Nucleation and Growth of Chrysotile Nanotubes in H2SiO3/MgCl2/NaOH Medium at 90 to 300°C

Herein, we report new insights into the nucleation and growth processes of chrysotile nanotubes by using batch and semi-continuous experiments. For the synthesis of this highly carcinogenic material, the influences of temperature (90, 200, and 300 degrees C), Si/Mg molar ratio, and reaction time were investigated. From the semi-continuous experiments (i.e., sampling of the reacting suspension over time) and solid-state characterization of the collected samples by XRPD, TGA, FTIR spectroscopy, and FESEM, three main reaction steps were identified for chrysotile nucleation and growth at 300 degrees C: 1)formation of the proto-serpentine precursor within the first 2h of the reaction, accompanied by the formation of brucite and residual silica gel; 2)spontaneous nucleation and growth of chrysotile between about 3 and 8h reaction time, through a progressive dissolution of the proto-serpentine, brucite, and residual silica gel; and 3)Ostwald ripening growth of chrysotile from 8 to 30h reaction time, as attested to by BET and FESEM measurements. Complementary results from batch experiments confirmed a significant influence of the reaction temperature on the kinetics of chrysotile formation. However, FESEM observations revealed some formation of chrysotile nanotubes at low temperatures (90 degrees C) after 14days of reaction. Finally, doubling the Si/Mg molar ratio promoted the precipitation of pure smectite (stevensite-type) under the same P (8.2MPa)/T (300 degrees C)/pH (13.5) conditions.