Structural investigation of gel-derived materials from the SiO2Al2O3 system

• DOI: 10.1016/j.molstruc.2018.04.085
• Publication Date: 2018-04-26T09:28:28Z
• Authors: Barbara Zagrajczuk; Michal Dziadek; Zbigniew Olejniczak; Bogdan Sulikowski; Katarzyna Cholewa...; Maria Laczka
• Keywords: Coordination number

Abstract Aluminosilicate glasses from the binary SiO2 Al2O3 system, AT1 (50% SiO2 - 50% Al2O3, %mol) and AS1 (80% SiO2 - 20% Al2O3, %mol), were obtained by the sol-gel process in the form of powders. Additionally, Al2O3 and vitreous SiO2 were synthesized by the same technique and used as reference materials. The essential information concerning samples structural properties was provided by the XRD diffraction and the FTIR and UV Raman methods. The XRD confirmed the amorphous character of the materials, except for the pure Al2O3, where a small tendency for crystallization of the γ–Al2O3 phase was noticed. The local environment of silicon and aluminum atoms was determined by the 29Si and 27Al MAS-NMR as well as 27Al 3MQ-MAS-NMR spectroscopies. Moreover, for the materials containing Al2O3, the average Al coordination parameter was calculated basing on the data provided by the 27Al MAS-NMR. The 29Si MAS-NMR spectra of the materials indicated various chemical environments around silicon amongst particular materials and presence of the Q2, Q3, and Q4 structural units. Moreover, the data provided with the 27Al MAS-NMR indicated the presence of aluminum in the AlO4, AlO5, and AlO6 coordination forms. Proportions of the particular units revealed favoring formation of the Al in the higher coordination (AlO5 and AlO6) over commonly the dominant AlO4 units, which can be explained by the charge balance requirement in the system that is deprived of charge compensating alkali cations.