Connectivities in Glass

Most of the applications of Si NMR to glass studies to date have been used to provide information about the nature and relative numbers of the Q structural units present. Another important structural detail is the way in which these units are connected together in the glass. Developments in two-dimensional Si NMR have allowed such 

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Silicate Glasses Deconvolution of Si NMR Spectra Connectivities in Glass Chalcogenide Glasses Gels... 

Dipolar Recoupling Studies of Network Former Connectivities in Glasses. 222... 

Modifiers in glass are compounds that tend to donate anions to the network, whereas the cations occupy "holes" in the disordered stmcture. These conditions cause the formation of nonbridging anions, or anions that are connected to only one network-forming cation, as shown in Figure 2. Modifier compounds usually contain cations with low charge-to-radius ratios (Z/r), such as alkali or alkaline-earth ions. 

Cascade coolers are a series of standard pipes, usually manifolded in parallel, and connected in series by vertically or horizontally oriented U-bends. Process fluid flows inside the pipe entering at the bottom and water trickles from the top downward over the external pipe surface. The water is collected from a trough under the pipe sections, cooled, and recirculated over the pipe sections. The pipe material can be any of the metallic and also glass, impeiMous graphite, and ceramics. The tubeside coefficient and pressure drop is as in any circular duct. The water coefficient (with Re number less than 2100) is calculated from the following equation by W.H. McAdams, TB. Drew, and G.S. Bays Jr., from the ASME trans. 62, 627-631 (1940). 

E. Ozone destroyer. Ozone is a powerful irritant. The maximum possible working concentration has been reported to be 0,15 to 1.0 part per million of air. It is necessary to destroy any excess ozone and to see that the exit tube from the above absorption assembly is connected to a good hood. It is safer to incorporate an ozone destroyer in the set-up. One such destroyer consists of two tall towers (30 in.) filled with broken glass moistened with 5% aqueous sodimn hydroxide and connected in series (Note 10). The room in which an ozonizer is used should be well ventilated. 

Liquid-in-glass thermometers measure the thermal expansion of a liquid, which is placed in a solid container, on a length scale. The mercury thermometer is one example of liquid thermometers. Alcohol is also used with this type of instrument. The temperature range is -80 to a-330 °C depending on the liquid. The quality, stability, and accuracy vary considerably. The advantages are a simple construction and low price. A disadvantage is that they are not compatible for connection to monitoring systems. 

The theoretical and measured results for E, are shown in Figure 3-41 as a function of resin content by weight. Theoretical results from Equation (3.64) are shown for C = 0,. 2,. 4, and 1, and the data are bounded by the curves for C = 0 and C =. 4. The theoretical curve labeled glass-resin connected in series is a lower, lower bound than the C = 0 curve and is an overly conservative estimate of the stiffness. 

Figure 8.15 Schematic diagrams of cross-sections of MD-TLC plates connected in series to ensure multidimensional separation on stationary phases of increasing polarity hatched lines, glass plate light shading, stationary phase A dark shading, stationary phase B.

The apparatus consists of a 100-ml distilling flask equipped with a dropping funnel and arranged for distillation through an efficient condenser. The condenser is connected to two receiving flasks in series, the second of which contains 20-30 ml of ether. The inlet tube of the second receiver dips below the surface of the ether and both receivers are cooled in ice baths. All connections in the setup are made with bored cork stoppers and all glass tubing is fire polished (Fig. 17.1). 

The films were then soaked in water and removed from the plates. Portions were mounted in glass cells which were filled with potassium chloride solution two Ag/AgCl electrodes were inserted into the limbs of the cells and the unit was placed in a thermostat. The resistance of the films was determined, from time to time, by connecting the cells in series with a known resistance and applying a potential of 1 V to the combination the potential drop across the standard resistance was measured by means of a valve potentiometer. 

The apparatus shown in Fig. 1 may be somewhat more simply constructed by using rubber connections in several places, thus eliminating a certain amount of glass blowing, and making a more flexible piece of apparatus. The side-arm of the separator may be made with two rubber connections,—one above and one below the tube leading to the potassium carbonate tube. The long return tube to the flask may be constructed with a rubber joint very near the carbonate tube and one near the flask. 

Fig. 4. Schematic vacuum system for metal atom reactions. X represents the stopcock or Teflon-in-glass valve. Satisfactory components (for a general discussion of vacuum line design see References 1 and 4) forepump, 25 L/min free air capacity diffusion pump, 2 L/sec main trap is removable and measures about 300 mm deep main manifold has a diameter of about 25 mm, stopcock or valve in manifold should be at least 10 mm substrate container is removable container with 1-2 mm Teflon-in-glass needle valve connected to bottom of container. Connection between this needle valve and the reactor may be 1/8 in. od. Teflon tubing is used. Alternatively, the substrate may be added as shown in Fig. 3.

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