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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 2 (1994), S. 239-244 
    ISSN: 1573-4846
    Keywords: thermoporometry ; permeability ; texture of gels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The textures of silica gels made by two-step acid/base and acid/acid catalysis of TEOS have been examined by thermoporometry (TPM) and NMR, and their permeabilities (D) have been measured by a thermal expansion technique. Using the pore size distribution given by TPM, which includes a large proportion of macropores (≥30 nm), calculated values of D are seriously overestimated. We conclude that, consistent with a theoretical prediction, compliant materials such as gels undergo contraction during freezing in the calorimeter, so that most of the macropore volume reported by TPM is actually extracted from mesopores. The mesopore radius reported by TPM is underestimated by only ∼20%, even if 50% of the pore liquid is drained during crystallization, assuming that the change in pore radius is related to the cube root of the volume change. NMR does not distinguish macropores, because of diffusional averaging, but provides an apparent distribution that permits an accurate estimate of the permeability.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 2 (1994), S. 363-366 
    ISSN: 1573-4846
    Keywords: silica-alumina ; hydrogel ; microwave drying ; convective drying ; texture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The porous texture of silica-alumina hydrogel can be taylored by controlling the operating parameters of the preparation process. As the drying drastically modifies the texture it is important to minimize pore volume and radius decreases. Owing to a low drying temperature microwave heating coupled with convective drying could be a way to preserve the hydrogel texture. Its effects have been studied and it appears that the characteristics of the air flow are the main parameters of this drying mode which does not present decisive advantages as compared with other drying modes.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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