Synthesis of porous inorganic materials from sol-gel precursors by cryochemical sublimation

This paper reports on the results of investigations into the synthesis of consolidated porous materials from sol-gel precursors based on gel-forming aqueous solutions of silicates in the R2O (.) nSiO(2) system (where R2O is Na2O (.) K2O). Cryochemical sublimation is used as a technological tool for preparing a porous structure. The sublimated material is studied using scanning electron microscopy, X-ray spectral microanalysis, and mercury porosimetry. It is demonstrated that the samples synthesized are characterized by a density of approximately equal to 0.5 g/cm(3), a developed biporous structure with 1- to 15-mu m pores, and a chemically homogeneous network. Comparative differential thermal analysis of the sublimated product and the xerogel prepared by traditional stepwise heat treatment in the temperature range 60-100 degrees C shows that there are substantial differences in the dynamics and character of the physicochemical transformations in the temperature range 20-800 degrees C. The results of X-ray powder diffraction analysis indicate that the sublimated composite has an X-ray amorphous structure.