Synthetic analogues of the microporous minerals umbite (AM-2) and
penkvilksite, polytype 2O (AM-3),
have been prepared. The facile syntheses of two other
titanosilicates, AM-1 and AM-4, have also been
reported. AM-1 and the previously reported, layered titanosilicate
known as JDF-L1 have been shown to
have the same structure. AM-4 is a new microporous titanosilicate
with a unique and unknown structure,
containing eight different Na sites. All AM-n materials
have been characterized by several techniques,
viz.
SEM, powder XRD, single- and triple-quantum 23Na and
29Si MAS NMR, water adsorption
measurements,
and TGA/DSC. AM-n materials are thermally stable up to
ca. 600 °C. The dehydration−hydration processes
seem to be reversible (or quasi reversible) for AM-1, -2, and -3 but
not so for AM-4.
ZnO and ZnS powders were prepared from aqueous solutions of zinc salts in the presence of ethylenediamine or triethanolamine. The morphology of the powders was analysed by scanning electron microscopy and infrared spectroscopy. The effect of the experimental conditions upon the size and shape of the particles is described with a special emphasis on the role of the organic ligand.
The thermal decomposition of cork has been studied by Fourier transform infrared (FTIR) spectroscopy and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy with cross-polarization and magic-angle spinning (CP-MAS), high-power 'H decoupling (HPDEC) and cross-polarization depolarization-polarization (CPDP). Waxes and other soluble components of cork begin to decompose at ca. 150°C. This is accompanied by partial decomposition of suberin, probably initiated at the points of attachment to the cell wall. The carbohydrates begin to decompose at ca. 200°C. The decomposition of lignin begins at 250-3OO"C, while suberin undergoes further degradation. Significant amounts of coke are formed in the process. At 400°C cork has been transformed into coke with traces of partially decomposed suberin. The thermal decomposition of cork is dependent on the calcination time, particularly in the 200-350°C range.
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