Porous glasses structure

Porous glass structures have not been marketed for membrane separation applications until recently, despite having been studied as a membrane material for a long time. A number of glass companies such as Asahi Glass... 

Once the model porous glass structures have been assembled using quench MD simulation, their geometric pore size distributions can be determined by sampling the pore volume accessible to probe molecules... 

Recently, many experiments have been performed on the structure and dynamics of liquids in porous glasses [175-190]. These studies are difficult to interpret because of the inhomogeneity of the sample. Simulations of water in a cylindrical cavity inside a block of hydrophilic Vycor glass have recently been performed [24,191,192] to facilitate the analysis of experimental results. Water molecules interact with Vycor atoms, using an empirical potential model which consists of (12-6) Lennard-Jones and Coulomb interactions. All atoms in the Vycor block are immobile. For details see Ref. 191. We have simulated samples at room temperature, which are filled with water to between 19 and 96 percent of the maximum possible amount. Because of the hydrophilicity of the glass, water molecules cover the surface already in nearly empty pores no molecules are found in the pore center in this case, although the density distribution is rather wide. When the amount of water increases, the center of the pore fills. Only in the case of 96 percent filling, a continuous aqueous phase without a cavity in the center of the pore is observed. 

Under certain time and temperature conditions, the homogeneous glass separates into two phases. One of the phases consists substantially of silicon dioxide which is insoluble in mineral acid. The other phase represents a soluble coherent boric acid phase rich in alkali borate. If the boric acid phase is dissolved out of this heterogeneous glass structure with a mineral acid, a porous skeleton of substantially insoluble silicon dioxide is left. The phase separation region occurs between 500°C and 800 C. 

Finally, we described the permeation characteristics of a thermosensitive gel supported on porous glass. The switch functional ability of the membrane was demonstrated in permeation experiments. It was pointed out that the change in the permeation characteristics resulted from that in the pore structure in the gel. 

In recent years investigations were begun in which the variation of adsorbent properties, such as electrical conductivity (1, 2), dielectric permeability (3-5), and linear sizes (6-11), were studied. In these systems the adsorbents were usually active carbons and porous glasses. Only a few studies were carried out on zeolites these studies are interesting because of the perfect porous structures (12-14) of zeolites. All these studies showed that during adsorption the properties of adsorbents do not remain constant. 

The conversion of porous glass into the zeolites with MFI- and FER-structure has been performed following various synthesis routes, with or without a template addition. Tetrapropylammoniumbromide (TPABr) or propylamine (PA) have been used as a so-called structure directing template. Starting reaction mixtures expressed in mole ratios of the oxides are given below ... 

Table 2 Porosity values of the starting porous glass, partial and fully crystalline composite materials with FER (ZSM-35) and MFI (ZSM-5) structure.

Bergman [46] and others [47-51] have used polycyclic aromatic hydrocarbons (PAHs, chemical structures shown in Fig. 12), which are found to be efficiently quenched by oxygen in the 0-40 kPa range. The PAHs are either dissolved in a polymer [48-51], soaked into porous glass [50], or covalently immobilized on a glass support [47]. Peterson et al., by combining Kautsky s... 

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