Microporous glass

Most glass-ceramics have low dielectric constants, typically 6—7 at 1 MHz and 20°C. Glass-ceramics comprised primarily of network formers can have dielectric constants as low as 4, with even lower values (K < 3) possible in microporous glass-ceramics (13). On the other hand, very high dielectric constants (over 1000) can be obtained from relatively depolymerized glasses with crystals of high dielectric constant, such as lead or alkaline earth titanate (11,14). 

Itoh, N., Y. Shindo, K. Haraya and T. Hakuta. 1988. A membrane reactor using microporous glass for shifting equilibrium of cyclohexane dehydrogenation. J. Chem. Eng. Japan 21(4) 399-404. 

McMillan, P. W. and C. E. Matthews. 1976. Microporous glass for reverse osmosis. J. Mater. Science 11 1187-99. 

Ohya, H., Y. Tanaka, M. Niwa, R. Hongladaromp, Y. Negismi and K. Matsumoto. 1986. Preparation of composite microporous glass membrane on ceramic tubing. Maku 11 41-44. 

Microporous glass tube (in double pipe configuration), wall thickness O.B mm, outer diameter 10 mm, mean pore diameter 300 nm. Feed enters the reactor at tube side, permeate at shell side. 

Kikuchi, E., S. Uemiya, N. Sato, H. Inoue, H. Ando and T. Matsuda. 1989. Membrane reactor using microporous glass-supported thin film of palladium Application to the water gas shift reaction. Chem. Lett. 3 489-492. 

K. Kandori Apphcation of Microporous Glass Membranes Membrane Emulsification. In A.G. Gaonkar (ed), Food Processing Recent Developments Elsevier, Amsterdam (1995). 

Y. Mine, M. Shimizu, and T. Nakashima Preparation and Stabilization of Simple and Multiple Emulsions Using Microporous Glass Membrane. Colloid Surfaces B Biointerfaces 6, 261 (1996). 

Note Microporous silica, microporous glass and zeolites are common examples of aerogels. 

In order to obtain satisfactory absorption spectra of the substance under investigation it is essential that the beam pass through a large number of adsorbed monomolecular layers. In practice this is most satisfactorily achieved by adsorption on transparent microporous solids with a high surface area to mass ratio (200-600 m2/g). The solids found most suitable have been silica gel, silicic acid, and microporous glass. 

The effect of zeolite porosity on the reaction rate was also well demonstrated in liquid-phase oxidation over titanium-containing molecular sieves. Indeed, the remarkable activity in many oxidations with aqueous H2O2 of titanium silicalite (TS-1) discovered by Enichem is claimed to be due to isolation of Ti(IV) active sites in the hydrophobic micropores of silicalite.[42,47,68 69] The hydrophobicity of this molecular sieve allows for the simultaneous adsorption within the micropores of both the hydrophobic substrate and the hydrophilic oxidant. The positive role of hydrophobicity in these oxidations, first demonstrated with titanium microporous glasses,[70] has been confirmed later with a series of titanium silicalites differing by their titanium content or their synthesis procedure.[71] The hydrophobicity index determined by the competitive adsorption of water and n-octane was shown to decrease linearly with the titanium content of the molecular sieve, hence with the content in polar Si-O-Ti bridges in the framework for Si/Al > 40.[71] This index can be correlated with the activity of the TS-1 samples in phenol hydroxylation with aqueous H2C>2.[71] The specific activity of Ti sites of Ti/Al-MOR[72] and BEA[73] molecular sieves in arene hydroxylation and olefin epoxidation, respectively, was also found to increase significantly with the Si/Al ratio and hence with the hydrophobicity of the framework. 

Acetylcholineesterase Biosensors were fabricated from filter-supported solventless bilayer lipid membrane (BLM) and used for the analysis of the substrates of hydrolytic enzymes in a flowthrough system. The codeposition of lipid (dipalmitoyl-phosphatidic acid) and protein solutions to form a BLM on a microporous glass fiber or polycarbonate ultra-filtration membrane disc was described. Enzyme was immobilized on the membrane by incorporation of protein solution into the lipid matrix at the air-electrolyte interface before BLM formation. 

In a related study, Farmer et al. studied the destruction of benzene by Ag(II) [50]. Unlike in the case of ethylene glycol, a maximum conversion of 60% was achieved after 5 h of electrolysis at 336 mA. The authors attributed the failure to achieve 100% conversion to the volatilization of benzene or one of its intermediates from the anolyte. Of the three separator materials, porous ceramic, Vycor microporous glass, and Nafion 117, which were investigated, the latter two were found to be effective barriers to HNO2 (formed by the reduction of HNO3 at the cathode) migration from the catholyte to the anolyte. 

Fig. 4 Chord-length distribution Y (d), 0.5 nm < d < 5 nm, inset the corresponding SAXS curve obtained for the microporous glass membrane...

Figure 6.13 Dependence of permeate flux of bovine plasma and bovine blood through microporous glass membranes on pore diameter under a TMP of 0.033 and 0.067 bar and at 37X (Sakai et al., 1989]...

Gels transform more or less gradually into a meso/microporous glass. A logarithmic plot of the weight loss vs. the inverse of the temperature allows the onset determination of water and hydroxyl departures, and hence the measurement... 

Figure 18 Pressure dependence of the CO2 permeability through a microporous glass membrane. Experimental results are compared to theory of combined gaseous and surface flow. (I Barrer = 3.35 X 10" mol m m Pa -sec". ) (Adapted from Ref. 38.)...

The apparatus consists of a tube with a barrier in its center. The barrier mav be either a microporous barrier (such as microporous glass) or a plastic membrane. The sample mixture is admitted to one side of the barrier after the other side has been evacuated. The passage of ma--woter-cooied terial through the barrier is noted by jacket increase in pressure on the low-... 

For special purposes, it is manufactured separately as the so-called microporous glass, whose porosity and pore size can be regulated within certain limits (pore diameter in fractions to tens nm), by adjusting the glass composition and conditions of separation (temperature, time). The glass shows selective absorptive properties its specific surface area amounts to several hundred m g and the pore space takes a third to half the volume. Microporous glass is used as an adsorbent, dessicant and catalyst carrier. 

A.B. Shelekhin, A.G. Dixon and Y.H. Ma, Adsorption, permeation and diffusion of gases in microporous membranes. III. Application of percolation theory to interpretation of porosity, tortuosity, and surface area in microporous glass membranes. /. Membr. Sci., 83 (1993) 181. 

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