Small-angle neutron scattering on silica glasses containing titania

Abstract

Small-angle scattering (SAS) of neutrons is applied to the investigation of the microinhomogeneous structure of glasses. The alumina-silica titania-containing systems are taken as the subject of the investigation. The negative sign of the Ti nuclear scattering amplitude sharply extends the sensitivity to fluctuations of the atomic density. The phase-segregation kinetics was studied in the temperature region 750-950°C. A comparison of neutron SAS data with the data from X-ray phase analysis and neutron diffraction has shown that the process of segregation into two amorphous phases is accompanied by the simultaneous ordering of the titania-rich phase up to the appearance of crystallites. The 'glass-in-glass' state corresponds only to the initial stages of the decomposition.

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

“…Furthermore, the spectra also show the presence of highly coordinated aluminum atoms, i.e. aluminum atoms with five ( [5] Al) or six ( [6] Al) oxygen neighbors. The 2D spectra were deconvoluted using the "dmfit" program [34] to retrieve the isotropic chemical shift, δ iso , and the mean quadrupolar product, C Qη , for each aluminum species.…”

“…These parameters were then used to simulate the 1D quantitative MAS spectra and estimate the amount of [4] Al, [5] Al and [6] Al as described earlier [35]. Values are reported in Table 2; error bars are ±0.5 ppm for the δ iso and about ±0.5 MHz for the C Qη , and the uncertainties on the proportion of five-fold coordinated, [5] Al, and six-fold coordinated, [6] Al, aluminum are around 1% [34]. No significant variations of chemical shift or quadrupolar coupling constant can be observed with the titanium content.…”

“…In fact, past studies have shown contradictory results. No SANS signal was observed in as quenched glasses [6,13], even after heat treatment at 720°C for 10 h [20] or at 750°C for 30 h [6]. The absence of two amorphous structures in the initial glass was confirmed in several studies using transmission electron microscopy (TEM) [19,21,22].…”

“…This was interpreted by the presence of titanium-rich droplets and the formation of titaniumrich and silicon-rich regions was confirmed later for heat-treated glasses [6,12,13]. These regions can be the starting point for the internal crystallization of the volume of the glass enabling, at higher temperatures, the nucleation of (Mg-Al)-titanate crystals before or simultaneously with a β-quartz solid solution [2][3][4]7,8,12,[14][15][16][17][18][19].…”

“…Upon the heat treatment that are used to obtained nucleation in the system MgO-Al 2 O 3 -SiO 2 -TiO 2 , the development of a micro-inhomogeneous structure with the decomposition to two amorphous states is often considered [2][3][4][5][6][7][8][9][10] and the terms phase separation or glass-in-glass separation are usually used.…”