Xerogels hydration

VAIVARS, G., KLEPERis, J., Lusis, A., Autimonic acid hydrate xerogels as proton electrolytes. Solid State Ionics, 1993, 61, 317-21. 

The hydrogel was dried at room temperature in air for 24 h to give hydrated silica, Si02- H20, the so-called xerogel. 

Aim 0.8% Sodium MFP 10% hydrated silica xerogel 19% hydrated silica 67% Sorbitol... 

The free and complexed Cd (II) are separated by two 25 cm HPLC columns of Sephadex G-10 (a cross-linked dextran gel of 40-120 p bead diameter). The mobile phase was distilled deionized water. Sephadex G-10 xerogel has an exclusion limit 700, that is, it can be used to fractionate species of molecular weight less than 700. The larger Cd-fulvic acid complex is unretained and elutes before hydrated Cd (II). As with the phosphorus esters above, SEC is a viable method not only for separating these complexes for analysis but also for purification. 

The obtained amorphous hydrated aluminum oxide has a surface area of 640 m g [40]. It remained amorphous up to 973 K and crystallizes to r]-alumina at 1123 K, resulting in a loss of surface to 230 m g . Wetting of this xerogel with water decreases the crystallization temperature to 873 K [41]. 

Zr(OR)4 is readily hydrolyzed. Direct hydrolysis produces a Z1O2 nH20 precipitate, which is imsuitable for the preparation of a homogeneous composite. In strongly acidic media, a flocculent hydrated gel layer is present on the surface of these particles. This layer helps prevent aggregation. It is believed that this layer makes it possible to perform repeated peptisation of Z1O2 from a xerogel. When... 

Room temperature chemical sensors for alcohol, acetone, water vapor and ammonia detection were developed [1,2] by using beta alumina and xerogel of antimonic acid hydrate. The sensitivity and selectivity depend on ion-exchange and preparative methods. Ammonia-exchanged samples of beta alumina were sensitive to water and ammonia vapor. Potentiometric and amperometric sensors are made by using ion conducting material as the substrate, an Au electrode as the reference and Pd (or Ag, Ni, Pt) as the sensitive electrode. 

Ti02 itself does not form glass, but hydrated titania or the xerogel which is produced from titanium alkoxides or salts through the sol-gel reaction is usually amorphous. Petkov et al. (1998) reported a stmctural analysis on such titania xerogels. Reverse Monte Carlo method was employed to simulate the X-ray RDF curve. In the structure model proposed... 

Next, I turn to work on water confined in porous media of carbon-based materials. Bardenhagen and co-workers studied fluid distribution and pore wettability for water and dimethylsufoxide in carbon xerogels. They used H relaxation measurements and related the results to the liquid exchange between micro- and mesopores. Wakai et reported a study of the hydration process of a nafion membrane by H... 

A desirable property of non-ionic xerogellants is their natural insensitivity to the presence of ionic solutes in the fluid being absorbed. Unlike polyelectrolytes, non-ionics can gel as much urine as pure water. A critical impediment to the effective utilization of the poly(ethylene-oxide) xerogellants in disposable diapers is the soft, almost flowable, nature of the gel. Even fully hydrated, the polyether macromolecule is a flexible coil. This flexible structure is manifested as weakness of the highly swollen gels. Increasing the crosslink density stiffens the gel but reduces swellability. 

Thus, in these hydrogels EWC and Dk are directly and positively correlated [50, 51]. Conversely, in the Si-Hy materials, oxygen permeation occurs mainly through the silicone-siloxysilane portions of the solid phase in the hydrogel, the contribution of the aqueous phase to gas permeation is very low for the first Si-Hy materials Compan et al. [52] found a slightly higher Dk value for the hydrated Si-Hy materials than for their xerogel (dry state). 

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