ESTIMATION OF THE STRUCTURE OF AN ANHYDROUS 2: 1-NA LAYER SILICATE SYNTHESIZED FROM TALC BY INTERCALATION PROCEDURE

Abstract

The structure of an anhydrous 2: 1-Na layer silicate (NLS), which was synthesized by heating a mixture of talc and Na₂SiF₆ at 800°C for 2 h, was estimated by MD simulation based on a 1 M mica structure (C2/m). The results of MD simulation showed that the top and bottom silicate layers moved in mutually opposite direction along the a- and b-axes, and the silicate layer stacking of NSL was similar to that of talc structure. The trajectory of the Na⁺ ions in the NLS structure from the MD simulation clearly shows two different movements as follows: one Na+ ion near the Mg²⁺ vacant site in the octahedral sheet was especially localized in the upper silicate layers, but the other Na⁺ ion apart from the Mg²⁺ vacant site in the octahedral sheet was placed in the middle position between the silicate layers. The ²³Na MAS NMR spectra of the NLS and Mg²⁺ ion-exchanged NLS also showed that the NLS had two different kinds of Na⁺ ions, one was exchangeable and the other was nonexchangeable. However, the MD simulation could not explain quantitatively the mass balance of the exchangeable and non-exchangeable Na⁺ ions in the NLS structure.