Crystallization and textural porosity of synthetic clay mineralsBasis of a presentation given at Materials Discussion No. 5, 22???25 September 2002, Madrid, Spain.

The crystallization of synthetic layered magnesium silicate hectorite clays from both silica sol and organosilane sources is compared. For the silica sol-derived clays, a templating method is employed wherein organic or polymeric molecules are included during clay crystallization that are then removed from the composites via calcination. The mechanism of silane-derived hectorite formation is followed by XRD, TGA, Si-29 MAS NMR, and small angle X-ray scattering (SAXS), and results are compared to those obtained for the sol-derived hectorite. The mechanism appears to be similar but the rate is approximately doubled when the silane is used rather than silica sol. Analytical transmission electron microscopy (TEM) is exploited to glean structural morphology information towards resolving the nature of the resulting pore network structures. Results are compared with nitrogen adsorption desorption isotherm behavior; dominant hysteresis loops are present in the type IV isotherms. Pore size distributions based on both the adsorption and desorption isotherms are compared. Small angle neutron scattering (SANS) experiments reveal that the average particle size increases as synthetic laponite < sol-derived hectorite < silane-derived hectorite v natural hectorite. Contrast matching SANS studies in aqueous and organic solvents are carried out to extract information about pore accessibility.