Dispersion, measurement volumetric method

Hydrogen uptake of reduced catalysts (X) was measured by volumetric method with an AUTOSORB-l-C analyzer (Quantachrome Instruments). Hydrogen adsorption was carried out at 373 K after in situ H2 reduction at 773 K for 6 h in the adsorption cell. The dispersion and particle size of metallic Co were calculated by the following equations, assuming that the stoichiometry for hydrogen adsorption on the metallic site is unity ... 

The chemisorption of carbon monoxide is an established method for determining the surface area of dispersal metals, particularly in supported catalysts. The average area occupied by each molecule depends on whether attachment is on one or two sites, a state that can vary from metal to metal and with surface coverage [85]. The quantity of chemisorbed gases is commonly measured by volumetric methods with apparatus similar to that used for static BET gas adsorption measurements. 

Gal-Or and Hoelscher (G5) have recently developed a fast and simple transient-response method for the measurement of concentration and volumetric mass-transfer coefficients in gas-liquid dispersions. The method involves the use of a transient response to a step change in the composition of the feed gas. The resulting change in the composition of the liquid phase of the dispersion is measured by means of a Clark electrode, which permits the rapid and accurate analysis of oxygen or carbon dioxide concentrations in a gas, in blood, or in any liquid mixture. 

Column 2 of Table 2 shows the dispersion values which we measured previously using conventional volumetric adsorption techniques. For the Pt/Rh catalyst, where it was necessary to use H2 as the probe molecule due to a strong and irreversible interaction of CO with one of the washcoat components (not present in the Pd/Rh catalyst), the volumetric chemisorption data agree fairly well with the CO-H2 methanation technique. However, for the Pd/Rh catalyst, the volumetric chemisorption method employing CO gave a nonsensical dispersion of 174% for the fresh catalyst and an implausible dispersion of 96% for the vehicle-aged catalyst. 

With known overall mass transfer coefficients kd and /tg, specific volumetric interface area Og and axial dispersion coefficient, the solution gives the actual concentration profile of the key component in the column. In [6.26], methods to measure the longitudinal mixing in countercurrent extraction columns are described and approaches to calculate the Bodenstein number and the axial dispersion coefficient for common extractor designs are given. 

Many chemicals used in water treatment are delivered and fed in dry form. Table 5-1 lists some common dry treatment chemicals and their common forms. Chemical feed systems measure these chemicals either by volume (volumetric) or by weight (gravimetric). Dry chemicals are sometimes delivered directly to the water. It is far more common, however, to mix the dry chemical with a small volume of water first. The concentrated solution or slurry is then fed into the water, where it is thoroughly mixed. This method is better at dispersing the chemical into the treated water. 

The conductivity of mesoscopic metals can be measured only by noncontact means. For this reason the particles were embedded in an insulating matrix. The manufacture of the (indium) particles was generally achieved by condensation from the gas phase in a rotating oil film [69]. This method yielded metal particles of about 20 nm that were (colloidally) dispersed in the oil matrix. By means of thermal coalescence, panicles with a diameter of up to several hundred nanometers were obtained. Thus the effective dielectric function (DF) of the heterogeneous oil-indium system was measured. At constant volumetric filling ratio it was possible to mea-... 

Both ESR and fluorescence spectroscopy give an indirect measure of motion in polymers as they make use of either spin label or probe methods. In the case of ESR, nitroxyl radicals dispersed (spin probe) in a polymer matrix or covalently bonded to the polymer chains (spin label) are employed to probe the local environment. Therefore, ESR spectra provide information on molecular motion and microstructure of polymer matrices. Similarly, fluorescent probes are sensitive to the glass structure. This is because photon emission increases when non-radiative processes are hindered by lack of mobUity of the probe. Interestingly, studies on poly (vinyl acetate) (PVAc) have shown that changes in the fluorescence intensities with aging time and temperature follow closely those observed by volumetric relaxation [85]. 

The dispersion of sulphur in rubber compounds was studied using radioisotopes. The radioactivity of the sulphur-35 isotope introduced into rubber compounds was measured by volumetric and surface methods. These methods could be used to investigate physical and chemical processes in rubber and to optimise technical conditions of tyre production. It was found that the radioisotopic methods could be used in studies of sulphur blooming. Experimental data were obtained on the effect of mixing and the storage temps, of the rubber compound on these processes. Rubber compounds containing soluble sulphur, insoluble Crystex sulphur and T-accelerator were used for the studies. 20 refs. 

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