Abstract
A new precursor, [RAl(μ-NHEt)(μ-NEt)2Si(NHEt)]2 (R = Et, Me), is proposed for the preparation of high-surface-area silicon aluminum nitride based xerogels. The conversion is carried out using ammonia gas and pentane/ammonia mixtures at low (1 bar) and high (200 bar) pressure. Materials with specific surface areas up to 800 m2 g-1 are obtained under high-pressure conditions. The enrichment of aluminum in the materials obtained at low pressure indicates the formation of Si(NHEt)4 as a side product that is also detected in NMR spectra. In scanning and transmission electron micrographs the materials appear with a flakelike morphology. The presence of NH groups is detected in IR spectra, and the 29Si MAS NMR signal is detected at −40.5 ppm. The materials are X-ray amorphous. The composition varies with the reaction conditions. After a high-pressure transformation, the Al/Si ratio is close to 1.0 (Al2Si1.8N8.7C1.3H11.6) but transformation at low NH3 pressure only produces Al-enriched materials. The solid imides...
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