High temperature ²⁷Al NMR time resolved study. Application to the CaO-Al₂O₃ binary system

In situ high temperature 27Al NMR study of structure and dynamics in a calcium aluminosilicate glass and melt

“…These data were plotted in Fig. 6, and show good agreement with shear relaxation time s s as estimated from viscosity, as has been seen previously for a number of aluminate melts at higher temperatures [24,25,35]. These results clearly show that NMR and shear relaxation are controlled by the same type of atomic motion, in both supercooled liquids (T g < T < T liquid ) and stable liquids (T liquid < T).…”

“…Previous studies have in fact suggested that the proportion of this species is dependent on temperature. For example, the fraction of pentacoordinated Al increased with increasing quench rate (higher fictive temperature) in SiO 2 -Al 2 O 3 glasses [21] and calcium aluminosilicate glasses [45,59] and with increasing temperature in calcium aluminate liquids [24,25,35]. The decrease in the isotropic chemical shift of the CAS melt became more prominent at 1400°C, reaching 63.3 ± 1 ppm.…”

“…Compared with these nuclei, however, little has been reported about 27 Al NMR relaxation behavior in glasses and melts with increasing temperature. Massiot and co-workers successfully measured in situ, very high temperature (1700-2400 K) 27 Al NMR spectra and T 1 values in molten calcium and strontium aluminates using a laser-heated apparatus and a containerless levitation system [25,35,36]. They demonstrated that measured values of T 1 were almost equal to T Ã 2 derived from the observed line width at half maximum (FWHM) in the extreme, high temperature narrowing limit, x 0 s c ( 1 (x 0 : Larmor frequency, s c : NMR correlation time, see below).…”

Al motion rates in levitated, molten Al2O3 samples, measured by pulsed gradient spin echo 27Al NMR

“…The laser is operated in this mode for all measurements, and is not switched off during data acquisition as in time-resolved experiments. 12 Conservative design of the high-temperature section of the NMR probe, using multiple cooling air streams for interior parts made from Vespel, allows stable, uninterrupted signal acquisition for periods up to several hours in length.…”

Melt and glass structure in the Al2O3–CaO–LaPO4 system studied by 27Al and 31P NMR, and by Raman scattering

“…5,6 Temperature measurements were performed using the technique of spectroradiometry, [6][7][8] and are accurate to ±25 • C. In the liquid state, the 27 Al chemical shift was found to be remarkably insensitive to temperature, varying less than 2 ppm from melting to 2450 • C. This observation is generally consistent with previous measurements in molten alumina 4 and in the CaO-Al 2 O 3 system. 9 Solid samples were characterized at room temperature by 27 Al and 31 P NMR measurements, performed either in the high temperature probe after sample melting and cooling, or separately in a type of probe used only for solids and called a Magic Angle Spinning (MAS) probe. In this probe, the sample is rapidly spun around an axis oriented at an angle θ, called the magic angle, with respect to H 0 .…”