Aerogels characteristics

Catalysis. Kistler explored the catalytic appHcations of aerogels ia the 1930s because of the unique pore characteristics of aerogels (24), but this area of research stayed dormant for about three decades until less tedious procedures to produce the materials were introduced (25,26). Three recent review articles summarize the flurry of research activities since then (63—65). Table 3 is a much abbreviated Hst of what has been cited in these three articles to demonstrate simply the wide range of catalytic materials and reactions that have been studied. 

Silica aerogels, a newly developing type of material, also have been produced as thermal insulations with superinsulation characteristics. The nanometer-size cells limit the gas phase conduction that can take place. The aerogels are transparent to visible light, so they have potential as window insulation. The use of superinsulations at present is limited by cost and the need to have a design that protects the evacuated packets or aerogels from mechanical damage. 

Both xerogels and aerogels are characteristically high surface area materials (surface areas normally exceed 500 m2/g). Unlike wet gels, many uses exist for dried gels due to their high surface areas and small pore sizes (typically, < 20 nm diameters). Examples include catalyst supports (12.). ultrafiltration media (18), antireflective coatings (19-20), and ultra-low dielectric constant films. (Lenahan, P. M. and Brinker, C. J., unpublished results.)... 

M2 Thickener A standard (for Air Force only) incendiary oil thickener. It is an intimate mixt of Ml thickener 95 devolatilized silica aerogel 5%- M2 thickener is an improvement over Ml, not only because of free-flowing faster setting characteristics, but also because the thickener itself ge 1 formed are more stable. It is used in fire bombs [Ref TM 3-215/AFM 355-7 (Dec 1963), p 4l]... 

The impact sensitivity of the aerogel thermite may make it suitable for use in primers, because all of the other preparatory methods for the iron oxide thermite produce thermites which are unsuitable for this application. The especially sensitive nature of aerogel thermites stems from the inability of the aerogel matrix to conduct heat, a characteristic which is only applicable to aerogels, due to their insulating property. 

It is plausible that the RF-backbone of the aerogels alone shows no resonant polarization in the frequency-band investigated. The molecules have no permanent dipole moment which could oscillate at these frequencies. All other possible relaxation phenomena (e.g. vibrational or electronic polarization) take place in frequency bands well above the one investigated. From results 8.3. we learn, that water has a strong influence on the impedance spectrum and thus on the relaxation, e" increases while the characteristic frequency (Uioss decreases with the amount of water adsorbed. 

The aim of this work was to examine and compare structural characteristics of vanadia-doped silica aerogels with standard liquid nitrogen adsorption and small angle X-ray scattering. 

The amorphous (nonordered) mesoporous materials such as ordinary SiC>2 aerogel and porous glass possess mesopores, but the channels or pores are irregular and the pore sizes distribute over a wide range. Most macroporous materials such as ceramics and cement have the same characteristics irregular pores and wide pore-size distribution. 

These three aerogel samples calcined at 773K show type IV isotherms which are characteristic of mesoporous solids (Fig. 1). However, the hystereses observed are not of... 

The accessibility of the primary amine functions of chitosan has been quantified in organic solvent by formation of a salicylaldimine Schiff base upon treatment with salicylaldehyde. When contacting salicylaldehyde the aerogel beads of chitosan become yellow and their UV-visible diffuse reflectance spectra exhibit the absorption band at 318 nm, characteristic of the Schiff base. Quantitative GC analysis of the remaining salicylaldehyde in the solution allows calculation of the fraction of reacted amino groups, which corresponds to the fraction of accessible sites. In the aerogel formulation, up to 70% of the amine groups are accessible [92]. 

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