Adsorption delay

Adsorption of Radionuclides. Other appHcations that depend on physical adsorption include the control of krypton and xenon radionuchdes from nuclear power plants (92). The gases are not captured entirely, but their passage is delayed long enough to allow radioactive decay of the short-hved species. Highly rnicroporous coconut-based activated carbon is used for this service. 

For the GPC separation mechanism to strictly apply, there must be no adsorption of the polymer onto the stationary phase. Such adsorption would delay elution of the polymer, thereby resulting in the calculation of too low a molecular weight for the polymer. The considerable variety of undesirable interactions between polymers and column stationary phases has been well reviewed for GPC by Barth (1) and this useful reference is recommended to the reader. Thus, the primary requirement for ideal GPC is that the solvent-polymer interaction be strongly thermodynamically favored over the polymerstationary phase interaction. 

Kurzendorfer [23] is of the opinion that in lime soap dispersions inversion does occur but that due to adsorption of LSDA on the surface of the lime soap micelle agglomeration is delayed, so that complete precipitation does not occur. 

Thermal reduction at 623 K by means of CO is a common method of producing reduced and catalytically active chromium centers. In this case the induction period in the successive ethylene polymerization is replaced by a very short delay consistent with initial adsorption of ethylene on reduce chromium centers and formation of active precursors. In the CO-reduced catalyst, CO2 in the gas phase is the only product and chromium is found to have an average oxidation number just above 2 [4,7,44,65,66], comprised of mainly Cr(II) and very small amount of Cr(III) species (presumably as Q -Cr203 [66]). Fubini et al. [47] reported that reduction in CO at 623 K of a diluted Cr(VI)/Si02 sample (1 wt. % Cr) yields 98% of the silica-supported chromium in the +2 oxidation state, as determined from oxygen uptake measurements. The remaining 2 wt. % of the metal was proposed to be clustered in a-chromia-like particles. As the oxidation product (CO2) is not adsorbed on the surface and CO is fully desorbed from Cr(II) at 623 K (reduction temperature), the resulting catalyst acquires a model character in fact, the siliceous part of the surface is the same of pure silica treated at the same temperature and the anchored chromium is all in the divalent state. 

After formation of a primary deposit layer on foreign substrates, further layer growth will follow the laws of metal deposition on the metal itself. But when the current is interrapted even briefly, the surface of the metal already deposited will become passivated, and when the current is turned back on, difficulties will again arise in the formation of first nuclei, exactly as at the start of deposition on a foreign substrate (see Section 14.5.3). This passivation is caused by the adsorption of organic additives or contaminants from the solution. Careful prepurification of the solution can prolong the delay with which this passivation will develop. 

Atom probe techniques have been used to investigate adsorption processes and surface reactions on metals. The FIM specimen is first cleaned by the application of a high-voltage field evaporation pulse, and then exposed to the gas of interest. The progress of adsorption and surface reaction is monitored by the application of a second high-voltage desorption pulse and a controlled time delay. 

The reduction of NO also produced water, which however did not desorb immediately, showing a delay of about 50 s due to adsorption onto the catalyst and most likely onto Ba sites to form Ba(OH)2. The stepwise addition of hydrogen to the reactor was accompanied by a small increase of the catalyst temperature (3-5°C), due to the occurrence of the exothermic reduction, so that the run was actually performed in the absence of significant thermal effects. The following main reactions were thus likely involved in the reduction of stored NO by H2 ... 

For adsorption, the potential was held at 0.35 V in the base electrolyte. The methanol containing solution (from 0.01 M to 5 M) was allowed to flow into the cell. After 15 min the electrode was pushed against the window (CaF2). The measurements started after a sufficient purging of the gas atmosphere in the IR box. Spectra were taken at potentials between 0 V and 1.5 V RHE with a delay of 1 min after setting each potential. 

Also, other dependent variables associated with CO2-foam mobility measurements, such as surfactant concentrations and C02 foam fractions have been investigated as well. The surfactants incorporated in this experiment were carefully chosen from the information obtained during the surfactant screening test which was developed in the laboratory. In addition to the mobility measurements, the dynamic adsorption experiment was performed with Baker dolomite. The amount of surfactant adsorbed per gram of rock and the chromatographic time delay factor were studied as a function of surfactant concentration at different flow rates. 

From Figure 2.114, it can be seen that the oxalate production was always delayed somewhat with respect to both CO - and glycolate. The authors postulated that this was as a result of the desorption and then subsequent re-adsorption, of glycolate. 

All preparations were structurally characterized by means of XRD (Siemens 5005). TEM imaging was performed with a Philips CM200 instrument. 27A1 and 29Si MAS NMR (Broker 500 MFlz and 360 MFlz respectively) was used to study the microporous phase and the kinetic of its formation. The relaxation delays were 0.2s and 200s respectively. Acidity was determined by the adsorption of carbon monoxide after activating the samples in vacuum (10 6 mbar) at 450°C for 1 h. The spectra were recorded on a Equinox 55 Broker spectrometer with a resolution of 2 cm 1 and normalized to 10 mg of sample. 

Figure 4. Adsorption-desorption of CO on Ni(III) at 175°C due to 200-ms doses (curve a) starting after 100-ms delays (from t = 0) and 300-ms doses (curve b)...

The criteria used at this point were that the predicted dependences of the delays between the appearance of the NH3 and H2O peaks and the N2 and N2O peaks on the duration of NO adsorption and the H2 partial pressure during reduction agree as closely as possible with the dependences found experimentally and shown in Figs. 5 and 8. 

The predicted effects of NO adsorption time on the time delay between the maxima in NH3 and N production and the maxima in H2O and N2 production are shown in Fig. 17. It is seen that the predictions bound the experimental observations and show the the proper trend with increasing NO exposure. 

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