Pore structure xerogel

As previously published [9], the MCMoidal material is classified as bridging the gap between highly ordered (MCM-41, MCM-48) and totally amorphous (xerogel) silica adsorbents in respect to their crystallinity, pore structure and behaviour towards water. 

Colomer, M.T., and Anderson, M.A. 2001. High porosity silica xerogels prepared by a particulate sol-gel route Pore structure and proton conductivity. Journal of Non-Crystalline Solids 290, 93-104. 

Adsorption-desorption isotherms demonstrate the sharp contrast between a small pore silica xerogel and a large pore aerogel structure. 

Figure 2. SEM (a,b) and TEM (c) micrographs of the structure xerogel/anodic alumina (a) - as anodized anodic alumina film of 5 pm thick fabricated on Si, (b) - after one spin-on deposition of Eu-doped titania xerogel (c) - ultramicrotomed sections of the terbium-doped alumina xerogel/PAA structure of 30 pm thick. Bottom of the pore was filled with terbium-doped alumina xerogel after five spin-on depositions.

Lin, C. J.A. Ritter, and B.N. Popov, Correlation of Double-Layer Capacitance with the Pore Structure of Sol-Gel Derived Carbon Xerogels. J. Electrochem. Soc. 1999, 146(10), 3639-3643. 

Chemists continue to explore means of synthesizing xerogels with tailored properties. One property which will be described in detail in this chapter is the internal pore structure. This pore structure can be controlled in a manner that makes it pos-... 

The pore structure (pore volume, surface area and pore size) of a xerogel is also a consequence of the sequential (or overlapping) gelation, aging and drying processes. 

Xerogel samples of silica or alumina doped silica were obtained by drying the corresponding silica sols in petri-dishes at 40°C and 60% relative humidity for one to two days. Silica adsorbent (in the form of thin sheet) was obtained by calcining the xerogel samples at 400°C for 3 hours with heating and cooling rate of 250°C/hour. Pore structure and surface properties of microporous silica were... 

In the non-densified xerogels, the Raman spectra show a relatively sharp band centered at about 16 cm , for the xerogel with % = 800°C, and at about 18 cm, for the xerogel with % = 860°C. In the samples treated below 800°C, it is not possible to observe the low frequency bump. The strong quasi-elastic scattering is due to vibrational dynamics of the porous fractal-like system, but probably also to residual water inside the pores. The low frequency bumps are attributed to surface vibrations of the particle-pore structure. The peak frequency increases with the annealing temperature, as the mean pore size, measured by SAXS experiments, decreases (see Raman Spectroscopy ofNanocrystals ). The Raman... 

---