A synthetic Na-rich mica: Synthesis and characterization by ²⁷Al and ²⁹Si magic angle spinning nuclear magnetic resonance spectroscopy

A swelling mica, Na₂Mg₃(Al₂Si₂)O₁₀F₂·xH₂O, (hereafter 'Na-4 mica') was synthesized from metakaolinite + MgO and Mg aluminosilicate gels at different temperatures and durations using NaF flux. The various samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and ²⁷Al and ²⁹Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The results showed that phase-pure Na-4 mica was obtained from metakaolinite which serves as a cost-effective aluminosilicate source. ²⁷Al MAS NMR spectra showed that all or nearly all Al is in tetrahedral coordination whereas ²⁹Si MAS NMR spectra showed that the nearest neighbor environment of Si is mainly Si(3Al), as expected based on the Si:Al ratio.