Environment of titanium and aluminum in a magnesium alumino-silicate glass

Abstract

The structure of the glass 2MgO-2Al 2 O 3 -5SiO 2 -TiO 2 was investigated using neutron diffraction with isotopic substitution. Reverse Monte Carlo (RMC) modeling was used to reproduce experimental structure factors derived from diffraction experiments. The local environment of titanium atoms was determined and it corresponds to an average of 5.4 ± 0.2 oxygen atoms at a mean distance of 1.86 ± 0.02Å. This coordination number agrees with the predominance of fivefold coordination, with the coexistence of four-and sixfold coordination in similar amounts. 27 Al nuclear magnetic resonance (NMR) results revealed that the proportion of highly coordinated aluminum atoms in this titanium-bearing glass was higher than in the titanium-free sample. RMC modeling was used to interpret the structural role of these [5] Al species and we show a trend for preferential bonding between [5] Al and Ti atoms. This favored linkage is important to understand the role of titanium dioxide as a nucleating agent in inorganic glass-ceramics fabrication.

Structural fluctuations and role of Ti as nucleating agent in an aluminosilicate glass

“…Similar results are also observed using neutron diffraction [45]. The correlations between the main atomic pairs (Si-O, Al-O, SiSi/Al…) occur at similar distances in Ti-bearing glasses than in the Tifree glass.…”

“…More recently, we reported the tendency for titanium atoms to bond with highly coordinated aluminum atoms by edge-sharing in the 2MgO-2Al 2 O 3 -5SiO 2 + 11.1 mol% TiO 2 glass [45]. Such an arrangement extracted from a Reverse Monte Carlo modeling is represented in Fig.…”

Structural Study of Glassy CaO–SiO2–CaF2–TiO2 Slags by Raman Spectroscopy and MAS-NMR

“…This dominant peak could correspond to F-Ca(n) (n represents the number of Ca coordinated with fluorine, and fluorine has an unknown number of exclusively Ca 2+ nearest neighbors, with n typically between 3 and 4) site. [18][19][20][21][22][28][29][30][31] Therefore, most of the fluorine is exclusively coordinate by Ca 2+ in the structure of present glassy slags. According to Zeng and Stebbins, 19) high-frequency shoulder at about -150 ppm may reflect Si-F site.…”

“…The 19 F MAS spectrum has a strong and broad peak centered at about -95 ppm, which is in close proximity to the chemical shift of the non-planar FCa(n)site. [17][18][19][20][28][29][30] At about -150 ppm, there is a small shoulder appearance in all samples, and shoulder become sharp in spectra of samples with 10% TiO2 content. It can be seen from Fig.…”

“…14) Another Raman spectral study conducted by Mysen et al 15) showed coexistence of six-fold and four-fold coordinated titanium, and four-fold titanium increases with increase of TiO 2 content. Raman and infrared spectral study by Bihuniak et al 16) showed that titanium is present in four-fold coordination in titanium-containing vitreous silicas, while X-ray Absorption Fine Spectra(XAFS) 17) and neutron diffraction 18) study showed dominant five-fold titanium existence in some glasses and melts. Regarding fluorine in structure of glass, 19 F nuclear magnetic resonance with magic angular spinning (MAS-NMR) study show that most fluoride is in sites that are structurally similar to the corresponding simple metal fluoride and a few present of Si-F bonds can be founded in the sodium silicates.…”