Porous Vycor glass

In the case of Ru(2,2 -bipyridine)3 adsorbed on porous Vycor glass, it was inferred that structural perturbation occurs in the excited state, R, but not in the ground state [209]. 

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. 

Vycor glass (Corning, 7930) is porous silica processed in the same way as CPG except that the last step of base etching is missing. Therefore the surface is rough. Only a 40-A pore is available. When porous silica with a pore size smaller than 75 A is needed, Vycor glass is the choice. Bulk pieces of Vycor glass are available commercially and need to be crushed into small particles before use. 

Fig. 15. Fluorescence spectra of porous Vycor glass after heating (a) in air at 100°, and (b) in oxygen at 550°. The spectra were run under the same conditions except that the amplification for (b) was ten times higher than for (a) (85).

For other centrosymmetric adsorbates such as C02 on zeolites X and Y (1) and ethene on porous Vycor glass (3), only marginal changes in line position were observed. 

We have also obtained measurements for the relaxation time of octafluorocyclo-butane (c-C4F8) gas in porous Vycor glass. Vycor (Corning Glass, -96.5 wt-% Si02) has a specific surface area of approximately 120 m2 g-1, and was cleaned using H202 and evacuated to 10-8 Torr before all measurements. The Vycor was placed in... 

Fig. 3.5.3 Spin-lattice (Tt) and spin-spin (72) relaxation times as a function of pressure for c-C4F8 gas in porous Vycor glass at 291 K.

Solid surfaces nature of the surface of colloidal silica, clays, zeolites, silica gels, porous Vycor glasses, alumina rigidity, polarity and modification of surfaces... 

Rgure 2.1. Pore radius distribution curve for a porous Vycor glass heat-treated at 500 C for 5 h (McMillan 1980). 

Kameyama, T., K. Fukuda and M. Dokiya. 1981. Possibility for effective production of hydrogen from hydrogen sulfide by means of a porous Vycor glass membrane. Ind. Eng. Chem. Fundam. 20 97-99. 

Decomposition of Hydrogen Sulfide Porous ir-AljOj/MoSj membranes Porous Y-AI2O3 membranes Porous Vycor glass membranes Abe (1987) Kameyama et al. (1981) Kameyama et al. (1979, 1981a, b)... 

Decomposition of Hydrogen Iodide Porous Vycor glass membranes Nonporous Pd/Ag membranes Itoh et al (1984) Yeheskel, Leger and Courvoisier (1979)... 

Porous Vycor glass tube (in double pipe configuration), wall thickness 3 mm, length 600 mm, outer diameter 15 mm, mean pore diameter 45 A. Feed enters the reactor at shell side, permeate at tube side. ... 

Dehydrogenation of Cyclohexane to Benzene Porous AljOj membranes Porous Vycor glass membranes Nonporous Pd/Ag membranes Fleming (1987) Shinji et al. (1982), Itoh (1987, Itoh et al. 1988) Sun and Khang (1988) Wood (1968), Itoh (1987), Gryaznov (1970)... 

The interaction of Ru3(CO)i2 with Si02 seems to proceed via a hydride surface carbonyl species. An ulterior decomposition under vacuum mainly gives Ru particles of 1.4nm and Ru(II) carbonyl species ]90]. Similarly, [HRu3(CO)io( t-OSi)]surface specics are generated by the reachon of Ru3(CO)i2 with a porous Vycor glass at 65 °C under air ]103]. Above 130 °C it was reported that the surface cluster breaks down with formation of ]Ru(CO) (OSi)2]surface species (n = 2 and/or 3). When the initial surface species was heated in air at T> 250°C, decomposition of the cluster and formation of RUO2 nanoparticles were observed. 

In addition to the nature of the cation at the adsorption site, the superhyperfine tensor can also give information on neighboring atoms further away. For example, OJ adsorbed on MgO exhibits a superhyperfine tensor ascribed to the presence of a nearby proton, presumably as a hydroxyl group (68) and this has been confirmed by isotopic labeling with deuterium (see Section IV,A). Superhyperfine tensors indicating the presence of nearby protons have also been reported for O J adsorbed on ferrocene deposited on porous Vycor glass (PVG) (120) and for alkylperoxy radicals supported on Ti02 (90). 

Similar results have been obtained by Ismailov et al. (240) in Y-type zeolites containing iron impurities (Section IV,C,3). The formation of 02 on the ferrocene/porous Vycor glass system has been observed by Vanderspurt et al. (120) with a g tensor of 2.0300, 2.0100, 2.0020 and a superhyperfine sextet centered on each g component. These results were interpreted in terms of 02 adsorbed on the cyclopentadienyl ring of ferrocene and, assuming an ionic model, the g2Z value of 2.0300 is broadly consistent with a +3 charge at the adsorption site. 

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