Dielectric-volumetric measurements

Combined dielectric volumetric measurements of adsorption equilibria Methane (CH4, 5.5) on dealuminated zeolite of Y-type (DAY, Degussa) (Fig. 6.26) ... 

This study has shown the possibility to measure segregation problems when discharging mixtures through a funnel. It has also shown the effect of the number of drum revolutions at a fixed speed on the quality of a mixture, as well as the effect of a static mixer. The axial structure of the mixtures through autocorrelation functions could also be studied from these data, but this has not been reported here for clarity of the paper. In addition, it must be remembered that we just studied the evolution of the dielectric permittivity, and that in most cases, we will have to follow the volumetric compositions of each component in order to characterise the homogeneity of the medium. The capacitive method is indeed full of promise for particulate systems, and it would be interesting to explore it much into details, particularly for determining the proportions of each component of the mixture. 

The volumetric, elastic and dynamic properties of internally and externally plasticised PVC were studied and compared with those of unplasticised PVC. The glass transition temperature for the plasticised samples was markedly lowered and this decrease was more important for the externally plasticised ones. The positions of the loss peaks from dielectric alpha-relaxation measurements confirmed the higher efficiency of the external plasticisation. However, the shape of the dielectric alpha-relaxation function was altered only for the internally plasticised samples. The plasticisation effect was linked with a decrease in the intensity of the beta-relaxation process but no important changes in the activation energy of this process were observed. The results were discussed. 47 refs. 

Figure 5.14. Training instrument for oscUlometric, volumetric, gravimetric, and dielectric measurements of gas adsorption equilibria in rigid and swelling sorbent materials. The pendulum (left) is covered by a plexiglass vessel allowing direct optical observations of its rotational oscillations.

Figure 10. Experimental setup for simultaneous volumetric-dielectric measurements to determine the amount of gas adsorbed and the dielectric permittivity of a sorbent / sorbate system.

The maximum pressure to which the gravimetric technique has been applied is about 15 MPa. The volumetric method is very seldom applied above 100 MPa [29]. Bose and co-workers [30] developed a precision dielectric method for the determination of gas-solid adsorption. This method is particularly suitable for adsorption measurements up to 200 MPa actually, adsorption data up to 650 MPa were reported [31]. The great advantage of the dielectric method is that it is self-sufficient up to the highest pressures and does not depend on the availability of compressibility factor values, as in volumetric or gravimetric measurements [29]. Other new, yet less widespread, adsorption measurement techniques include oscillometry [32,33], calorimetry [34,35], and electromagnetic measurements [36,37]. 

Other techniques measure the volumetric concentration of solids and firom this infer a linear mass density through the mass density of the individual particles. Probably the most common example of this technique is the use of capacitance measurement [e.g, 18], In this case, the volumetric concentration is established by measuring the capacitance and therefore the dielectric constant of the solids/ gas mixture. The overall dielectric constant will increase in proportion to the dielectric constant of individual particles multiplied by the volumetric concentration. As in the case of y rays, the interaction with the field will depend on the chemical composition as the dielectric constant will be different. However unlike the y ray interaction the influence of water is significantly different to that of the solids - the dielectric constant of water is 81 whereas for a typical solid it will be in the range 2-4. This means that a varying moisture content can have a considerable influence on the uncertainty of the measurement,... 

Electrical techniques detect a change in dielectric constant or conductivity from electrodes surrounding a cross-sectional area of interest. From these measurements, the area distribution of the phases in the cross-section can be inferred. By taking readings from two planes of electrodes, of known separation, cross-correlation can be used to calculate the velocity of material from point to point between the two planes. Thus the volumetric flow rate of the phases can be determined. 

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-... 

---