FTIR reflectance vs. EPR studies of structural iron in kaolinites

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Kaolin reinforced rubbers : physical dependance between cristallinity and mechanical properties

International audienceA long time ago, the properties of rubber-kaolinite composite materials have been described as a function of the amount of mica-like components and order-disorder properties of the kaolinite. If the mica negative contribution could be simply identified as due to the easy 001 cleavage of coarser illites, the contribution of crystalline order of kaolinite was more difficult to identify. The Mössbauer spectroscopy of disordered kaolinites shows that the real kaolinite contains sites with FeII-FeII-lacuna octahedral occupation, then developing materials with necessary cation compensation sites. According to the shape analysis developed from low temperature nitrogen adsorption, and calculations of the average surface of an exchangeable site on the lateral surface of kaolinite, it is possible to evaluate that the FeII-FeII-lacuna sites are in continuous sheets, leading to some kind of exchangeable material looking like swelling clays. Paying account of the solvation of the compensating ions, as shown by the water adsorption on pure smectite, it can be evaluated that such layers, mainly the Ca++ compensated forms, vehicles water that slows down the vulcanization process, leading to non reactive alcohol groups on diene latex molecules, and then perturbing the reticulation process

Thermal characterization of the clay binder of heritage Sydney sandstones

Thermal analysis has been employed in a study of the degradation of heritage Sydney sandstone used in St Mary's Cathedral in Sydney, Australia. TG and DSC have been used to characterise the clay components removed from weathered and unweathered sandstone. Two types of kaolin clays - kaolinite and its polymorph, dickite - have been identified. A higher amount of dickite present in the clay of weathered sandstone indicates that a kaolinite-to-dickite transformation occurs upon weathering. XRD hot stage analysis was also used to demonstrate the presence of a more thermally stable polymorph of the kaolinite. © 2008 Springer Science+Business Media, LLC