In this work, we combine 27Al, 29Si, 19F, and 23Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) to characterize the structure and interlayer cation environments in a strontium-saturated member of the swelling mica family before and after a heat-induced collapse of the interlayer space. The 27Al and 29Si MAS NMR demonstrate that the sample consists mainly of swelling mica, though the composition does not match the ideal structural formula. Aluminum NMR also shows that a portion of the aluminum shifts from a tetrahedral to an octahedral coordination environment upon heating. Changes in the 29Si and 19F NMR after heating are consistent with a structural rearrangement of the tetrahedral sheet to permit the binding of larger cations in the ditrigonal cavity. The 23Na MAS NMR results indicate the presence of three unique sodium environments before and after heating. The heat-invariant resonance is consistent with the presence of sodium carbonate. The other two resonances are associated with interlayer sodium and reflect a migration of sodium to a dominantly anhydrous ditrigonal binding structure with heating. Quantitative elemental analysis and NMR data presented here suggest strontium is bound deep within the ditrigonal cavity of the collapsed micas.
All Science Journal Classification (ASJC) codes
- Atomic and Molecular Physics, and Optics