Inert gas. adsorption

The specific surface area of the fibers was determined using inert gas adsorption in a commercial volumetric adsorption system (Micromeritics Instrument Corp.). Krypton gas was used because of its sensitivity to the small specific surface areas of the glass fibers ( 0.2 mz/g). The fibers were degassed at 100°C to a pressure of 80mTorr before introducing the adsorbate gas into the sample chamber. Several samples were also outgassed at 80 and 200°C (to 80 mTorr) to confirm that outgassing was sufficiently complete under the standard test conditions. A standard five-point surface area determination was made for each inert gas adsorption experiment. 

X-Ray Diffraction (XRD).—This technique has many features in common with neutron diffraction, such as low surface-bulk contrast but minimum disruption of the target. Few XRD studies of surface layers have appeared so far and for reasons outlined below in connection with neutron diffraction, attention has concentrated on inert-gas adsorption on graphite. Both XRD and neutron diffraction produce... 

The use of inert gas adsorption is a well established method for characterization of porous systems and their surfaces. From the literature it seems that this method has not been applied in the characterization of carbonate rocks, presumably due to the small specific surface area and porosity of the natural coherent rock. 

Other types of regenerators designed for specific adsorption systems may use solvents and chemicals to remove susceptible adsorbates (51), steam or heated inert gas to recover volatile organic solvents (52), and biological systems in which organics adsorbed on the activated carbon during water treatment are continuously degraded (53). 

In the standard lattice gas model of adsorption we assume that the surface of the solid remains inert, providing adsorption sites. This implies that the state of the surface before adsorption and after desorption is the same. This is not the case if the surface reconstructs or lifts the reconstruction upon adsorption. Such a situation we want to describe. We introduce occupation numbers for the surface = 0 or 1, depending on whether the surface... 

In general, the flow rate F(t) consists of the following additive components the controlled flow rate Fd of the entering gas, the flow rate Fi which is due to parasitic leaks and/or diffusion, and the flow rate Fw resulting from possible adsorption-desorption processes on the system walls (in Section I, references are given to papers dealing with the elimination or control of the wall effects in the flash filament technique). In each of these flow rate components a particular ratio of the investigated adsorbate and of the inert gas exists and all these components contribute to the over-all mean values Fh(t) and F (t). 

The principle underlying surface area measurements is simple physisorb an inert gas such as argon or nitrogen and determine how many molecules are needed to form a complete monolayer. As, for example, the N2 molecule occupies 0.162 nm at 77 K, the total surface area follows directly. Although this sounds straightforward, in practice molecules may adsorb beyond the monolayer to form multilayers. In addition, the molecules may condense in small pores. In fact, the narrower the pores, the easier N2 will condense in them. This phenomenon of capillary pore condensation, as described by the Kelvin equation, can be used to determine the types of pores and their size distribution inside a system. But first we need to know more about adsorption isotherms of physisorbed species. Thus, we will derive the isotherm of Brunauer Emmett and Teller, usually called BET isotherm. 

The eorresponding result for the surface tension [9] provides quite reasonable accuracy for a Leonard Jones fluid or an inert gas fluid, except helium whieh displays large quantum effeets. Thus we ean eonelude that the leading mechanisms of surface tension in a simple fluid is the loss of binding energy of the liquid phase at the gas-liquid interface and the seeond most important meehanism is likely to be the adsorption-depletion at the interface whieh ereates a moleeularly smooth density profile instead of an abrupt step in the density. 

If heating of amorphous selenium with absorbed ethyl radicals is conducted in presence of nitrogen or inert gas with pressure 100 Torr no signal is picked up from the sensor. This implies that in this case the signals of the sensor are controlled by adsorption of ethyl radicals on its surface. Consequently, the heating of amorphous selenium with adsorbed radicals and resulted crystallization lead to emission of radicals. 

Hazards attendant on use of ethylene oxide in steriliser chambers arise from difficulties in its subsequent removal by evacuation procedures, owing to its ready absorption or adsorption by the treated material. Even after 2 evacuation cycles the oxide may still be present. Safety is ensured by using the oxide diluted with up to 90% of Freon or carbon dioxide. If high concentrations of oxide are used, an inert gas purge between cycles is essential [7], The main factors in safe handling... 

The adsorption of inert gases onto solid materials represents the most widely used method for the determination of surface area, although other methods are available [6,7]. The BET method, developed by Brunauer, Emmett, and Teller [8], is generally used for gas adsorption surface area measurements. 

Ferric hydroxide coprecipitation techniques are lengthy, two days being needed for a complete precipitation. To speed up this analysis, Tzeng and Zeitlin [595] studied the applicability of an intrinsically rapid technique, namely adsorption colloid flotation. This separation procedure uses a surfactant-collector-inert gas system, in which a charged surface-inactive species is adsorbed on a hydrophobic colloid collector of opposite charge. The colloid with the adsorbed species is floated to the surface with a suitable surfactant and inert gas, and the foam layer is removed manually for analysis by a methylene blue spectrometric procedure. The advantages of the method include a rapid separation, simple equipment, and excellent recoveries. Tzeng and Zeitlin [595] used the floation unit that was devised by Kim and Zeitlin [517]. 

Various sample enrichment techniques are used to isolate volatile organic compounds from mammalian secretions and excretions. The dynamic headspace stripping of volatiles from collected material with purified inert gas and trapping of the volatile compounds on a porous polymer as described by Novotny [3], have been adapted by other workers to concentrate volatiles from various mammalian secretions [4-6]. It is risky to use activated charcoal as an adsorbent in the traps that are used in these methods because of the selective adsorption of compounds with different polarities and molecular sizes on different types of activated charcoal. Due to the high catalytic activity of activated charcoal, thermal conversion can occur if thermal desorption is used to recover the trapped material from such a trap. 

The positive S.P. observed when gases are adsorbed on a metal surface has been atrributed to (a) polarization of the adsorbate by the electron field of the metal double layer 73) and (6) charge-transfer effects 103). The importance of charge-transfer forces has been stressed by Mulliken 87) in his general theory of donor-acceptor interaction. If, as suggested, these charge-transfer forces contribute to the van der Waals attraction, then they probably take part in the physical adsorption process. The complex M X resulting from the adsorption of an inert gas on a metal surface M has been described as essentially no-bond with a small contribution from the structure As seen in Table VI, the S.P., and hence... 

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