Potassium adsorption, effect

Iodides can also be determined by this method, and in this case too there is no need to filter off the silver halide, since silver iodide is very much less soluble than silver thiocyanate. In this determination the iodide solution must be very dilute in order to reduce adsorption effects. The dilute iodide solution (ca 300 mL), acidified with dilute nitric acid, is treated very slowly and with vigorous stirring or shaking with standard 0.1 M silver nitrate until the yellow precipitate coagulates and the supernatant liquid appears colourless. Silver nitrate is then present in excess. One millilitre of iron(III) indicator solution is added, and the residual silver nitrate is titrated with standard 0.1M ammonium or potassium thiocyanate. 

Takai K, Suzuki T, Enoki T et al (2010) Structure and magnetic properties of curved graphene networks and the effects of bromine and potassium adsorption. Phys Rev B 81 205420... 

Table 3.3 shows the effect of method on ka values. The type of method clearly affected the ka values and, although not shown, the time required for equilibrium in potassium adsorption to be reached. In earlier work, Ogwada and Sparks (1986a) had found that with the vortex batch method, diffusion was reduced significantly and the rate coefficients one obtained approximated reaction-controlled rate constants. The data in Table 3.3 show clearly that significant diffusion exists with the static and miscible displacement methods because of limited mixing. 

The results for effects upon mechanical stability are summarised in Table II. That lithium laurate behaves similarly to, say, potassium laurate is perhaps surprising, in that it is known that a lithium salt is mor ffective in reducing the mechanical stability of natural rubber -ftian is the corresponding potassium salt (6.). The inference has been drawn that the counterion of the car-boxylate soap has a negligible effect upon the ability of the soap to enhance mechanical stability, relative to the effect of the anion, at least for those cations for which specific adsorption effects are absent. 

Potassium hydrogenphthalate is suited for the analysis of iodide, thiocyanate, and thiosulfate in combination with direct conductivity detection. When silica-based exchangers are used, some methanol or 2-propanol is added to the eluent to lessen adsorption effects. Fig. 3-77 shows such a separation, the characteristic of which is the elution of monovalent iodide prior to the divalent sulfate. Noticeable is the relatively long time... 

Surface Science of Ammonia Synthesis Structure Sensitivity of Ammonia Synthesis Kinetics of Dissociative Nitrogen Adsorption Effects of Aluminum Oxide in Restructuring Iron Single-Crystal Surfaces for Ammonia Synthesis Characterization of the Restructured Surfaces Effect of Potassium on the Dissociative Chemisorption of Nitrogen on Iron Single-Crystal Surfaces in UHV... 

The simplest interpretation of the promotional effect is based upon an electrostatic model.As reflected by the strong decrease in the work function upon potassium adsorption, there is a pronounced transfer of electronic charge to the substrate, leading to the formation of a dipole. A nitrogen molecule... 

Wesner, D. A., Linden, G., and Bonzel, H. P. 1986. Alkali promotion on cobalt Surface analysis of the effects of potassium on carbon monoxide adsorption and Fischer-Tropsch reaction. Appl. Surf. Sci. 26 335-56. 

The electrostatic potential in Fig. 9.10 (right) is that of a single potassium atom. It suggests that the promoter effect of the potassium atom is highly local and limited to the adjacent adsorption site only. What happens if the surface coverage of the alkali becomes higher ... 

A method [62] has been described for the determination of down to 2.5pg kg-1 alkylmercury compounds and inorganic mercury in river sediments. This method uses steam distillation to separate methylmercury in the distillate and inorganic mercury in the residue. The methylmercury is then determined by flameless atomic absorption spectrophotometry and the inorganic mercury by the same technique after wet digestion with nitric acid and potassium permanganate [63]. The well known adsorptive properties of clays for alkylmercury compounds does not cause a problem in the above method. The presence of humic acid in the sediment did not depress the recovery of alkylmercury compounds by more than 20%. In the presence of metallic sulphides in the sediment sample the recovery of alkylmercury compounds decreased when more than lmg of sulphur was present in the distillate. The addition of 4M hydrochloric acid, instead of 2M hydrochloric acid before distillation completely, eliminated this effect giving a recovery of 90-100%. 

Free energy variations with temperature can also be used to estimate reaction enthalpies. However, few studies devoted to the temperature dependence of adsorption phenomena have been published. In one such study of potassium octyl hydroxamate adsorption on barite, calcite and bastnaesite, it was observed that adsorption increased markedly with temperature, which suggested the enthalpies were endothermic (26). The resulting large positive entropies were attributed to loosening of ordered water structure, both at the mineral surface and in the solvent surrounding octyl hydroxamate ions during the adsorption process, as well as hydrophobic chain association effects. 

Intrinsic to interpreting catalytic poisoning and promotion in terms of electronic effects is the inference that adsorption of an electropositive impurity should moderate or compensate for the effects of an electronegative impurity. Recent experiments have shown this to be true in the case of CO2 methanation where the adsorption of sulfur decreases the rate of methane formation significantly. The adsorption of potassium in the presence of sulfur indicates that the potassium can neutralize the effects of sulfur. 

Relevant to the synthesis of ammonia over iron catalysts is the observation of Ertl et al. (54) that potassium preadsorbed by an iron catalyst ((7 = 0.1) increased the rate of synthesis at 430 K by a factor of about 300. This effect the authors attributed to an enhancement of the heat of adsorption of molecular nitrogen due to transfer of electronic charge from potassium to the surface of the iron catalyst. This would be entirely in keeping with the precursor model proposed for nitrogen chemisorption (55). 

The CEC of clay minerals is partly the result of adsorption in the interlayer space between repeating layer units. This effect is greatest in the three-layer clays. In the case of montmorillonite, the interlayer space can expand to accommodate a variety of cations and water. This causes montmorillonite to have a very high CEC and to swell when wetted. This process is reversible the removal of the water molecules causes these clays to contract. In illite, some exchangeable potassium is present in the interlayer space. Because the interlayer potassium ions are rather tightly held, the CEC of this illite is similar to that of kaolinite, which has no interlayer space. Chlorite s CEC is similar to that of kaolinite and illite because the brucite layer restricts adsorption between the three-layer sandwiches. 

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