Glass diffusion

Fig. 6. The Sofica LS photometer 1 - Hg Pump cooled by high pressure water, 2 - total reflection prism, 3 - achromatic condensing lens, 4 - wavelength filters, 5 - glass diffuser,...

The important effect of increasing pressure on the kinetics of chemical reactions has been noted since the hrst chemical experiments at high pressure. The simplest expectation derives from the observation that in liquids the viscosity rapidly increases with pressure. As a result, in strongly compressed liquids, and hnally in glasses, diffusion-controlled processes can be retarded. In contrast, however, other reaction pathways can be substantially accelerated. In general, the evolution of a reaction at high pressure can be heavily controlled by kinetic aspects, and these deeply involve intermolecular effects. 

In vitro permeation studies employ a glass diffusion cell with the buccal tissue mounted between the two halves of the eell whieh may be filled with constantly stirred buffer solutions. The bueeal mueosa is exeised from the eanine, porcine, or rabbit eheek immediately after saerifiee. Permeation studies may provide meaningful results on the simultaneous proeesses of drug transport and metabolism in the tissue... 

Diffusion is ubiquitous in nature whenever there is heterogeneity, there is diffusion. In liquid and gas, flow or convection is often present, which might be the dominant means of mass transfer. However, inside solid phases (minerals and glass), diffusion is the only way of mass transfer. Diffusion often plays a major role in solid-state reactions, but in the presence of a fluid dissolution and recrystallization may dominate. 

Efficient extraction of proteins has been reported with reverse micellar liquid membrane systems, where the pores of the membrane are filled with the reverse micellar phase and the enzyme is extracted from the aqueous phase on one side of membrane while the back extraction into a second aqueous phase takes place at the other side. By this, both the forward and back extractions can be performed using one membrane module [132,208]. Armstrong and Li [209] confirmed the general trends observed in phase transfer using a glass diffusion cell with a reverse micellar liquid membrane. Electrostatic interactions and surfactant concentration affected the protein transfer into the organic membrane and... 

Doremus, R. H. 2000. Diffusion of water in rhyolite glass Diffusion-reaction model. Journal of Non-Crystalline Solids, 261, 101-107. 

Small solute atoms in the interstices between the larger host atoms in a relaxed metallic glass diffuse by the direct interstitial mechanism (see Section 8.1.4). The host atoms can be regarded as immobile. A classic example is the diffusion of H solute atoms in glassy Pd8oSi2o- For this system, a simplified model that retains the essential physics of a thermally activated diffusion process in disordered systems is used to interpret experimental measurements [20-22]. 

A. Preparation of trane-S,3-dieb.loro-l,4-dioxane (Note 1). To a 2-L, three-necked, round-bottomed flask, equipped with two inlet tubes (with sintered-glass diffusers at the end) connected to a chlorine cylinder, and a... 

Matsuda, I, Matsubara, K., Yajima, H., Yamamoto, K. (1989) Anomalous Ne enrichment in obsidians and Darwin glass Diffusion of noble gases in silicate-rich glasses. Geochim. 

PG release from the two delivery systems was monitored using an automated, in vitro diffusion cell system. The devices were clamped in vertical glass diffusion cells with the releasing surface of the system facing into the receptor chamber. The latter contained NaCl-Na citrate buffer and was continuously perfused at 10 ml/hr. Perfusate was collected hourly for up to 48 hours. The receptor phase of the diffusion cell was magnetically stirred and was kept at 37°C. Samples were analyzed by liquid scintillation counting. For each delivery system, 6 replicates were run and the data provided both cumulative PG released and PG release rate per unit time. 

For years, glass diffusion pumps provided (relatively) easy attachment to a glass vacuum system (but rather difficult removal), are mostly free from attack by corrosive substances, provide easy observation of the materials inside the pump, and can be cleaned (with some difficulty). 

One of the problems in analyzing the speeds of any glass diffusion pump is the fact that all diffusion pump construction is handmade by a glassblower. There is... 

Fig. 7.22 Various forms of glass diffusion pumps. The potential speeds and ranges of glass diffusion pumps are shown in Table 7.8. From Journal of Chemical Education, 42, pp.A445-A459. (1965), reproduced with permission.

The cleaning of a mercury diffusion pump is somewhat simpler because mercury does not break down as most pump oils do. However, mercury gets dirty, and a dirty mercury pump still needs to be cleaned. After you have drained the mercury out of a glass diffusion pump, refill the pump with approximately a 6 molar nitric acid solution and let it sit until the mercury has been removed. Do not pour this liquid down the sink Check with local waste management and/or your health and safety officer. The pump should be flushed with distilled water and then rinsed with methanol for drying. 

Fig. 7.26 The procedure for closing the drain tube on a glass diffusion pump.

There are many companies that make equipment for vacuum systems, and most of them can provide a full range of materials from pumps to oils, and from gauges to leak detection equipment. Most of these vacuum systems and components are for metal systems. For glass components, such as vacuum stopcocks, joints, and even glass diffusion pumps, see the suppliers listed for Chapter 3. 

Most of the earlier studies on the immobilization of enzymes were directed towards the attachment of the enzymes to water-insoluble polymeric supports such as cellulose dextran derivatives, polyacrylamide and porous glass Diffusion problems and steric hindrance are two main factors affecting the application of such supports. The introduction of soluble polymers for immobilization purposes overcomes these difficulties to a greater extent. These soluble enzyme derivatives were synthesized in order to increase the effective molecular size of parent en mes this would rmit the use of ultrafiltration without any los of the enzyme. O NeiD etal. immobilized the enzyme chymotrypsin on soluble dextran for... 

In the course of these studies the most convenient apparatus in which to run these reactions was found to be a flask with a stirrer which has a gas inlet through it. This gives as good a dispersion of the gas in the liquid as does a fritted glass diffuser, and greatly simplifies the manipulations accompanying the reaction. It has the additional advantage that an insoluble product, if formed, does not interfere with the continuation of the reaction. 

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