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

Abstract

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 1 H Larmor frequency) to analyze the local 27 Al 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 27 Al resonance was detected in the low-temperature ash; structures in pre-molten ashes (as prepared at 815 and 1,000 ı C) located relatively integral and symmetric, while Al resonances in the ash prepared at 1,600 ı 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.

Evolution of Fly Ash Aluminosilicates in Slagging Deposition during Oxy-Coal Combustion Investigated by 27Al Magic Angle Spinning Nuclear Magnetic Resonance

“…When the solid samples contain paramagnetic cations (e.g., iron and nickel), magnetic moments of the unpaired electrons of paramagnetic cations are much higher than those of protons and therefore strongly affects the magnetic resonances of the observed nuclei. − When solid samples containing paramagnetic materials are analyzed using MAS-NMR, paramagnetic interactions are the major contributors to strong spinning sidebands in the NMR spectra. A few studies have been conducted utilizing the paramagnetic effect on the solid-state NMR to investigate the role of iron in some Fe-rich materials. , Iron is a common element in fly ash, and high-Fe fly ash normally has more paramagnetic materials, which then can significantly affect the MAS-NMR spectra . Because of the complexity of fly ash, the difficulty of its spectral resolution increases when 27 Al MAS-NMR is used to analyze it.…”