Dehydroxylation silicate lattice

The thermally induced interlayer reaction of -hexylammonium silicate complexes were studied by TG and DSC with a Dupont 1090 Thermal Analyzer. The dehydroxylation of lattice —OH groups, desintercalation and catalytic decomposition of -hexylammonium in interlayer silicates were measured in a flowing atmosphere of N2 with a flow rate of 1.0 cm /s. The heating rate was lOVmin. for both TG and DSC. 

The results of TG analysis of montmorillonite and its hexylammonium derivative support this concept the weight loss in the latter case in the temperature range 550-710 C, (where the former undergoes dehydroxylation), reaches only 52% of that of the former, however, the expelled H2O was not detected in GC analysis. As a consequence, the Bronsted acid sites which might catalyze the interlayer reaction of -hexylamine diffusing out from the silicate lattice cannot be formed on the surface. 

The thermal techniques are routinely used for quality control purposes. A typical TG/DTA analysis is shown in Fig. 13 for a Thessalian brick clay.t None of these clays contains kaolin and the characteristic mullite peak is absent. The endothermic peak between lOOand 160°Cisdue to the removal of adsorbed water, and its size is dependent on the surface area and crystallinity of the clay. The peak (400-700°C) is attributed to the dehydration of the combined water (dehydroxylation of the silicate lattice) and decomposition of the clay. The third peak (800°C) indicates decomposition of the carbonates and other salts present in the clays. 

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