For krypton

An example of a stepped isotherm, for krypton at 90 K, is shown in Fig. 2.21(a), where the adsorbent is graphitized carbon black, which is known to possess a very uniform surface. Figure 2.21(h) shows the steps obtained, also with krypton, on cadmium bromide. 

To prevent such release, off gases are treated in Charcoal Delay Systems, which delay the release of xenon and krypton, and other radioactive gases, such as iodine and methyl iodide, until sufficient time has elapsed for the short-Hved radioactivity to decay. The delay time is increased by increasing the mass of adsorbent and by lowering the temperature and humidity for a boiling water reactor (BWR), a typical system containing 211 of activated carbon operated at 255 K, at 500 K dewpoint, and 101 kPa (15 psia) would provide about 42 days holdup for xenon and 1.8 days holdup for krypton (88). Humidity reduction is typically provided by a combination of a cooler-condenser and a molecular sieve adsorbent bed. 

Except for helium, all of the elements in Group 18 free2e into a face-centered cubic (fee) crystal stmeture at normal pressure. Both helium isotopes assume this stmeture only at high pressures. The formation of a high pressure phase of soHd xenon having electrical conductivity comparable to a metal has been reported at 33 GPa (330 kbar) and 32 K, and similar transformations by a band-overlap process have been predicted at 15 GPa (150 kbar) for radon and at 60 GPa (600 kbar) for krypton (51). 

The molal diamagnetic susceptibilities of rare gas atoms and a number of monatomic ions obtained by the use of equation (34) are given in Table IV. The values for the hydrogen-like atoms and ions are accurate, since here the screening constant is zero. It was found necessary to take into consideration in all cases except the neon (and helium) structure not only the outermost electron shell but also the next inner shell, whose contribution is for argon 5 per cent., for krypton 12 per cent., and for xenon 20 per cent, of the total. 

Hyperbaric pressure may intensify odors or render odoriferous some odorless gases such as methane. Professional divers, experimentally exposed to hyperbaric pressures, detected odors of krypton and methane when sniffing these during the decompression phase of a dive. The threshold for krypton was 2 ATA (atmosphere absolute), and 100% positive responses occurred at 6 ATA. For methane, the threshold was 3 ATA (100% 13 ATA). The thresholds of individuals differed by as much as a factor of three (Laffort and Gortan, 1987). 

Table 2 Values of p(0) for Krypton provided by different approaches compared to the HF ones...

Self-consistent field results obtained with near-Hartiee—Fock wavefunctions of Clementi and Roetti [70] indicate similar patterns for Ti, Cr, Fe, Ni, Zn, Ge, Se, and Rr, namely, almost vanidiing integrals for = 2 andA = lOe [69]. A third point exists for krypton, forA = 28 e, where reaches a minimum [44]. 

On March 17, 1895, Ramsay wrote to Mr. J. Y. Buchanan, Crookes thinks its spectrum is new, and I don t see from the method of treatment how it can be anything old, except argon, and that it certainly is not. We are making more of it, and in a few days I hope we shall have collected enough to do a density. I suppose it is the sought-for krypton, an element which should accompany argon.. . . Before a week had passed, the new gas was shown to be identical with Lockyer s solar element, helium (21, 23, 24, 26, 52). 

In the pressure range useful for krypton adsorption the mean free path is approximately equal to the diameter of the stem of the sample cell. Equation (14.16) is not applicable in this range and an empirical equation devised by Rosenberg must be used. His equation is... 

The abundances of krypton and xenon are determined exclusively from nucleosynthesis theory. They can be interpolated from the abundances of neighboring elements based on the observation that abundances of odd-mass-number nuclides vary smoothly with increasing mass numbers (Suess and Urey, 1956). The regular behavior of the s-process also provides a constraint (see Chapter 3). In a mature -process, the relative abundances of the stable nuclides are governed by the inverse of their neutron-capture cross-sections. Isotopes with large cross-sections have low abundance because they are easily destroyed, while the abundances of those with small cross-sections build up. Thus, one can estimate the abundances of krypton and xenon from the abundances of. v-only isotopes of neighboring elements (selenium, bromine, rubidium and strontium for krypton tellurium, iodine, cesium, and barium for xenon). 

Values of Ki are given for krypton in Table IV for selected temperatures together with the coefficients Ko in the relation Ki = K0 exp — AE0/ RT, and the standard energies and entropies AE° and AS0 defined, respectively, by... 

The virial isotherm equation, which can represent experimental isotherm contours well, gives Henry s law at low pressures and provides a basis for obtaining the fundamental constants of sorption equilibria. A further step is to employ statistical and quantum mechanical procedures to calculate equilibrium constants and standard energies and entropies for comparison with those measured. In this direction moderate success has already been achieved in other systems, such as the gas hydrates 25, 26) and several gas-zeolite systems 14, 17, 18, 27). In the present work AS6 for krypton has been interpreted in terms of statistical thermodynamic models. 

Pure component experimental data for sorption of methane and krypton on 5A zeolite at 238, 255. and 271K, and in the pressure range of 0 to 97.36 kPa were also obtained during this work (shown in Figures 3 and U). Further sorption data for methane on 5A zeolite (10, 13, 1 0, and for krypton on 5A zeolite (10. 15) are also plotted for other temperatures, all of which appear to be consistent. These experimental data were used to derive the energy and entropy parameters in equation U for the isotherm model of Schirmer et al. by a minimization of a sum of squares optimization procedure. 

The resulting optimized parameters and for sorption of methane and krypton on 5A zeolite are shown in Figure 5 and are presented in Table 1. The calculated energy parameters -22000 Joules/mole for methane and - 16,725-0 Joules/mole for krypton were independent of the amount adsorbed and agree with... 

As the two sorbates methane and krypton on 5A appeared to have different mechanistic behaviour, further theoretical study appeared warranted. Two hypothetical gases P and Q whose properties are tabulated in Table 1 were used for comparison with the behaviour of methane and krypton. Hypothetical gas P was designed to have a Henry constant equal to methane, but to be a localized sorbate having entropy of sorption values decreasing incrementally as for krypton. Conversely, hypothetical gas Q had a Henry constant equal to that of krypton, but entropy of sorption values non-localized and decreasing incrementally as for methane. 

Figure 9.7 Left Frumkin-Fowler-Guggenheim (FFG) adsorption isotherms (coverage 0 versus the pressure in units of Kj 1). The curves were calculated using Eq. (9.35) with ft 0,2,4,6. For ft 6 the physically correct adsorption curve is plotted as a continuous curve while the one calculated with Eq. (9.35) is plotted as a dotted curve. Right Adsorption isotherms for krypton adsorbing to the (0001) plane of graphite at two different temperatures. The dotted curves were fitted using Eq. (9.35) with ft = 4.5. Experimental results were taken from Ref. [377],...

Most experimental groups have performed measurements of lowest energies the magnitude and the trend of aT, as observed by Dababneh... 

The theoretical shoulders for krypton and xenon were computed using values of aM(v) calculated by McEachran, Stauffer and Campbell (1980) and Schrader (1979) and values of Z [(v) calculated by the former. In the case of krypton, the experimental shoulder length and shape are reproduced well using the data of McEachran, Stauffer and Campbell but the results of Schrader give a much longer shoulder than is observed. For xenon, poorer agreement between theory and experiment has been found for both the shape and the magnitude of (Zef[(t)). 

A BET plot of all the data at 77° is linear over a wide range, and least-squares analysis of all the experimental values in the monolayer region (0.025 < p/p0 < 0.20) yields values of vm = 0.336 cc. per gram and c = 131. While the c value is very close to that previously observed for krypton adsorption on this mica (5), the surface area is appreciably smaller. This decrease in vm has occurred progressively with time for all our ground mica samples, and at present we have no... 

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