Hydrothermal synthesis of Mn–mica

Hydrothermal synthesis of Mn–mica was achieved using metakaolin and manganese carbonate or silicic acid and aluminum nitrate as aluminosilicate sources along with manganese carbonate in aqueous solutions of KOH. The mixtures of starting materials were treated under hydrothermal conditions at 100–200 °C for 24–48 h. The use of metakaolin and manganese chloride also led to the synthesis of Mn–mica under hydrothermal conditions. From metakaolin and manganese carbonate, fine well-crystallized Mn–mica was hydrothermally synthesized at 200 °C using different KOH concentrations. However, from the mixtures of silicic acid, aluminum nitrate and manganese carbonate, poorly crystallized micas were synthesized at 200 °C using different Si/Al molar ratios of starting mixtures. Increasing the duration of hydrothermal treatment from 24 to 48 h yielded somewhat better crystallized Mn–mica as determined by X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed a particle size of about 1 µm and plate-like shape of the synthetic Mn–mica.