Ronan Le Dred

19 F MAS-NMR study of structural fluorine in some natural and synthetic 2:1 layer silicates

High-resolution solid-state, fluorine-19, magic-angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR) was used to study natural and synthetic fluorinated 2:1 layer silicates of known composition. This technique enabled us to determine directly the coordination of structural fluorine and it was found to be sensitive to both the chemical nature of the octahedral elements (Al, Mg, Li) and the type of octahedral sheet (di- or trioctahedral). The observed chemical shifts at −132, −152, −176 and −182 ppm (relative to CFC13) were assigned to different environments of fluorine. The results were then used to characterize synthetic 2:1 layer silicates with unknown octahedral composition.

A new Al,Mg-organoclay

A new inorganic–organic solid, with a 2∶1 phyllosilicate layer structure and octyl chains directly bound to the inorganic sheets via Si–C covalent bonds, was prepared at room temperature from an ethanolic gel with the molar composition RSiO3/2 ∶ 0.255 Al2O3 ∶ 0.5 MgO ∶ 130 CH3CH2OH ∶ 0.62 Na2O. Octyltriethoxysilane was used as the silica source. The introduction of octyl chains in the interlayer space was confirmed by the high d001 spacing values (2.5 nm). Thermogravimetric analyses show a major weight loss between 230 °C and 500 °C corresponding to the release of organic matter. The mass spectrometry analyses of the evolved gas are in agreement with the presence of octyl chains. Infrared and 13C MAS NMR spectra indicate that the Si–C bonds are intact and that the siloxane functions are fully hydrolyzed giving Si–O–Al and Si–O–Mg bonds in the inorganic layers. The substitution of Si and Mg by Al was confirmed by 29Si and 27Al MAS NMR.

Synthesis and Characterisation of Organo Phyllosilicates Containing Both Si, Al, and Mg

Hybrid materials like organo-phyllosilicates exhibit new properties which make them potential candidates for many industrials applications as rubber reinforcement, environmental barriers…. With this aim, a series of new layered inorganic-organic solids, with organic functionalities directly bonded to the inorganic sheets via the Si-C bond, were prepared by a template sol-gel synthesis under soft conditions (room temperature) using octyltriethoxysilane as the silica source, aluminum acetylacetonate as the alumina source, magnesium nitrate and sodium hydroxide. These hybrid materials belong to the 2:1 trioctahedral phyllosilicates family with inorganic compositions close to saponite. The ratio of Al (x) could be varied between 0 and 0.33. The x-ray diffraction patterns agree with a layers structure (presence of the (00l) peak series and the (060) peak). The high d001 spacing values (2.4-2.6 nm) can be related to the octyl chains present in the interlayer space. DRIFT and 13 C NMR spectra indicate that the Si-C bonds are intact and siloxanes are fully hydrolyzed giving SiOAl and SiOMg bonds. 27 Al and 29 Si NMR were carried out in order to determine the repartition of the different elements in the layer: Al substitutes for Si in the tetrahedral layer and for Mg in the octahedral one. These results were determined by elemental analysis. The DTA-TG results show that the organic matter start to decompose in air above 250°C but its complete removal needs temperatures higher then 800°C. The aspect of the materials depends on the value of x; it varies from greasy, waxy, waxy powdery and finally powdery. The hydrophilicity of the solids depends strongly on the aluminum content.

Différenciation des espaces interfoliaires d'une vermiculite par l'échange d'ions 2 K+ ⇋ Ca2+ / Discrimination between vermicullte interlayer spaclngs as a result of 2 K+ ⇋ Ca2+ ion exchange

Differenzierung der Zwischenschichten einer Vermikulits mittels Kalium-Calcium-Austauschs. Die Grundsatze der Austauschthermodynamik zwischen einwertigen und zweiwertigen Ionen, so zum Beispiel K + und Ca 2+ Ionen, werden dargelegt und im Fall des aus einem Vermikulit und einer wassrigen Losung bestehenden Systems angewendet. Der Vermikulit ist in Form von in Wasser gequollenen Blattchen von Basisflache 1 bis 4 mm2. In diesem Fall wird eine Differenzierung der Austauschplatze in zwei Typen, mit Bildung regelmassiger Wechsellagerungstrukturen, klargestellt. Auf Platzen des einen Typs mischen sich die K + und Ca 2+ Ionen, auf Platzen des anderen Typs erfolgt eine Entmischung.