Smectites are widely used in (geo-) technical applications and are important components of soils. A definition gap exists between the uncharged non-swellable pyrophyllite and talc (ξ = 0) and the low charged swellable clay minerals (smectites) with 0.2 ≤ ξ ≤ 0.6. Furthermore, no reliable measurement method exists for ξ < 0.2. A recent theoretical study on the hydration of smectites (Emmerich et al. 2018) based on the density functional theory (DFT) indicates the existence of stable dioctahedral 2:1 layer silicates with ξ < 0.2 and substitutions either in the tetrahedral or octahedral sheet that are swellable. Therefore, our focus is to synthesize low charged smectites.
The Na2O-MgO-Al2O3-SiO2-H2O system was reacted for triocthedral smectite synthesis at 200℃, for 72 h, and with stoichiometric composition corresponding to ideal layer charge of 0.18. The XRD results showed that the synthesis of trioctahedral smectite was successful with a small particle size. Particle size will be confirmed by AFM measurements. The CEC indicates a low charge in the envisaged range. According to the principle of AAM method (Lagaly. 1981), under ideal assumptions, when the layer charge value is less than 0.2, the long-chain alkylammonium ions will only form a monolayer structure (basal spacing <17.7 Å) after being intercalated into the smectite layer, which can also be proved by measuring the d001 value of synthetic smectite. Similar results obtained through our experiments.
Emmerich et al. (2018) The Journal of Physical Chemistry C 122, 7484−7493.
Lagaly. (1981) Clay Minerals. 16, 1-21.
Yi-Yu Liu1, Nils Schewe2, Peter Thissen2, Katja Emmerich1
1Competence Center for Material Moisture (IMB-CMM), Karlsruhe Institute of Technology; 2Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology