Analyses of Aluminum Structures in a Chinese Coal Ash and Its Slag by STMAS NMR

Double-quantum filter satellite-transition magic-angle spinning experiments were tentatively carried out by one high magnetic field solid-state nuclear magnetic resonance (800 MHz for ¹H Larmor frequency) to analyze the local ²⁷Al structure in minerals of coal ash and slag. A high magnetic field offered higher sensitivity and resolution; hereby, the inconspicuous resonances of satellite-transition magic-angle spinning were obtained successfully at less stringent conditions. An obvious single 6-coordinate ²⁷Al resonance was detected in the low-temperature ash; structures in pre-molten ashes (as prepared at 815 and 1,000°C) located relatively integral and symmetric, while Al resonances in the ash prepared at 1,600°C after once completely molten demonstrated discrete and asymmetric distribution. Moreover, the detailed spatial correlations among various aluminum species in rapid quenching slag exhibited dispersive T-O-T structures with lower signal-to-noise ratio of resonances.