Cesium diffusion

The gas-phase diffusivity of sodium in helium Dvl may then be evaluated from the experimental data by using Equation 15. A value of 1.96 cm.2/sec. was obtained, which compares favorably with 2.11 cm.2/ sec. estimated from an equation given by Hirschfelder, Curtiss, and Bird (8), using Lennard-Jones parameters given by Chapman (5). The close agreement obtained here seems to justify the assumption of a stagnant gas layer through which both sodium and cesium diffuse. 

Unlike kaolinite and montmorillonite, there are several sites for ion exchange reactions to occur on mica and vermiculite (Bolt et al., 1963 Sparks and Jardine, 1984). Bolt et al. (1963) studied potassium exchange on mica and proposed three sites for reactivity. Slow reactions were ascribed to interlattice exchange sites, rapid reactions to external planar sites, and intermediate reactions to readily exposed edge sites. Sawhney (1966) found two distinct reaction rates for cesium exchange on a Ca-vermiculite. The first reaction was ascribed to a rapid exchange of cesium with cations on external planar surface sites and interlattice edges, followed by a second, slow reaction in which cesium diffuses into the interlayers. 

It has been shown that cesium diffuses into the lattice of micaceous minerals, resulting in its entrapment (12) The 35 to 40% "fixed" cesium (Figure 4) is, therefore, likely bound internally at lattice sites, which would have to be destroyed in order to release the cesium. The extraction of cesium by KTOX in these experiments is likely due to dissolution of iroir-bearing minerals, such as biotite and horneblende rather than oxyhydroxides. If sorption by oxyhydroxides had been involved, a trend of increasing sorption with granite alteration, similar to that exhibited by cobalt and selenium, should have been observed. 

According to Helms and Klemm, the reaction of Cs with HgO cannot be used to prepare pure CsaO. Instead, in a procedure identical to that described for K3O and RbaO, metallic Cs is incompletely oxidized and the excess metal is distilled away in high vacuum at 200°C. Care must be taken that no cesium diffuses back into the CsgO during cooling. 

The only metals having good or excellent resistance to corrosion by amalgamation with mercury are vanadium, iron, niobium, molybdenum, cesium, tantalum, and tungsten (8). The diffusion rates of some metals in mercury are given in Table 5. 

Sediments in the Mississippi River were accidentally contaminated with a low-level radioactive waste material that leaked from a nuclear power plant on the river. Pore water concentrations of radioactive compounds were measured following the spill and found to be 10 g/m over a 2-mm depth. The water contamination was 30% radioactive cesium ( Cs), with a half-life of 30 years, and 70% radioactive cobalt ( °Co), with a half-life of 6 years. Objections by the local residents are preventing clean-up efforts because some professor at the local state university convinced them that dredging the sediments and placing them in a disposal facility downstream would expose the residents to still more radioactivity. The state has decided that the sediments should be capped with 10 cm of clay and needs a quick estimate of the diffusion of radioactive material through the clay cap (Figure E2.8.1). If the drinking water limit (10 g/m ) is reached at mid-depth in the cap, the state will increase its thickness. Will this occur ... 

The tungstophosphoric acid shows high activity, close to H2SO4 used as a benchmark. Regrettably, this acid is soluble in water and hence not usable as a solid catalyst. However, the corresponding cesium salt (Cs2.5) is also super acidic and its mesoporous structure has no limitations on the diffusion of the reactants. Cs2.5 exhibits low activity per weight, hence it is not suitable for industrial applications. 

Because of the high value of pc the cesium atoms will remain in the position c for most of the time. Since the 011 planes on the tungsten wires used by Taylor and Langmuir might have had several steps, diffusion may not have occurred on the planes themselves but along the... 

This bimodal dynamics of hydration water is intriguing. A model based on dynamic equilibrium between quasi-bound and free water molecules on the surface of biomolecules (or self-assembly) predicts that the orientational relaxation at a macromolecular surface should indeed be biexponential, with a fast time component (few ps) nearly equal to that of the free water while the long time component is equal to the inverse of the rate of bound to free transition [4], In order to gain an in depth understanding of hydration dynamics, we have carried out detailed atomistic molecular dynamics (MD) simulation studies of water dynamics at the surface of an anionic micelle of cesium perfluorooctanoate (CsPFO), a cationic micelle of cetyl trimethy-lainmonium bromide (CTAB), and also at the surface of a small protein (enterotoxin) using classical, non-polarizable force fields. In particular we have studied the hydrogen bond lifetime dynamics, rotational and dielectric relaxation, translational diffusion and vibrational dynamics of the surface water molecules. In this article we discuss the water dynamics at the surface of CsPFO and of enterotoxin. 

The diffusion constant of Mo03 in the calcium aluminum silicate (CAS) melt may differ appreciably from that in the clay loam melt. However, Norman et al have also compared the diffusivities of cesium in CAS and in a melt of soil from the Nevada Test Site and found that the difference in diffusivities in the two matrices was smaller than the experimental uncertainties (12). They concluded that the CAS melt was a fair model of the Nevada soil with respect to the diffusion of most radionuclides of interest in fallout. 

Transport Model. A general release equation is developed by considering diffusion in both the liquid and gaseous phases. Figure 1 is a sketch of a vessel containing liquid sodium, blanketed by a flowing inert gas and maintained at constant temperature. The assumed cesium concentration profiles for both phases are shown in the sketch. Fick s law of diffusion may be applied to the liquid phase ... 

The fractional cesium release during any given time period may be calculated, provided that all of the constants in Equation 8 are known. Unfortunately, however, liquid-phase diffusivities can be estimated only to within an order of magnitude. An alternative approach, therefore, is to evaluate the constants D and a from two sets of experimental release data and to use these values to predict the fractional release for other conditions. 

C = liquid-phase molar concentration of cesium D — liquid-phase diffusivity of cesium Dv = gas-phase diffusivity f = fractional release J = mass flux... 

Francois and Varoqui (34) measured diffusion rates of Cs+ in the hexagonal liquid crystalline phases of the water-cesium myristate and water-cesium laurate systems. In each case diffusivity was obtained as a function of temperature for a given liquid crystal composition. Values of 1-2 X 10"5 cm2/sec were reported for 60°-80°C. Diffusivity was about an order of magnitude lower in the gel phase of the cesium myristate system. 

A two-site model has been used (18) to model cesium transport in soils. In this model a Langmuir-type model, Equation 3,was used to represent surface sorption and a first-order model, Equation 1, was used to approximate interparticle diffusion. Extraction with CaC was used to verify the exchangeable site inventory. 

The most common quenchers are oxygen, acrylamide, iodide, and cesium ions. The kq value increases with probability of collisions between the fluorophore and quencher. Oxygen is a small and uncharged molecule, so it can diffuse easily. Therefore, the bimolecular diffusion constant kq observed for oxygen in solution is the most important between all cited quenchers. 

Potassium and cesium salts of HPAs which have high surface areas are useful supports for HPAs. Increased stability as well as improved yield in selective oxidation of acrolein is observed when H3+ PVxMoi2-xO40 compounds are supported on K3PM012O40 [47, 48], It was claimed that free acids covered epitaxially the surface of the support, but also the possible formation of a solid solution of H(K,Cs)3PWi2O40 [93] and H(K,Cs)3PMoi2O40 [94] due to the diffusion of K+, Cs+ and H+ need to be considered. 

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