Small angle X-ray scattering of aerogel densification

Silica aerogels were densified by isostatic compression or by thermal sintering. Small angle X-ray scattering experiments show that both types of aerogels exhibit oscillations around Pored behavior at high q values. Oscillations were modified by sintering but remain unchanged by compression. According to the Babinet's principle, it is not usually possible to associate intensity change with a peculiar phase of the porous solid. However. the fact that the oscillations remain unchanged with compression, which only acts on the porous part, indicates that SAXS intensity experiments can be directly linked to the solid part. Using the Pored law [G. Pored, Kolloid Z. 124 (1951) 83; P. Debye, A.M. Bueche, J. Appl. Phys. 20 (1949) 518], the specific surface area has been estimated. Surface area of the compressed aerogels does not change with density. In contrast. the specific surface area of the sintered samples decreases markedly. The absence of shape changes of SAXS curves indicates that the mean size of the solid phase remains constant during the compression densification. (C) 1998 Elsevier Science B.V. All rights reserved.