29Si and 27Al MASNMR Study of Stratlingite |
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Authors: | Stephen Kwan Judith LaRosa Michael W Grutzeck |
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Affiliation: | Intercollege Materials Research Laboratory, The Pennsylvania State University University Park, Pennsylvania 16802 |
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Abstract: | Strätlingite (2CaO·Al2O3·SiO2·8H2O) is a complex calcium aluminosilicate hydrate commonly associated with the hydration of slag-containing cements or other cements enriched in alumina. Strätlingite can coexist with the hydrogarnet solid solution hydrogarnet (3CaO·Al2O3·6H2O)-katoite (3CaO·Al2O3·SiO2·4H2O)] and calcium silicate hydrate (C-S-H). Since Strätlingite is present in many blended cements, the knowledge of strätlingite's characteristic silicate anion structure and how aluminum is accommodated by the structure is important. Phase pure Strätlingite samples have been synthesized from oxides in the presence of excess water and from metakaolinite, calcium aluminate cement, CaO, NaOH, and water. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) and then further examined using 29Si, with and without cross-polarization (CP), and 27Al solid-state magic angle nuclear magnetic resonance spectroscopy (MASNMR). For the most part, NMR data for these strätlingites corroborate structural information available in the literature. The aluminum atoms are both tetrahedrally and octahedrally coordinated, and the silicon atoms exist predominantly as Q2, Q2(1Al), and Q2(2Al) species. The presence of alkali affects the structure of strätlingite in subtle ways, significantly reducing the AlIV/A1VI ratio. |
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