Influence of calcining temperature on the mesopore structures and surface fractal dimensions of MgO-Al2O3-SiO2 xerogels

This investigation deals with the effect of calcining temperature on the me sopore structures and surface fractal dimensions of MgO-Al2O3-SiO2 xerogels prepared via a two-step acid-base-catalyzed sol-gel process with/without a lcohol washing before drying. The mesoporosity and surface fractal dimensio ns are evaluated by image analysis methods, based on FE-SEM (field emission gun-scanning electron microscopy) images. The results show that samples wi th alcohol washing before drying exhibit finer textures and lower sintering temperature. The mesoporosity increase before 700 degreesC might be attrib uted to the microporosity reduction during large extent of further condensa tion (detectable weight loss), and continuous further condensation and sint ering resulted in the monotonic decrease of mesoporosity above that tempera ture. Smoothing and sintering effects also contributed to the general decre asing trend of surface fractal dimensions with increasing temperatures. Com plication of surface textures caused by heterogeneous distributions of pore s resulted in the abnormal high surface fractal dimensions. (C) 2001 Elsevi er Science Ltd. All rights reserved.