Compaction, adsorption

This is in contrast to semiflexible or rigid chains, which can form dense and compact adsorption layers. 

Strictly thermodynamically, the electrosorption valency only shows that no other co-adsorption of other ions occurs. However, there may be a compact adsorption layer. STM gives images for the two surfaces (Figure 4.32). For Pb on Ag(l 11) the image was interpreted to be a so-called filled honeycomb 3(2X2) structure and a compressed hep layer. For Pb on Ag(lOO) a c(2X2) structure was observed. Otherwise the adsorbed mass was similar to the Ag(l 11) substrate which lead to the model of a bi-layer. 

These sulfonates can be used to optimize the efficacy of cationic inhibitors for protecting metals against corrosive acids. Such inhibitors form adsorption layers on the surface of a metal which will act as a penetration barrier for the acid medium, as well as for the reaction products. However, there is no continuous layer formed by the cationic surfactant because the surfaces show sites of different charges. An inhibitor consisting of a mixture of cationic and anionic surfactants leads to a compact adsorption layer and to a high effectiveness of the inhibitor system. Although the adduct of anionics and cationics is poorly soluble in aqueous acid solutions, an inhibitor concentration of ca. 5 ppm is already sufficient for the protection of the metal. 

The so called mass transfer zone of H2O and CO2 in the adsorbent is short. This is the zone where the components are adsorbed and which is moving forward with ongoing time. Due to this compact adsorption front the bed height can be reduced to about 1 m with a correspondingly small pressure drop ranging between 2 and 5 kPa. 

Make a numerical estimate, with an explanation of the assumptions involved, of the specific surface area that would be found by (a) a rate of dissolving study, (b) Harkins and Jura, who find that at the adsorption of water vapor is 6.5 cm STP/g (and then proceed with a heat of immersion measurement), and (c) a measurement of the permeability to liquid flow through a compacted plug of the powder. 

Fig. 230 Adsorption of nitrogen at 77 K on a silica powder a) adsorption isotherms b) /-plot. Broken line, uncompacted powder continuous line, power compacted at 2-00 x 10 N m (130 ton in ). (—>—) adsorption (—<-) desorption. / is the ratio of the amount adsorbed on the powder to the amount adsorbed on the compact at the same relative...

Fig. 3.4 Compaction of alumina powder. Isotherms of nitrogen at 77 K, on (A) the uncompacted powder, and (B) on the powder compacted at a pressure of 1480 GN (96 ton in" ). Open symbols, adsorption solid symbols, desorption.

Fig. 3.20 Pore size distributions (calculated by the Roberts method) for silica powder compacted at (A) Ibtonin" (B) 64tonin (C) 130 ton in". The distributions in (a) were calculated from the desorption brunch of the isotherms of nitrogen, and in (h) from the adsorption branch.

Fig. 3.22 Adsorption isotherms of nitrogen at 77 K on silica powder and its compacts. (A) uncompressed (B) 10 ton in (C) 40 ton in" (D) 50 ton in (E) 100 ton in . Open symbols represent adsorption, solid symbols desorption. (Courtesy Ramsay.)...

Fig. 3.Z3 Adsorption isotherm of n-butane at 273 K on a sample of artificial graphite ball-milled for 192 b. The shoulder F appeared at a relative pressure which was the same for all six samples in the first milling run, all six in the second milling run, and also for two of the milled samples which had been compacted. The milling time varied between 0 and 1024 h, and the BET-nilrogen areas of the surfaces between 9 and 610 m g ...

Figure 3.26(a) and (h) gives results for nitrogen on a compact of silica. Curve (a) is a comparison plot in which the adsorption on the compact (ordinates) is plotted against that on the uncompacted powder (abscissae) there is a clear break followed by an increased slope, denoting enhanced adsorption on the compact, at p/p° = 0-15, far below the lower closure point ( 0-42) of the hysteresis loop in the isotherm (curve (b)). A second compact, prepared at 64 ton in" rather than 130 ton in", showed a break, not quite so sharp, at p/p° = 0-35. 

A final example appears in Fig. 3.26(c) and (d) where the experimental substance was a magnesium oxide prepared by hydrolysis of magnesium methylate followed by calcination at 500°C. Curve (c) gives a comparison plot of adsorption on a compact against the adsorption on the... 

Fig. 3.26 Comparison plots for compacts of silica and magnesia. In each case the adsorption of nitrogen at 78 K on the compact is plotted against that on the uncompacted powder, (a) and (b), comparison plot and adsorption isotherm for silica powder compacted at 130 ton in (c) and (d), comparison plot and adsorption isotherm for precipitated magnesia compacted at 10 ton in. Note that the upward sweep of the comparison plot commences at a relative pressure below the inception of the loop.

Fig. 3.28 The Kiselev method for calculation of specific surface from the Type IV isotherm of a compact of alumina powder prepared at 64 ton in". (a) Plot of log, (p7p) against n (showing the upper (n,) and lower (n,) limits of the hysteresis loop) for (i) the desorption branch, and (ii) the adsorption branch of the loop. Values of. 4(des) and /4(ads) are obtained from the area under curves (i) or (ii) respectively, between the limits II, and n,. (6) The relevant part of the isotherm.

The swelling of the adsorbent can be directly demonstrated as in the experiments of Fig. 4.27 where the solid was a compact made from coal powder and the adsorbate was n-butane. (Closely similar results were obtained with ethyl chloride.) Simultaneous measurements of linear expansion, amount adsorbed and electrical conductivity were made, and as is seen the three resultant isotherms are very similar the hysteresis in adsorption in Fig. 4.27(a), is associated with a corresponding hysteresis in swelling in (h) and in electrical conductivity in (c). The decrease in conductivity in (c) clearly points to an irreversible opening-up of interparticulate junctions this would produce narrow gaps which would function as constrictions in micropores and would thus lead to adsorption hysteresis (cf. Section 4.S). 

Fig. 4.27 Swelling and low-pressure hysteresis in the adsorption of n-butane on compacts of coal at 273 K. The following are plotted against the relative pressure (a) the amount adsorbed (b) the percentage increase on length (c) the decrease —Ajc in electrical conductivity. The curves for ethyl chloride were very similar to the above curves.

Fig. 4J2 Adsorption isotherms of carbon tetrachloride (at 298 K) on ammonium phosphotungstate compact, (1) before, (2) after preadsorption of n-nonane. (3) is the isotherm of nitrogen, after preadsorption, for reference. Open symbols, adsorption solid symbols,...

Adsorption Kinetics. In zeoHte adsorption processes the adsorbates migrate into the zeoHte crystals. First, transport must occur between crystals contained in a compact or peUet, and second, diffusion must occur within the crystals. Diffusion coefficients are measured by various methods, including the measurement of adsorption rates and the deterniination of jump times as derived from nmr results. Factors affecting kinetics and diffusion include channel geometry and dimensions molecular size, shape, and polarity zeoHte cation distribution and charge temperature adsorbate concentration impurity molecules and crystal-surface defects. 

Generally, adsorption, absorption, and biofilter units require more space than compact incinerators and condensers. If the plant room is restricted, a local roof-mounted system may be the best alternative. However, roof structural reinforcement may be required even for small and lightweight units. Consideration must be given to the effects of noise and vibration. Small adsorption systems, such as adsorption canisters, require an additional central regeneration unit on site, or they must be regenerated or disposed of off site. A central regeneration unit may require long runs of costly ductwork." ... 

C, E curves have been obtained for Zn(0001) andZn(lOTO) at various crci with different additions of tu.630,634-636 The data for Zn(0001) at Cju = const have been used to obtain C"1, Ql plots. Nonlinear plots have resulted, with the value of the reciprocal slope remarkably dependent on ctu- At c-ru = 0 1 M, the reciprocal slope of the PZ plot is 1.1, increasing with decreasing c-ru Such an effect has been related to the weak specific adsorption of OH" on Zn. This explanation has been critically discussed by Vorotyntsev,74 who has assumed that the effect635,636 is connected with the variation in the compact layer composition of the Z11/H2O + TU interface as cjv varies. 

We have developed a compact photocatalytic reactor [1], which enables efficient decomposition of organic carbons in a gas or a liquid phase, incorporating a flexible and light-dispersive wire-net coated with titanium dioxide. Ethylene was selected as a model compound which would rot plants in sealed space when emitted. Effects of the titanium dioxide loading, the ethylene concentration, and the humidity were examined in batches. Kinetic analysis elucidated that the surface reaction of adsorbed ethylene could be regarded as a controlling step under the experimental conditions studied, assuming the competitive adsorption of ethylene and water molecules on the same active site. 

A one-dimensional isothermal plug-flow model is used because the inner diameter of the reactor is 4 mm. Although the apparent gas flow rate is small, axial dispersion can be neglected because the catalj st is closely compacted and the concentration profile is placid. With the assumption of Langmuir adsorption, the reactor model can be formulated as. 

Polymeric aliphatic carboxylates, the poly(alkenoic add)s, were very much more strongly adsorbed than the difunctional carboxylates (Ellis et al., 1990). Results showed that adsorption depended on the conformation of the polyanion. When extended, as in dilute solutions, a polyanion is adsorbed onto a relatively large number of sites and further adsorption is hindered. Thus, increases in acidity (and concentration) were found to result in greater adsorption because the polyanion adopted a more compact... 

Consider first the situation when specific adsorption of ions is absent. In this case the ions cannot penetrate to the inner Hehnhoftz pfane, the charge density i is zero, and hence = — Qg. Since no charges exist in the compact EDL part, JC2 x > 0, the vafue of d /dx wiU be constant and the potentiaf wiU vary Unearfy from /q to /2- For the Hefmhoitz fayer we can write... 

Conventional colloid chemistry and elaitrochemistry have always been clo ly related with each other, the keywords electrophoresis, double layer theory, and specific adsorption describing typical asp ts of this relationship. In more ro nt times, new aspects have arisen which again bring colloid chemistry into contact with modem developments in electrcolloidal particles as catalysts for electron transfer reactions and as photocatalysts. In fact, the similarity between the reactions that occur on colloidal particles and on compact electrodes has often been emphasized by calling the small particles microelectrodes . 

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