al lactate precursor has been studied by Si-29 and Al-27 single- and double-resonance solid-state NMR techniques. For high-alumina samples Si-O-Al connectivities are detected by Si-29 MAS NMR as well as by Si-29[Al-27] rotational echo adiabatic passage double-resonance (REAPDOR) spectroscopy. To boost the signal-to-noise ratio, the REAPDOR experiment was combined with a Carr-Purcell-Meiboom-Gill (CPMG) echo train acquisition. While all five silicon units Q(mAl)((4)) (0 <= m <= 4) are detectable in appreciable concentrations for x = 1, the spectra indicate that the average number of Al species bound to silicon, (m(Al)), gradually decreases toward higher x values, as expected. The Al-27 MAS NMR spectra reveal four-, five-, and six-coordinated aluminum in these glasses. For x >= 3, the Al species detected are essentially independent of sample composition indicating a constant structural environment of Al. In contrast, for x = 1 and 2, an increase in the Al-27 isotropic chemical shifts suggests an increasing number of Al.. Al proximities. Consistent with this finding, two-dimensional Al-27-Al-27 double-quantum/single-quantum correlation spectroscopy reveals spatial proximities among and between all types of aluminum species present. On the basis of the complementary evidence from these single- and double-resonance experiments, a model for the medium-range order of these glasses is developed. (AU)

Processo FAPESP: 13/07793-6 - CEPIV - Centro de Ensino, Pesquisa e Inovação em Vidros
Beneficiário:Edgar Dutra Zanotto
Linha de fomento: Auxílio à Pesquisa - Centros de Pesquisa, Inovação e Difusão - CEPIDs