Low-temperature synthesis of micas under conventional - and microwave-hydrothermal conditions

Several micas containing different octahedral and interlayer cations were synthesized at different temperatures under conventional- and microwave-hydrothermal conditions and these phases were characterized by powder X-ray diffraction, solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. A Zn K-mica with Zn in the octahedral sheets and K in the interlayers was synthesized in the temperature range 150-200°C and a novel Zn Rb-mica with Zn in the octahedral sheets and Rb in the interlayers was synthesized at 200°C. The synthesis of either Mg, Co or Ni K-micas, however, was found to be difficult or impossible at these low temperatures. Solid-state ²⁹Si MAS-NMR revealed that the Al in the tetrahedral sites is disordered with several nearest-neighbor Si environments. In general, microwave-assisted hydrothermal conditions led to better crystallization of the Zn K-micas compared with the conventional method.