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Eingeladener Vortrag
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Porous and finely divided solids are distinguished by a large surface to volume ratio. As a result, they have specific properties, such as enhanced reactivity, a high adsorption capacity, and a lowered sinter temperature.
This contribution gives a survey over selected aspects of porous solids, with tlfe main emphasis on methods of characterization and their applications. We treat porous solids with a regular pore network (zeolites) and irregular pore structure (sintered compacts,rocks). After a short review of the possibilities orf characterization, we wilI describe the methods of gas adsorption and Hg intrusion in detail. Furthermore, we will give a critical assessment of the measurement of typical characterization parameters, such as the spedfic surface area, the pore volume and the pore volume distribution. The fractal character of large-surface and porous solids and the related uncertainty of the outcomes of measurements result in the necessity of standardization of experimental procedures and in the need for reference materials.
The section on applications treats examples of porous solids from different areas: densification of ceramic materials, porous ceramic carriers for flue gas desulfurization, technical catalysts (zeolite/binder), zeolites for the separation of substances, sedimentary and crystalline rocks.
X-ray refraction reveals the inner surface concentrations of porous materials within the range of (µm- to nm-dimensions. This technique is compared to mercury pressure porosimetry which is a standard method for pore size determination in porous solids. The mean pore size of several ceramics are investigated over a range of porosity between 30% to 60%. Complementary to high pressure mercury intrusion the refraction technique detects the spatially resolved inner surfaces of both, open and closed pores. Furthermore, X-ray refraction scanning topography visualizes integral interface properties up to 50 m spatial resolution by two-dimensional topographic images. Characteristic microstructure parameters, i. e. inner surface density, porosity and mean pore sizes of some Al2O3 and SiC ceramics are presented. The specific surface data of Al2O3 ceramics obtained from X-ray refraction agree well with the results given by mercury porosimetry. In contrast, the related mean pore sizes differs systematically by about 30%.