Na NMR Studies of Thermal Reactions

High-temperature Na MAS NMR has been used to study the exchange of Na among the alkali sites of nepheline ([Na,K]AlSi04) at 500°C (Stebbins et al. 1989). These materials are of interest because they display ionic conductivity. The Na exchange rates estimated from the temperature-dependent changes in the Na NMR spectra are consistent with the correlation times derived from cation diffusivity measurements. 

When the clay mineral kaolinite is heated to about 980°C, it transforms to an intimate mixture of amorphous silica and an aluminium-rich spinel phase, the latter having potentially useful catalytic properties if the silica can be removed. Selective leaching 

The Bayer Process produces a highly alkaline spent liquor which when treated with gaseous CO2 precipitates dawsonite, NaAlC03(0H)2 which can be recovered as a useful by-product or recycled into the Bayer Process. Na and Al MAS NMR, CP and DOR have been used to provide detailed structural information on dawsonite and on the X-ray amorphous phase which occurs as an intermediate in its thermal decomposition to NaA102 (Bastow et al. 1995). The Na and Al NMR spectra of dawsonite from Bayer liquor revealed the presence of the minor impurity phases NaHC03 and Al(OH)3 which were too amorphous to be detected by X-ray powder diffraction. The NMR spectra of dawsonite heated at 350°C for 16 h suggested the amorphous intermediate material contains a mixture of disordered phases related to NaHC03, NaAlOa and an amorphous alumina (Bastow et al. 1995). 

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Na NMR Spectra of Sodium Compounds Relationships between the Na Chemical Shift and Structural Parameters Na NMR of Crystalline Materials Na NMR Studies of Thermal Reactions Na NMR of Glasses... 

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